Bicycle geometry is a fancy topic. Like utilized arithmetic, it entails numbers and angles, however not like that self-discipline, there isn’t all the time one single reply. Generally, there’s room for interpretation. Particular outcomes can typically be achieved in a number of methods, and totally different philosophies prioritise totally different features of geometry design. Nobody angle or quantity can definitively describe a bicycle’s traits—it’s the sum of the elements that decide how a motorcycle rides.
A geometry sheet comprises a bafflingly extensive number of data, which might appear daunting. How precisely do the numbers on the web page translate to the bike you’re using round on? Loads of riders have little interest in this stage of granular element, and that’s high-quality. It’s not essential to be literate in trivialities to take pleasure in pedalling a motorcycle. However these measurements don’t should be a thriller both.
I’m not going to delve into everything of motorcycle geometry right here, however I’m going to take a look at how the entrance finish (the a part of the bicycle that does the steering) works a bit. The important thing takeaways listed here are that small modifications can have huge results, and nothing may be examined in isolation: it’s all related.
What’s the head tube angle?
(Picture credit score: Pinarello)
How a motorcycle handles is essentially determined by how the body works in live performance with the design of the fork. The primary piece of that is the pinnacle tube angle. Head tube angle is greatest envisioned as an imaginary line that runs by means of the centre of the pinnacle tube, in profile. That is the place round which the fork’s steerer tube rotates and is named the steering axis. Usually talking, a steeper angle (nearer to 90 levels or vertical) will really feel extra responsive however twitchier, whereas a slacker angle might be extra steady at decrease speeds however really feel correspondingly sluggish in its reactions to inputs.
What’s bike frames fork offset (or rake) and path?
(Picture credit score: Josh Ross)
The subsequent piece of the puzzle known as fork offset. Fork offset, also referred to as rake, is the quantity wherein the fork is offset from the steering axis. In different phrases, how far the axle sits in entrance of the imaginary head tube line.
With these two components, along with wheel and tyre measurement, you possibly can decide a bicycle’s path determine. That is the gap between the centerline of the steering axis and the centre of the place the tire hits the bottom. A racier, efficiency bike will sometimes have much less path than a extra endurance-oriented design. Highway bikes often keep inside a reasonably tight vary, however gravel bikes can be found from road-esque path figures all the way in which to full-on mountain bike numbers. Clearly, bikes at both finish of this spectrum really feel very totally different when ridden and arguably shouldn’t even be thought-about a part of the identical class.
The complicated factor about all of that is that two bikes can have the identical path quantity however deal with very in another way by utilizing totally different head angles and fork offsets. These variables may be manipulated for various outcomes, resembling decreasing toe overlap or optimising dealing with for various tire sizes. Every method modifications how the bike steers and the rider’s weight distribution over the entrance wheel. Bike designers have to account for all of those elements, as altering one facet will have an effect on the others.
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Do tyres have an effect on how my bike handles?
(Picture credit score: Future / Tom Davidson)
Path isn’t the one factor to consider when speaking about how a motorcycle handles both; additionally it is affected by tyre measurement too, by means of what’s known as pneumatic path. Put merely, a bigger tyre will make extra contact with the bottom, which implies it takes extra effort to make it flip. Wider tyres, particularly at decrease pressures, will make a motorcycle really feel extra steady whereas using, and thus path figures on these bikes are sometimes adjusted to compensate.
For those who want to change the dealing with traits of your bicycle, altering your tyre measurement is an efficient place to start out. Narrower tyres will make it really feel extra skittish, whereas wider tyres will gradual issues down.
What about stem size and handlebar width?
(Picture credit score: Future (Andy Jones))
Yet one more a part of this dialogue is the affect of stem size and handlebar width, which additionally have an effect on dealing with. Longer stems decelerate dealing with, since actions equate to a smaller quantity of the fork turning; ditto for wider bars. There are further elements of bicycle geometry to contemplate, resembling backside bracket peak, however for the needs of our dialogue, I’ll go away issues right here. As you possibly can see, there’s a lot to consider.
The entrance finish of a bicycle has quite a bit occurring. In broad phrases, the interaction of fork rake, path and head tube angle decide a motorcycle’s general geometry and dealing with traits. A motorbike designed for high-speed stability will sometimes have a slacker head tube angle, longer path, and extra fork rake, whereas a motorcycle designed for fast dealing with and agility might need a steeper head tube angle, shorter path, and fewer fork rake. Understanding these components may help you to discover a bike that works greatest for you and the place you journey. There isn’t a proper or fallacious (often), however there are an terrible lot of prospects.
To study extra about bike geometry, see our information right here. And, in case you, like me, respect visuals as a part of this dialog, there’s fairly an excellent video right here. The path and fork rake part dialog begins round 5:50.
