Talk:Bicycle and motorcycle geometry

message: "the influence of the position of the center of pressure of wind forces" Sure... 2001:9E8:B08:3F00:2EFD:A1FF:FE73:84E6 (talk) 16:09, 7 December 2021 (UTC)
thread_title:  Mechanical Trail 

message: I've tried to incorporate all the details from 
*Trail (bicycles)
*Mechanical trail 
*Rake (angle)
*Rake and trail
into one comprehensive article. Any reasons left not to redirect them all to here now? -AndrewDressel 16:21, 12 December 2006 (UTC)
thread_title: Merger candidates

message: It would be a valuable addition to this article to add information about how each characteristic influences the handling ("behavior") of bicycles and motorcycles and which geometries and characteristics are best suited to different types of riding.
For example, I believe that a bicycle with more trail is more stable at higher speeds while a bike with less trail is easier to handle at lower speeds and/or when there is a load on the front wheel.
Steeper head angles are used on time-trial bikes and less steep on touring bikes.
Etc.
:There is already a good start in the Bicycle frame article. Perhaps it should be moved here and expanded, as necessary. -AndrewDressel 14:01, 26 June 2007 (UTC)
thread_title:  How geometry affects handling 

message: I might be misunderstanding, but in the picture of the chopper, doesn't it have an unusually long trail? The rake doesn't seem that different.  —Preceding unsigned comment added by 144.212.105.66 (talk) 20:19, 22 April 2008 (UTC)
replies: text: I cannot tell what the trail might be, the fork is turned and it is difficult to guess where the steering axis might intersect the ground, relative to the front wheel contact point. However, the angle of the steering axis, which in motorcycles, is called the rake and is measured counter-clock-wise from the vertical when viewed from the right side, appears to be quite a bit more than usual. It might be as much as 45° instead of the 23.7° (with 3.8 in of trail) listed for a 2007 Honda CBR® 600RR, or the 29° (with 4.5 in of trail) listed for a 2008 Harley FXD Dyna® Super Glide®. -AndrewDressel (talk) 21:25, 22 April 2008 (UTC)

text: I was going to raise the very same point. Head angle, trail and obviously fork length are unusual but rake is small as normal.  —Preceding unsigned comment added by Killerisation (talk • contribs) 00:11, 31 December 2009 (UTC)
replies: text: Probably should be made clear that 'rake' and 'head angle' are synonymous. - 68.109.89.36 (talk) 04:53, 1 October 2012 (UTC)
replies: text: The article already states "in motorcycles, the steering axis angle is called the rake," and "in bicycles, fork offset is also called fork rake." Is that not sufficient? -AndrewDressel (talk) 13:15, 1 October 2012 (UTC)
thread_title:  Errors? 

message: I'd like to discuss this in the article, but I can't find a good source for it:
*Wilson's Bicycle Science doesn't mention it by name, and doesn't tell how to calculate it, but does mention a reduction in potential energy when the front end is turned.
*Foale's Motorcycle Handling and Chassis Design doesn't mention it by name, and doesn't tell how to calculate it, but does mention a reduction in potential energy when the front end is turned.
*Cossalter's Motorcycle Dynamics doesn't mention it by name, and doesn't tell how to calculate it.
*Sheldon Brown doesn't appear to mention it at all.
*Bicycle Quarterly lists it in their glossary, but doesn't tell exactly how to calculate it. Instead, they say "The amount of wheel flop is determined by the factor "f", the weight distribution of the bike, and an eventual front load attached to the bicycle's forks," and "Wheel flop factor "f" = b sin ∂ cos ∂ (b = geometric trail, ∂ = head angle). The amount of wheel flop (how much the front of the bike lowers when the handlebars are turned) is directly proportional to f."
*yojimg.net calculates a value, but doesn't reveal how. Are they just calculating the b sin ∂ cos ∂ that Bicycle Quarterly mentions?
*kogswell same here.
Any ideas? -AndrewDressel (talk) 20:12, 6 April 2009 (UTC)
replies: text: I could model it and develop equations, which I could publish in Cycloculture, but I'm not sure that Cycloculture would be viewed as a reliable source.  Thoughts?  Ebikeguy (talk) 22:35, 1 June 2010 (UTC)
replies: text:  You are right about Cycloculture. I guess it just isn't that big a deal if we can't find it written up in any reliable source. If you had an equation with more detail than Bicycle Quarterly's, you could just post it here for now, but it begs the question: where did you get it? If you derived it, where did you find the definition of wheel flop detailed enough for you to base an equation on it? -AndrewDressel (talk) 01:25, 2 June 2010 (UTC)
replies: text:  The basic equation should not be that difficult.  You've got a defined geometry and one degree of freedom.  I think I could figure it out without too much trouble, although I've done a lot more acceleration modeling in the past than stuff like this (See "The Other Side of the Mountain" in BQ a couple years ago).  That said, I have put the question to a couple of people who might already have the equation(s).  Let's see what they say before I go trying to derive anything.  Ebikeguy (talk) 04:33, 2 June 2010 (UTC)

