Tyre pressures

oh gosh just ran outside and checked  - the red line is at 80

they've always seemed pretty hard at that level and the last few pushes on the track pump are always hard work?? I normally go to just over the 80 to allow for air escaping when I take it off.

very confused now

80 bar? 

I pressume we are talking road tyres Pix, not Moutain bike...  80 is a bit squishy. 

yeah road - I've just used the 80 red line! I assumes psi

what should I look at?

I do my hybrid tyres at the same level -  I am officially a bike numpty, my biggest tri fear is a puncture as that would basically be game over for me!

don't go to 80 bar - I was pulling your leg - sorry about that!  It will be PSI.  You are more likely to puncture at lower pressures and you will also be working harder too as some of your energy is being absorbed by the squishyness of the tyre..  Hybrid tyres do run at lower pressures, and MTB tyres lower still.  But road tyres need the air in them to work properly.  If you look on the side of the tyre it will probably say something like "max pressure 140 psi".

What sort of pump is it... the red line maybe there to stop someone pumping their air bed up too hard!! 

And don't be apologetic for being a bike numpty..  we all were once excpet perhaps a few on here who I reckon were concieved on bikes and therefore know lots about sprockets and stuff. 

I've had it a few years but it's this one I think http://www.wiggle.co.uk/topeak-joe-blow-max-ii-track-pump/ 

Getting much above the 80 is hard work!! I'd best get some more upper body strength too.

I know I need to learn a lot about bikes - I love my LBS as they do everything for me! I bought some hard wearing tyres (think they said they had ceramic in them as the kevla ones didn't come in 650s) and they fitted them, and they changed my peddles from normal to spd ones for me even though they said "you sure you don't want to do this?" as if to say sorry for taking the money off me!!

If their 650s then 80psi may be all that is needed. There is alot less volume in a 650 than a 700.

What does it say on the side of the tyre for pressure range?

no idea IC never looked!!

interesting article on Sheldon Brown's site... HERE which would indicate that tyre width is more important than wheel diameter.. What is clear is the relationship between pressure and rider weight...  same as a car.  A heavily loaded car needs mre air in the tyres!

The pump looks fine Pix, but you will probably find that the grey bezel bit outside the dial with the red arrow on it will rotate so that you can use it as an indicator of where you want your pressure to be. 

mine just gives the mke details and my spare inner says "check pressure regularly" but nowt else

i'm lardy so i guess higher is better

I use Conti GP4000s's or Gatorskins and they're always pumped up to 120psi

Pixie,

650 wheels are smaller than 700s. If you tried to fit 700s they wouldn't fit - so don't do it. We are talking distance from axle to edge not tyre width here.

115-120 for Conti GPs for me as I am lardy. Training tyres a little less and also tend to do a about 5PSI less on the front.

Please remember that the the valve is non-return on the tyre so unless you knock the valve you won't lose any. What will rush out is all the air in the pump also at 110 PSI.

M.eface

I normally pump my clinchers (Continental Gatorskins) to 110 (sometimes up to 120) on the back, slightly less on the front, in the winter maybe 10 less.  Its worth checking pressures every week as they'll bleed air, maybe loosing 10 PSI in a week.

fanks meface ... I did say I was a numpty

IronCat5 in the Hat wrote (see)

If their 650s then 80psi may be all that is needed. There is alot less volume in a 650 than a 700.

What does it say on the side of the tyre for pressure range?

cat - you are an engineer, no??  then you should know that volume does not equate to pressure.  so tyre size has no meaning here - you need the same pressure irrespective of size.

Thanks FB - I was having a thick day.

I'll now say that as 650 has a smaller volume they'll need a higher pressure. Volume is related to area.

Pressure = Force / Area.

Force (rider + bike weight) is a constant here, so as the internal Area of the tyre increases (say from 700x23C to 700x25C) the Pressure required to support the Force reduces.

By the same token as you reduce the area of the tyre (650x23C) then the pressure must increase for a given force.

Your MTB tyres support your weight the same your road bike tyres, but at a lower pressure. The volume of the tyre is bigger. Perhaps my explanation/understanding is amiss, but the theory is sound.

you run MTB tyres at lower pressure for grip off-road - it has little to do with support.  there's nothing to stop you running them much higher but a) it's bloody hard work pumping that volume up, and b) they would be skipping and jumping all over the place on the knobbies.