Tire pressures?

[Gundy]

I was doing some routine stuff on the BE today.
Adjusted the toe in a little from 1/8 to 1/16.
Adjusted the valves. #4 was way off. Cam calls for
16 and 18 for lash. The #4 was 20. Annoying tick is gone.
Anyway....I checked the tire pressures. 10 lbs in the fronts and 18 in the rears. The manual called for 18 and 20 or so.
These tires aren't stock. 185x55x15s. I went with 22 lbs
in all four. I note the manual calls for 24 lbs or so for
high speed driving with stock tires.
Is there any way these things would require such low pressures?
At 10 lbs in the front I'm surprised I didn't pop a bead on a hard run up a mountain recently.
Am I screwing something up running 22 lbs?

 

[twas_brillig]

The original pressures (at least for the bug-eyes) were for bias ply tyres. We're running 28-30 psi in 155R90/13 radials, based on advice that I've forgotten from decades ago.
If anyone has some practical/theoretical knowledge as to how to figure out what pressures should be, I'd sure like to hear: we're running 255/60R15 tires on 15 x 7 rims on our VW Beetle based Meyers Manx clone dune buggy, and I have no idea what I should be running for pressures on pavement - currently I'm at 18 psi - as it only weighs about the same as the Bug-Eye and sure has a lot more rubber.

Doug

 

[walshja]

I don't think there's a right or wrong answer with tire pressures.

Over-inflating your tires will give you a bouncy ride and an ill-handling car, while under-inflated tires can develop premature wear from increased friction.

finding the right pressure depends on your goal.

if you want to extend the life of you tires, that would call for more pressure (never go over what is stated on the side of the tire, in fact, you shouldn't even approach that limit under most circumstances)

if you want to increase grip, lower the pressure in your tires. but that will increase wear on your tires since friction is increase (more friction = better grip)

it is all about finding that spot you are comfortable with. start with what the manufacturer suggests, then increase or decrease based on your desired performance.

 

[JPSmit]

Haynes says

Crossply

Normal Car Load Front 18 Rear 20
Maximum Car Load Front 18 Rear 24
Sustained High Speed Front 22 Rear 28

Radial

Normal Car Load Front 22 Rear 24
Maximum Car Load Front 22 Rear 26
Sustained High Speed Front 28 Rear 30

I picked #3

 

[Trevor Jessie]

I generally run 26 front and 28 rear.

 

[Gundy]

It sure drove/handled better with the increased pressure.
Steering was MUCH lighter.
I think I'll bump 'em up a bit more to say 25 and 27 and see
how that feels.
I really hadn't thought about the bias vs radial aspect. Good point.
Thanks to all for the input!
I also noticed the front tires had begun to have edge wear
greater than center wear. 10 psi will do that.
In my land Cruiser I run 40 psi normally and 10 psi on the rocks. Way different animal. It's amazing the traction difference you get at 10 psi. The tires at those pressure
really wrap around irregular surfaces when crawling along.

 

[Pythias]

First.... 175/70 13s--stock rims.

I felt mine rode more like a truck than a car when I filled 'em up over 25 or 26 lbs. Then I realized that the sidewalls of the tires are a part of the suspension. I've running 20 front, 22 rear, except on long trips where I want slightly better fuel economy. Then I'll go 24/26. Keeping the rear higher than the front helps control the oversteer.

One thing to keep in mind is that the car themselves are very light, so a lower pressure is needed for a full contact patch than would be required for a heavier car. .....

This brings up an interesting point. The amount of rubber on the road is the same for a tall skinny tire as it is for a short wide tire, assuming the same air pressure. The difference is the SHAPE of the contact patch.

 

[bugimike]

Generally speaking, if you are getting edge-wear then pressure is to low, and if the center is wearing faster, it is too high! I have found with my BE that anything under 18psi seems to be too low, and over 26psi is to high. Hope that helps a bit.

 

[Gundy]

I tried several different pressures both front and rear.
I settled on 22 in front and 25 in rear.
Any higher in front and the steering seems a bit "harsh".
Any higher in the rear and the ride gets bumpy.
I'm amazed how minor psi changes can greatly effect how this
car rides/performs.
I'll keep my eyes on tire wear pattern and adjust if the
pattern is not even but these pressures seem a happy medium
for my car/tire combo.

 

[jlaird]

Running 24 front 26 rear in Miss Agatha.

 

[Trevor Jessie]

Tire pressure on these cars will vary greatly due to modifications and tire/rim sizes. So, experimentation is the key. I use to run my tires much lower, but increased the to even out the wear.