Tyre pressure and punctures.

[TissoT]

Slightly different question to the OP but on the same topic so didn't think it warranted a new thread...

I'm a newbie to road bikes, have only had mine 4 weeks, no p*******s so far so no practice with pumps and presta valves etc for me as yet, but as I'm coming up to 550 miles I thought I ought to check the tyre pressures. I did 43 miles last night no probs and the tyres feel pretty rock hard to me, but when I got home and connected up my track pump (Joe Blow) it was reading just 20psi on the front tyre! I find this hard to believe tbh - would a road tyre with 20psi feel hard still? Cos mine did - hardly any give in them at all when pressed with my thumb. I gave it 4 or 5 pumps and this took it up to around 85psi but by this point the pump was giving lots of resistance to pushing down and I was worried I might explode my tube. I connected it up to the rear tyre and same story - reading 20-30 psi initially, then soon up to 80-90 but lots of resistance from the pump at that point. Tyres were def hard before pumping and afterwards were like rock.
My tyres are 25mm Conti Grand Sports and claim a max psi of 120.
I use the bike for commuting on bad roads quite a bit so some 'give' in the tyre is not necessarily a bad thing comfort wise, but I was really surprised at what the pump was reading last night and how hard it was to get beyond 80psi. Am obv keen to avoid punctures so would appreciate advice on what pressure I need to run them at. Do I need to force more air in? Or could I have a dodgy gauge on my pump (it's only a few months old and barely been used)?
Cheers, Andy

Hi Andy
I run on 5bar on the road and track
After reading your post I think that there is a problem with your pressure gauge .. I am not a fan of "Joe blow" for this reason .

 

[youngoldbloke]

Hi Andy
I run on 5bar on the road and track
After reading your post I think that there is a problem with your pressure gauge .. I am not a fan of "Joe blow" for this reason .

Read Sittingbull's post. The JoeBlow pump is not a pressure gauge. It will not show the pressure in the tyre when you first connect it.

 

[RhythMick]

Slightly different question to the OP but on the same topic so didn't think it warranted a new thread...

I'm a newbie to road bikes, have only had mine 4 weeks, no p*******s so far so no practice with pumps and presta valves etc for me as yet, but as I'm coming up to 550 miles I thought I ought to check the tyre pressures. I did 43 miles last night no probs and the tyres feel pretty rock hard to me, but when I got home and connected up my track pump (Joe Blow) it was reading just 20psi on the front tyre! I find this hard to believe tbh - would a road tyre with 20psi feel hard still? Cos mine did - hardly any give in them at all when pressed with my thumb. I gave it 4 or 5 pumps and this took it up to around 85psi but by this point the pump was giving lots of resistance to pushing down and I was worried I might explode my tube. I connected it up to the rear tyre and same story - reading 20-30 psi initially, then soon up to 80-90 but lots of resistance from the pump at that point. Tyres were def hard before pumping and afterwards were like rock.
My tyres are 25mm Conti Grand Sports and claim a max psi of 120.
I use the bike for commuting on bad roads quite a bit so some 'give' in the tyre is not necessarily a bad thing comfort wise, but I was really surprised at what the pump was reading last night and how hard it was to get beyond 80psi. Am obv keen to avoid punctures so would appreciate advice on what pressure I need to run them at. Do I need to force more air in? Or could I have a dodgy gauge on my pump (it's only a few months old and barely been used)?
Cheers, Andy

It's important not to run tyres at too low a pressure, mostly because the air pressure keeps the tyre on the rim but also to avoid pinch flats. When you hit a pothole/kerb/rock/whatever, you need to have enough pressure in there to avoid compressing the tube enough to pinch it and cause the "snake-bite" holes.

Sheldon Brown has (as usual) a good page on this : http://sheldonbrown.com/flats.html

... and here discusses optimal pressures : http://sheldonbrown.com/tires.html#pressure

I also run 25mm tyres. I'm a smidge under 100kg so total load is around 110kg. I would guess 60% of that goes to the rear and 40% to the front so wheel load at rear is around 65kg, 45kg front. I inflate to 120psi rear, 100psi front. Linking back to the OP, I carry a Topeak Road Morph which isn't TOO big but transforms into a floor pump and I can get 120 with that (with some time and effort). I can't bring myself to use CO2 because of the material waste (perhaps I'm wrong, do they get refilled ?).

One more point - check your tyre pressures before every ride. Certainly don't leave it weeks. Depending on the tube you use, they don't hold air forever and I wasn't at all surprised to hear you were down to 20/30 after such a long time - even though SittingBull is probably right. Anyway you don't need to be down by much to increase the likelihood of pinch flats a lot, especially on rough surfaces.

 

[sittingbull]

Read Sittingbull's post. The JoeBlow pump is not a pressure gauge. It will not show the pressure in the tyre when you first connect it.

After posting I connected my Beto track pump to a tyre (presta valve) I had inflated a few hours earlier to 90 psi. The gauge didn't flinch, absolutely nothing, 2 or 3 "pumps" later and it was indicating 90 psi

 

[Nigelnaturist]

My Blackburn Air Tower, shows about 80psi after connecting, no matter how long between inflations ( I don't get punctures), this is before anything is put in the tyre, two or three pumps and its back up at 100-110psi

 

[sittingbull]

Presumably it (the Blakburn Air Tower) opens the valve on connecting, which doesn't happen with mine, it only grips the valve body

Wish I didn't get any........

