knapplc

I've been riding a 1992 Giant Iguana for the past couple of decades. A couple of years ago I put heavy-duty tubes in my tires and they held air pressure well. They were 1 1/2" tires and I kept them at about 50lbs psi.

Last month I rolled my bike and banged it up a bit, so I bought a new one: A Giant Escape 2, with Giant S-X3, 700x32 tires. These are narrower tires than my old bike. The shop says to keep them at about 70psi, and I've been trying, but every time I ride I lose about 10lbs of pressure in the back, and up to 5lbs pressure in the front.

Note - I'm a big dude: 6'2" & 310lbs.

I'm mostly riding bike paths/streets, with some grass and crushed-rock trails mixed in.

TL;DR: Big guy with new bike/narrower tires is losing air pressure every ride.

Question: Do I need to upgrade my tubes to something better suited to a heavy rider? If so, any recommendations?

dcwldct

It is normal to lose a little bit of pressure, but your values sound like a lot. Granted, I'm short and 150lbs.

There are a couple of things I'd suggest.
1)Most tires I've bought (Michelin fanboy) have a weight to pressure chart on the box. I know yours came on your bike, but you could try looking up that specific model online. It's normal to need more pressure for heavier loads. The reason for higher pressure is to maintain ideal deformation at the contact patch, not to compensate for losses.*
2)If leakage is an issue, check out swapping tubes before swapping tire (assuming you're running clinchers). That's what actually holds the air, tubes are much cheaper than tires, and it never hurts to have some spares lying around.
3)IMPORTANT: ​Many have done it, but I would NOT recommend inflating beyond sidewall pressure. You may be fine, but better safe than sorry.
4) If the tires still ride fine at that lower pressure and you aren't getting pinch flats, don't sweat it. Don't obsess too much over the number. The important thing is that the desirable characteristics of the tire are maintained for the duration of the ride.

Hope some of this helps.

*Note: Can anyone elaborate on this? Would too much deformation increase pressure loss? It seems to me that the increased heat might have the opposite effect? Any ideas?

Milton Keynes

I'm wondering if there's a tiny leak somewhere. It's normal to lose pressure over time, but I would think 10 lbs every time it's ridden is a bit much.

ypsetihw

my 700x28 tires on my road bike lose about 5psi per day at full pressure, and that's totally normal. how often do you air up? it's probably a good idea to get into the habit of checking/topping off pressure before every ride.

ypsetihw

also, at your size height/weight, you might want even more than 70psi in a 700x32, at least on the rear tire. maybe 80 or more. there are lots of threads on the subject if you search or google it.

GerryinHouston

I always lose about 10 psi in a 2 hour ride. 250 lbs myself. It is normal, it gets worse in the summer. Normally I inflate 75/85 psi (F/R). By the end of the week I am at 55/60. It happens with every bike ( of those) and a few more tubes (I moved my hybrid from 35 mm to 28 mm).

Nothing to worry about, just buy a good floor pump (I have a 110V compressor which will wheeze all the way to 120 psi

EDIT: I would consider 55 my limit riding 32s on potholed pavement, over ridges about 1" tall. At about 45 once, I felt the rim hitting a ridge, thankfully without the snakebite flat...

deapee

70 sounds about right for 32mm tires. See what the sidewall says -- if it says MAX 80 -- you could try 80 since you're a bit heavier. I wouldn't exceed the MAX, however.

That being said...if it's a new tire freshly filled with air, it's going to be about 78% nitrogen and 21% oxygen, 1% other gasses...

The oxygen will get lost quicker than the Nitrogen. So you figure if you lose 10 PSI, you might be at 80% nitrogen, 19% oxygen, and further and further down the road, you will start losing less pressure because there will be more and more Nitrogen in the tire and less oxygen.

So for the first month or so, you will notice you lose more pressure.

PS I'm not a scientist, just base this off logical thinking, evaluation, trial and error, and opinion.

knapplc

I check pressure and fill up before every ride. It's been a consistent loss of pressure for the past ten days, which was five rides of between five and seven miles each.

I'll check my side walls, but I think they say max psi is 70lbs. I found a chart online that says for a 280lb rider with gear, I should run about 80 psi. Not sure how accurate it is.

https://www.bccclub.org/documents/Tireinflation.pdf

Does anyone know about tubes that are built specially for heavier riders? I know I'm off the charts compared to most riders.

