17" or 18" ??

[ZX12-R]

I've got a feeling that this topic has been discussed a multitude of times already, but this is my first visit here. I own a 1995 525i, and I am considering an upgrade from the stock 15 inch wheels and tires to either 17 or 18 inchers. In general, how significant is the difference in overall ride quality between the two? Any helpful suggestions or input will be greatly appreciated.


Thanks

[DueyT]

Welcome, ZX-12!

A "moderately" firmer ride compared to 15's, if you just change tires/wheels. If you change springs and lower the car, it will be much firmer. My 95 540i/6 has a factory M-Tech suspension and even with my current 15" winter steel rims (compared to my summer 17's), the ride is very firm. I think the biggest difference in ride quality actually comes form the springs and shocks, not so much the tires. That's just my take on it.

Cheers,
Duey

[spddmn713]

I would not go any larger than 17". I am not sure but I believe that there is a chance to severely damage the suspension by putting that large of a wheel/tire combination on the car.

[bahnstormer]

most everyone agrees that for street, +2 is the most suitable.

[Incantation]

i don't agree. i have a sacks kit and 18"s and the car is very comfortable to drive. i was very worried that it would be terribly bouncy (as per what everyone in the forum says and also the guy at the tire shop) but to my surprise it wasn't far from my 15"s

shrug

[Paul in NZ]

on a smooth road (surprise surprise ) there isnt much difference,i have mtech suspension like duey and it is firm but the low profile tyres come into play if the surface is uneven say like badly patched/repaired expansion strips or sharp edged potholes....the other factor is with low profile tyres and esp aftermarket wheels someday somewhere you will bend them......even the ricers with their little 1100 kg cars bend em

[ZX12-R]

Thanks for the feedback!

[Randell]

i have 18"s on mine, i have to brace myself every time i see a pothole coming... it's pretty bad if i had the money i'd dump these and put 17"s on! I think 17" wheels suit the car better anyway

[jplacson]

Just my 2 cents worth... btw, I live in the Philippines... where not a single road is pot-hole-free.

http://www.photos.ph/image/135384/large

http://jplacson.multiply.com/photos/photo/5/13.JPG

I'm on 18's btw.

[jplacson]

spddmn, why would it damage the suspension? weight?

[DueyT]

AFAIK, the biggest change actually comes from lowering, and then we're talking abount increased negative camber on the rear wheels (hence the infamous wearing of the inner portion of wide, rear tires on lowered cars.) Yes, firmer springs would result in higher force impulse for specific components, but I'm not sure it's anything out of design limits. I think worse damage to components can come from improper installation (thrust arms installed not under load comes to mind.)

2 more ¢

Cheers,
Duey

[ZX12-R]

jplacson Thanks for the pics. Looks sharp!!

[jplacson]

Ok, lowered E34 owners... is there anyway to correct the increased negative camber? H&R camber correction bolts? Is there anyway to correct negative camber on the rear wheels? I don't want an absolute 0 reading... but close to standard ride-height camber would be nice.

[DueyT]

Korman does...second item form the bottom:

http://www.kormanfastbmw.com/e34suspe.htm

[Karl]

On my e12 car that is lowered, I chewed up the first set of rear tires pretty quickly. But the info I got indicated that the toe change from lowering is much harder on the tires than the camber. So I used eccentric trailing arm bushings to get the toe straight and left the negative camber for handling. Even with fairly soft Yokos tire wear is not an issue this way.

[Mobius]

AFAIK, the biggest change actually comes from lowering, and then we're talking abount increased negative camber on the rear wheels (hence the infamous wearing of the inner portion of wide, rear tires on lowered cars.) Yes, firmer springs would result in higher force impulse for specific components, but I'm not sure it's anything out of design limits. I think worse damage to components can come from improper installation (thrust arms installed not under load comes to mind.)Just to correct a couple things..

1: The major difference in alignment is in rear toe, not camber. My lowered 535 is completely within factory rear camber specs - however the toe is a bit outside of spec (though not as much as you would think). I think the major reason for increased tire wear has to do with the rear alignment settings coupled with the lack of a large, supple sidewall. A tire with a huge sidewall has the give to conform to the road surface - a low profile, wide tire with a very stiff sidewall will likely put more pressure on its inside edge.

That said, I've got about 30,000mi out of my 265/35-18 GForce T/A KDWs - and they're just now getting to the wear bars. My rear end is on sagging (and debatebly junk) Jamex springs - I don't think it could get much lower. I have a set of eccentric bushings - but I haven't installed them. I'm not sure they're really necessary, now.

2: Firmer springs don't beat on suspension components so much as they do the entire car. The large (and usually heavier) wheels will stress suspension components more, as more force is required to turn them, and they have to handle the extra stress associated with swinging a heavier weight around.

Not that any of the suspension bits on an E34 aren't MORE than up to the task of holding on to even the heaviest blinged-out 18" wheel - but they will wear out a bit quicker.


Personally; I think 18s ride great (or they did, when my shocks weren't dead). Yes, potholes can be jarring - but I think the difference between 17 and 18 in that respect isn't very large - certainly much less than the difference between 15 and 17.

I love my 18"s for the appearance. In my opinion, they fill the wheel well aesthetically perfectly. 17s look smallish, to me - 19s look like a cartoon.

