Tire size quick adjusts

[Bdogg]

Does the predator give the ability to adjust a staggered fitted set up

Ex: 295/40/20 rears
245/40/20 front

I know it can adjust. but not sure of staggered adjustment?

[mikel]

All the PCM cares about is the rear tire size.

[Quick]

ummm... it's been a couple of years, but the SRT engineers said the Jeeps had to be wiithin 5% front to back?
and then there's traction control. Taller tires in the back would be the opposite of spinning them but I would expect some sanity checks between front and rear tire rotation. Not so?

[Bdogg]

Thanks Mike....
Quick, I am not sure if your comments are directed towards mike's response or the posted question? Either way, can you clarify what you are indicating?
Thanks

[Quick]

I posted this before but I must have fumbled on the submit or it got deleted.

According to the SRT engineers in one of the chat sessions a couple of years ago, the Jeeps are sensitive to too much difference in tire height/circumference from front to back. If you use different size wheels/tires on the front than the back they should be within 5% of each other. I think this is primarily to protect the transfer case. I got the impression that exceeding that difference by some amount will cause the car to go into limp mode. Don't know if it's the PCM or TCM that would do that. If it doesn't then you may end up hurting the transfer case or trans.

The tires you gave for an example were:
245/40/20 == 27.72" height
295/40/20 == 29.29" height
Thats just over a 5% difference

For the LXs I don't know if there is the same restriction. I know our cars do a boat load of "sanity" checks. rotation on each side of almost every major component for example. Input shaft to the trans, output shaft, wheel rotation, pitch, yaw, longitudinal g forces, etc. Then there's the ESP, BAS, and ABS. A lot of that is based on wheel rotation relative to the other wheels. In your example the rear tires are going to be turning over slower than the fronts. More than 5%. I don't know that the ESP or ABS will care about that or not. For example if you hit the brakes hard, is it going to think that the rear tires are locking up and try to compensate for that?

[concoursd]

quick, that is because each wheel has a speed sensor and the PCM is comparing difference in speed for the various strategies you mentioned above. The PCM can only adjust the tire size for the rear tires because that is what controls the speedometer. The issue you are referring to does not have to do with the speedometer.

bdogg, speedometer readings come off the transmission which is tied to the rear tire size and gear ratio.

[Bdogg]

awsome info....much appreciated

[mikel]

Yeah, I should say all we care about is rear size, to calibrate the speedo, if the car gets pissed about the height difference from front to rear, not sure what to do about that.

[Quick]

quick, that is because each wheel has a speed sensor and the PCM is comparing difference in speed for the various strategies you mentioned above. The PCM can only adjust the tire size for the rear tires because that is what controls the speedometer. The issue you are referring to does not have to do with the speedometer.

bdogg, speedometer readings come off the transmission which is tied to the rear tire size and gear ratio.

I know that. (Not sure if the rear wheels have a speed sensor or if it's taken off the tone rings on the half shafts).

I think bdogg was asking if the Predator could adjust for a stagger. Of course "stagger" usually refers more to a difference in tread width and not so much tire/wheel height/circumference.

I've never been clear on exactly where the Predator makes the adjustment for rear tire size. Yes, the Predator adjustment will correct the speedometer reading. I'm thinking that it *might* also take care of more than that? I believe the car will go into limp mode if the transmission output shaft rpm is too far out with respect to the rear wheel rpm. If the predator adjustment takes care of that then it's more than just the speedo. Same for the rear end gears.

[Bdogg]

correct...I would like to go with a wider tire in the rear...therfore based on the info, if the stock tires are 245/45/20...and i wanted to go to a 295 in the rear, what would the front and rear need to be? Or is this too wide?

[Quick]

Kinda depends. Basically you want to keep your tire heights about the same (looks better). Tread width is in mm. sidewall height is % of tread width. You have 2 of those (top and bottom) plus your wheel diameter which is in inches. Stock is 28.6" or 29".

Then it depends if you're just going for looks or you want to put the extra rubber on the road.
You have 9.5" wide wheels? a 295 tread is 11"? If you could get it on the rim it's going to be bulging on the sidewalls. Kind of like the Michellin man wearing a belt that's too tight. Might not stay on the rim either.

I think you have room for a 295 under there but you'd probably want to get your wheels widened. I think you can get a 305 or even a 315 under there but you're going to be doing a bit of body work on the inside sheet metal, cutting and modifying the plastic shields and you'd need a wider wheel and spacers.

275's will go on the stock wheels at all 4 corners just fine with no clearance issues.

[DGatzby1]

correct...I would like to go with a wider tire in the rear...therfore based on the info, if the stock tires are 245/45/20...and i wanted to go to a 295 in the rear, what would the front and rear need to be? Or is this too wide?

275 is the max safe recommended width on our 9" wheels. I believe some have tried the 295's. If you are interested in getting your wheels widened look at this link: http://www.300cforums.com/forums/srt8-s ... erged.html

beware: too much grip + horsepower = snapped 1/2 shafts

[Bdogg]

thanks again gang....awsome info