Seatpost diameter for 1995 Orange P7

Hi, I'm new to this retrobike lark so please be gentle with me.
I've got a 1995 Orange P7, frame no. A50201657, the prevous owner had fitted a nasty promax suspension seatpost which is 25.4 dia with the seat clamp bolt cranked up to the max and beyond. There is a shim hammered into the seat tube which is never coming out, and the 25.4 dia seat post is way too small. I've tried fitting a 26.2 dia post but this is too big, just.
My question is, which new size post shall I go for, 25.8 or 26.0? Any advice will be welcome.

Many thanks, Rich

The shim will be original and to allow for a 26.4mm seat-post. Presumably the I.D. has been reduced by the over-tightening of the clamp and ovalising the shim.

The shim isn't bonded, although it may be corroded and seized. If you can get a flat-bladed screwdriver beneath the lip of the shim, you could try and gently tap it out. Once it's out you could buy a USE shim to fit either a 25.0mm or 27.2mm post, the actual I.D. of the seat-tube would need to be measured - Orange claim that it was 30.0mm in 1995, but their information is wrong as they also say the shim reduced the diameter to 27.2mm when we know that it's 26.4mm. I suspect the correct I.D. is either 29.6mm or 29.8mm but you'll need to measure the diameter with some accurate calipers to be sure.

One word of caution, the overtightening of the clamp may have ovalised the seat-tube as well as the shim in which case you'll be no better off with the shim out...

http://www.orangebikes.co.uk/support/faqs

I've removed the shim, the only markings on it is a 3. The seat tube is ovalised, I'm measuring between 29.8 and 30.2 ID, so should I get a new shim to fit my existing post which is a 25.4? Or is the frame too far gone?
Any suggestions?

Richteacurry":2in7eplv said:

I've removed the shim, the only markings on it is a 3. The seat tube is ovalised, I'm measuring between 29.8 and 30.2 ID, so should I get a new shim to fit my existing post which is a 25.4? Or is the frame too far gone?
Any suggestions?

Click to expand...

Sorry, at this point I'm out. Being steel I wouldn't think it's beyond salvation, if you have a good local bike shop you could talk to them or speak to someone like Bob Jackson or Argos Cycles.

I'd imagine that someone on here with more experience of such issues will be along shortly...

If like this one......

http://www.retrobike.co.uk/forum/viewtopic.php?t=124251

....it should be 29.8mm, possibly with shims to use a smaller post.

If overtightened by a PO it should be saveable without too much difficulty.

Richteacurry":19nlj4uc said:

I've removed the shim, the only markings on it is a 3. The seat tube is ovalised, I'm measuring between 29.8 and 30.2 ID, so should I get a new shim to fit my existing post which is a 25.4? Or is the frame too far gone?
Any suggestions?

Click to expand...

How far down the tube is it ovalised?

I can't really tell, doesnt appear to be too far down.

If it's not far down, it shouldn't stop you fitting a post. Once you've got it in and clamped, the clamp will reinstate the round shape automatically.

If you're going to stick with your 25.4 post, it's just a question of what shim to buy. Orange say it's a 30.0, I thought it was 30.0, Mr Panda says 29.8 and Mr Panda ought to know. I do recall when I fitted mine, I worked on the assumption that it was a 30.0 but I did need to try a few shims before I got the right one. Maybe I ended up with a 29.8, I can't recall. This was a few years ago when Chain Reaction were more laid back. The guy just sent me three shims of different sizes and said send back the two you don't need. That's what I call service. If you go for a 25.4-29.8, I would say a USE thermoplastic 25.0-29.4 will do the job for you.

Thanks for the advice.
I reached the same conclusion and was going to buy a 25.4 to 29.8 but I noticed you said get the 29.4, I assume this just for some tolerance and fudge factor.

No, what I meant was that Chain Reaction only sell USE shims based on 25.0 not 25.4, but if you get a 25.0-29.4 that will be adding 4.4mm and should do the same job for you as a 25.4-29.8 shim would - both adding 4.4mm. As the shim is plastic, there shouldn't be any difficulty getting your 25.4 post into a 25.0 shim.