Tire Tech, lots of useful info

[Brandon J]

Here is a general tech about tires. Take information you want. Ignore information you don't want. I tried to keep things simple so everyone can understand. Lets see if I am clear enough for you guys.

Ever wonder why e34s work so well with 16in and 17in tires? I am sharing my knowledge about tires with the bimmer.info community.

I am going to break it down to 3 categories:
1. General info
2. Tire size and contact patch
3. Performance threshold and Roads

This information was generated on bimmer.info, for bimmer.info, and bimmer.info e34 owners/contributors.members. I made the quick drawings and thought they would help in the understanding of tires.

General Info
The purpose of the tire is to do work and to make contact with the road. Tires are designed to work just like a shock absorber. It take-up the bumps, irregularities, and shocks to the wheels so the tire itself stays on the ground. If you look at the shoulders of a tire, you will see how it is round. This design allows that cushioning effect. So, a more square-ish shoulder may in fact restrict the tire from doing the work it is suppose to do.

We should all know tire speed ratings and so forth. If not, look on tirerack's website for more general tire information.

Tire Size and Contact Patch
The most common upgrade for tire performance is to up size your wheels and tires. So, a 15in 205/65 goes to 225/55 R16 for plus 1 and a 235/45 R17 plus 2. What does this do, well the tire width is greater and there is less tire shoulder.

http://bimmerd00d.com/pictars/brandonj/tiretech1.jpg

Here is a hands on approach. Look at figure 1. Take 2 pencils. The first pencil has all the original eraser. Now move the upper wooden part side to side with the eraser on a piece of sandpaper...making sure not to let the eraser slip. What do you notice? The eraser moves or flexes. This is like the tire wall on a turn.
Take the second pencil with about half of the eraser shaved off and do the same thing. What do you notice? There is less flex in the eraser. This is what accounts for that quick turn-in feeling.

Since there is less tire wall on the plus size tires, there is also less tire to do work. Now lets look at the contact patch also.

So, you bought wider 18in tires and swear that it was the best upgrade for looks and for handling. Well, you do get more grip because you probably went with a stickier tire, but you did not necessarily gain more contact area. Look at figure 2 above for what the different contact patches look like for a right side tire. If you remember how the second pencil eraser had less give/flex in it, the lesser tire wall means the tire has a harder time conforming to the road. So, the contact patch actually moves towards the center of the e34, not necessarily gains in area. The tire cannot flex as easily to accomodate for the road or the suspension.

Once you begin removing the amount of tire wall, suspension & suspension angle become more critical and sensitive. This is why on an e34 street car, going to an 18 or 19in size wheel/tire combo can actually hurt the suspension. So, the tirewall size that is optimized for the e34 suspension lies in the 16 and 17in sizes.

Isn't this information great. See the type of information we talk about during the bimmer.info e34 meets.

Performance Threshold and Roads
Now which tire should I get? Well, lets look at the performance sweet spot and the performance threshold. The stock tires are pretty much progressive. They begin to lose grip in a linear fashion and they tell you when they are losing grip because the squeals get louder. In a performance tire, the progression is not linear and the squeals are not as helpful as we are already close or at our breaking point (threshold).

http://bimmerd00d.com/pictars/brandonj/tiretech3.jpg

If you look at figure 4, you will see the progression of grip and the sweet spot. The diagram represents how much the tire can grip as far as side force and how long it takes to get there. So, an all season tire does grip better when warm, but it takes some time to get to its sweet spot. The performance tire can quickly get to its sweet spot. The drawback with the preformance tire is there is less predictability before losing its sweet spot and thus the tires break loose. Since the sweet spot is larger, it is more difficult to know where you are in the sweet spot and predict the breaking point. That's how the tires have to be designed for the performance tire. Those with better compounds and testing can better engineer these aspects. Weird huh. That's what you pay for. Imagine your e34 getting to the sweet spot faster and you feel comfortable so you continue to push the turn. What also happens is your e34 is also arriving to the breaking-point faster without us knowing it. Keep on reading.

Tire performance around corners is also dynamic. So, the actual breaking point threshold might be the same on performance and non performance tires. How is this so? I thought performance tires have a higher threshold for gripping. Well, think how you don't get to the the apex (sharpest point of a turn) right away in a turn. It is usually around the middle. So, the performance tires grip and work the lateral forces within its sweet spot before reaching the threshold (the apex) and afterwards. Thus, collectively, the overall grip throughout a turn is greater with the performance tire. It's that sweet spot.

So, ever wonder how those people on the videos with so-so stock tires can keep up with the same car in plus 2 size wheels and tires? Well, pehaps it is easier to drive with the stock tires as the driver knows where the sweet spot is and can balance the sweet spot and breaking the tires loose. The tires are more predictable.

