Tire pressure Forester - Fiberglass RV


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Old 03-17-2011, 12:11 PM   #1
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Tire pressure Forester

I am at my mechanics with my 2000 Subaru Forester and he says the door sticker says 24 lbs in front and 36 in back. I have always run 32 or 36 everywhere. He says it says for towing 41 in back, which I think exceeds the tire specs. What do you do, and why would tire pressure be lower in front when not towing, other than comfort which costs gas mileage?

Bobbie
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Old 03-17-2011, 12:30 PM   #2
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The simple answer is under steer. Lower front tires pressures generally induce under steer.
Why is the front tire pressure recommendation lower than the rear? - BMW 3-Series (E90 E92) Forum - E90Post.com

Improve handling (reduce understeer) with tire pressure! - VW Passat Forums : Volkswagen Passat Forum

Reccomended tire pressure - fronts lower? does that make sense? [Archive] - Toyota Nation Forum : Toyota Car and Truck Forums
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Old 03-17-2011, 12:38 PM   #3
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Follow the tire manufacturers recommended air pressure, obviously those are not the original tires.
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Old 03-17-2011, 12:59 PM   #4
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Originally Posted by Bobbie Mayer View Post
I am at my mechanics with my 2000 Subaru Forester and he says the door sticker says 24 lbs in front and 36 in back. I have always run 32 or 36 everywhere. He says it says for towing 41 in back, which I think exceeds the tire specs. What do you do, and why would tire pressure be lower in front when not towing, other than comfort which costs gas mileage?

Bobbie
I'm not familiar with your tires but I do know that the maximum tire pressure is listed on the tire. Mine is 44psi. We increase our rear tire pressure to 39#s when towing to increase their load carring ability and stiffness.

We also increase our front tire pressure to 32 psi. I don't have any science for the numbers.

Norm
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Old 03-17-2011, 01:03 PM   #5
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What is understeer? Obviously if I've always driven with all four the same I drive fine that way. I can see bumping up for towing but not if the tires won't support it.

I remember when the Ford's were rolling over; one issue was under-inflation of tires as the manufacturer recommended lower pressures to make the ride better. At that time they said go with the tire's recommended rating, not the vehicles.
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Old 03-17-2011, 08:16 PM   #6
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Originally Posted by Bobbie Mayer View Post
I am at my mechanics with my 2000 Subaru Forester and he says the door sticker says 24 lbs in front and 36 in back. I have always run 32 or 36 everywhere. He says it says for towing 41 in back, which I think exceeds the tire specs. What do you do, and why would tire pressure be lower in front when not towing, other than comfort which costs gas mileage?

Bobbie
Bobbie:

We drive a 2003 Forester. The door sticker says: Light load 29 psi front, 28 psi rear, Full load 29 psi front, 36 psi rear, Towing 41 psi rear.

We use Michelin Energy MXV4 plus tires which have maximum rated pressure of 44 psi. We have a small 12 volt air compressor which I use to adjust the pressure. When we are not towing, ride is better using the rated Light load pressures. When we are towing I put 38 psi in the rear tires which seems to work okay with our light trailer.

Brian
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Old 03-17-2011, 08:43 PM   #7
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I need to check- I think he misread 29 as 24. 41 rear is what mine said for towing but I think that exceeds the tire rating; I'll check that, too. But I don't see how they can rate the car rather than the actual tire unless you keep putting the same tires back on (and mine were not available by the first time I needed tires.)
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Old 03-17-2011, 10:16 PM   #8
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That's pretty much what I said earlier, follow the tire makers instructions not the car makers. the car maker put those pressures on there for the original tires.
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Old 03-18-2011, 06:29 AM   #9
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That's pretty much what I said earlier, follow the tire makers instructions not the car makers. the car maker put those pressures on there for the original tires.
Tires come in a wide range of sizes and specifications. When purchasing tires consider how they will be used. The car owner's manual will specify the size range. If the car owner's manual specifies 41 psi for the rear tires while towing it is likely there is a tire available that will accommodate that but they may not be 'in stock' at every tire store. If your tire store doesn't have a tire in stock that will meets your needs you may have to wait for them to order them in or go to another store.
Good luck,
Barrie
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Old 03-18-2011, 10:06 AM   #10
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Yes Barrie your right, but car makers put tires on the car at the factory, lets say Detroit, Mi. This week they have a warehouse full of Goodyears, so the cars built this week get Goodyears with the proper size and weight capabilities of the car, next week they have a warehouse full of Generals, those cars are going to get the Generals, the Goodyears and the Generals will both be capable but that doesn't mean they will have the same inflation recommendations. The door tag is good for tire size and weight carrying capabilities but I will always go by the tire makers recommendations not the car makers.
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Old 03-18-2011, 11:48 AM   #11
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I'm getting a new car soon so what new tires I put on is moot but I may try varying the pressure and see what pulls best if I use the trailer before getting the new Forester. I can see there is little agreement on this issue, though! That's what I find online, too, little agreement.
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Old 03-18-2011, 12:49 PM   #12
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What is understeer?
(Geek hat on!) In broad terms, an understeering vehicle leaves the road front first. An oversteering vehicle leaves the road bass-ackwards. In both cases I'm assuming the driver has lost control in a corner and something bad is about to happen.

Tires develop lateral force as a function of slip angle, tire pressure and load. Increasing any of them increases the cornering ability of the tire. Both the front and rear tires must develop lateral force (a turning force) in a turn. All a tire can do on its own is to increase the slip angle (the direction the tire is "facing" relative to where it's going.) It's en-tire-ly (pun intended) possible for the front tires to get the vehicle turning more quickly than the rear tires can keep up. .

Generally, it's thought that it's better for a customer's front tires to "wash out" before the rear tires. Therefore they specify less pressure in the front tires so that front tires run out of traction sooner than the rears. So as the road turns, the driver turns the steering wheel (and tire) more and more until the limits of the front tire are exceeded. The vehicle is understeering with respect to the curve.

There's actually a bazillion things going on from the tire's perspective during a corner but this is sort of the big picture…
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Old 03-18-2011, 01:08 PM   #13
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Sure Steve you took the words right out of my mouth!

Oh and don't mention what you do during the day?

Ed
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Old 03-18-2011, 01:13 PM   #14
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I am at my mechanics with my 2000 Subaru Forester and he says the door sticker says 24 lbs in front and 36 in back. I have always run 32 or 36 everywhere. He says it says for towing 41 in back, which I think exceeds the tire specs. What do you do, and why would tire pressure be lower in front when not towing, other than comfort which costs gas mileage?

Bobbie
I towed aprox. 6000 Km with my 98 Forester/Surfside combo at the recommended 42 psi. rear tire pressure, with the fronts at 36. No issues, nor abnormal tire wear.
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