got new rear tires put on...couldn't go above 27 mph???

AZIROC · 10-26-2021, 02:20 PM

2018 zl1 A10 55xx miles, car always in sports mode unless at the track.

Track season is here in 2 weeks (atleast for me) and I needed to swap rear tires. I had a set of M/T ET streets (305/35/20) on and got a new set of SC3's (305/30/20) put on yesterday. I left the discount tire to the side road to hit the light, never got above maybe 20 and it drove fine. When the light turned green I made the left to get on the main road and gave it some gas to get up to speed (45 mph zone). The car felt REALLY down on power, the traction light was flashing and the car wouldn't get above 26-27 mph. I even floored the gas pedal and the car still stayed in the 26-27 mph area. The tires weren't spinning..aka I wasnt roasting them, but I wasn't going past 27.

I made it to the next light and stopped. traction light went away as well. When the light turned green I gave it some gas, again like normal, and it drove fine. I even floored it and acted like it normally does and got up to 60. Got on the freeway to go home, and again, it drove fine.

So what the heck happened? to "sticky" of a tire?

squish72 · 10-26-2021, 11:51 PM

What size are your fronts? Too big of a difference in front to back is my guess

AZIROC · 10-27-2021, 12:56 AM

Quote:

Originally Posted by squish72

What size are your fronts? Too big of a difference in front to back is my guess

Fronts are the factory 285 sc3's. Had 305/35/20 MTs and went back to the factory 305/30/20 sc3s

Dabjbr · 10-27-2021, 09:36 AM

Difference front to back was also my guess. Perhaps the car “learned” and adapted to the tall 35’s and when you went back to the shorter 30’s, it it thought the additional revolutions was loss of traction and triggered ice mode.

Far fetched? Maybe but it seems logical. Perhaps it will relearn and adapt to the correct 30 profile and your experience will be a one time occurrence.

ctrlz · 10-27-2021, 10:38 AM

Quote:

Originally Posted by squish72

Too big of a difference in front to back is my guess

This is almost certainly the problem. Inflation can also affect the diameter the car "sees." In other words, you can slightly underinflate a larger diameter tire and slightly overinflate the smaller tire and it may get you out of low power mode.
The slight warming during the driving you describe may have been enough to bump the diameter within range. May have just been one tire throwing things off. Pull up the pressure display and see what's going on.

MP3BOOSTED · 10-28-2021, 07:06 AM

to answer everyone, i messed up at first and ran a 26 inch front skinny with a 28 inch tall rear and i was able to hit speeds over 100 but i did throw a CEL as well as felt like car was down on power. my point is i was able to go faster then 27 mph. i think this might be a different problem. Could be wrong but sharing my 2 cents

ctrlz · 10-28-2021, 10:50 AM

Quote:

Originally Posted by MP3BOOSTED

i was able to hit speeds over 100 but i did throw a CEL as well as felt like car was down on power. my point is i was able to go faster then 27 mph. i think this might be a different problem.

You have a lot of mods, so I assume some ECU adjustments were made.
HPTuners, for example, has places to change the tire circumference:
https://forum.hptuners.com/showthrea...ramaters/page3

MP3BOOSTED · 10-29-2021, 07:22 AM

Quote:

Originally Posted by ctrlz

You have a lot of mods, so I assume some ECU adjustments were made.
HPTuners, for example, has places to change the tire circumference:
https://forum.hptuners.com/showthrea...ramaters/page3

this happened when i was just H/C FBO.

Tuner came out to make those adjustments and still failed and threw a CEL. but could be it

10-26-2021, 02:20 PM	#1
AZIROC Drives: '86 IROC-Z '18 ZL1 Join Date: Jul 2019 Location: Arizona Posts: 734	got new rear tires put on...couldn't go above 27 mph??? 2018 zl1 A10 55xx miles, car always in sports mode unless at the track. Track season is here in 2 weeks (atleast for me) and I needed to swap rear tires. I had a set of M/T ET streets (305/35/20) on and got a new set of SC3's (305/30/20) put on yesterday. I left the discount tire to the side road to hit the light, never got above maybe 20 and it drove fine. When the light turned green I made the left to get on the main road and gave it some gas to get up to speed (45 mph zone). The car felt REALLY down on power, the traction light was flashing and the car wouldn't get above 26-27 mph. I even floored the gas pedal and the car still stayed in the 26-27 mph area. The tires weren't spinning..aka I wasnt roasting them, but I wasn't going past 27. I made it to the next light and stopped. traction light went away as well. When the light turned green I gave it some gas, again like normal, and it drove fine. I even floored it and acted like it normally does and got up to 60. Got on the freeway to go home, and again, it drove fine. So what the heck happened? to "sticky" of a tire? Last edited by AZIROC; 10-26-2021 at 02:32 PM.

10-28-2021, 07:06 AM	#6
MP3BOOSTED Drives: 2017 Camaro SS 1LE (F1A-94 FBO H/C) Join Date: Jun 2017 Location: San Antonio Texas Posts: 843	to answer everyone, i messed up at first and ran a 26 inch front skinny with a 28 inch tall rear and i was able to hit speeds over 100 but i did throw a CEL as well as felt like car was down on power. my point is i was able to go faster then 27 mph. i think this might be a different problem. Could be wrong but sharing my 2 cents __________________ Performance Mods: F1A-94, DSX Flex Fuel Kit, MSD Spark Plug Wires, KOOK 2" off road headers, MBRP Race catback exhaust, Pray Performance Custom Boost Cam, Rocker Arm Trunion Upgrade Kit, 7.850" Hardened Chromemoly Length Pushrods and Johnson Racing 2110R Lifters, TSP CNC'd Heads, Ported MSD intake manifold, 103mm Katech Throttle body, Forged Pistons/Rods, RPM Meth kit, DSX Aux Fuel system, AEM Failsafe and banks gauge, LT4 HPFP, LT4 injectors, BMR motor mounts, Hurst Short Throw, Manley SS exhaust valves Videos of my car? Check here: https://www.youtube.com/channel/UCNi...Qy1OL4NVGlPogw

10-26-2021, 11:51 PM	#2
squish72 Drives: 2016 2SS 8AT Join Date: May 2018 Location: Nevada Posts: 358	What size are your fronts? Too big of a difference in front to back is my guess

10-27-2021, 09:36 AM	#4
Dabjbr Drives: 2020 SS 1LE Join Date: Aug 2020 Location: NorCal Posts: 658	Difference front to back was also my guess. Perhaps the car “learned” and adapted to the tall 35’s and when you went back to the shorter 30’s, it it thought the additional revolutions was loss of traction and triggered ice mode. Far fetched? Maybe but it seems logical. Perhaps it will relearn and adapt to the correct 30 profile and your experience will be a one time occurrence.

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