Tyre pressure tolerance

[magiccarpet]

I am looking for min/max. pressure values in order to setup the warning levels of my TPM BT sensors.
What values do you think are still acceptable before inflating is required.
My nominal value is 22psi for the nose wheel and 25psi for the mains.
Thanks a lot.
Chris

 

[Iluke]

I don't have an answer to your actual question, but I am very curious about using tire pressure monitors on an RV. Do they work? Do they affect tire balance? If they work I think it would be a great addition because checking tire pressure is a pain, even with an access hole in the wheel pants.

Any info would be appreciated.
thanks
Ivan

 

[mmcmanus]

I think the TPMS monitor is a great idea if balance etc doesn't become a problem. Taking the wheel pants off to check tire pressure can be such a pain.

However, I think those minimum values you mentioned (22 / 25 psi) are way too low. I sold my 7A last year, but a few years ago I had some pretty significant wheel pant damage due to low tire pressure on the mains and those pressures were in the low 40s at the time of the problem. So I recommend something much higher. Just my $.02.

Matt McManus

 

[azonslow]

I think the TPMS monitor is a great idea if balance etc doesn't become a problem. Taking the wheel pants off to check tire pressure can be such a pain.

However, I think those minimum values you mentioned (22 / 25 psi) are way too low. I sold my 7A last year, but a few years ago I had some pretty significant wheel pant damage due to low tire pressure on the mains and those pressures were in the low 40s at the time of the problem. So I recommend something much higher. Just my $.02.

Matt McManus

I don't have an answer to your actual question, but I am very curious about using tire pressure monitors on an RV. Do they work? Do they affect tire balance? If they work I think it would be a great addition because checking tire pressure is a pain, even with an access hole in the wheel pants.

Any info would be appreciated.
thanks
Ivan

The POH lists the "optimum" tire pressures at 22 front and 25 mains with 23 and 28 being the "maximum" respectively. I'd go with the POH.

 

[Piper J3]

I installed TPM’s on my RV-12 several years ago, but only on the main wheels. The fork on the nose wheel does not allow clearance for TPM to be installed. I used a ¼ ounce stick-on wheel weight to offset the TPM and balance is uneffected.

That said… I run the TPM app and place cell phone on pilot-side wing walk at beginning of preflight inspection. By the time I have fisnished my walk-around the TPM has registered for both wheels. I then log the readings to plot air loss over time. By setting phone on wing walk… it is almost impossible to forget phone before climbing into cockpit. Not impossible… but close to it.

 

[Iluke]

I installed TPM’s on my RV-12 several years ago, but only on the main wheels. The fork on the nose wheel does not allow clearance for TPM to be installed. I used a ¼ ounce stick-on wheel weight to offset the TPM and balance is uneffected.

That said… I run the TPM app and place cell phone on pilot-side wing walk at beginning of preflight inspection. By the time I have fisnished my walk-around the TPM has registered for both wheels. I then log the readings to plot air loss over time. By setting phone on wing walk… it is almost impossible to forget phone before climbing into cockpit. Not impossible… but close to it.

Thanks. I'll order a TPMS today!

 

[mstrauss]

Has anyone tried integrating this into the EFIS? I would think with an an Arduino and GAD27 (Garmin), you could get a warning if to low/high.

 

[liuk]

I installed TPM’s on my RV-12 several years ago, but only on the main wheels. The fork on the nose wheel does not allow clearance for TPM to be installed. I used a ¼ ounce stick-on wheel weight to offset the TPM and balance is uneffected.

That said… I run the TPM app and place cell phone on pilot-side wing walk at beginning of preflight inspection. By the time I have fisnished my walk-around the TPM has registered for both wheels. I then log the readings to plot air loss over time. By setting phone on wing walk… it is almost impossible to forget phone before climbing into cockpit. Not impossible… but close to it.

I'm always wondering: does this cap sensor operate by pressing against the Schrader valve to gauge the pressure? If so, does this imply that the thread on the cap is the only thing maintaining the pressure?

 

[seagull]

“If” you have low pressure can you add air with this monitor in place? Would you be able to remove the monitor and add air through the 1” hole in the wheel pant, or is removing the back of the pant required?

 

[jrtens]

Back to the OPs original question, I use 22-25 for the nose and 25-30 for the mains.

 

[magiccarpet]

I'm always wondering: does this cap sensor operate by pressing against the Schrader valve to gauge the pressure? If so, does this imply that the thread on the cap is the only thing maintaining the pressure?

I believe that‘s exactly the case.

 

[magiccarpet]

I installed TPM’s on my RV-12 several years ago, but only on the main wheels. The fork on the nose wheel does not allow clearance for TPM to be installed. I used a ¼ ounce stick-on wheel weight to offset the TPM and balance is uneffected.

That said… I run the TPM app and place cell phone on pilot-side wing walk at beginning of preflight inspection. By the time I have fisnished my walk-around the TPM has registered for both wheels. I then log the readings to plot air loss over time. By setting phone on wing walk… it is almost impossible to forget phone before climbing into cockpit. Not impossible… but close to it.

