I replaced my 305/30/20 tires in the rear with a set of 305/35/20's and now the car's sensors are freaking out. If I replace the fronts with a 255/40/20 vs the 255/35/20 will that fix the problem? The sensors light up after i drive @ 1/4-1/2 mile. The sensors flashing are abs, e brake, tpms, check engine, adaptive dynamics, e diff system fault, dsc not available, e brake assist not available, ebd fault. I have this posted on the f type page and they recommended the front tire change

 

The tire change or size should not have caused this issue unless there has been some damage done by the tire changer. I would inspect under the car first and if all looks OK I would get a code reader and erase all of the codes. If they return I would do a battery disconnect and touch to reset factory settings. If that fails then you may need the dealer or a good shop. Good luck and keep us posted

 

The difference in rolling diameter of the new tires is causing the noted problems. Figure out what % increase your new rear tires have in circumference and get new front tires with the same % increase. You'll have to do the math yourself or get your tire shop to do it- as they should have in the first place.

This problem is not unique to Jags, and car with ABS will do the same thing.

 

The difference in your tire diameter front to back is now out of range, this will cause ESP, traction control, ABS and many other errors to trigger and will result in reduced performance.
ESP, traction control systems are designed to work with similar sized tires to what were fitted stock from the factory, if you put larger tire on either end of the car, the ESP freaks out and thinks tires are slipping due the difference in diameter, hence the warning lights.
Go to tire rack and compare the tire diameters you have on the car currently.
Putting larger diameter tire on the front is not a good idea as the ESP programming is designed to work around the stock diameter.

 

Minimize aggravation and you'll live longer and be happier.

Put new 305/30/20 tires back on the rear, and ask your tire dealer to take the 305/35/20's back. After all, it their fault for letting you put the wrong size tires on your car.

If they won't take them back, dispute that charge with your credit card company in writing (assuming you paid for the tires with a credit card). Wait for a resolution from your CC company before you put the 305/35/20's up for sale on eBay, since they may require you to return those tires to your tire dealer.

Good luck, and let us know how you resolved this issue.

 

This exact issue is the biggest hurdle I'm looking to face with the 3.58 diff ratio upgrade I'm planning on doing

 

Correct me if I'm wrong but Draguar has essentially dropped his final drive ratio down from 3.31 to 3.16 based on the fact of a 4.4% increase in rolling diameter and this has sent his system into haywire .

I went the other way with my rolling diameter by decreasing the overall size by 3.4% i have shortened my final drive ratio from 3.31 to 3.42.

The only time i actually have issues is immediately after start up, if I attempt to put the foot down the engine mangement cuts all power however by the time i reach the end of my street I have no issues i thought this was due to the system re-calibrating the new ratio .

 

The car no idea how fast it's actually travelling, just how fast each wheel is turning with respect to each other. If the OP were to keep all four tires within the circumference ratio limits of the factory design, the car wouldn't know the difference.

The real problem would be that the speedometer and odometer would under indicate by 4.4%. I see speeding tickets in the OP's future.

 

Because of the OP's other new thread https://www.jaguarforums.com/forum/x...e-xkrs-179516/ and no reply to this one, I'm suspicious - is the OP for real or is he the NavTool troll under another name? His sketchy personal profile and spelling errors fit the troll's modus operandi. He even snookered me into replying to this thread.

My apologies to draguarxkrsgt if you're not a troll. How about proving it by posting a picture of the back end of the 2014 XKR-S GT you claim to own, including the license tag and your local newspaper or something else to prove the date that picture was taken and that you're in Pennsylvania?

I suggest no further replies until we hear back from the OP.

 

+1

 

This statement is incorrect. The ECU and TCU knows that for any given speed, the rpm's should be within a certain range. If they are not within that range, the car will go into limp mode, normally locking the transmission in second or third gear. You will get transimission code saying turbine speed does not match output speed. Increasing tire size beyond a certain point will cause limp mode issues even if all of the tires are similar size. It seems that the threshold differs from manufacturer to manufacturer.

 

The car has no knowledge of what it's actual over-the-road speed is. It knows for a given engine RPM the wheels should rotate at a certain speed depending what gear the transmission is in. The speedometer gets it's input from wheel RPM, not actual vehicle speed.

Changing tire circumference does not affect the ratio between engine and wheel rpm.

 

Go ahead and fit some 24" or 30" overall diameter tires and then tell me it makes no difference. It does and you will have check engine lights and transimisson will go into limp mode.

 

Why?

The ratio between wheel speed and engine rpm does not change.

 

Who cares if he is a troll or not. This is an interesting topic and I am learning quite a bit from reading it.

 

Your problem is a low-dying battery. The tire change is just a coincidence.

 

Those are very real faults- you would have to be an xkr/f type owner to know them. I got the exact faults when my battery was going weak.

 

Mufc I'm totally with you on this but how do explain this ..This particular model was fitted with 3.69:1 final drive with codes blaring however it didn't go into limp mode ?

Is there a way it was bypassed or do the older 4.0s/c units have a different system in place / Ecu/ tcm


http://www.caranddriver.com/amp/revi...ad-test-review

 

ordered 255/40/20's to put up front. Will be checking the battery as well buy had no issues with the car until I put on the rears. The diameter changed 5.4% between the fronts and rears with the 305/35's. Installing the 255/40's will bring that down to 1.4% so hoping that should do it. Thx for the feedback.