What tire pressure are you using for your 20's
11-29-11, 08:05 AM
#1
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What tire pressure are you using for your 20's
I am running on my IS 250 235/30/20 with 38psi and 275/30/20 in the rear with 38 psi. To me the 38 seems to be rough, what are you thoughts and recommendation.
11-29-11, 04:37 PM
#4
Up front answer:
Fronts 41 psi
Rears 44 psi
The correct pressure is based on the load index of the tires compared to the stock spec. I'm assuming yours are 88 XL on the front and 97 XL on the rear.
The stock 18" on the front has a load index of 88 and recommended pressure of 35 psi so that's rated for a 1190 lb load, and the rear is 95 @ 38 psi so that's 1521 lb.
88 XL front tires will need a pressure of 41 psi to support the same 1190 lb load, and 97 XL rears will need 39 psi, but increase that to 44 psi to maintain the same 3 psi front-to-rear differential as stock.
Yes, your car will ride like **** with these pressures, but that's the problem with running 20s and super low profile tires--the sidewall is not strong enough so you end up having to run higher pressures to support the load.
An 88 XL tire @ 36 psi is rated at 1091 lb so the other guy is running 100 lb under spec on each front tire.
Fronts 41 psi
Rears 44 psi
The correct pressure is based on the load index of the tires compared to the stock spec. I'm assuming yours are 88 XL on the front and 97 XL on the rear.
The stock 18" on the front has a load index of 88 and recommended pressure of 35 psi so that's rated for a 1190 lb load, and the rear is 95 @ 38 psi so that's 1521 lb.
88 XL front tires will need a pressure of 41 psi to support the same 1190 lb load, and 97 XL rears will need 39 psi, but increase that to 44 psi to maintain the same 3 psi front-to-rear differential as stock.
Yes, your car will ride like **** with these pressures, but that's the problem with running 20s and super low profile tires--the sidewall is not strong enough so you end up having to run higher pressures to support the load.
An 88 XL tire @ 36 psi is rated at 1091 lb so the other guy is running 100 lb under spec on each front tire.
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11-30-11, 07:24 AM
#8
Every tire shop should have the manual to work this out. Toyo happens to have theirs available online: http://www.toyotires.ca/sites/defaul...ationtable.pdf
11-30-11, 07:44 AM
#9
Trust me, this guy knows what he's talking about. Load Range is extremely important when changing tire sizes. You must know what the stock tires load range is and not drop below that number. If you do the new tires will run hotter and fail prematurely. The air chamber in a 20" tire with the same OD as an 18" or 19" tire is smaller and the only way to compensate for the disparity is by increasing air pressure. IMHO, a 20" wheel/tire combo on a any IS is for show only, not the street.
Lou
Lou
11-30-11, 10:09 AM
#12
