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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHAnalysis Paralysis on C4S tire sizing
Leading reported evidence
Run across the tire dimension conversation and the differential
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This only came to the surface when I was looking through the forums and ran across the tire dimension conversation and the differential.
Leading evidence: 'Run across the tire dimension conversation and the differential' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Run 235/35/19' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
FWIW a lot of guys including myself run 235/35/19 with 315/25/19.
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Suggestion
I found a set of OEM 4S wheels for cheap - had a bunch of scuffs; but wanted to run these for track days....
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Suggestion
I will be running the Toyo Proxes R888R this weekend.
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Not sure why the pic didn't work, but it looks good!
I could use some help here.
I am having 19x8.5" and 19x11" Forgestar wheels built for my 04 C4S. So, obviously, I'm moving to 19" tires.
From the reading I have done, I have to take into consideration of the tire speed in relation to front and back because of the viscous coupling for the AWD system.
Factory tire size:
F: 225/40-18
R: 295/30-18
Roughly looking at revolutions per mile charts and tire diameter charts, the front tires rotate approximately 4.007% faster than the rears
19" tires
F: 235/35-19 (for 8.5" width wheel)
R: 305/30-19
This would equate to the front tires rotating more per mile by a 2.95% difference.
Would this drop in difference cause a problem with the drivetrain?
You need the rear tires to rotate faster than the front. The rear tire has to have a smaller diameter. The set up you have will seldom direct any power to the front wheels.
This shroud have been determined BEFORE commissioning the rims. My suggestion is to stay as close to the OE ratio as you can.
As a side note, all the racing watercooled 911s that I've seen had 18" rims. None went bigger than that. Something to think about when looking for performance enhancements in the future.
255 would be the max I think. It could also affect driving characteristics.
Much depends on which particular tire you will choose as each of them has a different shoulder profile.
For example ... I had a 295/35/18 Bridgestone S02A on a 10J rim which was way to big. The tire lost its squareness at the shoulder. Which influenced cornering stability. However when I put on the Yokohama AD08r295/35/18 it looked much more tight and square then the Bridgestones. Most probably due to its extra stiff and stronger carcass.
So each tire type will cope differently with the extra width. Me personally, I would not go wider then 245. Moreover the balance between width in the front and rear is also important. So it depends also on that. But of course each person has its preferences and if it is for cruising around then it is less important.
I found a set of OEM 4S wheels for cheap - had a bunch of scuffs; but wanted to run these for track days.... keep my 4S wheels in the great shape they're in. This way I didn't have to speculate on ratios and sizes, etc
I will be running the Toyo Proxes R888R this weekend.
I am staying as close to the ratio as possible. Also, my car will never see the track. I'm not really into that side of things. My C4S is a nice weather driver and "cars and coffee" regular. It probably sees less than 3000 miles a year. So I don't consider the wheels a "performance enhancement".
This only came to the surface when I was looking through the forums and ran across the tire dimension conversation and the differential. I was not aware of the rotational speed difference between the front and back. I assumed the overall tire circumference was the same front to back.
There is an allowable variance in all the dimensions between tire manufacturers. Go on a site that states actual tire diameter for a specific tire that you are looking to buy and then calculate the ratio. This way you'll know exactly what you are buying.
Well, I just got lucky! My source for the wheels didn't enter the order yet!!! I had him switch back to 18" wheels 18x8.5 and 18x11. Now I can just go back to OE sizing!
Your analytical abilities regained by a wise decision.
Had my own 19" back to 18" revelation last year and
can reassure you the car will perform much better when back
to OE 18's.
Try to go light weight with the wheels to save unsprung weight
so to compensate for the addition of 14 on the rear and 7mm
spacers upfront.
Some titanium lug bolts, perhaps later lower it...C4S perfection.
The Forgestar wheels will be pretty light. I do plan on the titanium bolts as well. Probably this coming winter or next spring I'll be getting the PSS10 set up to bring it down a bit. My Porsche allowance is limited per year by the wife!
I would save the money for something else that actually make either a performance of visual difference. The titanium bolts won't do either. Maybe have the mufflers modified to make the engine sound better or buy a spare ignition key switch so when it breaks, you don't have to wait for the replacement or a new pair of headlight bulbs (they do get dimmer as they age).......pretty much anything but titanium wheel bolts.
My bolts now are pretty ugly so I want to get something nice to look good against the candy red.
I have already done quite a bit of repair and preventative maintenance on the car. It's also getting a full wrap in a few weeks after I am done wet sanding it.
No need! Paint them with a spray can of silver or whatever shade titanium is and they will look new. A buddy of mine did it to his 996 and didn't even had to remove the wheels. Did one batch of 3 per rim and then the other two afterwards. His bolts now look new.
here is a before and after pic of the new R888R's - I've never run any track tire - so nothing to compare them too - but ohhhh my how they grip.
#before
after 8 sessions
This is a source reference. Confirm exact model applicability in the original material.
