- 1 week ago
Unlock the secrets of bicycle geometry to find your perfect ride. This guide explains the key metrics you need to understand, such as stack and reach, to compare different bikes and choose one that perfectly matches your riding style and body.
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00:02now the geometry of a bicycle is incredibly important and it's something to study really
00:08carefully if you're thinking about buying a new bike geometry very much defines the
00:13personality of a bicycle whether it's fast and flicky and nimble or if it's stable and
00:19feels particularly comfortable at lower speeds the problem is that different brands provide
00:24different lists of numbers so for example giant might provide one list of numbers and
00:29specialized might provide another and they might not be directly comparable unless you're looking
00:34at exactly the right metrics we're going to look at the important metrics that you need to look at
00:39if you are thinking of buying a new bike so before we go into the details of geometry just going
00:46to
00:46spend a second focusing on the difference between geometry for handling and geometry for fit now if
00:52you're buying a new bicycle first you need to look at the geometry for handling because you want to
00:57determine if this is the right bike for you the numbers you're going to look at are stack and reach
01:02wheelbase relationship between the front center and the rear center particularly the chain stays also the
01:08head angle and trail we're going to look at all of those in this video so once you've chosen a
01:14bike
01:14based on handling then you're going to look at a bike based on fit but the two really do need
01:19to
01:19interact be honest with yourself about the kind of rider you really are about your strength about
01:25your flexibility and the sort of speed you're going to be riding on as well as the kind of roads
01:29you're
01:29going to be riding on now if you are comparing a bike that you currently have with a bike you
01:34are
01:34considering buying there are some really really useful websites out there it says geometrygeeks and
01:40bikeinsights.com both of those include huge databases of various different bicycles and have
01:47all the geometry details so you can compare different bikes
01:56so stack and reach is relatively new in terms of bike geometry charts however there's a very very good
02:03reason for its emergence in the past brands would use top tube and head tube as a marker of how
02:10aggressive
02:10so long and low or relaxed high and short a bicycle was the problem with these metrics is that top
02:19tube
02:19could be measured from various different points you could have effective top tube or centered center top
02:24tube or actual top tube and it was never entirely clear which brand was using which metric which made
02:30them not very comparable the problem with head tube is that fork lengths now vary quite a lot in part
02:37because of
02:37the emergence of disc brakes and also tire clearance as well so neither of those metrics were actually
02:43particularly useful for customers so now we use stack and reach so in order to explain this i'm going to
02:50need the post-production guys to draw some fancy lines on a bicycle stack is the vertical distance from the
02:55center of the bottom bracket to the central point at the top of the head tube reach is the horizontal
03:01distance from the center of the bottom bracket to the middle of the head tube so a long reach and
03:07a short
03:07stack will put a rider in a position that feels aggressive and fast they'll also be more aerodynamic
03:13which is why it's often favored by racers of course in order to maintain that position you need to know
03:18that you
03:19have the flexibility and the strength to stay there without getting injured a shorter reach and a higher stack
03:25will feel much more comfortable and will suit riders that are going to be out all day riding usually at
03:30slightly slower speeds
03:32for example a 56 centimeter specialized tarmac has a stack of 555 millimeters and a reach of 398 millimeters
03:40versus a 56 centimeter specialized roubaix at 611 millimeter stack and a 381 millimeter reach those are quite
03:48notable differences so some people like to use stack and reach ratio which is stack divided by reach as a
03:56rule of
03:57thumb a lower number is going to be more aggressive and a higher number is going to be more relaxed
04:02and
04:02comfortable it sounds perfect right but there are caveats to bear in mind stack and reach does not take
04:09into account various different components on the bicycle for example the stem length and also handlebar reach
04:16a very good example of this is the difference between a canyon air road and a trek madone in h1
04:21.5 fit
04:22the air road in a large comes with a reach of 403 millimeters versus the madone's 391 millimeters in a56
04:30however the madone uses a much longer reach handlebar and that is a factor that would not be immediately
04:36obvious from the geometry chart you can often see the handlebars reach if you actually go to the spec
04:42sheet for that particular component alternatively at that point you are looking at speaking to bike
04:47fitters or also calling in a test bike which is something i always always recommend if you're
04:52really looking seriously at investing in a new bike so thankfully some brands are actually starting to
04:57take this into account for example canyon has started listing stack plus and reach plus and that does take
05:04into account the stem and also handlebar reach do remember though that you need to look at the bike in
05:09your specific size that is because at times bike designers will make the bike more or less aggressive in
05:16smaller or larger sizes using the middle size as a median or average this is often a cross-cutting
05:23method because it allows them to use the same mold for various parts of the frame across different sizes
05:29so one final thing that you should also bear in mind is that stack and reach does not take into
05:33account the effect of spacers so if you are running all the spacers below your handlebar it will bring
05:39the stack up and it will also bring the reach very slightly back because of course you've got a diagonal
05:44line here
05:51for offset sometimes called rake trail and head angle are intrinsically intertwined it's quite
05:58impossible to look at one without looking at the others so head angle is the angle at which a line
06:04would travel through the head tube to the steering axis to hit the floor steeper head angles will handle
06:10more quickly it'll take less input from the rider in order to get that bicycle to turn quickly however
06:17they can feel a little bit twitchy at slower speeds whereas a slacker head angle will feel a little bit
06:24less nippy and a little bit less twitchy when traveling at fast speeds but will feel more stable at slower
06:30speeds so this is a really interesting one to look at when we're talking about the new crop of gravel
06:36bikes
06:36because it will really show you whether this bike is tending towards the mountain bike end of the