I plan to the same and will maintain a log to more precisely monitor pressure loss over time.

 

[Piper J3]

I'm always wondering: does this cap sensor operate by pressing against the Schrader valve to gauge the pressure? If so, does this imply that the thread on the cap is the only thing maintaining the pressure?

The TPM has a rubber diaphragm that presses against the schrader valve to hold it open. The rubber diaphragm seals against the end of the brass threaded valve stem. I use a thick silicone grease (dielectric grease) on the face of the diaphragm to maintain the seal.

 

[Webb]

I bought a set but don’t need since I built access doors in my wheel pants. Will post in classifieds later today unless some wants them before I post. NIB $25 and shipping on me.

It’s just one thing less to get rid of later

 

[Brett H]

I bought a set but don’t need since I built access doors in my wheel pants. Will post in classifieds later today unless some wants them before I post. NIB $25 and shipping on me.

It’s just one thing less to get rid of later

I realize that TPMS wasn’t the original focus of this post. But, in the constantly changing world of electronics, what are people using for TPMS monitoring? What do they like and what do they dislike? What has been learned since using them?

Thanks.

Brett

 

[PilotjohnS]

I am using 40 psi. Add air at 35 psi. (Broke wheel pants too many times)

 

[dmattmul]

I'm always wondering: does this cap sensor operate by pressing against the Schrader valve to gauge the pressure? If so, does this imply that the thread on the cap is the only thing maintaining the pressure?

Yes, I didn't feel that lucky to use this set-up. 25 psi seems very low. I use 40 psi min and air up to 60 psi. That is what Beringer recommends for the Michelin Aviator.

 

[DanH]

The POH lists the "optimum" tire pressures at 22 front and 25 mains with 23 and 28 being the "maximum" respectively. I'd go with the POH.

It's an optimum (for some) in terms of shimmy reduction. It's far from optimum if you want long inner tube life and fewer wheelpant repairs.

 

[seagull]

Any idea why Van’s recommends the lower pressures?

 

[Piper J3]

Any idea why Van’s recommends the lower pressures?

I think I remember reading that it has to do with dynamics of the landing gear – softens some the impact forces transferred into the airframe. There are a couple of SB’s to strengthen the landing gear carry-through channel...

 

[Bob Y]

Any idea why Van’s recommends the lower pressures?

Certainly can’t speak for Van’s, but can’t help but notice how due to the camber of the main gear, that the higher the tire pressure, the more the tire rides on its outer edge. That, plus riding on a smaller area seems that it would accelerate tire wear. And the lighter the plane is loaded, the more pronounced it is. Might not be as bad if operating off grass, but on pavement it seems like it would cause earlier tire wear with higher inflation pressures.

 

[N8DAV8R]

I think I remember reading that it has to do with dynamics of the landing gear – softens some the impact forces transferred into the airframe. There are a couple of SB’s to strengthen the landing gear carry-through channel...

This is also what I understand to be a reasonable explanation. This is common thinking on light sport designs, landing gear design is unfortunately part of the formula to hit 1320. I personally think of the tires as a consumable part of the landing gear system and would rather live with replacing those than other parts of the structure.

 

[dmattmul]

Certainly can’t speak for Van’s, but can’t help but notice how due to the camber of the main gear, that the higher the tire pressure, the more the tire rides on its outer edge. That, plus riding on a smaller area seems that it would accelerate tire wear. And the lighter the plane is loaded, the more pronounced it is. Might not be as bad if operating off grass, but on pavement it seems like it would cause earlier tire wear with higher inflation pressures.

I know landings are an important criterion but since I don't track these, I got 450 hrs. on my mains then changed and at 550 hrs. nose wheel has at least another 200 hrs. All pavement and my home base 3,500 ft with trees and power lines to contend with. RV-14A. Average about 45 mins per L&TO. Never a shimmy at 40 - 60 psi. Michelon tubeless tires. Did swap and flip the mains at 250 hrs. Solid tone on AOA point of contact with ground or at least goal.

 

[DanH]

I think I remember reading that it has to do with dynamics of the landing gear – softens some the impact forces transferred into the airframe. There are a couple of SB’s to strengthen the landing gear carry-through channel...

My bad...I failed to note this thread is in the RV-12 forum. I have no idea why Vans specified the low pressure. However, compared to the 6-7-8-9, the 12's lower gross weight would not mash the tire so much during a sudden arrival.

 

[BillL]

I installed TPM’s on my RV-12 several years ago, but only on the main wheels. The fork on the nose wheel does not allow clearance for TPM to be installed. I used a ¼ ounce stick-on wheel weight to offset the TPM and balance is uneffected.

