Trail

 

Doesn't matter what trail you're 'running', you're going to need some spokes and a tyre.

Almost everyone I meet, who a) gives a shit and, b) should no better, misunderstands what trail is.  I’m weary of hearing that Poloist A, who has just bought an embarrassingly mass-produced pompino/plug/bowery for polo, plans to ‘quicken up the handling’, by putting on a ‘straight’ or ‘low-rake’ fork. 

I’m going to karate-chop a commonly-held misconception here (Hiiiiiyah!), hold on:  Reducing fork rake increases trail which slows down handling.  

Read that last sentence.  Take it in.  Notice how it’s the opposite of what you thought. 

I’ll stop being a dick for long enough to accept that, before I looked into it, it was the opposite of what I thought too.  It just looks so right that putting on a fork with less rake will speed up the handling.  But it’s not.  Sorry.  It could be that people are simply confusing ‘rake’ with ‘trail’, as less trail will decrease a bike’s tendency to roll in a straight line.  It could be that people are stupid.

Time for some disclaimers.  Firstly, I’m talking about trail on its own, which is governed by your head angle, fork rake and wheel diameter.  Secondly it’s debatable how much of an effect changing trail has, partly because, (thirdly) you can’t just change your trail in isolation without swapping a whole lot of bits and comparing with accurate measuring tools.  Let’s say, for example, you foolishly change to a lower-rake fork (which theoretically ‘slows down’ the steering); you’ve also reduced your wheelbase.  Which affects the ride more?  You can’t tell.  To change just the trail, you’d have to get a different frame (or at least one with an adjustable head-angle) too.

I’m sure there are frame-builders and experts out there who could probably shed more light onto this than I can, but to be honest, I’ve met some of them, and asked them these questions, and they haven’t been able to confidently answer them.  If you’re reading this, and have good, evidence-based opinions of what would improve polo-bike handling, feel free to comment.

It’s  worth acknowledging here that the way a player turns a bike on a polo court is mostly very different to how you’d turn the same bike when you’re ‘just riding along’.  On court, most of the time, you’re travelling so slowly that you’re manually turning the bike with the bars.  When you’re riding along, you first counter-steer, and then lean.  Who has experimented or researched how a given geometry responds differently to these two opposed conditions?  Nobody, that’s who.  Or maybe someone has, and their only crime is that they didn’t tell me about it. 

Most importantly for polo, in my opinion, is creating a predictable and ‘jacking point’ (where the front wheel ‘tucks under’ and throws you off).  Although I’m not even sure this is possible.  Of course, the jacking point is dependent on your speed and the tightness of your turn, but somehow making it more predictable would allow you to be more confident pushing the limit of your bikes’ turning circle.  You obviously want a bike that ‘turns quickly’, but if the jacking point is knife-edge thin, you’ll be falling off more often, which will somewhat limit your ability to win games.  

I’ve experimented with a few different frames, forks and consequentially trail measurements.  I’ve decided that, for me, more trail helps (if it comes in the shape of a fork with less rake, rather than a slacker head angle).  It seems to make the bike less nervy and unpredictable.  I’d like to try even less rake (more trail), but as far as I’m aware, nobody makes a zero-rake, 700c fork with cantilever mounts and clearance for 38-40c tyres.

Ultimately, though, I think that so much bike-geometry is illusory.  Maybe if they were ridden by robots (BikePolo 2.0) these things would make a difference, but a human is going to adapt to his or her bike’s idiosyncrasies by say, turning the bar faster, so even though you’ll notice the difference when you step on a friend’s (or enemy’s) bike, if you were forced to ride that one forever, you’d subconsciously modify your actions and in the end you’d still be the same player/rider.

For my money, there are some desirable geometry-related qualities for a polo bike: short wheelbase (reduces your turning circle), short chainstays (easier to pick up the front wheel, easier to reach behind you/play behind the rear wheel), high bottom-bracket (reduces pedal strike, especially for people riding fixed) and probably a few more I haven’t thought about.  Also, I won’t argue that some geometry factors can change the way you play: a steeper seat-angle and shorter front-centre measurement would make it easier to play, and shoot, around the front wheel, for example.  Just don’t talk to me about trail, unless you want me to re-hash this same post, with added profanity.

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2 Responses to Trail

  1. EoD says:

    Clearly, having a straight fork would place point A (point of contact between the tyre and the ground) further away from point B (where the steering axis ‘meets’ the ground). Hence, an imaginary circle on the ground, with A as the centre and B as the edge of the circle, would have a larger radius. The larger this circle, the greater the distance B moves for a given angle. Thus, making the steering ‘slower’.

    When you think about it in terms of the position of the steering axis relative to the tyre’s contact point, it becomes really obvious, but it’s still very counterintuitive. Without the diagram and the knowledge of rake and trail how many people would have thought anything other than the common misconception?

    Before I spent the last 30 minutes thinking about this, even I thought a straight fork would make steering quicker, and I’ve been given really good explanations of how rake and trail affect steering in the past (including an excellent video that compared shopping trolley wheels with that of a bike’s front wheel, and the stability of a wheel with the steering axis behind tyre contact point vs. in front of it). No matter how much I think about it in a rational way, a straight fork still looks like it would make the steering ‘quicker’.

    This post is a really good example of how certain physical concepts can be very difficult to understand without the aid of drawings and experimentation (or knowledge based upon someone else’s experimentation). And I’m now late for work because of it. Thanks a lot ya bastard!

  2. danwentskiing says:

    I’m not sure if EOD’s comment is supposed to be complimentary or not, but it illustrates how annoying this whole area can be.

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