Why do cross bike tyres need less pressure?

[grellboy]

Moronic question time again. Can anyone clarify for me why cx tyres need less pressure? Sure it's a simple explanation, but I can't figure it out. Is it just because the bike is supposed to be on trails? In which case if it is often on the road can the pressure be increased?

 

[Spiderweb]

Lower pressure gives the tyre more grip and allows for a more comfortable ride off road. I occasionally ride my CX bike on the road and will inflate to 60-70psi.

 

[Jimidh]

Moronic question time again. Can anyone clarify for me why cx tyres need less pressure? Sure it's a simple explanation, but I can't figure it out. Is it just because the bike is supposed to be on trails? In which case if it is often on the road can the pressure be increased?

No such thing as a moronic question in my opinion - the moronic thing is not asking when you don't know the answer.

 

[grellboy]

Lower pressure gives the tyre more grip and allows for a more comfortable ride off road. I occasionally ride my CX bike on the road and will inflate to 60-70psi.

So why can't you put 100psi in cx tyres when on the road, like a normal road bike tyre? What would happen?

 

[T.M.H.N.E.T]

So why can't you put 100psi in cx tyres when on the road, like a normal road bike tyre? What would happen?

The CX tyre in front of me is max 80psi. Im not sure I want to find out what over inflating it would do

 

[Diggs]

If you're on the road you can inflate to a higher PSI, as you don't need that grip - within the tyre's recommended limits as @T.M.H.N.E.T states . Although specific tyres are for specific surfaces and the range of pressures vary according to this.

 

[Spiderweb]

So why can't you put 100psi in cx tyres when on the road, like a normal road bike tyre? What would happen?

You don't want to inflate the tyre to more than it maximum recommended limits, this you can see on the side of the tyre. If it states 100psi as a maximum then you'll be ok running them at that pressure.
What does it read on your tyres?

 

[mythste]

I think we're missing an obvious point here! Cross tyres are typically larger volume - 35mm+. There's some science as to why you don't want to inflate those as much as a smaller volume tyre but it escapes me at this moment in time!

If the rims will take 23-25mm tyres you can inflate them to the usual 100psi and beyond.

 

[grellboy]

It says 85 psi max. Not that I have a very scientific approach: the guage on my pump is broken so I just pump them up to slightly below exploding level!

 

[Yellow Saddle]

Mytste is right. It is not that you inflate cross tyres less because you'll be riding cross, you inflate them less because wider tyres can't take as much pressure as narrow tyres. The reason for this is simple. Tyre pressure is given in Pressure per Area. So, if you have a pressure of 100 on an area of 5 and that's the maximum that tyre bead can resist being pulled off the rim, then that same tyre bead won't be able to resist a pressure of 100 on an area of 10. The force is cumulative. on the first example the bead experiences 500, on the second one it experiences 1 000. Dont' worry about the units, just look at the numbers.

 

[rualexander]

Mytste is right. It is not that you inflate cross tyres less because you'll be riding cross, you inflate them less because wider tyres can't take as much pressure as narrow tyres. The reason for this is simple. Tyre pressure is given in Pressure per Area. So, if you have a pressure of 100 on an area of 5 and that's the maximum that tyre bead can resist being pulled off the rim, then that same tyre bead won't be able to resist a pressure of 100 on an area of 10. The force is cumulative. on the first example the bead experiences 500, on the second one it experiences 1 000. Dont' worry about the units, just look at the numbers.

"Tyre pressure is given in pressure per area"?!
Tyre pressure is tyre pressure.
Think your physics is a bit confused there.

 

[Profpointy]

"Tyre pressure is given in pressure per area"?!
Tyre pressure is tyre pressure.
Think your physics is a bit confused there.

force per area - slip of the finger only

 

[Cubist]

MTB tyres on the other hand, large volume, knobble pattern, thrive on lower pressures as they deform to mould themselves and their footprint/contact patch to trail surface. MTBs need to prioritise grip over rolling resistance or a lack thereof. The limits here are how low dare / can you go before getting into pinchflats territory, or risking rim damage if you're running tubeless.

 

[Yellow Saddle]

"Tyre pressure is given in pressure per area"?!
Tyre pressure is tyre pressure.
Think your physics is a bit confused there.

You are right, it was late and I should not have been posting under the influence.

 

[mythste]

Mytste is right. It is not that you inflate cross tyres less because you'll be riding cross, you inflate them less because wider tyres can't take as much pressure as narrow tyres. The reason for this is simple. Tyre pressure is given in Pressure per Area. So, if you have a pressure of 100 on an area of 5 and that's the maximum that tyre bead can resist being pulled off the rim, then that same tyre bead won't be able to resist a pressure of 100 on an area of 10. The force is cumulative. on the first example the bead experiences 500, on the second one it experiences 1 000. Dont' worry about the units, just look at the numbers.

I'm surprised a didnt get a CC award for being right according to Yellow Saddle