so i've got my 285/75/16 nitto's with steel crager rims on my X..

my jeep seems a little slugish, gas mileage has gone down, and i feel like i'm running a higher RPM..

i was running the 255/75/17 SR-A..

i THOUGHT i saw someone here post that i should go to the dealer and they can adjust something in the computer since i wen up in ture size..

maybe i'm just paranoid since the fit with no hassle...

help please
steve

 

its shouldnt be noticable.. almost the same size. check out this link to compare tires sizes

http://www.miata.net/garage/tirecalc.html

 

probably just your imagination. good luck.

 

Do you have an auto? More tire/wheel weight and rolling resistence can be a negative to performance. As mentioned the dealer can only flash up to the 32" size, but some have used the Hypertech (especially with the auto) to improve things a little bit.

 

Also - many steel wheels weigh more than their alloy counterparts. give and take - more durability off road - greater weight... As mentioned above your Nittos weigh more too - so your rotating mass is higher than it was before - hence you need more effort to get it going. the wider tread means more friction - more energy to keep it moving... all of these are amplified if you have an auto with the higher gears...

 

Yeah - you are trying to accelerate to a higher speed than you thought, because your speedometer is telling you you have not reached the speed you THOUGHT you were accelerating to, so, you THINK its slower.

In reality, you only increased tire size by a measly 3%.



Your jeep computer has to relearn how to move the damn thing now too.

If you unplug the battery for a few hours (Overnight is good...), when you reconnect it...the jeep will need a week or so of driving to relearn the new set-up....so it gets WORSE at first, and then, it gets BETTER.

You will want to re-program though for the best overall utility, as your speedometer and odometer will still be off by that 3%, and your gas gauge will still say too low a mpg, etc.

 

Make sure you definitely remember your speedometer is off, that way when you see 14mpg you don't flip out too much.

 

Good point about disconnecting the battery...also make sure when you do so to depress the brake pedal for about 15 seconds...its drains all the power from the ECU and it starts fresh...or leave the battery disconnected overnight, that will do it aswell..

KSK

 

I would consider re-gearing!!! It would give you the stock feel with added power. My jeep felt really sluggish after I changed the stock x wheels to rubi's....After I re-geared it was back to normal!!