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Bigger tires+10 bolt rearend

Chris97K1500

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Chris97K1500 Enthusiast

Chris97K1500

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Posted

Well, I've been saving my $$ and almost have enough to get either the 35" X-terrain's or the 36" STS Radials. Just wondering if the rearend will hold up with these larger tires? Also, any problems with the front diff possibly? The 35's will fit with no problems, but the 36x14.50's are going to need some air dam and bumper trimming. Thanks, Chris

Ben Enthusiast

Ben

Posted
Posted

A 1997 GM Truck will have come with stock 30 inch dia tires, so going to 35" or 36" tires will be about 20% larger.

 

That means the diff ratio will change by about 20%, meaning all things that count tire rev's will be off by about 20%. Speedo, tranny computer, ABS computer, etc.

 

Also means the brake lever arm has been effectively reduced by about 20%.

 

You'll need to change your diff ratio to higher numeric ratio by about 20% to keep things close to what they were.

 

Nothing can be done with the brakes other than to go to Praise Dyno Brake pads/shoes or to larger dia rotors (which will require larger dia wheels).

 

Then the known weakness of a 10 bolt and it's JB5 rear brakes. Better to consider 12 bolt (and the JB6 drum brakes) or even 14 bolt (this is an 8 lug wheel...though there are some 6 lug on the "small" 14 bolt semi floater).

Chris97K1500 Enthusiast

Chris97K1500

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My truck already has 4.10's put in. As well as a Superlift Truspeed Calibrator to get the speedo, ABS, Shift points all in line with the change in gearing and bigger tires that I now have. The Truspeed is adjustable, so that won't be a problem. But the rearend will have to stay the same. Not worth it to me to change it considering I'll be getting a D/A CC GMC truck around '06-'07. The truck originally had 3.42's. Any other thoughts? Chris

Chris97K1500 Enthusiast

Chris97K1500

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Not to say yours doesn't work right, but if you put the settings at a 35" tire, then you'll be off to start with. BFG 315's aren't a true 35" tire, they're a little less. My tires aren't a true 33", they are 32.6 or something. I got mine dialed in perfect with my GPS. At what speed are you off by 5mph? I can't be throughout the range, since it's percentage you are off. If you are off 5mph at 65mph, it would be off by like 1.5mph at 20mph, not bad. Try to adjust it some more, you should be able to get it as close a 1% off. Maybe you got a bad unit? Chris

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