Speedo recalibration w/285s

Offroadr · January 30, 2002

Can this be done to get it accurate?

Shaners · January 30, 2002

You can buy a HyperTech programmer that will alow you to do this along with change your fuel curves and shift points too. The downside is they are about $300.

Offroadr · January 31, 2002

for $300 I'll stick to having the speedo off!

DigUout · February 2, 2002

Another option for 1/2 the price is Jet Performance Chips, SCU. Speed Control Unit. This chip allows you to change the speedo and remove the top speed limiter. No changing the fuel curves or shift points though. They are available everywhere and run about $160 -

radrado · February 5, 2002

You could also let your dealer recalibrate you speedo for the new tire size.

CMNTMXR81 · February 6, 2002

You could also let your dealer recalibrate you speedo for the new tire size.

Dealers are limited only to the sizes offered by GM for that particular vehicle. 285's weren't an option for our trucks, so GM can't reprogram the PCM with them without having to contact the Warren Tech Center and then asking for them to create a download. Of course they're going to ask questions as to "why" you need this re-programming which can be frowned upon by them.

THE BIGPUNN · February 10, 2002

i have 285's and havent noticed any speed o meter trouble. i think you'll be ok with out any recalibration.

CMNTMXR81 · February 11, 2002

Computing with the stock LT245/75-16 setup and going to a LT285/75-16 tire, his speedo will be 7.752939656286334% too slow.

Here is a useful tire size calculator I use.

http://www.secret-secret.com/turbo/DIY/tir.../turbotire.html

Vette Hauler · February 20, 2002

You can buy a HyperTech programmer that will alow you to do this along with change your fuel curves and shift points too. The downside is they are about $300.

If you have the Allison transmission, Hypertech can't help, There is a differant computer that controls it and GM has not released it's codes. The best you can do is have your Dealer reset it for 265 tires.

Dave

RedHawk · February 21, 2002

If you have the 4l80 tranny , then I say the hypertech is the way to go..You can do all kinds of things besides just adjust tires for 300 bucks.. Timing, rev. limitor increase, tire size, raise shift rpm, make tranny shift firmer, etc, etc.

I have 285`s and set my tire height for 32.5" tall tires.. Speedo is dead on now..Plus I droped a 1/2 second off my ET at the track..