Got bigger tires and now I’m losing more traction?? - Ford Mustang Forum
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post #1 of 6 (permalink) Old 4 Weeks Ago Thread Starter
smecla's Avatar
Joined: May 2016
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I just switched from 255/40r19 nitto nt555 g2 to 305/35r20 general g max. Ever since I put on the bigger ones I’ve had good traction at lower speeds but for some reason my traction light keeps coming on going into 3rd at wot. It never happened before with the nittos. Anyone know what could be going on? Thanks

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post #2 of 6 (permalink) Old 4 Weeks Ago
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1st check wheel sensors, but my gut is telling me it is a speedo/tire diameter calibration issue..... may just be a hair off.

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post #3 of 6 (permalink) Old 4 Weeks Ago Thread Starter
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I contacted my tuner (Lund) and they said the 2015-2017 mustangs automatically recalibrate. Maybe I just need to reflash the tune so it learns new size?
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post #4 of 6 (permalink) Old 4 Weeks Ago
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I really don't know what is going on but here are some thoughts:

255/40-19's are about 27.1" diameter; 305/35-20 are about 28.4 . . . that is about 5% change so it probably does need to be recalibrated (speedometer will read 5% low, if nothing else)

I don't understand how the system can automatically recallibrate, if nobody tells it that the tire diameter has changed . . . does it check speed versus GPS or something? If you reload the tune I would expect that it will just reload the old diameter, unless you change it in the parameters before loading. I would definitely update the tire diameter (actually revolutions/mile) and reload the tune, to make sure that is not the issue.

Can you tell if the light is traction control or stability control? Could be stability control because it thinks it is seeing a difference in speed between the front and rear tires?

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post #5 of 6 (permalink) Old 2 Weeks Ago
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You definitely need to recalibrate for tire size. If its automatic then Speedo will be off so shift points will be off so power band will be off and so on
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post #6 of 6 (permalink) Old 2 Weeks Ago
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100% agree with everybody here that changing tire size needs to be manual calibrated. I bet what your tuner is thinking is the TPMS which will auto calibrate after so many miles and time, but not different tire size.

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