Tandem Cycling - Child stoker problem
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05-12-08, 02:03 PM
I ride a tandem with my 7 y/o daughter. The stoker kit is as low as it can go with out intefering with the bikes pedals. The problem is that she likes to stand going up hills (and it helps!) but the stoker kit tends to slide down and then we have to stop to adjust.
1. Any solutions to making the stoker kit not slide? (FYI this was not a problem last year but she has increased power a lot over the winter.)
2. The other question I have is if anyone has used a crank shortener? It states that is it is used for child riders. She needs about 2-3 inches to reach the pedals without the kit. Here is a link to the shortener that I found. http://www.bikemannetwork.com/biking/p/COMPCRNKTDM/CR8870
Any help appreciated. We are riding GOBA this summer and I don't want to stop all the time and I want her to cont to love riding.
Pedal blocks are going to be a whole lot cheaper than that crank shortener-you can even make them yourself. The crank shortener is also going to offset the stokers feet (make the stance wider) quite a bit.
As far as your child stoker bb moving, have you tried putting a piece of folded over sandpaper in there?
05-12-08, 02:50 PM
Is there a shim between the child stoker BB shell block and the seat tube?
Can you tighten the BB shell block seat tube clamp tighter?
What's the sliding doing to your seat tube paint job?
05-12-08, 04:35 PM
Sounds like a thin shim may need to be installed. You can make one cheap out of beer/pop can.
Great stoker power!
05-12-08, 06:21 PM
I used the very same model you posted, and they are quite effective in helping a kid use a tandem. In fact, my daughters never used a stoker kit, but started using the regular rear seat (18" compartment) with a low seatpost and crank shorteners.
Regarding their use, they don't work like wood blocks. Wood blocks will raise the effective crankset, but your child will still be pedalling a 170-mm or 175-mm circle. So she'll be able to reach the bottom of the stroke, but with her short legs, she'll eat her knees at the top of the stroke. Crank shorteners, on the other hand, make the cranks shorter, so she'll be pedalling a 110-145 mm circle. A child bike and a Trail-a-Bike have 135 or 145-mm cranks (I'm going by memory here), and considering the length of her legs, you should ideally aim for something like that, which would mean the second hole from the top (i.e. 2nd largest circle available with the shorteners). I had to start my then 7.5 year-old daughter from the third hole, but within a few months, I moved her to the second hole and I removed the shorteners when she was 9.5.
You might also want to look at the seatpost. The standard seatpost supplied by Co-Motion has a gracious curve, but there has to be at least 10 or 15 mm of seatpost showing. The LBS swapped that seatpost with a Burley, and with it no seatpost needs to appear. In other words, I gained an extra 10 or 15 mm there.
my daughter uses crank shorteners, they work fine. be sure to use loctite when you install them.
05-13-08, 07:24 AM
I agree with the postings that a shim should solve your problem. You might even try wrapping the seat tube with duct tape, or perhaps slice open an inner tube as a shim, both to protect the paint and for some thickness.
FYI - I took a different approach. I bought a cheap tandem crankset and drilled and tapped new holes for the pedals. Ended up costing about the same as a set of crank shorteners but I got a set of taps out of the deal.
05-13-08, 07:30 AM
I would not use duct tape as a shim. You want something that is reasonably hard, but not hard enough to scratch up your paint. Pop can makes a good shim material, but it is very thin. I cut a shim for my kid stoker kit out of a flexible sink drain fitting.
But the OP has not really indicated that a shim is required...?
05-13-08, 06:57 PM
Thank you everyone. We tried wood blocks, but she likes toe clips and those are hard to attach to the block. I will try a shim. (And in answer to the question, there are scratches to the paint job, but not too bad....oh well we can just now try to stop further scratches.) If the shim doesn't work, will try the crank shorteners since those appear to be successful, just want to save the money if possible.
05-14-08, 06:53 AM
Try to make sure everything is nice and clean and not at all greasy upon installation. Use some kind of degreaser (brake or carb cleaner?) to make sure the surfaces will have maximum friction.
