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Doubts setup

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

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passerBy

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.

Quote
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.

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.

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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.

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?

HornetMaX

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.

passerBy

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. 

BOBR6 84

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.

Grooveski

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).


passerBy

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?

passerBy

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.

Grooveski

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

Grooveski

April 24, 2017, 01:25:06 am #38 Last Edit: April 24, 2017, 01:26:45 am by Grooveski
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!   :)