Motorcycle geometry thread : V-Twin Forum: Harley Davidson Forums
» Sponsors

» Insurance
Go Back   V-Twin Forum : Harley-Davidson Motorcycle Forums > General Discussion Forums > Harley-Davidson FXR
New User? Register Forgot Password

Reply
 
LinkBack Thread Tools Display Modes
Old 11-12-2012, 11:48 AM   #1 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
Motorcycle geometry thread

How about having this discussion in just one thread instead of having it spread all over the place?

This is what we're talking about... right?





My thinking is that you can change the length of the forks without affecting trail. The only thing that will change trail is rake angle.
You can change rake by cutting and re-welding frame neck, using "raked" triple trees or bearing cups or simply using taller or shorter shocks.
In my personal experience, on the street, I've dropped rear of a motorcycle by 2-3 inches and have not noticed much of a difference in steering. Lowering shocks tend to have less of a travel and stiffer springs. That is much more noticeable than minimal changes in steering.
Going the opposite way (on the track) was a bit more noticeable to me.
Several years ago I was racing Yamaha singles.
My "A" bike had 13in shocks and 18in front wheel. By back-up, "B" bike had a 19in wheel that was quite a bit taller and I noticed some difference in the the it turned in, but my lap times did not reflect that at all. Just out of curiosity, I tried a set of taller shocks. The bike now set closer to my "A" bike, but was 1.25 inches taller in back and about 1in taller in front due to wheel/tire size. That change helped with the "feel" of the bike, the way it turned in to corners and under heavy braking, but again didn't change my lap times. Biggest thing I noticed was not dragging my knee witch saved $$ on knee sliders.
__________________
AL

Last edited by ALAY191; 11-12-2012 at 11:51 AM.
ALAY191 is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 11-12-2012, 06:54 PM   #2 (permalink)
IronButt
 
Rollmeaway's Avatar
 
Join Date: Oct 2010
Location: Kent County, Ontario Canada
Posts: 2,148
Rollmeaway wants to know Dino or Syn?
I am wondering what the question is in your thread.
You are correct in stating that fork length does not change rake angle or trail. Fork length is measured from the top of the fork tubes to the front axle centreline.
Raked trees of over 3* are typically not recommended by most manufacturers or retailers for the reason as you increase the degree* of rake by using raked trees you infact decrease trail. Trail is what will or will not allow for a stable ride.
The proper way to increase the rake is to have the frame neck cut, repositioned & then rewelded.
Raked trees are actually used to reduce trail on a frame raked out so handling is not lazy & more responsive

Most Softails run a 31-33* raked frame with a 3* raked tree for a trail of approx. 5.1-5.75"
Dynas 28-32*
FLH uses 26* ... while Sporster use a 29*-30*
__________________
We never even said a word,
We just walked out and got on that bike
And we rolled...
And we rolled...... clean out of sight




Dare...

2000 FXST - Carbed
Rollmeaway is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 08:23 PM   #3 (permalink)
Master Motorhead
 
Thermodyne's Avatar
 
Join Date: Mar 2011
Location: V-Twin Forum Elite
Posts: 5,230
Thermodyne is reading this now saying WTF is this? Thermodyne is reading this now saying WTF is this?
Increasing rake (laying the fork back at the top) increases steering axis inclination. The greater that number in degrees, the more the wheel rotates on the center-line and the less it yaws. The center line rotation is unwanted.

Adding rake to the trees increases the rotation for a given degree of rake. Example would be a scooter that had a 40 degree steering head and 0 trees having less rotation than a scooter with 32 degree steering head and 8 degree trees. This can be corrected by properly designing the tree so that the upper fork mount is behind the steering head center-line. But this introduces sweep into the equation, so is only used where steering head angles are nearly 0 to perpendicular with the ground or with difficult to steer rigs like side cars and trikes. And usually they just alter rake, lacking the space to back mount the forks.

Adding fork tube length alone does alter the rake, assuming all the addition length is below the head. The longer tubes rotate the frame so as to increase the measured rake. Your confusing advertised rake and actual rake. Advertised rake is measured with the frame at what ever the maker says is level. Usually the lower frame bars are level to the ground, but not always.

Rake and trail are for two dimensional equations and best suited for working with paper designs. Front ends or axles to be precise move in three dimensions. And while the rules of trail still need to be applied, you can have a seriously ****ed up front end with good trail. And you can have a front end that rides just fine with a seriously bad trail measurement.

