Over-inflating tires

[Fat Charlie]

Operating a motor vehicle isn't "safe." Neither is anything else that you do.

I always recommend to my customers that they not change tire sizes or pressures, but I've done both without feeling that I've added any additional risk to my life.

[user removed]

I have measured tread depth with a dial caliper after 25k miles on brand new tires and there was no difference in tread depth across the tire after running sidewall max from the day the tires were installed. The pressure on the sidewalls is the same as the tread.

Tires will last a lot longer since you are reducing heat from friction in the tire as it flexes.
Ride quality is another thing altogether. My Fiesta does not seem to mind higher pressure at all.

I'll run sidewall max until I can't drive anymore. The wife doesn't complain about her Sorento with 42 PSI (sidewall max is 44), and she likes to complain about just about everything you could imagine.

regards
Mech

[SentraSE-R]

Darin did the definitive inflation testing here. The results showed big gains up to 50 psi, but nothing above that.

Darin's results:
psi / ft. traveled
20 / 479.3
25 / 524.8
30 / 621.0
35 / 621.0
40 / 639.6
45 / 687.5
50 / 702.0
55 / 699.3
60 / 702.0

[GreenHornet]

I would like to share some data with all of you on testing that was performed for the Shell eco marathons. This data is out of the book by W.S. Affleck and G. B. Toft Fuel economy of the gasoline engine. While the book was published back in 1977 the research that was done into the science of fuel economy is very relevant today as well as pertains to this thread!

Chapter 12 Mileage Marathons

Under rolling resistance it states that

"Rolling resistance is, in a properly prepared vehicle, largely determined by tyre size,profile,structure and inflation pressure. Increasing inflation pressure on a conventional cross-ply 14" tyre from 25 to 40 1b/in2 reduces Cr from 0.018 to 0.015. Changing from cross-ply to a radial-ply tyre, inflated to 40 lb/in2, will further reduce Cr to 0.011. Investigation with the Wood River Fiat 600 showed further reductions in rolling resistance as tyre pressure was increased to 100 1b/in2. Increasing from 20 to 100 1b/in2 increased the 16.5 to 0 mile/h coast distance by 50%."

It went on to further say

"Large wheels show useful reductions in rolling resistance over small ones, thin sectioned tyres over thick sectioned ones, and treadless tyres over fully treaded ones. TRC specials have used high-pressure racing bicycle tyres and probably achieve values of Cr of 0.003."

"For a 'modified' car a reduction in Cr to 0.01 appears plausible, with a significant further reduction available to the special builder. Recalculating equation 12.1 with these data for a 2000 lb vehicle,

at 10 mile/h, bhp = 0.0267(20 + 2.08) = 0.59
Fuel economy at 0.08 bsfc = 212 mile/gal

at 30 mile/h, bhp = 0.08(20 + 18.72) = 3.09
Fuel economy at 0.08 bsfc = 121.0 mile/gal "

So from this data and research, improvements can be seen up to 100 lb/in2
However at these inflation pressures I don't know if a cush air ride would even help a street car LOL I doubt 100 lb/in2 would be safe for every day road use. But it is interesting test data none the less.

Hope some of you find it interesting.

GH..

[California98Civic]

Originally Posted by SentraSE-R

Darin did the definitive inflation testing here. The results showed big gains up to 50 psi, but nothing above that.

Thanks for the find. He does great testing and this is a great test. I agree. But even he was not willing to call the results definitive: "there obviously aren't enough data points to call these results representative. They're not rigorous tests (thus the "snapshot" title)."

I have no evidence to challenge the claim that more than 50psi on a 44 max sidewall tire is better. I originally boosted to 60 to follow the PaleCivic example. His tires were 60+psi and we all know the amazing results he used to get from his 1996 almost totally unmodified DX.

Originally Posted by GreenHornet

Investigation with the Wood River Fiat 600 showed further reductions in rolling resistance as tyre pressure was increased to 100 1b/in2. Increasing from 20 to 100 1b/in2 increased the 16.5 to 0 mile/h coast distance by 50%."

... So from this data and research, improvements can be seen up to 100 lb/in2 However at these inflation pressures I don't know if a cush air ride would even help a street car LOL I doubt 100 lb/in2 would be safe for every day road use. But it is interesting test data none the less.

Hope some of you find it interesting.

GH..

That is interesting... but 100? Not for me.

[aerohead]

Originally Posted by GreenHornet

I would like to share some data with all of you on testing that was performed for the Shell eco marathons. This data is out of the book by W.S. Affleck and G. B. Toft Fuel economy of the gasoline engine. While the book was published back in 1977 the research that was done into the science of fuel economy is very relevant today as well as pertains to this thread!

