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Wheels and Tires Talk Sponsored by The Tire Rack Discuss issues related to wheels and tires

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Old 10-19-2013, 02:16 PM   #1
CocoaKid
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Drives: 2011 Camaro LS
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Location: Calgary
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Having Problems

So I changed my summer wheels for my winters

Im going from 245/35/20 and 295/35/20 (summers)

to

245/40/18 and 255/45/18 (winters on stock v6 rims)

I know my winter tires are a bit smaller (than factory) but I was told by GM in my city it would still be fine for the car.

My problem is immediately after I had them changed (professionally) I was braking before turning onto the main road, and I could feel the brake pedal getting harder and there was a vibrating sort of grind feel/sound.

About a minute after the car was saying to "Service Stabilitrak" and the parking brake, ABS, Traction Control, Stabilitrak and drifty car lights all came on and stay on. I tried shutting off the car and starting up again but they all came back on after a minute or so. I would like to note the car physically drives fine, with no noise other than the brakes being weird (rare, they were fine for 95% of the 20 min drive home)

I've booked an appointment at the dealer already, I'd just like to hear any thoughts on what could be messing my car up, or any experiences like this!


Thanks!
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Old 10-19-2013, 03:54 PM   #2
130R
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The sound you heard was likely the ABS kicking in. You should be able to replicate it by aggressively hitting the brakes. That's the only time it should kick in: when you're aggressively on the brakes to the point the tires want to skid, the ABS takes over and pulses the pressure to the calipers to keep the tires from skidding.

The ABS uses wheel speed sensors to help decide when to kick in. Wheel speed is obviously a function of tire diameter.

My understanding is the diameters front-to-back need to be within a certain % for the ABS to function properly. The stock tires, though different sizes, have the same diameter front-to-back.

Both sets of your aftermarket tires are in excess of 1" difference in diameter front-to-back. Your 20's have a 1.2" difference, the 18's a 1.3" difference (or ~5% difference).

You might have been on the edge with the 20's, and going to the 18's was enough to freak the system out.

Just a thought. Let us know what you find out...


BTW, you would have gotten more responses if you'd asked in the Suspension / Brake / Chassis section...
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Last edited by 130R; 10-19-2013 at 04:07 PM.
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Old 10-19-2013, 09:04 PM   #3
CocoaKid
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Thanks for the tips! I'll post this there too. I had a feeling it was something along those lines, with such a difference in wheel diameters. Shell be in the shop Tuesday, I'll post the results for anyone else after!
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Old 10-22-2013, 07:01 PM   #4
CocoaKid
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Drives: 2011 Camaro LS
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So got the car in and out today, and that was the problem basically, my front wheels being slightly smaller than the rear wheels, causing the computer to lose it. I can just live with it (the many dash lights and lack of anything besides speedometer, still is ok to drive technically) or get front tires to match the rear, which is what I'm going to do. I'm going to get tires to match because if I don't it will trip the ABS off at weird times when it doesn't need to, and tires are cheaper than a $700 module and shop time.

What made me almost lose it was the service manager told me $53 something , after I specifically asked what the charge was upon pickup. They tried charging me almost $150 when I got there, an extra $75 bucks to unplug (quick connects) one of my headlights and back in, no new bulbs or anything. I did ask them to look at it because one was dimmer than the other this morning, but all it was causing that was a single red wire (for a electro deer alarm) in the connector, but I know for a fact it takes less than a minute to do and doesn't require tools. On top of that my car was filthy on the outside since I brought it in that morning.

I made it clear I was TOLD $53... and the service manager can call me in the morning about billing. Grabbed my keys and left.
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Old 10-24-2013, 10:24 AM   #5
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Good to know. Thanks for reporting back...
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