When you look at the first drawing, there is no value for the distance that the fork center-line is forward of the steering head center line. It only shows the angle and the amount of difference as tree rake. The offset of these center-lines is as important as any measurement on the whole set up. But everyone ignores it. And some tree builders will increase it to gain clearance on wider trees.
__________________

Last edited by Thermodyne; 11-12-2012 at 08:28 PM.
Thermodyne is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 08:56 PM   #4 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
Quote:
Originally Posted by Thermodyne View Post
Increasing rake (laying the fork back at the top) increases steering axis inclination. The greater that number in degrees, the more the wheel rotates on the center-line and the less it yaws. The center line rotation is unwanted.

Adding rake to the trees increases the rotation for a given degree of rake. Example would be a scooter that had a 40 degree steering head and 0 trees having less rotation than a scooter with 32 degree steering head and 8 degree trees. This can be corrected by properly designing the tree so that the upper fork mount is behind the steering head center-line. But this introduces sweep into the equation, so is only used where steering head angles are nearly 0 to perpendicular with the ground or with difficult to steer rigs like side cars and trikes. And usually they just alter rake, lacking the space to back mount the forks.

Adding fork tube length alone does alter the rake, assuming all the addition length is below the head. The longer tubes rotate the frame so as to increase the measured rake. Your confusing advertised rake and actual rake. Advertised rake is measured with the frame at what ever the maker says is level. Usually the lower frame bars are level to the ground, but not always.

Rake and trail are for two dimensional equations and best suited for working with paper designs. Front ends or axles to be precise move in three dimensions. And while the rules of trail still need to be applied, you can have a seriously ****ed up front end with good trail. And you can have a front end that rides just fine with a seriously bad trail measurement.

When you look at the first drawing, there is no value for the distance that the fork center-line is forward of the steering head center line. It only shows the angle and the amount of difference as tree rake. The offset of these center-lines is as important as any measurement on the whole set up. But everyone ignores it. And some tree builders will increase it to gain clearance on wider trees.
Actually, I'm not confusing anything.
The diagrams I posted should shed some light to those who don't know the what rake and trail mean and how they would or NOT be affected much (if at all) by changing shock or fork length by an inch or two.
I agree that some really smart people spend weeks in R&D departments coming up with a perfect compromise of numbers. Those numbers represent the closest to ideal combination for good handling, comfortable ride and ride height to suit most size riders. Variation of shock length and fork length will not affect motorcycles in the real world. Not enough for an average rider to complain about.


So, Krowbar,
you can lower your bike 2 inches in the back and leave your forks stock without altering your trail enough to worry about.

BTW, I didn't bring up triple tree offset so not to muddy the waters even more.
Funny how many guys read magazines, study and memorize numbers that really don't mean anything to them.
__________________
AL
ALAY191 is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 09:44 PM   #5 (permalink)
IronButt
 
Rollmeaway's Avatar
 
Join Date: Oct 2010
Location: Kent County, Ontario Canada
Posts: 2,148
Rollmeaway wants to know Dino or Syn?
A little while back I was in contact with RB Racing to find out from the pros what I could do to increase the rake on my bike & still have a safe & stable ride.

They stated & quote " On a 2000 FXST with a head rake of 31* you can safely go to 3* raked cups, a 3* raked tree & a 3" extension on the fork tube length"
No need to be concerned with handling at all.

By doing so I now have a 37* rake.
Attached Thumbnails
Click image for larger version

Name:	raketrail.gif
Views:	45
Size:	30.7 KB
ID:	74738  
__________________
We never even said a word,
We just walked out and got on that bike
And we rolled...
And we rolled...... clean out of sight




Dare...

2000 FXST - Carbed

Last edited by Rollmeaway; 11-12-2012 at 10:07 PM. Reason: Additional info
Rollmeaway is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 09:59 PM   #6 (permalink)
IronButt
 
Rollmeaway's Avatar
 
Join Date: Oct 2010
Location: Kent County, Ontario Canada
Posts: 2,148
Rollmeaway wants to know Dino or Syn?
Quote:
Originally Posted by Thermodyne View Post
Increasing rake (laying the fork back at the top) increases steering axis inclination. The greater that number in degrees, the more the wheel rotates on the center-line and the less it yaws. The center line rotation is unwanted.

Adding rake to the trees increases the rotation for a given degree of rake. Example would be a scooter that had a 40 degree steering head and 0 trees having less rotation than a scooter with 32 degree steering head and 8 degree trees. This can be corrected by properly designing the tree so that the upper fork mount is behind the steering head center-line. But this introduces sweep into the equation, so is only used where steering head angles are nearly 0 to perpendicular with the ground or with difficult to steer rigs like side cars and trikes. And usually they just alter rake, lacking the space to back mount the forks.

Adding fork tube length alone does alter the rake, assuming all the addition length is below the head. The longer tubes rotate the frame so as to increase the measured rake. Your confusing advertised rake and actual rake. Advertised rake is measured with the frame at what ever the maker says is level. Usually the lower frame bars are level to the ground, but not always.

