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Discussion Starter #1
Have 09' M6 sedan, makes 770ish whp, car was tuned a yr ago and have had zero issues since, now I've replaced my 28" dia rear DR's with 26.9" DR (both are MT ET/SS just that the 28's rubbed) and now when I press the TC button to disengage (once or twice does not matter) and punch it, once it hits 8-10 psi the TC gives the audible pinging and turns back on, meaning the nannies are back on. My front tires are the same I've had on the car for 20k, conti 26.2" dia, so they are smaller than the rears, where I've read guys having issues with smaller rears than fronts.. Is there something in the tune for M6 cars to adjust the tire sizing?, I've had the battery disconnected a couple times while messing with the trunk tank pump, but the wiring is still the same, and it hasn't seemed to reset the computer (if thats a thing) for a tire relearn? Thanks.. Jeff
 
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Discussion Starter #2 (Edited)
Anyone? umm.. cunts time to post..
 

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I don’t see a 26.9” rear and a 26.2” front causing an issue...

Is it possible your current tune was adjusted to accommodate your previous 28” rear tires with the 26.2” front tires; Now that you’ve replaced the rear with a 26.9” it’s causing the issue?
 

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Discussion Starter #5
I don’t see a 26.9” rear and a 26.2” front causing an issue...

Is it possible your current tune was adjusted to accommodate your previous 28” rear tires with the 26.2” front tires; Now that you’ve replaced the rear with a 26.9” it’s causing the issue?
Thats why I'm asking guys that do/have done tuning to reply back.. I don't play with my tune, set it and forget it. I have looked around in my tune, but I dont know enough on where to look if its even possible to adjust on a M6 car. The weird thing is it only happens when I get in the throttle..
 

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The speedometer calibration is in the ECM. There's a wizard in one of the pull down menu's that will adjust the settings for you based on old and new tire size. It's only 4 entry blocks on one of the tabs. I could look up what the stock tire size values and where they are on my car later if you can't find it.

I'm not sure if it would cause the car to kick out of TC off mode. As far as I understand (not a lot) it only affects your speedo.
 

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I am pretty sure the ECM compares front wheel speed to rear wheel speed to look for "slip," so if the adjustments are off, he could very well be overwhelming the T/C system. Yes, the speedo would be off a few mph but few would notice it in most situations.

Hell, my car would literally shut off until I disabled it.
 

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Discussion Starter #8 (Edited)
OK update. We went into the tune and adjusted the rear tire size, which was not much and the rears are still larger than the front. I've pulled all the ABS sensors to clean and check the hub bearings, everything looks fine. Rechecked all the connections on the shock towers good.. Go for test hit, and as soon as I get in the throttle, Service Traction control pops up and the TC (nannies) all turn back on.. I've not done anything to the car in the last 6 weeks other than put the new DR's on... Any clue where to look next? It has to be something with a sensor is my guess, once the car makes power/tq it happens, every time. ABS module? BCM??
Edit: I have also looked at both fuse boxes.. no luck.
 

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Does it do it when you hit a given RPM, or do you have to hit it hard enough you might be getting the beginnings of wheel spin?

TC measure axle RPM and compares front/rear to decide if the rear wheels have lost traction. The TC computer compensates for tire stagger, If you go to a smaller rear tire diameter, that makes the rear tires look like they're going faster relative to the front, and that can trick TC in to engaging sooner. You went from 28" to 26.9", which is about a 4% change. The TC thinks the rear tires are spinning 4% faster relative to the fronts compared to the old 28" tires. That's almost certainly going to cause a problem. Even if TC doesn't cut in immediately, at the slightest hint of any wheel spin it's going to cut in hard. You get the service TC warning because the computer sees the rear wheels are always going faster than they should be and it decides that's an indication of a fault with the system.

IMO your issue is tire diameter. And I don't know of any tool that lets you reprogram the TC to tell it the tire diameters have changed. The setting in the ECM only controls the speedometer calibration. Your only solution if you want to keep these smaller diameter rear tires is to reduce the diameter of the front tires a bit to compensate.
 

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Discussion Starter #10
Does it do it when you hit a given RPM, or do you have to hit it hard enough you might be getting the beginnings of wheel spin?

TC measure axle RPM and compares front/rear to decide if the rear wheels have lost traction. The TC computer compensates for tire stagger, If you go to a smaller rear tire diameter, that makes the rear tires look like they're going faster relative to the front, and that can trick TC in to engaging sooner. You went from 28" to 26.9", which is about a 4% change. The TC thinks the rear tires are spinning 4% faster relative to the fronts compared to the old 28" tires. That's almost certainly going to cause a problem. Even if TC doesn't cut in immediately, at the slightest hint of any wheel spin it's going to cut in hard. You get the service TC warning because the computer sees the rear wheels are always going faster than they should be and it decides that's an indication of a fault with the system.

IMO your issue is tire diameter. And I don't know of any tool that lets you reprogram the TC to tell it the tire diameters have changed. The setting in the ECM only controls the speedometer calibration. Your only solution if you want to keep these smaller diameter rear tires is to reduce the diameter of the front tires a bit to compensate.
Thanks Rocket,, It does it happens every time i roll into the throttle, not rpm, maybe boost level.? (8-10psi) It has Not done this every time.. When I 1st put the tires on I didn't notice it happen, then it was intermittent, now it happens every time.. As far as tire dia. the new rears are the same size as my rear street tires that i run every now and again without issues.. With the fronts at 26.2 dia, they are still within the margin of the TC compu to over come (per what i've read) and I dont think it would be intermittent at first. Cal and I went into the tune and adjusted the tire size with the tire wizzard, still no luck.
The only thing I've notice is my TB has been acting weird when I let off the throttle, acting like it does not slam shut all the way when I let off after WOT.. May swap TB's to see.. I'm also going to reset the TPMS sensors (relearn) and see if that makes any difference. There isn't much on the forum on this issue, hard to believe I'm so isolated on this issue.
Thanks, Jeff
 
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Maybe it’s not a tire size thing. You saying it happens every time you get on the throttle makes me think throttle body. What throttle body do you have?

There are two parameters that should be opened if you have any throttle flutter and one is hidden.
 
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Was gonna ask as well the other day Jeff. I forgot! Knew you were running an offshore tb
 
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