June 4, 2013

Reading Time: 18 minutes

The abbreviated guide to bicycle dynamics


For better or worse, marketing departments managed to get their hands involved in telling people how bikes worked, meaning there has been an ever growing tide of misinformation about how and why bikes do what they do.

While very occasionally there is a major breakthrough that does actually change the way things work and the way you ride, for the most part the endless renewal is just an aid to sell people something ‘new’, not improved. Naturally things have been refined over time, with performance being increased at small, incremental rates, but ‘groundbreaking‘, ‘huge impact‘ and ‘change the way you ride‘ is 95% of the time just plain old marketing hype. Suspension Mountain Bikes are the prime victim of this hype. While the number of suspension systems continues to increase, with much of the afore mentioned claims attached, the reality is that true and innovative changes are few and far between. While advances in shocks have continued to make steady progress, to the point that they now are on par with the actual suspensions systems themselves (so now they can work together as a true single unit), there are still only a handful of suspensions systems that truly stand the test of time; the rest of them being an excuse to try and sell you something; usually replaced the following year with something else that of course is ‘newer and better’.

Note: Our objective here is to provide information that allows you to familiarise yourself with the dynamics of your bike. While we could go into the minute details and complex equations of all the parameters, forces and dynamics that are applied to your bike as you ride around, and probably loose many people in the process, we have tried to simplify everything as much as possible and keep to the most relevant information. Naturally by doing this we will not talk about all the factors that make up the dynamics, so if you are familiar with this subject, please do not email us telling we’ve missed this or that – we know we have and have done so for the purpose of simplicity. We have referenced key texts on the subject in compiling the ‘Guide’, which we list on the last page, as well as at the start of key topics. If you are so inclined, track them down and have a read for the full and detailed explanation. We can assure you, after you do, you will not take your bike for granted again! PS: Pretty little pictures to illustrate things are in the works…

The fundamentals…
(or why I stopped complaining and accepted a really crappy design scenario)

The truth is that a suspended mountain bike is actually a terribly underpowered motorcycle, meant to take a hammering while still remaining light enough to be pushed around all day. The engine (you) is an unbalanced, horribly underpowered, two cylinder engine directly connected to the drive sprocket (the cranks) with no counter balance (to offset the balance issue) and a gear box that mostly hangs out the back, at the wrong end of the chain!

To amplify issues, suspension is added into the mix but due to the need to be light and allow for the somewhat unique need for the suspension to cancel out the wildly mashing pistons, it can neither be sized accordingly or valved for maximum efficiency to do what it’s supposed to do. Yet despite this, all the same dynamics that govern motorcycles (that do not suffer from the unique issues of the mountain bike) govern our mountain bike. The identical principles that keep a motorcycle upright, reactions under braking or applied power and the affects of geometry, are all the same, all that changes are the scales that are applied – weight, velocity and power. It is truly remarkable that mountain bikes perform as well as they do and for the most part it’s a testament to the design and engineering efforts of all those working in the industry today.

After 20 odd years working in and around the cycling industry, for myself and others, I decided riding bikes was more fun than working with them. Over that time though, I wrote (and some wrote for me) a lot of stuff about bikes, on blogs and the like. Some was good, some, well... not so much. Rather than loose it all when I shut everything down once and for all, I have kept some of my favourite, and more popular pieces here for... prosperity?

I also am working on new pieces as well...


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