Rake and trail are for two dimensional equations and best suited for working with paper designs. Front ends or axles to be precise move in three dimensions. And while the rules of trail still need to be applied, you can have a seriously ****ed up front end with good trail. And you can have a front end that rides just fine with a seriously bad trail measurement.

When you look at the first drawing, there is no value for the distance that the fork center-line is forward of the steering head center line. It only shows the angle and the amount of difference as tree rake. The offset of these center-lines is as important as any measurement on the whole set up. But everyone ignores it. And some tree builders will increase it to gain clearance on wider trees.
That is so true & a very good point. Offset is not to be ignored. There is far more to a stable front end that handles as it should over one that doesnt.
I have always said & live by "anytime a front end is altered it must be checked before riding so you know for sure where your at"
Trail is the make or break measurement, it should never be a guess or bygolly.
__________________
We never even said a word,
We just walked out and got on that bike
And we rolled...
And we rolled...... clean out of sight




Dare...

2000 FXST - Carbed
Rollmeaway is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 10:10 PM   #7 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
just out of curiosity ....
how many of you have built or ridden a long 60's style chopper?
__________________
AL
ALAY191 is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 10:16 PM   #8 (permalink)
IronButt
 
Rollmeaway's Avatar
 
Join Date: Oct 2010
Location: Kent County, Ontario Canada
Posts: 2,148
Rollmeaway wants to know Dino or Syn?
I have to confess I didnt start til 1972 so you've got a few on me.
__________________
We never even said a word,
We just walked out and got on that bike
And we rolled...
And we rolled...... clean out of sight




Dare...

2000 FXST - Carbed
Rollmeaway is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 10:20 PM   #9 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
Quote:
Originally Posted by Rollmeaway View Post
I have to confess I didnt start til 1972 so you've got a few on me.
I started few years later than you, but that wasn't the question.
__________________
AL
ALAY191 is offline   Reply With Quote Quick reply to this message
Old 11-13-2012, 11:11 AM   #10 (permalink)
Master Motorhead
 
Thermodyne's Avatar
 
Join Date: Mar 2011
Location: V-Twin Forum Elite
Posts: 5,230
Thermodyne is reading this now saying WTF is this? Thermodyne is reading this now saying WTF is this?
Quote:
Originally Posted by ALAY191 View Post
just out of curiosity ....
how many of you have built or ridden a long 60's style chopper?
Back in the early to mid 70's I rode a few. And had a Sporty with 10 over forks. That's all most people did to em back then. Put some forks tubes in based on the length of our legs. Geometry, what geometry? We pulled the front brakes to keep from spilling them, be we didn't really think too hard on it. Stretch the forks, chrome the frames, put a four foot sissy bar and king and queen seat on em, then wonder why the rear fenders and struts would always crack. Those scooters were all show and no go. If you rode em someplace where looks mattered, ya needed to get there an hour early. So you could wipe the oil off the shinny parts.

To give an example of how little handling was an issue, we ran car tires on the rears. Didn't take much of a lean to make them get real stupid and evil.

This was back when Harleys were right side shift. So you put a guy off a Honda or Yammie on a Sporty with long forks and right shift, they were usually a little overwhelmed at first.

Where I lived back then, Triumph was king in the late 60's early 70's. Mostly because the Local AMF dealers were only interested in selling new scooters and a guy named Sonny Routt had a local Triumph Shop in the area.

Any of you old enough to have seen one of these on someone?

__________________

Last edited by Thermodyne; 11-13-2012 at 11:32 AM.
Thermodyne is offline   Reply With Quote Quick reply to this message
Old 11-13-2012, 12:30 PM   #11 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
Quote:
Originally Posted by Thermodyne View Post
Back in the early to mid 70's I rode a few. And had a Sporty with 10 over forks. That's all most people did to em back then. Put some forks tubes in based on the length of our legs. Geometry, what geometry? We pulled the front brakes to keep from spilling them, be we didn't really think too hard on it. Stretch the forks, chrome the frames, put a four foot sissy bar and king and queen seat on em, then wonder why the rear fenders and struts would always crack. Those scooters were all show and no go. If you rode em someplace where looks mattered, ya needed to get there an hour early. So you could wipe the oil off the shinny parts.

To give an example of how little handling was an issue, we ran car tires on the rears. Didn't take much of a lean to make them get real stupid and evil.

This was back when Harleys were right side shift. So you put a guy off a Honda or Yammie on a Sporty with long forks and right shift, they were usually a little overwhelmed at first.

Where I lived back then, Triumph was king in the late 60's early 70's. Mostly because the Local AMF dealers were only interested in selling new scooters and a guy named Sonny Routt had a local Triumph Shop in the area.

