Hi all, someone can explain to parts of the motorcycle referred the following geometry parameters and generates modification effect?
Thanks
Quote from: Adalgood on February 19, 2016, 03:13:16 PM
Hi all, someone can explain to parts of the motorcycle referred the following geometry parameters and generates modification effect?
Thanks
I'm sorry Adalgood, I'm not sure we understand what your asking there? Maybe if you ask a more specific question we could help you. ;)
Hawk.
Reads like hes asking for someone to explain the parts that are adjustable on the bike in the setting and how they effect the bike in general?
jeje sorry...my english is very bad. The question is...
"Fork Offset" What is this?
It is what I say to my dog called 'Set'. ;D
Quote from: Adalgood on February 19, 2016, 10:58:00 PM
jeje sorry...my english is very bad. The question is...
"Fork Offset" What is this?
That is a good question and something I'd like to know too......
It's not the "rake" because that's already there....
It brings to mind the forks being offset to the side but I cannot believe that surely??? That would be weird! Hehe ;D
Aaarh! I think I know what it is!!!! It will be the adjustment for shortening or lengthening the fork tubes inside the fork yokes, for want of a better way to describe it. Thank you for bringing this up Adalgood, I'll have to give this a try because this should really have an effect on handling! Nice one! ;D 8)
Hawk.
I had to look it up. Rake and Trail I was happy with, offset not so. I found this pretty good explanation?
http://bikearama.com/theory/motorcycle-rake-trail-explained/
Quote from: Napalm Nick on February 20, 2016, 08:57:56 AM
I had to look it up. Rake and Trail I was happy with, offset not so. I found this pretty good explanation?
http://bikearama.com/theory/motorcycle-rake-trail-explained/
Very useful link explaining front fork rake, trial and offset Nick...... I'm eager now to give this a test! ;D
Thanks Nick! ;D 8)
Hawk.
I think I posted this before but w/e
Race Tech's Motorcycle Suspension Bible
http://www108.zippyshare.com/v/Iidaqkpb/file.html
enjoy friends
Best way to learn is to just try it all out! Go to the extremes and see what happens then and go to opposite extreme (lowest and highest setting) and just try it out, slowly you will get an idea of what works on what problems :)
I learned it the tough way on my 125GP and Moto3 bike, learning by doing and taking some chances with the setup to see i went in the right direction, paid off much better than people telling me all the fancy words haha (learned those afterwards)
Yeah !! Thank you very much to all !! Now I'll try playing track ends to feel what effect generated on the bike.
https://www.google.es/search?q=bike+OffSet&biw=1745&bih=868&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiP6PXqqYbLAhWKbxQKHdwwDdoQsAQIGw#imgrc=BKnpBNiFCJk8sM%3A
Already I think an increase in offset should cause a reduction in trail, so a more nimble bike but less stable on the straight, but in game it seems to be opposite hahahaahaa maybe I measure from the wrong point or backwards or something. (Engine Braking phenomenomenona) ;D
Quote from: Adalgood on February 20, 2016, 12:23:28 PM
https://www.google.es/search?q=bike+OffSet&biw=1745&bih=868&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiP6PXqqYbLAhWKbxQKHdwwDdoQsAQIGw#imgrc=BKnpBNiFCJk8sM%3A
That's a good animation and gives a better idea of the adjustments we are looking at here. ;)
Nice one mate. 8)
Hawk.
Quote from: Napalm Nick on February 20, 2016, 12:38:31 PM
Already I think an increase in offset should cause a reduction in trail, so a more nimble bike but less stable on the straight, but in game it seems to be opposite hahahaahaa maybe I measure from the wrong point or backwards or something. (Engine Braking phenomenomenona) ;D
Increase in offset will cause an increase in trail too as you see in the illustration linked by Adal.
It shows it pretty well what the offset is :)
er, no, me old mate you can clearly see an increase in offset (24 - 28mm) is causing a reduction in trail (106 - 99mm) ??? that's what I would expect anyway!
