Rob101's explanations for e34 suspension components

[Brandon J]

I am posting this in his own thread as requested to share his insight to suspension for the e34:

"I've realised that nobody is going to read past the first page of the tyre tech thread that brandon J's started.
why bigger isn't necessarily better when it comes to Tyres and rims

wider tyre.

Cornering
Pro's
- Tyres react faster to steering inputs
- Tyres do have ultimately a higher capacity for "lateral force"
Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (harder to keep contact on bumpy surfaces)
- tyres are more sensitive to changes in camber
- tyres will be breakaway in a less progressive way at their limit
- tyres will steer themselves more (increased self-aligning torque)

Ride
Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (degrades ride on bumpy surfaces)

Lower Profile tyres and increased wheel diameter

Cornering

Pros
- Improved steering feel
- Improved steering response
- Lower rolling resistance
- Improved sidewall stability under braking
- Room for bigger brakes
- Less camber distortion when cornering. (not sure 100% how this effects)
- Greater steering accuracy
Cons
- tyres will breakaway in a less progressive way at their limit
- More susceptable to sidewall damage
- Heavier (harder to keep contact on bumpy surfaces)
- More expensive
- More susceptable to tram tracking
- More critical to tyre pressure

Ride

Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (degrades ride on bumpy surfaces)

In general bigger wheels
Further to that larger sizes of wheels will usually have an increased rolling radius.


Now my theories about the e34 in general and these tyres-

- the M5 was designed to utilise the 17 in wheels with 235s and 255s (which have roughly the same width of sidewall)
- "lesser" e34s uses narrower tyres with larger sidewalls

M5

m5 rolls less and the wheels are keep flatter on the road during corner (stiffer springs and sway bars)
- this was not done by accident, in fact they probably did this in order to use the wider tyres better.
- Ride has been comprimised slightly in this car for sportiness this is a result of the stiffer suspension setup.

m5 bushes have been beefed up
- increased "reaction forces" in lower profile and wider tyres. places added stress on suspension pivots.
- increases preciseness of setup and thus sportiness

m5 has alloy control arm in place of steel arm
- counteracts the increase of unsprung mass with the bigger wheels/tyres thus helps ride/tyre contact.

M5 shocks are stiffer
- since we have more unsprung mass we must stiffen the shocks in bounce in order to maintain wheel contact.
- this increase the force transmitted to the rest of the car reducing ride
- need to increase because of stiffer springs to help ride quality (otherwise will be underdamped)

M5 brakes are bigger (and lighter?)
- well you can fit more under there so why not?
- car is faster so needs more brakes
- (and lighter?) unsprung mass again

M5 has staggered setup rear tyres are larger
- i'd expect that is to help high speed stability which is reduced by putting more responsive tyres on
- however i agree it is also because this is where the torque is transmitted to the road is also another reason.

Now lesser e34s

cheaper is better in components we don't necessarily need as much handling but ride is still important also.

body rolls more and thus wheels experience more camber, but less stiffness helps ride somewhat.
- narrower tyres with larger sidewalls can handle more camber but are not are precise and do not give as high of a limit in handling.
- setup is more forgiving due to predicability at the limit of the tyres.
- ride is good also due to less unsprung weight in the wheels and less stiffness in the setup overall.

bushes are cheaper.
- don't need them to be as strong. tyre doesn't stress bushes so much due to less tramlining besides only m5 drivers goto the track

steel arms
- less unsprung mass due to smaller wheel and narrower tyre
- steel's cheaper

Shocks are softer
- reduced unsprung mass
- softer springs need softer shocks to maintain ride.

Brakes are smaller
- cheaper
- might not fit m5 brakes under 15"s



If you want to use wider tyres and thus smaller side walls:

they will give you more cornering
- KEEP in mind the setup with regards to reducing body roll and thus keeping the tyres flatter on the road during cornering.
- the wider the tyre the less it tolerates camber, and will fall out of its optimal area for cornering and braking/acceleration.

they will be less predictable at the limit,
- too bad thats just the way it is. see next point.
- might consider tuning a little understeer at the limit (anyone for 255 at the rear?)

they will be more precise and respond quicker.
- thats actually related to the previous point so thats your consolation.

