Taller tires - computer recalibration

Slap a power programmer (you +about$300) or their computer (them + whatever they decide to charge) into the diagnostic terminal on your truck, inputting tire size change at appropriate prompt, wait a couple minutes, drive away calibrated.

Danno,

I saw a recalibration gizmo in either Jeg's or Summit's catalogue.

Call em' and see what they can do. IIRC it was around $149.

Doc

I would find someone with a GPS and clock it to see.

When I went up from the stock 215's to 235's, my speedo was right on. it was off before...

Mike

mxz1972 wrote:

Going up from a 215 to a 235 will not change the speedo. That is the width of the tire in millimeters. The second number is what determines how tall the tire is.

Going from 215/75 to 235/75 *will* change the calibration because 75% of

I agree with another suggestion, find a GPS and try it before sweating the issue too much. My Toyota Avalon indicates a bit slow, my Sonoma is maybe

About the only issue you will have with ABS is if all wheels are not of the same size, or if the size changed so much that it moved the low speed disable-ABS point.

Maybe you should explain that the width of the tire is 235mm and that the height is an aspect ratio of 75% of that width.

~KJ~

thats right, but just going the 215 to 235 will not, no aspect ratio was listed.

If not listed, I assume it to be the same for both 215 and 235. Same aspect ratio (say, 70%, 75%, 80% or whatever) and tire height changes when the width changes. This is by definition.

Here's a decent calculator:

I understand completely how tires are sized. I was just stating the 215 and

Jason

Taken from the original post.. '2000 GM 4x4 - switched from 265/75/16 to

I would think that a 285/70/16 would be closer to the original size..

-- History is only the past if we choose to do nothing about it..

It sure will unless you radically change the profile.

I went from P215/75's stock to P235/75's.

It is a lot taller tire.

Mike

What's funny though is how everybody else knew what the original poster meant without the mention of aspect ratios........

Matt

I didn't bother to list the aspect ratio, it was the same, that's why it changed my speedo.

In order for those tires to be the same, the aspect ratio would have to be radically different, something like a 75 series and a 50 series.

If I did that, it really wouldn't make any sense to post about it would it?

Mike

I am not speaking of the original post, I am speaking of one deeper in the thread. Obviously, the profile was stated in the original post

Whats even funnier is I'm not speaking of the original post. I am speaking of the one to which the response was to.

In order for the heigth of a 215 and 235 to be the same, there be by no means a radical difference. Maybe 5% at most.

A lot taller? 15 mm (just over 1/2 inch) is a lot taller?

Ok - so i have been to 3 gm dealers today and they all told me it is not possible to recalibrate for 285/75/16 tires. So what is the deal - the hand held aftermarket power programmer will work but the dealer says impossible. Can anyone shed some light on the topic for my feeble brain. Is it even really necessary except for the speedo and maybe the shift points? The tires are only about 1 - 1.5" larger in diameter. What are the consequences of leaving it as is?

impossible.

work out the Pi R squared formula from high school and work out how long the circumferance of the 285s are and the originals there will be a difference, divide the number of feet in amile by the circumferance in feet and thats how many times the wheels turn in a mile. the smaller wheels will turn more often and the mileometer will be out by however many turns of the wheel the

fun maths. not sure if it will help.

rhys