Haha i agree mate! Was mixing it all up there :D
Yeah i agree with you, haven't tested so much offset in GPB, will try when i get online later And see what i feel on the offset settings :)
no wonder you let me do your setups haha ;) Wish I could get as much out of them as you do tho ::)
Hey hey! For A1 i am on my own setup and see where it brought me ;) love the new rideheight options :P
Yes they are great.
Forget your old times they are already smashed in Qually ::) even I have a '27
Well well well, my times was on old worn out hards, will be faster now when testing softs and more setup work ;)
I've been riddin since i was able climb on the seat & confess i still refer to Google more than i like to admit for moto component(s) geometry interaction & effect on performance.
I've been always left unsatisfied with rake/trail explanations you can usually come across. From what's being told, naturally, you'd have a question, "so, what's the difference between these values?"
Here's my take on the answer:
The more there's trail, the more torque is applied from the contact patch up to the fork to straighten it up if it's not aligned with the direction of travel.
Rake angles closer to 0 degrees translate into more efficient bike leaning, due to the fact that any torque applied to the axis of a spinning mass that would tilt the mass, manifests itself 90 degrees of phase later in the same direction. So, if you want all your steering effort to be effectively converted at speed into the bike leaning moment, you need the axis of the fork's rotation to be perpendicular to the road surface. Ideally.
With these considerations in mind, I don't quite see why one would want less trail with bigger rake angles and not the other way around. Shouldn't having almost upright fork coupled with a considerable amount of travel be a win-win situation?
Edit: Maybe for the sake of introducing less disturbances in the steering from the imperfections of the road surface. More effort to lean the bike with the help of the gyroscopic precession, but less resistance from the trail's aligning moment. Might be more helpful for medium speed turns.
@passerBy: get THE book on bike dynamics (Cossalter, Motorcycle dynamics), it contains all the answers to this kind of questions (including stuff on suspension, bike stability, ...).
On a given bike (with usual front fork, let's forget exotic designs), rake angle and trail are linked: if you increase the rake angle you automatically increase the trail (unless you can change the front tyre diameter).
Pretty good explanation: http://www.motorcycle-superstore.com/4125/mngr/rake-and-trail-explained.aspx (http://www.motorcycle-superstore.com/4125/mngr/rake-and-trail-explained.aspx)
Quote from: HornetMaX on April 20, 2017, 11:13:40 AM
@passerBy: get THE book on bike dynamics (Cossalter, Motorcycle dynamics), it contains all the answers to this kind of questions (including stuff on suspension, bike stability, ...).
One of these days I will. I'm sure though there is an easier way to answer this without reading the book to find the answer.
QuoteOn a given bike (with usual front fork, let's forget exotic designs), rake angle and trail are linked: if you increase the rake angle you automatically increase the trail (unless you can change the front tyre diameter).
That's obvious. And as we could see above, the offset can help in manipulating the trail without affecting the rake.
QuotePretty good explanation: http://www.motorcycle-superstore.com/4125/mngr/rake-and-trail-explained.aspx (http://www.motorcycle-superstore.com/4125/mngr/rake-and-trail-explained.aspx)
I didn't like the explanation on the rake, and the trail is an easy subject as it is already.
Judging by the finishing part of the article, I guess the rake angle helps in retaining the original direction of motion of the whole system (shouldn't having two gyros in it be enough as it is?), while the trail is all about keeping the thing upright.
Quote from: passerBy on April 20, 2017, 11:42:33 AM
Quote from: HornetMaX on April 20, 2017, 11:13:40 AM
@passerBy: get THE book on bike dynamics (Cossalter, Motorcycle dynamics), it contains all the answers to this kind of questions (including stuff on suspension, bike stability, ...).
One of these days I will. I'm sure though there is an easier way to answer this without reading the book to find the answer.
OK.
Quote from: passerBy on April 20, 2017, 11:42:33 AM
QuoteOn a given bike (with usual front fork, let's forget exotic designs), rake angle and trail are linked: if you increase the rake angle you automatically increase the trail (unless you can change the front tyre diameter).
