Geometry problem - FWD delta trike
- Thread starter stormbird
- Start date
Hugh
0
One obvious point, a 2 wheeled bicycle has the ability to lean. So it doesn't want to follow the camber of the road. On a personal note my wife tried what I would call a "granny" trike in our back lane and it has a slight camber for run off. After 10 feet she felt very uncomfortable and refused to ride it due to needing to continuously having to countersteer. Perhaps if your FWD had a pivot point behind the seat allowing a small amount of lean it might negate the effect.
One tilting trike I saw a video of used a disc brake rotor cut in half with a caliper mounted atop allowing the rider to lock it in an upright position for starting off then it could be released allowing lean into corners. Interestedly enough I have 2 delta trikes, one RWD and the other RWD with a front hub motor and they are only effected a very small amount by the camber in a road. On both the steering angle is approx 67 degrees.
One tilting trike I saw a video of used a disc brake rotor cut in half with a caliper mounted atop allowing the rider to lock it in an upright position for starting off then it could be released allowing lean into corners. Interestedly enough I have 2 delta trikes, one RWD and the other RWD with a front hub motor and they are only effected a very small amount by the camber in a road. On both the steering angle is approx 67 degrees.
You are quite right lot's of those style of trikes are positively evil !
I have had to Hase Kettwielsel and built 3/4 Pythons and non had this problem so I suspect I have got something wrong.
First though is the head tube angle came from one kids bike and the fork from another.
Now trail is dependent on a combination of rake [ head tube angle ] and axle offset from the steering axis so it could be wrong.
Thanks for your 67 degrees mine is nearer 72 ' , could you give me a figure for the trail ? I measured mine @ 1.75"
Paul
I have had to Hase Kettwielsel and built 3/4 Pythons and non had this problem so I suspect I have got something wrong.
First though is the head tube angle came from one kids bike and the fork from another.
Now trail is dependent on a combination of rake [ head tube angle ] and axle offset from the steering axis so it could be wrong.
Thanks for your 67 degrees mine is nearer 72 ' , could you give me a figure for the trail ? I measured mine @ 1.75"
Paul
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DannyC many thanks , I think I need to explore my lack of trail and I have a cunning plan to add some trail AND reduce the torque steer all in one operation ?
What I shall try is welding another drop out [ red spot ] but behind the original ......
this will do 3 things :-
1) increase the trail to about 3" a better figure I think
2) it will put the axle under the centre line of the fork - this will move the cassette back - which will...
3) allow the main pulley pivot to be moved to get the chain as close to the front fork and parallel to it reducing torque steer
Fingers crossed it works , there is no doubt it will do something
Paul
What I shall try is welding another drop out [ red spot ] but behind the original ......
this will do 3 things :-
1) increase the trail to about 3" a better figure I think
2) it will put the axle under the centre line of the fork - this will move the cassette back - which will...
3) allow the main pulley pivot to be moved to get the chain as close to the front fork and parallel to it reducing torque steer
Fingers crossed it works , there is no doubt it will do something
Paul
DannyC
0
Good Luck! I hope it fixes it for you.
I found this.
Extremely stable, solid feel at high speeds
Will lean heavily into turns
Best for off-road riding requiring self-correcting steering
Reacts quickly to light input at low speeds
Light feeling handling at low speeds
Stable, solid feel at high speeds
Will lean into turns
Responds more significantly to rider input than lower trail
Steering self-corrects more easily but may require more adjustments to hold a curve
Best with narrower tires (low pneumatic trail)
Reacts quickly to light input at low speeds
Shifting weight to steer has greater effect than on lower trail geometries
Moderately stable at low and high speeds
Will hold a line in turns
Precise, quick steering at low-moderate speeds
Less affected by involuntary inputs such as cross winds
Stable at low speeds
Less stable at high speeds (vague, wandering feeling)
Requires more effort to lean into/out of a turn, but will easily hold a line
Best when balanced with extra weight in front and/or with wide tires
Trail balanced with wider tires (higher pneumatic trail)
Steering is less self-correcting than higher trail
Shifting weight to steer has lower effect than on higher trail geometries
One quick way to check for this design compromise is to see if there is a sharp jump in trail on the smaller sizes of a bike model.
I found this.
Trail Ranges and Characteristics
Very High
> 80mm trailExtremely stable, solid feel at high speeds
Will lean heavily into turns
Best for off-road riding requiring self-correcting steering
Reacts quickly to light input at low speeds
High
65 - 80mm trailLight feeling handling at low speeds
Stable, solid feel at high speeds
Will lean into turns
Responds more significantly to rider input than lower trail
Steering self-corrects more easily but may require more adjustments to hold a curve
Best with narrower tires (low pneumatic trail)
Reacts quickly to light input at low speeds
Shifting weight to steer has greater effect than on lower trail geometries
Mid
45 - 65mm trailModerately stable at low and high speeds
Will hold a line in turns
Low
30 - 45mm trailPrecise, quick steering at low-moderate speeds
Less affected by involuntary inputs such as cross winds
Stable at low speeds
Less stable at high speeds (vague, wandering feeling)
Requires more effort to lean into/out of a turn, but will easily hold a line
Best when balanced with extra weight in front and/or with wide tires
Trail balanced with wider tires (higher pneumatic trail)
Steering is less self-correcting than higher trail
Shifting weight to steer has lower effect than on higher trail geometries
Inconsistent Trail
As a bike design is scaled down to fit smaller riders, Toe Overlap (the tendency for the rider's toes to catch on the trailing edge of the front wheel when wide turns are taken) can become a problem. One approach bike designers take to mitigate this is to slacken (decrease) the Head Tube Angle in order to push the front wheel out farther from the rider's toes. This increases trail and, in extreme cases, can result in compromised handling.One quick way to check for this design compromise is to see if there is a sharp jump in trail on the smaller sizes of a bike model.
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Hugh
No need to but thanks for offering.
It has been pointed out to me that I am not comparing like for like.
E.g whilst the KettWiesel is an excellent delta trike it has a very long wheel base compared to mine and so a lightly loaded front wheel also of course is not FWD so any comparison will be flawed.
It has been suggested :-
You want less trail, not more trail, which is what you are doing. Trykits run steep head angles and a mile of fork rake to reduce the trail to around 25mm.
Lots of trail means the cycle turns into a lean. Crossfall is the same as leaning (on a trike), so your trike turns downslope.
The low weight on the front wheel of a Kett reduces the crossfall steering effect quite a bit. You don’t have that particular advantage because your BB is in front of the front wheel.
So next experiment is to hack it in half and find a way of getting the trail down
Paul
