Spreading a seat collar?

[A1A]

Posted a thread the other day about a new saddle for my Hors Categorie leading to a new seatpost (slightly undersized 27.2 Thomson, non setback) leading to an issue with wanting to change the existing Serotta seat collar to a Thomson 29.8 (which works fine on my Legend). So the 29.8 won't work on the Hors, too big. So I ordered a 28.6 and of course it appears to be too small. Seat Tube OD is about 29.1 ish. So wanted to ask is it is ok to spread the clamp as much as .5 mm to make it work? Probably resort to using a large screwdriver or is there a better way? Hate to mar the new seat collar. The reason I don't plan to use the existing Serotta seat collar even though it would work is because Thomson says not to use a collar where the inside top lip of the collar touches the post. Looking at that collar installed there may or may not be a gap, it feels flush to my finger but very hard to judge. I also kind of like the Thomson collar. Thanks for any advice!

[paredown]

Check to make sure that there is nothing physically impeding the post--roughness or ridges.

What I have done (assuming this is 1" tubing)--is using a quill stem that has a good expansion plug, and then tightening it in the opening, tighten/loosen and move it around the opening--go gently--and tighten well each time, not too deep, but not tightening so much that you try to fix it first try. 5 or 6 movements around the opening each pass. Check as you go--it usually does not need much.

If you can't seem to get any movement that way--and does seem undersized farther down--you could use a hone. (For minor ridges/roughness I've used a home-made flap wheel with strips of emery in a slotted dowel to clean up.)

It's better than just spreading the ears, and you can use it if the opening has been deformed from round...

[ultraman6970]

Put a coin between the slit. And put the bolt at the other side, where the threaded part it. That will open the clamp. Just put some grease 1st so the clamp slide in smoothly.

[Velocipede]

Put a coin between the slit. And put the bolt at the other side, where the threaded part it. That will open the clamp. Just put some grease 1st so the clamp slide in smoothly.

You can't spread a Thomson like this. The bolt threads into a barrel nut.

[Velocipede]

Posted a thread the other day about a new saddle for my Hors Categorie leading to a new seatpost (slightly undersized 27.2 Thomson, non setback) leading to an issue with wanting to change the existing Serotta seat collar to a Thomson 29.8 (which works fine on my Legend). So the 29.8 won't work on the Hors, too big. So I ordered a 28.6 and of course it appears to be too small. Seat Tube OD is about 29.1 ish. So wanted to ask is it is ok to spread the clamp as much as .5 mm to make it work? Probably resort to using a large screwdriver or is there a better way? Hate to mar the new seat collar. The reason I don't plan to use the existing Serotta seat collar even though it would work is because Thomson says not to use a collar where the inside top lip of the collar touches the post. Looking at that collar installed there may or may not be a gap, it feels flush to my finger but very hard to judge. I also kind of like the Thomson collar. Thanks for any advice!

I've done it but I don't like doing it. The Thomson collars are very stout and don't like to stretch. just go slow.

[Rusty Luggs]

I had a Thomson seatpost collar that broke - was installed on a bike for probably at least a year, rolled bike out to load up to go to a race, bumped seat and it rotated a bit -found seatpost collar fractured clean through.

[A1A]

Thanks guys. It's just that I'm a little at a loss as to what to do otherwise other than just use the original Serotta collar and assume that the inside top lip isn't touching the post. It feels flush on the inside when I rub my finger around so it's probably fine. Just don't want to screw up a brand new Thomson Masterpiece post is all. I think I mentioned in my first thread that I looked closely at the Campy carbon seatpost I used for at least 10 or 12 years with the Serotta collar and see no evidence of damage from the collar lip pushing on it.

So the original bolt is too short to spread the collar using the clever "penny in the slot" trick so I'm off to the hardware store to buy a longer 4mm cap bolt. That should work. I guess if I snap the collar I'll know it was too much spreading. I just hate trying to cob up some sort of shim to use around the seat tube so worth risking a $25 collar I guess.

Worst comes to worst I'll just use the Serotta collar. Thanks for all your advice.

[charliedid]

Seems like a terrible idea to me.

[A1A]

Well the longer M5 cap screw worked fine with the "penny" trick. Seemed to spread very easily but did it slowly. I think about .5 mm. Seemed to "seat" on the seat tube fine and the seatpost slid in ever so lightly tighter than before which I thought was actually a plus. Still nowhere near as tight as the Campy carbon 27.2 post. So I tightened everything up slightly and will try a test ride a little later. No idea whether it is not that unusual to have to resort to this or a really bad idea as the previous poster said. I do know there is now the gap around the top inside lip of the collar that Thomson insists be there that I couldn't really see using the Serotta collar so that also seems a plus.

