Custom built question - fork rake and trail

[Ken Marcet]

Okay here it is if someone could help me with this one I would be very
greatful.
I just finished my first custom built swb bent and on my first test ride I
noticed the steering is ultra sensitive.
I and using a standard Murray 10 speed road frame, forks off of the same
roadie and a 20 rim / tire.
I measured the trail and it looks like I have about 1 inch of negative
trail, I projected a line from the center of the headtube and a line through
the center of the axle and the projected line from the headtube is about 1
inch in front of the projected line of the axle. Correct me if I am wrong
but that would be considered negative trail correct?
Anyway the steering is really sensitive and seems to be suffering from
oversteer. It make the bike almost unridable, Of course some of this could
be me not being used to the bike. Most of the custom bikes I have seen have
forks that are bent to give more rake, my question is how much trail would
be considered normal.

Ken


--
It has yet to be proven that intelligence has any survival value.
Arthur C. Clarke
English physicist & science fiction author (1917 - )

[S. Delaire \Rotatorrecumbent\]

Somewhere close to 2" of castor / trail (trails behind the steering axis) for a
typical swb
Think of it like a flag with wind blowing on it. A flag always trails behind the
pole.
The fork would really like to trail behind the steering axis but you, the rider,
is forcing it to stay in front.
Turn the fork around and see how it feels.
Check frame alignment.
Speedy

Ken Marcet wrote:

> Okay here it is if someone could help me with this one I would be very
> greatful.
> I just finished my first custom built swb bent and on my first test ride I
> noticed the steering is ultra sensitive.
> I and using a standard Murray 10 speed road frame, forks off of the same
> roadie and a 20 rim / tire.
> I measured the trail and it looks like I have about 1 inch of negative
> trail, I projected a line from the center of the headtube and a line through
> the center of the axle and the projected line from the headtube is about 1
> inch in front of the projected line of the axle. Correct me if I am wrong
> but that would be considered negative trail correct?
> Anyway the steering is really sensitive and seems to be suffering from
> oversteer. It make the bike almost unridable, Of course some of this could
> be me not being used to the bike. Most of the custom bikes I have seen have
> forks that are bent to give more rake, my question is how much trail would
> be considered normal.
>
> Ken
>
> --
> It has yet to be proven that intelligence has any survival value.
> Arthur C. Clarke
> English physicist & science fiction author (1917 - )


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[[email protected]]

Ken Marcet wrote:
> I measured the trail and it looks like I have about 1 inch of
negative
> trail, I projected a line from the center of the headtube and a line
through
> the center of the axle and the projected line from the headtube is
about 1
> inch in front of the projected line of the axle.

I don't think you're measuring trail correctly. Trail is the distance
from where the head angle hits the ground to a point directly below the
front axle. Here's a good article, picture, and calculation method:
http://www.phred.org/~josh/bike/trail.html

Jeff

[Bill Patterson]

wrote:> front axle. Here's a good article, picture,
and calculation method:
> http://www.phred.org/~josh/bike/trail.html
>
> Jeff
>
Jeff has hit it on the head. AS the bike gets lower and the seat tilts
back, we need a little more trail to keep the bike from being twitchy.
The problem is that more trail also gives more control force. You can
also go to a steel rim on the wheels or add tiller to reduce the twitch.

I would turn the fork around first. It's easy and cheap.

--
Don’t be a 0 to 60 sheep, be a 60 mpg wolf. Yes Miles Per Gallon.

See some Bikes At:

http://home.earthlink.net/~wm.patterson/index.html


Class and Helicopter

http://www.calpoly.edu/~wpatters/

The Pony Express
http://www.geocities.com/Pentagon/Base/6850/PonySong.html


Reply to

[Ken Marcet]

That is how I measured my trail, and the line extended from my forks hits
the ground about 1 and 5/16 in front of the line I dropped down from the
axle. I was or should I say still am a bit confused about whether this is
considered positive or negative trail. I have been emailing back and fourth
with A.D. Carson of recycledrecumbents.com and he has told me that it is
positive trail, and after sending him a couple of digital photos of my bike
he has figured that my headtube angle is really steep at about 81 degrees..
He has also told me that raking my fork further will not help, but suggests
that I try a 24 inch tire if it will fit or learn to love my twitchy
steering.

