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Tire pressure loss due to heavy rider?

Old 08-21-20, 12:32 PM
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teeebone
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Tire pressure loss due to heavy rider?

Newbie here. I weigh around 235 pounds and ride a Trek Dual Sport 3 with Bontrager GR2 700C X 40MM tubeless tires. If I set my pressure at 50 psi after every ride (average ride is between 20 and 30 miles) it will go down to 40 psi. It doesn't matter if I am riding gravel or road - the exact thing happens (I usually set it lower for gravel but the times I did try 50 it went down to 40). When I asked the guy at the bike shop he told me I should not be at 50 and I should be at 40 and because of my weight it will lose air. Is this normal?
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Old 08-21-20, 12:38 PM
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Originally Posted by teeebone
Newbie here. I weigh around 235 pounds and ride a Trek Dual Sport 3 with Bontrager GR2 700C X 40MM tubeless tires. If I set my pressure at 50 psi after every ride (average ride is between 20 and 30 miles) it will go down to 40 psi. It doesn't matter if I am riding gravel or road - the exact thing happens (I usually set it lower for gravel but the times I did try 50 it went down to 40). When I asked the guy at the bike shop he told me I should not be at 50 and I should be at 40 and because of my weight it will lose air. Is this normal?
Unless you want to spend untold hours sealing and resealing, I would put light weight butyl tubes in and enjoy your life and bicycle. Many people in your shoes take this route, happily I might add.

I think your bike guy is blowing smoke up you no where.
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Old 08-21-20, 12:41 PM
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Originally Posted by teeebone
Newbie here. I weigh around 235 pounds and ride a Trek Dual Sport 3 with Bontrager GR2 700C X 40MM tubeless tires. If I set my pressure at 50 psi after every ride (average ride is between 20 and 30 miles) it will go down to 40 psi. It doesn't matter if I am riding gravel or road - the exact thing happens (I usually set it lower for gravel but the times I did try 50 it went down to 40). When I asked the guy at the bike shop he told me I should not be at 50 and I should be at 40 and because of my weight it will lose air. Is this normal?
Does it go down after each ride or overnight? If it is overnight, that’s perhaps a bit much but not outside of the expected pressure loss due to diffusion. Tires lose some pressure over time because the rubber is only mostly sealed. Nothing about your weight should have an impact that would cause a change in tire pressure.

40 PSI is rather low for your weight. It’s probably fine for the front but for the rear, you really should be running around 60 to 70 PSI. Any lower and you risk bottoming out on bumps and damaging the rim.
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Old 08-21-20, 12:47 PM
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Pressures seeking equalization over time, will always be with you NB Tubeless is not air tight ..

I have a few wheels with the thick wall heavy duty thorn resistant inner-tubes OTOH, they hold air for a long time..
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Old 08-21-20, 12:47 PM
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Originally Posted by cyccommute
Does it go down after each ride or overnight? If it is overnight, that’s perhaps a bit much but not outside of the expected pressure loss due to diffusion. Tires lose some pressure over time because the rubber is only mostly sealed. Nothing about your weight should have an impact that would cause a change in tire pressure.

40 PSI is rather low for your weight. It’s probably fine for the front but for the rear, you really should be running around 60 to 70 PSI. Any lower and you risk bottoming out on bumps and damaging the rim.
I have to check that out. I ride just about every day so I just assumed it lost the pressure right after the ride (I don't check it until before the next day's ride). The tires say max 50 PSI so I figured for my weight to start there and see how it feels....but it always goes down to 40.
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Old 08-21-20, 12:50 PM
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Originally Posted by Mulberry20
Unless you want to spend untold hours sealing and resealing, I would put light weight butyl tubes in and enjoy your life and bicycle. Many people in your shoes take this route, happily I might add.

I think your bike guy is blowing smoke up you no where.
Down the line I will consider that but since I paid for the conversion labor (and the tubeless tires) when I purchased the bike last month I want to give these a chance for a while.
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Old 08-21-20, 12:56 PM
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Proper tubeless rims, like those on cars, only hole is for the valve stem.
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Old 08-21-20, 12:59 PM
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As mentioned above, change over to tubes and use tires with higher pressure ratings; I'm not sure if there are any 700x40 with higher pressure ratings. I'm only slightly lighter than you and I run 700x35s tires with tubes at 80 psi. I loose about 5-10 psi per week (which I consider normal). Plenty of good 35s tires on the market that'll handle gravel and graded dirt.
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Old 08-21-20, 01:12 PM
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OP: I believe that when a shop sets up tubeless tires, they don't necessarily have time to do all of the things that help create a good tight seal. I suggest that you read up a bit on the 'net and do these things yourself at home. It's not a big deal, and it will optimize your setup. Try steps 9-14 at this page.

PS: Make sure the sealant level is adequate. On initial install, some of it seals up the sidewalls and other gaps, so you may need to add a bit.

Last edited by Koyote; 08-21-20 at 01:50 PM.
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Old 08-21-20, 01:40 PM
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Why not check immediately after a ride? How much is lost overnight is less of a concern. You probably should not exceed the max pressure on the sidewall, especially with tubeless. Remember, you'll often lose a few psi while removing and attaching the pump.
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Old 08-21-20, 02:21 PM
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Keep in mind you loose air and pressure when you pop the pressure gage on and off.


