Anyone gone down in wheel size?

L

lmacmil

Member
 Indiana, USA
I have a 2006 3.0si roadster with M-sport suspension and 18" staggered wheels. Even with regular (not run-flat) tires the ride is pretty punishing on anything but the smoothest roads. I need new tires (currently have Conti Extreme Contact summer tires) and plan to go to all-seasons to extend the driving season slightly (I currently store the car from mid-November to end of March.) In an attempt to improve the ride I am considering two alternatives: 1) up the aspect ratio and decrease the section width on the 18" tires or 2) dropping down to a 17" square setup which would increase the aspect ratio the same as option 1 on the front and even more on the rear. Option 2 would require new wheels but my stock were pretty beat up by the 1st owner (I bought the car in 2015). I have never seen curb rash this bad on a car.

So back to the subject question, has anyone dropped down in wheel size and if so, was the ride improvement noticeable? FWIW, this car is primarily a weekend cruiser so I'm not concerned with the potential degradation in the handling from the smaller wheels.
 
When I bought my MC it had 19" CSL Reps fitted. While they looked great nearly every other E85/86 had some sort of CSL style wheel so I bought a set of OE 18" Style 224s.

Both had non-runflats because Ms never had run-flats. The ride is a bit better but the difference isn't massive, even though I got 255/45 rear tyres instead of the OE 255/40 size.

So an improvement, but not exactly night and day.
 
I went the other way around, from 17” square 103 non-rft to staggered 18” 224 non-rft. 18” feels more responsive but comfort is roughly equal. I have the standard suspension.
 
Just look for a different tyre, you’re running a UHP tyre with stiff sidewalks to give sportier handling, if you change to a tyre with comfort as a priority ride will improve
 
I also went for bigger wheels. From 103's with run flats, to 18" 107's with non RF tyres.
These are sports cars, remember.
 
lmacmil said:
17" square setup
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My winter set are 17s. You can't go any smaller due to the front brake size.

Not a huge difference in 'comfort' but definitely the option I would pick over messing with different sized 18" tyres.
 
My last car (2.5si sport) came with a staggered 18" set up and I found it a bit too harsh for general town driving (and pothole avoidance), so I changed to a square 17" set up running Uniroyal RainSports. Very happy with the ride and handling. I've now changed my car to a 3.0si sport, and immediately I was reminded why I'd changed to 17".
I'd swap straight back to 17" again, buit the 18" MV2s have got new Goodyears fitted and are in great condition. And whereas my 17" have been refurbished and still got loads of tread left, the non-standard shade of silver might not suit the new car. I'm not getting a third set of wheels, that's for sure!
Sorry, went slightly off topic - in answer to the OP's point, get a set of 17" to help the ride soften (noticeably though not substantially). And the tyres are cheaper too! Also, slightly decreased chances of kerbing the rims :thumbsup:
 
I have 18 MV2 summer wheels and just upped the rears to 255/40/18. It has made a slight difference in comfort, although still not perfect.

I have 17 winter wheels which are more comfortable but do squirm around when pushed, but that may be due to them being winter tyres so not really comparable.

What suspension are you on? M-sport, SE, bilstein? As that also makes a difference.
 
dhobbs said:
I have 18 MV2 summer wheels and just upped the rears to 255/40/18. It has made a slight difference in comfort, although still not perfect.

What suspension are you on? M-sport, SE, bilstein? As that also makes a difference.
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M-sport. So you went from 255/35 to 255/40 and could tell the difference in ride comfort?
 
If its on the original suspension then changing it will make a whole world of difference. Bilstien B4's all round on mine and its just about perfect (on 18" wheels).
 
dhobbs said:
I have 18 MV2 summer wheels and just upped the rears to 255/40/18. It has made a slight difference in comfort, although still not perfect.
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I think I'll do that one day, but as I've got good PS4's on at the moment I can't bring myself to waste them.

Interestingly, whilst playing with NCS Expert I noticed that you can adjust the 'number of impulses per km' and 'number of impulses per km/h'. I presume therefore you can get the speedometer to read correctly for different circumference tyres. Anyone done this ?

Edit:
I've just taken my own advice, and done a search. I found this thread:
https://z4-forum.com/forum/viewtopic.php?t=90748
 
Zulu4 said:
I presume therefore you can get the speedometer to read correctly for different circumference tyres. Anyone done this ?
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Yes that's exactly what it's for, the different wheel sizes from the factory. I've not done it but it should be easy enough to calculate :)
 
Rockhopper said:
If its on the original suspension then changing it will make a whole world of difference. Bilstien B4's all round on mine and its just about perfect (on 18" wheels).
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I only drive about 1500 miles per season so I probably wouldn't spend that much money on it.
 
Could cost less than a decent set of tyres, in the Uk probably £80 a corner. Totally transformed my cars crashy harsh ride.
 
I also wonder if going from an XL tyre to non-XL would make for a softer ride.
 
lmacmil said:
dhobbs said:
I have 18 MV2 summer wheels and just upped the rears to 255/40/18. It has made a slight difference in comfort, although still not perfect.

What suspension are you on? M-sport, SE, bilstein? As that also makes a difference.
Click to expand...
M-sport. So you went from 255/35 to 255/40 and could tell the difference in ride comfort?
Click to expand...

It is better now with the larger profile. I also went for non xl load index tyres, couldn't see anywhere that the z4 needs them so went for normal tyres.
 
Rockhopper said:
Could cost less than a decent set of tyres, in the Uk probably £80 a corner. Totally transformed my cars crashy harsh ride.
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Just the parts are over $400 USD and I don't have the skill or the tools to do it myself. I need tires regardless. Interesting that it made that big a difference.
 
The only decent brand 255/40R18, non-runflat, non-XL tyre I can find is the GOODYEAR EAGLE F1 ASYMMETRIC 5 AR 95Y. The AR stands for Alfa Romeo.
Anyone have experience of this tyre (or know of any others) ?
 
Rockhopper said:
If its on the original suspension then changing it will make a whole world of difference. Bilstien B4's all round on mine and its just about perfect (on 18" wheels).
Click to expand...

I'd second this. Having owned a zed with stock msport suspension and one with aftermarket stuff the difference is night and day.
 
Mine an Msport. Even the Mrs noticed how much better it was after I’d changed them! It passed the MOT with no issues but all four corners had no damping left whatsoever when I got them off.
 
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