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Tire pressure

What is the tire pressure for a RV7?

This will be a process of finding the optimum pressure for your particular RV-7. You will see RVers using pressure as high as 45 and as low as high-20's. Much of this depends on whether or not your RV is prone to gear shimmy during taxi. If not then the higher pressures should work fine. If shimmy is a problem, you might experiment with lower pressure which will either inhibit shimmy or move it to a speed that is less problematic. On my RV-6 I start out with 35 and air the tires back up in a few months when they are down to 28 or so. This has been my standard practice since I started flying this plane in 1999.
 
Every RV seems to have its own "sweet spot" for main wheel tire pressure, depending on several factors including gear leg stiffeners, tire size and gear alignment. I have experimented between 25-40 psi for my mains and have settled on 30 psi running 380x150 oversize tires with wooden gear leg stiffeners. I have a Flyboys Condor II pneumatic tail wheel which likes 45 psi. These pressures seem to work well for my bird, with no main or tail wheel shimmey . My mains will develop a shimmey over 35 psi, and a grooved runway seems to exaggerate the problem.
 
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If you run 25 I suggest you carry a jack and spare.
I run 45 all around on my A model.
 
I recently added some Bluetooth tire pressure monitors that I found on Amazon $54. I put two on my RV7 and gave the other two to my hangar neighbor who also has an RV7. You screw them on to the air valve.
Just did a tire and tube change and started out at 37psi. The tire monitors connect to an APP on my iPhone. It reads both temperature and pressure. I compared the reading against my regular tire pressure gauge and it seems accurate.
I did a test flight with two full stop taxi backs. When I got back to the hangar I checked the APP and it showed 40psi and a temperature increase of about five degrees C.
To add air to my tires requires me to take half of the wheel pant off to access the air valve. So far these monitors are working great.
 
If you run 25 I suggest you carry a jack and spare.
I run 45 all around on my A model.

I can attest to that. Was experimenting trying to solve a vib issue and lost a tire in landing when it slipped on the rim. The tire was still good but it went flat with a leak at the stem junction.
 
I can attest to that. Was experimenting trying to solve a vib issue and lost a tire in landing when it slipped on the rim. The tire was still good but it went flat with a leak at the stem junction.

+1. This happened to me once. Since then I keep them at 40-42 and have not had a recurrence.

Low tire pressure to fix a shimmy is a bad bandaid at best. Balance the tires and for nose wheel guys use the very nice Matco axle instead of the stock set up: http://www.matcomfg.com/AXLEASSEMBLYA24125INCH-idv-3657-1.html

Carl
 
Yeah, but did you prime your wheels?

I knew this thread would prompt all sorts of blanket statements and dire predictions, these tire pressure threads are very predictable. But maybe the original poster can see that optimum tire pressure may be dependent on his particular RV-7.
 
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I knew this thread would prompt all sorts of blanket statements and dire predictions, these tire pressure threads are very predictable. But maybe the original poster can see that optimum tire pressure may be dependent on his particular RV-7.

How exactly is it dependent on his particular aircraft?
Other than weight I can't think of anything that would make his "special" and all RV's are pretty close in weight give or take a few pounds.

Maybe we need a poll, has anyone ever had a flat that was by a puncture, or was the tube torn/worn in some way (usually on the sidewall caused by low tire pressure)?

If you suffer from wheel shimmy the right answer is not to keep lowering your tire pressure to fix it.

35psi is my lower limit, if you start at 45 it will likely be at 35 after 3-4 months (depends on what brand tube you use to some degree).
 
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Walt, you have strongly stated your opinion about tire pressure in several threads over the years.

Please be advised that not everyone agrees with your opinion. :)
 
Walt, you have strongly stated your opinion about tire pressure in several threads over the years.

Please be advised that not everyone agrees with your opinion. :)

You're right, just offering my opinion/advice when folks ask and in the interest of safety.
Do you think perhaps the folks are asking because they have not seen the past threads on the subject?

As a guy who works on lots of RV's as well as other stuff I've probably seen more problems than the average RV owner so take it for what it's worth.

And I do realize that most RV6's seem more prone to shimmy than the later models and most need gear leg stiffeners, but what works on your 6 may not be best practice for the 7/8/10/14 owner.

My first experience with tube failure was as a kid riding a HD Panhead chopper I built, but not knowing much at 18 I took the advice of a "more experienced" guy who told me to run 15lbs in the rear tire for better traction, well that advice almost killed me when I had an instant flat from tube failure on the highway with my girlfriend on the back. Live and learn....

So I guess if you don't like my advice, you may certainly disregard it, and I understand why, but I'm gonna keep posting as long as people ask.
 
My opinion

Walt, I agree with your tire pressure recommendation BECAUSE we had a series of 4 flats on our RV7a after running mains at 35 pounds. That was what we always used in our Cessna and so did the same in our RV7a. That worked for several years then something changed and over a 2 year period we had 4 flats. Small holes in the sidewall of the tube, no nails or punctures. So we increased the tire pressure to 45 and have not had a flat since! Probably been 5 years now. So my experience supports a higher tire pressure. Just my opinion based on my experience.
 
