Wore my tires out.

[svx_commuter]

Thanks for all the toughts and comments. Inside tire wear seems to be common on higher performance tires when the tire pressure is 33/28 psi. This can be corrected by using a higher pressure say 40/37. Where as for a Pontenza or similar (tire what all-season tire?) 33/28 is just fine.

[svx_commuter]

Originally posted by mbtoloczko

Were the insides of both the front and rear tires worn out?

Wear was rate was certainly dramatically increased by the lack of tire rotation and low tire pressure. I doubt your struts are bad if you are on your 2nd set within 80k miles. Do they feel bad?

The inside of the front tires worn a lot more than the backs. The backs looked pretty good. I think that at 33 psi the rolling resistance of these tires is high. Say higher than an all season tire. This tends to kick the toe out when the tire rolls. The toe was wide but not real bad.

As far as ride comfort goes, I think it is better at 37/34 than it was at 33/28. At 33/28 I think the tire is very flat across the bottom and this why the inside edge wears and is a rougher ride. All the bumps go into the sidewall. At 37/34 the tire has some crown to it so it sits more on the middle of the tire.

The struts do not feel bad to me.

[kuoh]

Radius? Did you mean circumference? If it's the same tires and wheels, then why would the "circumference" change given the same air pressure? I understand that the SVX is not a 50/50 car, but it certain isn't so far off that the aspect of the tire would be so severely affected. Perhaps you should describe your procedure again but in more detail.

KuoH

Originally posted by mbtoloczko
If you are running your tires in the 30-40 psi range, for the front and rear tires to have the same *rolling* radius, the front tires will need to have much more pressure than the rear tires. I verified this myself using whiteout to mark the tires and a straight piece of road. With my 225/45-17 tires, to get the same rolling radius in the front and rear, I had to run 38 psi in the front and 30 psi in the rear. With a 4 psi differential, there was a 0.12% difference in rolling radius. With equal psi, there was a 0.25% difference in rolling radius.

[mbtoloczko]

Originally posted by kuoh
Radius? Did you mean circumference? If it's the same tires and wheels, then why would the "circumference" change given the same air pressure? I understand that the SVX is not a 50/50 car, but it certain isn't so far off that the aspect of the tire would be so severely affected. Perhaps you should describe your procedure again but in more detail.

KuoH

If the SVX weight distribution is 60f/40r, the front wheels support 2100 lbs and the rear wheels support 1400 lbs. So a front wheel supports 350 lbs more than a rear wheel. I think that's a pretty big difference. Anyhow, I used the phrase "rolling radius", but "rolling circumfrence" is fine if you want to use that term. For info on the rolling radius measurements I performed, see my posts on this thread:

http://www.subaru-svx.net/forum/show...rolling+radius

My posts are on pages 5 and 6.

[kuoh]

Ahh...you were talking about differences of less than 1 percent. I missed your decimal points and thought you were posting numbers like 12% and 25%, which would be a big difference. Considering the amount of variance between the tires under different conditions like accelerating, decelerating, and turning, and the fact that we're not running a locked center diff, figures like 0.12% and 0.25% don't seem to be substantial enough to cause me any great concern.

KuoH

[mbtoloczko]

Yeah, 0.12% is not that big of a deal, especially when considering all the things you mentioned.

Originally posted by kuoh
Ahh...you were talking about differences of less than 1 percent. I missed your decimal points and thought you were posting numbers like 12% and 25%, which would be a big difference. Considering the amount of variance between the tires under different conditions like accelerating, decelerating, and turning, and the fact that we're not running a locked center diff, figures like 0.12% and 0.25% don't seem to be substantial enough to cause me any great concern.

KuoH

Well, actually the center diff begins to lock up when there is a difference in rotational speed F/R. If your rolling radius is not the same front and rear, there will always be a difference in how fast the shafts are turning where they interact in the center diff. This causes heat buildup and causes the center diff to slowly build towards lockup... since this is a constant state it creates wear on the diff through heat and unnecessary friction. I prefer to stick with what Subaru recommends, regardless of the tires pressures you choose to run in general.... keep a difference of about 3-5psi front to rear, with the fronts higher than the rears.

Actually, 0.25% is quite a difference in rotation in absolute terms. Think of it in terms of alignment specs... very small differences make a world of difference in how the vehicle behaves.

