Advice on a bent design

[Sticker Jim]

After a couple more trikes, I'm going to try my first bent.
From reading sites, checking dimensions and looking at
commercial bents, I came up with a pretty standard version
of a semi-low racer (I guess it would be called) made out of
2" box tube. One thing I realized is that the front end
design is pretty dependent on how much foot/wheel overlap
you decide is acceptable. At any rate, the main question is
about rake and trail. I have the design set to 70 degrees
and about 3" of trail. I tried 60 degrees, but it looked far
too laid back and the boom had to be very long to reduce
heel/wheel overlap, or I had to raise the pilot position
higher than I wanted. I remember reading that the optimum
place to start was about 65 degrees for rake, and to aim for
4" to 4.5" for trail. The wheel base is 50" and I'm not sure
of the weight (likely around the 30 LB mark) but I'm not
worried about the frame flexing or the swing arm. Based on
experienced bent riders, does the basic design at least look
rideable and will the 60 deg/3" trail work ok with the 50"
wheel base?

Thanks.

http://bikes.jkcc.com/cads/1st%20bent%202.jpg

 

[Tom Sherman]

Sticker Jim wrote:

> After a couple more trikes, I'm going to try my first
> bent. From reading sites, checking dimensions and
> looking at commercial bents, I came up with a pretty
> standard version of a semi-low racer (I guess it would
> be called) made out of 2" box tube. One thing I
> realized is that the front end design is pretty
> dependent on how much foot/wheel overlap you decide is
> acceptable....

Moving the BB higher relative to the seat will also reduce
foot/wheel interference. The only reason not to use a higher
BB (6+ inches/16+ cm) on a SWB bike is foot numbness. The
shorter boom will also improve weight distribution. Others
may disagree, but I have found the best handling SWB bikes
to be those with a slight rearward weight bias.

--
Tom Sherman - Quad Cities (Illinois Side)

 

[Robert Haston]

2" box tube home built you say? How about this one?

http://home.earthlink.net/~rehaston/

The angles and trail are identical to a road bike,
around 1" of trail. This is also similar to my M5. That
is if I am defining trail correctly as the distance from
where the steering axis intercepts the ground to where
the tire contacts.

The tiller available with the handlebars tilted down
desensitizes the steering, so it handled well at low speed.

"Sticker Jim" <[email protected]> wrote in message news:%pQ5c.305-
[email protected]...
>After a couple more trikes, I'm going to try my first bent.
> From
> reading sites, checking dimensions and looking at
> commercial bents, I came
> up with a pretty standard version of a semi-low racer (I
> guess it would be
> called) made out of 2" box tube. One thing I realized is
> that the front
end
> design is pretty dependent on how much foot/wheel overlap
> you decide is acceptable. At any rate, the main question
> is about rake and trail. I have the design set to 70
> degrees and about 3" of trail. I tried 60 degrees, but
it
> looked far too laid back and the boom had to be very long
> to reduce heel/wheel overlap, or I had to raise the pilot
> position higher than I wanted. I remember reading that the
> optimum place to start was about 65 degrees for rake, and
> to aim for 4" to 4.5" for trail. The wheel base is 50" and
> I'm not sure of the weight (likely around the 30 LB mark)
> but I'm not worried about the frame flexing or the swing
> arm. Based on
experienced
> bent riders, does the basic design at least look
> rideable and will the 60 deg/3" trail work ok with the
> 50" wheel base?
>
> Thanks.
>
>
> http://bikes.jkcc.com/cads/1st%20bent%202.jpg

 

[Sticker Jim]

> > One thing I realized is that the front end design is
> > pretty dependent on how much foot/wheel overlap you
> > decide is acceptable....
>
> Moving the BB higher relative to the seat will also reduce
> foot/wheel interference. The only reason not to use a
> higher BB (6+ inches/16+ cm) on a SWB bike is foot
> numbness. The shorter boom will also improve weight
> distribution. Others may disagree, but I have found the
> best handling SWB bikes to be those with a slight rearward
> weight bias.
>
> --
> Tom Sherman - Quad Cities (Illinois Side)

I wanted to try to keep the BB as low as possible for the
reasons you mentioned - foot problems. I broke my back and
have numbness problems and occasional hotfoot when I ride my
trikes as it is, but the problem is slowly taking longer and
longer to present itself the more I train on the trikes. I
decided with the bent I would try to start out with only
about 4 to 5" between the seat bottom and the BB and try it
from there. So, while trying to minimize seat to BB
distance, keep the seat as low to the ground as possible and
minimize wheel/heel interference, the only option seemed to
be stretch the boom a little. It'll be about 19" from head
to BB, a little long I think, so for stiffness, that's why I
went with 2".

