I’m 5ft 8in and 29inside leg,normal but lardy body and short arse legs 🙂 Always been on medium MTBs in 26+27.5 but my first foray in 29ers was a small hardtail and it fits just fine though the sizing guidance states they come up large-Octane Prone.Now looking at a full sus 29er and have seen a small Marin I’m keen on but online only so I can’t get to try it.All the numbers and angles are more or less the same as my 29 hardtail except the seatube C to C,385 as opposed to 432 on my hardtail.Brand sizing guidance indicates I am one inch into the medium in height but inside leg indicates small.Am I likely to encounter any issues if I go for the small?

I’m the same height and inside leg as you and I tend to ride a large 29er, to get the length I like on a bike.

Cotic are the current exception, as their medium is 460mm reach and that’s my preference for a trail bike.

So in summary, the small is likely to be too short.

“S”, “M”, “L”, etc. don’t really mean very much. Actual sizing varies between manufacturers and bikes have gotten longer, but with shorter seat tubes in the last few years. A modern “S” is likely to be as long as an older “M”. Different people have different body proportions, so two people of the same height might need different sized bikes.

Ideally, you’d compare reach (the horizontal distance from the bottom bracket to the top of the head tube), but that is tricky to measure. An easier thing to measure is effective top tube, which is horizontal distance from center of steerer to center of seatpost. Only problem with that is that newer bikes tend to have steeper seattubes, so you might find that you set your saddle further forward on older bikes, which has the effect of shortening the effective top tube.

Seattube length doesn’t matter within reason except that you need to check that you can fit a dropper post in with enough drop for what you want to do.

Apart from the C to C being shorter the stack is `also 16mm shorter than my HT.However the ETT is 4mm longer and the reach 5mm longer on the full sus which was why I was erring on the small but apparently I should be looking at a large 😉

29″ trouser inside leg or 29″ book-rammed-in-crotch? I am increasingly convinced that the sizing charts are made by people that have never stood over their bikes. I’m not ridiculously out if proportion but lots of size guides put me on bikes that would have me sitting on the TT with my feet dangling above the ground.

What model is it?

I’m 5’8” with 30” inside leg. I’m on a medium cotic rocketmax and it’s a good fit. I don’t think I would want to ride a small