[LA1Z24]

Can anyone confirm if DSC will freak out if your tires are more than 1% difference on a RWD car? Currently on 275-35-19 and 225-40-19. In tight turns, like a cloverleaf the DSC light if flashing and I can feel the car fighting itself. Also on hard acceleration I can feel the car trying to correct nothing.

Can anyone confirm that even RWD needs the tires within a certain diameter? Is there an adaptions reset that could fix this?


CONFIRMED - RWD MUST BE WITHIN 1%

[weehe126]

RWD only need the tires to be the same size on the same axle. So unless you are running 275 on the right and 225 on the left, you are probably losing traction

[alohasurftoad]

Originally Posted by LA1Z24

Can anyone confirm if DSC will freak out if your tires are more than 1% difference on a RWD car? Currently on 275-35-19 and 225-40-19. In tight turns, like a cloverleaf the DSC light if flashing and I can feel the car fighting itself. Also on hard acceleration I can feel the car trying to correct nothing.

Can anyone confirm that even RWD needs the tires within a certain diameter? Is there an adaptions reset that could fix this?

only x-drives require front/rear diameter differences to not be greater than 1%(1.2%)

my speculation is your tire width stagger, 50mm between front and rear, is too great causing much understeer(push) while pushing it in a small radius turn and it is somehow upsetting some traction parameter enough to cause the dsc to activate. what are the offset of the front and rear wheels?

increasing your front tire size to 245/40/19 will make the tire width stagger more reasonable

[LA1Z24]

Originally Posted by alohasurftoad

only x-drives require front/rear diameter differences to not be greater than 1%(1.2%)

my speculation is your tire width stagger, 50mm between front and rear, is too great causing much understeer(push) while pushing it in a small radius turn and it is somehow upsetting some traction parameter enough to cause the dsc to activate. what are the offset of the front and rear wheels?

increasing your front tire size to 245/40/19 will make the tire width stagger more reasonable

Front and rear wheels are +35. Do you think increasing the front tire size will still help?

[alohasurftoad]

Originally Posted by LA1Z24

Front and rear wheels are +35. Do you think increasing the front tire size will still help?

on this platform, with a 30mm width stagger example of 245/275, it is better to have the front offset 10-15mm lower than the rear, ET +32f/+42r. since your f&r offset is the same understeer is further increased with the 50mm tire width stagger of 225/275. OEM staggered is 225/255, 30mm difference, at offsets of +34-36 front, +47 rear.

handling will definitely improve with increased grip of a 245/40/19 up front and a 3mm front spacer to lower the front offset to +32. however, since i'm not sure what activates the DSC, i'm not sure any of that would resolve it. i'd feel bad if you spent money doing so and the problem isn't resolved.

[thakid22]

Originally Posted by LA1Z24

Can anyone confirm if DSC will freak out if your tires are more than 1% difference on a RWD car? Currently on 275-35-19 and 225-40-19. In tight turns, like a cloverleaf the DSC light if flashing and I can feel the car fighting itself. Also on hard acceleration I can feel the car trying to correct nothing.

Can anyone confirm that even RWD needs the tires within a certain diameter? Is there an adaptions reset that could fix this?

The problem you are having here is that the rear tire is taller in diameter than the front. The ABS, DSC and traction control systems assume that you are using stock tire sizes or at the very least tire sizes with the same overall diameter.

What is happening is the mismatch in tire sizes that you have, is causing the computer to think that the rear tires are rotating slower than they are relative to the front. This will cause power cuts in turns and during moderate to hard acceleration. This also makes the ABS system less effective during hard braking.

If you want to keep 225/40/19 on the front, you need 255/35/19 @ the rear.
If you want to keep 275/35/19 on the rear, you will need to change the fronts to 245/40/19.

225/40/19 front and 275/35/19 rears simply won’t work together because of the difference in overall diameter of those setups.

This applies to RWD and X-Drive.
In addition, if this was an X-Drive model, the 225/275 combo would wear out the transfer case as well.

To fix all of this, decide do you want to keep the front or rear as is, then change the other to match.

[visionaut]

Originally Posted by thakid22

What is happening is the mismatch in tire sizes that you have, is causing the computer to think that the rear tires are rotating slower than they are relative to the front.

Rest of your sizing advice is good, but this part of trying to explain it is wrong.

There’s no “computer thinks it’s different than it is”. We have TPMS, with individual wheel accelerometers - the car always knows the exact rotational speed and direction of all four wheels. What is happening is it sees the differences in the wheel rotations and it’s intervening to try to get them closer (more equal).

And, of course, for handling even when diameters match, with great stagger, comes great understeer…

[LA1Z24]

I will keep the 275's in the rear. They are brand new. The 225's up front are from last season.

Last season I ran a different set of wheels, same specs. Same 225 up front, but I ran a 265-35-19 without issue. that combo is less than 1% difference. how confident are you this is an actual thing on rwd? as you can see there are some naysayers

[Jvac]

Originally Posted by LA1Z24

I will keep the 275's in the rear. They are brand new. The 225's up front are from last season.

