Unscrew presta valves all the way for easier pumping to 120lb with blow joe type pumps etc.

[night cycler]

I feel sure that most of you on here will already know that you can fully unscrew a presta valve and it won’t drop out. I have to say, I did not know that until I tried it during the course of repairing a tube a few days ago.

I had only ever managed to get about 95lb in the tyres which was kind of ok, but the last 10lb of this was always a real struggle using the blow Joe type pump without fully unscrewing the valve. I used to have to put most of my weight on the handle to get the pressure past 90lb.

So today, I tried the new method. I attached the blow joe and managed to put the desired 120lb in with much less effort than all the other occasions. At 120lb of pressure I feel it is a noticeably easier ride too.

 

[T4tomo]

I'm not sure I'd want 120psi in my tyres. Too many fillings that would rattle out, but each unto his own as they say.....

 

[night cycler]

I only have that pressure in the back tyre at the moment. Not sure what to do about the front, as I guess higher pressure means a bit less rubber in contact with the road.

 

[S-Express]

120psi??? Hope your dentures are fixed in well...

 

[Lilliburlero]

I ride 120 psi, no probs.

My mate rides 140

 

[si_c]

Lower pressure is faster if your tyres are wide enough to take it.

 

[S-Express]

I only have that pressure in the back tyre at the moment. Not sure what to do about the front, as I guess higher pressure means a bit less rubber in contact with the road.

Please tell me you are not running 120 on the bike in your avatar?

 

[raleighnut]

I run my Continental Grand Prix 'Supersonic' 18x622 at 160psi rear (and that is below their rated limit)

 

[S-Express]

I run my Continental Grand Prix 'Supersonic' 18x622 at 160psi rear (and that is below their rated limit)

on the boards, presumably?

 

[Ajax Bay]

Lower pressure is faster if your tyres are wide enough to take it.

Please could you explain why a lower pressure in a tyre is 'faster'? I always thought that, for a given tyre, higher pressure would result in lower rolling resistance.
You can enjoy the same – or a lower – rolling resistance with a wider tyre at a lower pressure, but the same wider tyre will be 'faster' if you pump it up.

 

[S-Express]

Please could you explain why a lower pressure in a tyre is 'faster'? I always thought that, for a given tyre, higher pressure would result in lower rolling resistance.
You can enjoy the same – or a lower – rolling resistance with a wider tyre at a lower pressure, but the same wider tyre will be 'faster' if you pump it up.

Higher pressure = lower RR only if the surface is smooth, like an indoor track, or brand new tarmac. For all other applications, a lower pressure will allow the tyre to absorb road impurities, rather than have its energy diverted upwards. Obviously there are limits either way.

 

[mjr]

I feel sure that most of you on here will already know that you can fully unscrew a presta valve and it won’t drop out. I have to say, I did not know that until I tried it during the course of repairing a tube a few days ago.

It depends! On some of them, if you unscrew the locking nut all the way and then keep on unscrewing, it'll start to undo the core. I've not seen one like that for a few years, though. I had some Continentals which used a spoke key to remove the cores and others with non-removable cores.

What do you mean by a "blow joe type pump"? A floor pump? Or are you just insulting someone called Joe by suggesting they self-gratify with a bike pump?

 

[Ajax Bay]

OK - here is a download from a rolling resistance site:
Brand Model Width (mm) Pressure: 60 PSI 80 PSI 100 PSI 120 PSI
Schwalbe Durano 25 Watts: 24.7 21 18.8 18

If 'faster' is the criterion, which is what you (@si_c and @S-Express) have described, then the higher you pump these, the less rolling resistance and the faster they are. NB diminishing returns. But this test simulated a relatively smooth road surface, I think.

Higher pressure = lower RR only if the surface is smooth, like an indoor track, or brand new tarmac. For all other applications, a lower pressure will allow the tyre to absorb road impurities, rather than have its energy diverted upwards.

So where is the sweet spot and how do you calculate it, for a given width of tyre and your average British road surface? I've been using this for some time - see attachment.

 

[S-Express]

So where is the sweet spot and how do you calculate it, for a given width of tyre and your average British road surface? I've been using this for some time - see attachment.

There is no single answer to that unfortunately. Trial and error comes to find. As everyone will be different.

 

[Ajax Bay]

Lower pressure is faster if your tyres are wide enough to take it.

"Where is the sweet spot [minimum rolling resistance on surface of specified roughness] and how do you calculate it, for a given width of tyre and your average British road surface?"

There is no single answer to that unfortunately

I'll try a different tack, then. @si_c - lower than what? How low?