ISP conversion to standard seatpost

[ghammer]

Hello There,

I have an Aluminum bike with an ISP. It looks cool, it's beautiful actually, but it's a pain. I love the bike and don't/won't sell it, but am ****ing tired of cracking ISP toppers. They're made light, but eventually they fail and there goes $100-150. I'm on the light side and there's no reason for that. Plus, every time I need to adjust it (like now, with a shorter crankset), I get paranoid of cracking it. Again.

So I'd like to inquire how to go about it. The tube is 34.9 wide. I know I need a seatpost shim, a seatpost and a collar. I also know I need to cut it carefully. What are the next steps? Has anyone done it here? All info welcome.

Thanks,

G

[batman1425]

Cracking toppers is a new one for me... I've had an ISP Ridley for years that has worked with out issue. Maybe your seatmast is slightly undersized and you are getting a lot of deflection in the clamp to get it tight leading to early failure?

There are a few different options for toppers if it is a straight 34.9 interface - maybe try a different manufacturer if you haven't done so already. Also they don't have to be crazy tight as vertical slippage isn't a concern. Really just snug enough so that it doesn't spin laterally or pop off. Some friction assembly paste might help.

Back to your original question if you want to convert to a standard post - you are going to need more information. You need to investigate the inner diameter of the seat tube at and below the top tube junction. It may not be a "standard" size which would then require reaming for traditional post to fit. Also be aware that the stressing and loading on an ISP is different than a standard post - so the welds/geometry/tube sizes/butting may not accommodate a standard post, even if it fits, safely.

The short answer is - find a custom builder in your area that is familiar with aluminum and bring it in for them to check it out. It could be as easy as 2 cuts (length and clamp relief), or it could end up being more work than the frame is worth.

[chiasticon]

my advice: contact a local builder and have them do it. you need to chop, slot and ream it. chopping and slotting aren't that hard, but they're also easy to screw up. you likely don't have a reaming tool and you won't want to buy one just for this one job. I had this done on a Gaulzetti Corsa a year ago and it cost me $60 at a local builder. he turned the job around in a day. took him an hour or so. Boston has plenty of builders in the area, so I'm sure you can find someone willing to do it. and they can figure out the best inner diameter to ream the tube to, keeping mindful of the butting and such as well.

[R3awak3n]

I would have a builder do it too probably. ISPs look cool and I love it on my english but I would take a normal seatpost setup anyday. Unfortunetly I have an aero tube so I cant just chop it. Also if that toper every cracks, its $600 from Rob lol.

[zank]

Most ISP seat tubes are 2.0 - 2.2 mm wall at the top. You will need to ream the seat tube to 30.9 or 31.6 for a seatpost. If it's a proprietary drawn tube, you might get lucky and the ID of the tube will match a seatpost. But yoi will still need to ream to clean up the ID. Aluminum sinks into the ID of the tube when you weld it. I usually grind the remnants of the bead and then ream. You will also need to slot the seat tube and drill a relief hole at the bottom of the slot.

All of this is tricky to do without dinging up the paint. A solid vise with soft jaws clamping the faces of the BB is the safest bet, but the shell will need to be faced after. You would need to make sure that the width would still be in spec after another facing.

This isn't a fun job and carries a lot of risk.

[gospastic]

Which brand toppers are you cracking?

[ghammer]

KCNC and woodsman.

[El Chaba]

I would try the PMP topper before putting the frame through a circumcision....