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Basis for a good handling bicycle...(3 posts)

Basis for a good handling bicycle...PT
Jan 4, 2004 1:52 PM
I have four bicycles that I ride quite a bit, but one stands head and shoulders above the rest in terms of handling -- my cyclocross bike. It is no liability on the road and it handles exceptionally well on the trail -- it's more nimble than my mtb and only lacks the meaty tires and suspension to make it faster down rocky trails. I started looking into the respective geometries of the individual bikes, particularly the head tube angle and rake of the fork, and then of course the trail. Using an Excel program I found somewhere on line to calculate trail, here are the relevant numbers for the four bikes:

Seven Muse Cyclocross:

Fork Rake is 50mm
Head Tube angle is 72°
Trail is 59.8mm

Bridgestone MB1

Fork Rake is 40.4mm (rigid fork)
Head Tube angle is 72°
Trail is 66mm

Moots YBB

Fork Rake is around 42mm (suspension fork)
Head Tube angle is 71.5°
Trail is somewhere around 65 mm?

Merlin Road

Fork Rake is 40mm
Head Tube angle is 72.5°
Trail is 63.4mm

So, the bike with the least trail is my favorite. I have several questions. The first is how much is the trail difference between the bikes contributing to my preference for the cyclocross bike? Should I be considering additional factors such as wheelbase or seat tube angle? Finally, one of my goals of this effort is to make my Moots YBB handle better (for me), perhaps by getting a rigid fork that would approximate the handling of the cyclocross bike (which would require a rake of about 49mm and which is apparently huge for mtb forks). Does anyone have an opinion on whether or not such an experiment is worth the effort?


(PS - I asked this question over on the MTBR site and it was ignored. I hope I do better here).
Rake and trail are important aspects of handling, butBowWow
Jan 5, 2004 10:49 AM
other factors come into play. I think front-center and wheelbase measurements will also affect handling. I'm interested in the Moots experiment. I think matching trail on the Moots with your CX bike may illustrate the effect other geometries have on the handling. You may get a very sweet handler, or she may just get evil on ya! Try it and let us know what you learn!
re: Basis for a good handling bicycle...aaroncvc
Jan 5, 2004 1:01 PM
hey, i suggest reading this article:

"As a general rule when dealing with 700-C wheels, a trail of about 5.6mm will give a frame set "neutral" handling. My use of the term "neutral" here refers to two things. First, neutral handling means that a frame set will respond to steering input in the same manner no matter what speed the bicycle is traveling. Second, while cornering, a neutral handling bike will have neither a tendency to climb out of a turn nor have a tendency to dive into the turn, it will simply hold the line that the rider sets up unless further rider input is applied.

"Decreasing trail below the neutral range has a couple of effects as you might expect. The first thing a rider will notice about a low trial bike is that it appears to resist attitude changes (or lean angles). It requires more physical effort to get the bike to lean into a corner and more effort to get it to straighten up. The second thing that you will notice is that while cornering at higher speeds, the bike will have a tendency to climb out of the turn on its own. Finally, you will find that the way the bike responds to rider input is effected by the speed of the bike. As you might have guessed by now, at lower speeds, a low trail bike will have a tendency to want to go straight and do so pretty much on its own. What you will find at higher speeds (like over 30mph) is that a low trail bike will become quite vague in the front end. The front wheel will feel as though it is wandering a bit and the contact patch feel will go away.

"Increasing trial above the neutral range will cause opposite effects for the most part. At lower speeds, handling response will be light and consequently, attitude changes will be much easier. During cornering, the bike will have a tendency to drop into a tighter arc than the rider might have intended. Finally, speed's effect on handling is reversed. While low speeds give a light feel during handling maneuvers, high speed sets up a very solid front end feel.

"Although high trail frame sets give safer (more inherently stable) handling than low trail frame sets do, high trail frame sets are still inconsistent in the way they respond to rider input. Interpreting from the basics above you can see why we usually aim for neutral trail. It does not require the rider to consciously hold a bike down during hard cornering, nor does it require different rider input depending on changing speeds.

"For some frame designers though, it is not always that simple. For example, look at the way Eddy Merckx designs most of his frames. He usually uses less trail than the "ideal" as he did much of his racing on the pave and likes the way a low trail frame tracks under really horrible conditions. Granted, they do not act as consistently under a variety of speeds on good roads, but they really work on northern Europe's country tracks.

In that last paragraph, I think your observations are basically summarized. The lower trail, in addition to the longer wheelbase, makes the cross-bike handle better in the conditions it was suited to be ridden in. Keep in mind that the stem length has a noticable effect on handling as well... the longer your reach, the more input required to achieve the same steering angle... of course that's assuming all things are equal, and since there's a change in geometry from bike to bike, things never are equal...

i've been thinking about this alot, since on friday i'm going from a 53cm lemond buenos aires, that i raced on last season, to a 55cm zurich. i'm a little cramped on the 53, which is really a 54.5, and the 55 (really 56.5) should be a little bit better... the 55 that i'm buying (from a friend who's my exact size) has a shorter stem and a 1.1cm longer wheelbase. also the head tube angle is changing from 73 to 73.5. so in theory the larger bike should handle "slower", but the reduction in the stem l