[pmlmotorsports]

Ok, now that just about everyone has mentioned their 2 cents worth, here's mine. The original E36 M3 was offered with 17x7.5 forged rims mounted with 235/40-17 tires on all four corners. After many BMW owners complained about harsh ride quality and the "costly" bent rims, BMW decided to change the factory offering to 17x7.5 fronts with 225/45-17 and 17x8.5 rears with 245/40-17. If the ride quality of an E36 can be refined/improved by increasing the sidewall height by 4-5mm, one can only assume the benefits will be even more recognized in the larger, heavier E34. Personally, I feel the 18" offerings look too large given the size of the rotors and the skinny sidewall of a 235/40-18 tire. In fact most aftermarket dealers will suggest a 245/40-18, the same size tire that BMW chose to offer on the E39 M5. I'll take a 17" staggered 8" fr and 9" or 9.5"rr set-up any day w/235/45-17 front and 265/40-17 rear. Hope this helps some members in making their decision.

[jplacson]

What are eccentric bushings? And where can I get them (online?)? Thanks!

[Geoff Hoad]

Whilst it is possible to fit 18" wheels to E34's the suspension geometry doesn't like it too much and there is more wear on suspension components as a result. In addition if you have upgraded the suspension it will become very uncomfortable. Therefore 17" is the best compromise. After all, it was good enough for E34 M5's so it will be great for you too. Hope this helps.

[Mobius]

Whilst it is possible to fit 18" wheels to E34's the suspension geometry doesn't like it too much and there is more wear on suspension components as a result. Your worry about accelerated suspension wear has everything to do with overall wheel WEIGHT and little to do with wheel SIZE. When switching to an 18" wheel; nothing 'geometric' changes (as long as you're paying attention to tire sizes - as you should).

A 265/35-18 tire, for example, is actually slightly smaller in overall diameter than the stock 225/60-15 tire.

The point that matters is that 18" wheels typically weigh more than smaller wheels. This means that if you're worried about increased suspension wear you should pay closer attention to weight than size. It is absolutely possible for a 17" wheel to weigh more than an 18" wheel.


In addition if you have upgraded the suspension it will become very uncomfortable. Therefore 17" is the best compromise. After all, it was good enough for E34 M5's so it will be great for you too. Hope this helps.My 18s are hardly "very uncomfortable" - except on significant bumps. Between a 17" wheel and an 18" wheel with a tire of the same overall diameter (i.e. 225/50-17 and 225/45-18) you only gain an extra half-inch of sidewall between the rim and the road. A bump that's significant enough to be unfomfortable in my car is not going to be absorbed by that extra 1/2" of rubber.

That said; for most people 17s are perfectly fine. Everyone seems to like to draw some sort of huge evil line between 17 and 18, though - and there really isn't much reason for its existence.

Don't forget that 18" tires tend to cost a good bit more than 17" tires do. :)


What are eccentric bushings? And where can I get them (online?)? Thanks!In this case - eccentric trailing arm bushings.. They allow you to adjust the axis the trailing arm pivots on - allowing you to adjust for rear camber and toe. I don't think they're very necessary (except for track use, obviously) - but I know Bavarian Autosport sells them; as does Korman (http://www.kormanfastbmw.com/e34suspe.htm).

[stx133]

I have a 95 540 with factory M5 18" rims. tyres are 235 45 18. handles excelently and the suspension is set up for these rims. not lowered too much so the camber change does not scrub out the corners too much.

Have fun.

[Badkrma]

I jsut purchased a 1990 535 and it has 17's on it. I like them and they look great. I really didn't notice any differance in the ride compared to my brothers 740 with 15's.

What years is your zx12r. I also ride a 12. I have the 2001 faster silver one. Do you ever go to zx-12r.org forum? Great stuff there.

Stephen

[jplacson]

Thanks Mobius re eccentric bushings. Now another question... what would the disadvantages be if you ran the rears at STOCK height so that camber and toe wouldn't be an issue and just lower the front slightly? Since the front camber/toe can easily be adjusted, would this setup be a better compromise? Or would running the rear at stock height, and the front slightly lowered (1" lower) introduce more geometry problems?

[ZX12-R]

I jsut purchased a 1990 535 and it has 17's on it. I like them and they look great. I really didn't notice any differance in the ride compared to my brothers 740 with 15's.

What years is your zx12r. I also ride a 12. I have the 2001 faster silver one. Do you ever go to zx-12r.org forum? Great stuff there.

Stephen

I just wanted to say thanks again for everybodys input, I really appreciate all of the helpful information and people on this site. Hopefully, I'll be getting my new wheels in the next couple of weeks.

Badkrma: I have the first generation (2000) 12R, and even with all of the controversy, it's one of the best bikes that I've owned. I agree that 12.org is one of the better 12 sites.

[Mobius]

Thanks Mobius re eccentric bushings. Now another question... what would the disadvantages be if you ran the rears at STOCK height so that camber and toe wouldn't be an issue and just lower the front slightly? Since the front camber/toe can easily be adjusted, would this setup be a better compromise? Or would running the rear at stock height, and the front slightly lowered (1" lower) introduce more geometry problems?First; you can't adjust front camber - only toe. Front toe is the only adjustment possible on a (stock, non-M5) E34.

Just lower the whole car. I'd imagine you'd introduce some odd handling problems by using stiffer springs on one end of the car only. You're not really saving yourself any trouble by going that route anyways - really. I'm still managing 30,000 miles out of the rear tires on my lowered 535. The edge wear is a little heavier than the wear on the center of the tread, but it's really not that bad. You will want to have the rear tires swapped side to side when the inside edge wears to the bars, still.

In fact, last year I had my car on the rack three times in as many months while I was replacing suspension components trying to get rid of the damn shimmy. The one time I forgot to fill my gas tank up first, my rear suspension was completely within spec. It's only when it had a full tank that the rear ride height was low enough to actually push the toe out of spec.

[jplacson]

Oh ok. Thanks! :)