High tire pressure will wear out the tires in the middle. Around 25 psi will get you more even tire wear with no risk of spinning tires on rims and damaging valve stems. I am brutal on tires. I use the same tubes through several tire changes. Never had a flat. I can go through a set of tire in 100 hours but probably 1,000 full stop take-offs and landings.
 
I recently added some Bluetooth tire pressure monitors that I found on Amazon $54. I put two on my RV7 and gave the other two to my hangar neighbor who also has an RV7. You screw them on to the air valve.
Just did a tire and tube change and started out at 37psi. The tire monitors connect to an APP on my iPhone. It reads both temperature and pressure. I compared the reading against my regular tire pressure gauge and it seems accurate.
I did a test flight with two full stop taxi backs. When I got back to the hangar I checked the APP and it showed 40psi and a temperature increase of about five degrees C.
To add air to my tires requires me to take half of the wheel pant off to access the air valve. So far these monitors are working great.

Which Bluetooth system did you buy. I would be interested in trying that. Thanks.
 
I recently added some Bluetooth tire pressure monitors that I found on Amazon $54. I put two on my RV7 and gave the other two to my hangar neighbor who also has an RV7. You screw them on to the air valve.
Just did a tire and tube change and started out at 37psi. The tire monitors connect to an APP on my iPhone. It reads both temperature and pressure. I compared the reading against my regular tire pressure gauge and it seems accurate.
I did a test flight with two full stop taxi backs. When I got back to the hangar I checked the APP and it showed 40psi and a temperature increase of about five degrees C.
To add air to my tires requires me to take half of the wheel pant off to access the air valve. So far these monitors are working great.

Do you have more info on these BT sensors? I'd like to try something like that instead of relying on eyeballs for most flights and removing the front of the wheel pants to check pressures every couple of months. Yes, I know, it's not that hard, but color me lazy :)

TIA!
 
The brand is " Invtek" they are on Amazon right now for $44. That's a set of four. So far they have worked great. I check them every time I'm at the hangar and compare the temperature to a thermometer I have on the wall. I had no clearance issues with the tire pressure cap and the large axle nut. Very simple to download the APP and set up on your cell phone.


Pat
N931CB
RV7
KHAF
 
could lower tire pressure decrease the tendency to bounce on touchdown? especially taildraggers....
 
Kay, I guess it will help some, to a lesser degree. Proper flying technique helps tremendously :D

I am running a tire P of 25-30 on my -6.9 with -7 gear and stiffeners... and just suffered 2 sidewall punctures in the last 2 weeks, one on each side :(
Guess I’ll try to increase that pressure somewhat, but have memories of regular after landing only shimmy occurrences.
 
Opinions vary, so let's move to fact.

Landing gears are generally designed for a 500 FPM arrival, which depending on leg design and other factors, is generally a bit over 3 G's. We want all the undercarriage components to meet this standard.

3-4-6-7-8-9's mount a 5.00-5 6-ply. Inflated diameter at 50 psi is about 14". The bead diameter beyond which the tire cannot possibly be compressed is 6.5", thus the max tire deflection available is 3.75", less the thickness of the tread carcass and the bead structure.

Given the above max arrival, the tire deflection at 36 psi is about 3.6". The tread carcass is smashed hard against the bead structure, with the sidewall in the immediate vicinity bent 180 degrees. Picture the effect on the tube.

For comparison, tire deflection at 50 psi is 2.75".

The above landing load spreads out the tire contact patch a lot. Consider what happens when the contact point is a square-edged pavement transition.

So (switching to opinion), given a pilot who produces consistently good landings, and a smoothly paved airport with no pavement height transitions, yep, low pressures will work. However, it won't take much to exceed the limits of tire deflection when using low pressures, and may not take more than one instance to result in a pinched tube.

Me? I set 50, and add at 45, but I have slab legs with no shimmy issue. One of many RV-8 advantages over lesser models ;)
 
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Pressure

I have tried 30-35-40-45-50 on my 1100 lb (dry wt) RV9a. My best compromise for wear, landing characteristics, rolling resistance, etc is 45 lbs-I add if below 40.
Cheers
db
 
High tire pressure will wear out the tires in the middle. Around 25 psi will get you more even tire wear with no risk of spinning tires on rims and damaging valve stems. I am brutal on tires. I use the same tubes through several tire changes. Never had a flat. I can go through a set of tire in 100 hours but probably 1,000 full stop take-offs and landings.

25 is quite low in my opinion. Glad that you have been lucky, but I feel that luck is more in play here. That leaves little margin and as many know, our tires tend to lose a good amount of pressure over time. If they drift down to 20, I feel that your risk goes WAY up for tube failure. There is PLENTY of engineering data out there for how much PSI is required based upon type, size and weight carrying. auto manufacturers routinely play with tire pressure to adjust handling, but ALWAYS above a minimum recommendation from the tire engineers. Suggest that folks find that data instead of following recommendations with a sample size of 1.

