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  1. #1
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    bike geometry question - trail and handling

    What's better - a more stable bike that has a larger amount of trail, or a 'less' stable bike that has less trail? By stable I mean 'self steering'.

    I'm asking because I have two bikes (both 1980's vintage) that are pretty similar in size, except they differ in the amount of trail. I haven't measured it, but the one bike has more of it because that bike tends to steer into a turn much more easily at low speeds (the bars literally 'fall' into the turn if I lean into the turn). As well, the bars flop from side to side if I lean the bike over (standing next to it) far more than the other bike. The high trail bike also has a longer wheelbase by about 1.5 cm, but yet it has shorter chainstays! I can only guess it has a lower head tube angle.

    So, I was expecting the 'less stable' bike (the one with the shorter front end, steeper head angle and less fork offset) to be harsher and more difficult to ride, but I think I'm finding the opposite to be true! But I'm not sure if I'm fooling myself because I prefer the color or brand of that particular bike. Is the handling really going against what I 'think' should happen? I even rode them with the same wheels and tires just to get that variable out of the equation.

    Any opinions from some of people out there with LOTS of experience riding lots of bikes? My riding is mostly solo riding 20 to 50km distance as I don't have the time for 5 hr rides. Which one should I keep? Which one would be better when I finally do get to do that 5 hour ride?

  2. #2
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    less fork rake means more stable.
    steeper head angle means less stable.

    slacker head and seat angles should mean a more comfortable ride.

    i like short rake forks myself.
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  3. #3
    Senior Member SweetLou's Avatar
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    Which is better? Neither. The trail will influence the riding characteristics of the bike. Which is better a Ferrari or a Land Rover? Well, that will depend on how and where you ride. If I was off roading, I wouldn't want the Ferrari.

    A bike with more trail will be more stable. For loaded touring, I want a long wheelbase bike with a lot of trail. For riding fast on a curvy MUP, I would want a short wheelbase bike with less trail.

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    Quote Originally Posted by hhabca View Post
    I haven't measured it, but the one bike has more of it because that bike tends to steer into a turn much more easily at low speeds (the bars literally 'fall' into the turn if I lean into the turn). As well, the bars flop from side to side if I lean the bike over (standing next to it) far more than the other bike. The high trail bike also has a longer wheelbase by about 1.5 cm, but yet it has shorter chainstays! I can only guess it has a lower head tube angle.
    I'm a bit confused by parts of your statement. You say "the one bike has more" (trail), but then you say that is because it turns more easily - which actually would be a characteristic of a low-trail geometry. You are guessing as to the head tube angle. You later say that the theoretically "less stable" bike is the one with "less fork offset," which I take to mean less rake. You report that in actuality, this bike is the more stable one. Yet less rake in fact means higher trail, which one would expect to be more stable. So it is hard to sort out what is really going on.
    In my experience, you will appreciate higher trail on longer rides, on which a bike that dives into turns can challenge frayed attentiveness. On the other hand, having to "push" a high-trail bike around turns, especially when descending, has it's own lack of charm. It also depends how much stuff you think you may like to take with you on those potential longer rides: bikes generally handle better when front rather than rear loaded, and a low-trail geometry does not take to front loading well. My favorite bikes on long rides that don't involve packing too much gear are balanced in terms of their handling - easy to ride no hands; steer from the hips.

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    Dave Mann has lots of useful info about frame geometry and performance:

    http://home.comcast.net/~pinnah/dirt...-function.html

    I seem to have sipped the low-trail Kool Aid, given my Kogswell (40mm trail) and my homemade St. Etienne Porteur on which I installed a fork with much more rake than the original so as to lower the trail. But I also have a front rack on that bike, and low-trail designs are better for carrying weight on the front.

    Neal

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    Picchio Special, thanks for pointing out my confusing descrition. (I'm used to the term offset, not rake. Rake for me is steering axis angle.)