What does this all mean....performance tire grip thresholds and sweet spots should be balanced with the suspension of the e34. This is critical to get the sweet spot that works in a balanced fashion to the long wheelbase, the suspension upgrades, the suspension angle, etc. We want balanced work in the tires & suspension, we want both predictable sweet spot & break loose threshold, we want the tires to stay on the ground and to get good grip, we also want all this for safety.

Now to the roads....
You drive on them everytime you are in a moving car. So they are very important to learn about. If you look at figure 3, you will see cross sections of different roads types. Roads are engineered for grip, longevity, and water drain. There is a lot more that go into them, but we are concerned about these.

http://bimmerd00d.com/pictars/brandonj/tiretech2.jpg

Asphault generally uses bigger pebbles (in its mixture when compared to concrete). The larger the pebbles and its mixture, the more grooves there are for water to escape. Now there is myth that temperature does a lot in reducing tire life. So, if you live in a warmer climate, then your tires will wear out faster. There is some truth, but temp does not play as big of a role as you think. The road surface does.

We have asphault with the big pebbles. We have concrete with typically smaller pebbles or mixture. Then we have the worn concrete that is polished. As cars and trucks drive on concrete, they wear it down smoother and smoother. What is used in different mixtures is usually based on location. In Hawaii, they use the porous lava rock in their asphault. In Florida, you can find sharp seashells in their concrete. What do these local resources do to the road surface? They increase the grip and grooves for water passage. Isn't the information on bimmer.info great! Almost finished.

Pro race car drivers make going into a turn at 150mph with 3 different road surfaces look easy. Asphault wears out faster than concrete so race tracks like to replace the turns that use asphault (the place where the most force and wear happens) with concrete. There could be patches in a race track and even wear grooves. The racers and tire techs have to learn them for grip. Now you have just learned some of the same important information to keep your grip and keep you safe.


Thoughts
So, I hope this tire tech info session helps you with your BMW e34. Our tires work and we need them to do work. They have to grip, shock absorb, conform to the road, they talk to us by squealing, they help our e34s perform, they help us drive in a safe manner.

My personal experience and my theory: I use the larger front tires 245/45-R17 to absorb shock, have a wider contact patch, along with the suspension upgrades & angle, I can run a softer tire pressure so now the tires can conform to the road better. I do raise the pressure a little at the track only. I chose Michelin because of the progressiveness, grip, longevity, tire wall design, engineering and the Michelin quality. I balanced the size so all four corners can break loose predictably. I can push the front, I can break the rears loose, in a controlled and predictable manner.

I think that my tires have 25k miles on them and can get another 5k miles because of the balance of tire preformance to suspension and suspension angle, as well as the roads. Here in Chicago, I accomodated for the potholes with a larger tire wall, but the roads can be engineered to have less water grooves because of the big road crown and organized sewer system that rain the water. Also, with Chicago being a transportation hub, there are a lot of trucks that cross through. They wear down the concrete so it is more polished. Smoother road, less tire wear, but also less grip.

So you ask what tire is the best. It depends what you need for your balance. Hope this info helps all you bimmer.info e34 members.

[attack eagle]

you forgot that increasing the tire width changed the shape of the contact patch from being biased fore and aft, giving good straight line stability to shaped left right and increasing drag and decreasing stability.

addin extra caster or slightly more toe in can compensate for the reduction in wheel stability caused b the change in contact patch shape, but as indicated above these were designed in based upon the original tire sizing.

it is not th tire sidewall but the contact patch shape that affects stability, and it isn't so much the sidewall height as the unsprung weight vs. spring/shock combo that affects ride quality negatively.

[bimmerd00d]

This info doesn't apply only to the E34, i've talked with BrandonJ a bit and this stuff applies directly to the E39's, and i'm sure every other vehicle out there.

Back when I had my '93 525i 5-spd, I went through an assortment of wheels and tires for it. The original setup were 235/45 17" Mille Miglia wheels with some Kumhos on them. Sure it looked sweet with them, but it was very unpredictable on the backroads. As soon as i got my 16" E31 turbines, and stuck some decent BF Goodrich's on them the car completely changed. It felt much more predictable, and to me, it handled better. It may not actually gripped any better, but I felt much more in control and didn't feel i had to back off as much through the corners. With the 17's, I would take a corner and then bam, snap oversteer. The 16's produced a much more progressive slippage at the limit, the tires talked to me. The same thing applies to my E39 540i right now, the el cheapo Kumhos that came on my new wheels are doing the same thing. The BFG's that were on my old wheels were MUCH better for my driving style.

