Upgraded from 18 to 19" rear wheels - How do I recalibrate everything?

[bloose]

Upgraded from 18 to 19\" rear wheels - How do I recalibrate everything?

I've done some searching but all I can find are references to gearing changes, not wheel size.

I bought a second set of wheels for my ACR, (Silver painted SRT Sidewinders) upgrading from 18 to 19" wheels in the rear. (Btw, they look great on Gen II silver striped cars. Pics shortly).

The tire sizes are:

OLD - Michelin Pilot 335/30ZR18 diameter 26.1", 795 rev/mile @ 45mph
NEW - Michelin Pilot 345/30ZR19 diameter 27.4", 787 rev/mile

27.4 / 26.1 = approx. 5% larger diameter (1.0498)

Does this mean that my speedometer/odometer will always read about 5% slower/lower? How do I correct this, or is it such a small change that you just accept it and move on?

Thanks!

 

[brap]

Re: Upgraded from 18 to 19\" rear wheels - How do I recalibrate everything?

bump, because I'd be interested in seeing the photos.

 

[bloose]

Re: Upgraded from 18 to 19\" rear wheels - How do I recalibrate everything?

A few pics for those interested in the wheels. There are few vendors out there selling them. They are the refurbished Sidewinder wheels that are normally polished, but because of blemishes they painted them silver. You should be able to find them for $2495. 18" front, 19" rear.

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[ViperArry]

Re: Upgraded from 18 to 19

It looks really great with your stripes!

 

[brap]

Re: Upgraded from 18 to 19

I've been trying to find another Gen II viper that is using those rims. It is in my opinion the best looking rims for the gen II (the '99-'02 rims coming in second). Thanks for the photos! I know what my next purchase will be

BTW, your speedometer will read slower, so you are correct. I'm sure this is can be corrected in the ECU, however I don't know how they go about doing that on the Vipers. Other cars they would probably chip the ECU to correct it. Maybe someone with more experience on this can chime in.

 

[bloose]

Re: Upgraded from 18 to 19

Thanks Brap I agree of course. They clean up incredibly easy, after 4 hours of tracking the car over 2 days, I took them off to put on my stock BBS wheels and I had all 4 wheels 95% cleaned up inside and out in about 15 min. with detailing spray and a few microfiber towels.

The only downside is that the 19" 345/30 tires are about 10% more expensive than the 18" 335's but it really fills up the fender much better too.

 

[Bill B]

Re: Upgraded from 18 to 19

Call parts rack. Jon offers a calibration kit for different rear ends. It may work with tire size.

 

[bloose]

Re: Upgraded from 18 to 19

Thanks Bill, I'll give it a try. If I take my 5% correction and apply it to my 3.07 gear ratio I think a calibration unit that that could simulate a 3.22 gear ratio would probably get it pretty accurate, but that's just a half-educated guess.

 

[Viper X]

Re: Upgraded from 18 to 19

I put 18's on my SRT-10 for traction purposes and get the reverse, speedo a bit higher now.

It's so small, you should just get accustomed to it and keep driving.

 

[Marc Lublin]

Re: Upgraded from 18 to 19

Call Roe Racing. They sell a calibration box that you just adjust with potentiometers. Install the box and then run the car at let's say 60mph. You will need to know your speed either by using a GPS or having another car next to you letting you know when you are at the desired speed. Then just adjust the screw on the box so your needle reads 60mph. Only takes a few minutes to install.

 

[Batboy]

Re: Upgraded from 18 to 19

You may want to still get it calibrated but IMO the difference will not be much. I recently got larger wheels and tires on my pickup. I went from a 31x10.50 to a 305 70R16 (which translates to about 32.8x12.0). So I increased my tire diameter almost 2 inches, which is way more than your situation. After lovely conversation with Virginia's finest one morning I decided to get it calibrated. At 65 mph my speedometer was only 4 mph off. Now at 150mph (which my truck can't do) the speedometer would be more like 8-10 mph off. So, my guess is at the higher speeds is where your speedometer will be further off. So, before you go spend a boat load of cash to try and fix this just realize what the gain truly is. Hope that helps.

On a side note, where can you get those rims? Brap, do you have them on yours? I have a silver/blue and would like to see them on a silver car.

 

[bloose]

Re: Upgraded from 18 to 19

Thanks for all the input guys. I've got a Tom Tom GPS so it will be easy to calibrate once I decide I want to spend money, I just wasn't sure if the hardware was available to do it.

Batboy, Parts Rack and Archer Racing both have the wheels. Here are pictures of SylvanSRTs silver car with the Sidewinder's on it.

Close-Up
Silver SRT w/Sidewinders

I bought mine from Archer because they were onsite at Mid-Ohio raceway and already had tires mounted and balanced which I also needed badly.

I can't say enough about how accomodating Archer Racing was at Mid-Ohio. I was really late in deciding whether I could make Viper Days or not due to a recent new addition to the family. Between that and a wheel that I couldn't bust the lugs on kept me from performing any service on the car prior. Two hours before my track time Archer flushed my brake fluid, put on new pads all around as well as the new wheels and I had an absolute kick-ass time.