Minimum MTB tyre pressures?

[Kermit power]

Morning all,

Does anyone have any thoughts on minimum tyre pressures?

I'm trying to figure out the best pressure for my kids' tyres. My only frame of reference is my own 30psi tubeless setup, but as I probably weigh twice as much as the two of then put together, they'd be pinging off every root and rock at that pressure!

Obviously I could just use trial and error, but I was wondering if there's a minimum pressure I shouldn't drop before regardless of rider weight if I don't want pinch flats or tyres/tubes rolling off the rims?

For reference, they're a girl of 12 and a boy of 10 on 27.5" & 26" tyres respectively, mostly riding the likes of the red trail at Swinley.

[Kermit power]

richardxjr said:

^ that. 30psi tubeless is LOADS. Are they really narrow mud tyres or something?

No, there's just 110kg of me on top of them! I find that anything less than that, they start rolling when cornering.

[Kermit power]

Herman Toothrot said:

30psi tubeless isn't loads for an adult it's about the minimum unless you are built like an 11 year old. Any less than 30psi tubeless and I'm creasing the casing shredding tyres to pieces in no time and I'm only 72kg. For reference Jared Graves 76kg I think the interview said published his full setup after last years or maybe the years before (anyway whenever he won't the Enduro world championship), tubeless he ran 26psi front and 29psi rear or higher, 30/32 if knarley.

If I go below 30, I can guarantee almost everyone I come across on a ride will tell me I've got a flat!

[Kermit power]

yellowjack said:

Good grief!

I don't think I've ever run a MTB tyre below 45psi !!!

On the road, I've chickened out of trying anything below 80psi.

I think I must be doing this wrong. I am using tubes, not tried tubeless (yet), if this makes any difference? I was last on the scales in September this year, and weighed a smidgin under 75kg.

Should I be looking to run lower pressures on any/all of my tyres then? I've always used the top end of the range stated on the tyre casing as a start point, then reduced it incrementally if it wasn't working out for me. But I've never run a tyre at less than the manufacturer's recommended minimum inflation pressure. I'm probably just too much of a "square"

Road bikes and mountain bikes are two totally different things. You might want to reduce your tyres pressures a bit on a road bike in the rain to get better grip, but my 23c road tyres are set at 110psi, and my 35c commuter tyres at around 65psi.

Off road though, you want and need your tyres to be able to deform as you go over roots & rocks and the like, as this is what keeps you gripping, rather than bouncing off everything and pinging all over the place.

The difference between tubed and tubeless primarily is that you can run tubeless at lower pressures, as you don't have the risk of pinch punctures, as there is no tube to get pinched. If you let the pressure go too low, you can "burp" (it's a similar noise) air out of the join between tyre and rim, but that's at much lower pressures.

There is a rule of thumb cliché that says mountain bike tyres should feel more like an orange than an apple when you press your thumb into them.

[Kermit power]

yellowjack said:

Not at all. I rode a couple of laps of the Gorrick Summer monkey MTB race on an old road bike running 25c tyres, and only walked one little gully that was soft sand.

I don't currently have a MTB that works, but if I did I'd be out about 3 times a week, most often at night, tearing up some of the most popular MTB racing venues in the area, and the odd visit to Swinley. I'm not fast, I'm the first to admit that, but (apart from massively overinflated tyres, it would seem) my technique isn't too bad. There are plenty of slippery exposed roots in Minley Woods to practice on, for instance.

I kind of knew I was running my tyres at higher pressures than many riders, but I just didn't realise quite how low people were prepared to go these days. Now I just need to get my groupset replaced so I can get out and experiment with some lower pressures, but as a long time roadie I fear that lower pressures will have me paranoid about riding on flat tyres. I'll spend more time checking for p**ctures than pedaling if I go below 40psi, I swear...

Do you run your car tyres at 100psi because that's what you have on your road bike?

[Kermit power]

yellowjack said:

Kermit power said:

Do you run your car tyres at 100psi because that's what you have on your road bike?

Eh? You've lost me now....

You're projecting your perfectly sensible road bike paranoia about low pressures onto your MTB tyres, even though they have much tougher construction, and far, far greater air volume inside them.

There's no rational reason to do that any more than there is to feel paranoid about running your car tyres at lower pressure than your roadie tyres. You're only doing it because both are pushbikes, so you instinctively think of them as the same thing.

[Kermit power]

yellowjack said:

Erm? No, I'm not 'projecting' anything onto anything else. Nor do I fail to notice the many differences between my road and mountain bikes.

Current tyres on the MTB? 26" x 2.0" Maxxis Beavers. Recommended tyre pressure range, as stamped on the sidewall? Minimum 35psi to maximum 65psi. So 45psi would seem be closer to the lower recommended pressure than the maximum recommended pressure.

Nothing to do with my road tyres, nor my car tyres, nor the temperature of my bathwater, FWIW. Just what was recommended by the science and engineering types what designed the tyre. I'm not disputing the fact that many riders seem to have used similar tyres well below these recommended limits, quite succesfully. But I haven't. Oh, and no kittens were harmed as a result of this "over inflation" (?) of my tyres...

[sigh]

...and as soon as the MTB is running again, I'm going to try lower pressures to see whether or not I can teach myself to get along with them.

You were the one who said you'd get paranoid about punctures running normal pressures on your MTB because of your roadie background. I was merely pointing out that the pressure of your road tyres is really no more pertinent to your MTB tyre pressure than it is to your car tyre pressure. Hardly calls for a

I have no idea why MTB tyre manufacturers quote tyre pressures way above the range that anyone would ever use off road, but they do. Maybe they know that the majority of riders won't ever take their MTBs off tarmac?

[Kermit power]

PomBstard said:

Interesting thread. Intriguing too, as I'd be interested to know the type of terrain people might usually ride - I'm guessing as usual its not one-size-fits-all

I run c.35psi F/R on my FS mtb with 26" wheels shod with 2.1" Maxxis Larsen TT - perhaps a little high, but then I've got a 4-5km ride to get to my local tracks and the tracks themselves are predominantly fairly hardpacked singletrack/firetrail with lots of sharp stones and ledges. I used to ride around 25-30psi but found I was getting lots of pinch flats which has been all but eliminated with higher pressures. Grip is not much of a problem except for some of the sandier parts - top lips of waterbars for example - and these can be easily negated by shifting weight.

I used to run at 35-38psi when I used tubes. Since going to tubeless, I run at 30, and last weekend I dropped to around 28 as it was muddy.

[Kermit power]

Just by way of an update on this, I bought myself an SKS pressure gauge. The indicated 30 PSI on my Joe Blow track pump turned out to actually be 22 PSI!!!