How much air to put in tyres ?

[theDaveB]

Just got new tyres and on them for inflation it says 40-100 psi and don't really understand.

My last tyres said 40-60 and I always inflated to 50, for now I have done the same and they feel fine.

Should I be putting more in ?

They are Marathon tyres on a 20" wheel and am around 17 stone.

Dave

[reohn2]

Tyres should be inflated for load/width,this is a good guide:- http://www.bikequarterly.com/images/TireDrop.pdf
Once you've inflated to the table's tyre drop recommendations you can tweak the TP's to suit.
I find 5psi either side make big differences in comfort.

Note; the figures in the table are per wheel load.

[simonineaston]

Invest in a track-pump if you haven't already got one - I would say you'll be just in time to get a letter to Santa if you're quick...

[reohn2]

Invest in a track-pump if you haven't already got one - I would say you'll be just in time to get a letter to Santa if you're quick...

+1

[OldBloke]

Get someone to measure the amount of bulge in the tyres with your full weight on the bike. I think I read somewhere that the maximum should be 15%. Its always a balance between comfort, tyre wear and risk of pinch flats. [SMILING FACE WITH SMILING EYES]

[theDaveB]

I have a track pump, how does that help ?

How do I measure the bulge as a percentage ?

Dave

[Vorpal]

If you are comfortable with the current inflation, leave it as is.

If you experience any pinch punctures (they look like someone made two little cuts in the inner tube), increase the pressure.

[reohn2]

I have a track pump, how does that help ?

How do I measure the bulge as a percentage ?

Dave

A track pump will give accurate TP's
Tyre drop(bulge is the wrong term) is explained in the link,but as I mentioned in my first post the tyre drop chart is fairly accurate and a good place to start to find optimum TP.

[Graham]

Tyres should be inflated for load/width,this is a good guide:- http://www.bikequarterly.com/images/TireDrop.pdf

Yep, this is good guide which corresponds to my own experience.
It would appear that a lot of newcomers think that "the-harder-the-better-for-easier-rolling" is the simple rule to follow.
As for many things in the real world, the reality is rather more complicated . . . .

[beardy]

Tyres should be inflated for load/width,this is a good guide:- http://www.bikequarterly.com/images/TireDrop.pdf

Yep, this is good guide which corresponds to my own experience.
It would appear that a lot of newcomers think that "the-harder-the-better-for-easier-rolling" is the simple rule to follow.
As for many things in the real world, the reality is rather more complicated . . . .

A lot of people keep that idea for decades and tens of thousands of miles. Which includes me, around the max rated pressure is where I keep most of my tyres. I often compensate for the lower load on the front by fitting thinner tyres there.

[Brucey]

the OP doesn't say how wide his tyres are, but at 17 stone, 50psi mightn't be anywhere near enough in the rear tyre.

I'm guessing that the old tyres may be wider than the new ones, simply because wider tyres are not rated to 100psi as the new ones seem to be.

cheers

[reohn2]

A lot of people keep that idea for decades and tens of thousands of miles. Which includes me, around the max rated pressure is where I keep most of my tyres. I often compensate for the lower load on the front by fitting thinner tyres there.

Tell me the logic in that?

[beardy]

Because (within the bounds of keeping the tyres integrity) minimising rolling resistance is the biggest priority to me when choosing the tyre pressure.

I accept a loss of grip and dont seriously lack for comfort.

Though with fatter tyred bikes I dont bother checking my tyre pressures on the daily basis that my thin tyres get, so they start with high pressures and that gives me much longer before they are low enough to want attention.

[simonineaston]

I have a track pump, how does that help?Dave

It doesn't help with the question of how much pressure to use, which has been answered by contributors more experienced than me, but it is sterling advice for anyone who doesn't have a track pump. I'm delighted to learn you do have one.
If it helps, I've taken to using 65psi on both front and back, on my 20" Schwalbe Marathons, but I'm only nine stone... and am fairly certain you'd need much more in the rear tyre. If you're as simple minded as I am (and I'm sure you are not ) it's tempting to think that if you're twice the weight (nearly) you might need twice the pressure.
Seriously, I agree with all who've said it's all down to how much air keeps the tyre at the right profile and I'm sure a bit of experimenting with increasing pressures until you get up to one that keeps your tyre good and round while you're riding will provide you with the answer.

[Brucey]

A lot of people keep that idea for decades and tens of thousands of miles. Which includes me, around the max rated pressure is where I keep most of my tyres. I often compensate for the lower load on the front by fitting thinner tyres there.

Tell me the logic in that?

well I think the logic is that if you have a fat front tyre and it is pumped hard, you can kind of bounce around on certain types of rough road (because the contact patch is short and the tyre tracks every bump), which is annoying.

If you set the tyre pressure lower, to the 15% drop level (to allow for the lower front loading), it can roll around horribly when cornering hard, unless it is mounted on a rather wide rim.

So you can fall between two stools here. I've quite often run tyres that are slightly narrower at the front on unladen solos, and it can feel like each tyre is 'working' about right because they can both be set to 15% drop at about the same pressure. I'm sure this wouldn't suit everyone.

cheers