Your ride will suffer (due to more unsprung weight) (doing anything in this area is good for grip also)
- look for a lighter rim if you can
- get lighter brakes
- get alloy m5 arms

your ride will suffer (stiffer springs and sways)
- make sure you have adequate shocks to counteract the springs (helps handling also)
- other than that like everything its a trade off.

increased tramlining/wandering/high speed instability
- would be trying increase in toe in. due to a increased rolling resistance on each tyre the dynamic toe in (that is the toe when the vehicle in motion) is less than with smaller tyres. but this will decrease turn in responsiveness a little
- get stiffer bushes should help reduce play in the steering.


"So What you're saying is if i get 300 wide tyres and stiffen up my suspension enough as well as do shocks Its worth it?"
- No because there comes a point where the increase grip due to the width of a tyre isn't enough to make up for the increase in unsprung mass (and its effects on both ride and grip)
- Perhaps for a road car: we want good ride as well, a kind of trade off. This is what the M5 has set out to do and has achieved.
- Unsprung mass' effect on grip (keeping wheel in contact with road) can be reduced by increasing spring rates and shock rates however this will make the ride even worse in the process of aiding the grip.

Thus we reach our "limit state" for the road car.

it is determined by:
- by the roughness of the road you drive on regulary (on smoother roads larger wheel and tyre combinations because the disadvantage of higher unsprung mass is proportional to this.)
- unsprung mass of desired wheel/rim setup.
- unsprung mass of e34's suspension links springs shocks and struts. (alloy arms and lighter brakes help)
- Weight of the e34 in total (and thus sprung mass, more sprung mass = better ride)
- how harsh you can tolerate the ride.
- how responsive/twitchy/unstable at speed you like your car (less progressive behaviour at the limit, high speed instability/tramlining is a downside with more responsive tyres)



M division has done a good job at balancing these. I think there are many lessons to be learnt from how they've modified the base e34 to achieve a good balanced car.
Some of these may not be immediately obvious and by no means do I understand the setup in its entirity.
I intend eventually to map out some of the suspension geometry of the e34 and gain some more insight.
So. in case you haven't noticed its not an easy subject. but you weren't seriously expecting to be smarter than companies that spend millions of $s in R&D
Did you?"


The above is Rob101's explanation of suspension in the e34. He had it posted under my tire tech thread so I moved it to its own since it is talking about suspension.

[rob101]

thanks for that i actually meant for yang to post that in a new thread.
otherwise that first statement doesn't really make sense lol
I really confused as to why it times out... if i write more than a couple of paragraphs.
anyway have a go at me if you want pick apart my arguments these are my impressions from what i've learnt and my musings they aren't by any means complete and aren't a substitute for experimentation perhaps some sort of rationale at interpreting the things people have experienced.

[rob101]

And its not really talking only about suspension.....

[krzysiom5]

My current M5 a(nd my previous M5) came with stock 235/45 17s all around. The staggered set was an option later in the years. The 18in wheels on the latter M5s used the same width front and rear tires, 245. Wasn't the M5 designed for same size tires front and rear just like the same width tires of non M5 e34s? I think the M5 calipers and carriers are almost the same weight of the non M5 e34s, but the rotors are definitely heavier because they are larger. I know the aluminum arms in the M5 were also found on some 525s, 530, and 540 e34s that came here to the states. They all came with stock 15in wheel and tires, I was wondering why did they add them to those e34s too when the wheels and tires were the same size?

[rob101]

I didn't know about the alu arms on other e34s that came into the US. regardless its a good idea to have the lightest and suspension arms you can have really the only downside is cost. less unsprung mass is universally good. you don't NEED to have 17inch wheels to benefit from that

[Turbo Ready]

Should be made a sticky

[rob101]

perhaps we should make a knowledge repository thread where all the big write ups are kept. and thus stickied

[krzysiom5]

Alright. Yeah, I already knew that about not needing 17in wheels to benefit from aluminum lower control arms. Thats a given.

I am in the process of fine tuning my M5 suspension. Many M5 owners still face the front tire outside wear and understeer. BMW even made strut mounts for the M5 to give more camber. While the M5 suspension is good I noticed how Dinan's M5 suspension set-up actually rode better and handled better? Can you tell me your experiences with different e34 suspension set-ups that you have worked on. thanks

[rob101]

Alright. Yeah, I already knew that about not needing 17in wheels to benefit from aluminum lower control arms. Thats a given.

