Christer

John

Or you could go to 225/45/17's on the front.

slant911

Chris,

Will 225 work O.K.? I'm afraid they would rub on extreme turns. Haven't measured, but, I think that would be the case.

My original question though is will any of these set-ups screw up the PDAS as Adrian states above afetr a 4-6% differential from stock?

John K

I've got Toyo Proxes T1S's, 225-45-17, on the front and I get no rub at all. The suspension is all stock and it's not lowered. They handle great.

Adrian

Dear John K,
The C2 does not have a PDAS/ABS control unit to mess up. A 1992 C2 also has the correct steering stops installed for 17 inch wheels. The 1989 through to 1990 models do not.
Dear John of Slant911 fame,
205/50s are okay. Going to 205/40s would not be something I would recommend. However you need to check the specs of specific tyres you are looking at. They vary quite a bit. Do not forget, mixing tyres on a C4 is not a good idea either. If you change the fronts you really should change the rears as well.
If I get a chance I will check the specs myself,
Ciao,
Adrian

PS: This is for Nick I. The tyre calculators are all well and good. Unfortunately they are not set up to do what Porsche did for their calculations and programming. What we are trying to avoid here is people spending large amounts of money on new tyres and then finding they cannot be used because of traction control problems or wheel rub problems etc. All readers please note. Tyre widths can vary by up to 12.7mm from brand to brand for the same dimensions tyre. Take care least you be parted with money for nothing but problems!!!.

rich beebe

wow! i'm checking this topic out because i'm looking for 964 owner's opinions on whether there are 'actual' problems associated with running 18" rims on an RSA. what do i see but a picture of my RSA, lowered with 'enhanced' 19" rims and tires. the car in the picture is actually not lowered yet (springs are in my kitchen as i write this) and those are 18" Fikse FM5s (for sale, btw). i'm wondering if anybody has actual accounts of 18" rims doing any damage to a 964, specifically the RSA. the RSA came with 17" rims, and with 40 and 35 series tires, the 18" combination is only marginally taller. i currently have a set of Ruf rims in 18" (about to go on the car) and i'm wondering why someone like Ruf would build 18" rims, specifically for the 964, if the car/chassis could not handle them. so, does anyone know of anybody having 'real' damage done by 18" rims? if so, how long before the problem arose and where were the problems? btw, where's my RSA wing???

rich beebe

wanted to add one more thing to my last post. i have been running the 18" Fikse rims, with 225/40-18 and 265/35-18 tires, with no problems whatsoever. i fully plan to move to the even heavier Ruf rims and expect to have no problems with them either. many RSA owners run 18" with no difficulties (Rufs, fikses, kinesis, etc.). i realize this is a +1 size for an RSA, but it's still a +2 for the C2 in general. ymmv.

Adrian

Dear Rich,
The RS America is a 1993 and 1994 model year Limited Edition 964. A lightweight C2 yes but cannot be compared at all in the wheel or suspension department to pre Nov 1990 built C2s and C4s and still some fairly significant differences between 1993 models and 1991/1992 models in the same department.
You must isolate the various models. Just because it works on a RSA does not mean it will work on something else. I know Turbo (91/92) guys who run RUF 18 inch wheels. They had wheel rub issues at full lock until they installed the RUF steering stops designed for the job.
The changes across the 964 series over the years was extensive.
The Porsche "Non" Approval for 18 inch wheels let alone 19 inch wheels was for all pre 1993 models except the Turbos and was later extended to pre 1996 models except those that came "Standard with 18 inch wheels. Structural failure being the problem.
Never believe the "I have that and have no problems". Often people have no idea what has been carried out on the 964 in the past. 225 tyres up front, run 5mm spacers to be sure. I still have the damage to my rear whell arches following the advice I now say do not follow. Measure, Measure and Measure again. Be sure, trial fit, check full wheel movement up and down on the suspension as well as from the steering. Just because it is claimed that something works for one it most often does not work for you. Take Care!!!.
Ciao,
Adrian
911C4

PS: You ask about the damage done. Well I have lots of photographic and written evidence of damage done. I have even helped re-adjust a RSA to get rid of the wheel rub up front. Only took 3mm but it was wheel rub on the springs. Read up about the Audi RS4 and its 18 inch wheel collapsing problem. Nobody has yet come up with a replacement wheel that works. I believe the contract for a super strengthened wheel has been given to Sportec.
PSS: It may be less of a problem in the USA on RSAs and the like because the ride height is so much higher. We cannot play with ride heights at these levels without wearing oxygen masks (just kidding guys).

Adrian

Guys, just a quick warning here about tyre sizes and the 964 C4s.
I have just been checking out tyres (for different reasons) but I have discovered that 205s, 225s and 235s as examples, even with the same basic profile, say 55 have quite significant differences in rotational speeds.
As an example go to web site www.toyo.co.uk enter the site and click on T1S. This will brin gup all these tyres. Check out the revs per mile. You will see that some tyres just based on width not profile, are outside the limits.
Please take care when selecting tyres. This helps avoid wasting money and creating faults which can only be fixed by removing the new tyres,
Ciao,
Adrian
911C4

PS: Extreme tyre and wheel size changes will also affect the C2 ABS. Takes a lot more to mess it up but it can happen.

Nick I

Haha... erm... well I saw this topic and was intrigued by the idea. I took that picture that I took of your car at the BMWCCA autocross and made it into a stock(ish) 964, lowered and with no wing and 19" wheels. I picked yours because those rims are amazing

BTW, I've heard that RSAs can run 18's with no problems.

