Speedometer?

[HummerB]

will 33" or 35" tires mess up the speedometer readings? If so is there a way to adjust it?

[HummerB]

will 33" or 35" tires mess up the speedometer readings? If so is there a way to adjust it?

[StarsnBars]

Upgrading to a larger tire will throw off the speedometer. Your dealer can recalabrate your speedometer for you. It cost me 50$ for my 33's.. And when I upgraded to 35's they said GM wont do them because they are not rated or something like that for the H3. So I'm just running them for now. Not sure if it affects shift points though. There are alot of experts on this forum that might give you some insight on this...

[Grandman]

My understanding is , if the auto was not set up for a tire size such as a 35 " then they cant reprogram the pc correctly for that tire size . Thats what i was told on my Dodge dually any way . I think there is an after market way to do so though .

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by StarsnBars:
Upgrading to a larger tire will throw off the speedometer. Your dealer can recalabrate your speedometer for you. It cost me 50$ for my 33's.. And when I upgraded to 35's they said GM wont do them because they are not rated or something like that for the H3. So I'm just running them for now. Not sure if it affects shift points though. There are alot of experts on this forum that might give you some insight on this... </div></BLOCKQUOTE>

How will the dealer recalibrate the speedo?

[StarsnBars]

Not real sure there f5. I had the smaller 31's when I bought it and got the 33's as a upgrade. They hooked up there ------ told me my speedo was now caled for the 33's. I suppose it was just a plug in off there equipment. I wasnt standing there watching them. My dealer told me I should get the speedometer reclabrated so I did. I hope I didnt get shanked 50$ for nothing.

[Planohummer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by StarsnBars:
Not real sure there f5. I had the smaller 31's when I bought it and got the 33's as a upgrade. They hooked up there ------ told me my speedo was now caled for the 33's. I suppose it was just a plug in off there equipment. I wasnt standing there watching them. My dealer told me I should get the speedometer reclabrated so I did. I hope I didnt get shanked 50$ for nothing. </div></BLOCKQUOTE>
Dealers can recal speedos for different tire sizes available on the vehicle from the factory. Due to liability reasons, GM doesn't supply the info on alternate tires/wheels.
The big change on speedo readings comes from rolling diameter, not actual diameter. Try to remember your high school geometry(I can't) and look at the relationship between radius and circumference(rolling diameter). It's a geometric progression, which means that the net effect on circumference is a compound effect from radius change.
getting away from the $5 words-bigger tires change rolling diameter more than the diameter change. Shift points AND ABS braking are affected by tire size. The pulsating rate on ABS application changes according to the rolling wheel speed that the brake module reads.
Don't forget that the difference on speedo will be a % change, not a flat amount. 10% difference at 80 mph is twice what it is at 40 mph.

If you want, disregard all the above and go by any competent 4wd shop-Hypertech programmers any many others will let you input any tire size.

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by StarsnBars:
Not real sure there f5. I had the smaller 31's when I bought it and got the 33's as a upgrade. They hooked up there ------ told me my speedo was now caled for the 33's. I suppose it was just a plug in off there equipment. I wasnt standing there watching them. My dealer told me I should get the speedometer reclabrated so I did. I hope I didnt get shanked 50$ for nothing. </div></BLOCKQUOTE>

I guess the reason I asked is I can't find where on the Tech 2 you can change the tire size. Guess I should spend some more time looking for this information. If it is there, it can only be used to switch between the two factory sizes as others have mentioned.

[nmikes]

if all this is the case, will changing your tire size also throw off your odometer as well? Saying it went only a mile when it might actually have gone a few feet further... I think a few feet every mile would really add up over time.

[timgco]

35's will throw your speedo off by 4mph around 70. you would be doing 74mph. The slower you are going, the less you are off.

[NEOCON1]

i have heard from a couple sources that there is no calibration change from 31's to 33's but have also heard oposite lately from a few different posts someone sayed tire shop did a re-cal . are people getting billed for a re-cal that doesant even excist? can i re-cal for 35's

[HummBebe]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by nmikes:
if all this is the case, will changing your tire size also throw off your odometer as well? Saying it went only a mile when it might actually have gone a few feet further... I think a few feet every mile would really add up over time. </div></BLOCKQUOTE>


Yep.

[HummBebe]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NEOCON1:
i have heard from a couple sources that there is no calibration change from 31's to 33's but have also heard oposite lately from a few different posts someone sayed tire shop re-cal . are people getting billed for a re-cal that doesant even excist? </div></BLOCKQUOTE>

We all need to keep in mind the Stock tire sizes for the H3 are 32" and 33".

[NEOCON1]

thanks Bebe i just have odd #'s in my head tonite was thinking 31-33-35 my commercial truck tires at work are 11r22.5 almost chest high but real skinnnnnnnnnnnnyyyyyyyy to much so for wheelin or id bee lookin for a 10 in lift and runnin those for free

[HummBebe]

LMAO!!! That would be a sight!

[NEOCON1]

they have swamp buggies like that dont laugh LOLOL

[f5fstop]

My speedo was off by under 2 MPH, according to two different GPS units. This is with the 33 inch tires, and still within Fed Regulations.
I have been told there is no recalibration possible by the dealers using a Tech 2, but I have not spent enough time with a Tech 2 to verify this.
Other aftermarket companies might produce a tool that can alter the tables in the computer to adjust for different size tires...not sure.

[HummerB]

Does anyone have some definitive information on altering the spedo readings?