Tyre pressures
Posted: Fri Mar 04, 2022 7:17 am
by 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.
Re: Tyre pressures
Posted: Fri Mar 04, 2022 9:25 am
by 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.
Re: Tyre pressures
Posted: Fri Mar 04, 2022 6:15 pm
by Skippydiesel
DCASonex wrote: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.
Re: Tyre pressures
Posted: Fri Mar 04, 2022 6:24 pm
by 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?
Re: Tyre pressures
Posted: Fri Mar 04, 2022 7:16 pm
by jaflint
I run Goodyear Flight Custom III tires. 28 psi, over 1000 (tire) trouble-free landings on the current set.
Re: Tyre pressures
Posted: Sat Mar 05, 2022 4:36 am
by Skippydiesel
GraemeSmith wrote: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
Re: Tyre pressures
Posted: Sat Mar 05, 2022 4:39 am
by Skippydiesel
jaflint wrote: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.
Re: Tyre pressures
Posted: Sat Mar 05, 2022 10:22 am
by markschaible
https://www.sonexaircraft.com/instruction-sheets/#gear
Re: Tyre pressures
Posted: Sat Mar 05, 2022 6:49 pm
by 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.”
Re: Tyre pressures
Posted: Sun Mar 06, 2022 3:53 pm
by 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 pressure
Re: Tyre pressures
Posted: Sun Mar 06, 2022 7:03 pm
by Skippydiesel
GraemeSmith wrote: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
Thanks Graham - In the Sonex advice there was no mention of tyre brand or size. You are most likely correct in your assumption (smaller tyres).
It seems to me that the teams advised pressure range, at least initially, has narrowed considerably. We seem to be in the 30-40 psi range (given manufacturers advice & real world experience).
For the most part I will be operating of grass. This environment combined with the light weight of the Sonex (yet to be weighed) suggests to me that 35 psi might just be a good start point.
Initial taxi testing should give some indication of tyre heating - to hot (above + 4 C rise) increase the pressure, to low (below 4 C) reduce pressure.
Re: Tyre pressures
Posted: Tue Mar 08, 2022 6:54 pm
by GraemeSmith
I run my 5" Airhawks (horrible tires - but I bought cheap while trying out a larger tire) at 45psi on grass and pavement. 40psi on ice for a little more contact patch.
Re: Tyre pressures
Posted: Wed Mar 09, 2022 6:21 am
by Skippydiesel
GraemeSmith wrote:I run my 5" Airhawks (horrible tires - but I bought cheap while trying out a larger tire) at 45psi on grass and pavement. 40psi on ice for a little more contact patch.
Good info Graham and directly relevant to my 5" Goodyear’s.
Thankfully I rarely have to deal with ice.
Re: Tyre pressures
Posted: Wed Mar 09, 2022 12:09 pm
by GordonTurner
Rarely? Does that include sometimes?
Re: Tyre pressures
Posted: Wed Mar 09, 2022 1:31 pm
by N190YX
45 PSI is a little high for a 5:00X5 tire, the data for my factory airplane for the 5:00X5 tire on the nose gear specifies 40 PSI.
Re: Tyre pressures
Posted: Wed Mar 09, 2022 3:06 pm
by GraemeSmith
N190YX wrote:45 PSI is a little high for a 5:00X5 tire, the data for my factory airplane for the 5:00X5 tire on the nose gear specifies 40 PSI.
It’s not that simple. The tires have a maximum ply/load/pressure from the manufacturer. You can then work under those parameters to see what works best for you:
Product Code Size Ply Rating Max. Load Inflation Pressure
AB3D2 5.00-5 4 800 31
AB3D4 5.00-5 6 1285 50
AB3D8 5.00-5 10 2150 80
Re: Tyre pressures
Posted: Wed Mar 09, 2022 4:26 pm
by radfordc
Whatever the right pressure is I can tell you what happens if the pressure is too low and you land on pavement. Shears off the valve stem and makes it very hard to taxi!
Re: Tyre pressures
Posted: Wed Mar 09, 2022 5:49 pm
by Skippydiesel
N190YX wrote:45 PSI is a little high for a 5:00X5 tire, the data for my factory airplane for the 5:00X5 tire on the nose gear specifies 40 PSI.
I “guild the lily” - Where I live and have lived around NSW & a little in Vic, we do get a few early morning frosts per year. If there is standing water (puddles, water troughs, etc) a thin film of ice can form - short lived, as frosty mornings are usually followed by beautiful clear warm days - great flying. I have never lived in the Australian high country where winters are similar to the northern hemisphere.
Re: Tyre pressures
Posted: Thu Mar 10, 2022 4:49 pm
by DCASonex
Take a look at your AUSA wheels. There is a max pressure listed on them that as i recall was about 35 PSI. 50 PSI may be okay with the small tires, but the larger ones put more pressure on the rims trying to separate the two halves and there have been reported problems with the thru bolts on those. I have found 25 PSI works fine on mine for the last 10 years mostly on hard surfaces but occasional on turf as well. I would not recommend over 35 PSI.
David A. Sonex TD, w/ 3300