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Tire pressures

Ferreip

Ferreip

Member
Did a search for tire pressures, and similar to "what oil to use", there are many different opinions, but for a -9, is 35 psi a good overall pressure to inflate the tires?

Paul
 
It depends on what you want.

Reduced rolling resistance, longer stopping distance, lower tire wear, firmer landings on hard surfaces -- Run higher pressure 45 - 50psi
Increased rolling resistance, shorter stopping distance, higher tire wear, cushier landings on hard surfaces -- run lower pressure 35 - 40psi

Lower pressure can cause the tire to do unpleasant things when sideloaded.

FWIW, I run my RV-7 at ~50PSI.
 
I've had a few "firm" landings which I believe didn't result in a flat because I keep my tires up at between 45 and 50 psi. Ok, I've had more than a few firm landings... I'm not really seeing a reason to run lower tire pressure.
 
After 26-years RV-6 flying, I tend to inflate on how the tires look. I like the outside rib of the tire to just touch the ground. In the past, that has tended to be between 35 and 42 PSI. Typically I find 30 PSI too low and too high of rolling resistance. Changing tires tend to be a few pounds more or less from what the old ones use to use.

Your tire pressure may be more or less what everyone else is using.
 
Running too low pressure will also create more tire flexing and rubbing of the inner tube, resulting in abraded spots that leak, and you'll have a flat at some point.

I used to run about 30 psi, got tired of flats and replacing inner tubes, changed to Michelin Airstops ($$!!) and keep mine at 45-50 psi now. No more flats in the last 1000 hours with that.
 
Ferreip said:
Thanks everyone for your answers; I'm going to try running 45 psi. Appreciate your recommendations.

Paul
Click to expand...
Just be prepared for potential main gear vibration. Higher pressures reduce gear leg dampening. I ran 32-35 psi for 15 years and never had and gear vibration. Based on posts here, I increased my pressures to 38-40 and got some pretty significant main gear vibration. I have since added wood strips to my main gear legs to act as dampeners. Now I am running 35-38 psi with no issues. I will probably let it migrate to 40 psi as the weather heats up (and tire pressure increases with the temp) but don’t feel the need to go above 40.
 
plehrke said:
Just be prepared for potential main gear vibration. Higher pressures reduce gear leg dampening. I ran 32-35 psi for 15 years and never had and gear vibration. Based on posts here, I increased my pressures to 38-40 and got some pretty significant main gear vibration. I have since added wood strips to my main gear legs to act as dampeners. Now I am running 35-38 psi with no issues. I will probably let it migrate to 40 psi as the weather heats up (and tire pressure increases with the temp) but don’t feel the need to go above 40.
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Truth.

My nose gear has a "taxi-too-fast" alarm that now goes off at exactly 18 knots groundspeed with tire pressure at 45 or above.
 
Just an update on running 40 psi on my -9. Braking caused extreme shimmy, so this weekend changed back to 35 psi. I felt the vibration, but someone filmed one of my landings, and it appeared the 2 tires were angry with each other! 😳

Haven't flown, but I'm hoping this will not happen again. I have to research why the tires shimmy so badly when lightly applying brakes. Is there a solution to minimize this?
 
Ferreip said:
Just an update on running 40 psi on my -9. Braking caused extreme shimmy, so this weekend changed back to 35 psi. I felt the vibration, but someone filmed one of my landings, and it appeared the 2 tires were angry with each other! 😳

Haven't flown, but I'm hoping this will not happen again. I have to research why the tires shimmy so badly when lightly applying brakes. Is there a solution to minimize this?
Click to expand...
I start at 60 psi. When I get to 45 psi add air. Never a shimmy. First set of tires changed at 450 hrs. (Mains) Nose wheel at 600 hrs. still ok. I do have my nose wheel break out force on the high side of the spec.
 
For what it's worth, I asked Mike Seager this and he said he runs the mains on the RV7 at 32 psi. That plane gets all sorts of abuse, plus it doesn't have wooden dampers, but there's no gear shimmy whatsoever.
 
Just to be a contrarian, I run 25 psi in my RV-4, never had a flat, no shimmy. Tires wear evenly if I turn them over about halfway through.
 
While tire pressure changes wheel shimmy symptoms, it does not correct the root issues.

What I found effective:
- Balancing tires. My experience is the main gear tires out of balance create more nose gear shimmy than the nose wheel out of balance.
- Replace the old “tighten the axle bolt just enough” nose gear approach with the very nice Matco axle. This axle provided means to set the bearing pre-load independent of the axle bolt (as in the axle bolt gets fully tighten). This also elimates the wheel bearing inserts from rotating on the aluminum nose gear fork (not good for the fork).
matcoals.com

AXLE ASSEMBLY, A24 1.25 INCH - Matco Aircraft Landing Systems

Nose Wheel Axle Assembly for 1.25 inch TRB Wheels.
matcoals.com matcoals.com

For what it’s worth, I run 45psig tire pressure.

Carl
 
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