BILL BOSTON CYCLES

Did you ever wonder about bike handling geometry?

Have you ever read a road test that described the handling characteristics of a bicycle as “squirrelly,” “quick,” “heavy,” or “light,” and wondered if that was the same as “over-steer,” “under-steer,” or “twitchy”? I have.

Have you ever wondered if there was some way to objectively measure and compare the handling characteristics of bikes instead of relying on subjective feedback? I have. 

Have you ever wondered if the 51 cm model you want to buy handles the same as your friend’s 61 cm model in the same product line? I have. (Hint, most likely they don’t.)

In some cases, you may still want a bike that is described as heavy or light because of the type of events you ride, so you need more information. The problem is that bike handling creates a single impression from two different forces – stability and maneuverability. 

A little stability in life, please

We do not ride bicycles in perfectly straight lines. A bicycle scribes a path along the ground that resembles a low frequency sinus curve due to small steering inputs  that compensate for various angles of lean caused by wind gusts, road irregularities or shifting rider weight. A bicycle with a moderate degree of stability can actually help you automatically correct for these situations, while an unstable bicycle will exaggerate the curves.

Let’s define stability as the tendency of the front wheel of a bicycle to return to the centered position when disturbed. Stability is then a self-centering tendency or steering feedback, which exists in varying degrees on all bicycles. At the highly stable end, it actually takes a great deal of force to turn the bicycle, while highly unstable bikes have no self centering tendencies. Riding such a bike was once described as “trying to walk a dog that was sniffing both sides of the street,” which is a heckuva lot more fun than merely giving it a –3 on our stability scale.

Somewhere just slightly above the point of instability is a point where the front wheel knows that it is not in the centered position and will begin to return to the center. Unfortunately, the wheel is unable to recognize the center when it gets there and continues beyond far enough to again recognize that it is past center. Then the hunting process starts over again in the opposite direction with relatively no reduction in amplitude. This is neutral steering. What we want is steering feedback or stability that returns the front wheel to center, quickly recognizes that it has gone past center, and then returns and settles at center, thereby dampening out any oscillation.

Maneuverability

Maneuverability is the amount of steering input required to turn. Criterium and Sprint track events require a high degree of maneuverability. Straight line events like touring, time trials, and bikes used for Kilos require far less maneuverability.

A common misconception is that more maneuverable bikes are faster. In practice, the opposite is the case. If the bike that you are riding is more maneuverable than it needs to be for the event, you are wasting energy (both physical and mental) keeping the bike in a straight line. Needless to say, this energy could better be used in a sprint at the finish line or to get to that campground before dark.

Determine how much maneuverability is required for the type of riding that you do, then only look at bikes that meet those requirements.

Now What?

It is difficult to assess the stability separately from the maneuverability of a bike. Quite often, instability can make a bike appear to be highly maneuverable when it is in fact merely unstable. On the other hand, a bike that is not very maneuverable may seem stable until you try to take your hands off the handlebars.

Because of the difficulty in accurately accessing both the stability and maneuverability of a bike, I developed a system for rating both of these. I have been quite successful in improving the handling characteristics of some very ill-handling bikes, sometimes by recommending a different fork rake.  

Below is a summary of the rating indexes for maneuverability and stability. As you can see, Stability is rated on a scale of –6 to +6 with  a preferred range of 1 – 3, and  2 being optimal. Ratings of 4 or above provide excessive steering feedback; ratings below 1 are unstable.

Maneuverability is rated on a scale from 1 – 10 with 1 being the most maneuverable and 10 the least. My computer program is an aid in the analysis and rating process and will be posted on the web soon. In the interim, I will be happy to provide an analysis of your bike’s handling characteristics via email.

Please E-mail the address at the bottom of this page and include:

Your name, city and state, make, model and size of your bike, head tube angle, front wheel size and current fork rake.

If you don't know the head tube angle and rake of your bicycle, see Measuring Instructions to find out how to get them.  

I will provide the analysis and a recommended rake for a new fork if your stability is outside of the 1 – 3 stability range.

Request Analysis 

Stability Rating

Maneuverability Rating

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For More Information Contact:

BILL BOSTON CYCLES
11 Deer Run Drive, Wilmington, DE 19807
Tel: 302-559-9896
Email: Handling%billbostoncycles.com    

Due to the amount of spam generated by having email addresses posted on my web site, I have had to remove all of them You can copy the above email address and replace the % with @ and the email address will work.

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Copyright © 2003 BILL BOSTON CYCLES
Last modified: July 09, 2014