What size mountain bike do I need?

If you’re unsure as to what size mountain bike to get, don’t worry. You’re not alone. It is not always obvious these days.

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By ben_haworth

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What size mountain bike do I need?

Reach cannot be adjusted.

Given you hold onto the handlebars rather than the head tube, surely stem length adjusts the effective reach?

“What is reach in bike geometry?
Reach is the horizontal distance from the centre of the bottom bracket to the middle of the head tube.”

So the technical description of reach isn’t affected by stem length, but you can certainly change the distance to the bars by a different stem, or rolling your bars, or fitting a higher/lower-rise bar, or a bar with different sweep. I guess that’s what the reach measurement exists: to be independent and a comparable standard.

On the subject of Spesh and Cotic not using the more typical S, M, L, XL sizing nomenclature, my favourite sizing chart was the previous Geometron one:

Long
Longer
Longest
Extra-longest
XX Longest

😀

Given you hold onto the handlebars rather than the head tube, surely stem length adjusts the effective reach?

It’s a measurement, you can customise the bike by adding a different stem, sliding the saddle back etc. but it doesn’t change the reach. In the same way being 5’2 but using a step ladder doesn’t make you 6’4.

My bike has 440 reach which is too short according to this. In reality it’s fine and very comfortable.

Stack, stack, stack!!!!

It’s important if you are tall.

Stack hight is often overlooked. Really frustrating that bike manufacturers to often spec very short headtubes, and then cut the steerer tube with almost no room for spacers. What good does 520mm reach do if you have to hunch over like it’s s triathlon bike? I wonder how their testriders are built.

I do feel any XL bike with a reach less then 505mm isn’t working for people over 6ft2. I’m 6ft3 on a bike with 522mm reach and it’s the first bike I’ve ridden that really fit me. Just because some brand make them that short on XL it doesn’t mean it’s right.
Also stack height is very over looked in these kinds of things and so is chain stay length. If you have a bike with the same chain stay length on the XS across to the XL, that bike is only really designed for the medium rider, as it will ride differently for each height.
Also a small shout out to steepening seat angle for taller heights. All this makes a huge difference.

Definitely read the manufacturers size guidance! I’m 6ft but ride a medium Canyon Lux Trail.

It fits me perfectly and there is no way I thought I’d ever ride a medium!

Interestingly the most critical review of the Lux trail was from a 5ft 10″ guy riding a large frame size…

footflaps

Given you hold onto the handlebars rather than the head tube, surely stem length adjusts the effective reach

Thats a different thing… reach is behind the steerer, stem is in front. Bikes (well, enduro style ones) are meant to be used with short stems, you don’t get the stability benefits by moving your weight out past the axle

Some key bits missing from this article

Stack.

Generally too little on large and xl bikes, hence stacks of spacers and riser bars

Reach, useful to know when out of the saddle, less so for fitting for in saddle use.

Stack hight is often overlooked. Really frustrating that bike manufacturers to often spec very short headtubes, and then cut the steerer tube with almost no room for spacers

This. This. This. It drives me mad. I don’t want my bars level with my ankles

I agree with the above on stack.. Why on L and above is it always so little?

Yep at 6’5″ and not being very bendy a low stack height is a proper arse. You can pop a load of spacers on the fork, but it looks gash.

You can pop a load of spacers on the fork, but it looks gash.

And reduces your effective reach too.

I’m another one on the boundary of M and L on size charts at 5’10” current 2015 stumpy is a M, from looking at the specialized geo charts the difference in reach is 20mm, obviously more current frames are literally multiple inches longer and several degrees slacker for the same equivalent size.

The thing is I only really notice the deficiency on much steeper climbs, the whole back end of the bike is identical same from sizes S to XL it was only the reach, stack and seat tube they bothered to vary from size to size until relatively recently….

And TBH for the faff/cost that it would take to get a longer frame today, in the middle of summer 2022, I’ll tolerate not having the optimal tool for the job. I’m running a 50mm stem I might try a 55 or even a 60mm to sneak a little extra reach even if it is the “wrong” way of doing it. I’ve got longer forks on the way which will no doubt cock the climbing geometry a bit further, but it’s more of a sedate trundle up and plummet type bike than an outright race everywhere sort of rig…

I think people can get a bit caught up agonizing over these sorts of things when most of the time “run what ya bung” is the better mindset…

Ritchie Rude laughs in the face of your recommendations.