    Maybe I'll clear it up a bit up with this:

    Bike A: longer wheelbase, but shorter chainstays. Has a fork with visibly more rake (offset) than bike B. Bars flop over easily when standing beside it compared with B. Seems to steer too easily at low speeds, almost 'self steering'. Riding at a slow walking pace and turning the bars to one side makes the bike 'fall' into the turn. The bike is not as easy to control when sprinting as bike B. Is this a high or low trail bike?

    Bike B: shorter wheelbase than A, but longer stays. Has a fork with visually less rake (offset), but the head angle is different too so the actual amount of trail is unknown. Seems to steer less easily at low speeds - riding at a walking pace and turning the bars to the side does not cause the bike to roll into a turn as easily. The bike remains straight and I can easily control it when sprinting hard out of the saddle. Is this a high or low trail bike?

    Both bikes have the same BB height, and I rode them with the same seat-pedal distance, and bar to seat distance. I was amazed I could sense such a difference in them, as I am not some ubber experienced roadie with 100,000km under my belt - I'm more of a 2000km/year guy, on a good year.

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    Another good concise explanation:

    http://www.calfeedesign.com/frontendterms.htm

    I'd guess that Bike A might actually have fairly high trail due to a slack headtube angle (hence the longer wheelbase with shorter chainstays as compared to Bike B).

    Neal

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    Quote Originally Posted by nlerner View Post
    But I also have a front rack on that bike, and low-trail designs are better for carrying weight on the front.

    Neal
    Yeah, I mis-spoke on that point. Oops.

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    Quote Originally Posted by nlerner View Post
    Another good concise explanation:

    http://www.calfeedesign.com/frontendterms.htm

    I'd guess that Bike A might actually have fairly high trail due to a slack headtube angle (hence the longer wheelbase with shorter chainstays as compared to Bike B).

    Neal
    I agree. A high-trail bike is more likely to be unstable at very slow speeds, but more stable at high speeds. It doesn't steer as well from the bars, but steers more from lean and shifts in body weight. That may also explain why it's not as good sprinting out of the saddle, where your body weight is shifting a lot to produce power rather than to steer - in a sprint, your steering more from the bars rather than with lean, making the low-trail bike the better sprinter.

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    Quote Originally Posted by nlerner View Post
    Another good concise explanation:

    http://www.calfeedesign.com/frontendterms.htm

    I'd guess that Bike A might actually have fairly high trail due to a slack headtube angle (hence the longer wheelbase with shorter chainstays as compared to Bike B).

    Neal
    Thanks for that link Neal, that was an excellent explanation of the terminology.
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  11. #11
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Picchio Special View Post
    I agree.

    A high-trail bike is more likely to be unstable at very slow speeds, but more stable at high speeds. It doesn't steer as well from the bars, but steers more from lean and shifts in body weight.


    That may also explain why it's not as good sprinting out of the saddle, where your body weight is shifting a lot to produce power rather than to steer - in a sprint, your steering more from the bars rather than with lean, making the low-trail bike the better sprinter.

    I don't think I agree with your second sentence here. I think more trail results in better low-speed stability, at least while climbing. I find my two Italian-style road racers, a 1980 Masi and a 1984 or so Mondonico(both have between 60 and 65 mm trail), are both fairly stable clinbimg at low speed (no comments about slow 50 + climbers!). In contrast I have a Trek 610 and a Woodrup Giro Touring, and both of them have trail figures in the 50 to 55 mm range. They both are hard to keep in a straight line while climbing, and while at speed on a road with a little roughness.

    So I find more trail to be more stable at high speeds and at low speeds while climbing. The mid-trail bikes also can shimmy a bit while descending, either no-handed or with a rear load. The Giro is worst than the Trek, but it has a more flexy frame. I don't think either of them have loose wheels or bad headsets.

    It's a bit surprising that the Woodrup and the Trek have such similar steering behavior. The wheelbases are very different (Woodie is about 5 cm longer), BB is different (Trek is about 1.5 cm lower), and the head angles are different (Woodie is around 71 degrees and Trek is around 72.5). The head angle definitely allows the Woodie to absorb road shocks better.