[Brandon J]

I am glad you added. Yeah, I left a lot out because this much information is already difficult to grasp and to remember. Also, I wanted to focus more on the e34. I actually learned a lot of this from the tire tech guru at Tirerack. He does articles for Grassroots, and the other notable car magazines.



you forgot that increasing the tire width changed the shape of the contact patch from being biased fore and aft, giving good straight line stability to shaped left right and increasing drag and decreasing stability.

addin extra caster or slightly more toe in can compensate for the reduction in wheel stability caused b the change in contact patch shape, but as indicated above these were designed in based upon the original tire sizing.

[Jon K]

So, you bought wider 18in tires and swear that it was the best upgrade for looks and for handling. Well, you do get more grip because you probably went with a stickier tire, but you did not necessarily gain more contact area. Look at figure 2 above for what the different contact patches look like for a right side tire. If you remember how the second pencil eraser had less give/flex in it, the lesser tire wall means the tire has a harder time conforming to the road. So, the contact patch actually moves towards the center of the e34, not necessarily gains in area. The tire cannot flex as easily to accomodate for the road or the suspension.


This is why a lot of people get a kick out of "spinning tire" to confirm their power output. "Oh yeah? My M30 w/ ______________________ mods can spin 2nd and chirp third" and then you get people wondering why theirs can't and they fear something is wrong with the car.

WRONG! I can spin the CRAP out of my 255/40/17 but I get surpringly nice traction with 205/65/15's with 28 psi in them. How can that make sense? Contact patch. The 255/40/17 are wider yes, but it's a lower profile tire without much deformation and thus lesser in-line contact patch. This is why you see guys struggling for traction at a drag strip with 23-24" tall slicks 11" wide. Switching to a 26 - 28" tall slick with 9" width will yield a solid chunk more of traction promised!

[repenttokyo]

A friend of mine can't hook up at all with his Mini. Formerly powered by a civic SI engine, he had 10 or 12 inch (diameter) slicks on the car, but there was nowhere near enough sidewall to get any traction at the strip. For some cars, there really aren't any definite solutions due to design. Even finding slick tires for that size wheel was difficult. Most of what is available is designed for go kart applications, which have a much lower mass to move.

[Barney Paull-Edwards]

Bloody good thread, the only thing I would add is to check the date stamp on new tyres,if they were not wrapped then they will degrade in open air in about six months. UV degradation affects rubber badly,check out window rubbers.To my suprise BFG`s came out top in a recent UK survey,eagle F1`s grip good enough to frighten me!

[bimmerd00d]

Bloody good thread, the only thing I would add is to check the date stamp on new tyres,if they were not wrapped then they will degrade in open air in about six months. UV degradation affects rubber badly,check out window rubbers.To my suprise BFG`s came out top in a recent UK survey,eagle F1`s grip good enough to frighten me!

This is interesting, if you find any sites that confirm this please post them. That's VERY good info to have if it's true.

[rob101]

I think also people underestimate how hard it is to get the correct tyre pressure the only way to work that out definitely is with a pyrometer this could be another contributing factor. this makes a huge difference to contact patch.

Another thing to point out is. going to a larger wheel actually increases the unsprung mass. not hugely but it does. This is another reason why the ride of lower profile tyres is harsher than the higher profile the other reason being that you're replacing some of the rubber sidewall with steel/alloy aluminium which obviously is going to stiffen the whole wheel tyre assembly up in bump.

On a side note its good to see some interesting technical discussion here, i mean apart from Jon's powder coating and turbo forays.

One not of warning though. don't try and deduce effects from things that are anologies. a rubber does not behave as a pneumatic tyre an eraser has most of its stiffness in its centre whereas a tyre has most of its stiffness on the outsides where the sidewall is. This is one major difference there certainly are similarities, but they aren't the same and people should not be under that illusion.

[attack eagle]

verytrue, the weight of the car is not held up of the ground by the squish of the lowersidewall, but HANGS from the upper sidewall.

if you don't have a pyrometer, you can chek for drastily off tire pressures by driving across a strip of wet concrete and reading the "foot print" it leaves.

About the tire's degrading immediately once manufactured... absolutely true. ozone and uv affect the rubber, so a set of 5 or 6 year old tires, even if new or low miles are worn out.

http://farmindustrynews.com/news/Date-stamped-tires-110904/

wrapping might help postpone it, but it will happen nonetheless.

[Brandon J]

Well, some truth some not. Glad you pointed them out. Mercedes uses heavier wheels to make-up for the light aluminum suspension. The extra mass actually helps in ride comfort because more mass is more stable. In regards to the e34 only, yeah, the wheels available generally weigh more than the light stock 15in 205/65. Remember, tire work and suspension work can offer stock comfort with sporty handling. The temp is important, but we need to know the specs of the tires, the type of road, weight, etc. to make effective calculative decisions. Most people with performance tires are not going to reach the max temp on the street. We can check tire pressures when cold and when hot, but why? I put my baseline tire pressure and adjust warm. The tires are warm after they have been moving, thats when handling the turns occurs.

