Hyperinflating tires

[adam728]

Yea, at 8psi a week drop you definitely have a leak. If you have a valve core tool I would try and tighten them. They can come loose. I fought with one on my Jeep for a while before replacing the whole stem. It would hold pressure fine for weeks, then suddenly go flat overnight. Tighten the valve core and repeat the process. Luckily I have an on board compressor! I've also battled the stem that leaks between it and the wheel. Usually blamed on mud/debri getting packing in while off roading. I doubt your Vibe has that issue though

[SuperTrooper]

Originally Posted by CapriRacer

I think you will find that drag slicks are bias ply tires. It's the belts, not the sidewalls that prevent the growth due to centrifugal forces - and if the belt isn't enough, circumferential cap plies are added.

Right. I forgot to note the different type of tire. My point being that tire "growth" has no effect on passenger car tires at conventional speeds.

[cfg83]

trikkonceptz -

Originally Posted by trikkonceptz

I have noticed that in order for me to keep my tires @ 50psi I have to stay on top of them more often. At 44 psi I was checking my tires once a month with no problems. Now that I am up to 50psi I am checking them weekly and noticing a drop in pressure each time. The drop varies, 2-3psi in the rear, as much as 8psi in the fronts. I am going to blame the valve stems since they are the cheasy rubber ones you get at the tire store, but otherwise the wheels have no punctures ... and the FE gains I got are indisputable.

But yeah, I may rename my Vibe the Radio Flyer, because it does ride rougher, but coming from low riders, it is very tolerable.

I heard that you can request "high PSI" valve stems that are designed for truck tires (I think). I would have done that had I known about them.

CarloSW2

[Frankenstipe]

I'm going to inflate my tires to 45 psi on Sunday to see how much it helps with MPG, grip, cornering, traction etc. I'm going to be driving 330 miles from Lodi, CA to Arcata, CA via HWY 36 which is very windy and twisty so it'll definitely be interesting. I just drove down that way with my tires at 31 psi, should have inflated them to 32 before I left (door placard number) but I felt it would be fine.

I'm very new to all things cars in general but have been trying to learn as much as I can. The way I understand tire inflation is that you want to have as square a contact patch as possible within recommended psi, ie between door placard psi and max sidewall psi. I have aftermarket rims and tires (225/45/17) so my max sidewall psi is 51 as opposed to the stock tires (195/65/15) 44 and my door placard psi is 32.

Now I'm curious about something, if I over-inflate my tires to 50 psi, will they still wear evenly or will they unevenly. The car only weighs about 2600lbs so I don't want to over-inflate it too much to cause too much uneven tread wear.

[vtec-e]

Hi CapriRacer, Earlier you said: "That probably also means that hyperinflating tires would result in a fatigue failure many cycles down the road - due to the overall stress in the tire caused by the inflation pressure."
But by hyperinflating a tire, it will wear so little and last much longer than a tire at "normal" pressures. So even when it does fail due to stress and number of cycles, it still lasted longer than the "normal" tire.(and gave savage mpg) From my experience (not a lot!!) i reckon i'd be scrapping a tire because it has aged and become hard instead of wearing out. I do 30,000km per year so my tires are lasting a good while.
Anyway, i respect all you have to offer here on this subject since you DO work in this field and know far more than i do. Cheers to learning more!

ollie

[stiles]

Hi, new guy here. ASE Master tech (14 years)

A few things of note:

Stock rubber auto tire (snap-in style) valves are only rated to handle around 45 psi max. Higher pressure tires use different, bolt-in stems. It's unlikely you'll eject a stem at 50 psi but it is worth considering, if you run at max pressure all the time - particularly in hot weather and high speed freeway driving where heat build up will be the most noticeable.

Tires inflated to the sidewall max will run cooler but may not last longer because of premature center channel treadwear due to carcass distortion, and faster sidewall and tread cracking from pressure stress. Think of a balloon - inflated to the max it is highly stressed, relative to the stress level @ 50% inflation. Fatigue cracking in the rubber is faster in tires left inflated to 100% max all the time.

[CapriRacer]

Originally Posted by Greenblazer

.........