And then goes on to win every race he enters on a bike ‘too small’ for him.

As always, intended usage is a key element here. Different requirements for xc bikes when youre mostky in the saddle, than for enduro. Worth bearing in mind that with bikes with steep seat-tubes you can have lots of reach, but a comparatively short effective top-tube, cramping you when in the saddle, especially if you’re tall.

Stack, stack, stack too. Test rode a Bird Aeris 120 a few years back. Loved the ride, but after 90 minuted had the sorest neck I’d ever had.

Length of stem is irrelevant to reach. In terms of handling characteristics the reach measurement should be looked at as a percentage of the bb to bars measurement, in that everything else being equal, a bike with 480mm reach and a 70mm stem will handle very differently to one with 500mm reach and 50mm stem.

Ritchie Rude laughs in the face of your recommendations.

And then goes on to win every race he enters on a bike ‘too small’ for him.

A lot of the EWS racers ride ‘too small’ bikes, however they’re good enough that they don’t need the straight line stability that a bigger bike gives them and they’d rather be able to make time up in the corners. Vastly different skill levels 😁

Effective top tube is an important measurement too, which is affected by both reach and seat angle. 2 bikes with 30mm different reach measurements came have identical ETT thanks to much steeper seat angles.

6’4” and I find out my bike has a reach in the riders under 5’2” category… the only thing long, low and slack round here is my process of evolving beyond the 1990s 🙂

I guess if we’re honest with ourselves, you could ride anything on anything, and ultimately the arbiter of whether your bike geometry is any good is you yourself. So this article could be distilled down to “run what you like” 🙂

But nonetheless, it’s useful to have some ballpark guidance. And really, if your existing bike has short reach and a steep headtube angle, and it’s OK for you, then what the heck, go and ride it and more power to your elbow.

But if you’re in the enviable position of buying a new bike, there’s no real drawback to getting something longer, lower, slacker. I know people talk about bikes making trails dull, but as a noob I’ll take maybe-slightly-duller over will-send-you-otb-like-a-flash-on-anything-steep.

True, but I wonder if some riders will never go fast enough to benefit from that extra stability, but would benefit from more manoeuvrability a smaller bike might offer?

You can pop a load of spacers on the fork, but it looks gash.

And reduces your effective reach too.

This is an underappreciated detail. If you have to put 4″ of spacers under the stem, the effective reach will be much shorter.

I think, in Benji’s defence, he’s not personally attacking anyone for riding an older shorter bike. I used to think anything over a size medium felt hopelessly unwieldy, then I got enough time on newer longer bikes to get used to them, and now when I get back on a shorter bike I feel a lot less comfortable (and I’ve also had some nasty unexpected crashes due to not weighting the front tyre enough).

If you chat to someone like Chris Porter about it, he’ll insist that longer slacker bikes are great for newer or less skilful riders too. I can’t see an argument against that, unless you want to ride skateparks or pump tracks.

Stanton have got the reach wrong on most of their HT’s then. Lots of reach is good for stability but there’s more to riding for me than just speed in a straight line. More than happy with 440 reach at 5ft 9” and I’m all arms.

But if you’re in the enviable position of buying a new bike, there’s no real drawback to getting something longer, lower, slacker. I know people talk about bikes making trails dull, but as a noob I’ll take maybe-slightly-duller over will-send-you-otb-like-a-flash-on-anything-steep.

Bit of hyperbole there. We all rode shorter and steeper bikes until relatively recently. Despite being told that long, low and slack 29ers are great my fastest times on some local segments are from years ago on a 26” wheeled Bfe. Never went OTB on it despite being relatively new to MTB at the time and rode some steep and silly stuff on it.

The advice in the article is great but test riding is key. Not everyone wants long, low, slack. It has definite advantages for sure but it’s got silly with some bikes.

Hardtails are a bit different. The reach increases with fork sag.

Length of stem is irrelevant to reach. In terms of handling characteristics the reach measurement should be looked at as a percentage of the bb to bars measurement, in that everything else being equal, a bike with 480mm reach and a 70mm stem will handle very differently to one with 500mm reach and 50mm stem.

