People often say presta valves are better for high pressure and claim it is harder to get higher pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).
Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap H*lfords track-pump.
And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many an (old) fire extinguisher which uses a schrader valve for filling; and is usually charged to *16* bar.
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
People often say presta valves are better for high pressure and claim it is harder to get higher pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).
Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap H*lfords track-pump.
And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many an (old) fire extinguisher which uses a schrader valve for filling; and is usually charged to *16* bar.
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
I'm not sure about a limit for schraders (I also remember blowing them up rock hard with garage compressors in my yoof!) but one reason they're normally not recommended for HP is because more force is required to pump by hand to overcome valve resistance. Also the better narrow road tubes just tend to come in presta versions only.
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
I used to use schraeder valves and found them no more difficult to pump 100psi into than presta valves. Presta valves hold the pressure better, though. With presta valves I don't need to top up my tyres as often as I did with schraeder valves.
Have a look at air shocks and the pumps to go with them. They use schraeder adaptors and are normally pumped upto around 200-250psi using a pump with a small piston area to achieve the high pressure. The general reason that schrader valves are hard to pump above 4 bar is because ordinary pumps aren't designed to go that high.
Have a look at air shocks and the pumps to go with them. They use schraeder adaptors and are normally pumped upto around 200-250psi using a pump with a small piston area to achieve the high pressure. The general reason that schrader valves are hard to pump above 4 bar is because ordinary pumps aren't designed to go that high.
The fact remains that schraeder's are harder to pump to the same pressure with the same pump than prestas.
People often say presta valves are better for high pressure and claim it is harder to get higher pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).
Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap H*lfords track-pump.
And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many an (old) fire extinguisher which uses a schrader valve for filling; and is usually charged to *16* bar.
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
Alex
I've used metal faced Schraders on lab equipment which held in 700psi quite successfully. However I would imagine that lover pressure ones found on cycles probably use rubber sealing faces.
Quoted message said:
-- 79.84% of all statistics are made up on the spot. The other 42% are made up later on. In Warwick - looking at flat fields and that includes the castle.
"Pete Biggs" <[email hidden]> wrote in message "]news:[email hidden]...
Quoted message said:
The fact remains that schraeder's are harder to pump to the same pressure with the same pump than prestas.
Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's spread over 16 wheels or so!
Really?
Assuming the contact patch per tyre is 15 inches wide and 15 inches long (wild guesses but I don't think they can be that far out) then 16 wheels gives a total contact patch of 3600 square inches.
44 tonnes is about 100000 lbs so contact pressure is about 30psi
I can't think of any reason why the tyre pressure should be higher than the contact pressure (stiff sidewalls allow it to be lower e.g. run flat tyres).
Regards,
Tim.
-- God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
I should imagine the latter. Trucks routinely run tyres at similar pressures to bicycles, and *they* use Schraeder. You wouldn't want to pump up a big tyre like that by hand, though. A friend was obliged to put the spare on his mother's Fiesta once, which he found to be flat. Salvation was at hand in the form of a track pump, but even getting up to 25 or 30 psi was, apparently, a considerable effort.
ttp://legslarry.crosswinds.net/ =========================================================== Editor - British Human Power Club Newsletter bhpc.org.ukbhpc.org.ukOpen ↗ ===========================================================
Being the helpful friendly guy that I am, I have assist one young mother with a roadside flat. She wasn't carrying a pump and I thought would be a good time to dust off the hardly ever used Zefal I've got clipped onto my frame. She was driving a Ford Serria and even with the thing up on the jack (her spare was flat also), it took both of us 45 minutes to get the tyre to a decent enough pressure for her to drive to Kwik Fit.
Moral of this story really goes to car drivers. Carry a pump for your car.
I'm not sure about the psi ratings, pumping rating, etc but I do know its hard work to pump up a tyre if you ain't got the right pump. Where I work we frequently get HGVs that routinly use the yard pump to top up their tyres and I know that it takes them at least 5 minutes a tyre. When you have 16 you just pray you don't need to do all of them.
"Dave Larrington" <[email hidden]> wrote in message "]news:[email hidden]...
Quoted message said:
Alex said:
Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some bad quality ones being sold on cheap inner tubes?
I should imagine the latter. Trucks routinely run tyres at similar pressures to bicycles, and *they* use Schraeder. You wouldn't want to
pump
Quoted message said:
up a big tyre like that by hand, though. A friend was obliged to put the spare on his mother's Fiesta once, which he found to be flat. Salvation was at hand in the form of a track pump, but even getting up to 25 or 30
psi
Quoted message said:
was, apparently, a considerable effort.
I had a slow puncture on my ex-car and had to park at the airport for a wekk. Took my track pump, one thing that was noticeable was the rubber pipe got really really hot. Glad I didn't melt it.
"Tim Woodall" <[email hidden]> wrote in message "]news:[email hidden]...
Quoted message said:
Assuming the contact patch per tyre is 15 inches wide and 15 inches long....
Surely a 15" *long* footprint would require a huge deformation of the tyre!
Yes, probably it would. I was getting confused between eye level on the windcheetah and eye level in a car and thinking that truck tyres were about four feet in diameter.
Also, someone has posted toyo.co.ukpressure.htmlOpen ↗ which seems to say that the tyres are about 12 inches wide so I have probably overestimated the contact patch by about 3-4 times which would tally with the 90-120psi that this page suggests.
Oh, well. The theory was good anyway ;-)
Regards,
Tim.
-- God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.
Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's spread over 16 wheels or so!
(and to pete and tim too)
Seen on the side of a tesco petrol lorry above the tyres - "150psi max".
I stand corrected. Thanks for checking. So max pressure a little higher than common racing bike tyres. Still, doesn't change the argument - which is about how easy they are to inflate using a normal bike pump.
Trucks routinely run tyres at similar pressures to bicycles, and *they* use Schraeder.
If you consider the volume of air in a truck tyre, the amount which makes the difference between 100psi and 70psi on a bike tyre (about a week's worth with a decent Schraeder tube IME) would make a difference of about 0,0000001psi [1]
[1] Yes, you're quite right, I did make that up :-)
Guy === ** WARNING ** This posting may contain traces of irony. chapmancentral.comchapmancentral.comOpen ↗ (BT ADSL and dynamic DNS permitting) NOTE: BT Openworld have now blocked port 25 (without notice), so old mail addresses may no longer work. Apologies.
