E Bike Geometry Explained | How E-MTB Dimensions Affect Your Ride

E Bike Geometry Explained | How E-MTB Dimensions Affect Your Ride


– Hi guys, today we’re gonna be looking at some basic ebike geometry
and how that’s critical whether you’re on or off
the bike and how it impacts whether you’re actually
setting your bike up or indeed riding it out on the trails. (digital beeping) Now first up I wanna point out that there’s geometry which is fixed and there’s geometry which is adjustable. You could I suppose compare
it to the size of your bike which is fixed, you can’t move on that, or the fit of your bike
which is adjustable. For example, this distance
here between the head tube and the top of the seat tube. Now as you can see the frame dimension, that is fixed, you can’t change that, however the fit of the
bike can be affected by you moving your seat
forwards and backwards or indeed putin’ a longer
or shorter stem up front. (upbeat music) Now the first geometry measurement I’m going to discuss is reach. Now this is measured from
the center of the head tube for a line that goes across and intersects with a line
which comes vertically up from the bottom bracket. So basically it’s that measurement there. And all these measurements can be found on each manufacturers website. Okay, so why is reach so important? Well it’s actually quite
a good indicator of size and it’s usually quite
consistent amongst brands however there are some manufacturers who do tend to measure
differently on occasions. Now when it comes to
numbers my reach measurement is usually about 485
and I’m six foot tall. So for example if you’re five foot 10 then I think you need to be
looking at a number about 20 millimeters less whereas
if you’re over six foot maybe a reach measurement
of 20 millimeters more. Now what I want to point out is that if for example you’re in a bike shop and you’ve got a sales guy
who’s trying to sell you a bike with a reach
measurement of 440 millimeters and you’re six foot tall then maybe the alarm bells should start ringing. You know, reach really does have an impact when you’re out on the trail because if you have a bike
and it’s too small for you with a small reach then
you’ll constantly be thrown forwards or rearwards on the bike trying to overcompensate for that bike which is too small for you. And what that leads to is a lot of fatigue as you’re moving forwards
and rearwards on the bike. Remember that reach-in itself
cannot be viewed in isolation because it too is impacted by such things as the bottom bracket type which is gonna push your
weight up in the air or a stem which is gonna push you too far forwards or too far back. But reach, when it
comes to a balanced ride it really is quite critical. (upbeat music) The top tube is a
frequently quoted dimension on every mountain bike and of course, as I mentioned earlier,
it is fixed on every bike. However I think on an e-bike
a more important dimension is actually the bar to the seat because that’s going to
affect your climbing ability and your comfort on your ebike. Now the bar to seat measurement
is affected by many things, first of all the seat tube angle, secondly where the seat is in its rails, the length of your stem, and the shape and height
of your handlebars. Now remember, on an ebike
it’s really important to be able to get that
traction onto that rear tire which means you’re
gonna be shifting around in the cockpit area of
your bike a lot more than you will be on a non ebike. (upbeat music} Chainstay is a dimension which is fixed on most mountain bikes although
there are some on the market where you can adjust that on the rear axle and the dimension’s actually
measured from the center of the bottom bracket to
the center of the rear axle. So why is it important? Well, it affects climbing
quite considerably because longer chainstays, say from around 470 to 480 millimeters, put more of a bias on
the front of the bike whereas shorter chainstays
create a more snappy ride, that bike really does heel into the corner much more quickly. That’s not to say you can’t
learn to corner quickly on a bike with longer chainstays, it’s just about adaption. Now what you really need to be aware of is if you do have a bike
with super short chainstays then that’s going to bias your weight quite a lot of rearwards,
you need to counter that by leaning slightly further forwards or moving your body onto
the front of the seat more when you tackle in those hill climbs. Now as you can see
there’s a huge difference in each brands philosophy when
it comes to chainstay length. Have a look at that 426
millimeter dimension on the Rocky Mountain compared
to the 490 millimeters on the Mondraker Level,
these are huge differences and they will affect handling both uphill and downhill on the bike. Now as with any other
