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Tire Pressure

Guilhermepilot

Well Known Member
hello captains

aero classic 11.400 says 70 psi, I found it very high, is that correct?
for mains 500.5 I could no find values, all shipped by vans
 
Captain.... we call them tires. Unlike the British, who can't spell worth a toot.
72 psi is pretty high. Try what the first poster said and see how your mileage is.
And, have a great weekend.
 
If I recall and understand the world of tires correctly, the tire pressure stamped on any given tire, is the max pressure it is rated for. The actual pressure you should use is based on several factors. The main factor (in my opinion, correct me if I am wrong), is the load the tire is expected to carry. The higher the load, the higher the pressure up to the max rating. NOW, since we do not carry a static load anywhere near the max rating of the tire, are we to consider dynamic loads (normal and hard landings)? And if so, how do we calculate the dynamic load? I think this may be where the confusion comes from. And when in doubt, do we use the max (pressure) that the tire is rated for? 70 lb would be very high compared to what we usually use, but the question remains, what are we supposed to use? If we were flying jets onto carriers, the tire pressure would be very closely monitored and kept at the higher limit would it not? Do your landings resemble a carrier landing? If the answer is "never", then use a lower pressure. Just how much lower, is the question? and does it hurt err on the side of higher pressure? Possible down side of overly pressured tires could be shimmy, ride quality (while taxiing), tire wear, lack of natural braking. But the most important of these could be shimmy.

No expert here. My opinions only.

Bevan
 
If I recall and understand the world of tires correctly, the tire pressure stamped on any given tire, is the max pressure it is rated for. The actual pressure you should use is based on several factors. The main factor (in my opinion, correct me if I am wrong), is the load the tire is expected to carry. The higher the load, the higher the pressure up to the max rating. NOW, since we do not carry a static load anywhere near the max rating of the tire, are we to consider dynamic loads (normal and hard landings)? And if so, how do we calculate the dynamic load? I think this may be where the confusion comes from. And when in doubt, do we use the max (pressure) that the tire is rated for? 70 lb would be very high compared to what we usually use, but the question remains, what are we supposed to use? If we were flying jets onto carriers, the tire pressure would be very closely monitored and kept at the higher limit would it not? Do your landings resemble a carrier landing? If the answer is "never", then use a lower pressure. Just how much lower, is the question? and does it hurt err on the side of higher pressure? Possible down side of overly pressured tires could be shimmy, ride quality (while taxiing), tire wear, lack of natural braking. But the most important of these could be shimmy.

No expert here. My opinions only.

Bevan

Instructions for my 9A (recent kit) recommend 25 psi for nosewheel tire, said to reduce likelihood of shimmy. The free-castoring nosewheel on my DA-20 trainer could shimmy like a bad shopping cart :)eek:), so we're not the only ones with the affliction.
 
I generally run 45 psi all around in my 7A

This would be a post to follow. Low tire pressures carry risks on the nose wheel that the mains do not. You should understand the limitations due to a small percentage of nose rollovers.
 
Instructions for my 9A (recent kit) recommend 25 psi for nosewheel tire, said to reduce likelihood of shimmy. The free-castoring nosewheel on my DA-20 trainer could shimmy like a bad shopping cart :)eek:), so we're not the only ones with the affliction.

Read the NTSB report in 2007 on RV A model nose gear incidents that recommends a minimum of 35 psi for the nose tire. I run 40 psi in my 9A but switched to the aviation Aero Classic nose tire. Dresser told me the Lamb was designed for 25 psi and less than 50 mph so having a 70 psi and 120 mph capable tire with a higher load capacity seems prudent. No shimmy problem with recommended tension. This tire is flatter and probably has more contact and damping area. Only about $10 more than the Lamb.
 
I have this tire - the Lamb 11x4.00x5 8 ply - on my Lancair. It is used on all 3 tires of the Lancair which touches down well over 50 mph. I have never had a problem with the tire related to speed.

I have had a problem with this tire going flat on at least 4 occasions. Every time it is when I allowed the tire to decrease air pressure to less than 30-35 psi or so. Every time there was evidence on the sidewall of the tube of chafing where it was pinched between the rim and the tire as the low pressure allowed the tire to flex and catch the tube between tire and rim.

I have had a problem with this tire developing a flat spot when allowed to sit with low tire pressure when the plane was not moved for a month or more. Even after increasing the tire pressure to 50-60 psi, the flat spot persisted for some time producing a noticeable wobble when taxiing.

I have a 9A which touches down maybe a little slower than the OP's 7A but both should be under 50 mph for ground operations so I would not be concerned whatsoever with the speed rating.

