I searched and really don't know what to type in to find the answer to this. I'm sure it's in here somewhere.
I just bought new wheels for my car and 19x9.5 and 19.13 rears. I have 345/30/19's on the rear and due to concern regarding rotational speed differences, I chose a front tire height that closely matched it. Many of you probably already know or guessed that it looks bad. I know if the speeds are too far off between the front and rear it can cause problems, but am wondering how much difference I can get away with before I begin having problems.

Thanks

 

C5 stock are 245/45/17 front and 275/40/18 rear, that is a difference in the overall diameter of just less that an inch. So that is what I would be looking for.

 

 

Toque posted a very informational thread on this subject. Your best bet is to use a tire calculator that can be found anywhere on the net. As stated by TR6Speed and Allegro, it's all about the overall diameter.

 

Thanks guys. Any advice on key words to type in to find Toque's thread?

When it comes to upsetting the active handling I'm thinking that one inch difference between the front and rear tires running 17-18's will make more difference vs 19-19's since that one inch will have a greater RPM difference on the smaller wheel/tire setup.

Any other rules of thumb that I should be aware of when re-selecting my front tires? I mentioned my rear tire size, but neglected to mention that currently my fronts are Invos 255/40/19 with a listed height of 27.17 compared to the rears having a height of 27.36

Nitto also offers a 255/35 with a height of 26.10" and a 30 with a height of 25.12"
Looks like the 30 may be too short or too much difference. Thoughts?

 

Hey Bret,

The other cure is just to turn off your active handling and then you can run any tire size you want. With the power that you put down I can't imagine that you use the the AH system anyway.

As others have stated a 1/2" stagger height minimum is needed. That's why most guys do 18" or 19" wheels, but nowhere near as wide as you run.

Michelin offers the best array of sizes however they are probably nowhere near as sticky as you need them.

 

Toque posted this tire size calculator :


http://www.rimsntires.com/specs.jsp

I found it useful when I changed my wheels

 

I can't find the link but here's Toques outstanding post:

Guys:

I have been seeing a bunch of posts recently with folks asking questions about what sized tires to go with their rims. They are also asking if there Active Handling, and Traction control will have issues.

First off, I would like to say that your Rim size has NOTHING to do with the stagger that GM built into these cars. You do not have to upgrade to a 18/19 combo, or 19/20 combo. You can upgrade to 18/18 or a 19/19 combo with no issues. The TIRE sizes is what maintains the built in stagger from GM. As long as you choose the correct tire size then you will NOT have issues with Traction control or Active Handling.

Check out this great little wheel/tire calculator I have been using for years.
http://www.rimsntires.com/specs.jsp

If you input the original tire you have now, and input the proposed size you want to go with, it will output the differences.

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Here is an example of the Calculator output comparing a stock sized rear Z06 tire to a larger tire size (the size I upgraded to in my rear).

Tires:.................Tire 1..................Tire 2
Tire size..............295/35-18...........305/30-19
Section width.......295 mm (11.6'')....305 mm (12'')
Sidewall..............103 mm (4.1'').......92 mm (3.6'')
Tire diameter.......663 mm (26.1'')......667 mm (26.3'')
Rim sizes.............18x9 to 18x11.......19x9.5 to 19x11.5
Circumference......2082 mm (82'').......2094 mm (82.4'')
Revs per mile........773.....................768. 4
Speedometer: Assuming that this is OEM tire and speedometer readings are correct.When speedometer reads 60mph (96.6km/h) actual speed will be 60.4mph (97.2km/h): 0.7% faster.

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Stock C5 Tire Sizes to use in calculator:

Using the original size of your tires (see below). Use the above calculator and do the math. If you up size your tires, you want to make sure you up size the front and rear the same amount (or as close as possible). That way you avoid the computer seeing a mismatch in tire speed between the front and rear tires. Thus eliminating Active handling, and Traction control issues.

Stock C5 (97-04):
Front
Rim size = 17x8.5" rim
Tire Size = 245/45/17
Circumference = 2047mm
Diameter = 652mm
Rear
Rim Size = 18x9.5"
Tire Size = 275/40/18
Circumference = 2126mm
Diameter = 677mm

Stock C5 Z06 (01-04):
Front
Rim size = 17x9.5" rim
Tire Size = 265/40/17
Circumference = 2022mm
Diameter - 644mm
Rear
Rim Size = 18x10.5"
Tire Size = 295/35/18
Circumference = 2082mm
Diameter - 663mm

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Here is an example of what I did when I upgraded to a 19/19 combo.
I have had no issues with traction control, or active handling since I got this combo.

Using the calculator above I calculated up sizing my front and rear tires to a size that kept me very close to my stock tire circumference/diameter, AND made sure that both tires increased/decreased the same amount.

Front
Stock Z06 = 265/40/17 = (Circumference = 2022mm)(Diameter 644mm)
Proposed = 275/30/19 = (Circumference = 2038mm)(Diameter 649mm)

Rear
Stock Z06 = 295/35/18 = (Circumference = 2082mm)(Diameter 663mm)
Proposed = 305/30/19 = (Circumference = 2094mm)(Diameter 667mm)

So with my proposed new tire setup:
Front --> Increased the Circumference by only 16mm (Diameter 5mm)
Rear --> Increased the Circumference by only 12mm (Diameter 4mm)

As you can see above (for my situation), both proposed tires are barely larger than my stock Z06 setup. The most important thing is that they both increased the same amount (ish). Thats the key to keep the traction control, and active handling in check.

**************************************** **************************************** *************

I also recommend that you verify the calculator values by going to the tire manufactures web site to verify the sizes this calculator spits out for the specific tire you plan to purchase. Just to be sure...

If something does not make sense above feel free to ask.

Hope this helps !
Toque

 

FWIW: I run 275x35x18 and 345x30x19 on my car with no problems. PS2's all the way around. Be warned - Michelin is very proud of these tires - $$$ - but I still think they are the best overall tire for these cars.

Note: I don't drive my car when the road surface gets below about 50 degrees. Everything goes up in wheel spin.