05-14-08, 04:15 PM
I used the crank shorteners and will recommend them over the pedal blocks. First, I used them with clipless pedals. I feel much more secure having my daughter semi-permanently attached to the bike. Second, they decrease the effective crank length that is friendlier for shorter legs. Yes, they spread the pedals wider but I think it is better for the knees than what blocks do. Third, they are easy to remove to adjust the bike for full size stokers.
I am not using them anymore as my younger one does not need the them. I am keeping them for grandchildren though...
1. The shorteners left small marks on the cranks where cams were contacting the cranks. The marks, at least in my case are small and only cosmetic.
2. Even with clipless pedals my daughter managed to slip out of the pedals and rip her calf on the chain ring ending up with 14 stitches. I changed clipless pedal brand after that.
3. Depending on bike/stoker size combination you may need a ridgid seat post instead to allow lower seat position.
I took the smallest child cranks that I could find and cut them down and then re drilled and tapped the holes for the cranks, I used a center distance of 100 mm for my 2 1/2 year old daughter. I have a machine shop so this was quite easy to do, however any local machine shop in your area should have no problem doing the same. I would recommend buying the LH & RH taps for the pedals from a bike supplier as these are not common thread sizes to make it easier for the shop. It is important that you have the equipment to hold accurate center distances as well as keep all the holes straight in relationship to centerlines of the crank mounting holes so that there is no wobbling of the pedals.
tie dye tandem
04-20-09, 10:59 PM
I agree that if you remove all the grease and grime and you have the right size clamp, you should be able to make the child stoker kit stay in place for a seven year old. I like the idea of a section of an old inner tube to squeeze down in the clamp if you do need a shim. We have used both child stoker kits and crank shorteners on our bikes. Both work well, but serve different needs. If your daughter only is 2 inches shy, she may be big enough for the crank shorteners, especially if there is any way to lower the seat more, but not if she is 3 inches shy. When it looked like I was going to need a second set of crank shorteners, I too balked at the price. I contemplated machining my own, but then realized that the cranks I had were very beefy aluminum, so I carefully drilled out a hole on each crank to move the pedals in. Buying the taps was more expensive than taking the bike to the local shop and asking them to run their taps through the holes I had drilled. All the shops have these taps to clean up threads, but if you drill the holes right, they can cut new threads for you. This saves money and weight, as well as eliminating the widening of the stance. We will be at GOBA this year as well. Hope to see you there! Our kids are 5 and 10 and had a great time last year. As you might have noticed, this year's course appears to be pretty flat, so you may not need so much standing from your stoker.
05-08-09, 12:21 PM
Hi. We had a similar problem in that my (at the time) 6-year old was just a little short of the pedals with seat all of the way down and crank shorteners installed. To solve the final 2-inch problem, I customized and old seat post and seat so i could lower it all of the way down until the bottom of the seat is on top of the seat tube. I did this by removing the binder attachment, then threading a 4-inch bolt at an angle through an old seat post as close to the top as I cold, then epoxying the seat bottom directly to the bolt and seat tube top. This allowed me to have the underside of the seat within 1/2 inch of the top of the seat tube. To secure the seat to the seat tube, I threaded a small bolt into the back of the seat post where it can pass through the split is in the back of the seat tube. I also added a gel seat pad to his seat to compensate for the lack of damping in the new mounting system. We ride a Raleigh Coupe tandem (not the cheap steel Raleigh, but the much nicer aluminum version) and have completed 2 MS-150s and numerous day trips with this arrangement. We are also planning to ride from DC to Pittsburgh with this setup this summer. I will post detailed pictures of our setup later, but for now here is a picture of us riding. This has been a FANTASTIC setup for us...
Keep the rubber side down!
05-12-09, 03:18 PM
Our Co-Motion Bofus, circa 1992, can't take a child stoker kit so we had to wait until my daughter was 7. At that point we bought a cheap seatpost that will drop lower and the Ride2 Crank Shorteners.
Something I read said that kids are bothered less by a wide "Q-factor" than by long cranks.
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