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What’s The Best Stem Length For You? | GCN Does Science


– If you have ever thought in the past about stem length on your road bike, it is probably because you’ve been thinking about comfort
and fit on your bike. However, mountain bikers, when they think about the length of their stems, they are thinking more about
the handling of the bike, and the way it feels when they stear. – Yeah, so could we change the
way that our road bikes feel by messing around with stem length? Could we make them more nimble,
more agile, faster even? – We’ve been thinking about this subject because of the current trend
amongst professional cyclists who are trying to get longer
and lower at the front end, in order to become more aerodynamic. The problem with that is that they are choosing frames which are one size smaller than they really should
be riding, and therefore, the reach is too short. And to compensate for this, they are using some humongous stems, sometimes up to 14 or even 15 centimeters long. – 15 centimeters, that’s
like six inches Dan, and that is huge. Surely, that is gonna
make things a little bit difficult in the steering department. Surely they’d be better off
with an 11 centimeter stem, a bit more standard, but even, wouldn’t things
be better with an 8. – Oh. – Should we find out? – Let’s do it. We’ve got a selection of the
new PRO vibe aerodynamic stems to try out on Dan’s bike. First of all, we’ve
got this little stubby, eight centimeter number. We’ve got an 11 centimeter
one already on the bike, and then finally, we’ve got this humongous 14 centimeter stem. – That looks longer than 14
centimeters. That’s six inches. – It does look big, doesn’t it? It depends on where you measure it from. You always go from center to center when you measure the stem. – Slight illusion there. What we are going to do is a little course we’ve set here in suburbia, a little bit like a kid’s day skills course. What we’re gonna do is weave
in and out of these cones, around the round about just
behind you, and back again. At first to see, and
mainly to see, how it feels with the different stem lengths, but we are also going to time it, just to see if there’s any
statistical difference. – And also find out who’s
king of the car park skills. – Me or Dan, bring it on. – Three, two, one, go. Oh, no, he’s 11.98, but
with a 10 second penalty. – Ten second penalty?
No, I’m not having that. Three, two, one, go. I think he’s fluffed it. – Have I? – 11.77. – Three, two, one, go. Whoa, oh looking fast,
looking really fast. 11.17, it’s a PB. – Oh, it is, is it? – Yeah. Three, two, one, go. 12.14. – Whoa. – The reason that we think
there might be a difference is that stem length
affects the steering arc. The shorter the stem,
the less you will need to move your hands in order to
turn the wheel a set amount. That’s one reason why mountain
bikers prefer short stems, better for weaving around trees. Now, stem length isn’t the
only thing governing handling. The head angle and the trail of the bike give built in handling traits, like the DNA of the bike. But changing stems can
have a huge difference. What happens, then, on
the slow speed test? – The results are in, Si,
and what I can tell you is that basically, we
got better as we went on, with practice. We were both quickest on
the 8 centimeter at the end. And I also have to tell
you, unfortunately, you were better on every single run. I’m devastated. – I don’t feel so bad about
the rubbish results, then. Okay, given that practice
clearly makes perfect, can we infer anything from the feel? Did it feel different? – Well, I was expecting
a much bigger difference in feel between the stems,
because there’s quite a big difference between 14 and
8, but actually, what I felt was that I was just comfortable
in the 14 centimeter, ’cause that’s closest to
my normal riding position. – Yeah, well I definitely
felt that the 8 centimeter was easier to weave through the cones then weirdly, it was actually harder to get around the bottom corner, so I feel that maybe we need to move from this kind of artificial challenge to a real world challenge, cause, how many Tour de France stages will have
riders weaving through cones and then chuck in a u-turn in a road? – That is true. There’s the occasional dog runs out into the peloton, isn’t there, and sometimes you have
to weave around a couple of spectators to get to the
sign on, but I take your point. Descending challenge, you think? – Descending challenge. – Real world. – You know, it does feel twitchy. My god. – Aaa. – It’s responsive. Maybe a bit too responsive.