Any of you old enough to have seen one of these on someone?

Can't say that I've ever seen one. At least no recollection of it ...
I bought my first Sporty in Feb of 1980. It was a '69 XLCH with 9 over girder, spool front wheel, tall twisted Z-brars, twisted sissy bar and twisted highway pegs way up on the front tubes of the frame. Non matching twisted RR spikes for pegs. It was a real beaut, but it it was all mine. After that I rode a mostly stock '75 XLH that shifted on the left along with a BSA. Next came my '77 FXE with 4over forks and reverse shifting on the left and my bar hopper was a '67 Triumph with bolt-on rigid an 6over forks ...
I guess I've been up and down the block with 2 Sporties, 3 Shovels, 4 Evos, a Twinkie, several Brits, several BMWs and a dozen or so *** bikes...and that doesn't even include any MX bikes since I was 7.
The moral of this story is that I never knew what the trail of any of them was.
When we raked one of my Triumphs in the garage we cut the frame tube below the neck and with longer forks still in the trees, we heated top tube and bent the neck back till the bike set level ... was it 10 or 15 degree rake? no idea ... but the bike set low and parallel to the ground with 6over forks. I'm not a fan of long bikes, but I did just to be able to say "I did it". I still have another long Triumph, but plan on de-raking it soon.
__________________
AL
ALAY191 is offline   Reply With Quote Quick reply to this message
Old 11-14-2012, 09:24 PM   #12 (permalink)
IronButt
 
Rollmeaway's Avatar
 
Join Date: Oct 2010
Location: Kent County, Ontario Canada
Posts: 2,148
Rollmeaway wants to know Dino or Syn?
Quote:
Originally Posted by ALAY191 View Post
I started few years later than you, but that wasn't the question.
Its like I said I didnt ride & build til '72 so the 70's style choppers were all I rode. I would hope no further explanation is needed to grasp what has already been said.

Im not into explaing who's hammer or wrench is bigger & besides I thought this thread was about steering/front end geometry.

Maybe I misunderstood your intentions on geometry.
__________________
We never even said a word,
We just walked out and got on that bike
And we rolled...
And we rolled...... clean out of sight




Dare...

2000 FXST - Carbed
Rollmeaway is offline   Reply With Quote Quick reply to this message
Old 11-14-2012, 10:40 PM   #13 (permalink)
IronButt
 
ALAY191's Avatar
 
Join Date: Jul 2010
Location: NOMAD
Posts: 581
ALAY191 wants to know Dino or Syn?
Quote:
Originally Posted by Rollmeaway View Post
Its like I said I didnt ride & build til '72 so the 70's style choppers were all I rode. I would hope no further explanation is needed to grasp what has already been said.

Im not into explaing who's hammer or wrench is bigger & besides I thought this thread was about steering/front end geometry.

Maybe I misunderstood your intentions on geometry.
???
I started a discussion thread and thought some resident experts would participate.
I'm confused as to why you'd take it any other way.
__________________
AL
ALAY191 is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the V-Twin Forum : Harley-Davidson Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself. WE WILL SEND A CONFIRMATION EMAIL TO THE ADDRESS YOU PROVIDE. If the email address is NOT VALID, you will not be given access to the system!
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Powered by vBadvanced CMPS v3.2.2

All times are GMT -5. The time now is 07:09 AM.


Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO 3.6.0
(C)2001-2012 V-twinForum.com All Rights Reserved (C)2001- V-twinForum.com All Rights Reserved
Motorcycle News, Videos and Reviews
Honda Grom Forum Harley Davidson Forum Honda 600RR Kawasaki Forum Yamaha R6 Forum Yamaha FZ-09 Forum
1199 Panigale Forum Roadglide Forum Honda CBR1000 Forum Vulcan Forum Yamaha R1 Forum Yamaha R3 Forum
Ducati Monster Forum Harley Forums Honda CBR250R Forum ZX10R Forum Star Raider Forum Yamaha Viking Forum
Suzuki GSXR Forum V-Rod Forums Honda Shadow Forum Kawasaki Motorcycle Forum Star Warrior Forum KTM Duke 390 Forum
SV650 Forum BMW S1000RR Forum Honda Fury Forum Kawasaki Versys Forum Drag Racing Forum Ducati 899 Panigale Forum
Suzuki V-Strom BMW K1600 Triumph Forum Victory Forums Sportbikes BMW NineT Forum
Volusia Forum BMW F800 Forum Triumph 675 Forum MV Agusta Forum HD Street Forum Suzuki GW250 Forum
Yamaha Motorcycles Victory Gunner Forum Honda Vultus Forum HD LiveWire Forum Ninja H2 Forum Ducati Scrambler Forum