Downhill bike Sizing

Chris Porter explains why he thinks mountain cycle developers are receiving it all incorrect.

Hill bicycle size is trapped inside rock Age, and I think it’s as a result of our shaven-legged, tarmac-riding compadres.

I’ve never really had a hill cycle which includes certainly fitted me until I got certainly one of Mondraker’s first ahead Geometry frames. With that cycle i really could eventually operate a quick stem, to obtain steering accuracy, but nevertheless have sufficient size in top pipe and wheelbase. My knowledge about this initial Foxy XR has sent me down a path of development, and I’ve yet to find its end – I’ve since made a much longer customized framework therefore’s however not too-big.

Fitting an extended stem is NOT the same as making the frame larger – there’s some guidance toward hill bike business… free-of-charge!

In several ways it appears as though the mountain bike has actually evolved along similar outlines to an off road motorcycle; suspension system, braking and tyre technology have actually much in common. But it’s additionally clear that stem lengths and sizing conventions have actually developed from roadway bikes. The issue is, mountain cycling has a totally different group of concerns.

Road to perdition

On a road bike, the seated pedalling place is crucial. Standing just becomes a problem when climbing (you won’t see many bikers descending out of the seat). I’ve also heard it said (and once again I’m not a professional, nor do I want to be) that smaller the wheelbase the greater a slipstream you could get through the driver ahead, because you can virtually get closer without humming tyres. The fact that the stem and handlebar is sticking way out across front side axle whenever standing climbing on a road cycle is not any huge price. it is additionally why it's crucial that you remain seated when descending on a road bike to keep the weight behind the front axle as much as possible.

So road bicycles are made to pedal really and draft really, however they are perhaps not designed with excellent control performance at heart. I’d go as far as to state the maneuvering of a road bicycle is truly terrible consequently plus the quick wheelbase and long stem has to take a number of the obligation for the. Although it is a long time since I have ridden a suitable road bike, the UCI has actually restricted geometry and stifled development, so I the stand by position the declaration.

Half human vs full human

One area where road bikes nonetheless shape mountain bicycle size is seat pipe size. Think about this; the chair pipe measurement relates to your saddle level, and therefore your seated riding place and interior leg length. That’s about 50 % your overall level, or, when I like to think about it, the ‘half human’ measurement. The top tube and down pipe length comes into play when you stand-up – in order that’s your top and low body, or ‘full human’ dimension. Why can it be that seat pipes grow by 25-40mm between sizes, yet top tubes lengthen by 10-20mm? Clearly it should be another method round?

The standing relationship amongst the handlebars and cranks is vitally important in terms of getting around on a mountain bicycle, so it's crucial to every part of managing. Because we stand up to descend, and possibly handle steep, technical mountains, having an extended stem hanging on the axle isn't any longer a benefit. Indeed, it becomes a fricking responsibility! Call me personally cynical, but I suspect a lengthier stem is cheaper and simpler to fabricate than a lengthier frame. Can it be that shorter structures take up less room in a container? We question how much which could save your self multiplied some thousand times? Hmm…

If you’re tall, your options tend to be limited. You can hunch your self up-and exposure a huge chiropractor costs, or evolve withered arms, like a Tyrannosaurus Rex. The fact is, some makers remain trying to make their particular larger bicycles fit by bunging on a lengthier stem. Argghhh! How come the seat pipe lengths have to transform a great deal? Can’t we just stretch the chair post? If I lifted the dropper post in my XL framework into the minimum insertion marker it would fit a 10-foot monster!

Today for the research…

To illustrate this time, I did some measuring. Joe Taylor is one of the specialists here at Mojo. He’s won some Gravity Enduros into the senior group and is 5ft 6in tall (1, 676mm). Joe’s seat rails-to-crank-centre measurement is 665mm and his crank-centre-to-handlebar-end measurement is 850mm.

Im 6ft 1in (1, 854mm), my chair rails-to-crank-centre dimension is 720mm and my crank-centre-to-handlebar-end measurement is 915mm. For both folks, our general height is 2.5 times the exact distance between our cranks and our seat and two times the length from cranks to taverns.

A 125mm Fox DOSS dropper post has actually 93mm of level adjustment in the framework. Enough, multiplied by 2.5, to accommodate riders with a 232mm (9in) variation in height! On the same medium frame!

Taking place our earlier measurements, that 232mm height variation would need 115mm of extra length from shortest into the tallest rider. Because 50mm is approximately the shortest generally offered stem, you’d be viewing a 165mm stem in order to avoid the tallest driver becoming bent double.

Definitely, there’s a flipside to any or all this. Joe could easily get on my XL Mondraker Dune XR (presently one of many largest hill bikes worldwide), run an ordinary seatpost, a 10mm stem and a low-rise bar and end up in precisely the right place. An XL! He’s 5 ft 6in!