I run my 6A and 10 at 45 psi, with 50 on the 6A main. I agree with Walt that low tire pressure is the wrong way to address shimmy issues. IMHO, shimmy is far less of an issue than a blown tire on landing.

Larry
 
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I don't have a shimmy problem. I do have a tire wear problem even with flipping the tire over halfway through.
 
High tire pressure will wear out the tires in the middle. Around 25 psi will get you more even tire wear with no risk of spinning tires on rims and damaging valve stems. I am brutal on tires. I use the same tubes through several tire changes. Never had a flat. I can go through a set of tire in 100 hours but probably 1,000 full stop take-offs and landings.

That's a LDG/TO every 6 minutes, do you ever leave the pattern?
You obviously believe in being very frugal, std. practice is to install new tubes with new tires.
You've been pretty lucky IMO, maybe you should buy a lottery ticket.

I don't have a shimmy problem. I do have a tire wear problem even with flipping the tire over halfway through.

Maybe a higher quality tire would help, of course if you're trying to use every available ounce of rubber before changing tires that could be a problem as most RV's don't wear tires evenly.
 
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Opinions vary, so let's move to fact.

Landing gears are generally designed for a 500 FPM arrival, which depending on leg design and other factors, is generally a bit over 3 G's. We want all the undercarriage components to meet this standard.

3-4-6-7-8-9's mount a 5.00-5 6-ply. Inflated diameter at 50 psi is about 14". The bead diameter beyond which the tire cannot possibly be compressed is 6.5", thus the max tire deflection available is 3.75", less the thickness of the tread carcass and the bead structure.

Given the above max arrival, the tire deflection at 36 psi is about 3.6". The tread carcass is smashed hard against the bead structure, with the sidewall in the immediate vicinity bent 180 degrees. Picture the effect on the tube.

For comparison, tire deflection at 50 psi is 2.75".

The above landing load spreads out the tire contact patch a lot. Consider what happens when the contact point is a square-edged pavement transition.

So (switching to opinion), given a pilot who produces consistently good landings, and a smoothly paved airport with no pavement height transitions, yep, low pressures will work. However, it won't take much to exceed the limits of tire deflection when using low pressures, and may not take more than one instance to result in a pinched tube.

Me? I set 50, and add at 45, but I have slab legs with no shimmy issue. One of many RV-8 advantages over lesser models ;)

We can always count on Dan for the science, which just happens to coincide with real world experience in this case!
 
Walt, with all due respect, not gonna call that science:
One of many RV-8 advantages over lesser models ;)

Hopefully meant as "lesser" in the value of used numbers ;)
 
I guess RVers who aren't running at least 45 in their tires just aren't living in the real world..... ;)

Yep, the RV-8 is fortunate not to have shimmy issues due to the slab gear...I won't disagree with Dan about the superb qualities of the -8. :)

I also suspect the -14 and the nosegear RVs have little problems with shimmy as well. But for some of us unfortunate slobs adjusting tire pressure is one means for fine-tuning the gear on our RVs. The original poster has a RV-7 so maybe there has been info in this thread that will be useful for him.
 
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37 . . . .

. . . . is what I run in my -7. I can still get some shimmy occasionally, but it's not bad. Much higher psi and it can rattle your teeth. YMMV.
My goal was to find the highest pressure that would still yield acceptable shimmy results. 37 seems to be it. Had the result been much lower than that, I would probably investigate the wooden leg dampers, etc.
 
I guess RVers who aren't running at least 45 in their tires just aren't living in the real world..... ;)

Sam, you are the good pilot based at the very fine airport. That's mighty real in my book.

Then there's the big dummies like me, trying be a hero and do a STOL arrival on this displaced threshold, steeper than normal to miss what I think was a bank building (remarkably close to the runway by Alabama standards), all at about 50 over gross, because we were going to a family wedding, and Ms. Patti doesn't travel light even under normal circumstances...

Get a little slow and it just doesn't flare like a fella might expect ;)
.
 

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That's a LDG/TO every 6 minutes, do you ever leave the pattern?
You obviously believe in being very frugal, std. practice is to install new tubes with new tires.
You've been pretty lucky IMO, maybe you should buy a lottery ticket.



Maybe a higher quality tire would help, of course if you're trying to use every available ounce of rubber before changing tires that could be a problem as most RV's don't wear tires evenly.

I can actually do a stop and go every 5 minutes. I am frugal, don't know about very frugal. I have been using the Monster retreads. I've even been known to patch tubes. I've been given a couple of lottery tickets over the years but have never bought one.
 
35psi is my lower limit, if you start at 45 it will likely be at 35 after 3-4 months (depends on what brand tube you use to some degree).

Just a data point, but I did find DanH and Walt's advice helpful, it has not changed in years.

Not that "I" need to reinforce Walts comment, but I will. I use 45-47 on my 7 and it will hold a little longer that 3-4 months before reaching 35 (Air-Stop). The next set may not.

No one asked but -my tires don't wear in the middle, but on one side. Turning them around seems like more trouble that it's worth. (I am lazy)
 
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