The pencil/eraser analogy was actually used by John Rastetter of the Tire Rack. I with a few other M5 owners had a tire tech session exclusively with him in August. He even had about a dozen road samples taken from all over the country, the autobahn, and a few other places. That is how I know first hand about the road surfaces. When I was at Tirerack, John was in the middle of testing different brake pads with those BMW e90s. It's fun to see the actual testing. It's fun to get the tour of Tirerack.

Here are a few articles that feature John in Grassroots Magazine: http://grassrootsmotorsports.com/news/012005/when-shopping-for-wheels-is-bigger-really-better.php
He has the reocurring Dear John section in that magazine. He has been solely contracted to help a few big tire manufacturers and race teams to set-up the correct specs for tires during races. He does many tech sessions and travels once in a while to only help race teams on tires at the track. He has been in the field for a very long time. I thought the eraser analogy he did was a great way to see the effects of tire wall. There aren't any calcualtions because the pencil is a model and demonstration people can do themselves to get the idea. I don't think people are going to think on an extreme level like, "well a pencil eraser does it so the car must do it."


I think also people underestimate how hard it is to get the correct tyre pressure the only way to work that out definitely is with a pyrometer this could be another contributing factor. this makes a huge difference to contact patch.

Another thing to point out is. going to a larger wheel actually increases the unsprung mass. not hugely but it does. This is another reason why the ride of lower profile tyres is harsher than the higher profile the other reason being that you're replacing some of the rubber sidewall with steel/alloy aluminium which obviously is going to stiffen the whole wheel tyre assembly up in bump.

On a side note its good to see some interesting technical discussion here, i mean apart from Jon's powder coating and turbo forays.

One not of warning though. don't try and deduce effects from things that are anologies. a rubber does not behave as a pneumatic tyre an eraser has most of its stiffness in its centre whereas a tyre has most of its stiffness on the outsides where the sidewall is. This is one major difference there certainly are similarities, but they aren't the same and people should not be under that illusion.

[rnrn]

I guess this helps explain why my orig 15" basketweaves and Michelins felt so good even though I enjoy the ride much more on 235/40/17s BFGs. There are times, now with the Sachs, that I wish I had the old rims on b/c the sidewall took so much abuse without distorting the ride.

Thanks B for putting this together.

[rob101]

Mercedes uses heavier wheels to make-up for the light aluminum suspension. The extra mass actually helps in ride comfort because more mass is more stable. In regards to the e34 only, yeah, the wheels available generally weigh more than the light stock 15in 205/65.
um.......
heavier SPRUNG mass helps ride
heavier unsprung mass hinders it
wheel is most def unsprung mass. I have no idea where you got the idea that heavier wheels make ride better.

[bimmerd00d]

verytrue, the weight of the car is not held up of the ground by the squish of the lowersidewall, but HANGS from the upper sidewall.

if you don't have a pyrometer, you can chek for drastily off tire pressures by driving across a strip of wet concrete and reading the "foot print" it leaves.

About the tire's degrading immediately once manufactured... absolutely true. ozone and uv affect the rubber, so a set of 5 or 6 year old tires, even if new or low miles are worn out.

http://farmindustrynews.com/news/Date-stamped-tires-110904/

wrapping might help postpone it, but it will happen nonetheless.

I actually saw this on dream car garage. They said to light up the tires and you can tell if you have the correct contact patch by the width of the contact patch. Granted, this was for some old classic muscle cars doing some drag racing. However, the same method could be applied if you measure the correct pressure and then get a baseline for the contact patch size.

[rob101]

I was having this problem earlier, i've notified the administrator and he said he'd take a look at it tonight.
I see...

on a side note to the actual topic. brandon when i say pyrometer i mean checking the temps of the tyres from the inside middle and outside of the tread. The TEMP isn't important it is only a way of comparing the wear on different parts of the tread. when the outside and inside are the same as the middle then you have the right pressure (this can help you set static camber also but thats another topic).

[Brandon J]

How about asking John from Tirerack yourself and let us know. That is the information he told me. Look at weights for MB wheels and you will see how heavy they are. What he did say is there is a noticeable difference when switching to lighter aftermarket wheels in performance. It would be good to clarify.

Heavier wheels do make sense as far as unsprung mass is concerned. Now, as far as reacting to handling, it will react slower. That slower action, extra mass, and MB's suspension tuning rates, it does make sense how the heavier wheels make the ride a smoother one. If I were in a plush luxurious vehicle, a smoother ride would have a slower frequency of suspension cycles. Reducing quick impacts. Comparing with the same tires, heavier wheels will have this effect. Slow the force and allow more time to let the suspension absorb the force. The effect is reducing a sharp impact so it is smoother and slow it down so the suspension can smoothly react over time. Makes perfect sense to me.

