Question For Tires Pressure?
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Posts: 18,369
From: Reno, NV
Car Info: 1993/2000/2001 GF4 mostly red
A lot! Probably not too far below the max cold pressure listed on the sidewall. After that precise and scientific answer, try to email Dexter. He can calculate it out for you once he knows what tires you are running.
Registered User
Joined: Mar 2003
Posts: 681
From: Warsaw, Indiana
Car Info: 02 WRX Wagon White
At 35 psi it's underloaded by about 200 lbs. If it's reinforced or branded "extra load" it's only under by about 80 lbs. Rough calculations show between 48 and 50 psi to get correct load on the standard-load variety, but DO NOT exceed the max cold air pressure listed on the tire itself. Max should be 51 psi but you need to check it out prior to inflating.
This size of tire on the WRX is ill-advised because of, what I consider, insufficient load capacity.
This size of tire on the WRX is ill-advised because of, what I consider, insufficient load capacity.
Last edited by Dexter@tirerack; Jun 2, 2003 at 04:22 PM.
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From: Reno, NV
Car Info: 1993/2000/2001 GF4 mostly red
Can you give a list, perhaps in a new thread, of 17,18, and maybe even 19 or 20" tires that will handle decently and meet the load factors? Very few of us, including myself, ever even think about that.
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On the tire pressure thingy:
why does Sub insist in their manuals that pressure be in the 33-35 range, (Legacy L wagon) when the tires are cold rated to 44? With all the hoopla over underinflated tires in the last year or so, does this make sense? The way I figure it, based on the cold pressure rating, the tire is 25% UNDERINFLATED. This can't be right. I figured since the cold rating was 44 I would go between and run them at 40. (btw, they're the stock RE92's. Haven't needed to change them yet even though I don't like them...)
Ideas? Reasons? Suggestions?
Thanks
Finn
why does Sub insist in their manuals that pressure be in the 33-35 range, (Legacy L wagon) when the tires are cold rated to 44? With all the hoopla over underinflated tires in the last year or so, does this make sense? The way I figure it, based on the cold pressure rating, the tire is 25% UNDERINFLATED. This can't be right. I figured since the cold rating was 44 I would go between and run them at 40. (btw, they're the stock RE92's. Haven't needed to change them yet even though I don't like them...)
Ideas? Reasons? Suggestions?
Thanks
Finn
Registered User
Joined: Mar 2003
Posts: 681
From: Warsaw, Indiana
Car Info: 02 WRX Wagon White
Subaru, and all manufacturers, recommends pressure based on how the car handles best combined with sufficient load capacity. The "44 psi" is the "Max Pressure." Though it carries more load at max pressure, the combination isn't the best because you get a rough ride with load capacity higher than the car will ever need in normal use.
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Is the max cold pressure listed on the tire not the rated pressure for the max load listed on the tire? If not ...??? Granted, I will probably never exceed the max load capacity of the vehicle, but running a tire at a lower pressure than the rated max can't be beneficial to the longevity of the tire. Agreed, if I was running close to or at the max load of the tires, then I would be worried. But with the reduced pressure in the tire, does it not allow the tire to flex more, generating more heat in the sidewall area, creating the possiblity of weakening the tire, or allowing more heat to be built up than would normally build up if the tire were at max? The theoretical increase in air mass at higher pressure would allow the heat to dissipate faster than at lower pressure...?
I understand that mfg's decide what they think is best based upon certain criteria, but then why use a tire that is potentially overrated for the job at hand? It seems that quite a few tires these days are running at a much higher pressure (low-mid 40's) compared to tires, say 10 years, ago (mid 30's). Why the sudden change? Better tire tech, more demands by the auto mfg's...? I could go on...
Finn
I understand that mfg's decide what they think is best based upon certain criteria, but then why use a tire that is potentially overrated for the job at hand? It seems that quite a few tires these days are running at a much higher pressure (low-mid 40's) compared to tires, say 10 years, ago (mid 30's). Why the sudden change? Better tire tech, more demands by the auto mfg's...? I could go on...
Finn
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From: Reno, NV
Car Info: 1993/2000/2001 GF4 mostly red
Lower tire pressure equals better ride, higher pressure equals better handling. Subaru assumes (correctly, I would say) that the enthusiasts know how to correct the ride/handling balance, while the non-racers don't. So they recommend to those who may not know better the ride-biased settings for pressure.
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Joined: Mar 2003
Posts: 681
From: Warsaw, Indiana
Car Info: 02 WRX Wagon White
On the WRX, the placard (driver doorjamb) tells the story. Both standard and OE 17" upgrade numbers are there. It says:
205/55-16 32PSI(F) and 29PSI(R)
215/45-17 33PSI(F) and 32PSI(R)
The respective load capacities at listed PSI:
205/55-16 1213lbs.(F) and 1157lbs.(R)
215/45-17 1135lbs.(F) and 1135lbs.(R)
Our recommended sizes are:
205/55-16
225/50-16
215/45-17
225/45-17
235/40-17
215/40-18
225/40-18
You can jump around these sizes a bit, as long as the 1135 load capacity is met or exceeded.
205/55-16 32PSI(F) and 29PSI(R)
215/45-17 33PSI(F) and 32PSI(R)
The respective load capacities at listed PSI:
205/55-16 1213lbs.(F) and 1157lbs.(R)
215/45-17 1135lbs.(F) and 1135lbs.(R)
Our recommended sizes are:
205/55-16
225/50-16
215/45-17
225/45-17
235/40-17
215/40-18
225/40-18
You can jump around these sizes a bit, as long as the 1135 load capacity is met or exceeded.
Last edited by Dexter@tirerack; Jun 5, 2003 at 08:00 AM.
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So basically, it all boils down to making sure that you have at least the minnimum air pressure in the tire for the required load rating/axle. If your at or above the car mfg's pressures, then all is good.
Now the question beckons me. Do all tires of the same size, from different mfg's, have the same load ratings? If not, does the equation get complicated as far as minimum pressures?
Finn
Now the question beckons me. Do all tires of the same size, from different mfg's, have the same load ratings? If not, does the equation get complicated as far as minimum pressures?
Finn
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Dex- Subaru recommends 32F and 29R pressures for the 16/55 stocks. Got 17" wheels and ContiExtremeContacts now, and I gather (tho don't seem to have the paperwork with me) that these are supposed to have 35 psi F&R. Load's not an issue, I rarely serve as chauffeur for "BBW" conventions (big, "beautiful" women):-)
Should I stick to the higher pressures for routine street use?
Should I stick to the higher pressures for routine street use?
Registered User
Joined: Mar 2003
Posts: 681
From: Warsaw, Indiana
Car Info: 02 WRX Wagon White
There's no right or wrong pressure as long as load is met and max isn't exceeded. On 17s, I run about 39 PSI because I want to protect my wheels and I like a responsive ride. I generally recommend starting at about 36 in this situation and see how you like it. Too rough - lower a couple lbs. Just right - add a couple.
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