I went from a stock 16 rim (steel - 22570R16) to a stock 17 rim (alloy - 255/75R17). I know my speedo is now about 7-9% off (calculated 11%). Question is this. I think the change is affecting my torque-on-demand AWD and I'm now getting a noise when I "jump on the gas" that wasn't there before. If I reflash the computer to account for teh tire profile, should that fix it?
Changed Tires/Wheels 2000 Expy
- Thread starter takem01
- Start date
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tonydiv
technical advisor
Most programmers will allow you to set the new tire size in Expy's that are 99 and newer. (and technically 98s, if they have the digital odometer)
It would be an easy way to try to solve the issue before you resort to taking it to the dealer.
It would be an easy way to try to solve the issue before you resort to taking it to the dealer.
OK, I'm a real newby at this
Does the programmer stay with the truck or is it a program and forget process? According to the dealer, it's like $90 to flash the computer for tire size (or, pretty much anything else) and it's more than twice that for a programmer. Can I rent/borrow a programmer somewhere and do the or what? I've only heard of programmers since I bought the tires and wheels a couple of days ago.
I think I answered my own question. I did a search on the forum for "programmer" and found a ton of info. I think that the programmer is sort of a second VMC that looks at the drivetrain performance data, tunes it and sets new control set points for the engine/tranny/transfer case. it lets you account for things like tire profile, lift above OEM frame height (?), etc., as well. That sound about right?
Does the programmer stay with the truck or is it a program and forget process? According to the dealer, it's like $90 to flash the computer for tire size (or, pretty much anything else) and it's more than twice that for a programmer. Can I rent/borrow a programmer somewhere and do the or what? I've only heard of programmers since I bought the tires and wheels a couple of days ago.
I think I answered my own question. I did a search on the forum for "programmer" and found a ton of info. I think that the programmer is sort of a second VMC that looks at the drivetrain performance data, tunes it and sets new control set points for the engine/tranny/transfer case. it lets you account for things like tire profile, lift above OEM frame height (?), etc., as well. That sound about right?
Last edited:
Problem solved
Was getting a rumbling from the TC under heavy acceleration. Went to Ford and the shop manager (a real nice guy) diagnosed the problem right away. At no cost. Seems that the new tires I put on the front had a different profile than those on the rear (about 20000 miles on them by my estimate), even though they were the same profile (255/75R17).
Guy says 'you're not going to fix the rumbling/thumping by reflashing for tire size, and explains that a difference of as little as 1/8" in profile results in enough mismatch in RPMs to mess up the control equations for the A4WD. He says you have to replace all 4 tires at the same time, etc., of you're going to get this kind of a problem. I went back to the 16's (all 4 new). problem solved. Once I get enough $$ to buy 4 17's, I'll go back.
Oh, and by the way, I'd assume that tire pressure differential front to back, etc. might induce problems similar to this. Can you put a switch on teh magic brown wire?
Was getting a rumbling from the TC under heavy acceleration. Went to Ford and the shop manager (a real nice guy) diagnosed the problem right away. At no cost. Seems that the new tires I put on the front had a different profile than those on the rear (about 20000 miles on them by my estimate), even though they were the same profile (255/75R17).
Guy says 'you're not going to fix the rumbling/thumping by reflashing for tire size, and explains that a difference of as little as 1/8" in profile results in enough mismatch in RPMs to mess up the control equations for the A4WD. He says you have to replace all 4 tires at the same time, etc., of you're going to get this kind of a problem. I went back to the 16's (all 4 new). problem solved. Once I get enough $$ to buy 4 17's, I'll go back.
Oh, and by the way, I'd assume that tire pressure differential front to back, etc. might induce problems similar to this. Can you put a switch on teh magic brown wire?
outkast
Full Access Members
maybe, but the best way to do it is remove fuse 104 (I think) and rpace it with a fused,switched wire...this way you can turn it all off, then back on when you need 4wd. (your shift motor is off when you pull this fuse)
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