# Tyre Pressures



## Lurcher (31 May 2012)

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


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## black'n'yellow (31 May 2012)

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


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## ianrauk (31 May 2012)

it's a yes from the ianrauk jury.

They are minimum and maximum pressures the tyres take.


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## Lurcher (31 May 2012)

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

Julian


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## citybabe (31 May 2012)

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


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## ianrauk (31 May 2012)

Lurcher said:


> 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.


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## Lurcher (31 May 2012)

Thanks for the replies


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## calibanzwei (31 May 2012)

Run mine at 80-85 - no probs.


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## black'n'yellow (31 May 2012)

ianrauk said:


> 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'...


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## ianrauk (31 May 2012)

black'n'yellow said:


> 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?


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## MrJamie (31 May 2012)

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?


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## tyred (31 May 2012)

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.


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## machew (31 May 2012)

MrJamie said:


> 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 _p_0, _V_0 and _t_0 are the pressure, volume and temperature


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## black'n'yellow (31 May 2012)

ianrauk said:


> 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...


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## black'n'yellow (31 May 2012)

MrJamie said:


> 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.


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## MrJamie (31 May 2012)

black'n'yellow said:


> 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 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.


 What would be the correct pressure for me?

Most of my 18stone+ weight is sat fairly upright over the back wheel, with a saddlebag that has been known to hold tools plus a 12 pack of beer  (or similar heavyish shopping) so I was guessing that i should be nearer the max end of the psi scale for mostly road riding. Also I read that because the M+ puncture protection strip is central to the tyre tread, its important to keep well inflated so they roll on the strip.

As you say though, a cartwheel is a pretty accurate description in terms of shock absorbtion, with alu frame my lower back always gets really annoyed with me pumping the pressures up. About 60-65 feels more like a comfortable compromise.


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## black'n'yellow (31 May 2012)

from what you've said, I'm guessing 65-70. Bear in mind that nobody buys Marathons for their 'supple' ride qualities..


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## Recycler (31 May 2012)

black'n'yellow said:


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


 
Cartwheel or not, I'm with ianrauk on this. I ride my Marathons at the top end of the range. It may be a fraction harsher, but it is certainly quicker.


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## black'n'yellow (31 May 2012)

Recycler said:


> Cartwheel or not, I'm with ianrauk on this. I ride my Marathons at the top end of the range. It may be a fraction harsher, but it is certainly quicker.


 
interesting - how are you quantifying that..?


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## Recycler (31 May 2012)

black'n'yellow said:


> interesting - how are you quantifying that..?


 
To be honest, I've not done a proper test to check it out. To do so would mean doing several rides at different pressures, and then trying to eliminate all the other variables.....life's too short.

I do know that when I was trying to push a wheelbarrow around the garden the other day it was a lot easier when I inflated it properly.

But, it definitely feels faster on the bike and logic alone tells me that it is likely to be.

This is not intended as a tit-for-tat response but, have you been able to quantify your earlier rollling versus bouncing comments in #9 ?


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## Psycolist (31 May 2012)

black'n'yellow said:


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


 Wot he said


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## Peteaud (31 May 2012)

Run my 35's on the hybrid at 80 and never had a problem. Same as the wifes bike, 32's on 80psi.


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## black'n'yellow (31 May 2012)

Recycler said:


> This is not intended as a tit-for-tat response but, have you been able to quantify your earlier rollling versus bouncing comments in #9 ?


 
it's not down to me to quantify it, because it's not my theory. Plenty of studies and articles available to read if you google it...


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## black'n'yellow (31 May 2012)

Peteaud said:


> Run my 35's on the hybrid at 80 and never had a problem. Same as the wifes bike, 32's on 80psi.


 
I bang my head against a wall several times a day and I've never had a problem. Doesn't make it the right thing to do...


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## Boris Bajic (31 May 2012)

I think the OP was looking for impartial advice, so I will help where others seem unable or unwilling to oblige.

I run totally different tyres from a totally different manufacturer.

I run them at nothing like the pressures you mention. Far from it and contrariwise is every respect.

You may be able to use these figures to arrive at a rule of thumb for your own tyres.

My bicycle is black and red.

I hope this helps, but fear it may not.


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## Thomk (31 May 2012)

I was under the impression that the quoted maximums on tyres were quite a bit lower than their true maximums.