Chapter 12 Mileage Marathons

Under rolling resistance it states that

"Rolling resistance is, in a properly prepared vehicle, largely determined by tyre size,profile,structure and inflation pressure. Increasing inflation pressure on a conventional cross-ply 14" tyre from 25 to 40 1b/in2 reduces Cr from 0.018 to 0.015. Changing from cross-ply to a radial-ply tyre, inflated to 40 lb/in2, will further reduce Cr to 0.011. Investigation with the Wood River Fiat 600 showed further reductions in rolling resistance as tyre pressure was increased to 100 1b/in2. Increasing from 20 to 100 1b/in2 increased the 16.5 to 0 mile/h coast distance by 50%."

It went on to further say

"Large wheels show useful reductions in rolling resistance over small ones, thin sectioned tyres over thick sectioned ones, and treadless tyres over fully treaded ones. TRC specials have used high-pressure racing bicycle tyres and probably achieve values of Cr of 0.003."

"For a 'modified' car a reduction in Cr to 0.01 appears plausible, with a significant further reduction available to the special builder. Recalculating equation 12.1 with these data for a 2000 lb vehicle,

at 10 mile/h, bhp = 0.0267(20 + 2.08) = 0.59
Fuel economy at 0.08 bsfc = 212 mile/gal

at 30 mile/h, bhp = 0.08(20 + 18.72) = 3.09
Fuel economy at 0.08 bsfc = 121.0 mile/gal "

So from this data and research, improvements can be seen up to 100 lb/in2
However at these inflation pressures I don't know if a cush air ride would even help a street car LOL I doubt 100 lb/in2 would be safe for every day road use. But it is interesting test data none the less.

Hope some of you find it interesting.

GH..

An SAE Paper about the Mobil Economy Runs of years past talked of closed-course,competition,at very low average velocities with no chance of standing-wave hysteresis losses,and up to 200-psi inflation pressure on bald-only tires.
None of this was germane to 'real-world' motoring.
From one source,the minimum R-R is not attained at maximum pressure,but is a function of actual load vs maximum rated load for the particular tire.
Current production radials have their standing-wave effects occur much above regulated driving speeds,so they won't self-destruct in normal driving.
Racing tires will have maximum rated velocities indicated by the manufacturer.(Bugatti has to electronically limit the top speed of their Veyron to keep it within safety parameters specified by Michelin.
Since tires are the first 'spring' in the suspension system,over-inflation can create an undue burden on Heim joints,leading to premature wear and instability.

[brucepick]

For my Civic, I have Kumho all seasons and Michelin (low rolling resistance) winter tires. I run the Michelins in mid-50's psi and the Kumhos in upper 50's. Tread wear has been nice, not going thin at the center as so many have predicted.

This is my second set of Kumho's, and the second set to have side bubbles and supposedly belt separation. No such issues with the more expensive Michelins.

I bought some used tires (Kelly brand, cheapos) on rims for my Accord, presumably not overinflated by previous owner. Some of those have side bubbles too.

I definitely see fuel economy improvements from increased pressure. I'm also convinced that lower priced tires will have issues regardless of air pressure.

[niky]

With low priced tires with soft sidewalls, under-inflation is definitely dangerous.

Originally Posted by SentraSE-R

Darin did the definitive inflation testing here. The results showed big gains up to 50 psi, but nothing above that.

Darin's results:
psi / ft. traveled
20 / 479.3
25 / 524.8
30 / 621.0
35 / 621.0
40 / 639.6
45 / 687.5
50 / 702.0
55 / 699.3
60 / 702.0

I've used that data myself when writing about tire pressure, but of course, it's data for only one type of tire, and shows that going up to maximum sidewall pressure for that specific tire is beneficial, but exceeding it gives diminishing returns.

I frequently pump up to 45 psi myself on cars that are stickered at 28-35 psi. I'd go higher, to 50, but that causes some vehicles to wander a bit on grooves on the highway. I can deal fine, but I'm not the only driver in the family.

After a year or two at 45, nobody complains. They've gotten used to it.

[cbaber]

I've had pretty good luck with the Kumho's so far. I'm at 30,000 miles of the advertised 80,000 mile lifespan. I rotate them every 7,500 miles and keep the pressure up.

The only instance where I tire has bubbled on me (cheap or expensive) has been when the tires were not balanced regularly. In high school (I was stupid and careless) I drove on an unbalanced tire until the shaking made it almost impossible to drive. When I took it off, there was a bubble the size of a football in the tire, and wires showing on one side!

Thanks for all the replies everyone. I've decided to stay at 45 psi for a few tanks and then bump it up to 55 psi for a few tanks. If I see a significant difference then I will decide at that point.

[mcrews]

Originally Posted by Honda

The center tread of over inflated tire wears faster.

False
think steel belts. 4 sets of kohmos on the Q45. 40k plus on each set. The high performance summer tires. Never had uneven wear ran 40 plus psi