As for weight distribution, with the size of my butt, as my
pedaling technique improves, I'm hoping both weight
distribution and pedal steer will not be an issue. If it is,
I take the saw to it and try again

 

[Sticker Jim]

Uhmmm, I should have said 2" steel (not Chro Mo, just mild),
vs aluminum which is what yours appears to be made out of? I
was going to use 1 1/2" x .064 box steel but thought there
would be too much boom flex at the length I was going to
make it, so switched to 2".

I think that's a cool looking bent too Nice short boom
and looks as if it has a little more wheel/foot overlap than
mine will. I think your seat solution is excellent. I might
"borrow" a slightly modified version of that cool little
triangle for my seat as well. The actual seat I'm going to
use will have more of a "C" shape to it, but I haven't
rendered it out yet, so used a trike seat instead. I really
like the nice straight chain line on yours as well. I wanted
to get my seat a bit lower than yours so I had to sacrifice
chain line to do it.

I will decide what type of steering I'll try once the wheels
seat and cranks are on it, but I'll make provisions for it
to be able to have both OSS and/or USS.

"Robert Haston" <[email protected]> wrote in message
news:[email protected]...
> 2" box tube home built you say? How about this one?
>
> http://home.earthlink.net/~rehaston/
>
> The angles and trail are identical to a road bike, around
> 1" of trail.
This
> is also similar to my M5. That is if I am defining trail
> correctly as the distance from where the steering axis
> intercepts the ground to where the tire contacts.
>
> The tiller available with the handlebars tilted down
> desensitizes the steering, so it handled well at low
> speed.

 

[Jeff Wills]

"Sticker Jim" <[email protected]> wrote in message news:<%pQ5c-
[email protected]
>... <snip>
> At any rate, the main question is about rake and
> trail. I have the design set to 70 degrees and about
> 3" of trail. I tried 60 degrees, but it looked far too
> laid back and the boom had to be very long to reduce
> heel/wheel overlap, or I had to raise the pilot
> position higher than I wanted. I remember reading that
> the optimum place to start was about 65 degrees for
> rake, and to aim for 4" to 4.5" for trail. The wheel
> base is 50" and I'm not sure of the weight (likely
> around the 30 LB mark) but I'm not worried about the
> frame flexing or the swing arm. Based on experienced
> bent riders, does the basic design at least look
> rideable and will the 60 deg/3" trail work ok with the
> 50" wheel base?

It sounds like a recipe for fork flop. The low racers that
I've seen use about a 73 degree head angle and almost no
offset on the fork. The OHPV Varna gang built their chassis
around these dimensions and all were ridden very
successfully: http://www.ohpv.org/pir2003/varnas/index.htm .
All the riders were comfortable on their bikes with or
without the fairings.

BTW: careful with the terminology. "Rake" to bicycle people
means "distance from the front axle to the steering axis"
aka "offset". "Rake" to motorcycle people means "angle of
the steering axis from vertical" aka "head angle". I prefer
to avoid the term altogether.

Jeff

 

[Tom Sherman]

Sticker Jim wrote:

>>>One thing I realized is that the front end design is
>>>pretty dependent on how much foot/wheel overlap you
>>>decide is acceptable....
>>
>>Moving the BB higher relative to the seat will also reduce
>>foot/wheel interference. The only reason not to use a
>>higher BB (6+ inches/16+ cm) on a SWB bike is foot
>>numbness. The shorter boom will also improve weight
>>distribution. Others may disagree, but I have found the
>>best handling SWB bikes to be those with a slight rearward
>>weight bias.
>>
>>--
>>Tom Sherman - Quad Cities (Illinois Side)
>
>
> I wanted to try to keep the BB as low as possible for the
> reasons you mentioned - foot problems. I broke my back and
> have numbness problems and occasional hotfoot when I ride
> my trikes as it is, but the problem is slowly taking
> longer and longer to present itself the more I train on
> the trikes. I decided with the bent I would try to start
> out with only about 4 to 5" between the seat bottom and
> the BB and try it from there. So, while trying to minimize
> seat to BB distance, keep the seat as low to the ground as
> possible and minimize wheel/heel interference, the only
> option seemed to be stretch the boom a little. It'll be
> about 19" from head to BB, a little long I think, so for
> stiffness, that's why I went with 2"....

The other option to reduce boom length while keeping
foot/wheel interference to a reasonable level is to use a
smaller front wheel. There is decent selection of ISO 305-mm
tires, as long as one uses cantilever, direct pull
cantilever (V-brakes), or hub brakes (drum and disc).

--
Tom Sherman - Quad Cities (Illinois Side)