I understand where your theory is coming from. However, based on ride, not handling, the heavier wheels can help ride. If it's handling were are talking about, then the lighter wheels help the suspension react faster to the needs of performance handling.




um.......
heavier SPRUNG mass helps ride
heavier unsprung mass hinders it
wheel is most def unsprung mass. I have no idea where you got the idea that heavier wheels make ride better.

[bimmerd00d]

It's simple, more tire is just simply going to act as extra suspension to reduce jarring over road imperfections. The general theory is you sacrifice ride quality for good handling with low profile tires. With the right setup, you can achieve both. Well-matched wheels/tires with the right suspension setup does wonders. Watch the first clip from the transporter where Statham explains how the extra guy in the car will hinder him from escaping the cops because his car was setup for a specific weight. As ridiculous as it sounds from a movie, that part is 100% correct. I went through 2 tire setups with the same suspension on my '93 525i. I had H&R's and Bilstein sports, and I felt more controlled using the 225/50 16" tires than with the 235/45 17" tires. It was a great match for ME. I could have handed the keys to Brandon J and maybe he would have said it's terrible. It's has to be a match for the driver and the car.

[attack eagle]

mbs have heavy wheels because their clientele is VERY unlikely to appreciate being left on the side of the road due to a bent wheel, despite the factthey were driving hru Ny potholes at beyond stupid speed...
IF they could get away with using lighter wheels they would.

[bimmerd00d]

mbs have heavy wheels because their clientele is VERY unlikely to appreciate being left on the side of the road due to a bent wheel, despite the factthey were driving hru Ny potholes at beyond stupid speed...
IF they could get away with using lighter wheels they would.

I highly doubt that is the main reason. That seems more like a by-product. Go to Germany, find the real following of the Mercedes Benz.

[Brandon J]

mbs have heavy wheels because their clientele is VERY unlikely to appreciate being left on the side of the road due to a bent wheel, despite the factthey were driving hru Ny potholes at beyond stupid speed...
IF they could get away with using lighter wheels they would.
Umm do you have any empirical data, or real world data to back that up?

I was taught by the tire guru at Tirerack. He talks with the tire and wheel manufacturers. He even trains their sales people because of his qualifications. Again, you can ask him directly and let us know. Contribute.

I gave real world and credible examples and sources. I will give one more. Everyone has seen this formula for FORCE. Force=Mass x Acceleration. So, with the same force of a bump pushing up on a tire/wheel, if there is more mass, then it equates to less acceleration. Again, slower cycle, smoother impact, better ride.

I started this thread to help educate facts away from myths and theoretical benchtop racing. I gave real examples, have credible sources, and even threw in universal physics law. I hope other bimmer.info members will follow suit and contribute real answers instead of waste bandwith with benchtop racing. There is still a lot of good info in this thread and I hope others share their real world experiences. We can all help each other separate fact from fiction and perhaps help another member understand their observations of their e34.

Many people asked for my info so I thought it was a good idea to share to the community. Like I said in the first line of my original post:
"Here is a general tech about tires. Take information you want. Ignore information you don't want. I tried to keep things simple so everyone can understand. Lets see if I am clear enough for you guys."

[rob101]

I understand where your theory is coming from. However, based on ride, not handling, the heavier wheels can help ride. If it's handling were are talking about, then the lighter wheels help the suspension react faster to the needs of performance handling.
Its not my theory. its a theory that can be seen in virtually any reputable book written on the subject. its because the kinectic energy of a higher sprung mass is higher for a given acceleration due to a bump.
http://www.rqriley.com/suspensn.htm the ratio between sprung and unsprung mass is talked about here. and its pretty much the same as the point i am making.

[bimmerd00d]

Its not my theory. its a theory that can be seen in virtually any reputable book written on the subject. its because the kinectic energy of a higher sprung mass is higher for a given acceleration due to a bump.
http://www.rqriley.com/suspensn.htm the ratio between sprung and unsprung mass is talked about here. and its pretty much the same as the point i am making.

So ultralight wheels on a heavier car are what works? If the suspension isn't designed for that, it's not going to work correctly. Same goes for heavy wheels. Putting the lightest wheels on any car is not the answer. There's a reason the M5 works well with the forged 17" wheels, because that was the best design for the suspension. Look at the E30 M3 for instance. Throwing 17" wheels on it actually degrades the handling compared with the stock 15" wheels.

[rob101]

I gave real world and credible examples and sources. I will give one more. Everyone has seen this formula for FORCE. Force=Mass x Acceleration. So, with the same force of a bump pushing up on a tire/wheel, if there is more mass, then it equates to less acceleration. Again, slower cycle, smoother impact, better ride.

force isn't the input into the system the input is acceleration. therefore for a given bump (with the tyre the same)the acceleration is the same mass is higher -> higher force which is transferred to the sprung mass

[rob101]

So ultralight wheels on a heavier car are what works? If the suspension isn't designed for that,...
This is only for ride i am talking about. I am not disagreeing with you about the suspension being a complete system. its all a trade off in the end.