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    Quote Originally Posted by Road Fan View Post
    I don't think I agree with your second sentence here. I think more trail results in better low-speed stability, at least while climbing.
    OK, but having researched this, that's not the consensus. Climbing is different from most low-speed riding. You're using the bars to help generate power by pulling on them, usually while trying to ride in a straight line, which is going to be unhelpful on a low-trail bike which will tend to be more input sensitive at the front.
    Generally, low-trail should be more stable (i.e. steer straighter) at low speeds. With high-trail at low speeds, attitude changes (i.e. steering by weight shifting) will be easier, creating a "wobbling" sensation, i.e. less stable. The high-trail bike will be more stable at higher speeds - it will hold a line more easily. Note that your "low-trail" examples - at 50-55 - are in actuality pretty close to neutral.

  13. #13
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    Quote Originally Posted by Scooper View Post

    Thanks - that helps to explain it a bit. Lots of other really good articles there too. I'm still not sure which is the 'better' bike so I'll continue riding and see. I'll try to measure the trail to see which one is larger and see if it matches the observations here. I'm also beginning to see why some of you have more than 1 or 2 bikes :-)

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    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Picchio Special View Post
    OK, but having researched this, that's not the consensus. Climbing is different from most low-speed riding. You're using the bars to help generate power by pulling on them, usually while trying to ride in a straight line, which is going to be unhelpful on a low-trail bike which will tend to be more input sensitive at the front.
    Generally, low-trail should be more stable (i.e. steer straighter) at low speeds. With high-trail at low speeds, attitude changes (i.e. steering by weight shifting) will be easier, creating a "wobbling" sensation, i.e. less stable. The high-trail bike will be more stable at higher speeds - it will hold a line more easily. Note that your "low-trail" examples - at 50-55 - are in actuality pretty close to neutral.
    I don't know what consensus you're really talking about, but having researched it I'm sure you can shed some light. I agree with you regarding low trail v. medium trail, my 2 bikes have more trail than some, to be sure! But there is still a difference in the riding experience.

    But my experience is my experience, and as many times as I've gone out on the Trek or the Woodie thinking "that issue isn't gonna happen again," the bike is again hard to keep on-line while climbing slowly, seated BTW, with a relaxed upper body, trying to keep my body still and my cadence high.

    I dunno, but that's what they do.

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    Quote Originally Posted by hhabca View Post
    Thanks - that helps to explain it a bit. Lots of other really good articles there too. I'm still not sure which is the 'better' bike so I'll continue riding and see. I'll try to measure the trail to see which one is larger and see if it matches the observations here. I'm also beginning to see why some of you have more than 1 or 2 bikes :-)
    And you can find a trail calculator here: http://kogswell.com/geo.php

    Neal

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    Quote Originally Posted by Road Fan View Post
    I don't know what consensus you're really talking about, but having researched it I'm sure you can shed some light. I agree with you regarding low trail v. medium trail, my 2 bikes have more trail than some, to be sure! But there is still a difference in the riding experience.

    But my experience is my experience, and as many times as I've gone out on the Trek or the Woodie thinking "that issue isn't gonna happen again," the bike is again hard to keep on-line while climbing slowly, seated BTW, with a relaxed upper body, trying to keep my body still and my cadence high.

    I dunno, but that's what they do.
    Maybe "consensus" was too strong a term, but all of the sources I found that specifically addressed the issue of trail and low speed handling (and none of these specifically mentioned climbing, and in my previous post I indicated it may well not apply to climbing, as the forces acting on the bike are different) indicated that low-trail is more stable at low speed:

    http://bikebuilding.blogspot.com/200...-on-trail.html

    http://www.spectrum-cycles.com/612.htm

    and

    http://kogswell.com/products.html

    Where you'll have to click on the PDF on the lower right which contains the road test of the Kogswell with forks giving varying trail, and in which the lower trail fork was found to clearly have the more stable low-speed handling.
    I didn't find any sources that contradicted this, although quite a few discussed trail and geometry without addressing low-speed handling per se.

