Wheel Upgrade Question

[slvrsrfr]

Hi All,

I'm thinking about upgrading my stock wagon wheels to bigger wheels and tires. If I do, will I need to make any modifications to the computer? I was thinking about going with these with 18x9.5 in the front and 19x11 in the rear:
2009 ZR1 Reproduction Wheels with Machined Face - Free Shipping

Thanks,
Phil

 

[zagger]

No modification just a reprogram for the new tire size, and only if you really have to know how fast you are going.

 

[slvrsrfr]

No modification just a reprogram for the new tire size, and only if you really have to know how fast you are going.

Thanks for the response. Is the reprogramming something I can do myself? Would the speedometer be the only thing that is effected if I didn't reprogram? I thought the ABS and traction control might be effected as well.

Thanks,
Phil

 

[Hib Halverson]

Be careful when purchasing reproduction wheels.

Wheel backspace for various C5s and C6es can be different. If you're buying reproduction wheels to fit an 05-09 and you put them on a 97-04, you're may have a fit problem.

In addition to the above-mentioned possible need to reprogram, you also should not change the bias of front size to rear size as that can affect ABS operation.

Lastly, if the wheel size also bring a tire size change, if you significantly alter the tire diameter, the car's acceleration performance may change.

 

[slvrsrfr]

Be careful when purchasing reproduction wheels.

Wheel backspace for various C5s and C6es can be different. If you're buying reproduction wheels to fit an 05-09 and you put them on a 97-04, you're may have a fit problem.

In addition to the above-mentioned possible need to reprogram, you also should not change the bias of front size to rear size as that can affect ABS operation.

Lastly, if the wheel size also bring a tire size change, if you significantly alter the tire diameter, the car's acceleration performance may change.

Hib,

Thank you for the information. I will definitely check the backspacing beofre purchasing.

Could you please explain what you mean by the "bias of the front size to the rear size"? I probably should be, but, am not familiar with the terminology.

You also mentioned that the acceleration performance may change. I'm guessing that since you mentoned it, the acceleration would be degraded. Why would that happen with a larger (diameter) tire size?
Thanks again,
Phil

 

[Jistari]

The bias is the difference in tire size. Stock is 17 and 18 and you are thinking about 18 and 19.

A more knowledgable tech will chime in but the way I understand it is that you are good to go if you maintain the bias (two sizes as you are speaking about) and the speedo and TCS ABS all that jazz will work if you maintain the same outer diameter for the wheel/tire assembly.

So simply stated, if you go to bigger rims you have to use thinner (shorter sidewall) tires so the overall dimension stays the same as stock.

 

[slvrsrfr]

The bias is the difference in tire size. Stock is 17 and 18 and you are thinking about 18 and 19.

A more knowledgable tech will chime in but the way I understand it is that you are good to go if you maintain the bias (two sizes as you are speaking about) and the speedo and TCS ABS all that jazz will work if you maintain the same outer diameter for the wheel/tire assembly.

So simply stated, if you go to bigger rims you have to use thinner (shorter sidewall) tires so the overall dimension stays the same as stock.

Thanks for the clarification! It is much appreciated.

 

[Gorgon]

Post pics when(if) you get them because they look like they will really stand out on the car.

 

[zagger]

As Hib stated above the 17/18 or 18/19 is only the rim size and has nothing to do with ABS or speedometer. What will make the difference is the size of rubber you will mount on the rim. For instance a 245/45-17 tire has a diameter of 25.7", if you were to mount a 245/40-18 on your new 18" rim the diameter would still be same at 25.7". Same goes for the 275/40-18 which is 26.7" diameter and in 19" rim size a 275/35-19 will be 26.6" in diameter. That equates to a difference of little more that 1/64th of thread wear from new stock tire which will have no impact on your ABS or Speedometer. God luck and post some pictures .

 

[slvrsrfr]

Thanks all! I'll definitely post pics if I pull the trigger on the new wheels!

 

[Hib Halverson]

(snip)
Could you please explain what you mean by the "bias of the front size to the rear size"? I probably should be, but, am not familiar with the terminology.

On the "bias" issue, "Justari" is correct. If the difference between the ft. and rr. size with the new tires is greater than it was with the old size, the ABS/TCS/SES controller gets the wrong wheel speed data and ABS operation can become faulty. If the "difference" between the two differences is great enough, you can get unintended operation of ABS.

You also mentioned that the acceleration performance may change. I'm guessing that since you mentoned it, the acceleration would be degraded. Why would that happen with a larger (diameter) tire size?
Thanks again,
Phil

As for acceleration change, in effect a tire diameter change does the same thing an axle ratio change can do, especially if the diameter change is significant. Typically, a tire swap such as you are considering will not appreciably change acceleration but it will change the VSS signal and that's why you need to reprogram. On the other hand, if you're going to go really big in back, it will be like going to a lower ratio or "taller" gears.

 

[napacruzerC5]

Aside from the front/rear size bias also be careful about weights. Repro wheels (especially the cheaper ones) tend to be heavy compared to the stock wheel/tire combo. I picked up a set of repro Z06 wheels, all chromed up with appropriately upsized tires. They looked great (read "bling") but weighed (by my bathroom scale) at least 25-lbs MORE EACH. Can't tell the difference in daily driving but I noticed a greater separation between me and others in my class during last year's autocrosses. So I'll keep the bling wheels for the street and mount some sticky tires on my OEM thin spokes for autocrosses. BTW - noticed that my mileage has gone down a bad 2 mpg not factoring in the taller and wider tires. Don't know what the correction factor would be.

 

[DS760]

Anyone know if going from a 295/35 to a 295/45 is going to make any negative difference? I'm trying to find soem replacement tires and cant locate the stock ones. I did find some 45's. I'm thinking the change is pretty minimal and I should be ok.

 

[Toms007]

Minimal??? That tire will about 2 1/4" taller. 295/35 vs 295/45. The math is as follows:

For the 295/35 x 18
295 (tire width in mm) x .35 (the aspect ratio) = 103.25 (sidewall height)

So 457.2 (wheel diameter in mm 18 x 25.4) + 206.5 (tire sidewall x 2, for top/bot) = 663.7/25.4 (convert to inches) = 26.12"

For the 295/45 x 18
295 (tire width in mm) x .45 (the aspect ratio) = 132.75 (sidewall height)

So 457.2 (wheel diameter in mm 18 x 25.4) + 265.5 (tire sidewall x 2, for top/bot) = 722.7/25.4 (convert to inches) = 28.4"

This is a significant difference. Too much?I would guess that this would not be a good choice.

 

[Pac-man]

45 might be too tall, call Tire Rack.

 

[DS760]

What about mixing a different brand such as BF Goodrich tires with original specs with my current Goodyear F1 supercar stock tires in the front. Will that be ok to do or cause some issue?

 

[Pac-man]

You'll be fine bro. Some people will tell you not to. Drag racers have been mixing tires for decades, flying down the track with no problems. For street use you will definatley be fine.

 

[bwing]

Tire size calculator

The above link will get you a tire size calculator.