Tyre Top Up?

[mick1836]

I have both Schwalbe tyres fitted to my Cube road bike and MTB and tend to ride each day alternatively, both bikes are kept in a plastic shed which in the Spanish sun can get over 90f inside.
I am wondering if this heat causes the tyres to slightly deflate?
I check the tyre pressures ( 100psi for road & 75psi MTB) and find I have to top each up a few pounds before each ride?
How often do you check and have to top up your tyre pressures?

 

[Jody]

I check my tyres every few months and they don't usually need much air if any. Maybe 1or 2 psi a month.

How come you are running the MTB at 75psi. Do you only run canal paths or flat ground?

 

[Yellow Saddle]

It is an interesting question. Tyres (tubes actually) leak because of some porosity in the butyl rubber they'e made of. That's normal and all tubes lose pressure over time. The thicker the tube, the less the loss and vice versa. Rate of flow (leaks) through holes increase with pressure and we're assuming your shed increases the pressure inside the tyres by cooking them. Therefore it would seem logical that the higher the pressure inside the tyres, the more they will leak.
However, we don't know how butyl's porosity behaves when the temperature increases. Does it become more, or less porous? I don't know.
Only a series of repeated experiments with careful measurements can answer the question for sure. You'll have to alternatively heat and cool the shed for various measurements as well.
What is certain, is that you will keep having to pump your tyres before every ride if you are that fussy about the exact pressure. I've adopted a regime of pumping it perhaps slightly too hard and then keep on riding until it is too soft. I can' be bothered with exact numbers.

 

[mjr]

The 60/80psi road bike gets checked before most rides. It loses 10psi in a week, easily.

The car-valved roadster and hybrids (various 30-65psi) also get checked about weekly or when next ridden and have usually lost some but not as much.

The 40/60psi Woods valved Dutch bike gets checked fortnightly and because I have to pump slightly to get a reading on a Woods, I usually have to deflate them slightly during the check because they lose almost nothing!

 

[mick1836]

I check my tyres every few months and they don't usually need much air if any. Maybe 1or 2 psi a month.

How come you are running the MTB at 75psi. Do you only run canal paths or flat ground?

Hi Jody, the Cube is a AMS 130 Pro full suspension bike and although I will ride it on roads in the area we are there are a lot of gravel 'off road' paths that I enjoy using, actually think I inflate to 70 psi not 75 psi

 

[Yellow Saddle]

The 60/80psi road bike gets checked before most rides. It loses 10psi in a week, easily.

The car-valved roadster and hybrids (various 30-65psi) also get checked about weekly or when next ridden and have usually lost some but not as much.

The 40/60psi Woods valved Dutch bike gets checked fortnightly and because I have to pump slightly to get a reading on a Woods, I usually have to deflate them slightly during the check because they lose almost nothing!

I don't think the valve type has bearing on air loss in tube.I would imagine (but not sure) that a tube with a Woods valve will be thicker than other tubes with say Presta valves, because of the market it is aimed at.

 

[gbb]

Check tyres with the thumb test only,road or hybrid. If they're hard, that's good enough for me...if they feel slightly less so...inflate. it's not an exact science for me.
Few of my bikes ever needed regular top ups...maybe once a month at worst.

 

[Spiderweb]

70-75 psi seem a lot of pressure for a mountain bike, I run mine at 40 psi and have friends that run 35 psi.

 

[mjr]

I don't think the valve type has bearing on air loss in tube.I would imagine (but not sure) that a tube with a Woods valve will be thicker than other tubes with say Presta valves, because of the market it is aimed at.

I think you're probably correct about Woods v Presta tubes, but the Schrader tubes are pretty similar to Woods (some the same brand) yet are lossier. I feel Schrader is just a worse design, with air going in and out by the same route and no way to screw the exit shut like the other two have.

 

[Yellow Saddle]

I think you're probably correct about Woods v Presta tubes, but the Schrader tubes are pretty similar to Woods (some the same brand) yet are lossier. I feel Schrader is just a worse design, with air going in and out by the same route and no way to screw the exit shut like the other two have.

Schrader seems to work for millions of cars and trucks.

 

[mjr]

Schrader seems to work for millions of cars and trucks.

I think that's confusing popularity with being the best, plus maybe wider tubeless tyres on vehicles with suspension are less prone to bouncing open valves.

 

[mick1836]

If I could fit schrader valves to my bikes I would but believe on BOTH it would involve enlarging the valve hole so may compromise the wheel rim. But I stick with the presta type which are the only type to have caused me problems when the lock nut / bolt has broken off

 

[Yellow Saddle]

I think that's confusing popularity with being the best, plus maybe wider tubeless tyres on vehicles with suspension are less prone to bouncing open valves.

A bicycle's vibration cannot generate enough inertia in those light parts to make the valves bounce open. You seem to think that leakage comes from the valve itself.

 

[mick1836]

A bicycle's vibration cannot generate enough inertia in those light parts to make the valves bounce open. You seem to think that leakage comes from the valve itself.

No, my choice to change from presta to schraeder is purely down to 'in my opinion' the better design and ease of use of the schraeder, the 'leakage' over a few days is so small must be similar to how your balloons go down over xmas

 

[cyberknight]

I check my tyres every few months and they don't usually need much air if any. Maybe 1or 2 psi a month.

How come you are running the MTB at 75psi. Do you only run canal paths or flat ground?

depends on the tyre as well, i use slicks on mine and i run at similar pressures , road bike runs at95-100 psi .