Impossible to get 120 PSI into my tyre?

[Profpointy]

Why does ther need to be a non-return valve in the pump ? Surely the tyre valve is the non return bit?

And to the OP 120psi sounds like a perfectly sensible pressure for a narrowish back tyre albeit at the high end.

 

[si_c]

And to the OP 120psi sounds like a perfectly sensible pressure for a narrowish back tyre albeit at the high end.

When I was running 23mm tyres I ran them at 110/120 front/rear, for comparison I'm now running 28s at 90/95, so the OP is certainly not doing anything unusual.

 

[smutchin]

Why does ther need to be a non-return valve in the pump ? Surely the tyre valve is the non return bit?

I believe the design of the Jow Blow head means the tube valve is always open while it is attached.

 

[Profpointy]

I believe the design of the Jow Blow head means the tube valve is always open while it is attached.

Ah, that does make sense. With pumps I've had (I think?) the tube was open and the tyre valve did the work. The can't pump effect was when you'd forgotten to unscrew the tyre valvue or it had got stuck and needed to be manually pinged to unstuck it.

 

[mjr]

Why does ther need to be a non-return valve in the pump ? Surely the tyre valve is the non return bit?

If the hose is long (or wide), it makes it easier to build pressure, reducing the amount of each stroke that is building pressure to reopen the tyre valve. More likely on a track pump.

Or if the head design holds the valve open, it's necessary.

 

[smutchin]

Ah, that does make sense. With pumps I've had (I think?) the tube was open and the tyre valve did the work.

Presumably a valve in the pump body would also make pumping more efficient because you're not having to bring the air in the hose back up to pressure with every stroke as well. (ETA: cross-posted with @mjr)

The can't pump effect was when you'd forgotten to unscrew the tyre valvue

I've never done that. Ever. Oh no. Not me.

(May not be entirely true.)

 

[MBosh]

I'm going to take it back to Halfords and see what they think is wrong. I hope the guy in the store doesn't just stick it on and pump it to 120PSI because I'm going to feel a bit daft if he does.

To me it feels like the pump has just stopped pumping air into the tyre when I get to 100PSI. I pump down and the pump just feels bouncy, that's the only way I can describe it. When I first start pumping air in it feels fine upto 100PSI..

 

[Edgy Dee]

Simple test: pump up with yours as far as it will go, then attach a guage or someone else's pump to see what it reads.
Also can get an issue with sticky valves. I always press down the button before I attach the pump head.

 

[Tin Pot]

I'm going to take it back to Halfords and see what they think is wrong. I hope the guy in the store doesn't just stick it on and pump it to 120PSI because I'm going to feel a bit daft if he does.

To me it feels like the pump has just stopped pumping air into the tyre when I get to 100PSI. I pump down and the pump just feels bouncy, that's the only way I can describe it. When I first start pumping air in it feels fine upto 100PSI..

As someone else posted. The only time I’ve had a similar feeling - I use joe blow sport - is when you need to unclip, check the valve is open, reattach and try again.

Happens quite often.

 

[Venod]

When I was running 23mm tyres I ran them at 110/120 front/rear, for comparison I'm now running 28s at 90/95, so the OP is certainly not doing anything unusual

A few years ago I would have agreed with this statement, but since using tubeless I have been converted to lower pressures, I run 2 CX bikes and a MTB tubeless, 32mm on the CX 45 psi on one 55/55 ish on the other, very comfortable and still quick on the road I run the MTB 30 to 35 psi, could go lower, because of the comfort and no difference in speed I have been gradually been lowering the pressures on my road bike with 25mm and tubes, I have settled on 65 psi front 70 psi rear very comfortable, 40 miles today @ 17 mph average, I am running H Plus Son Archetype rims which are nice and wide that may help with lower pressure, I have read that people have used these tubeless successfully so when my Michelins have worn out I will be trying tubeless on these rims.

So if you haven't tried riding with lower pressure, why not give it a try if you can't get on with it just pump them up a bit.

 

[si_c]

So if you haven't tried riding with lower pressure, why not give it a try if you can't get on with it just pump them up a bit.

I understand what you're saying, but my experience is that I get start getting pinch flats once the rear drops below about 85. So I top up once a week so I don't have to worry about it. If I was significantly lighter, then I'd adjust my tyre pressure accordingly, but I'm not and I do stupid things like hopping off curbs.

 

[Venod]

but my experience is that I get start getting pinch flats

That's the one thing that concerned me with low pressures and tubes, but so far no problems, of course one advantage of going tubeless is pinch flats are not a problem.
I am no lightweight, about 80kg dressed for the bike.

 

[si_c]

That's the one thing that concerned me with low pressures and tubes, but so far no problems, of course one advantage of going tubeless is pinch flats are not a problem.
I am no lightweight, about 80kg dressed for the bike.

Yeah I keep toying with the idea of tubeless for that reason, but tubes just work so well! I'm around 95kg fully dressed at the moment, so a bit heavier, but I probably could run lower pressures, maybe I'm just overcautious.

 

[DRM]

Ah, that does make sense. With pumps I've had (I think?) the tube was open and the tyre valve did the work. The can't pump effect was when you'd forgotten to unscrew the tyre valvue or it had got stuck and needed to be manually pinged to unstuck it.

This press the valve pin down first before inflating, if your on 25 or 28 mm tyres it’s too much pressure and will give no grip

 

[Edgy Dee]

This press the valve pin down first before inflating, if your on 25 or 28 mm tyres it’s too much pressure and will give no grip

The valve will close again. It's just to overcome the initial stickiness. If I'm topping up the valve often won't open, even with high pressure in the pump. (But then I subscribe to the HP school of thought in this thread.) Sometimes it helps to wiggle the head (the pump's, not your own of course).