phatline

FYI, I took it in yesterday and he said it'd take longer b/c he has to clean all the pebbles out of the tire. Guess I was lucky to find someone who would even consider it. It would cost $75 to dismount, shave, balance, and re-mount two tires. We decided the tread was low enough that it's best to just buy new tires and be done with it. The rears have a higher treadwear rating thant he fronts, so even if I got them matched up now the fronts would wear down and create a mismatch in the future. Which begs the question, any tire recommendations? Is it even worth putting an "SUV" (light truck) tire on the Forester, or is an all-weather passenger tire adequate? I want something quiet and efficient on the highway but capable of decent mud/snow/gravel driving a few times a year. I'm a little cautious about passenger tires w/ sloping sidewalls--dont' want to get a flat 20 miles down a fire road. At least there is a full size spare in the Forester...

Hi Glenn, I think I came across your issue in another thread. It's interesting that our cars whine in opposite conditions (acceleration for me, deceleration for you). I can't spatially locate the sound.. it sounds "everywhere" which is why I think it comes from below the car or under the hood.

Subjfd, Did you ever get to the bottom of this? I have the exact same problem in my 1999 Forester (manual). At highway speeds there is a whine whenever the accelerator is engaged. If I'm coasting--no whine. I'm also the guy with different sized front and rear tires (.65" more circumference in back)--does anyone think it could be my differential or viscous coupling complaining?

I'd love to attain that kind of mpg. My 99 Forester (2.5L) MT got 24 mpg on the first tank, then I changed the oil (valvoline high mileage, dunno if that matters or not) and filters--now I'm getting 28 mpg highway. Have you done anything special to get up to 32? That seems an astounding number for the 2.5L engine which has an EPA of 27 hwy.

Otis, thanks for the data point. My fronts and rears agreed with themselves (right and left) almost perfectly (no detectable shift). I just bought this car used but it looks like it's been running on the two different sets of tires for 20k. Due to warnings from folks here (and the .25" Subaru tolerance spec) I'm seriously considering having the larger tires shaved down, or even replacing all four tires.

Hi everyone, Ok I used frag's parking lot method today. 42 revolutions of the front tires resulted in 41.66 revolutions of the rear tires. Assuming an 80" tire circumference, that means the rear tires are about .65" larger in circumference. Significantly past the .25" specification given by Subaru. I'm going to check into the economics of shaving down the rear tires since there's good life left on the fronts. I'm curious what measurements others have made of their tires? I also checked the axel heights: 31.2 cm front, 31.6 cm rear. Letting out 1.5 PSI only brought the rear axel down 0.1 cm, so I concluded there was no reason to repeat the circumference test or try to achieve another .3 cm drop.

Hi Frag, Thanks for humoring me . I agree that pressure will affect circumference. What I propose is that inflation pressure affects two quantities: (1) the actual circumference of the tire (stretching/deforming the tread shape) and (2) the rigidity of the tire's shape (affecting axle height). Portion (1) should result in a change of the axle's RPM, but not (2). What this means to me is that having two different tire sizes inflated to achieve equal axle heights does not guarantee equal RPM at the axles. What do you think? I will test this theory tonight by adjusting my tire pressures until the axels are of equal height, then checking the rotations/circumferences using the "parking lot" method suggested on these forums, and post back here. My tires are of different brand/treadwear.

Carl, that was an entertaining thread but I feel more confused coming away from it! I now agree with the original idea that shape doesn't matter--one revolution of tire tread equals one shaft revolution, and tire tread "length" (circumference) does not change much with inflation (steel belts limit the extent to which the tire can deform). It will certainly change some (as evidenced by uneven treadwear), but the shaft-to-ground distance should not in itself have any effect on rotational rate. It can't, unless the rubber is slipping. I guess Frag's suggestion is the only way to actually verify this. Measure the rotations/distance and calculate circumference that way. Has anyone done this test with varying tire pressures? My guess is there will be a change, but it's entirely due to actual tire stretch (which is minimal) and nothing to do with the axle-to-ground height.

Hi Carl, Thanks for your reply. I understand what you're saying (BTW I have some mechanical engineering education). It seems to me that keeping proper inflation (so as to keep the axle-to-ground heights equal front and back) is actually more important than having matched tires. Improper inflation could easily throw new tires out of spec, and likewise judicious inflation could "correct" for improperly matched tires. Is there an approved method for measuring the axle-to-ground? It's not quite as easy as it sounds. I can easily measure from the center of the rim to the ground, but it isn't perpendicular to the ground surface. Doing so yielded 32 mm rear and 31 mm front--I'm going to play around with inflation (a couple PSI up or down should be safe to do) and see how that affects the heights.

The 99 forester 5MT I just bought has two different brands of tires (michelins on back, bridgestones in front). The tread depth is very close between them (maybe 2/32" more in the back). What is freaking me out is that there's no way the circumference is within 1/4" and I don't think it would be even if the tires were all 4 new and of-a-kind because the front end is so much heavier. Also general variations in tire inflation and cargo load would easily overcome this miniscule tolerance. I just measured with a string (tires on the car) and got a circumference of 79" in front and 82" in back---12x the tolerance! PSI is 28.5 front/26.5 rear (sub spec is 29/26). What should I do? Replace all four tires? I estimate they have 30k miles left on them... And what about the issue that even with new tires, the circumference is not going to be perfect? I'm not trying to beat a dead horse, here. If this has been covered adequately in another thread please be kind . As far as symptoms go, the only time I notice anything is a brief feeling of "hesitation" when starting from a dead stop. It happens between 0-3 mph (my estimate) and I do get a sensation that power is moving front-back-front-back. It's all over in less than a second.

As a new owner, I find myself wondering what I should be doing to keep my used subie in shape. Any recommendations? It's a 1999 Forester S, purchased at 137k miles (138k now--still new to me). I've done the no-brainer stuff like checking fluid levels and changing the oil. The carfax indicates the car saw frequent visits for service checks but it hasn't been seen by the shop in almost 20k. It had the major service (timing belt) done.

For the record, I took it in to a mechanic. There was no refrigerant. He filled it up and performed a leak test and found no leaks. So either the leak is very small or he missed it. Cost $143 (for labor and 1.5 units of refrigerant), but if it does leak over the next few weeks he will not charge labor to check the system again. It just seems to me like 100% bleed in 11 months (max) would be a fairly large leak. Thanks again!

I just ordered from http://www.subarupartsforyou.com and http://www.brandsport.com and both had fast email response to questions, good prices, and fast shipping (the latter had free shipping as well).

Thanks again. I verified the pressure switch reads open. I guess it's time to take it in to the shop. Much appreciated!

Thanks! This may be my problem. All I have been able to determine is that the AC button works and the AC relay is getting no signal from it. Is this the point that I should take it in to the shop and have them check the refrigerant? I'm not equipped to do that stuff.