Let me simplify and ask again, is it, or is it not safe to run tires at MAX sidewall PSI in your educated opinion? A simple less technical answer would be appreciated.

..............

I tend not to use terms such as "safe" and "unsafe" - too "black and white". I prefer to use terms such as "risk", which to me is a bit more accurate and descriptive.

So let me answer your question this way: Using up to 5 psi more than the vehicle placard pressure (assuming the same size as listed on the placard) is likely a small increase in risk. The footprint size and shape isn't much different and the tire's spring rate is only up at most 15%, so I don't think the handling will behave much differently (other than be a little more responsive). The impact risk is higher, but again this is less than a 15% increase in stiffness, and the risk of an impact event is fairly low to begin with, so while the liklihood of a failure from the event is somewhat larger, the overall risk is still fairly low.

Using up to the max pressure on the sidewall is a little more risk, but I've explored some of the handling issues when I raced. The only issue I feel uncomfortable about is the impact situation, but, as I explained in the paragraph above, the increase in risk of a failure is mitigated somewhat by the overall liklihood of the event in the first place. The problem here would be that sometimes tire impact failures lead to fatal accidents.

[CapriRacer]

Originally Posted by vtec-e

Hi CapriRacer, Earlier you said: "That probably also means that hyperinflating tires would result in a fatigue failure many cycles down the road - due to the overall stress in the tire caused by the inflation pressure."
But by hyperinflating a tire, it will wear so little and last much longer than a tire at "normal" pressures. So even when it does fail due to stress and number of cycles, it still lasted longer than the "normal" tire.(and gave savage mpg) From my experience (not a lot!!) i reckon i'd be scrapping a tire because it has aged and become hard instead of wearing out. I do 30,000km per year so my tires are lasting a good while.
Anyway, i respect all you have to offer here on this subject since you DO work in this field and know far more than i do. Cheers to learning more!

ollie

You've glossed over a point that I think is important here - What happens when a tire fails?

Most of the time the vehicle can be brought to a stop with no damage to anything (other than the tire). Sometimes, the tire deflation will allow the rim to contact the ground - and that's gonna mean a new rim.

Sometimes the rapid release of the air will damage the fender - not to mention what the pieces flying off the tire are going to do.

But every so often a tire failure will cause the vehicle to go out of control - perhaps even flip over - and we all know what else might result.

Please keep this in mind as we discuss this issue. I don't want anyone to become a statistic.

[Daox]

Of the few FE boards I'm on I have yet to see any tires fail due to fatigue. The only thing I have seen (from other's reports) is that tires are more likely to be punctured at high pressures. Heck, one guy ran his 40,000 tires @ 50 psi and replaced them at 75,000 miles and they still had even tread wear. No offense, but you guys have yet to provide any hard evidence that suggests overinflating or hyperinflating have major drawbacks.

[trikkonceptz]

Originally Posted by CapriRacer

You've glossed over a point that I think is important here - What happens when a tire fails?

Most of the time the vehicle can be brought to a stop with no damage to anything (other than the tire). Sometimes, the tire deflation will allow the rim to contact the ground - and that's gonna mean a new rim.

Sometimes the rapid release of the air will damage the fender - not to mention what the pieces flying off the tire are going to do.

But every so often a tire failure will cause the vehicle to go out of control - perhaps even flip over - and we all know what else might result.

Please keep this in mind as we discuss this issue. I don't want anyone to become a statistic.

On those statements I have to say that tires do not cause rollovers, drivers do. I do not want to estimate how many millions of miles I have logged driving vehicles of all kinds and towing trailers from small to large. NEVER have I lost control of a vehicle with a blow out. And I have had blow out from disintegrated tires, straight to the rim down to trickles where you here the air leaving one revolution at a time. When a driver panics and gets stupid, stupid things happen. And honestly the only tires I have ever seen physically fail are tractor trailer recaps. They get hot, usually from under inflation and over loading and the glue that holds the caps on fails and lets go, causing either a blow out with launches tread, or tread loss without a blow out.

Unless tires are manufactured with defects, like the Firestone recal, a tire won't fail, it will blow out due to a puncture, but tires do not fail. Obviously some may think I am wrong, but site situations when tires can fail where their maintenance and or abuse is not a factor.