If you're interested, here is the original pic:

rich beebe

nick,

you did a great job with photoshop on the image. i also did a 'lowered' version of the car, after the autox, but you did a better job than i did. it was quite a shock to scroll down through the posts and run across a picture of my car. ironically, those rims are for sale and might be sold already.

adrian,

thanks for the clarification on the C2/C4/RSA issue. i was coming at it from the RSA point of view and hadn't considered the differences between the models. thanks for the info.

rich

Adrian

Dear Rich,
The RSA is much more modification friendly. One important reason is the lack of power steering. You would be surprised how much this helps in the room and loading departments. Drivers muscles versus engine driven muscles,
Ciao,
Adrian
911C4

Marc '91 C2 Coupe

As a brand new 964 owner, I doubt that I can add much to this thread, however I do have one point to note:

I would guess that the only place you could drive a 964 with 19" wheels would be on an airport runway. No other piece of road would be smooth enough. Any little bump at all would, at the very least, rattle your teeth, and at the worst, dent your wheels.

As I live in Quebec, the capital of horrible, bumpy roads (frost heaves that never get repaired), I can say that I'd have to be crazy to consider going from my current 16" wheels to even 17". I like my teeth just the way they are...although 17"ers do look really great...

Marc
(see my nice teeth? Thanks to my 16" wheels!)

MikeF

Hope that pic worked.

Added 18x10's with 265-35 and 18x8's with 225's to my 94 C2. I discussed it with the suspension guy at Jim Ellis Porsche, Bob Sanderson of Performance Imports, and Robin Hayes of Black Forest and all said it would be no problem. So I chose a size that, although aggressive for my car, will also work if I upgrade to a 993 or 996 later. There is no rubbing whatsoever. The ride is stiffer than with my 17's but I like it (plan to use the 17's for DE). The car handles like it's on rails and looks great.

I'm a believer. I went with the Kinesis-made 3.6 Turbo style wheels. Couldn't be happier.

Rockymnt964

I felt obligated to post, although this is an older thread, I was looking into other's insights and experiences as well, since I own and drive a 1989 C4 964 with 19 inch rims (also own and read Adrian's book on the 964's as well ).

Ride is 'stiffish' and noisier as compared to the ride with D90 16inch stock setup that I run with too. That said, it's not a problem in that niether my self or anyone who has rode as a passenger makes any critisism as such... ya, it's a 'sports car' , go figure.

Acquired the car with the 19 inch setup from the prior owner. After reading Adrian's considerations I was ' worried ' , yet nothing ever manifested as a mechanical nor driving problem aside from some manageable ' rubbing ' in the fronts on slower speed tight turns.. and I put at least 10K miles on that setup before wearing out the remainder of tread and then trying the stock 16 inch, D90's in comparison ( which I like too and without the annoying occassional front rub around town. Interestingly, at speed in the local twisty's running the 19 inch setup , front rub is very infrequent, attributable I suppose to body and suspension shifting that favors tire/body clearance when really 'driving' the car ). Car is lowered also with Eibach springs, front fender lips rolled. Some tire marks / rubbing noted inside of front and rear wheel wells, yet again, nothing severe, yet not ideal either, more so cosmetic and " what if " concerns, vs. any true failure of components or driving experience. The rears are mounted with a wheel spacer on stock wheel studs and original Porsche lug nuts.

Technical concerns; Porsche recommends an available 'spacer' be installed on your rack and pinion to prevent front tire rub at wheel lock when using a ' Porsche approved' 18 inch wheel setup, and yes my 1989 model is not ' approved' for 18 inch wheel ( let alone 19's ). Longer than stock rear wheel studs for wide rims that require spacers, is a consideration as well. That said, as I said, I acquired this car with 19's !!! and it has done nothing but perform very well over all ..I do make a habit of re-checking lug torque if going out for a tripple digit drive on that setup. Speedo error (?).. well seems speedo is 'more accurate ' now as my experience is that speedo's typically say you are going faster then you really are, now with a slightly taller wheel/tire combo the calibration seems closer to reality and I see that when I strafe a roadside radar speed display and it actually matches what my speedo says. I don't push this car on the track as a hard core track driver would likely do, so I can't claim other issues of stress on components..etc.. would not arise. That said I'm pretty sure the prior owner tracked it with the 19's ,... lots of negative rear camber was evident and on inner tire wear... ya, sports car, go figure..

My Gestalt is that it's a beautiful looking setup that garner's many looks and compliments; drives well enough on the street to get you thrown in jail for way above speed limits and allows you to be a very satisfied driver too if 'the man' has not otherwise stopped you. Short of hardcore track driving stresses, my experience with street driving is that your car should not suffer. Respecting Adrian's research and all, if your aspect ratios match relative within spec front to rear, your Porsche wizz bang PDA, ABS ..etc.. will still give you a very appropriate driving experience as I can atest in rain, snow, mountain and shine. For true race or track, mods need respecting on multiple levels. As a street 'sports car' ... you will look like and drive like the Rock Star you feel... Since I am retiring my Rock Star status, I am selling my 19 inch rims, staying with the D90's or untill I can afford some 17 inch Zuff's. I don't think this site lets me post pics at my free member level, I'll try do so, also will follow up with exact tire sizes and rim widths was running as I don't wish to guess and be in accurate here, need to go look in my garage when I get chance ..soon

Rockymnt964

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