Something different on tyre pressures

[Haynes]

When I was studying years ago, I was taught this "rule of thumb" of determining tyre pressures by someone who spent 29 years working for a tyre manufacturer.

He claimed:

* Load the bike/car with its full load including fuel, luggage and passengers.

* Starting with low tyre pressures of about 16psi, measure and record the height from the road to the rim.

* Increase the pressure by 2 psi, measure and record the height.

* Repeat this until there is no change in the height for an increase of 2 psi.

This he called "the minimum working pressure" and it turned out to be 4-6 psi (car) higher than the tyre manufacturers pressures.

 

He stated that most tyre pressures are set low with the assumption that tyres will increase in heat due to the internal friction of the materials as they flex - hence increasing the pressure [i think this is known by almost everyone]. He claimed that an increase of 4-6 psi on cars and 2-4 psi on motorcycles will increase both tyre wear and performance. Tyres with higher pressures will flex less and produce less internal friction keeping their pressure more stable.

 

Some interesting anecdotes that he stated:

Tyres will hold at least 3 times the gauge pressure.

Rims will hold at least 3 times the gauge pressure.

 

Has anyone else heard of this "rule of thumb" for setting pressures?

Do you support the idea?

[ShovelStrokeEd]

It is not a bad idea. Problem keeping a motorcycle stable enough while loaded on its wheels to make the measurement accurately enough. Especially with the shape of modern radials where the outer edge of the tread is quite often outside the parallel line to the rim.

 

I used to subscribe to a little different theory and not check my tire pressures until 100 miles or so into the trip. Looked for max recommended cold inflation pressure (usually 42 PSI) with the tire hot. I don't do that anymore as it is a PITA to check with my bike loaded like it normally is. Checking the tire is no harder but getting the bike onto the center stand is tough since the rear shock sags due to the 100+ lbs of baggage.

 

I've been running 42/42, cold, as recommended by Honda, on my current set of Roadsmarts and the wear has been outstanding with little loss of comfort and none of handling. Since I plan on replacing them with a like set when they finally do wear out (10K+ so far), I think I'll stay with this plan.

[Quinn]

The way my tire guage works, it becomes more of an air change than just checking pressure. Getting the nozzle on the stem pretty well guarentees that I've lost three or four pounds, so I have to over-inflate it and then bleed off the difference once it's seated.