Originally Posted By: crinkles
so from what i read on this thread
a P tyre achieves it's load rating at 35 PSI.
Yes, except I think the post said there is also "XL" P tires that achieve an even higher rating at 41 psi
.
Quote:
Using the tables in the link above i have worked out that Toyota used exactly a factor of safety of 1.2 (20%) with respect to the carrying capacity of the tyres. this is with the recommended pressures of 30 front and rear.
I have 94 load rated tyres (670kg) at 35 PSI. max pressure stamped on the sidewall is 44 PSI. so this 44 is not the PSI where the load rating occurs but the max allowable pressure. Am i right?
Yes I think 44 psi is max pressure for the tire and 35 psi is
the minimum pressure to reach maximum tire load capacity. However your Toyota's maximum load rating only requires 30 psi. So even at maximum recommend load for the car,inflating to 35 may cause more wear in the tire's center, harder ride, and less grip.
Quote:
GVM (from owners manual) is 2085 kg (i.e. loaded). at 30 PSI the 94 rated tyres can carry 625 kg looking at those tables. 4 * 625 = 2500 kg, and 2500/2085 = 20% safety factor!!
they do however make the distinction that when loaded the rears at 34 PSI to account (i guess) for load distribution to the reat.
Yes the rear axle on this application apparently has a higher load rating than the front. Like you mentioned there is a safety factor for the tires, but like wise there's a safety factor for the chassis so you should only load to the car's maximum recommend load (and pressure) and not to the tire's higher maximum recommended load (and pressure).
Quote:
EDIT - i may add to this an anecdote. one day i was pumping my tyres my wife asked "are you pumping them to 35??" this was weird because we deal in kPa down here. i said no i di 210 kPa which is recommended, 30 PSI. she said her dad (my FIL) always said 35 PSI for cars end of story. now he is a crankyk [censored] but knows a lot. so i think he got is 35 PSI from this classification system as indicated on the links above, and just carried through with the 35 PSI for the rest of his life. I guess it's not a bad number to pump passenger car tyres to! i think 30 PSI recommended for my camry is quite low and it makes the tyre look like it only has 15 PSI in it, but hey, it's what's recommended???
Yeah the recommended pressure of 30 psi will carry the car's max recomended loaded and you won't be overinflating the tires especially when you aren't loading the car to max load.