H3 Tires

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Originally Posted by Spuds

I suspect he didn't have 33" in stock and was trying to sell you the 31" he had on the floor.

[06-H3]

Do you need to reprogram the vehicle computer when going to the 285 tire? I switched from stock to the 285/75/16 back in May with no problems. About a month ago the SERV TMP light came on. The dealer is telling me it is because of the larger tire and needing to reprogram the computer to recognize them, at $180. Ok, but why has it taken almost six months for it to be an issue? They said the bands in the tire are fine, it's the new tire size causing the service message.

[Sewie]

Originally Posted by 06-H3

Do you need to reprogram the vehicle computer when going to the 285 tire? I switched from stock to the 285/75/16 back in May with no problems. About a month ago the SERV TMP light came on. The dealer is telling me it is because of the larger tire and needing to reprogram the computer to recognize them, at $180. Ok, but why has it taken almost six months for it to be an issue? They said the bands in the tire are fine, it's the new tire size causing the service message.

You can reprogram the PCM for the difference in tire size, so that the speedo and odometer are correct. But tire size shouldn't affect the TPM system. As for reprogramming it, the steps are in the owners manual. You can do it yourself, FOR FREE! If that doesn't work, there may be a fault in the system (ie. bad sensor) and that should be fixed under warranty.

[3Hummer]

what i want to know is when you move u how do you re-adjust the speed gauge so it shows the actual speed my friend just moved up from 32" to 33" on his rig and it shows 78 when hes going 75 etc.... so anyone know how you re adjust this? and does the transmission need to be re adjusted as well?

[Sewie]

Originally Posted by 3Hummer

what i want to know is when you move u how do you re-adjust the speed gauge so it shows the actual speed my friend just moved up from 32" to 33" on his rig and it shows 78 when hes going 75 etc.... so anyone know how you re adjust this?

Originally Posted by Sewie

You can reprogram the PCM for the difference in tire size, so that the speedo and odometer are correct.

First sentence in the post above yours.

[Dave92270]

Originally Posted by 3Hummer

...32" to 33" on his rig and it shows 78 when hes going 75 etc....

I think it is the other way around; with larger tires speedometer will show less then the actual speed

you may want check one of many calculators, here for instance:
http://www.discounttire.com/dtcs/infoTireMath.dos

as Sewie said above, to adjust the speedometer, transmission shifting points etc you have to reprogram PCM. When I went from 32 to 33 I didn't adjust anything and all is OK. One of the reasons why I didn't step up to 35's was that I didn't want to bother with PCM adjustments which may have been needed after 32-35 step; the 32-33 seems marginal

[3Hummer]

whoops missed that post ya im sorry i did mean it the other way around. Can you adjust something like that yourself or do you need to bring it in to someplace to get that done?