Ben started cycle speedway as a tall seven year old. Archie Wilkinson advertises their Junior speedway bike as ‘from 7 years’, so I invested.
The bike fits him well, though the seat height meant he could only brush the ground while in the saddle. Not ideal. So I lowered the seat to the frame, as shown below.
Obviously you do this at your own risk. The seat post clamp is not intended to be load bearing.
Ben’s bike has been this way for a year, there are no signs of damage to the seat post clamps. I would not have written this page if I’d found any damage.
Ben is now 8, and its time to restore the original seat height.
 This is how Achie Juniors look out of the box. This method applies to bikes with a BMX-style separate seat post and seat clamp. If you have a one piece seat post + clamp, these 2 parts can be bought for under £10.
Note that the seat post is straight, with a separate silver clamp attaching the seat to the post. The plan is to invert that clamp, and bolt it directly to the seat post clamp bolts on the frame. The frame standover height is 25″. The height to the saddle is 29″. |
 Before bolting the seat to the frame, I want to protect the seat tube so it’s not crushed when the seat is boltted on. If I could leave the seat tube in there I would, but it stands too proud.
Therefore I cut the bottom few inches off the seat post, and with a hacksaw cut a few slots. I then used pliers to bend one tab over. I can now drop this tube in to the seat tube without losing it. |
 Here’s the shortened tube in the frame. Note the black tape on the top tube. The insulating tape is to protect the paint from the seat. I’ve also taped a couple of rubbers from bike light mounts across the top of the tube, to protect from the seat’s rails and the nose of the seat.
That’s track shale in there by the way, not rust. 🙂 |
 The fiddly bit. The rail clamps from the silver clamp are inverted and place around the the seat rails. I’ve inserted 2 or 3 washers, and slotted the bolt through the rail clamps and the seat post clamp on the frame.
Choose your washers so that you can get the seat tight enough that it won’t slide forwards or backwards along its rails, but don’t crush the seat post clampon the frame. Dont lose the seat post bolt or the big ring from the silver clamp. You’ll need them when you convert the bike back to normal in a year or two. |
 The finished job. Note the rails and nose of the saddle resting on the taped-on rubbers.
The silver clamp had meshing teeth to prevent the seat from rotating. As we only have half the mechanism the seat will lift if you sit on the very back. 3 cable ties have kept Ben’s seat in place all year. The height to the seat has been reduced to 27″. Which can get you on this bike about a year earlier. |
Thats a cracking article Phil and one which could be applied to all frame sizes I guess when riders of all ages are in that “inbetweeners” stage between the bike they have and the next one up until senior size.