Major Setback

[TheKid]

Riding the tadpole has become increasingly difficult, due to the seat height to BB height relation. I tried shorter cranks, but the pain in my knees is still unbearable. I raised the seat, but the handling changed quite a bit. At slower speeds, there's no problem, but in the 3 highest gears, stability is an issue. I'll try a new crossmember further forward to increase the wheelbase about 4". I'll also increase the track to 36". But I'll need a ride, so I'll either finish the DW first, which will also need some mods, or get all the parts back for the quad, which already has a seat height of 22" and a BB height of 14". The help I enlisted for the quad kind of quit, which is a shame. They are members of a local civic group, and one of them was going to ride it in the Memorial Day Parade. They did manage to finish the rear frame, which is similar to the Lightfoot trikes. I have some of the front end done, but the main frame has yet to be built. I might be able to finish by the end of May if I get enough days that I'm able to work. If so, there's an organization of women who would love to use it to represent their group in the parade.

[n9viw]

Is it the height, or the distance between the seat and cranks that's a problem? I know that hypO- as well as hypER-extension of the legs can cause a problem in riding. If your leg never fully extends, you're attempting to make power from what is essentially a crouching position. If your leg extends so far you can easily lock the knee, that can cause a problem as well.

[TheKid]

It's the height. Generally, the higher the BB is in relation to the seat, the shorter the cranks should be to avoid knee pain. I'm estimating that with 140mm cranks, I need the BB to be 6-7" below the seat. With the 140mm cranks on there now, I raised the seat so it's 5" above the BB. There's still some pain when my knees are bent at the top of the stroke. I tried 130mm cranks, but there was still some pain, and the leverage loss required too much power to the pedals when starting uphill. If I raise the seat any higher, I'll have to make a new crossmember to reduce the instability. As it is now, any faster than 12 mph makes the trike unstable, and one front wheel lifts off the ground on sharp turns going 8-10 mph. Leaning doesn't help much, due to the design of the comfortable mesh seat. I'll use it the way it is until I finish the quad or the DW, whichever I figure will take the least time. If I add to the frame of the DW, I could incorporate the rear of the DW with the some of the design aspects of the front of the Gladiator, which would make a very cool delta.

[TheKid]

Since I don't have a fairing yet, and when I do, it won't have a floor, it occurred to me that the BB could be lower. I reinstalled the BB so it's under the boom, which lowered it 2 1/2". I then lowered the seat 2 1/2". The handling improved enough so it feels safer to ride. I still have the brake problem that was present from the beginnining. From what I've read, it's a common problem with tadpoles if the COG is too far forward - the rear end lifts during hard braking. It's one of the reasons why many tadpoles are designed without a rear brake, or the rear brake is used as a parking brake only. So the future mod will entail making the new crossmember a bit wider, at a 42 degree angle, and mounted two inches forward. This will bring the COG rearward, and it will still be easy to mount and dismount. It will also make the trike much more stable for heavyweights like myself.
Brad's design for the crossmember makes mounting and dismounting much easier than most tadpole designs. I highly recommend the Streetfox for those who wish to build a tadpole.