I want to lower tire pressures in a manual trans AWD Subaru. It has a viscous coupling/diff. The auto uses electronically controlled clutches. Being AWD they say the fr and rr tires have to be the same size or damage can be done to the center diff. Wondering if lowering fr and rr pressures a few lbs will affect the tire dia? I've read that pressures could, but then read that with steel belts the tires won't balloon. Thought about dropping fr & rr pressures equal amounts. The factory calls fr 33 lbs in the front and 30 in the rear.
Tire pressures with AWD
- Thread starter VinceF
- Start date
- Status
It is true, with modern radial tires you have a lot more lattitude in the inflation pressure. Exactly how much depends on a whole lot of variables, like the tire being used, vehicle weight and weight distributtion, etc.
I've been running my Corolla that calls for 31/31 at 36/34 for over 30K miles and an no unusual wear. The ride is bumpier but it's good for almost 1MPG.
I've been running my Corolla that calls for 31/31 at 36/34 for over 30K miles and an no unusual wear. The ride is bumpier but it's good for almost 1MPG.
As long as the back and front tires are lowered the same amounts I see no problem.
I've driven thousands of miles with 45 psi rear and 34 front while towing. So I think the center diff can tolerate some deviances from optimal.
My manual calls for 29 front and 28 rear.
I've driven thousands of miles with 45 psi rear and 34 front while towing. So I think the center diff can tolerate some deviances from optimal.
My manual calls for 29 front and 28 rear.
Weight distribution is a huge factor, since it's the effective static load radius of all the tires that matters, not the actual air pressure. Different tire pressure will of course change the effective radius of the tire; all 4 should be within ±0.5% of each other. >1% differences in tire radii can be very hard on the viscous coupling.
Why do you want to lower the pressure? Just curious.
I run 39f/38r in the legacy since the contis have a soft sidewall for a AS performance tire. Running low at speed can be dangerous due to heat build up. 30 is not that low like the 26lb ford explorer spec that caused blowouts, but still low. You will wear the edges of your tires quickly. Economy will suffer some too.
If your running off road or gravel/sand and trying to gain traction, then running low is not that big a deal.
(I think this thread would be a better fit in the tires/wheels forum.)
I run 39f/38r in the legacy since the contis have a soft sidewall for a AS performance tire. Running low at speed can be dangerous due to heat build up. 30 is not that low like the 26lb ford explorer spec that caused blowouts, but still low. You will wear the edges of your tires quickly. Economy will suffer some too.
If your running off road or gravel/sand and trying to gain traction, then running low is not that big a deal.
(I think this thread would be a better fit in the tires/wheels forum.)
Originally Posted By: 05LGTLtd
Running low at speed can be dangerous due to heat build up. 30 is not that low like the 26lb ford explorer spec that caused blowouts, but still low.
It may or may not be worth mentioning that I run 40 psi on my Explorer. Handles noticeably better than when I had it at 28.
Running low at speed can be dangerous due to heat build up. 30 is not that low like the 26lb ford explorer spec that caused blowouts, but still low.
It may or may not be worth mentioning that I run 40 psi on my Explorer. Handles noticeably better than when I had it at 28.
I usually run 38-40 psi in the front and 30-34 psi in the rear of my Impreza, have done so since I bought it about 10 years and 90,000 miles ago. No center diff issues so far. I bought it with 80,000 miles on it.
I have all-season tires on it and since the sidewalls flex a bit I run the fronts a bit higher to try to keep them from rolling under.
What kind of tires do you have? How does the width of the wheel compare to the width of the tire? What sort of driving conditions?
I have all-season tires on it and since the sidewalls flex a bit I run the fronts a bit higher to try to keep them from rolling under.
What kind of tires do you have? How does the width of the wheel compare to the width of the tire? What sort of driving conditions?
Trying to make the ride a bit softer, since my back complains at times. I was after a WRX, but just a short test drive on a city street had me aching. I actually thought about buying the NA and turbo in the same color and swapping parts and selling the car with the parts I didn't like, like the lower profile tires and the hood that had the air scoop that I found distracting, but the rims were a different size to fit the brakes, and the scoop fed the intercooler. Suspension was probably stiffer also. Thought about changing the motor, but the motor harness is different for the turbo motor. I remember a time when you could build what you wanted from options from the factory. I used to get all the heavy duty and oversized police options which were cheap. Made for some interesting cars.
Originally Posted By: VinceF
I want to lower tire pressures in a manual trans AWD Subaru. It has a viscous coupling/diff. The auto uses electronically controlled clutches. Being AWD they say the fr and rr tires have to be the same size or damage can be done to the center diff. Wondering if lowering fr and rr pressures a few lbs will affect the tire dia? I've read that pressures could, but then read that with steel belts the tires won't balloon. Thought about dropping fr & rr pressures equal amounts. The factory calls fr 33 lbs in the front and 30 in the rear.
I would stick with factory.
