Post by "Chainsaw" Jim Johnson on Feb 26, 2015 22:14:55 GMT -5
Chainsaw wrote in October, 2007 ..... "Where to find springs for your bikes?
This topic actually came up over on another board.
Here are a few of the ideas of where to find them came.
Home Depot
www.choppersus.com/
www.mcmaster.com/
Northern Tool supply store
old/broken front susp. forks from mtn bikes
engine valve springs (Obtainable from a local engine reconditioner if you have one near by)
spring factory in your neighbourhood
U.S. "TSC" store (Porch Swing springs and under-seat springs off a "Yardman" riding mower)"
4th Horseman .... "Springer Fork ...
Here's John Brain's link to building a springer for reference.."
bikerodnkustom3.home/ stead.com/brainfork.html
Pulled off of the old ChopperBicycle.net board .....
4th Horseman ... "Here's an easily explainable sketch I made up a while back that shows the simplified reasoning behind trail calculation. If you use this method you should have good results no matter what RAKE (angle) you go with.
Draw a line through the center of your headtube and project it out all the way to the point where it meets the ground. (shown in purple)
Drop a vertical line down through the axle center to the point where it hits the ground. (shown in blue)
The difference between the two points is your TRAIL (shown in green). Some will say that this measurement should be between 2 and 6 inches. I say for what we do on a bicycle, the best bet is between 2 and 4 inches.
The greater this number, the more wheel "flop" you will have when riding slowly. This effect will diminish with speed but for relatively slow cruising you are better off with a smaller amount of trail.
Quote:
tinydb84
Here is a great site with rake and trail explained.
64.172.168.34/neatstuff/rakeandtrail.htm
Quote:
rockx
An other explanation and a calculator are right here: www.bikes.rockx.net/cruisinn/rake.htm
Quote:
Originally Posted by Leinad333
Okay, I'm new to bike engineeringses, and ignore me if this has been covered already. If it steers better with little trail why do you have it at all? I want to make a springer front end. Is it better to do leading or trailing? I kind of like the geometry of doing it where the wheel is trailing behind the fork, and I would like any advice on why this is not so popular.
Thanks to every one who is helping us nubies!
4th horseman
Good question.... like everything else, too much or too little of a good thing isn't always a "good thing". The whole exercise behind these calculations is to end up with predictable steering over the speed range that the vehicle is to be used in.
Fortunately, the speed range of these bicycles is very low and you can afford to take some liberties with design. A "slow" bicycle could ride very well with zero or negative trail.
To answer your second question, there's no reason why the fork structure can't be located in "front" of the wheel. If you do the rake and trail geometry correctly, the physical location of the supporting structure doesn't matter that much to steering "feel".
Don't forget that you can alter the fork leg location by using offset or angled crowns.
Here's an experiment done to check the theory of rake VS trail. Keep in mind that this is a motorcycle with much higher speeds and braking forces.
www.tonyfoale.com/Articles/RakeEx/RakeEx.htm
Quote:
Originally Posted by 4th horseman
To answer your second question, there's no reason why the fork structure can't be located in "front" of the wheel. If you do the rake and trail geometry correctly, the physical location of the supporting structure doesn't matter that much to steering "feel".
heist
except if that fork structure is heavy, then it will try to fall over (flop)
even more so with increasing rake. (like having a basket in front)
If you would take that purple line, I think it's best if the center of weight of the fork is located as close to that purple line as possible. The fork on the bobcat has it's weight above the purple line, and I do notice this difference compared to 'normal' forks.
It isn't raked that much, so it'll be fine..
Quote:
Originally Posted by Leinad333
If it steers better with little trail why do you have it at all?
txwayno
Newbie here. I am no expert, but I know a little about this topic. I use to run an online Harley parts biz and this issue came up a lot. The best way I found to describe what not having enough rake is like, is to refer to a shopping cart. You know how the wheels shake and shimmy as you push it?? If they had rake, they would track better.
Quote:
junkman
I remember seeing a show on TV where they took a diamond frame bike and pushed it down a hill with no rider, it went into the ditch,
Then they turned the handlebar around so the wheel was backwards.
