Hello, and thanks for the welcome. Pardon my bruskness at times, I don't mean to offend, but--
The energy loss in a tire comes from the work it takes to deform the rubber as the tire adjusts to make its contact patch. A hard rubber takes more work to deform it so it loses more energy, and is less efficient. A corollary is that a well-worn tire is more efficient than a new tire--less rubber to bend.
By the same logic, you should conclude that a low-profile tire is less efficient because more deformation in the wall is required to form the contact patch. This is verified by experiments, and common experience by drivers.
High tire pressure improves efficiency because the contact patch is proportionately smaller, and deformation is less.
About high pressure and tire life-- it's my experience that a good tire with a solid radial belt won't wear unevenly in the middle. Many police and highway patrol cars have tire pressures above 50 psi (for improved safety) with no such wear problems.
About wheel moment of inertia-- that's mostly an old myth too. Wheels and tires have double the effect on car total inertia because they both spin and move linearly. If you increase the weight of wheels and tires by 15 lb each, the total effect on the car is the same as adding 120 pounds in the trunk, or a small mother-in-law in the back seat. Smile, you will get by just fine.
Your comment near the bottom, about larger tires not always working for some cars, is probably true, especially with some automatics. For my car, it's speed for best mileage appears to be somewhere near 50 mph in fifth gear. And, I think you should only make small changes in tire diameter, less than two inches unless somebody has already tried it.
Sorry about the lecture.
Ernie Rogers
Quote:
Originally Posted by ConnClark
Welcome to the forum
Some things to note about tires.
A harder rubber compound makes a more efficient tire. It improves mileage in the same way as higher tire pressure does. Typically tires rated to last the longest have a harder compound. A harder rubber compound won't give you as good of grip as a softer one so you loose traction.
Also an over inflated tire tends to reduce the life of the tire because it causes more pressure and wear on the center of the tread.
Generally the low profile tires have less side wall flex which reduces rolling resistance. Unfortunately going to a larger rim to accommodate a lower profile tire may increase the rotational inertia of the wheel. Which way to go depends on if you do a lot of stop and go driving or if you do a lot of driving at constant speeds for extended periods of time.
Also its important to note if you go to a larger diameter wheel with a larger profile this will make your car handle worse and make it more prone to rolling over.
Changing tire diameter doesn't always help. Some cars have their gear ratios set to optimize the engines maximum efficiency rpm range to the typical speed limits.
In your situation with a diesel, peak efficiency typically occurs at the rpm where peak engine torque is generated.
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