[Closed] Tubeless 650b - how low can you go?

Depends on combined bike/rider weight surely.. and terrain, speed etc. And of course the security of the rim/tyre interface, and whether you care if your rims get dented.

I have ridden 17psi 2.25in front, 18psi 2.1in rear in the past with a combined rider bike weight about 70kg.

Lots of traction on scrabbly loose and rocky terrain. No rim clatters.

more commonly run a psi or 2 higher

There's a lot of variables here, so it's hard to say. I've never gone below 25psi on my own bike (29er FS, Maxxis Ikon 2.2s) as at 85kg, I need a bit more air under my backside! Personally, I've never felt the need to go "as low as it will go" as I don't actually like the feel of the bike when the tyres get below this level, as it tends to move around on the tread more which gives a slightly "mushy" feel to the handling. Personally, I'd prefer a bit more air and a bit more predictability.

Of course, if you want low...

(This was from my 9yo son's CX race bike, running 32mm clinchers with lightweight tubes just before a muddy race. Oh, what it is to be so light that you can't pinch flat even if you try!)

So how low can I realistically go?

The only way is to try and find out yourself, us lot on here can only tell you what we do, which is irrelevant, as we don't ride your bike, on your terrain, in the main won't weigh the same as you, go the same speed as you, or ride the same way.

Keep dropping a couple of PSI until you're happy.

According to manufacturers we shouldn't be going so low as we do else risk damaging the carcass and claim they work better at the minimum pressure they spec. Heard this a couple of times from people talking to Maxxis guys.

Though they're just covering themselves for warranty claims. Anything outside of what's printed on the sidewall and no claim. So run at rock hard at 35psi minimum, yeah right. Pinging of every tiny stone and root!

Don't forget that one mans 18psi is another mans 24psi.

Depends how accurate your PSI measuring stick is

Drop them until they start rolling on corners then add 2 psi.

19 psi here, my rims are on the expensive side so I'm a bit nervous about going any lower. Spent a sunday on rocky terrain with plenty of variation and didn't get any clangs

I usually go with Stans formula of weight in stone x 2 then plus two for the rear, -1 for the front. So 13 stone gives 26, meaning 28psi rear, 25psi front.

+1 on pump accuracy though.  My Joe Blow will say 30 and my Fabric Accubar gauge will say 27...

I stick about same pressure on 2 different 650B setups - FS with 2.25s on Hope 19.5mm rims and HT with 2.3/2.4s on 25mm rims.

Start with whatever it takes to get about 20% deflection when static with your weight on the bike and then adjust to taste. An old rule of thumb.

25 front, 30 rear on 2.3s. I'm 10.5 stone. Don't flat all that often, but my rims are covered in dinks and flat spots. Peaks and lakes, so no shortage of rocks.

Drop them until they start rolling on corners then add 2 psi.

Akira has it.

I’d probably not get much lower if at all than the numbers you’ve posted, OP, but as above there are many variables here. Just off the top,

Rider weight

Rim width

Tyre sidewall strength

Tyre actual size (not necessarily what’s in the side)

Terrain

Riding style

Attitude to rim damage

Accuracy of psi gauge (always stick to your own and don’t assume that your numbers on someone else’s gauge will give the same result)

I think that’s the biggies...

Thanks all - appreciate it's a 'how long is a piece of string' type question.

Will see how I get on with dropping a couple of psi at a time.

Will also check how accurate my guage is.

Also is the a specific way you orientate the valves to stop Stan's coming out when taking pressures?