In recent years bike geometry has become a big talking point among riders.
Longer reach, slacker head-angle, steeper seat tube, longer wheel base and the perpetual argument about if chainstays should be growing or shrinking. These are but a few of the aspects that make-up a good balanced frame design. But the numbers tend to be discussed in isolation from one another by riders when contrasting and comparing geometry tables. That being said, the more experienced (generally speaking) a rider is, the more of the geo-chart they take into account when making bike choices. However, the conversation rarely expands into how one element affects the other, and that is truly the crux of the matter.
But regardless of how informed the general biking public is to the finer points of frame design, the trend is that geometry is getting slacker, longer and lower.
The first thing we have to accept, is that there is no single magic set of numbers, no magic bullet, there is no such thing as “perfect geometry“. Geometry gives a set of characteristics and a certain feel to a frame (not withstanding the suspension platform if applicable). It will bias a frame to be better suited for certain types of riding and certain types of terrain. Whilst sharing the share same DNA, we can all agree that XC race bikes are different from DH rigs.
Whilst the “Enduro Bike” did start life as a beefed up trail bike, it has become a identifiable niche within the market and one where geometry is arguably, king.
It is also a perfect balancing act, If you change one thing you have to change it all, you cannot simple extend one aspect in isolation. A bike designer once described it to me as spinning plates.
For example if you extend the top tube and thus the reach, that will move the riders weight forwards and this may imbalance the ride. So a designer may choose to shorten the chainstays to account for that shift in the riders weight. If they don’t, then the back end may become unweighted more easily and be prone to breaking traction.
Now if we take the view that the best riding position is central on the bike (and ignore the impact differing wheel sizes have to the equation). Then we can make some objective observations on how frame geometry has evolved over the last 10 or so years.
To illustrate this, I will track the evolution of a fairly critical and influential bike, the Specialized Enduro. Whilst the “Enduro Bike” did start life as a beefed up trail bike, it has become a identifiable niche within the market and one where geometry is arguably, king.
But I thought the top tube and thus the reach, was meant to be getting longer as well?
Now lets have a look at some key figures, the headliners if you will.
- Head Angle
- Top Tube Length
- Wheel Base
- Chainstay length
The trend has been for the head angle to slacken, the wheel base and reach to grow and the chainstays to be kept as short (or as static) as possible.
|year||Head Angle||Top Tube Length||Wheel Base||Chainstay Length|
|2005||68º||623 mm||1156 mm||424 mm|
|2009||67°||620 mm||1177 mm||421 mm|
|2010||66.5°||620 mm||1185 mm||419 mm|
|2014||66.5°||617 mm||1183 mm||419 mm|
|2017||65.5°||604 mm||1201 mm||425 mm|
All of these sizes are taken from large size frames.
So whats actually going on here?
The head angle is consistently getting slacker and the wheelbase is getting incrementally longer. But I thought the top tube and thus the reach, was meant to be getting longer as well?
The wheelbase is being extended in two ways, by throwing the front wheel forwards from slackening the HA and latterly by extending the chainstays. But if we look closely, the reach is actually contracting, in a size large, it shrinks 7mm from 2010 to the current year model.
Specialized has a secret sauce in the Enduro, and people like it.
But if longer and slacker leads to a more stable and therefore, faster platform then why are the big S shrinking the reach of their race happy Enduro? Why not go all in and extend the top tube and the reach aswell? In my mind it comes down to two things, the elusive “ride feel” and the rider that they are selling this bike to.
Geometry gives a certain feel, some riders prefer a bike that is not to long as a shorter bike feels more “playful“. Specialized has a secret sauce in the Enduro, and people like it. They don’t want to move the position of the riders weight on the bike as that will change that feel. But riders have also drunk deep of the Enduro cool aid, so Spesh needs to not only make a bike that still feels like an Enduro, but also appears to be following the trend of longer slacker bikes being better without changing the taste of the secret sauce.
The second point that I feel is pertinent is the market that they are selling the bike to, or more accurately how broad that spectrum of riders is. A bike that is genuinely longer and slacker, regardless of what the chainstays or top tube are doing on paper, will appear to be very different to what has gone before. It will also feel different, and that will put some riders off.
Now there is no getting around it, if you are designing a race specific bike that is built around 160mm of travel, then you will probably come up with some more aggressive numbers than what the Enduro has. But the vast majority of riders don’t need a race specific bike, they would find it harsh and beyond what they were used to. So when your objective is to sell as many bikes as possible, which approach do you take?
Now this is by no means an attack on the abilities of this very capable bike or the riders who choose them. Change is generally slow and usually has interim steps, hybrids before full electric cars for example.
but when looking at geo tables and comparing bikes that are on the market, maybe compare them to previous iterations as well, to get a sense of how a frame has been evolving to see whether it is indeed the frame for you.