text:  A KOG member defines wheel flop, in mm, as "WF = Trail x sin(Head Angle) x cos(Head Angle)."  I am not sure what that means, though.  What is the significance of the calculated distance? Ebikeguy (talk) 15:10, 2 June 2010 (UTC)
replies: text:  Oops.  I just noticed where you listed that equation from the BQ glossary already.  Sorry I missed it at first.  Ebikeguy (talk) 17:45, 2 June 2010 (UTC)

text: I posted what I think is an adequate starter section on this topic.  The references are imperfect, but they seem good enough for now.  If anyone wants to improve on the section, please do!  Perhaps reading Foale's book or the BQ editions Jan references in the glossary would help, but I just don't have time to do that much research right now.  I was working off some graphs from Foale's book and the BQ glossary.  Cheers,  Ebikeguy (talk) 05:20, 4 June 2010 (UTC)
replies: text:  The formula may or may not be correct, but the symbol for head angle is incorrect: \partial is an operator (the partial differential operator), not a quantity. Assuming the customary symbol for head angle (if there is one) is \vartheta, I have edited accordingly. Lovibond (talk) 19:52, 23 March 2012 (UTC)
thread_title:  Wheel flop 

message: The BMW image shows the left side of the bike. Electricmic (talk) 10:33, 2 May 2009 (UTC)
thread_title:  Need to flip BMW Image ? 

message: I'd like to add more information on head angle, and include information on seat angle.  The seat angle info would have little to do with motorcycles, but is important to bicycle design.  Any objections? Ebikeguy (talk) 01:53, 23 March 2010 (UTC)
replies: text: Isn't this already covered in Bicycle_frame#Frame_geometry? -AndrewDressel (talk) 02:43, 23 March 2010 (UTC)
replies: text:  It is touched upon, but since this is the main article for bicycle geometry, I think it should be covered here in detail.  Note that the section to which you wikilinked links back to this article for more info.  Ebikeguy (talk) 14:45, 23 March 2010 (UTC)

text:  Or perhaps a previous poster was correct in saying that this article should be titled Bicycle and motorcycle steering geometry, since it deals primarily with the front end geometry.  Yesterday, I saw a request to create a Bicycle geometry page, so I just created a redirect to this page, but maybe we should create a separate bicycle geometry page which we would then link to this page for as the primary article on steering geometry.  The bicycle geometry page would flesh out the subjects touched upon in Bicycle_frame#Frame_geometry and cover new subjects as well.  If we do create the new article, we should probably rename this page "Bicycle and motorcycle steering geometry."  Thoughts?  Ebikeguy (talk) 15:10, 23 March 2010 (UTC)
replies: text: I guess you'll just have to add what you want before anyone else can decide how well it fits. It looks like the page only gets about 150 hits per day, and fewer than 5 people watch it, so I doubt many readers will be upset. -AndrewDressel (talk) 23:13, 23 March 2010 (UTC)
thread_title:  Head and seat angle 

message: do u know the roll of caster angle provided in bicycle? -117.241.64.222 19:51, 8 June 2010
:This article is merely about explaining what the parameters are and giving some sample values. For a discussion of their roll, see the separate article on bicycle and motorcycle dynamics. -AndrewDressel (talk) 13:09, 8 June 2010 (UTC)
thread_title:  roll of caster angle  

message: The image that is currently at the top of the article shows a bicycle with no bottom bracket drop.  I'd like to edit the image to have some BB drop.  If you have anything to say about that please leave a note on  (as the image is used on other wikipedia pages too)  --Keithonearth (talk) 23:45, 7 September 2011 (UTC)
replies: text: That would be great, and you might also want to define "BB drop" in the article, if you can find a suitable reference for the definition. -AndrewDressel (talk) 00:14, 8 September 2011 (UTC)
thread_title:  BB height/drop in the image 

