How do you pick an MTB frame size?

[Woody]

Guys,
How's the best way to choose/size an MTB?

I've alway s gone on inside leg measurement - wheel radius.

So as I'm a 31 inch'ish inside leg (just over 5ft 10in height) with a 26inch wheel that would equate to around an 18 inch frame.

Can just about stand over the frame without squashing the family jewels.

Is this the correct way, or should I also be taking arm reach into account?

Thanks

Chris

[lufbramatt]

Go and have a sit on one?

Not heard of your formula before tbh, not sure how it would work as different bikes can have varying bottom bracket heights which would make the wheel size irrelevant surely? Also, frame sizes don't change between say 26" and 29" wheel MTB's, but using your formula you'd end up on 16.5" 29er.

18" sounds about right for 5'10", although for a MTB you probably want to err on the side of smaller rather than bigger. I'm 6'1" and ride a 19" frame as I find them much better "through the twisties" than a 21" which, although more the recommended size, are like sitting astride a farm gate in comparison.

Bike from different makers are measured in different ways though and the geometry changes a lot (long/short top tube etc.) depending how the frame has been designed so it's very hard to tell without having a go. There's more to it than just standover height.

Edited by lufbramatt on Tuesday 20th May 10:50

Edited by lufbramatt on Tuesday 20th May 10:55

[anonymous-user]

Problem with MTBs is that what people use them for can be very different! A downhill bike will be long and low for stability, giving away optimum pedaling position for the ability to smash through stuff without getting upset. An XC bike will be shorter and taller, allowing max power transfer and agile handling, but at the cost of potentially getting upset in rought ground and steep descents. Somewhere in between is the modern "All Mountain" bike, and the trend is definitely heading towards the DH end of the spectrum, ie long/low as people want a more capabable descender of a bike.

So, what sort of riding are you doing? If you're riding fast but on not steep and smooth tracks then you would want a bike that is a smaller fit for you (more like a road bike fit) but if you're going to be doing more serious off road riding (blacks at trail centres, steep natural stuff (peaks, lakes, moors etc) or planning at trip to Europe (The Alps etc) then you might be better with a bigger bike. If you are between sizes, i would generally recommend you go up, not down a size, especially as you can re-claim a shorter "cockpit" by fitting wide bars and a short stem etc.

[Gren]

Don't forget the top tube - you don't want to feel stretched out or cramped and there's only so much a stem or saddle rail can do. You sepnd more time in the saddle than with your feet on the ground so that can be more important than the stand over height which can be different of bikes with the same frame size.

[Kell]

It can. I remember when I got my first MTB (some 26 years ago now) a nice Raleigh Maverick. I was measured at the bike shop in town who up until that point had only sold road bikes, and they measured me in the same way that you would a road bike - having just 1" clearance while stood above the bike. I don't remember the size off hand, but it was way too big. I think 23" or so.

It was fine to ride, but the first time I didn't quite get the front wheel up a big step, I know I'd wished I'd got a smaller frame.

My next bike (a Saracen Tufftrax - back when Saracen was acceptable) was 19"