So I remeasured the ID of the Serotta collar that would work if I wanted to file off the inner lip and it is about 29.0mm. So ideally that's what I need to find, a collar with minimal or no inside top inner lip that has a 29.0 ID. Understood the the inner lip is to keep the collar from sliding down the post. Anyone ever heard of a non - Serotta collar with a 29.0 ID?

At 6' and 150 pounds I'm kind of a light weight so I figure I don't put a lot of stress on a post and collar if that helps. Thanks again for the advice.

[ultraman6970]

I know it has a barrel nut, so whats the problem??? just put the thing backwards from the barrel nut in with the coin in the middle.

The bolt goes all the way to the other side so use the exit hole to get the bolt in... and put the coin in the middle.

https://lfgss.microco.sm/api/v1/files/a7df93ca6351635d6e86d52673cab1bf64b709b3.jpg



You can't spread a Thomson like this. The bolt threads into a barrel nut.

[prototoast]

You can add a little bit of tape to the inside of the bigger clamp and it should hold fine.

[A1A]

I know it has a barrel nut, so whats the problem??? just put the thing backwards from the barrel nut in with the coin in the middle.

The bolt goes all the way to the other side so use the exit hole to get the bolt in... and put the coin in the middle.

https://lfgss.microco.sm/api/v1/files/a7df93ca6351635d6e86d52673cab1bf64b709b3.jpg

That part worked fine, I just had to buy a longer cap screw because of the way the collar is shaped on the side where the barrel nut is. The original screw head hits the hump before you can screw it in far enough to spread the collar.

[ultraman6970]

As long as it worked... great :)

I had to do the same with a bike long time ago, I forgot the part about the longer bolt tho...

[charliedid]

Glad it seemed to work.

What I am thinking when I said I thought it was a lousy idea is that....you have pried open an aluminum collar to fit a slightly larger tube OD right? Okay now you install that and it has tension loaded in the direction not intended. Now you clamp it down and it is fighting that tension that shouldn't be there right?

Maybe I am over reacting but I once had a collar break (totally my fault) on a ride where I had to pedal back about 15 miles and couldn't sit down. That was a blast :)

I reserve the right to be wrong and anyone who can inform me of my error I am all ears.

[A1A]

I hear ya', I'm not thrilled about the way things worked out for something so simple. Not a risk taker other than for being a road rider in general these days... I love Thomson but the more I read the more I see that their seat posts tend to be on the small side of for example 27.2. I never realized seatpost sizes were "nominal" and vary by brand by as much as .1 to .2 either way. Learn something new every day.

But I have a plan "B". I was searching around and discovered that Wolf Tooth which is another made in the USA product spec's their 28.6 collar as fitting 28.6 to 29.0. My calipers aren't the greatest (composite arms) but I come up with an OD of the seat tube of around 29.0 to 29.1 so I ordered a Wolf Tooth to see if maybe that slides right on or worst case I have to spread it maybe .1 ish instead of .4 to .5 with the Thomson. Should have it by the end of the week and will test.

[Velocipede]

I know it has a barrel nut, so whats the problem??? just put the thing backwards from the barrel nut in with the coin in the middle.

The bolt goes all the way to the other side so use the exit hole to get the bolt in... and put the coin in the middle.

https://lfgss.microco.sm/api/v1/files/a7df93ca6351635d6e86d52673cab1bf64b709b3.jpg

Sorry. Meant to say you can't do that with a Thomson cause the bolt it comes with is too small to use a coin cause of the barrel nut vs it just threading in to the alloy itself. Typing too fast and wasn't paying attention.

[charliedid]

I hear ya', I'm not thrilled about the way things worked out for something so simple. Not a risk taker other than for being a road rider in general these days... I love Thomson but the more I read the more I see that their seat posts tend to be on the small side of for example 27.2. I never realized seatpost sizes were "nominal" and vary by brand by as much as .1 to .2 either way. Learn something new every day.

But I have a plan "B". I was searching around and discovered that Wolf Tooth which is another made in the USA product spec's their 28.6 collar as fitting 28.6 to 29.0. My calipers aren't the greatest (composite arms) but I come up with an OD of the seat tube of around 29.0 to 29.1 so I ordered a Wolf Tooth to see if maybe that slides right on or worst case I have to spread it maybe .1 ish instead of .4 to .5 with the Thomson. Should have it by the end of the week and will test.

Wolf tooth one is nice.

A never ending process sometimes. :-)

[ultraman6970]

Campagnolo ones are good aswell.

[jtbadge]

I dunno, man. Seatposts get scratched. I'd just use the Serotta collar that you know is the right size for your frame.