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## Peteaud (31 May 2012)

black'n'yellow said:


> I bang my head against a wall several times a day and I've never had a problem. Doesn't make it the right thing to do...


 
why is 80 wrong?

I am comfy, the bike handles well and i dont get that many p**********s


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## Boris Bajic (31 May 2012)

Thomk said:


> I was under the impression that the quoted maximums on tyres were quite a bit lower than their true maximums.


 
I stick to them these days. Many years ago I tried running Conti SportContact slicks on my MTB at 100psi (recommended max was 80).

They gave good grip, a nice ride and were *very* fast, but they punctured like a bastard every time I went near a piece of gravel. I went back down to 80 and all was well with the world.

It has been ever since.


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## black'n'yellow (31 May 2012)

Peteaud said:


> why is 80 wrong?
> 
> I am comfy, the bike handles well and i dont get that many p**********s


 
80 may not be wrong for you, because you haven't mentioned the kind of riding you do, the tyres you are on or how much you weigh...


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## black'n'yellow (31 May 2012)

Thomk said:


> I was under the impression that the quoted maximums on tyres were quite a bit lower than their true maximums.


 
the quoted maximum on the side of the tyre is NOT a 'recommended' pressure. It is the maximum pressure that the tyre will safely tolerate (albeit well within a safety margin, most likely).


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## Peteaud (31 May 2012)

black'n'yellow said:


> 80 may not be wrong for you, because you haven't mentioned the kind of riding you do, the tyres you are on or how much you weigh...


 
road / country lanes, bontrager tyres with small grooves and 15 stone.

Ive put less in and it felt wrong.

So for me 80 is right.


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## Recycler (31 May 2012)

black'n'yellow said:


> it's not down to me to quantify it, because it's not my theory. Plenty of studies and articles available to read if you google it...


 
I've tried, but can't find anything. Lot's of opinion and theory but no studies with quantifiable figures.

Do you have a link? It would be interesting to see what the figures are.


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## Thomk (31 May 2012)

black'n'yellow said:


> the quoted maximum on the side of the tyre is NOT a 'recommended' pressure. It is the maximum pressure that the tyre will safely tolerate (albeit well within a safety margin, most likely).


Yes but my point is that it is not the maximum safe pressure (with a reasonable safety margin) but rather the maximum safe pressure with an unfeasibly enormous safety margin.


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## black'n'yellow (31 May 2012)

Thomk said:


> Yes but my point is that it is not the maximum safe pressure (with a reasonable safety margin) but rather the maximum safe pressure with an unfeasibly enormous safety margin.


 
it's still the manufacturer's safety limit and consequently their arse is covered - take it or leave it.


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## Thomk (31 May 2012)

black'n'yellow said:


> I bang my head against a wall several times a day and I've never had a problem. Doesn't make it the right thing to do...


And it probably isn't so stop doing it please


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## Lurcher (31 May 2012)

I"ll stick at 60 on both and see how it goes for the time being and adjust if needed as I put the miles on .


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## black'n'yellow (31 May 2012)

Recycler said:


> I've tried, but can't find anything. Lot's of opinion and theory but no studies with quantifiable figures.
> 
> Do you have a link? It would be interesting to see what the figures are.


 
They're all out there somewhere, but I'm not interested in definitively proving the point, as it makes no odds to me what pressure you run your tyres at.

Having said that - Sheldon Brown has a pretty good page on the topic here - http://sheldonbrown.com/tires.html - the sections on 'rolling resistance' 'width & pressure' and 'pressure recommendations' are probably most relevant to this discussion. While I don't always agree with everything Sheldon has written, his info here is fairly accurate, IMO. Conventional wisdom - use it as you wish..


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## Jdratcliffe (1 Jun 2012)

Dont forgot thou your rims will have a max psi as well best not to exceed that!


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## buddha (1 Jun 2012)

Trial and error, in my limited experience.
I normally run Vittoria Diamante pro at 110/130 psi front/rear - I'm 12.5 stone.
Last week I fitted some Vittoria Zaffiros (cos they're cheap and more hard wearing!). At 110/130 I was bouncing around all over the place. Finally settled at 100/115.
Don't think I'd ever go near their top of 145psi.


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## youngoldbloke (1 Jun 2012)

Always think it is agood idea to consult the manufacturers - its all there - Schwalbe


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