GlenE

My current tire/wheel setup is as follows:

Front
18x9.5 ET55 with 275/35-18

Rear
19x11 ET62 with 295/35-19

Will need to replace the tires soon and seems the 295/35-19 has very little choice out there. Was thinking of going down to a 285/35-19 but may look a little odd on the wide rear wheel.

What about a 325/30-19? Too wide?

Tires in my current sizes I am thinking about are:

Michelin Pilot Sport
Conti ExtremeContact Sport

Suggestions on brands and sizes from those that have dealt with all of this sizing stuff would be awesome.

Present sizes flush tires with fenders almost perfectly.

Thanks in advance!

Route99

The change from a 295/35 to 285/35 is going to drop the height of the tire about .2" and the section width about .3-.4". Depends upon the manufacturer of the tire, of course.
At my feeble old age, I'm not sure I would see too much difference in 1/3".

striper

You should try a 265/35-18 in front and a 305/30-19 in the rear. Those sizes will be correct for those size wheels and are closer to the overall diameters of the original tire sizes.

LoneStarLizzard

I run 275/35-18 in front and 305/30-19 in rear (NITTO tires). Basically similar setup.

In any event the key is to keep the tire's outside diameter the same as stock so you don't throw electronic monitors/ABS out of whack. You can do your own geometry calculation to determine what wheel/tire configurations will retain a stock outside diameter (that's what I did), and some tire retailers have calculators that help you out.

Here's a link to calculator that former C5 owner (and tech contributor) Toque used: http://www.rimsntires.com/specspro.jsp

And here's a link to Toque's discussion of wheel/tire fitment issues: http://www.toquez06.com/wheels.html

Lots of good information there.

The Lizzard

GlenE

I haven't had any issues with TCS or ABS using the 275/35-18 and 295/35-19. Not sure if I would want to go to the 305 and the rears are flushed to the fender. Don't want them out any more. Thoughts on the 275/35 front with 285/35 rear? Would get the stagger much closer to stock. Only thing is the 19x11 wheel is that maximum for the 285/35. Would it look too stretched to fit that wide of a wheel?

93Polo

Tires are like shoes for your car, some brands run wider than others despite being the same size. Tirerack is a good place to look at section widths across various tires, if you pull up the tire and then look for specs. A 305 might not be the step you think it is.

GlenE

Here are the specs for the two rear sizes

295/35ZR19
(100Y) SL
300 AA A 1,764 lbs. 51 psi 7.5/32" 29 lbs. 10-11.5" 10.5" 11.9" 10" 27.1" 767 US
305/30ZR19
(102Y) XL
300 AA A 1,874 lbs. 50 psi 10/32" 30 lbs. 10.5-11.5" 11" 12.3" 11.7" 26.3" 792

Section width is close at 11.9 and 12.3. The big difference is the tread width 10.0 and 11.7. I would assume the section width would be the widest point, and at only .4" wider for the 305, that's only .2" inside and outside. Hmmmm, this may be the way to go.

Would it be better to stay with 275/35 in front or go down to 265/35?

275 is 25.6" diam and 265/35 is 25.3" diam.

These are taken from a Michelin Pilot Super Sport.

What would you choose?

Gordy M

The wheels you have are happy for use on a C5 so what you are interested is the ratio between front and rear and speedometer error. You need to keep a front/rear ratio of 0.3 to 1.1". An example would be front diameter of 25.3" and rears of 26.1" which give you a ratio of 0.8" and the car is happy. However if you car came with 25.7" fronts tires (standard C5) and you put 25.3" tires up front your speedometer will be off slightly.

GlenE

Is there a maximum difference between front and rear diameters that will for sure, cause errors in TCS or ABS? As I mentioned, running the 295/35-19 and 275/35-18 has never caused a problem.

LoneStarLizzard

Glen, my understanding is that the difference between front and rear diameters is NOT what is important to ABS. Instead, its is the circumference of the tire - the closer to stock circumference your aftermarket tires are, the more likely your ABS will function normally. You can run 17" rims up front and 19 or 20" rims in the back so long as the circumference of the front and rear tires is approximately stock.

Also, the stagger (tire width difference) between front and rear impacts handling, but not braking.