message: The terminology used throughout the Bicycle and motorcycle geometry page is confusing.  This seems to be in large part due to the different way that "rake" is used on bicycles and motorcycles.  I suspect that multiple authors were at work and they failed to seamlessly merge their contributions.  What follows is mainly an attempt to straighten this out.  I don't have a Wikipedia account and am new enough to editing Wikipedia pages that I thought it best to run this by you, who I gather is the biggest contributor to the page.  There are two images below that I couldn't insert, apparently because of my not having an account, so I've uploaded them to Tinypic and included links in the text.
Steering axis angle:
1. "In motorcycles, the steering axis angle is called the rake and is measured from the vertical." would be clearer if it read "In motorcycles, the steering axis angle is called the rake angle or rake and is measured from the vertical."
:Done.
2. As it's a motorcycle, the caption on the BMW would better be stated "Telescopic forks on a BMW motorcycle reveal the steering axis or rake angle".
:Done.
3. "A 0° rake would be vertical." could be improved to "A 0° rake would be vertical.  Note that as rake angle increases, head angle decreases.  Head angle = 90° - Rake angle."
:Not done.
Fork offset:
1. "Required rake angle arose from early times when lightweight bicycles suffered fork failures from road shock."  Bicycles are being mentioned here.  Use "head angle" instead of "rake angle".
:Removed entire long-unsourced paragraph.
2. "Before most roads were paved, fork rake had a lower angle so the fork would be loaded axially on rougher surfaces." I suggest "fork rake had a lower angle" be "lower fork angles were used".  Furthermore shouldn't it read radially rather than axially?  The author of this statement, which I hope isn't you, is careless.
:No, I didn't write it, but I believe 'axial' is correct.
3. "In motorcycles with telescopic fork tubes, fork offset can be implemented by either an offset in the triple tree, adding a rake angle (usually measured in degrees from 0) to the fork tubes as they mount into the triple tree, or a combination of the two."  "Rake angle" is confusing and inappropriate here as the term has already been defined.  I think "triple tree rake" is the appropriate term.  See it being used at http://www.rbracing-rsr.com/rakeandtrail.html.
:Done.
Trail:
1. "Trail is a function of head angle, fork offset or rake, and wheel size." tends to lead to confusion because of the use of "rake".  I suggest that the word either be removed or that the sentence be changed to "On bicycles trail is a function of head angle, fork offset or rake, and wheel size."
:Done.
2. "Motorcyclists tend to speak of trail in relation to rake angle. The larger the rake angle the larger the trail. Note that, on a bicycle, as rake angle increases, head angle decreases."  In view of the suggested changes in the steering axis section, I suggest changing it to "Motorcyclists tend to speak of trail in relation to rake angle, http://i44.tinypic.com/t0j2pd.png.  In terms of rake angle, the formula for trail is: http://i39.tinypic.com/293x091.png"
:Possibly done.
Mechanical trail:
1. "Mechanical trail is the perpendicular distance between the steering axis and the point of contact between the front wheel and the ground." This doesn't make sense.
:It makes sense to me, but go on.
The steering axis is just a line of infinite length.
:Yes.
Where on that line does the perpendicular measurement to ground begin?
:At the point from which a perpendicular line would intersect the point of contact between the front wheel and the ground.
If it begins at the steering head (I'm guessing), where on the length of the head does the measurement begin.
:Nope. On most bikes, that would be pretty from from correct.
I.e. a typical motorcycle steering head is around 6" in length.  Alternately, might mechanical trail be the perpendicular distance from the steering axis to the front axle?
-Bill Vyn
184.187.191.197 (talk) 21:39, 12 December 2013 (UTC)
replies: text: Nope. A picture would probably be worth a thousand words in this case. Let me see what I can find. -AndrewDressel (talk) 15:59, 14 December 2013 (UTC)
replies: text: On second thought, and after wasting an hour trying, I find the tools available that support the preferred SVG file format unusable. Someone else is welcome to play with it. A decent image can be found online at: http://www.peterverdone.com/wiki/index.php?title=Mechanical_Trail -AndrewDressel (talk) 17:01, 14 December 2013 (UTC)
replies: text: Good work Bill and Andrew. Thanks for fixing that.<P>On the KTM 390 Duke I noticed they were using steering head angle instead of rake , and it seems BMW does the same  now. Triumph still uses rake. A similar thing happened a few years ago, where without any kind of announcement, all the brands shifted from adverting dry weight to curb/wet weight. It would be nice to verify when BMW and KTM made this change, or if it was recent. --Dennis Bratland (talk) 20:18, 14 December 2013 (UTC)
replies: text: Hmm. So long as they don't start measuring from the vertical and calling it rake angle, we might be okay. It would be nice to find a reliable, third-party source to explain things, though. -AndrewDressel (talk) 16:38, 15 December 2013 (UTC)
thread_title:  Comments on differences in definitions between bicycle and motorcycles 

message: I've just updated the image for the Trail section, with the addition of a 3rd Variable (wheel size).  I've also redone the layout to accommodate the 4 variations (baseline + 3 variables).  Please have a look at the new image and let me know of any issues that could be addressed.  Thanks! --Keithonearth (talk) 20:05, 10 August 2014 (UTC)
thread_title:  New version of the Trail diagram 

message: Hello fellow Wikipedians,
I have just added archive links to  on Bicycle and motorcycle geometry. Please take a moment to review my edit. If necessary, add  after the link to keep me from modifying it. Alternatively, you can add  to keep me off the page altogether. I made the following changes:
*Added archive https://web.archive.org/20050404004810/http://www.american-v.co.uk:80/technical/handling/geometry/body.html to http://www.american-v.co.uk/technical/handling/geometry/body.html
When you have finished reviewing my changes, please set the checked parameter below to true to let others know.
Cheers.—cyberbot IITalk to my owner:Online 20:37, 19 February 2016 (UTC)
thread_title:  External links modified 

message: I've just read the sections on trail and mechanical trail, and I think that they are saying that less trail makes a bike more twitchy/agile and more trail makes a bike track better and less agile. That seems to be the central importance of trail, so I'd like to see it stated more clearly and more prominently. --Keithonearth (talk) 02:50, 22 February 2016 (UTC)
thread_title:  unclear trail section