BrownGill

I finally settled on a set of wheels. I am a total novice. I have learned everything I can possibly learn from the forums on wheels and tires. There are so many threads on this subject. I am sorry to post another one.

I made a deal on the wheel/tire combo below. Do you think they will fit on my 1990 964 C4 (obviously narrow body) without spacers? The offsets are so close. Also, do you think the tires will work without rolling wheel wells? I figure I am going to have to change out the 285's for something smaller. Lastly, how important is it for a C4 to have the same total diameter on the front and back wheels + tires? Thank you for your help Rennlisters.

Fronts: 993.362.134.06
7.5 x 18 ET 50
Tires 225/40

Backs: 993.362.138.01
9 x 18 ET 52
Tires 285/30

Porsche964FP

215 or 225 front & 255 or 265 rear

c didy

I've run 225/265 with no troubles. 245/295 gets problematic but can be done with some work.


I don't know about matching radius size with the C4, it's not an issue with my C2 but it makes sense that it would be an important consideration.

There are a lot of C4 guys who should be able to volunteer info.

pcarhiway

Based on a brief mistake I made one time when I was young and foolish with an Audi A4 Quattro I think you would be well advised to have very close to the same diameters front and rear for the AWD C4.

peterC2S

Agree - 225/40/18 and 265/35/18 works. Also 225/45/18 and 255/40/18. Both less than 1% difference in rolling circumference. Very important in a C4 to keep these as close as possible.

BrownGill

This is GREAT info. All of it! I think I'll trade the back tires out for 265/35. Do you think I can get away without spacers? Your thoughts?

peterC2S

Couple of things. As yours is a 1990 I think you will need the steering stops up front if you're going with bigger wheels (17s or 18s) to stop rubbing . I have a 92 so was already modified. Do a search for details on the stops.

The spreadsheet attached has been posted many times before - Courtesy of Jeff Phillips. I've found it the best resource other than actual measurement on the vehicle for getting an idea if things will fit. Input your current wheel and tire sizes (blue bold) then your new proposed sizes (red bold) and the output is your change in clearances and rolling circumference check. Changes in camber etc will also have a big impact on clearances as will your ride height.

https://rennlist.com/forums/993-foru...l-fitment.html

Looks like they will fit alright with the right tires. I'd get them on the vehicle first and then have a look at whether you need/want spacers.

BrownGill

I would love to hear what the mistake was with the Audi?

VR6-er

205 50 17 = 637mm diameter
255 40 17 = 636mm

225 40 18 = 637mm
255 35 18 = 636mm
265 35 18 = 643mm

BrownGill

After all of the great advice and my own reading. I am planning on keeping the front tires. I am going to change out the 285 rear tires for 265/35. Both front and rear will be within 6mm on each other. I will then have to decide if I need a spacer on the rear to make sure that it does not rub.

I am having a bit of buyers remorse. I kind of wish I had held out for 8J ET 52 and 10J ET 65 18 inch hollow wheels and then put the same size tires on and used a 15mm spacer in the rear. My big worry is that the 8's and 10's will fill the wheel wells fully. I am worried that the 7.5J and the 9J are going to leave too big of a gap between the edge of the fender and the edge of the tire. Are my fears off base? DO you yall think it is going to look right? I am going to play with them when they get here next week.

Jacke2c

I run 7.5" front 225 and 10" rear with 265 and just have clearance with a 15mm spacer..... just. I only very occasionally have any "rim" rubbing issues in the rear... when pushing it really, really hard in a turn. It barely rubs the inside panel. However, I would go with 9 inch rims and the 265's and then look. A slight spacer "MIGHT" be needed, however, you don't have to worry about rim rub issues. Tire rub issues are a separate issue for me. I only see very minor rubbing issue at full lock on the front. I rarely use full lock, but I do monitor the rub when working on my car. Your choice of rims and tires is sane. I am looking, funding permitting, of downsizing my rims in the future.

BrownGill

Holler at me if you think of selling. I may look at your 10J rear if you think of downsizing.

Navaros911

There is a certain maximum amount of difference in circumference between the wheels/tires you run and the reference setup allowed on a C4.

I believe you were allowed of up to 4% of difference between the reference tire (which has a circumference of around 1985mm for the fronts and 1983mm for the back, based on 205-55-16 and 225-50-16 respectively).

With the info you provided you would end up with 2001.8mm and 1973.5mm for front and rear respectively... or 0.84% and -0.51% off from the reference tire... so you're good.

newsboy

Watch your clearance to the front fenders at turn in.Also the clearance to the oil line on the right rear.
You might want to install 5MM wheel spacers.

sml

from on my research ... for C4 diameter requirements to be within 6% or something like that .. after the doing the calcs, the best fit was 235/40 and 265/35.

but find one of those tyre calculators and check diameters yourself.