I did some searching, I have the tiny 245's on the 2500HD now. I want to go up to the 285 and tweek the tortion bars.

Looks like the speedo will be off and the only way to fix it is with a Hypertec (or simmalar) programmer. Right? Can the dealer change it if I go to s bit smaller tire than the 285's?

What can I expect to loose power wise? I love the power now. My truck is STOCK. Also, how bout towing? My truck tows like a dream, I have a 32; 5th wheel, bout 12k. I am worried the rear will feel "squishy" wiht the big tires. Any feed back?


Now, I am gonna answer my own question I think. I have the boost and EGT gauge and senders, just not installed. Do I say Eff it and have them installed and just get the Hypertech to add a bit of power to compisate for the power loss of the bigger tires,and calibrate the speedo?

Hope this helps,

I had a 1500 2000 with 295's on it with a 4" lift, it ran 70 mph shown by GPS showing 65 on the speedo.

My 2500HD 2002 with 265's runs 67 mph shown by GPS showing 65 on the speedo.

So you'll be off by abought 3-4 mph with 285's.

As for towing. The stock tires suck so bad in so many ways your not gona notice any thing but good things towing with new rubber. Just get a E rated LT tire with good load ratings. I run Open Countries and love them. The stock tires had a 3032 lb rating the Open Countires have a 3400 lb rating. You will have to inflate them up when towing the 5er and you'll probly want to drop them down when empty.

I run 50 all around empty and 55 front, 65 rear and 40 psi in the air bags when all hooked up; our 5er is 28" 11500 gvwr, running abought 10.5K rolling down the road.

As you said if your getting work done that needs a programer you can get your speedo done then more than likly, I didn't bother getting mine fixed, I have a GPS on the dash ):h

I have 285s on my HD you dont need to crank the torsion bars, that really stiffens up the ride, go to your dealer and have them fix your computer it only cost me 30 bucks

You are most definitely going to notice a decrease in power towing 12K. A lot of people have posted they lost a little mileage also with the 285s and bigger. Later! Frank

I run 285's, Wild Countrys, load range D. They have a rating of 3305 @ 65 PSI. They work fine, and still retain a smooth ride, although I'm only towing a 20' camp trailer. I'm not EXACTLY sure what it weighs, but it is close to around 5,000 lbs.

I re-adjusted my speedo with my Predator. Simply plugging in 285's made it "off" in the opposite direction. I ended up using 268 and it's nearly perfect now, according to my GPS.

Thanks for the help. !!