Thompson Setback - Clarification on measurements
 

I'm thinking of getting a Thompson setback seat post and want to confirm it will work on my bike. With my current post I took the following measurements:

- 110mm of post extending from the top of the seat post clamp to the bottom of my Brooks saddle rail (is that enough height to allow for the Thompson setback?)
- 25mm of setback measured from the centre of the post to the centre of the clamp (I still have a bit of room on the rails, but you know those Brooks:()

If the Thompson doesn't work, what other options are there...this is for a chromoly steel frame bike that I use mainly on gravel roads, including 2-4 day "light" tours. I may get a 10+ litre seat post bag for tours and want to make sure the new post fits the bike, but can handle some weight from such a bag. The rest of the bike is bomb proof...

Thanks.

I don't know the portion of the Thompson post that is above the bend but I'll will say that this angling back of the post where a post mounted rack would attach will make the rack not sit as intended. The rack will also be angled down toward the tire. These racks are usually intended to fit on conventionally straight posts. Andy.

No p in Thomson. :)

Unusable length is either 97.05mm (under 350mm overall) or 110.42mm (over 350mm overall) so you're ok, but make sure you go with one of the shorter posts.

Setback is 16mm on all the Thomson setback posts.

its just a bend in the tube , head is still zero set back.. so you need the length out of the frame to be sufficient.

You are being pedantic. Yes, the head is in line with the upper portion of the post so there is technically no "setback". However the head is offset behind a vertical line through the seat tube so it gives the exact same effect as real setback.

Just saying OP got a sloping top tube frame ? lots of post showing.. fine..

Product in Question .. http://bikethomson.com/elite-seatpost-series/

You need this. 30mm set back, less post above the bend, ~half price, and good quality.

VO Grand Cru Seatpost, Long Setback - Seatposts - Components

Not necessary. I have Thomson "set back" seatposts in two bikes, both with level toptubes, and there is no problem with keeping the bend above the seattube top. The required seatpost exposure of about 100 mm isn't that much.

Agreed.

As I understand it, the Thomson Setback has the same amount of setback as other straight seatposts. I've compared mine with a non-Thomson (standard OEM) seatpost from my other bike, and it is the same. The non-Thomson has a separate head that incorporates setback when combined w/the straight seatpost - it is offset to the rear. The Thomson design is stronger & (maybe) lighter partially because the head is milled from the same piece of alloy. The bent tube allows for the same setback as OEM-type seatposts. It is a different approach to the same seat positioning.

I bought mine for the strength & looks, not to gain any setback. The product mentioned (VO Grand) does appear to have increased setback.

PS: I tried using a Brooks saddle w/the Thomson. Not enough rail for the position I needed.

I like the Brompton Pentaclip , it slips on top of the common, Round, seatpost .. which is offered (kalloy) in all sizes

though RivBike sells a fancier Nitto one in 27.2..

my Other Post , perfect for Brooks saddles, is the Traditional Campag 2 bolt the <C>771 wrench even has an open end that fits the Brooks tension Nut.

We need to measure the setbacks, not just say "it's setback."

If I hold a ruler up to my Thomson Setback (installed on wife's road bike), line up the ruler with the seat tube centerline, and measure parallel to the ground to the center of the seat rail clamp, I get about 17 mm ("about" because it's hard to see). I also get about 110 mm minimum height above seat tube end.

How does this compare? A "normal" Kalloy single bolt post has about 17 as well, as does a vintage two-bolt Campy Nuovo Record dating back to 1970 or so. In my recollection most seat posts until perhaps the '90s had this 16 mm setback value or something close to that. A current Campy carbon post I have shows 25 mm, and a current Nitto S-84 has about 37 mm. I think the FSA posts with different setbacks follow something like "zero, -15 and -30" conventions. Kudos to them

These longer setbacks can make a big difference in comfort, for better or for worse. We don't want to get them mixed up with the once-normal 16 mm posts and the now-normal (I guess!) zero-setback posts. If you are on BF looking for a high-setback post and a bunch of folks tell you "oh yeah, the Thomson has LOADS of setback," you might be shocked when you get the part, and angry at the seller and yourself for being mislead.

Not really! It has the same setback as other seat posts with the normal amount of setback, but more than zero-setback posts.

One reason the Thomson design is stronger is its material, 7001 I think. It is lighter because of the inside of the shaft is machined out at the sides, and the unit construction.

Check the weights of a Thomson Elite and Masterpiece posts with even some high-end carbon posts. Few carbon posts are lighter than even the Elite, in 250 mm length.

If your Brooks needs more setback than the Thomsons give, we're in the same boat. I have a CLB, a Nitto S-84, and a no-name that all have 30 mm or more. You'll probably need the V-O, which I haven't tried yet. You might like a Selle Anatomica on a Thomson Setback.