my daughter now should carry these for racing.
XC MTB so 29*2.1 ish tyres.

What should I get?
One with a built in mini pump to allow a bit of extra air?
What size cartridge for these tyres? she’s not heavy, currently running with tubes at about 30psi, but will soon be tubeless and a little lower pressure.

any makes better than others?

I bought CO2 inflator and Birdman mini pump from xcracer.com, ironically, since I’ve had them I’ve had zero punctures so not even use them yet.

I’d recomment the combined mini pump option for a few reasons.

Backup – the pump is rubbish but you’ll get some air in eventually id you have gas issues.
Control – you can inflate the first bit of the tyre slowly using the pump. I’ve seen people blow tyres off rims or pop tubes when there were issues with the bead. Getting a small amount of air in first prevents this normally

so will a 16g cartridge be ok for 29*2.1 tyre? Or do I need bigger 20 or 25g?

This is a great piece of kit: http://www.bontrager.com/model/07331 as it allows you to use a pump and a cartridge, it also lets you control the inflation easily. I never leave home without one!

You can put tiny fires out with them.

And make fizzy water?

For racing, co2 cartridges will do. 20g will put enough pressure in a 27.5 2.4″ Mountain King2 from completely flat, a 16g is only just enough for a 26″ 2.1 tire.
I’d carry a second cartridge over a pump tbh even if I was still needing to repair my reliable tubless setup with a tube.

edit: 30psi for a presumably light female is pretty high pressure unless its all buff trail racing. I’m a believer in lower pressure in higher volume tyres now but thats for more technically orientated XC racing.

[video]https://www.youtube.com/watch?v=ShFkBCO552o[/video]

bearback, thanks for the feedback about volumes. indeed, 30psi is fairly high, this is about what she will use at Cathkin Braes where it is 100% buff trails with a few big rocky sections. Other courses the pressure will be lower, around the 25 area. She is runing 29*2.1 crossmark or racing ralph

Careful with some inflators on the cartridge size. I had one that only took threadless cartridges and used a holder for the cartridge but this limited the size of the cartridge I could use.

I now have one that’s threaded and can use it without the supplied holder, so it’s a tiny amount of space in the bag just using the head of the inflator and a couple of cartridges and can use any size I want. Do need gloves though when holding! (and even then I’ve burnt myself through gloves). Or you can get grip things to cover the cartridge to hold them.

Don’t buy cartridges from an LBS or major online shop. Stupidly expensive. Try places like this – http://www.co2cartridges.co.uk/

Make sure you get threaded cartridges if you go for an inflator without a holder.

Anyway, I generally use 16g but carry a couple. Half of one is enough to seat a tubeless tyre which is what I mainly use them for. A full one will fill a typical 26″ MTB tyre to low pressure.

A 16g cartridge will pump up a 26″ 2.3 tyre from flat to a decent pressure to continue the ride for me but I’m fairly light (70kg). I’d presume a 29er tyre would need at least two 12g carts.

I usually carry a dedicated inflater (a Genuine Innovations one) and two cartridges alongside a Lezyne mini-pump when going on big rides as a redundancy in case of problems.