I want to lower tire pressures in a manual trans AWD Subaru. It has a viscous coupling/diff. The auto uses electronically controlled clutches. Being AWD they say the fr and rr tires have to be the same size or damage can be done to the center diff. Wondering if lowering fr and rr pressures a few lbs will affect the tire dia? I've read that pressures could, but then read that with steel belts the tires won't balloon. Thought about dropping fr & rr pressures equal amounts. The factory calls fr 33 lbs in the front and 30 in the rear.
I would stick with factory.
I don't beleve it. we agree. When Firestone got into that thing with Explorers and low inflation. If the ride is too harsh for you. I suggest a smaller diameter tire with a higher profile. Maybe I'm an old geezer, but low profile tires are a silly fad.
I have an 07' 5sp NA Impreza.
Never driven any other Subaru's except the WRX.
If you mean rim dia, 16". Tires are the Bridgestones that came with the car.
Never driven any other Subaru's except the WRX.
If you mean rim dia, 16". Tires are the Bridgestones that came with the car.
Originally Posted By: andyd
I don't beleve it. we agree. When Firestone got into that thing with Explorers and low inflation. If the ride is too harsh for you. I suggest a smaller diameter tire with a higher profile. Maybe I'm an old geezer, but low profile tires are a silly fad.
I always liked the look of the higher profile tires, and like them wide. Mine are 55 series. They went with bigger rims and skinny tires. Supposed to handle better. Talking to a young mechanic with a hot Civic, and he agreed about the tires.
I don't beleve it. we agree. When Firestone got into that thing with Explorers and low inflation. If the ride is too harsh for you. I suggest a smaller diameter tire with a higher profile. Maybe I'm an old geezer, but low profile tires are a silly fad.
I always liked the look of the higher profile tires, and like them wide. Mine are 55 series. They went with bigger rims and skinny tires. Supposed to handle better. Talking to a young mechanic with a hot Civic, and he agreed about the tires.
Most problems can be solved with just two things: time and money!
Take a look at some grand touring all seasons, like the conti Pro Contacts or Pirelli Cinturato P7. They are both available in 215/60/16's. Folks over at nasioc or dirtyimpreza should be able to let you know if they will clear ok for you.
Also new struts like kyb's might be in order. If you need to add spacers for clearance with plus size tires, then you'll already be in there.
Not sure if you can run 15" wheels and clear the front brakes. Well, at least not without coughing up for rally wheels. Again impreza forums will give you a answer. 90's subarus had 15x6 wheels which can be had pretty cheap.
Take a look at some grand touring all seasons, like the conti Pro Contacts or Pirelli Cinturato P7. They are both available in 215/60/16's. Folks over at nasioc or dirtyimpreza should be able to let you know if they will clear ok for you.
Also new struts like kyb's might be in order. If you need to add spacers for clearance with plus size tires, then you'll already be in there.
Not sure if you can run 15" wheels and clear the front brakes. Well, at least not without coughing up for rally wheels. Again impreza forums will give you a answer. 90's subarus had 15x6 wheels which can be had pretty cheap.
During the 1990s, some GM cars would detect low tire pressure by comparing tire revolutions from each ABS wheel speed sensor. The problem was that unless 1 tire was lower than the others by 10 PSI, the system wouldn't indicate an error. That suggests to me that you would need to seriously deviate from normal tire pressure to get such bad things to happen.
I drive a Jaguar X-Type with AWD. It clearly "likes" all 4 tires to have even pressure. It's a "dumb" system with open front and rear diffs, plus a viscous coupling in the transfer case.
Even so, when there is a tire pressure issue, the car has a distinct rumble. And it simply feels weird.
Even so, when there is a tire pressure issue, the car has a distinct rumble. And it simply feels weird.
Originally Posted By: VinceF
Trying to make the ride a bit softer, since my back complains at times. I was after a WRX, but just a short test drive on a city street had me aching. I actually thought about buying the NA and turbo in the same color and swapping parts and selling the car with the parts I didn't like, like the lower profile tires and the hood that had the air scoop that I found distracting, but the rims were a different size to fit the brakes, and the scoop fed the intercooler. Suspension was probably stiffer also. Thought about changing the motor, but the motor harness is different for the turbo motor. I remember a time when you could build what you wanted from options from the factory. I used to get all the heavy duty and oversized police options which were cheap. Made for some interesting cars.
That's an astonishing amount of work for a softer ride.
It would be cheaper to buy an RX350 or something else with AWD, if your environment dictates the extra traction.
Trying to make the ride a bit softer, since my back complains at times. I was after a WRX, but just a short test drive on a city street had me aching. I actually thought about buying the NA and turbo in the same color and swapping parts and selling the car with the parts I didn't like, like the lower profile tires and the hood that had the air scoop that I found distracting, but the rims were a different size to fit the brakes, and the scoop fed the intercooler. Suspension was probably stiffer also. Thought about changing the motor, but the motor harness is different for the turbo motor. I remember a time when you could build what you wanted from options from the factory. I used to get all the heavy duty and oversized police options which were cheap. Made for some interesting cars.
That's an astonishing amount of work for a softer ride.
It would be cheaper to buy an RX350 or something else with AWD, if your environment dictates the extra traction.
- Status