Ken

> wrote in message
oups.com...
>
> Ken Marcet wrote:
> > I measured the trail and it looks like I have about 1 inch of
> negative
> > trail, I projected a line from the center of the headtube and a line
> through
> > the center of the axle and the projected line from the headtube is
> about 1
> > inch in front of the projected line of the axle.
>
> I don't think you're measuring trail correctly. Trail is the distance
> from where the head angle hits the ground to a point directly below the
> front axle. Here's a good article, picture, and calculation method:
> http://www.phred.org/~josh/bike/trail.html
>
> Jeff
>

[Bill Patterson]

Again,

try turning the the front fork around. It will increase trail and take
away the twitch. ]

Bill

Ken Marcet wrote:
> That is how I measured my trail, and the line extended from my forks hits
> the ground about 1 and 5/16 in front of the line I dropped down from the
> axle. I was or should I say still am a bit confused about whether this is
> considered positive or negative trail. I have been emailing back and fourth
> with A.D. Carson of recycledrecumbents.com and he has told me that it is
> positive trail, and after sending him a couple of digital photos of my bike
> he has figured that my headtube angle is really steep at about 81 degrees..
> He has also told me that raking my fork further will not help, but suggests
> that I try a 24 inch tire if it will fit or learn to love my twitchy
> steering.
>
> Ken
>
> > wrote in message
> oups.com...
>
>>Ken Marcet wrote:
>>
>>>I measured the trail and it looks like I have about 1 inch of
>>
>>negative
>>
>>>trail, I projected a line from the center of the headtube and a line
>>
>>through
>>
>>>the center of the axle and the projected line from the headtube is
>>
>>about 1
>>
>>>inch in front of the projected line of the axle.
>>
>>I don't think you're measuring trail correctly. Trail is the distance
>>from where the head angle hits the ground to a point directly below the
>>front axle. Here's a good article, picture, and calculation method:
>>http://www.phred.org/~josh/bike/trail.html
>>
>>Jeff
>>
>
>


--
Don’t be a 0 to 60 sheep, be a 60 mpg wolf. Yes Miles Per Gallon.

See some Bikes At:

http://home.earthlink.net/~wm.patterson/index.html


Class and Helicopter

http://www.calpoly.edu/~wpatters/

The Pony Express
http://www.geocities.com/Pentagon/Base/6850/PonySong.html


Reply to

[[email protected]]

Ken Marcet wrote:
> That is how I measured my trail, and the line extended from my forks
hits
> the ground about 1 and 5/16 in front of the line I dropped down from
the
> axle. I was or should I say still am a bit confused about whether
this is
> considered positive or negative trail.

This is positive trail: the contact patch of the tire is behind the
rotational axis of the fork. It's not much trail- 2 inches would be
closer to "normal". If you take some rake out of the fork, you'll have
more trail.

Jeff

[Ken Marcet]

I have tried like you said to turn the fork around, however due to my
design, and lack of experience, I don't have enough clearence with my chain
management system pulleys. But after riding it a couple more times I have
started to become used to the twitchiness!

Ken

"Bill Patterson" > wrote in message
k.net...
> wrote:> front axle. Here's a good article, picture,
> and calculation method:
> > http://www.phred.org/~josh/bike/trail.html
> >
> > Jeff
> >
> Jeff has hit it on the head. AS the bike gets lower and the seat tilts
> back, we need a little more trail to keep the bike from being twitchy.
> The problem is that more trail also gives more control force. You can
> also go to a steel rim on the wheels or add tiller to reduce the twitch.
>
> I would turn the fork around first. It's easy and cheap.
>
> --
> Don’t be a 0 to 60 sheep, be a 60 mpg wolf. Yes Miles Per Gallon.
>
> See some Bikes At:
>
> http://home.earthlink.net/~wm.patterson/index.html
>
>
> Class and Helicopter
>
> http://www.calpoly.edu/~wpatters/
>
> The Pony Express
> http://www.geocities.com/Pentagon/Base/6850/PonySong.html
>
>
> Reply to
>
>