Hypertech and tires

[Ernie Italy]

Hi...
What happen if we set a 37" tires (or tyres) on programmer and use a 35 or stock size ?
Speedometer goes wrong or not ?
Thanks.

[HUM GOOD]

My question would be: When changing from stock to a larger tire, how does it effect the power - low end/top end. I'm sure it changes the ratios, but is it enough to effect power? If so, would just a change of tire size in the programmer fix the issue?

come on Taz - I know you got this one......

[tomp]

it affects power in two ways. One is the gear ratio is now taller, and the other is the sprung-rotational added weight of the larger tire. It also negatively affects brake performance as well.

Going to 35s does not hurt that much with stock gearing, but does affect it both ways above to a small degree.

Going to 37s is borderline where you might opt for 4.56:1 gears and, slotted rotors. Possibly a Programmer (a must for speedo).

[HUM GOOD]

Originally Posted by tomp

it affects power in two ways. One is the gear ratio is now taller, and the other is the sprung-rotational added weight of the larger tire. It also negatively affects brake performance as well.

Going to 35s does not hurt that much with stock gearing, but does affect it both ways above to a small degree.

Going to 37s is borderline where you might opt for 4.56:1 gears and, slotted rotors. Possibly a Programmer (a must for speedo).

I'm running 37s - what would be the cost of having 4.56:1 gears put in. I do feel like I'm pushing the truck a little to hard off the line.
My braking is not an issue....I always leave a large cushion between the lead vehicle and myself.

[tomp]

4.56 gears will put you right about where you should be, where the final drive ratio is really close to stock (with 37s). Actually, I feel the H2 should probably have had 4.56 gears from the factory.

Get the Yukon brand gears as they are rated very strong. Gears will run about 150 for front and 225 for rear. H2 GM diff is 9.5 for rear and IFS 9.25 for front.

You will need a rebuild kit for both front & rear. Depending on how many miles you currently have, will justify rather you need master rebuild kit or other - consult with gear manufacturer for their recommendation on the rebuild kit to use or just go all the way and get the master kit to reduce risk.

Might consider the front locker while you are in the front diff since it will be one prrice for labor for gears and locker.

Labor for both diffs should be right about $650

When you replace gears, put Dino fluid in for first 500 miles, drop fluid and switch to good synthetic.

[Ernie Italy]

....but....anyone have explain to me what happen if I use stock tire and program the Hypertech with 37"....

[tomp]

Speedo will be off, odometer will increase at faster than normal rate and shift points may be off

[Tallowood_Air]

If you have a GPS, check and see if your speedo is right, even stock. Mine is and was 5 MPH fast. (which may be so the warranty will expire ~sooner~)

[HUMMERcustoms.com/TAZ]

Good job tomp!!!

I just checked the thread and you covered all well. Stock gears just makes it real hard to get going out of the hole with stock motor etc. with bigger tires and rims. Programmers can help some but, if you are off-roading you really do not need to worry about take off.

I overcome the poor low end with more HP and torque with SC. I plan on 4.56's at later date after I get to see what topend speed runs I can come up with on an official track. The rig launchs great now but, the 4.56's will be for 1/4 mile track runs later when i go to embaress as many that I can for underestimating the mighty H2 that we all own. Also want to really go on a rice rocket eating binge real bad.

TAZ

[HUM GOOD]

Originally Posted by Tallowood_Air

If you have a GPS, check and see if your speedo is right, even stock. Mine is and was 5 MPH fast. (which may be so the warranty will expire ~sooner~)

Your right on with this - I was 5 mph with the stock tires - now with the 37s on on the money. I was always wondering why I was doing 80mph and not passing anyone.....lol.....

5mph helps the warranty to run out faster ----

no wonder I have 80,000 miles on my 2005 already

Tomp - thanks for all your info - it's been very helpful - I am begining to search out for the gears.

[tomp]

I recently picked up a set of brand new front & rear Yukon 4.56:1 gears for $250 for the set The expensive part is now going to be the labor and rebuild kits - not to mention the new front locker