I am in the process of fine tuning my M5 suspension. Many M5 owners still face the front tire outside wear and understeer. BMW even made strut mounts for the M5 to give more camber. While the M5 suspension is good I noticed how Dinan's M5 suspension set-up actually rode better and handled better? Can you tell me your experiences with different e34 suspension set-ups that you have worked on. thanks
I'll be honest I haven't worked on e34s, most of the stuff i did was on open wheelers. but in the future i really want to map out the e34s suspension geometry. perhaps when i am on hols in Xmas. I can't really "see" whats going on exactly until i know exactly what the geometry is doing. you need to get under the car and measure with plumb bobs really before you can know whats going on

[rob101]

Alright. Yeah, I already knew that about not needing 17in wheels to benefit from aluminum lower control arms. Thats a given.

I am in the process of fine tuning my M5 suspension. Many M5 owners still face the front tire outside wear and understeer. BMW even made strut mounts for the M5 to give more camber. While the M5 suspension is good I noticed how Dinan's M5 suspension set-up actually rode better and handled better? Can you tell me your experiences with different e34 suspension set-ups that you have worked on. thanks
actually i'd be interested to know what kind of mods they did to the M5 strut to give it more (negative?) camber. that is something I don't really know about (hence didn't mention)

[rob101]

yeah i think i'll just post my own thread that is Tire tech lots of useful info 2
perhaps then it'll actually represent what i want it to represent when people read it on the forum front page
and not conveniently be deemed a thread about "suspension components"
when it talks about wheels and rims MAINLY

[krzysiom5]

I'll be honest I haven't worked on e34s,
Ooo....

[Brandon J]

I'll be honest I haven't worked on e34s
Really?!

[attack eagle]

And you point is?
suspension theory and design is suspension theory and design. Badging doesn't change the laws of physics.

At least he isn't a follower of some unnamed Tire Rack employee who regurgitates what ever he is told even when it is wrong... Brandon. :p

[Brandon J]

And you point is?
suspension theory and design is suspension theory and design. Badging doesn't change the laws of physics.

At least he isn't a follower of some unnamed Tire Rack employee who regurgitates what ever he is told even when it is wrong... Brandon. :p
You said it. Theory.

I will go back to working on the e34 like I have been doing for the past 8 years. Yes, I do have a ton more experience with suspension combos, wheels, tires and brakes used on the BMW e34. I will report on my actual findings, help people on actual work, inform on actual test results, and report on actual (upgraded and stock) parts for the e34. As posted above, not sure if M5 brakes fit under 15in wheels? Well, 7 years ago the work I have actually done and posted can tell you. That is how the myth/fact/information roamed around for all to use.

If you guys want to stay with theory thats fine. My posts are about real world results and findings for the e34. One thing I did not do, as you both did, is try to insult personally instead of let your work and information speak for themselves. I encouraged you both to collect and spread your explanations so it is understandable to the rest of the board. I encourage you both to continue your research and knowledge about the e34 and to post your actual findings for all to see.

[bimmerd00d]

I'll be honest I haven't worked on e34s

Thanks for sharing all the E34 experience in this thread, it's much appreciated.



oh wait...:p

[attack eagle]

You said it. Theory.

I will go back to working on the e34 like I have been doing for the past 8 years. Yes, I do have a ton more experience with suspension combos, wheels, tires and brakes used on the BMW e34. I will report on my actual findings, help people on actual work, inform on actual test results, and report on actual (upgraded and stock) parts for the e34. As posted above, not sure if M5 brakes fit under 15in wheels? Well, 7 years ago the work I have actually done and posted can tell you. That is how the myth/fact/information roamed around for all to use.

If you guys want to stay with theory thats fine. My posts are about real world results and findings for the e34. One thing I did not do, as you both did, is try to insult personally instead of let your work and information speak for themselves. I encouraged you both to collect and spread your explanations so it is understandable to the rest of the board. I encourage you both to continue your research and knowledge about the e34 and to post your actual findings for all to see.
I encourage you then to refrain from discussing theory, attempting to discuss theory, attempting to create a suspension theory thread,Do not attempt interpret your interpretation of how it works into a comprehensive universal suspension design and theory... unless you are going to write a book. Then you can refer to your book.

