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Doubts setup

Started by Adalgood, February 19, 2016, 03:13:16 pm

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Napalm Nick

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!
"The post you are writing has been written at least ten times already in the last 15ish years. Its already been reported, suggested, discussed, ignored or archived (but mostly ignored). Why are you doing it again?"

Meyer#12

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 :)
Meyer#12

Napalm Nick

no wonder you let me do your setups haha  ;) Wish I could get as much out of them as you do tho  ::)
"The post you are writing has been written at least ten times already in the last 15ish years. Its already been reported, suggested, discussed, ignored or archived (but mostly ignored). Why are you doing it again?"

Meyer#12

Hey hey! For A1 i am on my own setup and see where it brought me ;) love the new rideheight options :P
Meyer#12

Napalm Nick

Yes they are great.

Forget your old times they are already smashed in Qually  ::) even I have a '27
"The post you are writing has been written at least ten times already in the last 15ish years. Its already been reported, suggested, discussed, ignored or archived (but mostly ignored). Why are you doing it again?"

Meyer#12

Well well well, my times was on old worn out hards, will be faster now when testing softs and more setup work ;)
Meyer#12

NorCal

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.

passerBy

April 20, 2017, 03:00:13 am #22 Last Edit: April 20, 2017, 04:13:43 am by passerBy
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.

HornetMaX

@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

passerBy

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

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.

HornetMaX

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.

passerBy

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.

Quote
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 ...

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".

HornetMaX

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.

passerBy

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.

HornetMaX

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.