They sent it down the hill with the wheel (and forks) backwards, and it went for about a half mile perfectly straight.
That must have been a lot of negative trail, just like a shopping cart wheel.
I think I have seen some bikes like that,
Here's one (sorta) www.flevobikeusa.com/ /
Quote:
Originally Posted by Junkman
I remember seeing a show on TV where they took a diamond frame bike and pushed it down a hill with no rider, it went into the ditch,
Then they turned the handlebar around so the wheel was backwards.
They sent it down the hill with the wheel (and forks) backwards, and it went for about a half mile perfectly straight.
That must have been a lot of negative trail, just like a shopping cart wheel.
I think I have seen some bikes like that,
Here's one (sorta) www.flevobikeusa.com/ /
Hannan customs
The term ''negative trail'' is a little confusing...
To me the axle is ''trailing'', (like stock bikes to raked choppers), or, ''leading'' (like typical lowriders).
Just my 2.34 canadian cents.
Eric.
Quote:
Kingpin
so if u have less angle to the forks (what i always thought of as rake) there would be less trail inherently?
Quote:
Rockx
I agree on Hannan's remarks on using the term 'leading' in favor of 'negative trail', it's just that calculators may come up with negative values.
@ Kingpin: Check the Rawbarian by Sami: It shows how the fork is raked in order to end up with about two inches of trail. Just follow the centerline of the headtube and you'll notice it hits the ground just in front of the wheel.
www.choppernewsnetwo/ rk.com...id=1462&Itemid=
Quote:
tomitiitto
if there was a lot of this "negative trail", would it mean to turn u would have to use some force to get the fork turn?
Quote:
Rockx
Quite the opposite... The bike sorta wants to overtake the frontwheel > makes you correct it all of the time, especially at higher speeds. Try riding a bent springer: when turning left it feels like the frame points to the right.
Quote:
5ugardaddy
I've seen alot of home jobs done by people whith no idea about geometry. A bike with bad geometry is DANGEROUS!! Choppers and stretched cruisers are already difficult to controle, if you jack-knife your fork on a busy road or highway you could be in trouble (the trail on my ride is 1.5"-2" which drops slightly when the fork is compressed)
This topic actually came up over on another board.
Here are a few of the ideas of where to find them came.
Home Depot
www.choppersus.com/
www.mcmaster.com/
Northern Tool supply store
old/broken front susp. forks from mtn bikes
engine valve springs (Obtainable from a local engine reconditioner if you have one near by)
spring factory in your neighbourhood
U.S. "TSC" store (Porch Swing springs and under-seat springs off a "Yardman" riding mower)"
4th Horseman .... "Springer Fork ...
Here's John Brain's link to building a springer for reference.."
bikerodnkustom3.home/ stead.com/brainfork.html
Pulled off of the old ChopperBicycle.net board .....
4th Horseman ... "Here's an easily explainable sketch I made up a while back that shows the simplified reasoning behind trail calculation. If you use this method you should have good results no matter what RAKE (angle) you go with.
Draw a line through the center of your headtube and project it out all the way to the point where it meets the ground. (shown in purple)
Drop a vertical line down through the axle center to the point where it hits the ground. (shown in blue)
The difference between the two points is your TRAIL (shown in green). Some will say that this measurement should be between 2 and 6 inches. I say for what we do on a bicycle, the best bet is between 2 and 4 inches.
The greater this number, the more wheel "flop" you will have when riding slowly. This effect will diminish with speed but for relatively slow cruising you are better off with a smaller amount of trail.
Quote:
tinydb84
Here is a great site with rake and trail explained.
64.172.168.34/neatstuff/rakeandtrail.htm
Quote:
rockx
An other explanation and a calculator are right here: www.bikes.rockx.net/cruisinn/rake.htm
Quote:
Originally Posted by Leinad333
Okay, I'm new to bike engineeringses, and ignore me if this has been covered already. If it steers better with little trail why do you have it at all? I want to make a springer front end. Is it better to do leading or trailing? I kind of like the geometry of doing it where the wheel is trailing behind the fork, and I would like any advice on why this is not so popular.
Thanks to every one who is helping us nubies!