So do as you suggested above and only post your personal experiences on the e34 chassis with specific details.
As for refraining from personal attacks, I say to you ********, and/or so did I... read that 3 times. My saying you are ignorant about suspension design, when you are espousing something against all suspension design and theory data because of one unnamed "guy who works at tire rack" is not an attack. It is a statement of fact. Tires not remaining in contact with the road does not = good ride.

Data that supports robs viewpoint has been listed.re: go read a dozen or so suspension design books and run the numbers yourself.

[Bimmer Nut Ed]

Stop Attacking People Who Are Simply Trying To Help And Provide Valuable Information.

[Brandon J]

I encourage you then to refrain from discussing theory, attempting to discuss theory, attempting to create a suspension theory thread,Do not attempt interpret your interpretation of how it works into a comprehensive universal suspension design and theory... unless you are going to write a book. Then you can refer to your book.

So do as you suggested above and only post your personal experiences on the e34 chassis with specific details.
As for refraining from personal attacks, I say to you ********, and/or so did I... read that 3 times. My saying you are ignorant about suspension design, when you are espousing something against all suspension design and theory data because of one unnamed "guy who works at tire rack" is not an attack. It is a statement of fact. Tires not remaining in contact with the road does not = good ride.

Data that supports robs viewpoint has been listed.re: go read a dozen or so suspension design books and run the numbers yourself.
Apparently you have a hard time composing yourself as your language displays. Too bad. I believe this is the wrong forum for such language. Whatever you call it, you might need more research on the actual tire experts. Not enough benchtop (desktop) racing research for you. Perhaps pick up a few magazines that cover SCCA racing. Those people are very good about taking suspension design theory and actually using it in a real world application, especially with a closed wheel street car. They also get advice from a certain tire expert. I bet you insult again. However, this board is typically better than that. Argue all you want, people can make their own decisions with an understanding that they should take any information on the internet with a grain of salt. Common sense. If there was a definitive answer to these type of questions then there wouldn't be any disagreements amongst people on messageboards let alone professional race teams and auto makers.

Now lets get back to the e34. How about designing a balanced BMW e34 suspension with real products in the market that fit people's needs. Lets theorize how the real products will work for people's e34s in real world environments. :)

[bimmerd00d]

Well, now that we got all that out of the way. How about some recommended setups for the various models? What's best for an '89 525i wouldn't probably be best for a '95 540i. Vehicle weight plays a lot in this. I liked my H&R/Bilstein setup mainly for the ride with the 16" 840Ci wheels on my '93 525i 5-spd. It needed a set of sway bars and possibly camber plates, but it was a nice street setup.

[Barney Paull-Edwards]

Well done for the thread,forget about the smart=alec`s. I`me in the middle of major upgrades and the following things have come to light,M5 arms are not only alloy but the set I aquired have spherical bearings.17" wheels and tyres are a hell of a lot heavier.My holy bible(Alan Staniforth) states that the inner arm pivot and outer lower pivot must be level with the ground at rest with weight of people, hence the reason I am fabricating coil-overs, to get the points level, and weight loading equal. Like most people I suspect I have a test road where each blade of grass is known,so far, in a fortnight i have improved my time by about 15% but more important, have a car that responds better,oh, and M5 early brakes are identical bar disc thickness to all E34`s, got three types in shed.Time taken in preparation is never wasted!

[bimmerd00d]

Well done for the thread,forget about the smart=alec`s. I`me in the middle of major upgrades and the following things have come to light,M5 arms are not only alloy but the set I aquired have spherical bearings.17" wheels and tyres are a hell of a lot heavier.My holy bible(Alan Staniforth) states that the inner arm pivot and outer lower pivot must be level with the ground at rest with weight of people, hence the reason I am fabricating coil-overs, to get the points level, and weight loading equal. Like most people I suspect I have a test road where each blade of grass is known,so far, in a fortnight i have improved my time by about 15% but more important, have a car that responds better,oh, and M5 early brakes are identical bar disc thickness to all E34`s, got three types in shed.Time taken in preparation is never wasted!