That's obvious. And as we could see above, the offset can help in manipulating the trail without affecting the rake.
Sure, but on most bikes you don't have that freedom on the fly (yes, you can change your triple clamps but that's not really practical).
Quote from: passerBy on April 20, 2017, 11:42:33 AM
I didn't like the explanation on the rake, and the trail is an easy subject as it is already.
Judging by the finishing part of the article, I guess the rake angle helps in retaining the original direction of motion of the whole system (shouldn't having two gyros in it be enough as it is?), while the trail is all about keeping the thing upright.
That's why you need the book. There's a part where a linearised model of the whole bike dynamics is extracted (at different forward speeds). The poles of the model are then plot and the local stability of the bike is deduced from the poles position in the complex plane. A sensitivity analysis is also done, varying the bike's basic parameters (e.g. mass, wheelbase, rake, trail, ...) and judging the effect on the bike's stability (as per the linearised model). If you find an easier way to explain that ...
P.S.
I wouldn't say trail is about keeping the bike upright. Even the article linked tells you much more than that.
The combination of rake and trail gives the "self aligning" behavior of the front. That's the easier to understand effect of rake and trail, but it's not the only one.
Quote from: HornetMaX on April 20, 2017, 12:11:32 PM
Quote from: passerBy on April 20, 2017, 11:42:33 AM
QuoteOn a given bike (with usual front fork, let's forget exotic designs), rake angle and trail are linked: if you increase the rake angle you automatically increase the trail (unless you can change the front tyre diameter).
That's obvious. And as we could see above, the offset can help in manipulating the trail without affecting the rake.
Sure, but on most bikes you don't have that freedom on the fly (yes, you can change your triple clamps but that's not really practical).
As long as we have GPB and BikeEd, we're free to explore many different designs.
QuoteQuote from: passerBy on April 20, 2017, 11:42:33 AM
I didn't like the explanation on the rake, and the trail is an easy subject as it is already.
Judging by the finishing part of the article, I guess the rake angle helps in retaining the original direction of motion of the whole system (shouldn't having two gyros in it be enough as it is?), while the trail is all about keeping the thing upright.
That's why you need the book. There's a part where a linearised model of the whole bike dynamics is extracted (at different forward speeds). The poles of the model are then plot and the local stability of the bike is deduced from the poles position in the complex plane. A sensitivity analysis is also done, varying the bike's basic parameters (e.g. mass, wheelbase, rake, trail, ...) and judging the effect on the bike's stability (as per the linearised model). If you find an easier way to explain that ...
I don't think all that is necessary to answer the question of "what is the significance of rake in isolation from trail; what consequences does increasing one relative to the other leads to and vice versa."
Sure, for coding my own motorcycling simulator, the book is indispensable. But if I haven't started it before, I doubt that I ever will. The time of me being actively interested in programming is in the past for quite a while already.
Also, I suppose that the majority of people checking this thread would expect to find a concise answer to the topic, but not quite as concise as "increasing rake and trail leads to better stability" (since this kind of popular answer doesn't really answer much).
QuoteP.S.
I wouldn't say trail is about keeping the bike upright. Even the article linked tells you much more than that.
The combination of rake and trail gives the "self aligning" behavior of the front. That's the easier to understand effect of rake and trail, but it's not the only one.
Well, also trail encourages the front end to follow the general direction of travel of the system (the effect utilized by drift-prepped cars to a great extent).
These parameters called "rake
and trail" for a reason. We can influence them separately. Therefore, there is a need to look at them separately as well. While at that, we can make simple and clear-cut conclusions in the vein of "increasing the shocks settings leads to decreasing the suspension oscillations' both amplitude and frequency" or "increasing the front ride height results in the static CoG being offset more to the aft".
Quote from: passerBy on April 20, 2017, 01:01:18 PM
Also, I suppose that the majority of people checking this thread would expect to find a concise answer to the topic, but not quite as concise as "increasing rake and trail leads to better stability" (since this kind of popular answer doesn't really answer much).
