Tire Engineer here - concerned about hyperinflating tires

[whitevette]

Originally Posted by CapriRacer

Whitevette,

As I indicated in the post right above yours, this is the "Introduction" forum, and not the place to have a technical discussion - so we've moved this discussion to:

Edit: The link doesn't take you to the followup thread. Here is a new link:


http://ecomodder.com/forum/showthrea...ires-2582.html

Nevertheless, your post has a couple of fallacies in it, so I think you would benefit from the discussion.

Hi, Capri!
I have moved over to the appropriate links ( as you suggested). I am a "newbie" to this geekspeak...so I'm a little slow. However, your mentioning of my post having a couple of "fallacies" in it...could you be more specific? I am not aware of any fallacies....

[Noel]

wow, onto page 3, and no response since the original post.

[Geonerd]

Originally Posted by tasdrouille

Rolling resistance coefficient (RRC) literature review:

At moderate speed, 90%-95% of the tire RRC is due to material hysteresis, 2%-10% is due to surface friction or micro-slip and 1%-3% is caused by air friction.

Tire inflation pressure is the main factor affecting hysteresis.

Warm tires have lower RRC than cold tires not only due to increased pressure, but also because the internal damping of rubber decreases when its temperature increases.

Given equal pressure, the initial RRC of a tire at -20 C can be more than twice as at 40 C.

The RRC is almost the same from 0 up to 55 mph, when it starts to increase rapidly. At 80 mph, it is roughly twice as much as 55 mph.

Worn out tires can have a RRC up to 20% lower than new tires as a significant part of the hysteresis happen in the thread which is not so much affected by inflation pressure.

The relation between tire pressure and RRC is almost linear, and is still significant in excess of 100 psi.

As a side note, it is interesting to note that fuel consumption can vary by more than 10% depending on the smoothness of the pavement.

Effect of width, aspect ratio and diameter on RRC:

Note: This applies to RRC only, not rolling resistance in terms of force, which is more important than RRC in stop and go driving.

This aspect of RR is very hard to tackle as there are multiple variables working in opposite directions. Nonetheless, by looking at the variation in RRC of the same tire when one variable is modified at a time, and by looking at average RRC for each tire size, we can conclude that generally, all other things being equal:

- Larger diameter tires have a lower RRC than smaller ones.
- The lowest RRC tire width is the closest one to the tire diameter times 14 (ignoring units of measure). (At max sidewall pressure and max load)
- The lowest RRC aspect ratio is lower as tire diameter gets larger. It appears as the the lowest RRC Diameter/Aspect ratio are: 13/80, 14/75, 15/70. (At max sidewall pressure and max load).

Overinflated tires will wear more in the middle than optimally inflated tires. However, optimal inflation varies with load and tire size.

Blowout risks related to sudden pressure rises in overinflated tires are non existent as radial tires will not unbed under 150 psi.

Overinflated tires have higher risks of cuts, but reduced risks of rim damage.

The temperature increase delta decreases as initial cold pressure increases.

References:

TYRE ROLLING RESISTANCE ON ROAD

Passenger Tire Rolling Resistance

Rolling Resistance Testing: California Energy Commission’s Fuel Efficient Tire Program

Excellent, thank you for the writeup.

[Ford Man]

Several of the comments are related to never running the tires above sidewall max, the max sidewall rating is supposed to be cold presure so I can't see any danger in the presure rising 5-10 psi on a tire that is running on 150*-200* asphalt in the summer. I'm running the the tires on my cars above max sidewall and I had an incident a few days ago where I had to make as sudden stop on wet roads and the traction was actually better than when I ran them at or below max. Very hard braking and never lost traction as apposed to breaking traction at or below posted sidewall. Maybe the tire engineer got blown up over inflating his tires. LOL

[CapriRacer]

I didn't realize this post was being taken so seriously. So here's my corrections to this. Apologies to Tasdrouille for not adressing this earlier.

Originally Posted by tasdrouille

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

The RRC is almost the same from 0 up to 55 mph, when it starts to increase rapidly. At 80 mph, it is roughly twice as much as 55 mph.

.......

RR is only 29% greater at 100 mph as it is at 35 mph for tires without cap plies - and only 13% greater for tires with cap plies.

Ref: The Pnuematic Tire, published by NHTSA Aug 2005, pg 494

Originally Posted by tasdrouille

.........

The relation between tire pressure and RRC is almost linear, and is still significant in excess of 100 psi.

The relationship between inflation pressure and rolling resistance is a decreasing curve (as the inflation pressure increases). The difference between 40 and 48 psi is only 2%.

Ref: SAE Paper 800087 - The Effect of Inflation Pressure on Bias, Bias Belted, and Radial Tire Performance by B. L. Collier and J. T. Warchol, B. F. Goodrich February, 1980

Originally Posted by tasdrouille

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

Blowout risks related to sudden pressure rises in overinflated tires are non existent as radial tires will not unbed under 150 psi.

A tire's ability to absorb an impact decreases 20% as the inflation pressure increases from 32 psi and 40 psi.


Ref: SAE Paper 800087 - The Effect of Inflation Pressure on Bias, Bias Belted, and Radial Tire Performance by B. L. Collier and J. T. Warchol, B. F. Goodrich February, 1980

[EXPIOWA]

CapriRacer, I will agree with you that over inflated tires are dangerous. The technique is dangerous and reaches the point of diminishing returns very quickly. It is not worth it.

[99metro]

Old thread, BUT... I think the over inflating of the tires comes from the attempt to decrease rolling resistance to increase fuel economy. Usually those over inflating tires are driving slower and using hypermiling techniques. They aren't concerned with speed/cornering/braking/acceleration performance as much. Most of a hypermiler's "performance braking" occurs at much less than 25 mph.

I would agree that if you use your vehicle for circle track/racing/drag strip etc, then how you inflate your tires is extremely important. Track temperature, weather conditions and lots of other variables all play a part in where the starting pressure is set, so that the tires will be at their best performance after they are "warmed up".

Good information though.

my 2 cents

[IsaacCarlson]

New tires should not be fully loaded or highly inflated because the steel bands in a new tire are all slightly different lengths and therefore some of them are bearing more tension than others. The steel bands in a used tire have been flexed and have stretched to the same length to bear forces evenly, making the tire MUCH stronger than a new tire. Inflate your tires to recommended specs for a few months and don't fully load them, to let the bands equalize, then increase your tire pressure, and payload.

I need two new tires this fall and will not be running my normal 50 lbs right off the bat.

Just my $.02 worth....

[RH77]

Wear Update:

Tire Model: Michelin MXV4-Plus XSE "Green-X" LRR
Sidewall Max: 44 PSI
PSI: 50-55 Continuous
Miles ~40,000
Road Conditions: 8 seasons, several large potholes encountered (look up the rating of Missouri roads)
Wear: Minimal; no abnormal patterns
Structure: No bulges or sidewall abnormalities
Handling/Traction, Dry: Improved
Handling/Traction, Wet: Normal, Somewhat diminished in heavy rain
Handling/Traction, Snow: Diminished
Traction, Ice: Compared to baseline, no change

One more date entry in support of over-inflation.

RH77