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Cycling culture is full of little idiosyncrasies. Some of them we love and respect, like the fact that a water bottle is a water bottle in all walks of life except when on a bicycle. Others can be infuriating – like the inconsistencies within geometry charts.
The geometry of a bike is hugely important when it comes to selection. Geometry creates personality - making the bike either more fast and flicky, or comfortable and stable.
The geometry of a bike is hugely important when it comes to selection. Geometry creates personality - making the bike either more fast and flicky, or comfortable and stable.
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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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