aprhockey

On Nova Cycles' website, it seems that the smallest outside diameter seat tube is 28.6mm. Is this pretty much the standard or could I find smaller (say 26mm OD)? I'm not looking for anything fancy, steel is plenty good enough.

I'm asking because I built a bamboo frame and I want to sink in a seat tube. The inside diameter of the bamboo seat tube is about 26mm.

If they don't make them smaller, I'll have to replace the bamboo seat tube with a larger pole that I have. Which requires grinding down the joint at the bottom bracket and the seat tube/stays cluster.

Any help is appreciated

unterhausen

you will have problems finding a seat post for anything other than a 28.6mm tube. But you can go to many suppliers of 4130 tubing and get something smaller. You will probably find yourself having problems with the seat post. You want .2mm of difference between the seat post and the inner diameter of the tube

mudboy

28.6 is standard. The only thing smaller was a Metric (French) seat tube, which was 28.0mm.

aprhockey

Alright. Thanks for the info.

I have a decent amount of work to do, but hey, that means I can try to make the frame better.

mudboy

I would think that building a "mast" type seat tube would be the way to go with bamboo.

aprhockey

I had never heard of a mast type seat tube. Rather than a seat post clamping into the seat tube, what you're referring to clamps around the seat tube? Unfortunately I don't have any spare bamboo poles long enough to give me the correct saddle height without a seat post. Currently my seat post extends almost 5 inches above the seat tube.



This is the bike I'm referring to. It was my first build. It took about a month this summer.

The seat post is currently held in place primarily by epoxy... I thought a liberal amount of grease on the seat post would allow me to slide it out of the seat tube when the epoxy had dried. I was trying to get a small build up of epoxy inside the seat tube to give the seat post a better fit. Anyway, I had set it to the correct height just in case and it worked fine.

~130 miles later I hear a distinct crack while riding. After inspection it looks like the joint at the bottom bracket and seat tube has cracked. This is where my original question came in. I will have to redo that joint, which will give me the opportunity to correct the sinking of the seat post by either keeping the same bamboo seat tube and finding a steel seat tube to fit inside (which would have to have an OD of 26mm) or I have one spare pole that is large enough to sink a 28.6mm seat tube.

Sorry for the book, but I never really told the whole story so here it is. If anybody can think of a better solution I'm all ears.

GrayJay

Try using a 1" (25.4mm) tube? Finding a standard seatpost to fit inside that tube would likely be tough.

JohnDThompson 

Try here: https://www.aircraftspruce.com/catal...bing_short.php

aprhockey

Thanks for the link JohnDThompson. Just ordered a tube from there... much cheaper than the tubes I was looking at before (nova cycles) since I only need about 6 inches.

I've decided I'll replace the whole seat tube with a bigger diameter bamboo pole I have. I think it'll make things easier in the long run.

rodar y rodar

APR, it might still be a good idea to replace that tube with a bigger one, but you might be able to save the one you have. I don`t know what tube you just ordered from Aircraft Spruce, but if the ID allows you slide a short 7/8 tube into it, you should be able to use an adaptor clamp thingie. At least I THINK that would work.

https://harriscyclery.net/itemdetails.cfm?ID=2536

aprhockey

I bought a tube with a 1 1/8" OD (28.6mm) and 1.055" ID (~26.8mm). I'm going to sink that tube into the bamboo seat tube, and then a standard 26.8mm seat post fits perfectly into the metal seat tube. The outside diameter fits a standard clamp. Unfortunately last night, what was going to be the replacement bamboo tube developed a tiny crack ... I cooked it too long in the oven. I'm running low on spare poles but I think I can still manage with what I have. I'll try to post some repair pics when I have them.