Tyre pressures

[Skippydiesel]

We all have to land sometime so tyre pressures should be a hot topic.

My new Sonex Legacy (A ) tail wheel, is fitted with Goodyear Flight Custom, 6 ply tyres .

Finding the correct cold inflation pressure seems unnaturally difficult.

As far as I can make out, from the variose Goodyear manuals, these tyres are rated at 50 psi for a maximum load of almost 563 kg/tyre. My max Take off weight is 544 kg so the tyres are well & truly over specified (probably to get the 6 ply rating for thorn resistance).

Your advice comments, on tyre pressure, will be most appreciated.

[DCASonex]

Assuming those tires you mention are the larger 5.00 x 5 and not the small standard Sonex tires, 50 PSI is way too high for both the load and the capacity of the standard AUSA wheels which as I recall are rated for 35 PSI max. I have the 5.00 x 5 tires on my A series Sonex tail-dragger with a 3300 engine and have found 22.5 to 25 PSI to be about right with those. Had about 400 hours in 8 years on first set before replacing them, but using the cheaper and lighter 4 ply.

While one might think 50 PSI would exert the same force on the wheel regardless of tire size, the wheels also hold together the sidewalls of the tires and the force the side walls of the tires exert on the wheels increases as the side area of the tires increases, so even though 50 PSI may be okay with the small tires, it should not be used with the larger ones.

David A.

[Skippydiesel]

Assuming those tires you mention are the larger 5.00 x 5 and not the small standard Sonex tires, 50 PSI is way too high for both the load and the capacity of the standard AUSA wheels which as I recall are rated for 35 PSI max. I have the 5.00 x 5 tires on my A series Sonex tail-dragger with a 3300 engine and have found 22.5 to 25 PSI to be about right with those. Had about 400 hours in 8 years on first set before replacing them, but using the cheaper and lighter 4 ply.

While one might think 50 PSI would exert the same force on the wheel regardless of tire size, the wheels also hold together the sidewalls of the tires and the force the side walls of the tires exert on the wheels increases as the side area of the tires increases, so even though 50 PSI may be okay with the small tires, it should not be used with the larger ones.

David A.

Thanks David - I forgot to mention the size. Yes 5.00 - 5, Part No.505C66-5.

I agree that 50 psi is far to high however this was the only pressure I could find in the various Goodyear manuals.

We have a thorn problem (puncturing tyres) on many of our dryer area (inland) grass strips. To combat this we often use much higher ply ratings than the weight of our aircraft would normally require.

[GraemeSmith]

Ply rating is a measure of load carrying - not thorn resistance (!!)

And modern tires are not really constructed with the extra plies implied in the rating these days anyway - so though they can carry a larger load - I'm not sure where you might get extra thorn resistance from.

That said - Goodyear Flite Specials do seem do have a better rubber compound and more of it than other brands. So perhaps that is why they perform better on the thorn resistance?

Do what the road bike guys do - Kevlar construction - though I haven't actually seen that for small GA tires. Anyone?

[jaflint]

I run Goodyear Flight Custom III tires. 28 psi, over 1000 (tire) trouble-free landings on the current set.

[Skippydiesel]

Ply rating is a measure of load carrying - not thorn resistance (!!)

And modern tires are not really constructed with the extra plies implied in the rating these days anyway - so though they can carry a larger load - I'm not sure where you might get extra thorn resistance from.

That said - Goodyear Flite Specials do seem do have a better rubber compound and more of it than other brands. So perhaps that is why they perform better on the thorn resistance?

Do what the road bike guys do - Kevlar construction - though I haven't actually seen that for small GA tires. Anyone?

True! The Goodyear tyres were fitted by the first builder - I only recently found out the same tyre comes in 4,6 & 8 ply. I assume he fitted the 6 ply (heavier and more costly than the 4 ) for a reason. I speculated thorn resistance. In this part of the World where we have thorns that can easily penetrate a tyre (& shoes) higher ply tyres do seem (hope?) to give extra protection. It is not uncommon to have vehicles and aircraft tyres fitted that have ply ratings well above the carrying capacity of the vehicle/aircraft.

My last aircraft came with 4 ply tyres - always seemed to be pumping them up/doing repairs. Had 8 ply road tyres fitted - never had a puncture

[Skippydiesel]

I run Goodyear Flight Custom III tires. 28 psi, over 1000 (tire) trouble-free landings on the current set.

Thanks Jason - you have addressed my question beautifully. I thaight I might start with 30 psi and see how that went. Given your experience I will go with 28 psi.

[markschaible]

https://www.sonexaircraft.com/instruction-sheets/#gear

[Skippydiesel]

From Mark;

Sonex instructions;

"Infl ate the tubes to approximately 50 psi. 30 psi provides
a bit more "cushion" but increases rolling drag and may
cause a pinched tu nched tube if fl ying off a hard surface runway. be if flying off a hard surface runway."

[GraemeSmith]

Yes but I think Sonex are talking about the 4" tires. By the time we are talking Goodyear we are at 5".

Generally - the smaller the tire the higher the oressure