Quote:
Originally Posted by aerohead
CapriRacer,I appologise for the digression,however you appear to be the only "insider" we have into the dark world of automotive tire manufacturing.I would like you to address something if you will,concerning the Tire Performance Criteria,published by General Motors Corporation in the 1980s,which essentially transfered tire design away from tire makers and put it in the lap of GM.I'm given to understand that,as the largest automaker in the United States,and controlling the largest share of new car O.E.M. tire ourchases,that GM essentially transferred authority away from tire manufacturers and specified how tires would be constructed from there on out.Since Ford Motor and Chrysler were minority customers,they were forced to go along with whatever GM decided.The issue has significance to ecomodders desiring certain LRR technology,as tire makers are not permitted to manufacture certain proven LRR tires,as they were not developed by the tire companies,but rather by GM,and cannot produce said tires without express permission from GM.
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ALL vehicle manufacturers - GM included - specify practically everything about the tires that get supplied to their vehicles. Individually, vehicle manufacturers buy so many tires that the tire manufacturers are more or less powerless to argue the point.
In practically all cases, the tires supplied to the vehicle assembly plants are different than tires that are designed for the replacement market.
Vehicle manufacturers have a select list of qualified tire suppliers (and other parts suppliers). The process to qualify a tire supplier (or any supplier of parts) is arduous, but the benefit to a tire supplier (or any other part supplier) is a fairly simplified supply chain - a steady shipment of a large quantity of parts going to a single drop off point for a long period of time - typically 3 years.
What usually happens is about 2 years before the start of production, there is a letter issued to each of the qualified tire suppliers specifying what the performance characteristics the tire is supposed to have. The letter outlines the tests that have to be performed and the performance level to be achieved. This includes rolling resistance, force and moment, traction (dry, wet, and snow), ride quality, handling, etc., and wear. The problem is that the inexpensive tests are run first - lab test (rolling resistance, force and moment, etc.) - followed by increasingly more expensive tests - traction, ride, handling, etc. Ride and handling test are performed by the vehicle manufacturer, although the tire manufacturers do a screening series of ride and handling to not only select the best tire candidates, but also to gauge the correlation with the vehicle manufacturer's ride engineer.
The last tests performed are wear tests as they are the most expensive. It is not uncommon for wear problems to surface. Sometimes this means starting over, but sometimes tires are pronounced ready for production with known wear issues. Sometimes the problem is in the vehicle and while tire testing is expensive, vehicle suspension redesign is many times more expensive.
In the case of General Motors, they have a Tire Performance Criteria, which delineates the performance of a particular tire. They require the TPC number to be branded on the sidewall to indicate the tire meets this criteria. Ford, BMW, VW, Mercedes also require indicators on the sidewall and each vehicle manufacturer's requirement is different. For example, BMW requires a 5 pointed star. I am sure other vehicle manufacturers have sidewall marking requirements, but I don't know them all.
It is not uncommon for what appears to be identical tires to be supplied to different vehicle manufacturers - and, of course, the tires are different - sometimes easy to see (such as a tread pattern difference) and sometimes not (say, tread compound)
For practical purposes, all vehicle manufacturers require tires with lower rolling resistance than is supplied to the replacement market. The classic triangle is rolling resistance / treadwear / traction (especially wet traction) Improvements in rolling resistance come at the sacrifice of one of these properties (sometimes both). That is why you will find many complaints about OE tires for treadwear and / or traction.
So, no, GM's TPC system is not holding back low RR tires. In fact the opposite is true. Low RR tires ARE supplied to the virtually all vehicle manufacturers but there are many complaints from consumers.
However, the average consumer doesn't connect fuel economy to tires. Most consumers demand long wearing tires - and since adequate traction is a given, that means high RR for replacement market tires. The exception here is high performance and ultra high performance tires. In these cases, treadwear is sacrificed to get traction.
BTW, OE tires do not have a treadwear warranty (and by that I mean the tires that actually come on the vehicle - not the same ones sold out of a tire dealership). The lone exception is GM, where they have a 3 year, 36,000 mile warranty on tires (with a couple of exceptions). However, this is a GM warranty not a tire manufacturer warranty. GM credits the vehicle dealer for tires that wearout prematurely, not the tire manufacturer. This is a fact not well known to GM dealers and it creates a lot of confusion.
Bottonline: If you are unhappy with the performance of the tires that came new on your vehicle, tell that to the vehicle manufacturer, not the tire manufacturer. The vehicle manufacturer is the one who specified the performance, who selected the tires, who knew how they would perform, and they are the ones who would have to change the specs to get the desired performance.