 

[EasyPeez]

When you connect the pump head to the valve just a small amount of air escapes from the valve as you dislodge the valve core, enough to take the gauge to 20 psi, the pressure inside the tyre/tube is much higher than this. It's only when you add additional air from the pump that the valve seal inside the tube gradually opens/closes and the pressure in the inner tube equalises with the pressure inside the pump connecting hose. It's only at this point that you get a true reading of the tyre pressure.

Essentially the gauge is reading the pressure inside the pump connecting hose that is required to force open the inner tube valve seal, which will be the same, or fractionally greater than the pressure in the tube.

Sometimes the reverse of what you've noticed can happen. When you start pumping the gauge goes instantly to 90 plus psi. This is because the valve seal is "stuck", it will release itself at which point gauge pressure drops. It's a good idea to depress the valve core once or twice before connecting the pump to prevent this.

Thanks for explaining - I didn't realise any of that, but now I'm confident my pump gauge is fine and tyres were never as low as 20psi. Also good to know that having to force a pump down is normal and not likely to turn my tyre into a rubber bomb!

It's important not to run tyres at too low a pressure, mostly because the air pressure keeps the tyre on the rim but also to avoid pinch flats. When you hit a pothole/kerb/rock/whatever, you need to have enough pressure in there to avoid compressing the tube enough to pinch it and cause the "snake-bite" holes.

Sheldon Brown has (as usual) a good page on this : http://sheldonbrown.com/flats.html

... and here discusses optimal pressures : http://sheldonbrown.com/tires.html#pressure

I also run 25mm tyres. I'm a smidge under 100kg so total load is around 110kg. I would guess 60% of that goes to the rear and 40% to the front so wheel load at rear is around 65kg, 45kg front. I inflate to 120psi rear, 100psi front.

Again, thanks for the education. Wasn't aware of pinch flats. I'll make sure to keep a much more regular check on my pressures from now on. My total ride weight is coming in around 30kg lighter than yours so I reckon my current 90psi should be about right, based on what you're running at and those Sheldon Brown charts?

( I don't get punctures),

What a brave/foolhardy thing to claim so boldly! Long may it continue, for you and me both

 

[Nigelnaturist]

What a brave/foolhardy thing to claim so boldly! Long may it continue, for you and me both

11,000 miles on the front 5,000 on the rear, need any more prove than that. The only once I have had 11,000 miles are two pinch punctures one that hard it did a rim and the tyre. (both stones by the way), the only time I take the tyers off is to change wheels as these wear out first, well more like fall apart. The front tyre is on its third wheel, though its the rear that fails.

 

[rb58]

11,000 miles on the front 5,000 on the rear, need any more prove than that. The only once I have had 11,000 miles are two pinch punctures one that hard it did a rim and the tyre. (both stones by the way), the only time I take the tyers off is to change wheels as these wear out first, well more like fall apart. The front tyre is on its third wheel, though its the rear that fails.

Marathon+ ??

 

[Nigelnaturist]

@rb58 Gatorskins.

 

[rb58]

@rb58 Gatorskins.

I use Gatorskins too, so I can only think the roads round your way must be pretty perfect to go that long without a p***ture. Or your middle name is 'lucky'!! I check mine before every ride but still get the occasional visit.

 

[Nigelnaturist]

@rb58 no worse or better than anywhere, in fact I ride (don't have to) a short gravel, pot holed broken glass strewn track before and after any ride its about 70-80 yards, roads are mainly rural, so mud covered most of the year, areas of hedgerows and as you know these are trimmed with the accompanying debris. I think the failure of of both rear wheels RS10's and 11's give some indication have bad the roads are. Rider and bike no more than 90Kg.

 

[nickyboy]

It's important not to run tyres at too low a pressure, mostly because the air pressure keeps the tyre on the rim but also to avoid pinch flats. When you hit a pothole/kerb/rock/whatever, you need to have enough pressure in there to avoid compressing the tube enough to pinch it and cause the "snake-bite" holes.

Sheldon Brown has (as usual) a good page on this : http://sheldonbrown.com/flats.html

... and here discusses optimal pressures : http://sheldonbrown.com/tires.html#pressure

I also run 25mm tyres. I'm a smidge under 100kg so total load is around 110kg. I would guess 60% of that goes to the rear and 40% to the front so wheel load at rear is around 65kg, 45kg front. I inflate to 120psi rear, 100psi front. Linking back to the OP, I carry a Topeak Road Morph which isn't TOO big but transforms into a floor pump and I can get 120 with that (with some time and effort). I can't bring myself to use CO2 because of the material waste (perhaps I'm wrong, do they get refilled ?).

One more point - check your tyre pressures before every ride. Certainly don't leave it weeks. Depending on the tube you use, they don't hold air forever and I wasn't at all surprised to hear you were down to 20/30 after such a long time - even though SittingBull is probably right. Anyway you don't need to be down by much to increase the likelihood of pinch flats a lot, especially on rough surfaces.

Wot he said. If you're going on a reasonable distance ride you need to have the ability to get your tyres back up to something like correct pressure. Otherwise you're risking another puncture. If you're under pressure you'll go slower due to resistance and the worry of the tyre rolling off on bends.

Topeak roadmorph is an excellent pump. Easily gets up to correct pressure. It's a bit bigger than a true mini pump but I just attach it to the underside of my top tube and its fine there. The last thing I want is being faced with having to ride 30 miles home with an underinflated tyre

 

[TissoT]

Read Sittingbull's post. The JoeBlow pump is not a pressure gauge. It will not show the pressure in the tyre when you first connect it.

 

[youngoldbloke]

? What's wrong with that? It will not indicate pressure until you have started to put air into the tyre. Nothing wrong with the gauge on the pump, just how it's used. Sittingbull explained this clearly.