A popular answer is what you're after. I pointed you to a more complete answer but that didn't satisfy you either. So I'm out of answers.
Quote from: passerBy on April 20, 2017, 01:01:18 PM
These parameters called "rake and trail" for a reason. We can influence them separately. Therefore, there is a need to look at them separately as well. While at that, we can make simple and clear-cut conclusions in the vein of "increasing the shocks settings leads to decreasing the suspension oscillations' both amplitude and frequency" or "increasing the front ride height results in the static CoG being offset more to the aft".
No you can't make simple and clear-cut conclusions on this kind of stuff. Otherwise anybody would be able to properly setup a motogp bike. Which of course is not the case.
Simplified explanations (like "if you have understeering, just change this or that") are just that, simplified explanations.
Looks like I was right after all. No much sense in bigger rake angles. Check the Tony Foale's book's appendix A1.
Quote from: HornetMaX on April 20, 2017, 03:11:18 PM
A popular answer is what you're after. I pointed you to a more complete answer but that didn't satisfy you either. So I'm out of answers.
Or you rather expect me to buy the book right away and wait till it arrives, then to read the whole book. Do you find that a satisfying answer? If you cannot tell me in your own words what does the rake do, what's the point in your having read that book then (and pointing me to it)?
Quote
No you can't make simple and clear-cut conclusions on this kind of stuff. Otherwise anybody would be able to properly setup a motogp bike. Which of course is not the case.
Simplified explanations (like "if you have understeering, just change this or that") are just that, simplified explanations.
So, of all things, the most arcane piece of knowledge about bike construction is the rake now?
I clearly said that I'm not satisfied with explanations like the one you just mentioned or like "rake and trail help with the stability". Also, I demonstrated my own reasoning based on pure logic (and some physics). And judging by the Tony's experiment, I was right in that you don't really need much rake at all. It's mostly the trail that does all the stabilizing.
Actually, I was extremely surprised he found steeper rake angles to be
more stable while crossing ruts and while at speed. Somehow he didn't say anything on how the bike behaved in a lean. I'd expect it to need to be pushed into the lean slightly all the time, since tilting into the turn is probably the only useful rake's feature.
Quote from: passerBy on April 21, 2017, 12:32:31 AM
Looks like I was right after all. No much sense in bigger rake angles. Check the Tony Foale's book's appendix A1.
Quote from: passerBy on April 21, 2017, 12:32:31 AM
And judging by the Tony's experiment, I was right in that you don't really need much rake at all. It's mostly the trail that does all the stabilizing.
I have T.Foale's book: he proved (in an era where computer simulations where not an option and understanding of bike physics far more limited than today) that you can have a stable behavior without any rake. I also have a research paper that proves that you can have a stable behavior without any rake nor trail. So what ? As I already told you, the rake also have other effects on the bike handling beside pure stability considerations.
Quote from: passerBy on April 21, 2017, 12:32:31 AM
So, of all things, the most arcane piece of knowledge about bike construction is the rake now?
Nobody said that.
Quote from: passerBy on April 21, 2017, 12:32:31 AM
I clearly said that I'm not satisfied with explanations like the one you just mentioned or like "rake and trail help with the stability".
And I told you you can find a lot more details on that in the book.
Call me lazy, but I'm not gonna do a summary of 100+ pages just for your own pleasure.
Quote from: passerBy on April 21, 2017, 12:32:31 AM
If you cannot tell me in your own words what does the rake do, what's the point in your having read that book then (and pointing me to it)?
Oh well, whatever. I think I recall the past discussions with you a bit better now. Bye.
Quote from: HornetMaX on April 21, 2017, 07:59:50 AM
I have T.Foale's book: he proved (in an era where computer simulations where not an option and understanding of bike physics far more limited than today) that you can have a stable behavior without any rake. I also have a research paper that proves that you can have a stable behavior without any rake nor trail. So what ? As I already told you, the rake also have other effects on the bike handling beside pure stability considerations.