The Lizzard

GlenE

Well, my tire purchase had to be delayed and I am now back at it. Trying to stay as close to oem OD, which is 25.7 front and 26.7 rear. As I have wider wheels than stock, I can go with a 275/35-18 front and a 325/30-19 rear. OD would be 25.6 front and 26.7 rear, almost exact as oem. Would the rears be too wide for the offset I have, ET62? I can always go the the 305/30-19 which OD is 26.3 and would probably fit a little better in the fender.

Any thoughts on which to go with or any other suggestions would be very much appreciated!

sstonebreaker

Just FYI, tire diameters are generally set to standard sizes, despite the fractions of an inch you get when you calculate based on the sidewall numbers. Tires are going to be 25, 26, 27, or 28 inches (or their metric equivalents) in diameter when new. You put a 265/35 R18 tire up against a 275/35 R18 tire from the same manufacturer and they're going to be exactly the same height. This makes it a lot easier for designers when they're designing the car, because they can spec for tire diameter and tire width separately. So don't worry too much about fractions of an inch. Anyway, tires are going to wear over time, so the diameter doesn't stay the same in any case.

Dark Sarcasm

Wouldn't a 275 on a 11" wheel get stretched as opposed to being on a 10" wheel? Therefore shortening the sidewall height? Therefore shortening the overall diameter? Not saying you are wrong but my experience has been tires vary differently from manufacturer to manufacturer.
Not sure about performance tires but off-road tires vary in height regardless of what is written on the sidewall. 33's measure 32" and 36's measure 35"s when mounted.

akanitro

I am running 19/20 wheels but I am running 285/35/19 up front and 305/30/20 in the rear and I have no clearance issues at all.

sstonebreaker

Tires don't stretch or contract all that much, sidewall or tread. Think about how they're constructed - the rubber is supported by nylon and/or steel wire, plus the internal air pressure.

You mentioned a tire that was stretched on a too-wide wheel, but think of the opposite case - a tire on a slightly narrow wheel. Does the tread expand so that the sidewall is straight? Or does the sidewall instead form a curve? It's more pronounced on high profile tires like off-roaders, but it's there on sports car tires as well.

A 26 inch tall tire does about 800 revs per mile. If you take a Y-spec tire that is rated for 186 mph (300 kph), that works out to about 2100 g's of centrifugal force on the tire at 186 mph. If the tread doesn't expand under that kind of load, then wheel width for sure isn't going to affect it much.

The only exception to this that I've ever seen is top fuel and funny car drag slicks, but those are a special case.

As far as tires varying by manufacturer, well sure, there's going to be some variation. But not enough to matter - if they're off by too much no one is going to buy their tires.

GlenE

Let me run this by everyone.
Stock sizes and diameters are:
Front 245/45-17 25.7"
Rear 275/40-18 26.7"

How about these sizes for 18" front and 19" rear?

275/35-18 25.6"
325/30-19 26.7"

Almost exact stock diameters. Question is, will the 325/30-19 fit with a 19x11 62ET wheel? Front is what I run now and no issues with fitment.

LoneStarLizzard

Fronts are fine. Rears are a scooch big, but not likely a problem. I run 275/35/18 up front and 305/30/19 in the rear. Those tires are exactly the same diameter/circumference as the stock wheels/tires.

GlenE

Lizzard

Went out and did some measurements. Yep, 325 would poke out too far for my liking. The 305 would be about as wide as I would dare do. The 305/30 is approx 26.3" diameter, just a hair shorter than the stock at 26.7" I have a coupe, the ZO6 sizes are slightly different.

What brand/model tires do you run? They can get really costly in the rear for Michelin 4S or Potenza RE-71R. Was thinking of Conti ExtremeContact Sport. Thoughts ?

LoneStarLizzard

Yep, 325's only fit if you flair the rear fenders.


I run Nitto INVOs...they're not the best tire for hooking up or high speed, but they do have the best tread wear ratings and they're very quiet. I ran 20k+ miles on my first set, and have 15k (so far) on the second set, without any hiccups on either set. They aren't the least expensive option out there...around $1,200 for a set through Discount Tire. You can go lower if that's your preference.

But IMHO the INVOs will last much longer than Pilot Sports or other tires that are built more for performance.

The Lizzard

Dark Sarcasm

Yeah that makes sense. Thanks.