I think the wheel size that works has to do with the type of tyre and camber/roll relationship (ie stiffness of sway bars springs and geometry)or camber curves as they called. you can use wheels so long as they are flat enough in the turns not to get camber "roll off" but there is a point it won't matter how much bigger you make the tyres because there isn't enough weight to increase the grip as you go bigger tyres (and thus add unsprung mass for no reason)

[rob101]

forgot to mention wider tyres with lower profile camber affects their lateral grip more than narrower tyres with larger profile.

I am i studied this so I could make a handling model for my honours mech engineering thesis for which i got a distinction. I don't work in the field but i am well read on the subject (ie miliken) as well as actual mech engineering basics which underpin the theory on the subject. which is why i find alot of this stuff inaccurate.

[attack eagle]

thank you...
I've never found the "tire gurus" at tire rack to be any better educated than anyone else. Being a good public speaker, and working asa consultant doens't mean you are the most educated person on the subject... If he was he'd work for Moton or In F1, not at tire rack.

I agree with some of the theories put forth herein, and some I absolutely think are hogwash. If anyone really wants to gain a basic understanding of this stuff, they need to get off the internet, read books, do calculations, and go out and experiment empirically... like SCCA SoloII.

[Brandon J]

Its not my theory. its a theory that can be seen in virtually any reputable book written on the subject. its because the kinectic energy of a higher sprung mass is higher for a given acceleration due to a bump.
http://www.rqriley.com/suspensn.htm the ratio between sprung and unsprung mass is talked about here. and its pretty much the same as the point i am making.
Your link states,
"When a tire encounters an irregularity the resulting forces tend to reduce contact pressure and therefore degrade adhesion. Obstacles impart a vertical acceleration to tires that increases in proportion to the forward speed of the vehicle and the size of the obstacle. The greater the accelerated mass (unsprung weight) the greater the kinetic energy. In a sense, a raised obstacle throws tires away from the roadway. "

Actually, you are misinterpreting what is written in that link. Before you talked about the added mass and the link talks about how you can loose adhesion. While RIDING not HANDLING, it is better for the tire/wheel to loose contact with the ground as it is taking the kinetic energy of the force from bumps. Now that means the wheel/tire is doing the work by moving up and down. That is what we want. The actual kinetic energy that you talk about is more so in the wheel/tire.

We can even relate it to our own riding experiences. In smooth riding vehicles you can hear the thumps as the wheel/tire move up and down on bumps. It takes the kinetic energy. The sprung weight vehicle takes less of that energy imposed by speed and the bump. I would rather hear the wheel/tire working instead of feeling it.

The article also supports everything else I have been saying about frequency relating to smooth ride. It also says that in order to keep tire contact, um in handling, that firmer springs should be used. This will make the ride harsher. We try to balance (it has been talked about a lot) with wheel travel and the balance of the tires/wheels/suspension to make the ride smoother from the smaller tire walls of plus sizing.

[attack eagle]

nope, that is the spring taking the force... and the shocks rebound setting (or blownness) allowing it to move that quickly upwards...


You are misinterpreting that link to be only ONE instance... it is TWO, and irregularity (dip, wrinkle etc) and then a discussion of raised obstacles.

Firmer springs do not necessarily make the ride harsher... firmer springs without accompanying shock changes do. I know people with 650 lb springs on cars that came with 400s, with less wheel travel and their ride is BETTER and smoother than OEM becasue they designed the suspension SYSTEM. Not jsut threw some lowering springs and random shocks into it like we generally do with e34s. Ideally you want to have unsprung weight minimized, because it is HARDER TO KEEP THE TIRE IN CONTACT WITH THE ROAD. IF you can't keep the tire on the road you have to run heavier springs to do it and you have to reduce the rebound permitted as a patch to try to do so.

heavier wheels = heavier springs and less compliant suspension settings.

[Brandon J]

nope, that is the spring taking the force... and the shocks rebound setting (or blownness) allowing it to move that quickly upwards...


You are misinterpreting that link to be only ONE instance... it is TWO, and irregularity (dip, wrinkle etc) and then a discussion of raised obstacles.

Firmer springs do not necessarily make the ride harsher... firmer springs without accompanying shock changes do. I know people with 650 lb springs on cars that came with 400s, with less wheel travel and their ride is BETTER and smoother than OEM becasue they designed the suspension SYSTEM. Not jsut threw some lowering springs and random shocks into it like we generally do with e34s. Ideally you want to have unsprung weight minimized, because it is HARDER TO KEEP THE TIRE IN CONTACT WITH THE ROAD. IF you can't keep the tire on the road you have to run heavier springs to do it and you have to reduce the rebound permitted as a patch to try to do so.

heavier wheels = heavier springs and less compliant suspension settings.


