Would you run for a 42kg child riding a xs 26″ 160 travel bike in the alps? 2.4 tires….

For dh only, as the child is lazy and will only use the lifts in les gets/morzine.

Simone

Tubed or tubeless? Dual or single ply?

27 psi.

15-20psi – don’t trust one gauge, many are way out at such low pressure. Lower if they’re dual ply and have thick tubes or rim strips to stop tubeless burping.

Single ply chunky monkeys with freeride tube in the back. On roval wheels (tubeless rim tape already fitted), so could go tubeless but husband thinks it’s not worth the hassle.

Forgot to ad, boy is a real wuss, slow but steady, only 11.

boy is a real wuss, slow but steady,

Tyre pressure doesn’t really matter then. Why not start at 25psi front, 30psi rear and let a little out on each run. Chances are, he’ll not notice any change.

Tyre pressure doesn’t really matter then. Why not start at 25psi front, 30psi rear and let a little out on each run. Chances are, he’ll not notice any change.

Does not compute! Slow lightweight riders who lack confidence benefit the most from low pressures.

It’s all about having the contact patch the tyre was designed for. If you read manufacturer test info they’re testing at 25-30psi on single ply with a grown man riding – that’s about 8 sq.in contact patch or 2″x2″ front and back. The CM 2.4 is a big tyre so going sub 25 wouldn’t be unreasonable under a mid weight bloke. Put a 42kg kid on that and he’ll be perched on about half that contact patch, the big side knobs won’t touch until the bike is cranked way over.

Many MTBers really seem to struggle with how much tyre pressures need to vary with rider weight and how low can be right – ask the pros and many of them are incredibly anal about what they’re running, especially the enduro racers who have to pedal uphill and pin it downhill.

I pump mine up if they feel a bit soft, give them a squeeze till they feel ok, never have a clue what pressure’s in them.
My track pump has a gauge but I doubt It’s accuracy.

Just wondering, why does it state on the tire 35-65 psi pressure?

I would run them about 20 front and 25 rear or something (maybe lower ), but husband seems less convinced. He always insists on putting in about 30-35 in the kids tires while in morzine.

So what is the advantage of running them lower? I think I know, just don’t seem to be able to convince the stubborn old bugger!

As chiefgrooveguru says really IMO. You’re looking for as full a contact area as possible without the tyre feeling squirmy, or burping. Lighter riders will feel the difference more as a too higher pressure will make the tyre not absorb the ground as well and feel like the rebound on the forks and/or shock are set too fast, thereby reducing control. Control is best when the tyres are in contact with the ground, possibly goes without saying 😀

I set mine from the basic formula given by Stan, which is so basic, I can’t remember it, but it’s something like divide the rider weight in lbs by 7 to give you front pressure in psi and add 2psi for the rear. Don’t quote me on that, but found it as a good start point and I set mine as 21psi front and 25psi rear as my track pump gauge reads. It’s accuracy is academic, it’s how the tyres I have fitted feel. I use lower pressures on my SS than my FS and lower with tyres that have stronger sidewalls.

Hope that helps?

set mine from the basic formula given by Stan, which is so basic, I can’t remember it,

Double your weight in stones, plus 2 psi on the rear, minus 2 on the front. Gives 15 rear, 11 front for a 42 kg (6.6 stone) rider.

Thank you Mr laidlaw! I better write that down 😀

Presume formula is for riding weight, incl kit?

Presume formula is for riding weight, incl kit?

Yes. It shouldn’t make too much difference though.

tyre