06:42spectrum or more towards the road bike end of the spectrum so the very perfect example of that is the
06:48evil chamois hagger which has a head angle of 66.67 degrees that is really really slack and it's very
06:57much
06:57in the arena of mountain bikes now on most road bikes we would generally see a head angle of around
07:0470 to
07:0571 degrees as being quite relaxed and more in tune with a sportive or endurance bike whereas 72 to 73
07:13degrees is something that you would see on a race bike those sound like really small differences but
07:19they're definitely not and they do make an incredibly big difference to the way a bike rides and handles
07:25there is a caveat to this in that in very small bikes sometimes we see the head angle becoming slacker
07:30in order to prevent toe overlap simply because the wheels are very large on the frame size brands
07:37have gone some way to counteract that as an example canyon releases its much smaller women's bikes with
07:43650b wheels so offset or rake is how far the front axle is offset from the steering axis imagine a
07:52straight line
07:53from the center of the steerer tube to the ground it's the gap between that and the front axle
07:58trail is the distance between the tire's contact patch with the ground and where the head angle
08:03hits the floor it's a product of the offset and head angle so a short trail number is going to
08:09involve a steeper head angle and less rake whereas a larger trail number is going to involve a slacker head
08:17angle and more rake so as a rule around 55 to 59 millimeters is the the kind of trail that
08:24you would see
08:24on a fast quick handling bike whereas 60 millimeters plus is more what you would expect from an endurance
08:30bicycle so as an example trexamonda in a size 56 has a trail of 58 millimeters and a head angle
08:38of 73.5
08:40degrees and that of course is a fast handling race bike comparatively the demane has a trail of 61
08:47millimeters and a head angle of 71.9 degrees and that is very much an endurance bike another one to
08:55bear in mind is also seat tube angle now in most road bikes this will vary between 72 to 74
09:02degrees and
09:03it generally remains fairly consistent across the sizes this can actually represent a problem for taller
09:09riders because the seat tube is longer it means that the saddle is pushed further back of course you can
09:16push
09:16forward on its rails but it can only go so far this can be counteracted with an inline seat post
09:23and
09:23that can help to get the saddle further forward however it'll only take you so far so if you want
09:30to understand what kind of effect that seat angle has it's worth having a look at the tt bikes you
09:35get
09:35on the market so both the specialized shiv and the giant trinity have a seat angle of 77 degrees that
09:41is
09:42much much steeper and it will put the rider much further forward up and over the bottom bracket
09:46allowing them to get that fast flat back aerodynamic position and really to push the power through the
09:52pedals
09:59wheelbase is another marker of how quick-footed or stable a bike will feel a longer wheelbase has a
10:06larger turning circle whereas a shorter wheelbase has a shorter turning circle wheelbase can be
10:12divided into front center the difference between the center of the bottom bracket and the front axle
10:17and rear center the distance between the center of the bottom bracket and the rear axle unfortunately
10:24not all bike brands do list this however they do generally list chainstay length which will of course
10:30give you a pretty good idea of rear center so in both those cases a longer number so a longer
10:37front
10:37center and a longer rear center will feel more stable at slower speeds whereas a shorter front center
10:44and rear center or chainstay length will feel much more nippy if you're riding at faster speeds
10:50of course the chainstays or rear center do need to be long enough to accommodate different tires
10:56which is why often on gravel bikes as well as them providing more stability we also see longer rear
11:02ends because this does allow for more tire clearance however there are some caveats to that so as an
11:09example a specialized diverge has shorter chainstays because it helps get the riders weight up and over
11:15when they're scrambling up those really kind of short steep climbs you find off-road so in the past
11:21disc brakes have interfered with this status quo that's not the case anymore group sets have changed
11:27so we don't need longer chainstays to account for disc brakes and we do see that in newer bikes as
11:33an
11:34example newest iteration of the canyon aeroad had shorter chainstays again which allowed it to keep its
11:40intended personality so last but not least is bottom bracket drop this is how far the bb drops from the
11:54two wheel axles you can also look at bottom bracket height which is the bb height from the floor however
12:02this is influenced by tire volume so i tend not to focus on it quite as much so a larger
12:08bb drop lowers the
12:10rider's center of gravity it's something you would still want on a fast handling crit race bike
12:15because you are going to be leaning hard into those corners and you want a low center of gravity
12:20the problem is if you go too low and you've got problems with pedal strike when you are leaning over
12:26into the bends and pedal strike can have some pretty nasty consequences i can tell you
12:34it's also a key measure that we look at when we're looking at off-road bikes because of course
12:39pedal strike and also clearance is something that becomes really really important so using specialized
12:45as an example a 56 centimeter specialized tarmac has a bb drop of 72 millimeters versus 76 millimeters
12:54on the specialized roubaix however on the cyclocross bike in the same size so still a 56 centimeter frame
13:01it's 69 millimeters on the crux cross bike however on the diverge it's 80 millimeters and that is a really
13:09really big difference it's going to make the diverge feel an awful awful lot more stable on gravel terrain
13:16however it gives you a lot less clearance whereas the cyclocross bike is much more tailored to that
13:21really thick mud and obstacles that you might find on a cyclocross course
13:27so there you have it i've tried to cover off the key metrics that you need to look at when
13:32you are
13:32considering buying a new bike in short if you're after a fast aggressive bike then look for a long
13:40reach a short stack a steep head angle and a shorter trail number alternatively if you after a comfortable
13:46ride in a more endurance position for those long days out in the saddle then look for a bike with
13:52a
13:52shorter reach a higher stack a slacker head angle and a longer trail number comparison sites are your
14:00friend compare bikes that you know that you like the handling of and new perspective bikes because they
14:06are kept they can be really really useful i hope you've enjoyed this video if you have hit like and
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