What tires do you have... the OEM tires on my 2003 HCH states 51psi.

 

I've got the OEM for the 2004, the Bridgestone B381, and I think the max PSI is 44 on the tire.....

 

Huh? Why do you think Nitrogen would behave differently? All common gases behave very similarly when the temperature changes. Regular atmospheric air is 80% nitrogen anyway.

 

Did you ever make an emergency stop where the tires were locked or ABS was activated? Was there ever enough water on the road to cause you to aquaplane while driving or stopping? If not, I wouldn't say you've really tested the safety of over inflated tires.

 

Well do some research and you will find that nitrogen filled tires will not vary as much in PSI as the tires warm up... this has to do with the amount of moisture in the air in your tires.

It's the moisture that causes the 4+ psi difference between warm and cold measurements.

 

Yes. If you recall not to long ago we had rain that flooded most of southern NH. It was in this weather that i took my hch with 51psi and conducted my test. Not only did i not aquaplane, ABS rarely engaged. Both were surprises to me.

I ran tests on both highway and regular roads and I have to say that I felt safer with the tires at 51psi then with the tires at regular pressure.

Highway test were:

70mph runs.
Lane changes at 70mph.
Running through big puddles on off ramps (much slower, 35 - 40mph), that was the only time I aquaplaned but I expected to.
I did not conduct any emergency stops on the highway... not a good move.
I did come to near stops (15mph) when exiting the highway where the off ramps were long and straight. I had no problems hauling down the car from 70mph.

Regular roads:
0-60mph... hehe. It was the only time i could get the wheels to actually spin. For about the first 10 feet.
40mph - 0 emergency braking. No problems. ABS would engage on emergency stops but if I just went for a hard stop I could get the car to stop in about the same distance without engaging the ABS.

The key here is that handling was improved by a noticable amount. So you felt more in control in all the above situations. FE did not improve at all in the rain. If it did, it was not noticeble over the life of a tank.

 

And you run 58psi? And how is that safe? Or am I missing something?

 

I believe you probably did receive some fuel economy benefit from the increased tire pressure. Some small amount.
The test you performed was done in rainy weather, which normally reduces fuel economy. Any gain from the higher pressure was nullified by the increased rolling resistance of the wet roads.

So maybe your gas mileage would have been worse. Hard to know for sure. There are so many variables that affect fuel mileage, it's hard to measure a small difference.

My tires are inflated to the cold sidewall max rating, and the handling has improved. It is a stiff ride, but not uncomfortable. The anti-lock brakes work fine.
The car has been set up this way since the second tank of gas.

Regards,

 

http://www.whynitrofill.com/benefits.htm

Howard

 

Braking performance in deep standing water should improve with a higher inflation pressure, although it will be the same or fractionally worse on a simply damp road. For snow or dirt, you'll want lower pressures too, and for any sort of serious snow and ice, just forget about the stock tires entirely and use snow tires.

58psi is definitely above the range I would use, but it's not nearly as dangerous as you'd think. I'd say that in the grand scheme of risk management, using 58psi and driving around the speed limit is still safer than 32psi and doing 5mph over, based on propensity for failure, any perceptible loss of traction from higher inflation pressures, and the increased braking distances associated with going 5mph faster.