Seat tube reamer

andy777

Hi,

My bike has a 30mm seat post and a 34.9 mm seat tube.

I really want a dropper post but no one makes one in a 30mm dia.

Pure racing 27.2 is an option but i thought i might be able to enlarge then seat tube id from 30mm to 30.9 with a seat tube reamer. Then I could fit the a 30.9 dropper post.

Obviously the risk is knackering the whole frame If the reaming goes wrong!

Any thoughts ideas?

Cheers

Andy

Anonymous

Taking nearly a mm off the seat tube sounds like a bad, bad bad bad bad idea.

cooldad

+ many bad potatoes.
Rather shim down if you have to.

paul20v

Sorry have to agree dont take anything out of the frame

stubs

This sounds almost as good an idea as the guy a few weeks back who wanted to drill a hole in his chainstay to fit a home made chain device.

andy777

Pure racing i7 it is then.!

Just to clarify the seat tube is 30mm id and 34.9 od. I have a giant bike which has a 30.9 id seat tube with a 34.9 od. so it would go from a 2.5mm to a 2mm wall thickness, the same as the giant.

Andy

stubs

andy777 wrote:

Pure racing i7 it is then.!

Just to clarify the seat tube is 30mm id and 34.9 od. I have a giant bike which has a 30.9 id seat tube with a 34.9 od. so it would go from a 2.5mm to a 2mm wall thickness, the same as the giant.

Andy

The Giant has been designed to have a thinner wall. Its not the thickness its just that your removing metal that the designer thought was important. You might get away with it and you might end up chewing the scenery when the bike folds in half.

nicklouse

andy777 wrote:

Just to clarify the seat tube is 30mm id and 34.9 od. I have a giant bike which has a 30.9 id seat tube with a 34.9 od. so it would go from a 2.5mm to a 2mm wall thickness, the same as the giant.

Andy

totally irrelevant.


as to the other part. you have made the only option.

RevellRider

nicklouse wrote:

andy777 wrote:

Just to clarify the seat tube is 30mm id and 34.9 od. I have a giant bike which has a 30.9 id seat tube with a 34.9 od. so it would go from a 2.5mm to a 2mm wall thickness, the same as the giant.

Andy

totally irrelevant.


as to the other part. you have made the only option.

As Nick says, totally irrelevant. The Giant may have an externally butted seattube.

andy777

Well I'll leave it as it is!
I didn't think it was a good idea in the first place, just it was suggested to me and I wondered if anyone had done it. Dont fancy going off a drop and snapping the seat tube :shock:

Cheers

Andy

andy777

Update.

My bike is a Cove Hustler. I was in the cove shop in North Vancouver today and they said "just ream it out to 30.9 thats what we do." They had a Cove G-spot there, which they had reamed out the seat tube for a customer, so a dropper post could be fitted.

Andy

cooldad

How about that. Some people don't agree on everything.

andy777

Update,
After my visit to the cove shop I also emailed them about the seat tube. This was the reply

Hi Andy, we have now done this to every g-spot frame in stock (it's being
done at the factory) and have done it to other customers hustlers as well.
It doesn't weaken the frame in anyway and we have had no problems with it.

I have gone ahead and reamed out my seat tube. Interestingly the internal diameter of the seat tube appears to be 30.9 lower down. Its only the first 100mm or so thats 30mm id. this means that there is no step, so no stress point, which was one of my worries. I finished off the job with a small honer to give a nice finish.

Now to fit my dropper post.

Cheers

Andy

The Rookie

andy777 wrote:

It doesn't weaken the frame in anyway and we have had no problems with it.

Clearly it MUST weaken the frame, whether it's critical/relevant or not is different!

Simon

S-M

if it is being done at the factory then i would not worry about it.

andy777

Simon,

Yes I agree removing material will weaken it. I guess its well within any design parameters. Plus Riding in the North Shore is hardcore so the frames they've done will had had a good workout.

I'll let you know if it snaps!!

Cheers

Andy

andy777

Update,

Its still fine after 4 years

Herdwick

you don't forget do you?

rockmonkeysc

Removing metal will only weaken the frame if that material isnt being replaced with something else. In this case there is a seat post clamped in place at the top and its only the top 100mm which has been removed. I would have been happy to do it.