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GM Tire Performance Criteria (TPC) "Survey" - READ ONLY

11 messages,  Last post on Feb 02, 2010 at 7:57 AM

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What is this discussion about? Chevrolet, Wheels, Safe Driving, Safety Technology, Tires, Sedan

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#8 of 11 Re: GM Tire Performance Criteria (TPC) "Survey" [capriracer] by e_net_rider

Feb 01, 2010 (4:03 pm)

Replying to: capriracer (Jan 31, 2010 3:51 am)
You are obviously right in the last paragraph, but GM claims that the TPC is supposed to address the best tire for a vehicle and from my earlier post about which tire size for what vehicle that seems to be an untrue statement. That is by looking at a couple of different tire manufacturers sites, they show either tire size, 215/55r17 or 225/50r17 were possible OE sizes for my model and trim level.
I did not realize the percentage of same size users was quite that high, but certainly there are a lot of choices within a size. Load, speed, temp, etc. which can all effect the performance of a particular tire on a vehicle.
The last tires I bought were for an Aurora. I used reviews of other owners to guide me. Those who had replaced the OE tires, Eagles or a Michelin, were much happier with other tires, especially over eagle, a high priced tire at that time. Reasons were improved ride, quieter, stickier, etc. and the hands down winner was half the price. I was so impressed I considered putting them on other two vehicles. One vehicle, customers loved them on it. The other it was rated poorly. So different tires can make the vehicle, the challenge is getting the right one. And from what I've seen of the TPC system so far, I'm not impressed.

#9 of 11 Your knowledge I hope? by e_net_rider

Feb 01, 2010 (4:12 pm)

Being a tire expert, I'd appreciate you insigt to the wear I'm seeing.
I'm only able to get a good look at the outer rib. I see a feathering of each block in that rib. On one side of the vehicle, there is more wear at the trailing edge of the block. It is the opposite on the other side of the vehicle. Both front and back are same on each side.
You might say rotate, but think about it. If I took wheel from LS and stood it next to wheel on RS, the wear pattern would then match.
Vehicle was aligned at 600 miles and rechecked at different dealer a couple of weeks later. Now almost 6K.
Do you have any ideas as to what might cause such wear?
BTW, vehicle handles poorly, like play in steering and different road surfaces effect it drastically. Sometimes it feels like I'm driving on a layer of ball bearings.

#10 of 11 Re: Your knowledge I hope? [e_net_rider] by capriracer

Feb 02, 2010 (4:22 am)

Replying to: e_net_rider (Feb 01, 2010 4:12 pm)
First, as I said in my very first posting, what YOU consider to be the things you would want in a tire, are not always the same as what GM thinks you want in a tire. The thing that is certain is that the tire with the TPC number was optimized according to GM's priority list for YOUR vehicle. If you have a different priority list, then you will come up with a different answer.
 
The wear you described has many names - feather edge wear, heel and toe wear - and it is caused by the natural rotation of the tire.
 
As a tread element transitions into the footprint, the element is bent out of the way and the leading edge is rounded. As the same element exits the footpint, it stays attached until it almost leaves the footprint, then suddenly releases causing an extra bit of wear to occur on the trailing edge.
 
So between each tread element, there will be "step". This is normal. However, the more toe the vehicle has, the worse this wear becomes. To keep this under control, regular rotation is perscribed. This is condition is also aggravated by low inflation pressure.
 
And I think all the other symptoms you've described might simply be due to underinflation.
 
But you should be aware that in my long career, I've determined that the alignment tolerances published by the car manufacturers are usually too wide - especially the toe spec. It is not uncommon for folks, especially those you don't rotate regularly, to complain about tire wear for vehicles that are barely "in spec". The key here is "barely". It's a matter of degree - and I think the vehicle manufacturers need to update their specs to reflect advances in technology. They've been using the same tolerance for over 50 years!

#11 of 11 Re: Your knowledge I hope? [capriracer] by e_net_rider

Feb 02, 2010 (7:57 am)

Replying to: capriracer (Feb 02, 2010 4:22 am)
As a tread element transitions into the footprint, the element is bent out of the way and the leading edge is rounded. As the same element exits the footpint, it stays attached until it almost leaves the footprint, then suddenly releases causing an extra bit of wear to occur on the trailing edge.
That makes sense, but is not exactly my case. On one side of vehicle it is trailing edge and the other it is the leading edge. So rotation is of no change to wear pattern whether rotating front to rear or cross.
Alignment might be something to look at although the two printouts I have look pretty good. It is not likely that the machines require the degree of calibration such as in aircraft assembly where sometimes it requires 8 feet of concrete to ensure nothing gets displaced.
I would think the best alignment would be when the vehicle is on the assembly line unless something happens to the vehicle. If that is not so, then it makes me question just how good the manufacturer spec is in the first place. Of course one can do some tuning to change handling, like buying different tires.

Messages Page 2 of 2

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