I'm a 270# Clydesdale and have no pressure loss issues once my 40mm tubeless tires have been properly sealed. In fact, they do better than my old road bike with skinny tires and tubes.
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Old 08-21-20, 03:45 PM
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Originally Posted by shelbyfv
Why not check immediately after a ride? How much is lost overnight is less of a concern. You probably should not exceed the max pressure on the sidewall, especially with tubeless. Remember, you'll often lose a few psi while removing and attaching the pump.
Just did a quick 15 mile ride on a paved trail. Started both at 50 and checked the pressure after the ride. Front was 46 rear was 48.
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Old 08-21-20, 04:00 PM
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Now pump them back up to 50 and check again after an hour or however long you were on your ride. That will tell you if the loss has anything to do with riding.
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Old 08-21-20, 05:24 PM
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How are you checking pressures? It's almost impossible for me to check pressures without the process causing the tire to leak down some.
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Old 08-21-20, 08:57 PM
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Low pressure also increases the risk of pinch flats. That's the tube getting squeezed between the rim and edge of a pothole or other abrupt edge.
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Old 08-22-20, 09:20 AM
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Originally Posted by Homebrew01
Low pressure also increases the risk of pinch flats. That's the tube getting squeezed between the rim and edge of a pothole or other abrupt edge.
teeebone has tubeless tires but many people don’t understand that tubeless doesn’t prevent the rim from bottoming out. Pinch flats are a symptom of a problem. The problem is still there with tubeless but there aren’t any symptoms. Bottoming out a rim can result in damage to the rim. Personally, I’d rather deal with fixing 25¢ pinch flat vs a $100 bent rim.
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Old 08-22-20, 01:20 PM
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Originally Posted by fietsbob
Proper tubeless rims, like those on cars, only hole is for the valve stem.
Originally Posted by HD3andMe
This is demonstrably false.
Each of my tubeless rims has 32 holes in addition to the one for the valve stem.
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Old 08-22-20, 02:13 PM
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Originally Posted by Koyote
Each of my tubeless rims has 32 holes in addition to the one for the valve stem.
33 potential leak points s + the 2 tire beads then .. Any how, it's not my problem I don't follow all the latest trends..
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Old 08-22-20, 02:28 PM
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Originally Posted by Koyote
Each of my tubeless rims has 32 holes in addition to the one for the valve stem.
Originally Posted by fietsbob
33 potential leak points s + the 2 tire beads then .. Any how, it's not my problem I don't follow all the latest trends..
You don’t need to follow trends to know that rims have spoke holes.

by the way, I only top off the air pressure in my tubeless tires every several days, about like my tubed tires.
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Old 08-22-20, 02:35 PM
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I put tubes in my tires , On my last loaded tour soloing I topped off the PSI every couple days,
because I ran thorn resistant tubes & I could feel a bit more rolling resistance with a bit less pressure

10 month tour, no punctures..
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Old 08-22-20, 04:41 PM
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Originally Posted by teeebone
When I asked the guy at the bike shop he told me I should not be at 50 and I should be at 40 and because of my weight it will lose air. Is this normal?
So, this is bad advice. It's kind of strange that people think about this backwards. Same for trucks and trailers when carrying a heavy load.
Some people actually think they're supposed to lower their tire pressure when hauling more weight, maybe they think the weight adds pressure or something.

Add *more* air pressure to compensate for more weight.. something has to push back when more weight is coming down to keep the tires in the right shape to perform.
Just don't exceed the max and you're good.
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Old 08-22-20, 08:35 PM
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OP, I wouldn't run tubes, especially on gravel. But as others have mentioned, it sounds like they didn't do a very good job taping the rims, or maybe didn't put enough sealant in. I've retaped two wheels that a shop did, and they're holding air better now, altho tubeless tires will always lose air, just the nature of the beast. But tubeless on gravel is def the way to go.

Last edited by LAJ; 08-26-20 at 07:34 PM. Reason: Clean Up
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Old 08-23-20, 06:51 AM
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Originally Posted by fietsbob
I put tubes in my tires , On my last loaded tour soloing I topped off the PSI every couple days,
because I ran thorn resistant tubes & I could feel a bit more rolling resistance with a bit less pressure

10 month tour, no punctures..
You probably would've gotten no punctures (at least none that didn't immediately seal up), and a smoother ride, with a tubeless setup. But you're free to do what you wish.
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Old 08-23-20, 09:46 AM
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load it up with tire sealant?

.. ride was plenty smooth with 40 poinds of camping gear and 3 season clothing. in my 4 panniers..
& atop the rear rack..
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Old 08-24-20, 05:45 PM
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Originally Posted by Moe Zhoost
How are you checking pressures? It's almost impossible for me to check pressures without the process causing the tire to leak down some.
Just by attaching the floor pump (Bontrager dual charger pump). Interestingly enough my wife has the exact same tubeless tire (bough the bikes and had them converted the same time) and she is not heavy and all our tires after inflated to 50 go down a little right after the ride but within 24 hours go down to 40. They seem to hold at 40 but won't hold at 50 (even without riding). Guess fat me isn't causing this but could a bad seal be stopping it from staying at 50 but holding steady at 40?
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