I’m not sure I like that. – And go. – That feels better, heaps better. – Wow, that made a heck of a difference. Just a totally different
animal down there. That’s the kind of bike
that I know and love. Size matters, clearly,
when you’re going fast. Those of you that are familiar with the new PRO vibe handlebar and stem will note that we’re not exactly getting the most out of its aerodynamic properties, and that’s because we’re still running this external DI2 junction box,
whereas, we should really be using a hidden junction box in the end of the handlebar there, ’cause all the cables can route internally, through the bars and
out at this point here, into the stem and then out of the stem through that hole at the back, then actually down into the steerer tube, completely hidden away. Three, two, one, go. Wow,
rolling out the big guns. – Whoa, well I’ll tell you what, the difference between
this and the 11, is nowhere near as
big as the 11 and the 8, but it does feel, it feels really stable, and particularly interesting, it feels really good around corners, like the bike just wants to rail. That has surprised me a lot. Dan, I’ve got some results. – Go ahead. – It’s highly traffic dependent. – Yeah. Yeah, I thought so. My last run was easily the fastest, because I wasn’t held up by
multiple cars and a tractor. – Well, you’ll also be pleased to know that you have the fastest of the day. – Oh, yes. – So I may be car park king, but you are downhill demon. – That is good to hear. In terms of how it felt
down the descent, though, I was really at home on this one. I realized when I was going down the hill that you don’t turn the bars much at all you’re literally
banking around the corners. Having that long stem
where it’s slightly harder to turn the bars actually made
me feel a lot more stable. I was carving and flowing
through those corners. – Carving and flowing. Well, in contrast, the 80 mm
stem was utterly terrifying from the moment I set
off and got above 20 mph, it felt way, way too twitchy, and really not good through corners at all, and then I suppose the 110
was the Goldilocks, really. It didn’t feel quite as stable, but then, it just felt right. – Yeah, I was happy enough on the 110. I think one thing we
should mention, though, is that in our pro days,
can we mention that? We were trying to get long
and low and aerodynamic, and so quite often we
favored the long stems, and so that is something
we’ve been used to for many, many years, isn’t it? – Well, it is, but I have, since
retiring and getting older, gone shorter, so I now use a 110 mm stem. But it did feel good, nevertheless, going back onto a longer stem. Should you go and buy a longer stem, then, to mimic these results? I don’t think you should,
given that, actually, bike fit would probably
be the determining factor. But don’t be put off by experimenting with a longer stem, I
think, bikes feel good. – Now before we conducted our very own stem length experiment, we did consult with bike design guru, Tom Sturdy, who typically has already done quite a lot of experimenting himself. And what he has found
is that you’re probably not going to be able to
find much of a difference between a long bike with a short stem versus a shorter bike with a long stem. But he does say that that
choice is very important for shorter riders due to
the limit of wheel sizes. If you are a shorter
rider, you really want to go for a longer frame
with a shorter stem. – Yeah, and then in order
to offset that twitchiness that we’ve just been
experiencing, you then hope that the actual geometry of the bike, like you talked about, the DNA of it, would actually mean that it
had more inbuilt stability. But then, thinking about
that point, actually, although stem length doesn’t
have much of an effect on the way it rides, actually,
in order to feel the bike as it was designed to be felt, you should probably use
it with the stem length that it was specced with, I guess, as the designer intended. – Yeah, it does start to get
a bit complicated, doesn’t it? But you can rest assured
that there is a good reason why bike geometry has
remained pretty much the same for decades. – Right then. I guess all we can ask at this point is for you to subscribe to GCN. To do that, just click on the globe. And if you’d like to watch
a couple more videos, Matt did a great video
where he asked the pros why they slam their stems,
that’s just down there. – Yeah, or a few years ago, Si had a look into how you set your bike and stem up, and you can find that
video just down here. – A few years ago. It goes back a bit now. – Yeah, you looked really young.

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