[aerohead]

Originally Posted by CapriRacer

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.

CapriRacer,thank you very much for your comprehensive "filling in the blanks"!I would like to impose upon you with one additional question,and I'll leave you alone.------------------------ Years ago a certain concept car was revealed,which was credited with 80-mpg potential.The car's two main attributes were never before offered aerodynamic efficiency,and very LRR tires.In the press kit,much was said about the tires and their remarkably low rolling resistance.When I contacted the tire maker,who manufactured the concept tire,and asked if it would be going into production,and would be available in the aftermarket,they thanked me for my interest and explained that the tire design belonged to the carmaker,and they would have the answers I seeked.------------------------ Upon writing to the carmaker,complementing them on their accomplishment,and what a benefit such a technology would be to so many aspects of the American economy and environment,I inquired as to whether they would consider a licensing agreement to allow tire makers to manufacture the LRR tires.The tires offered a 17% improvement in MPG.------------------------------ I received a polite letter from the legal affairs department of the corporation,thanking me for my interest in the tire,and after explaining how many parameters must be balanced,regarding tire selection,at that time,the corporation was not interested in a licensing agreement.---------------------------- In the meantime,the same corporation has subsequently developed another tire which offers over a 26% improvement in MPG.---------------------- As an ecomodder,you might imagine the frustration that might accompany anyone exposed to such a technological coup,realizing they may never have access to such cutting-edge technology.------------------------ Would you hold out any hope that we might see the commercial exploitation of such tire technology within our lifetimes? It seems like the time is right for such things,more so than at any other time. Please comment if you can.Thanks!