  18. #18
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Picchio Special View Post
    Maybe "consensus" was too strong a term, but all of the sources I found that specifically addressed the issue of trail and low speed handling (and none of these specifically mentioned climbing, and in my previous post I indicated it may well not apply to climbing, as the forces acting on the bike are different) indicated that low-trail is more stable at low speed:

    http://bikebuilding.blogspot.com/200...-on-trail.html

    http://www.spectrum-cycles.com/612.htm

    and

    http://kogswell.com/products.html

    Where you'll have to click on the PDF on the lower right which contains the road test of the Kogswell with forks giving varying trail, and in which the lower trail fork was found to clearly have the more stable low-speed handling.
    I didn't find any sources that contradicted this, although quite a few discussed trail and geometry without addressing low-speed handling per se.
    There's a way to objectively assess the stability of a bike, using a math model. Jim Papadopoulous has published one in the past few years, that allows one to compute the eigenvectors (engineers again, ya know!) of the bike, and those numbers allow an assessment of stability, defined mathematically as vehicle engineers have done for a few decades now. There are many models, but this is the best IMO. I haven't tried to apply the model, however, it's not really my field, and it would take me a bit of time to work out just how to do it.

    I believe it considers the direction of gravity, or equivalently the ascending v. descending condition of the bike. It should be possible to make an assessment (not a firm determination, mind you) of the effect of trail on stability while climbing v. while level.

    I think you need a lot of data about the bicycle to use the model effectively - again I haven't tried it. It's certainly not enought to say "I have an M52 California Masi S/N xxxxx!"

    Road Fan

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    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Picchio Special View Post
    Maybe "consensus" was too strong a term, but all of the sources I found that specifically addressed the issue of trail and low speed handling (and none of these specifically mentioned climbing, and in my previous post I indicated it may well not apply to climbing, as the forces acting on the bike are different) indicated that low-trail is more stable at low speed:

    http://bikebuilding.blogspot.com/200...-on-trail.html

    http://www.spectrum-cycles.com/612.htm

    and

    http://kogswell.com/products.html

    Where you'll have to click on the PDF on the lower right which contains the road test of the Kogswell with forks giving varying trail, and in which the lower trail fork was found to clearly have the more stable low-speed handling.
    I didn't find any sources that contradicted this, although quite a few discussed trail and geometry without addressing low-speed handling per se.
    Fact is we don't know if and how it may apply to climbing. I don't have the theory or data to prove that what I experience is in fact the result of trail, nor to prove that it is not the result of trail. I do have experience to report, but not an explanation. I tried to write my note in that way.

    I do realize that the sources you mention do not specifically address climbing/descending, but that doesn't mean it is NOT pertinent. It just means the people who wrote these notes did not choose to write about it, and suggests they may not have tested it.

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    Senior Member pinnah's Avatar
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    Quote Originally Posted by Road Fan View Post
    There's a way to objectively assess the stability of a bike, using a math model. Jim Papadopoulous has published one in the past few years, that allows one to compute the eigenvectors (engineers again, ya know!) of the bike, and those numbers allow an assessment of stability, defined mathematically as vehicle engineers have done for a few decades now. There are many models, but this is the best IMO. I haven't tried to apply the model, however, it's not really my field, and it would take me a bit of time to work out just how to do it.
    The eigen value analysis in the most recent paper by Papadopoulous et al establshes a good basis for the mathematical modeling, we are quite a ways off from answering questions like that of the OP.

    Most glaringly, the term "stability" is very much overloaded -- meaning very different things to different people. In the case of that paper, it means the ability to stay upright for some distance after getting a push and with no rider on it. This has little to nothing (that we know of) to do with handling feel.

    The first step of moving forward would be a controlled vocabulary that would allow us to speak about the different kinds of stability with some consistency. I describe 2 that I think about here but others may disagree.
    http://home.comcast.net/~pinnah/dirt...ion.html#SPORT

    Then it would have to be shown that the eigen value type of analysis could be correllated to the observed results on handling, just as the authors did in relating it to their observations of riderless bike stability.

    Lastly... their model considers both bike mass and rider mass. It is not clear that results about a specific rider could be generalized to an average rider based on "average" rider mass and position.

