do i have too?

[clg82]

I am getting new rims and tires with size 245/45/17 on the front and 284/40/18 on the rear. Do i need to adjust my pcm because of these tire sizes?

[third_shift|studios]

check the stickies in the tire/wheel section

[kirbbssters FireHawk]

The only reason you would need to change it is if your new rear tires are going to be taller than the stock ones.

[98T/Aformula]

Yeah if your rims are going to be bigger then the ones that you have now you will notice you will be be doing 10 over the speed limit and you speedomiter will read that your doing the speed limit haha just need to let the computer know whats going on if there is a change in size...

[tpilews]

I am getting new rims and tires with size 245/45/17 on the front and 284/40/18 on the rear. Do i need to adjust my pcm because of these tire sizes?

Like Kirbbs said, you only need to make an adjustment if the tire height is different than stock.

[mrr23]

I am getting new rims and tires with size 245/45/17 on the front and 284/40/18 on the rear. Do i need to adjust my pcm because of these tire sizes?

yes. the 285/40-18 are 27.1" tall. the 245/45-17 are 25.7" tall. this will cause the ABS light to come on and affect braking as well. for correct front to rear diameters, you need 285/35-18. they are 25.7" tall. doing it this way will keep the ABS system from freaking out and do not need to adjust the speedo calibration in the PCM.

[clg82]

yes. the 285/40-18 are 27.1" tall. the 245/45-17 are 25.7" tall. this will cause the ABS light to come on and affect braking as well. for correct front to rear diameters, you need 285/35-18. they are 25.7" tall. doing it this way will keep the ABS system from freaking out and do not need to adjust the speedo calibration in the PCM.

So I won't be able to drive? Because of the ABS system?

[clg82]

Well I installed the new rims and tires this evening and have no problem with the ABS light or the speedo being off. So I am not sure where you received the info about that but hopefully this helped.

[ZR28YELLOWJACKET]

Funny, I didn't seem to have that ABS and speedometer problem either. That .6 differance must not be enough to affect anything...

[Eugenio_SS]

you should be getting 275/35-18 for the rear... or 285/35-18... not 40 ratio.
The 40 ratio makes your rear tire taller by a full inch compared to the front and stock size.

[mrr23]

So I won't be able to drive? Because of the ABS system?

didn't say that. said it would kick off the ABS light, which, in turn affects your braking. the PCM sees the front tires turning faster than the rear and assumes the rears are sliding. when you hit your brakes, the ABS tries to compensate for that.

Well I installed the new rims and tires this evening and have no problem with the ABS light or the speedo being off. So I am not sure where you received the info about that but hopefully this helped.

how do you know the speedo isn't off? i received my info from me being in the tire and wheel business for many years. that and my personal experience with my race tires. fronts are 25.5" and rears are 27". going over 50 mph, the ABS light comes on.

Funny, I didn't seem to have that ABS and speedometer problem either. That .6 differance must not be enough to affect anything...

check your math. 27.1 - 25.7 = 1.4" difference. again, how do you know your speedo isn't off? speedo is calibrated based on gear ratio and overall tire diameter.

[mrr23]

http://www.ls1.com/forums/showthread...5&goto=newpost
here's thread in this forum where a member has this same setup and has issues with it.

[clg82]

didn't say that. said it would kick off the ABS light, which, in turn affects your braking. the PCM sees the front tires turning faster than the rear and assumes the rears are sliding. when you hit your brakes, the ABS tries to compensate for that.



how do you know the speedo isn't off? i received my info from me being in the tire and wheel business for many years. that and my personal experience with my race tires. fronts are 25.5" and rears are 27". going over 50 mph, the ABS light comes on.



check your math. 27.1 - 25.7 = 1.4" difference. again, how do you know your speedo isn't off? speedo is calibrated based on gear ratio and overall tire diameter.

Driving next to my wife we were reading the same on our spedos and also went 105 mph today and no abs light.

[mrr23]

well, consider yourself a marine. one of the few, so far.

and this is the tire sizes you have correct?
245/45/17 on the front and 285/40/18 on the rear

[clg82]

That tire size is correct!