Other effects like what, for example? Judging by the experiments, apart from the braking issue, which can be easily alleviated probably by simply making a purpose built bike instead of modifying an existing one, I don't see any problem with having very little rake at all. It wasn't just a couple of experiments, they put the bike through several thousands of kilometers of varying road conditions. Old or not, that sounds like a good proof of concept to me.
QuoteQuote from: passerBy on April 21, 2017, 12:32:31 AM
I clearly said that I'm not satisfied with explanations like the one you just mentioned or like "rake and trail help with the stability".
And I told you you can find a lot more details on that in the book.
Call me lazy, but I'm not gonna do a summary of 100+ pages just for your own pleasure.
I'm sure I can find a lot more details in different books, but I'm not exactly making another bike sim at the moment, which would justify buying the book. And I suspect you are not making one either (to be honest, I'm surprised).
If you have to make a summary of 100+ pages, that means you don't really remember what was written on these pages. I might theoretically not find the information I'm looking for there. At the end of the day, your pointing out to a book is not very helpful, Max.
Also, if I'm being asked a question, I usually try to answer it to the best of my knowledge. And if I point to a resource, it's only to back up my answer, not to brush off the one asking the question instead of giving an answer.
QuoteQuote from: passerBy on April 21, 2017, 12:32:31 AM
If you cannot tell me in your own words what does the rake do, what's the point in your having read that book then (and pointing me to it)?
Oh well, whatever. I think I recall the past discussions with you a bit better now. Bye.
And I remember you sitting on a lower horse back then. Maybe a good time to start treating other people as sentient species once again?
Quote from: passerBy on April 21, 2017, 08:57:57 AM
Maybe a good time to start treating other people as sentient species once again?
I cannot treat you more as sentient as what I'm doing. I'm telling you where to find the knowledge, better explained than what I could do and with diagrams and pictures. You don't like that, fine to me. Over.
Quote from: HornetMaX on April 21, 2017, 09:16:02 AM
Quote from: passerBy on April 21, 2017, 08:57:57 AM
Maybe a good time to start treating other people as sentient species once again?
I cannot treat you more as sentient as what I'm doing. I'm telling you where to find the knowledge, better explained than what I could do and with diagrams and pictures. You don't like that, fine to me. Over.
Max, imagine overhearing someone on the street asking about how to get to a particular location. You come closer to the person and dictate them an ISBN of a good, though expensive address book. Some seemingly ideal solutions are just sub-optimal for particular problems.
rake angle just changes the geometry right? ??? can change ride high't depending on how you go about it.. raising/lowering the forks through the clamp or full offset settings.. makes sense to have some rake angle for the braking forces.. mainly to push the front tyre into the ground for maximum grip. without rake angle id imagine the bike would want to endo more..
obviously changes turning ability and overall stability.. not easy setting a bike up properly so i wouldn't say there's a clear answer.. all the settings need to work together. which takes time and lots of laps.
My front end procedure is to decide which corner I want to set up for(it's usually a long 2nd-3rd gear affair), adjust the rake to suit it then lower the fork offset until the braking stability is good. If it's already stable I raise the offset until it isn't then bring it back a couple of mill'.
May spend days after that faffing around with springs, damping and rideheight :P but rarely change the front geometry again after the first few visits to the garage.
I find it easier if the fork springs are slightly soft to begin with. If they're too stiff the fishtailing on braking is very similar to too little trail so I set the geometry with the springs soft then stiffen them after(again, until things start getting hairy on braking then back a bit).
Quote from: BOBR6 84 on April 21, 2017, 02:35:41 PM
rake angle just changes the geometry right?
A lot can be understood under "just changing the geometry".
Quotemakes sense to have some rake angle for the braking forces..
I agree. After all, braking also changes the geometry. Hence, the 15° Foale's design makes more sense (than the 0° one), in my opinion.
Quotemainly to push the front tyre into the ground for maximum grip. without rake angle id imagine the bike would want to endo more..
Maybe it would be more preferable? Of course you don't want to cartwheel forwards after overusing the brake, but having all the weight on the front wheel only just after the fork has contracted and the dynamic rake came closer to 0 might prove beneficial for shortening the braking distance.