    I'm not saying we won't get there someday. But, we aren't there yet.

    To answer the OP's question directly, I prefer frames with 73.0/5.5 front ends (or there abouts) as I find they want to go down the road more easily for me. They don't feel as precise and they do tend to wander a bit. But the wandering is self correcting unlike race bikes that tend to dive into corners or off the road.

  21. #21
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by pinnah View Post
    The eigen value analysis in the most recent paper by Papadopoulous et al establshes a good basis for the mathematical modeling, we are quite a ways off from answering questions like that of the OP.

    Most glaringly, the term "stability" is very much overloaded -- meaning very different things to different people. In the case of that paper, it means the ability to stay upright for some distance after getting a push and with no rider on it. This has little to nothing (that we know of) to do with handling feel.

    The first step of moving forward would be a controlled vocabulary that would allow us to speak about the different kinds of stability with some consistency. I describe 2 that I think about here but others may disagree.
    http://home.comcast.net/~pinnah/dirt...ion.html#SPORT

    Then it would have to be shown that the eigen value type of analysis could be correllated to the observed results on handling, just as the authors did in relating it to their observations of riderless bike stability.

    Lastly... their model considers both bike mass and rider mass. It is not clear that results about a specific rider could be generalized to an average rider based on "average" rider mass and position.

    I'm not saying we won't get there someday. But, we aren't there yet.

    To answer the OP's question directly, I prefer frames with 73.0/5.5 front ends (or there abouts) as I find they want to go down the road more easily for me. They don't feel as precise and they do tend to wander a bit. But the wandering is self correcting unlike race bikes that tend to dive into corners or off the road.
    Granted, the semantic connection (obviously critical) has not been made between the mathematical definition of stability and the various cycling usages of the term, but all I am saying is that AN assessment, one of many possible, can be made, but with considerable effort that to me is daunting.

    Road Fan

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    Senior Member Lamplight's Avatar
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    My Univega has 38mm of trail, and a somewhat high amount of rake compared to most modern bikes. When I had a large saddlebag on it and nothing up front, I could barely ride the bike with no hands. Now I have a fairly heavy handlebar bag, and the bike is considerably more stable. I can ride it seemingly forever with no hands, and it seems more stable in regular riding as well. I have no idea what the head angle is, but I suspect it's fairly steep. The bike is surprisingly nimble, though I wouldn't want to stand up and sprint on it with the handlebar bag. For the way I ride, it seems low trail is ideal.

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    Thanks for all the links - very useful!

    A bit more info:
    Bike A is a mid level Bianchi (made in Italy) from 1988
    Bike B is a top end Miele (made in Canada) from 1983

    Riding the Bianchi I can ride no hands easily, and even hit the bars and the bike just keeps going in the direction it was originally - I would say this is a good way to say it is stable. However, at low speeds on a gravel road I had the bike flop out from under me - hard to describe but one second I'm making a slow turn around a rock the next second the bike is on the ground under me.

    The Miele reacts to the no-hands-bar-bump test differently - it recovers but steers slightly onto a new heading. I would say this is a good way to say it has neutral steering. It also seems less sensitive to undulations in the road (less self steering, so that makes sense..).

    I'm preferring the Miele so far, but it might also be because it is slightly larger (by 1cm) and fits me a bit better. Next step, if I get the time, is to somehow measure fork rake and head tube angle and figure out the trail.

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    Senior Member pinnah's Avatar
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    Quote Originally Posted by hhabca View Post
    I'm preferring the Miele so far, but it might also be because it is slightly larger (by 1cm) and fits me a bit better. Next step, if I get the time, is to somehow measure fork rake and head tube angle and figure out the trail.
    Based on your descriptions (and a hunch based on the years and brands) I'll wager that the Miele has more rake and less trail. What you describe is often what get's attributed to the difference between so-called low trail and high trail bikes.

    Ken Freeman submitted some excellent advice on how to measure frames to the Bicycle Geometry Project (see link in my sig).

    Once you get them measured up, submit the details and we'll add them to the list.

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