Yes, it does improve FE a bit, but as it turns out at a very high price.

A couple of weeks ago I had my '07 HCH in for its 45K maintenance work. Everything was fine -- except for the rear suspension, which had to be replaced, along with the tires. The culprit: overinflated tires (I was keeping them at 38-40 psi). Fortunately the car is still under warranty and I'd signed up for the dealer's "tires for life" policy, so I wasn't out any cash. Otherwise, the suspension cost alone would have more than negated any gas savings. Even worse, the new suspension & tires have essentially put me back into "break-in mode." My 1st tank afterward was an abysmal (by my historical standards) 49 MPG, and today's was a still-subpar 52 MPG. (Click on the lower banner for this car's history.)

Lesson learned: Don't exceed 35-37 psi. The cost-benefit ratio is in the wrong direction.

 

IMHO that sounds more likely to be cause by the negative camber problem, that this thread was talking about.

 

How does having your tires inflated on the high side hurt the suspension? What was the problem with it--was it control arm related or related to the shocks themselves? What parts were replaced? Did you notice any degredation in the ride quailty prior to service? Any change after they replaced it?

 

Yeah, I don't buy that one bit. I've had mine at 44psi since I've had the car (coming up 2 yrs). How can the amount of air in your tires affect the suspension? Doesn't add up.

 

Raising the tire pressure decreases the aligning torque of the tire. From wiki:


The cars rear suspension was designed with the tires at specified PSI. Over or under inflating will influence the dynamics of the suspension. Not saying that the over inflation is the culprit, but can definitely be a contributor.

 

So reduction of aligning torque is not a good thing? I would think that would put less stress on the parts. I guess you're just saying it's not necessarily good or bad, just out of spec.

 

Reducing SAT from .032 (Radial 32psi) to .027 (Radial 40psi) will have virtually nill effect on the wear of suspension components. The primary area of concern with SAT is its effect on steering input, i.e. pulling one way or the other. The fixed a-frames of the rer suspension aren't really affected by SAT. In fact reducing SAT will put less wear and tear on them. What will hurt the front suspension over time is constant running on under-inflated tires. This being said, even with under-inflated tires the vehile would need to be driven at extreme limits to cause any noticeable damage. As has been said in a previous reply... it's the a-frame problem that has brought this on, not the inflation pressure.

 

I also agree that tire wear on the center part of the tires will occur, that is why over inflating increases FE, less road surface/resistance. The suspension would not be affected.

The major concern would be hydro-plaining on wet/rain roads. An other result could be steering, pulling to one side when accelerating and the other side when decelerating. and trying to track in a rut/grove.

I have mixed emotions about hydro-plaining. We use to over inflate our race tires if it looked like rain or was raining. So who has tried it in the rain?

 

Try this article from the boys in blue. They count on their tires more than we EVER will. Make sure you read the part about hydroplaning.

http://www.officer.com/web/online/Ed...ssure/19$27281

 

The SAT is the only component of suspension model that is influenced by tire pressure. As I said not necessarily the culprit but a possible contributor. As long as you have a slip angle of zero (i.e. solid rear axle or most multi-link independent suspension) the SAT will have no influence on the suspension.

The difference in PSI changes the Mz by a factor of 16%. A poorly designed suspension or suspension components that allow slip angle (i.e. HCH rear control arms manufactured to the wrong spec) will be more affected by over/under-flated tires.