Last season I ran a different set of wheels, same specs. Same 225 up front, but I ran a 265-35-19 without issue. that combo is less than 1% difference. how confident are you this is an actual thing on rwd? as you can see there are some naysayers

The 1% is only relevant on x drive models. The stock differential really sucks though. It's weak and cuts power early and aggressively especially if you try to accelerate hard pulling out of a corner. Even more so if you are tuned for more than stock power levels. A proper lsd is a big help and really what this car needs to take full advantage of the engine.

[LA1Z24]

Originally Posted by Jvac

The 1% is only relevant on x drive models. The stock differential really sucks though. It's weak and cuts power early and aggressively especially if you try to accelerate hard pulling out of a corner. Even more so if you are tuned for more than stock power levels. A proper lsd is a big help and really what this car needs to take full advantage of the engine.

This is not an LSD or differential issue.

[thakid22]

Originally Posted by visionaut

Rest of your sizing advice is good, but this part of trying to explain it is wrong.

There’s no “computer thinks it’s different than it is”. We have TPMS, with individual wheel accelerometers - the car always knows the exact rotational speed and direction of all four wheels. What is happening is it sees the differences in the wheel rotations and it’s intervening to try to get them closer (more equal).

And, of course, for handling even when diameters match, with great stagger, comes great understeer…

I stand by what I said... Here is why.
The DSC computer expects the tire diameters to be roughly 26 inches both front and rear.
The OEM diameters are 26.1 inches at all 4 wheels on non staggered fitments.
For staggered cars, the OEM is 26.1 inches front and 26.0 inches rear. This describes the square 225 setup (26.1 all around) and staggered 225/255 (front 26.1/ rear 26.0) setup.
Basically, the DSC expects front and rear wheels with fairly equal diameters to be fitted front and rear.
This applies whether xdrive, rwd, staggered or square. The computer is tolerant of a slight amount of variance between front and rear to accommodate various degrees of wear between worn and new tires at various positions on the car.

Now, take a look at what happens when the rear wheels are switched to 275/35/19, whilst the fronts remain at the OEM 225/40/19 size... The rear 275 diameter increases to 26.5 inches while the front remains at 26.1 inches.
The 275 is half an inch taller than what the computer is expecting back there. You are correct that the computer always knows how fast the tire is rotating on the road. The wheel speed sensors measure this indepently of anything else. However, the car's actual speed is no longer accurately calculated. Remember the DSC computer counts the revolutions of the tires to determine vehicle speed. Wheel speed (in revolutions) is not necessarily equal to vehicle speed. That half inch taller tire in the rear turns less revolutions than the front, now, for any given vehicle (body) speed. This does through off the "thinking" or logic of the DSC computer.

The computer does not see speed. It only sees the rpm of each wheel, how many revolutions per minute said wheel is rolling. Those rpms are compared against the OEM tire diameters the DSC computer has programmed into it. This allows the vehicle to calculate the vehicle speed. When those diameters are too far out of spec, the computers logic surely suffers. The computer interprets 225/275 as wheelspin at the front, even though there is none. The results? Unnecessary throttle cut and brake activation to control slip that the computer thinks is there but isn't.

In any event, replacing the 225 with 245 will definitely fix this for the OP.

[thakid22]

Originally Posted by LA1Z24

I will keep the 275's in the rear. They are brand new. The 225's up front are from last season.

Last season I ran a different set of wheels, same specs. Same 225 up front, but I ran a 265-35-19 without issue. that combo is less than 1% difference. how confident are you this is an actual thing on rwd? as you can see there are some naysayers

Did your issues start to occur after the tire change? 225/40/19 and 275/35/19 are simply mismatched for the F3x platform. Half an inch in overall diameter difference is terribly significant as far as the DSC and ABS systems are concerned. I'm sure of it.

I can understand the reluctance to buy new 245's for the front, without knowing if that will fix the problem for sure.
I'm confident that it will.

It may make you feel better to test it by switching wheels with a friend temporarily to verify that your sizing is actually the problem.

There's not much else that could cause your issues...
Faulty DSC unit, mismatch tire models, mismatched tire sizes, and or faulty wheel speed sensors could be culprits.

But seeing your tire sizes, yeah, the sizes are the problem.

[thakid22]

Originally Posted by LA1Z24

This is not an LSD or differential issue.

I concur.

[LA1Z24]

I thought I had a set of 245 40 19 here in my garage but they are actually 245 35's. So I ordered the matching 245 40 19 indy 500's. They should be here tomorrow or Friday and I'll install them that day and report back.

[LA1Z24]

Ok, good news.

The 245-40-19s got delivered today. I installed them, and the issue is gone.

This extra-staggered setup also threw 2 codes in the DSC module

d35a62 d35a53

Which no longer come back. I saw quite a few threads with these 2 codes and no resolution. Well here you go!

[thakid22]

Originally Posted by LA1Z24

Ok, good news.

The 245-40-19s got delivered today. I installed them, and the issue is gone.

This extra-staggered setup also threw 2 codes in the DSC module

d35a62 d35a53

Which no longer come back. I saw quite a few threads with these 2 codes and no resolution. Well here you go!

I'm glad this fixed your issue!