Spring Tune-up: More Than Just Pumping Up the Tires

Dale Campbell: Co-editor

The focus of Jan’s article is the perspective that reducing vibrations can and will increase cycling comfort.  Humm, the first thought is that isn’t that what suspensions are supposed to do?  You’ve probably observed that most road bikes (a large majority, in fact) do not have suspensions.  There are reasons for this.  Jan goes on to describe the reasoning why bicycle suspension systems are not good at reducing that he labels as “road buzz.”  For those with an engineering perspective or those with some curiosity about the mechanics of this observation, Jan’s discussion focuses on unsprung weight, damping and frequencies of road vibrations.  Specifically, he notes that “By the time the vibrations reach the handlebars, half of the bicycle is moving up and down [at a frequency of about 200 vibrations per second].  The unsprung weight is 10 pounds or more, and handlebar tape will do little to dampen [those] vibrations.”
 
So, what’s the solution?  Jan promotes tires as the first line of defense in regard to road buzz.  To support this, he notes that professional racers have begun to ride 25 mm wide tires in lieu of the traditional 23mm wide tires, inflating the 25s to 100 psi, in lieu of the traditional 130 psi run in the 23s.  So, now you’re thinking – wider tires, more road friction, slower speeds….  Well that may not be the case.  Jan points out that there is testing underway whose results indicate that 32mm tires are just as fast as 25mm tires.  He notes that time will tell what this tire width study will lead to eventually.
 
Moving in this direction, Jan suggests that the first approach to reducing vibrations should be to reduce tire pressure.  He does note that this can be taken only so far; reduce pressure more that some limit and you end up with pinch flats or self destructing tires as a result of sidewall deformation.  And, the stiffness of the tire casing also comes into play – high stiffness prevents tire flexure and vibration absorption.  So, do you get a supple tire with a thin tread to be more comfortable?  Probably not, as these tires are more susceptible to punctures (remember the goat heads on trails?).
 
So, Jan Heine suggests that the best defense against flats and the probable answer to creating a more comfortable bike is to install wider tires and run them at a lower pressure.  As he notes, “damping is most effective near the source of the vibrations….”  Short of getting a “Fat Tire” bike, the wider tire/less pressure solution for vibrations is one that we all can employ.  So to me, this seems to be a pretty good approach for improving comfort on your bike when you get out and ride!
Bent Fork - Volume 8, Issue 1 - February 2015

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