I can't get it hard, do I just pump more?

[Pale Rider]

The diameter of a hand pump relates to the pressure it will pump.

A narrow diameter pump will give a higher pressure, so it suitable for narrow roadie tyres.

A fatter pump will give a lower pressure, but will shift volume so is suitable for wider hybrid/MTB tyres.

 

[Cyclist33]

W

The diameter of a hand pump relates to the pressure it will pump.

A narrow diameter pump will give a higher pressure, so it suitable for narrow roadie tyres.

A fatter pump will give a lower pressure, but will shift volume so is suitable for wider hybrid/MTB tyres.

Where did you read that?

 

[ayceejay]

I think the trick is to get someone else to do it.

 

[Markymark]

W

Where did you read that?

In any physics book.
Pressure= force/area

Increase pressure by either increasing force(track pump) or decreasing area.

 

[Slioch]

If you're running high pressure tyres at say 120psi then I would suggest investing in a good quality track pump for the garage which will get you to that pressure easily (mines a Topeak Joe Blow).

You then need a reasonably good quality hand pump to carry with you on the bike or in the back pocket (mines a Topeak Pocket Rocket). Realistically, that ain't going to get you back up to 120psi, but should get you to around 80-90psi without having a coronary, and that amount of pressure will be enough to get you home ok,

Alternatively, you could carry a CO2 canister. Again, depending on make etc that should get you up to around 90-100psi comfortably, which again will be enough to get you home ok.

 

[Cyclist33]

In any physics book.
Pressure= force/area

Increase pressure by either increasing force(track pump) or decreasing area.

Isn't the area in question the diameter of the receiving valve though?

 

[GuyBoden]

I'm a bit out of touch with current bike stuff, but can you still inflate it at a garage with a Presta to Schrader valve converter.

These:

 

[Markymark]

Isn't the area in question the diameter of the receiving valve though?

That's tge pressure going in but the pressure the user can generate is the pump.

 

[Pale Rider]

Isn't the area in question the diameter of the receiving valve though?

No, it's the same in all cases so cancels itself out.

The difference is in the swept volume of the chamber of the pump.

Thus with two pumps of the same length, the narrow diameter one will pump a higher pressure into a roadie tyre for the same effort/number of repeats.

But the narrow pump won't push volume, so is all but useless for a MTB tyre.

Quality of components, seals and the like will come into it, but the general point is true.

Thus something like a Blackburn Airstick is very narrow because it's designed to put 110psi into a roadie tyre.

A hybrid/MTB rider will want a fatter and often longer pump to achieve 40-60psi in higher volume tyres.

 

[Cyclist33]

Okay, but forgive my rather poor grasp of physics, but surely the point of entry is the key place where air inputted has an effect on a tyre's inflation, and if p = f / a, and a is constant for a given valve type, then p can only be increased by increasing f?

You said that a fatter pump would give lower pressure but shift a larger volume, but surely that volume is throttled by the valve area so that the equation above is the same as it would be for a skinny pump? As there is no v for volume in the equation, nor a velocity variable for the shifting of it.

 

[CopperCyclist]

I have a cheap hand pump with a gauge that goes up to 120. By a significant and concerted effort, I can get a tyre to 70 psi with it. It causes me to break a hell of a lot more sweat than actually riding the bike!


I have an expensive track pump that brings tyres to 120 psi without any true effort. I've never taken it above that, but the gauge does go much higher.

 

[Pale Rider]

Okay, but forgive my rather poor grasp of physics, but surely the point of entry is the key place where air inputted has an effect on a tyre's inflation, and if p = f / a, and a is constant for a given valve type, then p can only be increased by increasing f?

You said that a fatter pump would give lower pressure but shift a larger volume, but surely that volume is throttled by the valve area so that the equation above is the same as it would be for a skinny pump? As there is no v for volume in the equation, nor a velocity variable for the shifting of it.

The proof of the pudding is in the eating.

I have a stubby Lezyne hand pump and a Blackburn Airstick of the same length.

They perform as I have outlined, the Lezyne will not put much more than about 60 or 70 psi in a road tyre, but the Airstick will.

But try to pump an MTB tyre with the Airtstick, you will be there for ages, and you won't get 50psi.

Still don't believe me?

Take a look at the size of the air chambers on pumps designed for front forks/MTB shocks.

Again, very narrow because 100+ psi is required.

As with any product, the design of a hand pump is a compromise.

High volume/low pressure against low volume/high pressure, with most designs falling somewhere in between.

Even a track pump with it's wider diameter and longer chamber is more geared towards pressure.

It takes a fair time using one to inflate a 29er MTB tyre from flat.

 

[Milkfloat]

I have a hand pump that has a switch to choose between high volume and high pressure. It does not change the chamber size, but I have no idea what it does do It really does work though, but certainly won't hit 100 psi

 

[mjr]

I'm a bit out of touch with current bike stuff, but can you still inflate it at a garage with a Presta to Schrader valve converter.

Garages are being stingier with pumps. In my limited experience, many charge (Shell and Jet more often?) and some won't go over 70psi (and make heck of a racket above 50...).

 

[I like Skol]

THIS is the pump you need and the one I have for my road bike. It is cheap, light, small, powerful, reliable and comes with a clip to mount it next to a bottle cage. It easily gets my road bike tyres up to 110-120psi (checked with the track pump when back home) and is rated to 160psi. I have had it about 4 years now and it still works perfectly.

I have a large purple one from the late 90's that I carry around for the MTB and hybrid tyres but it is looking a bit battered and sorry for itself these days as it has seen a lot of action