That said… I run the TPM app and place cell phone on pilot-side wing walk at beginning of preflight inspection. By the time I have fisnished my walk-around the TPM has registered for both wheels. I then log the readings to plot air loss over time. By setting phone on wing walk… it is almost impossible to forget phone before climbing into cockpit. Not impossible… but close to it.

I assume they have internal batteries in the sensor? How long before they turn off communication (saving battery mode) if they are not moving? This was an issue some time ago, the plane had to roll to initiate, and in a long flight they would time out and not read for landing.
Thanks!!

 

[Iluke]

I assume they have internal batteries in the sensor? How long before they turn off communication (saving battery mode) if they are not moving? This was an issue some time ago, the plane had to roll to initiate, and in a long flight they would time out and not read for landing.
Thanks!!

I just installed a set on my RV7 and want to say thanks to the original poster for giving me the idea. I used the FOBO Bike 2 version, $99 on Amazon. Installation and set up could not have been easier. Remove the front half of the wheel pant, remove the valve stem cap, screw on the TPMS sensor, activate via the app. As a previous poster said, it seals to the top of the valve stem with a rubber gasket. Each sensor weighs 7.6 grams (1/4 OZ). I put a compensating 1/4 OZ stick-on tire weight (also Amazon) opposite the valve stem. Rolled the airplane back and forth to confirm they did not hit anything. The only possible interference might be the cotter pin, if it stuck out unusually far. Mine had plenty of clearance.
I'm a very happy customer so far. The sensors immediately read each pressure down to a tenth of a PSI and temperature too. Time will tell about battery life, but comments online suggest that it won't be a problem. It takes the common, cheap CR1632 battery and I plan to add changing them to my annual CI checklist.

Yes, you have to remove the sensors to add air. That's a downside and might be hard to do through a 1" access port. Being able to precisely check the pressure at every prefilght without having to get down on my hands and knees far outweighs having to remove the front half of the wheel pants once in a very long while to add air.
Again, thanks to the original poster for giving me the idea. I am only sorry that I didn't think of this long ago!

As to pressures, I run between 35 and 40 and it seems to work well. There seem to be lots of opinions and little authoritative guidance. My only real data point is that I've landed the airplane 314 times and the tires are still in very good condition (Thanks Foreflight!)

-Ivan

 

[Jetguy]

POH says set to 22PSI for Nose, 25 PSI for mains. So set the parameters to +- 5 psi and adjust over time. They make flow through TPMS so you don't need to remove to add air if they fit correctly.

 

[rvbuilder2002]

Regarding RV-12 recommended tire pressures….

A lot of people do not know that the tire and its internal pressure is part of the energy absorbing design of a landing gear system .
In an ideal world, the landing gear system would be capable of absorbing all of the energy from a worst case vertical drop, while reducing the vertical descent rate to zero.
Doing so keeps the load induced into the landing gear attachment structure to a minimum.
If the tire pressure is too high, more of the total energy gets transferred to the landing gear leg ( for an example think of a solid steel tire. It would have virtually zero compressibility so all of the vertical load would have to be absorbed by the landing gear leg.).
If the tire pressure is too low, it can be much more easily compressed. If during a particular load event it becomes fully compressed, it from that point acts like a solid steel wheel as in the previous example and transfers all remaining load to the landing gear leg.
This is why using the proper tire pressure on the RV 12 is important.
The lower specified pressures are not an issue for the RV 12 because the gross weight is about the same as the empty weight of all of the other two seat RV models, so the amount of tire compression and resultant tube movement is about the same as for other models.

 

[Piper J3]

Certainly can’t speak for Van’s, but can’t help but notice how due to the camber of the main gear, that the higher the tire pressure, the more the tire rides on its outer edge. That, plus riding on a smaller area seems that it would accelerate tire wear. And the lighter the plane is loaded, the more pronounced it is. Might not be as bad if operating off grass, but on pavement it seems like it would cause earlier tire wear with higher inflation pressures.

Yes, tires wear on outside edge because camber angle is excessive when gear is lightly loaded as when wheels just touch on landing. Tires can be unmounted and flipped on wheels so inside surface can be used before carcass gets tossed.

I changed to Desser Tire 500-5 6 PLY AWBS RETREAD ELITE PREMIUM 2 GROOVE (ELITE) which have a a thicker tread at the edges. Wheel pant opening needs slight trim to maintain 1/2" clearance to tire...

 

[Bob Y]

Yes, I flipped mine at 200 hrs and just replaced them last week at 400 hrs. No wheel pants, so width isn’t an issue for me. Any idea how the weight of those retreads compare with the Aero Classics that Van’s provided?

 

[Brett H]

I am looking for min/max. pressure values in order to setup the warning levels of my TPM BT sensors.
What values do you think are still acceptable before inflating is required.
My nominal value is 22psi for the nose wheel and 25psi for the mains.
Thanks a lot.
Chris
View attachment 57252

Chris:

Out of curiosity, what has been your experience using the FOBO TPMS system? How much clearance do you have between the sensor and the inside of the nose wheel fork?

Thanks.

Brett