Using a KH rail adapter on a Miyata Carbon seat base?

[TonyMelton]

I was about to merrily start drilling holes in a Miyata carbon fibre seatbase when I realised that the KH rail adapter (the one designed to fit the KH saddle) has a different curve to the Miyata CF base. This means that the only points of contact are the front and rear edges of the adpater. Will this put more stress on the seatbase and make it more likely to break? Or is carbon fibre strong enough to withstand these extra stresses? Should I stack washers on the bolts between the seat base and the adapter to take up the space between them? Has anyone tried this?

[tholub]

I put an inner tube in between the rail adapter and the seat base to help distribute the force and keep the adapter from eating into the carbon fibre. It's been fine so far.

[Tellurider]

I did the same thing as Tom, I had also already drilled mine for a miyata seatpost and I redrilled it for the seatrail with the standard bolt pattern and have had no trouble.

Dan.

[john_childs]

I use largish fender washers. The washers lay flat against the CF seat base. They prevent the rail adapter or seatpost bracket from contacting the carbon fiber at a point or along an edge. Spreads out the forces.

Other people use a thick rubber patch cut from an old inner tube and put the rubber patch between the carbon fiber and the rail adapter. The problem with the rubber patch is that rubber doesn't spread out the contact forces as well as the washers and the rubber can get cut through by the rail adapter over time. I think the fender washers will work better. You also have the option of using washers and a rubber patch.

[TonyMelton]

Thanks for your responses!

John - could you describe to me what a fender washer is? Is it just a large metal washer or something else? Is it the sort of thing you'd get at a hardware store, or would you have to go to a panelbeater / car wreckers yard to get some?

[john_childs]

Originally posted by TonyMelton
Thanks for your responses!

John - could you describe to me what a fender washer is? Is it just a large metal washer or something else? Is it the sort of thing you'd get at a hardware store, or would you have to go to a panelbeater / car wreckers yard to get some?

A fender washer is a washer with a larger than normal outside diameter compared to the inside diameter. So the actual metal part of the washer is wider.

Look for a washer with the largest OD that you can fit flat on the carbon fiber base while still having an inside diameter that's not too big for the bolt. You aren't going to be able to use a washer with too big of an OD because the radius at the edge of the carbon fiber seat base will get in the way.