Homebrew01

Some tubes seem to lose air faster than others. I have had some that lose a bit over night, and others I can go a week with barely a drop. I have not paid attention to the brands I buy ... whatever's on sale.
Just learn the pattern of your particular tubes, and top off as needed.

ypsetihw

There are heavy duty tubes but they are just thicker butyl, and not necessarily meant for heavy riders, just less prone to puncture from small stuff. I would say 80 psi is probably a good number to shoot for on your rear, and it's just a fact of cycling life, if you ride a lot, you should just check and air up your tires daily. Once you get used to doing it, it hardly takes any time at all, and helps you spot other problems early (like slow leaks, etc.).

ypsetihw

Also, sidewall pressures are determined by lawyers, not by the laws of physics. The safety margin engineered into these things is massive, because they don't want to risk blowouts that would come back in liability to the company. In my experience you can easily exceed the max sidewall pressure by 10-15% with no negative effects. So if it says 70, you're probably fine at 75-80.

knapplc

Great! Thanks for the tips!

prathmann

There's no need for special tubes based on rider weight and almost all of the pressure loss you're seeing is happening while the bike is just sitting without you on it. Air does slowly diffuse through rubber, so with typical thin bicycle tubes there will be some noticeable pressure drop over time even without any actual hole in the tube. This is more significant with thinner tire sizes since they hold less air and with higher pressures that increase the diffusion rate.

There are thicker tubes available (frequently labelled as 'thorn-proof') that would have much less loss of air - but the downside is that they increase your rolling resistance and are also heavier.

GerryinHouston

Schwalbe Marathon Green 28s have a max 95 psi.

Read this article and use the graph to find the air pressure optimized for your weight:

https://janheine.wordpress.com/2010/...-and-pressure/

work4bike

The OP has about 100lbs on me, so I can't really speak to the weight issue and maintaining psi; although I would recommend checking the psi on non-riding days to see if there's a similar loss of pressure.

My personal experience is that some tubes lose more air in a given period of time than others, but 10 psi/per day, seems a little excessive. I'd be really curious of the loss on non-riding days.

MRT2

I inflate my 700 x 32mm tires up to 95 psi in the back, 85 to 90 in the front. Every time I ride, the pressure is down a little from the previous ride, which could be a day, or it could be 3 or 4 days. Over time, you will discover what is normal air pressure loss, and what is a leak. If you come out the next morning after riding the previous evening and find the pressure down to almost nothing, you have a leak for sure. If it is just down 10 or 20%, that is normal. Just top off the pressure before every ride.

work4bike

Why would thicker tubes increase rolling resistance?

prathmann

As your tire rolls you're continually compressing the part that's in contact with the ground. The more stiff the tire sidewall and the tube inside are, the more energy that is consumed by that and the greater the rolling resistance.

italktocats

other way around

prathmann

No, it takes more energy to compress a stiff sidewall than one that is flexible. Similarly more energy is consumed in compressing a thick inner tube than to compress a thin one.

scott967

I don't see how rider weight would factor into air loss from tubes (assuming initial pressure is kept constant). I get that the tire has to flex more to support the weight, but I don't see how whatever flexing the tube does would make a difference. Also if initial pressure is increased to compensate, that I can see would increase loss rate (until the tire gets to nominal pressure, at which point loss would be equivalent).

scott s.
.

Jaywalk3r

Are you checking the pressure immediately after your ride, or are you waiting until before your next ride to check the pressure? If it's the latter, then how frequently are you riding?

If you are losing that much pressure during just the course of your ride, then that's a problem. It would suggest a slow leak. Small pieces of gravel from the crushed rock trails (or small glass fragments from the street, or small thorns from riding in grass/weeds) could have embedded themselves into your tires, barely penetrating the tube.

VegasTriker

If you are using a standard tire gauge every time you depress the valve on a Schrader valve tube to take a reading you lose some tire pressure. The ones that are on the pump might give a better indication if the actual pressure when you fill the tire. Ditto presta valves but maybe worse. I'd go along with all of those who think that you have a problem with a bad tube or maybe it has a slow leak at the valve if you are losing that much air. If you start to get pinch flats or worse dented rims then you know the pressure recommended by the bike shop is too low for your weight. I don't bother to take a reading but check the tire by pressing on it. I doubt I have to top off tire pressure more than once every couple of weeks.

fietsbob

Doubt you want to put Heavy Duty tubes in the tire , but Thicker = slower air loss thru porosity of the rubber..
But that would be my suggestion..


thinner lighter weight tube do have a natural air weeping thru the Butyl Rubber .


My Thorn resistant tubes keep the air in them longer. Months in the 559-47 size.


accurately sized to the large side tube in a thin tire has to expand less to fill the volume ,
so will retain air longer ..

italktocats

so bowlingballs should be made of fluffly stuff?

youre missing the point: softer material is more grip & more resistance
grip = resistance