Tyre Pressures

[Lurcher]

Just fitted a pair of Schwalbe Marathon Plus 700 x 38c to my Trek 8.2 DS Hybrid bike , on tyre says inflate between 50-85 psi .
Set them at 60 psi as thats what the original Bontragers were at , is this fine for these ?

TIA

Julian

 

[black'n'yellow]

60psi is definitely 'between 50-85psi' - so I'm gonna say yes. Fine tuning of that pressure should be down to you - nobody else.

 

[ianrauk]

it's a yes from the ianrauk jury.

They are minimum and maximum pressures the tyres take.

 

[Lurcher]

Thats what I thought , but much difference at 50 than 85 ?

Julian

 

[citybabe]

having them at 60 psi should be ok altho you could put a little more air into them if you wanted. Just a little thing to remember is that the less air you have in the tyre the more risk you run of getting pinch punctures which are caused by the tyre being squashed between rim and stone

 

[ianrauk]

Thats what I thought , but much difference at 50 than 85 ?

Julian

Try it and find out what is the most comfortable ride for you.
Highest is best if running on road and will run faster and help prevent punctures.

 

[Lurcher]

Thanks for the replies

 

[calibanzwei]

Run mine at 80-85 - no probs.

 

[black'n'yellow]

Try it and find out what is the most comfortable ride for you.
Highest is best if running on road and will run faster and help prevent punctures.

not this can of worms again...

The 'best' pressure on the road will be a compromise between the tyre's ability to absorb surface undulations (ie rolling over them, rather than bouncing off them), while remaining sufficiently inflated to avoid pinch flats. Unless you are riding on a glass-smooth surface like a velodrome, 'highest' is not 'best'...

 

[ianrauk]

not this can of worms again...

The 'best' pressure on the road will be a compromise between the tyre's ability to absorb surface undulations (ie rolling over them, rather than bouncing off them), while remaining sufficiently inflated to avoid pinch flats. Unless you are riding on a glass-smooth surface like a velodrome, 'highest' is not 'best'...

And at 85psi they will not exactly be at high racing pressure will they?

 

[MrJamie]

I pumped my same size M+ upto 85 because im heavy and they roll faster on the road when they deform less. The difference in road/trail vibration between 50 and 85 is huge though. Also i think the guage on my track pump underestimates after comparing with a pressure measure thingy that said about +10psi and when the tyres are exposed to the sun that increases the pressure further. Riding in the sun on sunday with what id though were 85psi tyres could have easily been the wrong side of 100

Any thermodynamics geeks know how much the pressure is likely to increase from shaded garage/room to sunny summer?

 

[tyred]

There shouldn't be any need to pump 38mm tyres up to 85psi. It defeats the purpose of having wide tyres and tyres this wide will be most unlikely to pinch puncture. 60 in the back and maybe a little less in the front if they were mine.

 

[machew]

I pumped my same size M+ upto 85 because im heavy and they roll faster on the road when they deform less. The difference in road/trail vibration between 50 and 85 is huge though. Also i think the guage on my track pump underestimates after comparing with a pressure measure thingy that said about +10psi and when the tyres are exposed to the sun that increases the pressure further. Riding in the sun on sunday with what id though were 85psi tyres could have easily been the wrong side of 100

Any thermodynamics geeks know how much the pressure is likely to increase from shaded garage/room to sunny summer?

Solve

where t is the Celsius temperature; and p0, V0 and t0 are the pressure, volume and temperature

 

[black'n'yellow]

And at 85psi they will not exactly be at high racing pressure will they?

you kidding..?? 38c Marathon Plus at 85psi will ride like a cartwheel...

 

[black'n'yellow]

and they roll faster on the road when they deform less.

like I said earlier - that is only true if you are riding on a 100% smooth surface, like a track, or if you happen to be riding on a ballroom floor. On real roads with varied surfaces, a rock-hard tyre will almost certainly be slower than the same tyre at the correct pressure.