It’s not so much “irrelevant” it’s just that unless you are running a slammed, inline stem the reach figure given on the geo charts is, at best, only an indicator of the assembled bike’s layout. real life “reach”, lets call it horizontal distance from your grip to a perpendicular point inline with the BB is affected by a number of components (bar/stem/fork and of course the frame)…

Geometry charts are lovely, but then you fit some parts, twiddle suspension and hoist your bulk on there and those variables utterly skew all of those numbers, plus every rider will prioritize different aspects if how the bike rides. Treating a manufacturers/journalists spreadsheets like gospel, especially as they’ve added a few chapters to that gospel lately, is kind of laughable, the “rules” are being rewritten on the fly. Which is fine, but it doesn’t make older bikes suddenly unrideable.

So Yes I should more than likely be on a longer frame, I don’t have a spare £1.5k or the inclination to make that happen any time soon. I mostly notice my frame’s short reach on climbs, and I can handle the compromise, it’s not bonkers to adjust contact points in the short to mid term just to try and address how the bike behaves a bit, I doubt I am unique in this…

No mention of dropper length implications of seat tube length?

5ft 6in to 5ft 10in (167cm to 178cm) = 440mm max

At 5ft6, that’d have you with a 100mm dropper.

I think that bikes have actually got bigger over the years, and not just the wheel size and handle bar width.

I used to happily ride medium frames but now feel I need a large.

I do have to cast some critique on the constant mention of ‘longer bikes are better becasue they are more stable’.

This was true a few years ago, when bikes hard short reach, long fork offset and steep head angles. This meant that trail was short (90mm was common), and front center too. So yet, high speed instability was a real issue, as was going over the bars.

But if we are talking about modern bikes (which the article is, since it is about picking a new bike size.

Modern bike with trail figures well over 110mm, and generally long front centers, are plenty stable for most people, even on high speed trails.

Also, since wheel base, front center and trail are already much longer due to the slack head angle alone, there is no need to upsize the reach to get ‘stability’.

You could sooner argue the opposite: to properly ‘Ride’, with a capital R, a longer bike, the cockpit needs to be smaller, in order to allow the larger range of motion required to ride the longer bike.

Recommended reach numbers for rider height:

Under 5ft 2in (157cm) = 410mm to 450mm
5ft 2in to 5ft 6in (157cm to 167cm) = 430mm to 470mm
5ft 6in to 5ft 10in (167cm to 178cm) = 450mm to 490mm
5ft 10in to 6ft 2in (178cm to 188cm) = 470mm to 510mm
6ft 2in or above (188cm+) = 490mm to 530mm

These number do seem quite a bit off to me. Of course, they don’t include stack, but assuming a somewhat common stack for each frame reach, the reach suggested here for short riders is way too long, and for tall riders, a bit too short.

This is generally the problem with frame sizing: the small, and especially the XS, are too long and too tall (stack), the XL is too low and the XXL is too short and too low.

Back to the reach chart:
There is no way a 5’2” rider can get a good fit on a bike with a 450mm reach. There simply aren’t short enough stems to get the grips in a close enough position for true, controlled riding, where the rider manipulates the bike, pushing and pulling the front up and down and sideways.

Stretching high and forward (too tall and too long bike fit), like a baseball player catching a high ball, is a position that makes it virtually impossible to either push or pull on the bars.
If you are a M or L size rider, you can try this out by grabbing a XXL from a friend.

This is compounded when we consider stack. To a certain degree, a long reach can be compensated with a low stack. Except, in realty, small and XS bikes have high stack (relative to seat height), so this is not an option here.

When my daughter was around 5’2”, her bike had a 390mm reach. Combined with a fairly tall stack, it gave an upright fit that allowed her great bike control.
The longest reach I would even consider for someone 5’2” tall would be 410, and even then I would want to carefully fit it before committing to buying.

On the other end of the chart, 490mm reach is pretty short for a 6’2” rider, let alone one taller than that.
Again, 490mm reach might work if the stack was high, and combined with high rise bars, but in reality the stack is low for on these biggest sizes.

Lee McCormack (Leelikesbikes.com), one of the best coaches around, has developed a fit system based on rider control. My experience as a bike fitter is that it ends up a bit on the small side of comfort for most people, but even if you go up a bit from his suggestion, you still end up far shorter (for short people) than the chart above suggests. Short riders need to really watch that their reach is not too long.

Here are two videos showing and explaining this: