I heard that this can be done if moving up from the 245 to a bigger tire.


When I get my new truck, I was planning on cranking the torsions to bring the front up an inch or two and putting a 16x8 wheel & 285 tire on there.


Anybody done this?? Anyone running a 285 tire without a lift kit?? Thanks for any info. :)


Brad

285s are easily done! I am running 315s without a lift... now that required alot of T-bar cranking (too much) and some trimming. I look forward to hearing more answers regarding your Alli question.

You can not have the trans reprogrammed, however you can purchase a programmer of your own and raise the tire size that the computer reads so the speedo and shift patterns with be like stock. But unfortunatley there is not reprogram from the stealer on this.

So if I had thought about this right, if you put bigger meats on and do not change the speedo with a predator/hypertech/quad/etc. programmer, the tranny will shift at the same visual speed (speedometer reading) as it does today.


For example... My truck usually locks up in 5th with the 245s at ~50mph (ground and speedo speed the same). With the new 315s the speedo would read ~42mph, with the ground speed at 50mph. Will the truck shift only when the speedo sees 50mph? Do I necessarily want it to shift then because of the new effective gear ratio?


http://www.dieselplace.com/forum/smileys/Confused.gif

good question - i have wondered that as well, especially in regards to rpm levels, do you get more revs with bigger tires or opposite ?

I went from the 245's to 265's and I started getting a bump when pulling up to a stop. It was like the trans went into neutral for a second then dropped hard into low. I have a friend at a dealer and he used the tech scan tool to check for codes. While he was doing that I asked if he could reprogram the truck for larger tires. He checked the available tire sizes on the tool and said no. As he scrolled down the list on the tech 2 at the bottom there was an option for the 265's, which were stock on a 3500 with single wheels. We entered that info in to my 2500 and now my speedo is dead on and I haven't had that bump from the trans. when stopping. Its been good for two months now, fingers crossed.

315's, speed-o corrected with predator. TC locks at 55mph.

shifts on allison are based on output shaft speed, which will be the same no matter what size tires are. But tires will change rolling speed vs output speed.

shifts on allison are based on output shaft speed, which will be the same no matter what size tires are. But tires will change rolling speed vs output speed.





So it sounds like it doesn't matter that the speedo is corrected or not... Thanks for the info!

outshaft speed will be different for vehicle speed of 55mph with stock tires and 55 mph with oversize tires...so, yes, it does matter


bigger tires and the ally will go up through the gears faster

so does this mean that if you correct the speedo there wont be any tranny problems?

So, if you would change to 4.56 gears with 35'' tires will it correct this problem?

OK. Let's get right to the point. What, EXACTLY, should be done when putting on larger tires? I am putting on 315's off of an H2 this week an am looking for a simple solution. Thanks.

Another question to add is if I reprogram for 285s with my Quad will this set any codes? ie.ABS light. I would like to go to 285/70R17 with H2 rims and I have been wondering if I am opening a can of worms. I hope others have had experiences they can share.