dimension on your mountain bike don’t forget that a chainstay alone cannot be measured in isolation because if you have a long chainstay then that needs to be balanced out with a long front center. Now the front center is the measurement from the bottom bracket to
the front axle on the bike so if you’ve got, as I say,
a long chainstay on the bike you need to have a long front center to balance that bike out so
your body’s in that sweet spot. (upbeat music) Bottom brackets, do you know what? It’s my favorite dimension
on any mountain bike. Now that is measured from the
center of the bottom bracket to the ground, although
a lot of manufacturers actually measure it, if
you have a line drawn from the front axle to the rear axle, it’s actually how much lower the bottom rack bracket is off that line. Now most of the time it’s
a negative measurement which means it’s underneath
that line from axle to axle. Why is it important? Because it really does affect
the handling of the bike, particularly in corners. It’s also affected by such
things as the style of bike, the wheel size, and the
amount travel on the bike. Now what about the numbers? Well if I’m riding a bike
which is 150 to 170 mil travel I’m looking at about
340 to 350 millimeters on the bottom bracket because that keeps my center of gravity low and when it comes to cornering it really get into those
corners so much more easier than a bike with a high bottom bracket which actually tends to stand the bike up and not corner quite as easily. Bottom bracket is both affected
by and affects many things. Remember, these are static numbers. The numbers when you’re sat on the bike will be affected by the sag of the bike and the suspension design, which will affect the bike
when you are riding it. For example, soft suspension
will lower that bottom bracket while hard suspension will
keep it in a high ride height. And don’t forget, progressive suspension and linear style suspension designs will affect that bottom
bracket height too. (upbeat music) The head angle really is a measurement which has settled down
in the last 10 years. If you’ve got a bike which
is 150 to 170 mil travel it tends to be around
about 64 to 66 degrees. And what that does is
provide a really stable bike when you descending because if you’ve got a head angle
in the 68, 69 degree ballpark then that does tend to skew the weight slightly further forward. It also provides a more
twitchy ride to the bike whereas a bike with a
64 to 65 heading angle is far more settled on those descents. When it comes to the adjustment and you can actually adjust
the head angle on some bikes by way of an angle set in the head tube. Remember, on other bikes such as this, the Canyon Spectral:On,
the head angle measurement is going to be changed if you change the geometry of the bike as there’s like that little chip there which
lowers the bottom bracket so that is gonna slacken
out that head angle. (upbeat music) Wheelbase is the measurement from the rear axle to the front axle. But remember, it’s all
about the proportions. You know, between the chainstay length and the front center length
because what you’re trying to do is get that sweet spot
in the middle of the bike where you don’t have to overcompensate both forwards or rearwards. Now, long wheelbase bikes
are amazing on descents, they really do provide
a really stable ride. However, when it comes to flatter terrain when you’re trying to pick
the bike up and move it around it can sometimes be a little bit boring. In terms of wheelbase numbers they are massively different
from brand to brand and as I mentioned, it’s
affected by such things as the chainstay, the front
center, and the head tube angle. So I won’t really give you a sweet spot because it really depends on
the style of riding you do. For example, some people who
ride 170 mil travel bikes tend to do more downhill
or intended riding whereas others do more enduro style riding so it really is up to you to work out the sweet spot of wheelbase on your bike. Those then are my
critical geometry figures which you need to be aware of both when you’re in the workshop or when you’re out and about on the trail. I suppose I could have thrown in the seat tube angle on the bike but that doesn’t seem to have
settled down in recent years between 74 and 75 degrees and that gives a good balanced position where you can climb or
descend really effectively. Remember, of course, it all depends where that seat is up or down,
actually, do you know what, if you want to look at a
video which is more dynamic in terms of the use of geometry check out the video which
myself and Chris did on seat up or seat down. Hope you like this video, let us know your comments on geometry, on any questions you
might have on geometry in the comments below and that’s about it. Don’t forget to click on
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