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- Plano, Texas, USA
Not necessary true. Mazda and other car manufactures have been recommending a range of tire pressures depending on weight and car speed in other countries. Also different tire brand may need different tire pressure to achieve optimal performance and tire wear. For example, the general consensus here is we want 2~3 more psi than Mazda recommended tire pressure on CX-5 for the best performance on popular General AltiMAX RT43 tire.I'd run what the manufacture recommends. The reason is that is the best pressure with respect to safety, handling and tread life. In my opinion 39 is too high because for a small amount of fuel savings, you will compromise the other features. This assumes the recommended pressure is 34 psi. Ed
Another extreme case is from my 1998 Honda CR-V. Honda recommends 26 psi, but I have to use at least 35 psi for a decent performance and tread wear.
I go with 39 psi cold too for all four 19 tires mainly for even tread wear to maximize the tire life. My experience on one-number-fit-all manufacture recommended tire pressure for US market is its usually a bit too low which wears out the outer sides of tread faster. Tire pressure should be flexible depending on many variables: tire type、brand (design characteristic)、temperature、speed、and load. For those who believe we should follow Mazda recommended tire pressure with 35 psi (36 for gen-1 CX-5) on 19 tires, see the different tire pressure recommendations for CX-5 from UKs 2017 CX-5 Owners Manual with wide range from 36 to 42 psi depending on load. One example even recommends 45 psi on winter tires!
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