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Folks,

I was preaching the hypermiling gospel to a friend of mine, and mentioned inflating the tires to max sidewall pressure, and he immediately brought up what he saw as a problem.

His claim: with higher inflation (not over-inflation, just max sidewall), the tires will 'punish' the suspension more. Has anyone found this to be even remotely true? Has anyone needed to repair/replace any suspension parts earlier than normal while using higher inflation? I'd like to let him down easy, so any tests/surveys/whatever would be useful.

I don't tend to believe it myself, but in the spirit of skepticism, facts are more important than opinion. Thanks ahead of time.

Tim

Even if it were true, the lower speeds reduced braking/accelerating tend to reduce wear on the suspension (and the tires, brakes, and engine).

It can't be any worse that the 16" and 17" wheels and low-profile tires that you can find on so many sports and sporty cars straight from the factory. I've ridden and driven some cars of European origin that were far more punishing at stock tire pressures than my own 65 profile tires at max sidewall pressure. That's not to say that there is no increased load on the suspension components, but certainly nothing that they can't soak up.

Brick,

Good point about the low-profile tires. Surely, 18'' rims must be more punishing to the suspension than 16"" rims pumped to 40 PSI. Thanks.

Tim

A car that ships with low-profiles would probably have suspensions designed to deal with it. However suspensions are usually about dealing with large changes where the tires are expected to deal with the micro changes in the road. Its not impossible that the additional vibration could do some damage, but it would probably be more minor...things like the dash getting loose and squeaky in 7 years instead of 10...that sort of thing.

For a given road, the suspension has to see more "action." Now, is that beyond design? I don't think so.

When I hypermile, I'm choosing the better roads, and when a road is pretty beat up, I'll ride the ridges or slip back and forth. On most of my routes, I already know where the bad spots are, and so drive as to miss them. I'm also driving slower than before, so when I do get to a rough spot, it is probably no worse for my suspension than before.

Since I'm leaving a buffer, I also have time to react to any hazards on the road.

So, I believe there is some offset here. Does it cancel out? Probably not, because I really feel the bumps. Then again, I'm over Max Sidewall, so I'm really asking for it. I expect my shocks and struts will need replacement during my ownership. Being at 60,000, I expect my shocks are at the standard replacement miles, yet they still feel pretty good.

Like eyesight, shocks/struts wear all the time, so as the driver, you just don't realize how worn they truly are until you replace them - it's like a new car.

There's almost definitely a bit more NVH, but it's not clear
to me that it's an "overtaxing" situation. My Prius is at 80K
on the original struts by now, and eventually I supposed it'll
be time to replace them, and I guess I'll get to see if there's
a difference. One thing that's easy to do in the meantime is
play around with different tire pressure over the same roads
and see if there's a sweet spot you might prefer.
.
_H*

Just another excuse.

Psyshack-

How do you mean?

Tim

Hi Te00294:

___The same excuse iswrt why most cannot follow the speed limits. They think that planning for rather then reacting too a traffic impediment is to hard. That RR is something so advanced it is impossible. That installing a low weight synthetic is bad rather than good. Same non-sense but different day. Taxing the suspension? All the while they travel at 80 + down our beat to hell Interstates and roadways hitting whatever is in the road and not really caring what it is doing to their vehicle.

___Good Luck

___Wayne

My first thought when max sidewall was first suggested was for the suspension. Undoubtedly, the door jam recommended pressure is mostly for passenger comfort, but the design of the suspension would be tied to that pressure. I do agree that the combination of max sidewall and altered driving habits should nullify the suspension wear difference.

I've wondered whether running max sidewall pressure (as I do) might reduce mileage on certain rough road surfaces compared to door jamb pressure. Any upward jolt I feel means that the entire car has been lifted a bit, which requires conversion of the forward kinetic energy of the car to upward kinetic energy, and there's no mechanism for converting the gravitational potential energy of the car's higher new position back into forward motion. Wasted energy. Also, if the tire is stiffer, more motion will be absorbed and converted into waste heat in the shock absorbers (dampers) and this energy cannot be recovered. If that exceeds the amount of energy absorbed by the tire's hysteresis as it flexes and rebounds, there would be a net loss.

