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You can easily end up with the wrong mountain bike frame size. You can’t go off the listed frame size anymore. Here’s how to avoid getting it wrong.

Bad news: mountain bike frame size is all over the place. There is no consistency. One brand’s Medium/17in a bike is another brand’s Large/19in. What’s more, a lot of bike manufacturers’ – and even bike shops’ – sizing advice is often wrong too.

Ultimately you do not have a foolproof frame size. Not one that tallies with what bike brands say, nor one that is consistent from bike to bike. This means shopping for a bike is not simple, particularly if browsing online beforehand. It is not a good idea to select just one frame size and filter the results by that; select the frame size the brand recommends and also the size above.

But with all that said, to give you at least a head-start on what frame sizes to shortlist, whether you’re looking to upgrade or are trying to choose the best beginner mountain bike, here is our mountain bike size guide:

Mountain bike frame size guide

Under 5ft 2in (-157cm) = 13in to 14in (XS)

5ft 2in to 5ft 6in (157cm to 167cm) = 15in to 16in (Small)

5ft 6in to 5ft 10in (167cm to 178cm) = 17in to 18in (Medium)

5ft 10in to 6ft 2in (178cm to 188cm) = 19in to 20in (Large)

6ft 2in or above (182cm+) = 21in to 23in (XL/XXL)

What to do if you’re ‘in between’ mountain bike frame size

We’d strongly advise going for the larger of the two options. It’s easier to make a large bike fit without impairing how it handles; fitting a shorter stem and/or sliding the saddle forward on its rails arguably actually improves bike handling. Trying to make a small bike fit by putting a longer stem on it and/or sliding the saddle backward on its rails will end up impairing the bike’s handling.

The thing to bear in mind when going up a frame size is to make sure there is sufficient standover clearance. Standover is how high the top tube is at the point where you’re astride your bike and straddling it. If the bike has enough standover, you’re on to a winner.

Why are things so messed up?

The problem is that bikes have always been sized by the length of their seat tubes. There’s no reason for us to go into why this is so (short version: blame roadies) but you do need to understand that this is a big problem.

Whilst seat tube length is important it is not the most important measurement on a bike frame.

The modern move away from frame sizes being listed in numbers of inches has been an improvement. Using ‘Small’, ‘Medium’ and ‘Large’ etc instead of ’16in’, ’17in’ or ’19in’ is a much better idea.

What measurement is the most important then?


Why is reach the most important measurement?

Reach is the distance between the bottom bracket axle and the center of (the top of) the head tube. See the diagram above.

This is a very difficult thing to measure on a bike in the flesh unless you’re happy to take plumb lines and tape measures into your local bike shop. Thankfully any bike brand worth its salt includes a reach measurement on the geometry charts of its bikes.

Why is reach the vital thing? Because it dictates how the bike fits you. It governs if a bike is too cramped or too stretched out for you.

And, unlike seat tube length, the reach cannot be adjusted. You can adjust your saddle height up or down to accommodate seat tube length. Reach cannot be adjusted. You’re stuck with it. A bike with too short a reach will always be too small.

Don’t think you can adjust incorrect reach by changing to a different stem length or by sliding your saddle on its rails backward. Changing stem length will impair how the bike steers and handles. And saddles slid far back on their rails won’t mean a thing when you’re stood up out of the saddle, and when you are seated slid-back saddles will result in inefficient pedal power and a wander, lift-prone front end.

Don’t end up with the wrong mountain bike frame size

A common result of going off sizing advice from a bike brand (or even a bike shop) is to end up with a bike that’s too short in reach and comes with a stem that’s too long.

A 6ft tall person would end up choosing a 21 inch frame mountain bike. Then the 29er Full Suspension Carbon MTB Frame MFM100 is the best option.

For more info please check our official website: https://www.trifoxbike.com/

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