Quoteobviously changes turning ability and overall stability.. not easy setting a bike up properly so i wouldn't say there's a clear answer.. all the settings need to work together. which takes time and lots of laps.
"Changes turning ability and overall stability" doesn't present us with any useful information on what exactly the rake value does. And it's not exactly obvious either how increasing the rake alone would improve on the overall stability. As far as the turning ability goes, I already mentioned the effect before: the closer the fork to vertical, the bigger part of the gyroscopic precession acts exactly laterally when you try to push the bars to a side. But what about the stability?
Quote from: Grooveski on April 21, 2017, 05:58:56 PM
My front end procedure is to decide which corner I want to set up for(it's usually a long 2nd-3rd gear affair), adjust the rake to suit it then lower the fork offset until the braking stability is good. If it's already stable I raise the offset until it isn't then bring it back a couple of mill'.
May spend days after that faffing around with springs, damping and rideheight :P but rarely change the front geometry again after the first few visits to the garage.
Why not set the rake to the minimum and just adapt to the resulting higher flickability? Sure, a particular swinging-over quickness might suit the flow of the track better, but you never know if there won't be an accident in front of you, for example.
QuoteI find it easier if the fork springs are slightly soft to begin with. If they're too stiff the fishtailing on braking is very similar to too little trail so I set the geometry with the springs soft then stiffen them after(again, until things start getting hairy on braking then back a bit).
I'm not quite sure if suspension in GPB works quite as it should. Sometimes even having the softest settings possible doesn't help much on certain tracks. And even at Victoria bumps can be pretty annoying.
Quote from: passerBy on April 22, 2017, 04:06:20 PM
Why not set the rake to the minimum and just adapt to the resulting higher flickability? Sure, a particular swinging-over quickness might suit the flow of the track better, but you never know if there won't be an accident in front of you, for example.
If I go lower on the rake than I have to the bike will want to oversteer in my chosen corner and I'll be having to pick it up a touch to hold the right line. That in itself is ok and allows for mid-corner corrections - for some folk that's just what they're after...
...but I prefer the bike to hold the right line by itself while I do any corrections on the throttle.
Too low a rake will cause the wobbles on the brakes(which most of the time the offset can help with), but it'll also make the bike twitchy through chicanes, prone to headshakes on acceleration, less planted through high speed kinks...
...and the biggie for me - more likely to washout the front on entry. It's top of my list of crash types(like Zarco and Marquez have done the last couple of races) so to me a 'good' setup is one that'll make me feel comfortable between half-full lean angle on entry.
I think it's what most folk are after in a setup, but everyone has their own traits for corner entry so everyone's setups are different. A late braker might want a touch more rake just to allow them to brake deeper into the corner. I sometimes go higher on the rake than I'd like at hairpin-infested hellholes like Motegi or COTA, means the steering will be a bit heavy through the twisty bits but traded off against even one front end washout in a race it's worth it. :)
May be worth mentioning that I generaly go for a shorter swinging arm. That probably has something to do with my rake decisions - short swinging arm and too little rake is an entertaining but not very practical combo. ;D
Quote from: passerBy on April 22, 2017, 04:06:20 PM
I'm not quite sure if suspension in GPB works quite as it should. Sometimes even having the softest settings possible doesn't help much on certain tracks. And even at Victoria bumps can be pretty annoying.
Bumps I deal with by doing a few laps then going into orbit replay mode, swinging it round to side-on and watching what's happening.
Wish I could give a two line procedure for that too but honestly - sometimes it takes ages. ::)
The front - as I said - I start with soft, then up the spring until it starts chattering on the heaviest braking spot on the track.
...then either back it down or increase the rebound damping until it stops.
That's just for the track in general - if there's a particular bump that's giving me grief I may be back in another few times just for it.
Sometimes there are bumps that you just can't tune out. The righthander before the rise near the end of the lap at the A1 Ring has been catching me out for the last few days. Eventualy I just took to doing a Dani and picking the bike up before driving through it - problem solved! :)