The arms you're talking about are the 850i ones right? The M5 ones are just heavier duty rubber bushings correct?

[Brandon J]

The arms you're talking about are the 850i ones right? The M5 ones are just heavier duty rubber bushings correct?
You are correct. The e31 control arms have bearings and cost a lot more. These don't need to be preloaded upon installation. Good luck with the coil over suspension. Knowing that it is has been done and manufactured before, the stock housing is cut to remove the spring perch. Then threading the coilover into the housing. Ground control offered them and used a different strut mount. What are you using for the coilover mount?

One caveat of the coilover is it can limit travel as the stock spring perch sits lower than the top of the strut housing. If you can manufacture the coilover so it sits lower than the stock strut housing height, that will benefit you even more for adjustments and fine tuning. If you get rattling from the coilover because of play inside the strut housing, you can add oil to take up the space.

Good luck with your coilover adventure.

[Brandon J]

Well, now that we got all that out of the way. How about some recommended setups for the various models? What's best for an '89 525i wouldn't probably be best for a '95 540i. Vehicle weight plays a lot in this. I liked my H&R/Bilstein setup mainly for the ride with the 16" 840Ci wheels on my '93 525i 5-spd. It needed a set of sway bars and possibly camber plates, but it was a nice street setup.
That combo can work well with the 16in as there is enough tire to work the bumps and shocks. I actually used 16in snow tires so things would stay nicely balanced with the sport suspension. The tires are Dunlops Wintersport M2s and they drove and handled amazingly in the dry. They are sporty so less grip than other winter tires, but that fits me here as Chicago is very quick in plowing the snow. On ebay, I bought e31 wheels for roughly $60 a wheel from some guy in a Honda shop who did not know what he had.

The 16in wheels is a great way to look closer to stock, and have a sport suspension. If you are certain to go to 17in for the look and the quicker response lower profile tires, then use a sport suspension that is softer. With the swaybars and camber plates the suspension will handle very well even with the softer springs.

H&Rs are quite stiff. Konis also. Racing Dynamics are not as stiff as H&Rs, but they also drop more as I noticed. Eibach and M-tech are great alternatives and very good companies. Dinan is even better. Sachs, as said by other e34 owners, uses Eibach springs tuned for the Sachs shocks. BavAuto and UUC springs are quite soft and tend to bottom out. I have used, installed, or driven all of these springs. I do like the progressive Eibach springs and they are very predictable.

I have also used aluminum and steel control arms. Does not do much difference while driving. Some switch to the steel ones as they are tougher. The aluiminum ones are good when combining with the rest of the upgraded suspension components.

[rob101]

wow glad i didn't read this thread for a while after i posted it.
I did the wrong thing by attacking brandon is his other thread and in effect I feel that i may have ruined it. Thats not to say that i don't stand by what i originally said but I should have not been so confrontational. I apologise Brandon for that. And I'll go further by saying its clear Brandon is obviously an intelligent guy who's done alot with his e34 without his know-how on this board many of us wouldn't be able to make informed decisions about modifications to their cars.

for the record i do work on e34s just haven't had the time yet to map out the suspension pick ups and work out cgs etc. as i have a job which takes up most of my time as an engineer (shock!). its all very well for people like bimmer dood to attack me. but the simple fact was i am a mechanical engineer and i have been in the past involved in suspension engineering I was thinking about the subject based on what i had learnt in FSAE the guy i was closely working with and learnt alot from, is now an engineer in V8 super cars apparently (found out from another FSAE guy who works with me in my current job).

Now all the weak people on this forum can come and attack me for admitting that i was wrong to act the way i did. go ahead it'll make you feel better about yourselves.

