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OT need GM mechanic input

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Old 05-14-2002, 08:18 PM
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Default OT need GM mechanic input

I have a 2500 Silverado with little 245/75-16 tires on it. I saw a same truck that had 285/75-16 that filled the wheel well nicely.
All the guy did was crank on the torsion bars to level the truck front to rear. It sat nice, but I just want to make sure I am not asking for, or creating problems by doing that.

And someone please explain to me why a 2500 comes with 245 series, and a 1500 comes with larger 265 tires !!!??? Go figure.
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Old 05-14-2002, 08:20 PM
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Old 05-14-2002, 08:51 PM
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Save your old tires, if you have a warranty problem GM is trying to use the tires as the cause of your problem. Other that that go for it. I did, just saved tires just in case.
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Old 05-14-2002, 09:32 PM
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The 285/75/16 tires would probably not cause any major issues with your truck. The speedo will read a little slow as the rotations will be less but as long as it doesn't fool the ABS module into setting a trouble code you should be alright Usually the ABS only dislikes a smaller tire as in the lowrider style. The 285's are 40 mm wider than your stock tires but the reason they fill up the wheel well is that the sidewall is 75% of the tread width. Therefore the 285/75 tires have sidewalls 30mm taller than your 245/75 tires but that is on BOTH top and bottom as you look at the tire from the sidel so that 285 tire is about 2 1/2 inches taller than your 245/75 tires. I would suggest that you leave the torsion bars alone as that screws up the front end geometry and will eat up your new tires. If you must play with the torsion bars get the front end aligned after you do it.
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Old 05-14-2002, 10:18 PM
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2 things to consider: You are changing the mechanical gear ratio by putting on taller tires. If you pull real heavy loads this could be a problem. Also the vehicle computer may(I repeat, MAY) see the increased throttle pressure needed to maintain the same speed and set a code. It may just readjust it's adaptations and live with it. In answer to your question-by putting on smaller tires they increase the amount of gear reduction and reduce rolling resistance-both these things help the truck do better for corp average fuel economy and make nicey nice for the EPA.
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Old 05-14-2002, 10:27 PM
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I put the 285s on my 93 Tahoe and didnt change anything. Works great and looks much better. I wouldnt touch the torsion bars. It does put a little more load on the engine when towing the boat though.

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Old 05-14-2002, 11:46 PM
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I only wanted to tweak the torsion bars for looks, to level the truck out. I would have it aligned after, I just didnt know if it would hurt anything raising it.
I also wasnt going to worry about the speedo, I talked to the guy I met and he said it was about 2-3 miles slower, and that wouldnt bother me much, I only pull about 6,000 lbs so no problem there. Thanks.
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Old 05-15-2002, 08:51 AM
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We have the same truck although a crew cab and put 255/85's on. I believe they are about the same height as the 285/75's you are looking at. Our ABS is fine and the speedo is off - we just drive the limit now. MPG is still 11. The truck has the 4.10 gears. These tires are effectively 10% taller and 3.73's are 10% taller too. So, I figure our tow rating is about 13,000 from looking at what a stock 3.73 truck will pull.

I am curious what will happen when you put a load on the truck if you crank the torsion bars - will it squat the rear? i.e. Level unloaded = sqatted loaded?
 
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Old 05-15-2002, 02:30 PM
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Quote:
Originally posted by insptech
2 things to consider: You are changing the mechanical gear ratio by putting on taller tires. If you pull real heavy loads this could be a problem. Also the vehicle computer may(I repeat, MAY) see the increased throttle pressure needed to maintain the same speed and set a code. It may just readjust it's adaptations and live with it. In answer to your question-by putting on smaller tires they increase the amount of gear reduction and reduce rolling resistance-both these things help the truck do better for corp average fuel economy and make nicey nice for the EPA.
3/4 ton fuel economy is not reportable
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Old 05-15-2002, 02:50 PM
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Not sure how true it is but I was told that it had to do with the tires/wheels as far as load/speed.
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