All theoretical stuff, of course. Wonder if anyone's done any empirical trials of mileage degradation over rough road surfaces, and how it changes with tire inflation?

It likely doesn't matter. It's going to be converted into energy anyhow. Which would you rather have do the conversion, a tire not explicitly designed for it, or your suspension designed to absorb that exact sort of motion?

Which would you rather have do the conversion, a tire not explicitly designed for it, or your suspension designed to absorb that exact sort of motion?

I see what he is getting at though. On very rough roads it might tax them a bit more.

If the shocks on the vehicles are chosen to be at the bare minimum needed when the tires are "properly" inflated, are they going to go through wear and tear that goes beyond their capabilities?

It won't make enough difference to most of us, since we don't travel on these types of roads on a regular basis (I am think of a very poorly maintained dirt road).

on 99.9% of driving conditions, stiffer tires work better.

The hysteresis is transferred from the tire to the suspension.

Anything in the form of speed bumps or similar, same size will have been better off at lower pressure, however, as soon as that bump is cleared, all gains had from a softer tire disappear as the harder tire has much lower rolling resistance.

My thoughts are that max sidewall will probably increase suspension wear, however automobile suspensions are designed for much harsher conditions than most of us would drive on, like washboard potholed gravel roads and such. So I don't believe running higher tire pressures would overtax suspension. It may cause the suspension to wear out sooner, however if that is the case then I would probably end up wearing out my suspension at door jamb pressures as well, just at a slightly slower rate.

I'm actually thinking about lowering my pressure because of all the pot holes here in Boston. I've hit some pretty nasty ones... with 38 PSI... ouch

Consider this, though. If your pressure is too low, a hard pothole hit can pinch the tire between the road and the rim, puncturing the tire. "Snakebite puncture", I've heard it called, because you get two holes, one on each side. If it's hard enough, you can bend your rim, too.

38 psi is not high at all. My last set of tires wore out on the edges at that pressure - the classic sign of underinflation. (car says 32 psi, tires max 44 psi)

Chicago has some NASTY potholes, and Wayne has over 100,000 miles on his accord's original tires, with high pressure the whole time. It's not a problem.

Chicago has some NASTY potholes, and Wayne has over 100,000 miles on his accord's original tires, with high pressure the whole time. It's not a problem.

Having driven through Chicago I can attest to the nastiness of those roads.

They are almost as bad as poorly maintained dirt roads.

For Prius (at least) quite a few have been driven quite a ways at well above mfr's 35/33. I see no evidence posted that those shocks and struts are caving in sooner, above hard tires. Have never heard of Prius ball joint replacements, so that does not appear to be a problem either.

DAS

I think going to higher pressures will tax the suspension more. Tires are a part of the suspension: stiffen them up with more pressure and the remainder of the supspension is going to take more jolting. If it's going to overtax the suspension is debatable.

I've raised our pressures about 2/3's of the way from Honda's recomendation to the max sidewall, and it does make you feel all the road irregularities more.

The steering/suspension component that sometimes wears out quickly on gravel roads is tie rod ends -- that's the component I'm keeping a particular eye on since I hardened up my tires. I doubt that harder tires would make much difference to shocks or struts and ball joints are usually tough enough to outlive the car.

All I know is that I jacked my tire pressure up because of how I drive.

Mostly hwy, 80-90km/h.

I guarantee you that people driving "normally" with their tires at the recommended psi are putting more wear and tear on their suspension than I am.

I have not had anything wear out or break. I have 50psi in tires rated at 44psi max sidewall. The car does ride rougher so I try to avoid rough, bumpy, potholed roads. A few years ago I broke a front coil spring but that was before I started hypermiling and inflating my tires to max sidewall and beyond.