[pundit]

...Now all the weak people on this forum can come and attack me for admitting that i was wrong to act the way i did. go ahead it'll make you feel better about yourselves.
http://3ec.us/creatingfun/imgs/albums/flame/FIRE.thumb.gifhttp://3ec.us/creatingfun/imgs/albums/flame/FIRE.thumb.gifhttp://3ec.us/creatingfun/imgs/albums/flame/FIRE.thumb.gif :D

[fukem5]

very humble of yu my fren, when in was testing ferrari and schui got his left ball caught on the pit fence we didnt make fun of him like we would in my home of where ever it was, we didnt take pleasure in making him feel bad because he went a little sideways for abit, we jush cut his ball off and got on wif the luv,

morale of the story, dont know, maybe good way to save 45grams off next years car

[Barney Paull-Edwards]

actually i'd be interested to know what kind of mods they did to the M5 strut to give it more (negative?) camber. that is something I don't really know about (hence didn't mention)
Good thread! Having done the thing before Christmas and a medical fight I can shed some light on the differences. The top mount of an M5 has 11/2 -2 degrees of extra camber by having the top spring mount eccentric to the strut,also a considerably thicker insert.Yes the arm is ali but its only just lighter,oz not lbs.M5 wheels will not fit standard struts without a 30mm spacer,but M5 brakes(early) will fit over standard metric/15" wheels.Having changed the whole front end I was not very impressed,but refering to above I found out why, the car just rolled more. When I finally fitted M5 sway bars the car was transformed, now turns in a dream, is responsive to conditions and never runs out wide, even the boost delay of a diesel is ok as the front grips enough til the power arrives.Its a conversion I would recommend to all E34 owners, after all, we all really want M5`s and BMW are not too well known for making quick cars with dodgy handling !! The proof of the conversion will be Flugplatz when I can get out of the morgue/CCU!!

[weazman187]

all i know is...

meaty> no meat.
http://i21.photobucket.com/albums/b279/CaliAgents1688/Mcoupe/P1050381.jpg
http://i5.photobucket.com/albums/y197/weazman187/mcoupe6vb4.jpg
http://i5.photobucket.com/albums/y197/weazman187/IMG_4190edited.jpg

[rob101]

very humble of yu my fren, when in was testing ferrari and schui got his left ball caught on the pit fence we didnt make fun of him like we would in my home of where ever it was, we didnt take pleasure in making him feel bad because he went a little sideways for abit, we jush cut his ball off and got on wif the luv,

morale of the story, dont know, maybe good way to save 45grams off next years car
LOL :)
btw before people start jumping to conclusions when i said all the weak people on this forum i didn't mean that this forum is full of bastards far from it, I just expect that some people will endulge in taking the mickey out of me for apologising. I guess thats their choice

[Paul in NZ]

M5 wheels will not fit standard struts without a 30mm spacer,
please explain..i thought 17x8 20 mm offset wheels were "M5" wheels

[philbyil]

Well, putting all personal differences aside ;)
Here's my comments on over 11 years experience of handling a 95 525i with STOCK Aluminum LCA's (they came on the last E34 build year) and suspension but with upgraded brakes. Brakes are Ate Powerdiscs on the front and EBC Redstuff pads fore and aft. I also have a JC chip.

1. Tire pressures.
I run 35 all round with my usual max of 2 of us in the car.

2. Tire wear.
It is exactly as BMW forecast with the front shoulders and rear center wearing first.

2. Wheel rotation.
I only rotate the wheels when the rears show them toward the end of their usual center wear as I then get a thousand or so more miles from the tires.

3. Handling.
Using 35 all around, I found that you get good ride quality plus it makes the handling more neutral. Having a manual, this adds to the driving experience for me...and I HATE understeer!!

4. Tires.
NOW....to me, this is the important component. A good set of tires will transform your car, especially if you are stock.
I've had Michelins, Dunlops and Yoko's on the car....my current Yokohama AVS dB's have been the best by far. Quiet, good turn in, predictable adhesion limit, excellent in the wet and did I say "QUIET". Chip and tar roads are noisy and hard on tires and the Yoko's have done well here in Texas. I will be buying tires this year and am leaning towards Yoko's but am still doing my research.

5. Brakes.
My brake combo....Ate Powerdiscs and EBC Redstuffs, can totally overpower the tires and keep the ABS busy if you hit them hard! After having this combo for years, I like the set up and know how to "warm up" and modulate the brakes to get the best out of them. They are awesome when braking at high speed!

So, there you have it....practical advice for anyone wishing to keep the stock set-up. Which, by the way, is pretty darn good for a sedan....In all the years I have had this great car, I have never been lost by ANYONE in the twisties :D :D :D !


