How to calibrate for new wheels?
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How to calibrate for new wheels?
Ok- I got some 19" MRR wheels for my vert. Pretty sure I'm going with the Hankooks. What is going to happen when I increase the overall diameter by about 2" on each wheel? I know the rears have to be about 1/2 bigger than the fronts. I'm concerned about speedometer calibration and what will I have to do to get it corrected?
Tech Contributor
Joined: Jan 2004
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From: Wylie TX --> Less is More, except under the hood !
Just because your rims increase 2" front, and 1" rear does not mean that your tires will increase the same.
Your goal is to try to maintain the same overall diameter of your new tires compared to stock.
Lowering your side wall of your tires is what you want when you increase your rim size.
You should not have to change your speedo if you size your tires right.
Sizing your tires is also very important to keep your active handling and traction control in spec.
I am also running 19/19 wheels.
See my post on the subject.
http://forums.corvetteforum.com/c5-g...ah-issues.html
Hope this helps !
Toque
Your goal is to try to maintain the same overall diameter of your new tires compared to stock.
Lowering your side wall of your tires is what you want when you increase your rim size.
You should not have to change your speedo if you size your tires right.
Sizing your tires is also very important to keep your active handling and traction control in spec.
I am also running 19/19 wheels.
See my post on the subject.
http://forums.corvetteforum.com/c5-g...ah-issues.html
Hope this helps !
Toque
Last edited by Toque; Jan 18, 2011 at 10:07 AM.
Thread Starter
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But I WANT a taller tire
My goal is not to keep the same overall diameter as oem. I WANT a taller tire on the 19" rim. Oem diameter is about 25.25" and if I go with 275-45 19 on the back the diameter will be 28". So I can get a front that matches and about 1/2" smaller to keep the proportion close.
I have seen this size on a non lowered c5 and it looks great. Ghats what I want, plus a little more sidewalk can soften the ride a little.
So- my question remains: how will I recalibrate the speedometer to work with the larger overall diameter tires? Also, I believe the speedo will show that I am going slower therm actual- correct?
Oh- and mucho thanks for the quick reply. I have the wheels now and I'm getting ready to order the tires.
I have seen this size on a non lowered c5 and it looks great. Ghats what I want, plus a little more sidewalk can soften the ride a little.
So- my question remains: how will I recalibrate the speedometer to work with the larger overall diameter tires? Also, I believe the speedo will show that I am going slower therm actual- correct?
Oh- and mucho thanks for the quick reply. I have the wheels now and I'm getting ready to order the tires.
Melting Slicks
Joined: Dec 2003
Posts: 3,315
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From: Near Jacksonville Fl.
You will need someone with tuning software like HPT, EFILIVE, or a Tech-II.
But I don't know about changing it for that much difference, GM designed the computer to compensate for "some difference do to different Mfg. of tires." But your asking for one h*ll of a lot.
But I don't know about changing it for that much difference, GM designed the computer to compensate for "some difference do to different Mfg. of tires." But your asking for one h*ll of a lot.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
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From: CA.
St. Jude Donor '13-'14-'15
Going to a bigger diameter tire on the rear will make your speedo show slower than you are actually going--TICKET TIME-- Your actual speed with the 28" tires on the rear will be off 10% !!! that's huge !! so if your speedo says 70--you are really going 77 MPH----
If your car is an automatic---it will also require a "shift point correction"
in order for it not to short shift and shift at too low an RPM--
A gear change correction however, is NOT required on a C5 besuase the speedo sensor is on the output side of the diff and not on output side of the tranny like on a Camaro---
If your car is an automatic---it will also require a "shift point correction"
in order for it not to short shift and shift at too low an RPM--
A gear change correction however, is NOT required on a C5 besuase the speedo sensor is on the output side of the diff and not on output side of the tranny like on a Camaro---
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
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Race Director
Joined: Apr 2007
Posts: 11,150
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From: South Western Ontario
I doubt your fronts will clear. My 275/30/19's just clear when turning (same diameter as stock but wider). I suspect you'll hit the inner wheel wells badly if you go 2" larger in diameter. Take a look. I'm not sure there is even 2" between the tires and the front side of the wheel wells when the stock wheels are straight.
Peter
Peter
Burning Brakes
Joined: Jul 2012
Posts: 944
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From: WV
Follow up
I have a similar question as the OP, but from the opposite perspective.
I am considering using stock c5 z06 wheels and tire sizes on my otherwise stock c5 A4 (NOT a z06). The new rear tires will be about 0.55 inches shorter than the current ones, front difference will be less.
I have read Toques excellent post for how to maintain original tire od, but I want to explore this exchange (to z06sizes) before I commit to my other alternative (an 18/19 combo maintaining stock od's as advised in Toques post).
I understand that a Tech II can reprogram for the new shorter tire size, but is this 0.55 inch change within the allowable range?
Will I also need to reprogram the shift points of the A4?
Will the above upset AH, ABS, etc?
Thanks for the help!
I am considering using stock c5 z06 wheels and tire sizes on my otherwise stock c5 A4 (NOT a z06). The new rear tires will be about 0.55 inches shorter than the current ones, front difference will be less.
I have read Toques excellent post for how to maintain original tire od, but I want to explore this exchange (to z06sizes) before I commit to my other alternative (an 18/19 combo maintaining stock od's as advised in Toques post).
I understand that a Tech II can reprogram for the new shorter tire size, but is this 0.55 inch change within the allowable range?
Will I also need to reprogram the shift points of the A4?
Will the above upset AH, ABS, etc?
Thanks for the help!
