No Minimum Pressure on Tyres?

[bungle73]

Another question about the new MTB. It came with a pair of Schwalbe Nobby Nic Performances. Having looked last night at the sidewalls to see what the pressure range is for them, I found that they gave a maximum, but not a minimum. That's very odd. Every bike tyre I've had as given both. How am I supposed to know how low I can go? I even looked them up on the Schwalbe website and that doesn't say either.

[Jdsk]

That's interesting.

What size, please?

Jonathan

[bungle73]

That's interesting.

What size, please?

Jonathan

29 x 2.25

[Jdsk]

Thanks

Jonathan

[Mick F]

I've never seen a minimum pressure on a bike tyre.
Just checked both bikes, and two different makes of some spare tyres, and no minimum pressure is stated.

[bikes4two]

By 'minimum' I think maybe the OP means the lower of the range of pressures given on the sidewall e.g. 30-60 PSI whereby 30 is the minimum?

[thirdcrank]

If there's nothing marked you have to go by "rule of thumb" literally. Squeeze the tyre and make sure it's hard - at least hard enough to withstand the biggest risk, especially if riding off carriageway, which is the wheel hitting an obstruction and the tyre not protecting it. That could result in wheel damage or "snakebite" punctures when the innertube is nipped between the rim and eg a kerb. Over time, underinflation may lead to damaged sidewalls through over-flexing.

[Jdsk]

I've never seen a minimum pressure on a bike tyre.
Just checked both bikes, and two different makes of some spare tyres, and no minimum pressure is stated.

By 'minimum' I think maybe the OP means the lower of the range of pressures given on the sidewall e.g. 30-60 PSI whereby 30 is the minimum?

Yes...

Jonathan

[DevonDamo]

Another question about the new MTB. It came with a pair of Schwalbe Nobby Nic Performances. Having looked last night at the sidewalls to see what the pressure range is for them, I found that they gave a maximum, but not a minimum. That's very odd. Every bike tyre I've had as given both. How am I supposed to know how low I can go? I even looked them up on the Schwalbe website and that doesn't say either.

The biggest limiting factor for how low you can go is pinch punctures and rim damage. I wouldn't worry too much about what's written on the tyre - damage like that will depend on how heavy you are and what riding you're doing. Unless you're really racing flat out on suicidal slippery roots and rocks, you're unlikely to want to go anywhere near the lower end of an mtb tyre's pressure range. And if you want to do that sort of riding, you'll probably be going tubeless which allows you to run lower pressures without worrying about pinch punctures.

I've previously been running very low pressure (14psi) on my new mountain bike - no particular reason - I just set it that way when I got it and never felt the need to change it. The tyres are extremely chunky downhill jobs, which I assume helped them get over sharp rocks etc without the tube getting pinched. However, yesterday I doubled the pressure in them as I wanted to learn jumps and, apart from making the bike a lot easier to pedal, I didn't notice any problems with grip. So maybe start with around 20psi as an opening gambit, and you'll probably find you can increase it a fair bit from there before you start to notice any loss of grip.

[Marcus Aurelius]

You can ( theoretically) run a tubeless set up virtually flat. However, a tyre de shipping is not fun, so I personally wouldn’t go below about 25 psi.

[tenbikes]

When fat biking I often run sub 5 and sub 3 in snow. 8 psi is considered very high......

[bungle73]

Well the tyres on my other MTB have a minimum written on them of 35. They've all had it. That's a 26 though, The new one is 29, which I have no experience of, and I don't know how pressures differ. I need a guide because otherwise I don't know how low I can safely go.

[DevonDamo]

Well the tyres on my other MTB have a minimum written on them of 35. They've all had it. That's a 26 though, The new one is 29, which I have no experience of, and I don't know how pressures differ. I need a guide because otherwise I don't know how low I can safely go.

Logic/physics would tell you that higher-volume tyres will be able to get away with lower pressures - i.e. a bigger ground contact area means less pressure is needed to resist the kinetic forces from you and the bike. This is borne out by what Marcus Aurelius (road bike) and Tenbikes (fat bike) are saying about minimum tyre pressures above. However, I've just been out and had a look at what it says on mine:

1. I've got an old 'Rocket Ron' on my XC hardtail. It's 29" and 2.25 wide. There's a bit of writing moulded into the tyre wall, just below the side-knobbles, alongside the 'rotation' arrow. This says 26 to 54psi. (I'd check your Nobby Nic - I'd imagine Schwalbe will be putting the same info on all their tyres, but it's hard to spot.)

2. My new bike has chunky downhill tyres. E.g. the front is a Maxxis Minion DHF. It's 29" and 2.5 wide. This one says 35 to 50 psi.

This doesn't fit my theory about tyre volume - i.e. the big volume, chunky downhill tyre should have a lower minimum pressure than the lower-volume, less-protected XC tyre. However, what I think you ought to conclude from this is that the manufacturers' minimum pressures aren't the result of careful testing, but simply whatever they think they need to specify in order to keep their lawyers happy about tube/rim damage accident claims. If you look on mtb forums and YouTube channels, you'll see what people are using in practice, and it's usually a lot lower than the above manufacturers' minimums, especially once people have taken other measures to avoid pinch punctures, i.e. going tubeless or adding those foam inserts.

As I mentioned upthread, on Thursday, I significantly upped my tyre pressure for a jumping session at a bike park. At that time, I thought the higher pressure was fine in terms of grip, so I planned to stick with that pressure (>25psi.) However, last night a few of us hit the local trails, and I realised I'd been fooled by the relatively manicured surfaces at the bike park: it was all steep, muddy, rooty chutes, and my front wheel was sliding/pinging off obstacles and nearly had me off a few times. Frankly, scary. I've since dropped the pressures (17.5 front, 20 rear) and am hoping this will make this kind of riding less terrifying/dangerous. The lesson I'd take away from this is that in terms of safety, the pressure numbers written on your tyre wall are of limited relevance when compared to whatever you need to (1) prevent punctures in practice and (2) get the traction you need.

[PH]

Well the tyres on my other MTB have a minimum written on them of 35. They've all had it. That's a 26 though, The new one is 29, which I have no experience of, and I don't know how pressures differ. I need a guide because otherwise I don't know how low I can safely go.

Here's a useful guide:
https://bikefaff.com/mountain-bike-tyre ... alculator/

I haven't come across tyres with no minimum before, though as it's missing from both the sidewall and the website it doesn't look accidental. I don't know what the minimum pressure normally indicates, for a heavier riders it's usually too low to avoid pinch flats, so maybe it was for something else, I don't know.

[Jdsk]

I haven't come across tyres with no minimum before, though as it's missing from both the sidewall and the website it doesn't look accidental.

I came to the same conclusion.

Jonathan