I am posting this in his own thread as requested to share his insight to suspension for the e34:

"I've realised that nobody is going to read past the first page of the tyre tech thread that brandon J's started.
why bigger isn't necessarily better when it comes to Tyres and rims

wider tyre.

Cornering
Pro's
- Tyres react faster to steering inputs
- Tyres do have ultimately a higher capacity for "lateral force"
Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (harder to keep contact on bumpy surfaces)
- tyres are more sensitive to changes in camber
- tyres will be breakaway in a less progressive way at their limit
- tyres will steer themselves more (increased self-aligning torque)

Ride
Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (degrades ride on bumpy surfaces)

Lower Profile tyres and increased wheel diameter

Cornering

Pros
- Improved steering feel
- Improved steering response
- Lower rolling resistance
- Improved sidewall stability under braking
- Room for bigger brakes
- Less camber distortion when cornering. (not sure 100% how this effects)
- Greater steering accuracy
Cons
- tyres will breakaway in a less progressive way at their limit
- More susceptable to sidewall damage
- Heavier (harder to keep contact on bumpy surfaces)
- More expensive
- More susceptable to tram tracking
- More critical to tyre pressure

Ride

Cons
- tyres are heavier which means higher unsprung mass which means increased disturbance by bumps (degrades ride on bumpy surfaces)

In general bigger wheels
Further to that larger sizes of wheels will usually have an increased rolling radius.


Now my theories about the e34 in general and these tyres-

- the M5 was designed to utilise the 17 in wheels with 235s and 255s (which have roughly the same width of sidewall)
- "lesser" e34s uses narrower tyres with larger sidewalls

M5

m5 rolls less and the wheels are keep flatter on the road during corner (stiffer springs and sway bars)
- this was not done by accident, in fact they probably did this in order to use the wider tyres better.
- Ride has been comprimised slightly in this car for sportiness this is a result of the stiffer suspension setup.

m5 bushes have been beefed up
- increased "reaction forces" in lower profile and wider tyres. places added stress on suspension pivots.
- increases preciseness of setup and thus sportiness

m5 has alloy control arm in place of steel arm
- counteracts the increase of unsprung mass with the bigger wheels/tyres thus helps ride/tyre contact.

M5 shocks are stiffer
- since we have more unsprung mass we must stiffen the shocks in bounce in order to maintain wheel contact.
- this increase the force transmitted to the rest of the car reducing ride
- need to increase because of stiffer springs to help ride quality (otherwise will be underdamped)

M5 brakes are bigger (and lighter?)
- well you can fit more under there so why not?
- car is faster so needs more brakes
- (and lighter?) unsprung mass again

M5 has staggered setup rear tyres are larger
- i'd expect that is to help high speed stability which is reduced by putting more responsive tyres on
- however i agree it is also because this is where the torque is transmitted to the road is also another reason.

Now lesser e34s

cheaper is better in components we don't necessarily need as much handling but ride is still important also.

body rolls more and thus wheels experience more camber, but less stiffness helps ride somewhat.
- narrower tyres with larger sidewalls can handle more camber but are not are precise and do not give as high of a limit in handling.
- setup is more forgiving due to predicability at the limit of the tyres.
- ride is good also due to less unsprung weight in the wheels and less stiffness in the setup overall.

bushes are cheaper.
- don't need them to be as strong. tyre doesn't stress bushes so much due to less tramlining besides only m5 drivers goto the track

steel arms
- less unsprung mass due to smaller wheel and narrower tyre
- steel's cheaper

Shocks are softer
- reduced unsprung mass
- softer springs need softer shocks to maintain ride.

Brakes are smaller
- cheaper
- might not fit m5 brakes under 15"s



If you want to use wider tyres and thus smaller side walls:

they will give you more cornering
- KEEP in mind the setup with regards to reducing body roll and thus keeping the tyres flatter on the road during cornering.
- the wider the tyre the less it tolerates camber, and will fall out of its optimal area for cornering and braking/acceleration.

they will be less predictable at the limit,
- too bad thats just the way it is. see next point.
- might consider tuning a little understeer at the limit (anyone for 255 at the rear?)

they will be more precise and respond quicker.
- thats actually related to the previous point so thats your consolation.

