QuestionSorry, just so I'm clear...
First, full load will probably never be a factor (don't think I'll ever have more than 500 lbs. in the car). Does that matter?
Anyway, so 30 psi? I thought low-profile tires required quite a bit more pressure.
Thanks a lot.
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The text above is a follow-up to ...
-----Question-----
After contacting a couple tire stores and even the manufacturer, I still don't know proper tire inflation for my tires. The information I've received has been conflicting, to say the least. On to it...
The data:
--after-market tires for a 2006 Scion xB
--tires: Riken (Michelin) ZR215/40ZR17 (87W)
--listing on tires' sidewall: 50 max psi (but no range)
--listing on vehicle's placard for original tires: 29 psi
Michelin told me to keep it at the same as listed on my placard, but these tires are much smaller, so that can't be right. A guy at a tire shop said I should fill them to about four lbs. less than the max. pressure. That sounds like too much.
Please help. Thanks.
-----Answer-----
Paul,
The first thing you should do is find the placard on the vehicle. It is usually located on a doorpost or in the glovebox and it will list the original tire size and the proper pressure for that size. Note the Load Index, too.
If my book is correct, your vehicle came with P185/60R15 84T inflated to 29 psi.
The new tires have an 87 Load Index and are Extra Load (XL) and that means that they require more inflation pressure to carry the maximum load. However, your original tires have a lower Load Index and are Standard Load (SL) and didn't use all the load carrying capacity available.
To get the equivalent load carrying capacity of a SL 84 LI you need to inflate an XL 87 LI 1 more psi.
AnswerPaul,
No matter how you slice it, load is always a factor - after all the tire is holding up the vehicle and everything in it.
No, lower profile tires require the same amount of pressure if the load carrying capacities are similar (and in this case they are close), except to say that low profile tires have improved resistance to rim damage if higher pressures are used.