Okay, here you go again. I apologize for the rest of the board. As one of the original members, I posted this informational thread to help. Now yo are getting bits and pieces and we can definitely get into further details. You start to mention springs and shocks as part of design. I already posted about balancing the suspension so people can get a smooth ride with sportier set-up. You are speaking the obvious here. Contact on the road is for handling. Managing the suspension frequencies is smoothing out the bumps. You don't have to add stiffer springs with heavier wheels. That is adding a variable to the mass confusion. Because the wheel is moving more, kinetc, it is doing work. We like work. Larger tire walls do more work. It is keeping the work at the wheels/tires that can help make a smooth ride.

I see you want to turn it into an argument, I speak in isolating and understanding that component. I speak to experts with Tirerack being a very credible source. So, unless you actually do you own work and find credible sources (plural) for all of us to see to back yor theroies this is more bench into racing. I clarified what you want to make confusing.

I began this thread to contribute. Obiously with your arguing, you do not understand the foundations of this e34 board. Argue the experts like Tirerack. Arguing interpretations is silly. Oh, btw, that expert at Tirerack does talk to the manufacturers about wheels and tires. That is how he knows about the Mercedes wheels.

Now Lets get back to real relevant information that as BMW e34 owners we are going to encounter with our e34s.

[Macv]

Great bunch of readings..... keep going.

[rob101]

okay lets see,

Miliken and miliken Race car vehicle dynamics (this is probably THE most important)
every carol smith book ever written.
Allan staniforth competition car suspension
PACEJKA's magic formula papers.
Fred Puhn's How to make your car handle (http://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468/ref=pd_bbs_sr_1/103-5766388-9437443?ie=UTF8&s=books&qid=1192742888&sr=1-1)
lets see.....
Claude Roulle's course notes if not goto his course.
go read yourself to death at FSAE.com's forum

[rob101]

yep i think thats everything i've ever read about it don't worry about the FSAE people i talked to because i worked there day and night for 8 months i am sure your tire rack guy knows more than them. so perhaps you can stop using the fact that you spoke to a tyre rack guy for maybe a week or so as that you know all there is to know about vehicle dynamics because thats not the case.

http://racingteam.manchester.ac.uk/racecar/ClaudeRoulleRacecarDynamicsSeminar.pdf
interesting little snippet on tyres etc.

[Brandon J]

Ok, as I said in my first line to take what you want and ignore what you don't want. As I remember, the title of this thread is about tires. As I stated, it is general so everyone can use it. I spent a great amount of time putting the information on TIRES together so that I could help the e34 community. Now, under the scrutiny of everyone, I did post to help.

I encourage you to organize and start a thread explaining the bits and pieces that are here. That way all of us can see everything you want to talk about. Do the work and contribute to this great online community. It's one thing to try to make one person understand. It's another when you present it to everyone so we all can try to understand what you have to say.

I did a brief talk about suspension set-ups for the e34 in my other thread about mods and my experience. That is specifically focused on the e34. Since most of us are not going to do a custom caster adjustment, I ommited that information. I laid it out so others can use it, learn from it, see what they can do differently, and compare their actual findings. I write about information on tires and e34 suspension so the whole community can use it. Thought it was a good idea since a bunch of the bimmer.info members do ask me questions everyday.

As a cummunity based message board, I again encourage you to post to the community a thread about your findings relating to suspension and wheel mass, MB suspensions and clientele in NY, etc.

As far as John Rastetter, he does not take the phone like the other salesmen do. He trains them. They go to him for answers. Agree with knowledge he spread or not. Your choice. A lot of Cart, Nascar, Solo II, wheel to wheel racing, teams do rely on his knowledge. That is why he gives the advice in Grassroots Magazine and Car & Driver, and other publications. I didn't learn everything from him, but I did learn a lot of very good information. Many of you would find this very interesting. Talking about tires, Discount tires gets all of theirs from Tirerack.

Under the scrutiny of the board, I encourage other contributors to chime in other relevant info on tires in this thread. For those of you who have or want to talk during the e34 meets, that is great too. Under the eyes of the whole board I put myself out there with the relevant information I have so as to share and help other bimmer.info e34 owners. I still encourage others to do the same.

[rob101]

here's a point:http://www.eng-tips.com/viewthread.cfm?qid=102250&page=2 for those who are interested.
specifically the post that starts : I think it important to separate the effects of ride & handeling into at least 2 different areas.
One is for vehicles with completely adjustable suspension such as race cars. For production based, even with some mods to suspension there are some other items at work which can make what is theoretically good for a race car not good for the car without completely adjustable suspension.