Your ride will suffer (due to more unsprung weight) (doing anything in this area is good for grip also)
- look for a lighter rim if you can
- get lighter brakes
- get alloy m5 arms

your ride will suffer (stiffer springs and sways)
- make sure you have adequate shocks to counteract the springs (helps handling also)
- other than that like everything its a trade off.

increased tramlining/wandering/high speed instability
- would be trying increase in toe in. due to a increased rolling resistance on each tyre the dynamic toe in (that is the toe when the vehicle in motion) is less than with smaller tyres. but this will decrease turn in responsiveness a little
- get stiffer bushes should help reduce play in the steering.


"So What you're saying is if i get 300 wide tyres and stiffen up my suspension enough as well as do shocks Its worth it?"
- No because there comes a point where the increase grip due to the width of a tyre isn't enough to make up for the increase in unsprung mass (and its effects on both ride and grip)
- Perhaps for a road car: we want good ride as well, a kind of trade off. This is what the M5 has set out to do and has achieved.
- Unsprung mass' effect on grip (keeping wheel in contact with road) can be reduced by increasing spring rates and shock rates however this will make the ride even worse in the process of aiding the grip.

Thus we reach our "limit state" for the road car.

it is determined by:
- by the roughness of the road you drive on regulary (on smoother roads larger wheel and tyre combinations because the disadvantage of higher unsprung mass is proportional to this.)
- unsprung mass of desired wheel/rim setup.
- unsprung mass of e34's suspension links springs shocks and struts. (alloy arms and lighter brakes help)
- Weight of the e34 in total (and thus sprung mass, more sprung mass = better ride)
- how harsh you can tolerate the ride.
- how responsive/twitchy/unstable at speed you like your car (less progressive behaviour at the limit, high speed instability/tramlining is a downside with more responsive tyres)



M division has done a good job at balancing these. I think there are many lessons to be learnt from how they've modified the base e34 to achieve a good balanced car.
Some of these may not be immediately obvious and by no means do I understand the setup in its entirity.
I intend eventually to map out some of the suspension geometry of the e34 and gain some more insight.
So. in case you haven't noticed its not an easy subject. but you weren't seriously expecting to be smarter than companies that spend millions of $s in R&D
Did you?"


The above is Rob101's explanation of suspension in the e34. He had it posted under my tire tech thread so I moved it to its own since it is talking about suspension.

[Brandon J]

Good thread! Having done the thing before Christmas and a medical fight I can shed some light on the differences. The top mount of an M5 has 11/2 -2 degrees of extra camber by having the top spring mount eccentric to the strut,also a considerably thicker insert.Yes the arm is ali but its only just lighter,oz not lbs.M5 wheels will not fit standard struts without a 30mm spacer,but M5 brakes(early) will fit over standard metric/15" wheels.Having changed the whole front end I was not very impressed,but refering to above I found out why, the car just rolled more. When I finally fitted M5 sway bars the car was transformed, now turns in a dream, is responsive to conditions and never runs out wide, even the boost delay of a diesel is ok as the front grips enough til the power arrives.Its a conversion I would recommend to all E34 owners, after all, we all really want M5`s and BMW are not too well known for making quick cars with dodgy handling !! The proof of the conversion will be Flugplatz when I can get out of the morgue/CCU!!
Hmm, I use standard M5 wheels (with staggered front and rear) without any rubbing. The M5 had an available camber correction strut mount that is offered over the parts counter. I installed these on an M5 and the camber built into these mounts are for camber correction and not for increased negative camber. They do not reach the negative camber that an aftermarket fixed plate can. So if you are thinking about ordering these camber correcting mounts, they are expensive and don't give the camber aftermarket camber plates do. The owner of the M5 that I installed the camber correction mounts said he would not do it again.

Now, I was one of the first ones to install M5 front brakes with 15in wheels and post it. I posted it on the original bimmer.info board that started in 2001. The trick with 15in wheels and M5 brakes are the calipers have to be shaved a little, a few mm can do the trick. What is the drawback? I posted before here that in the winter, there isn't enough room to keep the wheel clean from snow and the snow can affect the brakes. Also, if there is a chance you dent the rim slightly, the brakes will suffer from constant banging of slightly dented rims. So, I would suggest to skip the 15in wheels and go 16in, as intended by BMW for M5 brakes.