[STORMINORMAN]

"Verrrry interesting..." (I think it was Artie Johnson on Laugh-In

My $0.02's worth:

There a quite a few variables involved vis'-a-vis' "proper" tire inflation, "normal" wear, "expected" mileage, "perceived" ride & handling . Among these are, clearly

Tire size
Tire construction & weight
Tire pressure
Alignment
Wheel construction & balance
Suspension

Any one of these factors can affect wear, ride & handling. Start throwing in multiple variences (low pressure, misalignment & a defective strut) and things can get plenty interesting... FAST!

Debunk #1 "The manufacturer doesn't know what the tire pressures should be..." Well, they do have the design engineers...

Debunk#2 "Higher pressure noted on the sidewalls supercedes the manufacturer's recommendation..." Not necessarily true as the tires can go on DIFFERENT vehicles with DIFFERENT weights, drive systems & suspensions, etc.

I'm not questioning the previously opined statements re: specific (in some cases almost exotic) tire applications & experiences. What I'm trying to say is that for the average SVX running a stock size tire at the recommended pressure, with good alignment, true & balanced wheels, fully functioning suspension, driving on normal roads with normal loads at something less than top speeds "should" result in normal wear, reasonably expected mileage, and normal ride quality and handling. Which, for the SVX, is pretty damn good! IMHO

Riding a motorcycle, awareness of tire condition & pressure are extremely important for safety. Many motorcyclists DON'T EVEN BOTHER TO CHECK THE AIR PRESSURE ON THEIR BIKES BEFORE THEY RIDE When they crash they don't have a clue how they could have been responsible. DUH!

The Explorer/Firestone debacle was IMHO a combination of the wrong tire design (weak 1-ply sidewalls), a possible tire manufacturing defect, a tire pressure recommendation from Ford that was skewed towards ride considerations vs. load capability AND owners who didn't check the air pressure in their tires regardless of load, speed, temp, etc. Some of these incidents involved tires worn down to the steel belts. Running less than 20 lbs. pressure. Grossly overloaded at high speed.

The guv'ment's solution: tire pressure monitor systems for all cars.

The more basic problem is a society where there is ALWAYS someone else to blame because everyone is a potential victim... And another potential plaintiff.

Try the Yokohama avs db "S2" They are improved version of the original.

[mbtoloczko]

Originally posted by Porter


...

Actually, 0.25% is quite a difference in rotation in absolute terms. Think of it in terms of alignment specs... very small differences make a world of difference in how the vehicle behaves.

I still wonder if 0.25% is significant or not. I do think its more than zero, and it would be a good idea to run more air in the front not only to reduce this value but also to accommodate the extra load in the front on these cars. However, even when driving down a straight road in town, the constant little directional corrections will cause the front wheels to travel further than the rear wheels. I'd be willing to say that the difference travelled is in the range of 0.1%. Going around corners will further contribute to this difference.

Actually, those differences in turning are absorbed at the front and rear diffs independently. That difference in traveled distance is the reason why Subarus come stock from the factory with an OPEN front differential... an LSD in the front would actually be beneficial, but the mechanical problems inherent in such a design due to real-world driving use prevent it from being a cost-effective solution on a mass production vehicle.

It's a great solution for racing, where no-one expects a part to last 100,000 miles without service or failure.

[mbtoloczko]

I think its fair to say that for around town driving speeds and around town corners, the rear wheels take a shorter path around a corner (such as at an intersection) than the front wheels. That is, when going around a corner, the rear wheels follow a track that has a shorter radius of curvature than the radius of curvature defined by the track of the front wheels. Thus, the tranny clutch pack must slip to accommodate the differences in distance travelled between the front and rear.

I dunno man, I don't want to get into the whole diff argument again. I'll just fall back on the tried and true... Subaru wouldn't recommend the tire pressure difference unless there was actually a difference. Their procedure for fixing the deceleration noise issue with the WRX center differentials involved raising the front tire pressure to create a 4-5psi difference in tire pressure. It fixed the majority of the decel noise problems and is taken as more or less biblical fact on NASIOC.

[kuoh]

So Subaru intentionally designed the SVX with the pressure differentials but failed to do so with the WRX? Personally, I think the pressure recommendations for the SVX was more for ride comfort than any inherent binding or tranny noise issues. The fix may work for the WRX, but I have doubts as to whether it is the root cause of their problem.

KuoH

Originally posted by Porter
Subaru wouldn't recommend the tire pressure difference unless there was actually a difference. Their procedure for fixing the deceleration noise issue with the WRX center differentials involved raising the front tire pressure to create a 4-5psi difference in tire pressure.

[mbtoloczko]

hehe. I wasn't trying to start another argument about tire pressures. I'm a believer. :-) Just trying to convince you of my opinion that the front tires travel further than the rear tires in corners.