I never said you were wrong, you were the one who started lecturing me about a basic concept about ride and unsprung mass which you seem to have the wrong idea about. if you want to misinform everyone here go ahead but i am not going to sit here and pleasantly smile and nod.

[rob101]

heres another one on the effect of profile on the tyre's behaviourhttp://www.eng-tips.com/viewthread.cfm?qid=56923&page=3

[Brandon J]

here's a point:http://www.eng-tips.com/viewthread.cfm?qid=102250&page=2 for those who are interested.
specifically the post that starts : I think it important to separate the effects of ride & handeling into at least 2 different areas.
One is for vehicles with completely adjustable suspension such as race cars. For production based, even with some mods to suspension there are some other items at work which can make what is theoretically good for a race car not good for the car without completely adjustable suspension.

I never said you were wrong, you were the one who started lecturing me about a basic concept about ride and unsprung mass which you seem to have the wrong idea about. if you want to misinform everyone here go ahead but i am not going to sit here and pleasantly smile and nod.
Hmmmm, I think you need to read again that this thread is for tire tech. Is there a reason you won't write about your findings about suspension in the e34 in a new thread so everyone can see it here and read what you have to say? It would help the bimmer.info community if we can all understand the whole explanation by you. Oh, if you can, please include the off topic we were talking about. Given the exact same vehicle with the same tires, same speed over the same bump, but only swapping the wheels what happens to ride. So, without the turns or lateral movement, just straight line ride quality.

If you have more about tire tech, then I would be interested in hearing you.

[rob101]

If you have more about tire tech, then I would be interested in hearing you.
um all those links relate to tyre tech one is about contact area of a tyre
perhaps YOU should read.
TYRES ARE DIRECTLY RELATED TO SUSPENSION
you can't have one without the other. sorry to rain on your parade.

BTW the entire e34 community should thank you for your deligent attempts to stifle technical discussion here. I mean really you've done a really good job at telling me why i shouldn't share my views.

[Brandon J]

um all those links relate to tyre tech one is about contact area of a tyre
perhaps YOU should read.
TYRES ARE DIRECTLY RELATED TO SUSPENSION
you can't have one without the other. sorry to rain on your parade.

BTW the entire e34 community should thank you for your deligent attempts to stifle technical discussion here. I mean really you've done a really good job at telling me why i shouldn't share my views.
How did I know you were going to post here again. Now we could possibly mean the same thing with what we are saying on this off-topic wheel mass, but are misinterpretting each other. Again, I took the time to present the very useful tire tech information in an organized manner. It is much easier for others to understand what I want to say and what I am thinking if it comes from my own words. I encourage the same. The BMW e34 community thanks me a lot in messages and in person for my useful information. I think they will thank you too when your knowledge is fully explained and understood.

[Brandon J]

I am posting this on behalf of my buddy Rob101, this is he's written work. I take no credit for this material. He's currently having issues with his worksite computer lol...

I will repost to his own thread.

[Zeuk in Oz]

My personal experience and my theory: I use the larger front tires 245/45-R17 to absorb shock, have a wider contact patch, along with the suspension upgrades & angle, I can run a softer tire pressure so now the tires can conform to the road better (Zeuk in Oz's emphasis). I do raise the pressure a little at the track only. I chose Michelin because of the progressiveness, grip, longevity, tire wall design, engineering and the Michelin quality. I balanced the size so all four corners can break loose predictably. I can push the front, I can break the rears loose, in a controlled and predictable manner.

Interesting read and thank you to all who contributed.

I would like to raise one issue, however, which I feel has been ignored. That is how tyres behave when under stress - ie when cornering or braking and how this relates to tyre pressures.

My understanding, and I am not an expert so please feel free to correct me, is that the centre of tyres gets sucked in when stressed.

In other words, a tyre that is inflated to a pressure that allows the tyre to run flat on the road when not stressed, eg when travelling at a constant velocity, ends up with only the outside edges in contact with the road when stressed.

This means that in order to get all of the tyre in contact with the road when it is stressed, the tyre must be inflated so that it is running more on the centre of the tyre when not stressed.

In other words if your tyres aren't worn more in the centre than the outsides when you change them, you haven't been using enough pressure to get all the tyre on the road when you need it the most - when cornering of braking.

Therefore, Brandon, I would suggest that you might be doing yourself a disservice by having lower pressures in your front tyres.

[rnrn]

This is a blanket statement from some article I read a few years ago but the tests this guy ran (it was not in an alley, I assure you) produced the best contact patch at 4 psi over the recommended OEM psi. This was the average, there were some greater (not many) and certainly none under except for those that were gutted for the track and significantly reduced the load.

I'll try and find it but don't hold your breath.