4th horseman
Good question.... like everything else, too much or too little of a good thing isn't always a "good thing". The whole exercise behind these calculations is to end up with predictable steering over the speed range that the vehicle is to be used in.
Fortunately, the speed range of these bicycles is very low and you can afford to take some liberties with design. A "slow" bicycle could ride very well with zero or negative trail.
To answer your second question, there's no reason why the fork structure can't be located in "front" of the wheel. If you do the rake and trail geometry correctly, the physical location of the supporting structure doesn't matter that much to steering "feel".
Don't forget that you can alter the fork leg location by using offset or angled crowns.
Here's an experiment done to check the theory of rake VS trail. Keep in mind that this is a motorcycle with much higher speeds and braking forces.
www.tonyfoale.com/Articles/RakeEx/RakeEx.htm
Quote:
Originally Posted by 4th horseman
To answer your second question, there's no reason why the fork structure can't be located in "front" of the wheel. If you do the rake and trail geometry correctly, the physical location of the supporting structure doesn't matter that much to steering "feel".
heist
except if that fork structure is heavy, then it will try to fall over (flop)
even more so with increasing rake. (like having a basket in front)
If you would take that purple line, I think it's best if the center of weight of the fork is located as close to that purple line as possible. The fork on the bobcat has it's weight above the purple line, and I do notice this difference compared to 'normal' forks.
It isn't raked that much, so it'll be fine..
Quote:
Originally Posted by Leinad333
If it steers better with little trail why do you have it at all?
txwayno
Newbie here. I am no expert, but I know a little about this topic. I use to run an online Harley parts biz and this issue came up a lot. The best way I found to describe what not having enough rake is like, is to refer to a shopping cart. You know how the wheels shake and shimmy as you push it?? If they had rake, they would track better.
Quote:
junkman
I remember seeing a show on TV where they took a diamond frame bike and pushed it down a hill with no rider, it went into the ditch,
Then they turned the handlebar around so the wheel was backwards.
They sent it down the hill with the wheel (and forks) backwards, and it went for about a half mile perfectly straight.
That must have been a lot of negative trail, just like a shopping cart wheel.
I think I have seen some bikes like that,
Here's one (sorta) www.flevobikeusa.com/ /
Quote:
Originally Posted by Junkman
I remember seeing a show on TV where they took a diamond frame bike and pushed it down a hill with no rider, it went into the ditch,
Then they turned the handlebar around so the wheel was backwards.
They sent it down the hill with the wheel (and forks) backwards, and it went for about a half mile perfectly straight.
That must have been a lot of negative trail, just like a shopping cart wheel.
I think I have seen some bikes like that,
Here's one (sorta) www.flevobikeusa.com/ /
Hannan customs
The term ''negative trail'' is a little confusing...
To me the axle is ''trailing'', (like stock bikes to raked choppers), or, ''leading'' (like typical lowriders).
Just my 2.34 canadian cents.
Eric.
Quote:
Kingpin
so if u have less angle to the forks (what i always thought of as rake) there would be less trail inherently?
Quote:
Rockx
I agree on Hannan's remarks on using the term 'leading' in favor of 'negative trail', it's just that calculators may come up with negative values.
@ Kingpin: Check the Rawbarian by Sami: It shows how the fork is raked in order to end up with about two inches of trail. Just follow the centerline of the headtube and you'll notice it hits the ground just in front of the wheel.
www.choppernewsnetwo/ rk.com...id=1462&Itemid=
Quote:
tomitiitto
if there was a lot of this "negative trail", would it mean to turn u would have to use some force to get the fork turn?
Quote:
Rockx
Quite the opposite... The bike sorta wants to overtake the frontwheel > makes you correct it all of the time, especially at higher speeds. Try riding a bent springer: when turning left it feels like the frame points to the right.
Quote:
5ugardaddy
I've seen alot of home jobs done by people whith no idea about geometry. A bike with bad geometry is DANGEROUS!! Choppers and stretched cruisers are already difficult to controle, if you jack-knife your fork on a busy road or highway you could be in trouble (the trail on my ride is 1.5"-2" which drops slightly when the fork is compressed)