I would be concerned with allowing the tire pressure to run low. Under no circumstances will I intentionally run the nose tire under around 40 psi as an absolute minimum.
 
....since we do not carry a static load anywhere near the max rating of the tire, are we to consider dynamic loads (normal and hard landings)? And if so, how do we calculate the dynamic load?

Well, how about considering only a 1G unaccelerated flight load for the wing design? Methinks not ;)

I use a Neal Willford spreadsheet for landing gear design. The output includes tire deflection at standard limits of 3.2 and 3.4G (ballpark, 16~18 inch drop), for any tire pressure. Very educational. I set 50 psi on my RV-8.

.....does it hurt err on the side of higher pressure? Possible down side of overly pressured tires could be shimmy, ride quality (while taxiing), tire wear, lack of natural braking. But the most important of these could be shimmy.

350 hours now, and I like everything about the higher pressure. However, the -8 has slab gear legs, so shimmy isn't an issue.

Can't prove it, but I'd venture that sidewall flex due to low pressure is the number one cause of tube failures, and shortly thereafter, busted wheel pants.
 
I set 50 psi on my RV-8.

350 hours now, and I like everything about the higher pressure. However, the -8 has slab gear legs, so shimmy isn't an issue.

I used to have shimmy occasionally on my -6 and lowered the air pressure in the tires per conventional wisdom. Ultimately, I was running 22-25 PSI and still having shimmy, so I said "What the heck" and ran the pressures up into the 30's to see if I could change the dynamic. The higher pressures (my target is 35-37 psi) helped my situation a LOT. I assume that the rolling resistance at the low pressure was such that the gear would deflect aft due to the rolling resistance, then spring forward, lather, rinse, repeat, which we call shimmy.
 
I used to have shimmy occasionally on my -6 and lowered the air pressure in the tires per conventional wisdom. Ultimately, I was running 22-25 PSI and still having shimmy, so I said "What the heck" and ran the pressures up into the 30's to see if I could change the dynamic. The higher pressures (my target is 35-37 psi) helped my situation a LOT. I assume that the rolling resistance at the low pressure was such that the gear would deflect aft due to the rolling resistance, then spring forward, lather, rinse, repeat, which we call shimmy.
Interesting. To get the non-shimmy caster effect, it's probably good to have some resistance, but if it's at all grabby, then you get into the oscillation mode. It sounds like you've found the sweet spot. Just goes to show that theory and practice don't always coincide!
 
Kleet Pronisky from Michelin tire came to speak to our EAA chapter and he gave a formula for inflation. Gross weight of aircraft/ rated PSI = inflation pressure. 1800/50 = 36psi
 
more info relevant???

all good stuff here....I run about 42.388 psi on the mains, 35 up front.:rolleyes:

but have you ever noticed....say in the winter, the tire on the shady side, without wheel covers, is only 26, and the one that's been in the sun for an hour or 2, is 39.
These are tiny little rubber bags of gas, and I think we are kidding ourselves thinking that after a mile taxi, the pressures are anywhere near the same as upon landing, after a long fast descent from the temps at 10,000!:confused:

anybody actually have the little digital monitors to educate us????
 
Kleet Pronisky from Michelin tire came to speak to our EAA chapter and he gave a formula for inflation. Gross weight of aircraft/ rated PSI = inflation pressure. 1800/50 = 36psi

Did he explain why?
 
I have the Beringer tubeless nose wheel and Dresser recaps on the mains.
I adjust pressure to 50 in the nose and 36 in the mains. From experience, they loose about 5psi each in 60 days. I readjust pressures every 60 days.
 
Reviving this old thread...

There are so many different recommendations on this forum. I asked Vans, and they recommend 25 PSI on the mains and 30-35 PSI on the nose, but say to decide what works best for yourself. It's interesting that their recommendations are much lower than what most folks report using.

David Harris

---
From Vans Support 12/2/19

Those are our recommended operating pressures, but you'll end up deciding what works best for you, just like all the other guys.

-----Original Message-----
From: David Harris
Sent: Wednesday, November 27, 2019 9:41 PM
To: Support <[email protected]>
Subject: RV-7A recommended tire pressures

I?m looking for recommended tire pressures for the Vans RV-7A. I see initial pressures of 25 psi on the mains and 30-35 psi on the nosewheel in Section 10 of the build manual, but it?s unclear if these are the recommended operating pressures. Vans Airforce has extensive discussion on the topic and people seem to operate anywhere from 25 to 50 psi.

Thank you,

David Harris
 
God, that seems low to me, at least for the mains. 25 PSI? Mine look positively flat to my eye when they're that low :)

I run 38-40 PSI, no issues.
 
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