|i'm about to throw away this record ti post.||colker|
Dec 23, 2001 11:00 AM
|it's all looks and no function. the shinny ti surface makes it slip inside the seat tube. have already broken a bolt inside the seat lug. taking the remaining bolt from the frame wasn't fun. |
the saddle rails slip on the craddle. it needs constant readjustment. i hate to have the post slip in the midle of a ride.
a piece of junk.
|Thomson, all you need to know. nm||sprockets|
Dec 23, 2001 11:37 AM
|not for road bikes...||C-40|
Dec 23, 2001 12:08 PM
|The Thomson post, even the "setback" model doesn't have the amount of setback needed on most road bikes.
The setback model effectively increases the seat tube angle by about 1 degree, and the straight up model increases it by almost 2 degrees. Not a good thing for most folks.
Although the clamping mechanism looks good, they need to make the design compatible with standard road bike geometry.
|how much does 2degrees alter top tube length? n.m.||koala|
Dec 23, 2001 12:36 PM
|about 1 inch...||C-40|
Dec 23, 2001 3:24 PM
|The exact amount depends on your saddle height. The effect of seat tube angle on saddle position (and effective top tube length) is calculated as follows:
(cosA-cosB) x saddle height = effective change in TT
You can also estimate saddle height from frame size with the formula 1.32 x frame size = saddle height. This formula comes from the often used .67 x inseam = frame size and the .883 x inseam = saddle height formulas.
For a person that rides a 55cm frame, considering a 72 degree seat tube angle, compared to a 74 degree for example:
(cos72-cos74) x (1.32 x 55)= 2.4cm
The traditional road post has the front of the seat rail clamp in line, or slightly behind the centerline of the seatpost. Designs like the Thomson (straight-up model)have the clamp significantly ahead of the front of the post. The difference between the centerline and front side of the post is 1.36cm (equivalent to more than 1 degree). If the front of the rail clamp is 1cm ahead of the front side of the post, the total is 2.36cm, which is about 2 degrees.
|no||Woof the dog|
Dec 23, 2001 2:03 PM
|I think its fine. My knee is right above the pedal spindle, and my SLR's rails are clamped somewhere in the middle by the Thompson clamps. I can still move it a significant amount back if I want to. Its a setback model and it should work just fine. My bike is a standard road geometry as far as I am concerned. Where did you come up with this info? Tell me!!!!!!!!!!!!!!!
Woof the dog.
Dec 23, 2001 3:48 PM
|According catalog literature the setback model has 15mm or 1.5cm more setback than the straight-up model.
The front of the seat rail clamp on the straight-up model appears to be placed at least 2.5cm ahead of the centerline of the seatpost. The "setback" model should locate the front of the clamp about 1cm ahead of the centerline of the seatpost.
Traditional road posts have the front of the clamp near or slightly behind the centerline of the seatpost.
See my other post on how these amounts are converted to effective degrees of seat tube angle.
If the Thomson post allows you to achieve your desired KOP with room to spare, you have no problem. Some folks place the knee as much as 2cm behind the pedal spindle. The Thomson post is unlikely to work for them.
Changing from a campy post to the Thomson could cause problems with the reduced amount of rearward saddle movement that is available.
Jan 8, 2002 10:06 AM
|It's kinda funny how you've backed away from your broad sweeping use of the phrase "most people" to "some people". Face it - MOST people don't have a problem with the Thomson post. Setting your riding position up with your knee 2 cm behind the pedal spindle is _highly_ unusual - and in no way can be construed as normal for most people. Bottom line a correctly fitted frame (custom or not) for your riding style will not leave you craving extreme setback. One also has to remember that saddle choice and the design of the rails makes a huge difference also. |
It's also funny to note that while you criticize the clamping mechanism you've never actually used it. Kinda funny you can be such an authority yet have no experience.
After well over three years of using the Thomson seatpost on both my road and MTB bikes I have had zero problems and find that it out performs most of the rubbish on the market and in my parts boxes.
Dec 23, 2001 3:35 PM
|just check where your seat is on your "normal" layback post. If your seat is slammed back, the Thomson ain't gonna work. If you have another 2cm or so of rails in front of the clamp, you can go with Thomson. I could use one on my Merckx, which has a slack seat tube angle, but not on my other bikes. I also think they look wrong on road bikes.|
Dec 23, 2001 10:05 PM
|To say that the Thomson post is "wrong" for most folks is just plain naive - it's only "wrong" if you have a frame which requires you to move the saddle waaaaay back to get it to fit you. Not compatable with current road geometry? Give me a break! Unless your saddle is jammed all the way back (possibly indicative that you have a frame size issue...) it works fine - and it's an exceedingly strong seatpost. |
Isn't the "standard" setback for Campy 20mm? The Thomson setback post is 16mm, that's a whopping 4mm difference - and remember - the difference here ONLY matters if you are ACTUALLY USING the last 4mm of adjustability on the post (i.e., you have your saddle within 4mm of being jammed all the way back in the post).
Any seatpost alters the "effective" angle of the frame - the straight Thomson will let you keep the effective seat tube angle equal to the actual seat tube angle of the frame (that's a 0 degree shift) - but this is only one of it's adjustment points - it also gives you quite a bit of forward or rearward adjustability (how much depends on your saddle rails). Any post which has an offset clamp decreases the effective seat tube angle of the frame - the larger the offset, the more you can decrease the effective seat tube angle.
Dec 24, 2001 6:12 AM
|I just measure and state the facts. Traditional road posts(like campy's) have always placed the front of the seat rail clamp near or slightly behind the centerline of the post. This design permits steeper seat tube angles and shorter chainstays that are common to racing bikes.
To my knowledge there is no standard reference point from which to measure seatpost setback. Thomson's 15mm number merely compares their straight-up model to their setback model and has no relevance to other brands and has no particular point of reference.
If a point of reference was selected, the most sensible would be the center of the seatpost, in which case setback of traditional posts (like campy's) would be zero or slightly negative, compared to a positive 1.0-2.5cm for the Thomson designs. There's nothing wrong with using a Thomson if it permits the saddle to be placed in the desired position, but it can cause problems if you switch from a traditional design.
Dec 24, 2001 6:56 AM
|Well - you mis-measured in this case - it could be, in part, due to the shape of the clamp for the Thomson post - the part which grips the saddle rails is not even with the end of the clamp - take a look: |
The front of the seat clamp is actually very close to the centerline of the post - measuring an actual post, the distance behind the centerline is approx. 4mm.
Seatpost "offset" is measured from the center of the clamp to the center of the seatpost. Thomson's claimed 16mm offset (16mm - not 15!) is that measurement.
Once again - using the Thomson seatpost would be a problem if, and only if, you need that last few mm of adjustment.
|since we are nitpicking millimeters...||C-40|
Dec 24, 2001 10:02 AM
|Wow, 16mm not 15! Thanks for the web address though. I've never even had a Thomson post to measure, but my figures weren't far off for eyeballing photographs. The clamp obviously protrudes beyond the 40.6mm width shown on the drawings, which makes the (lack of) setback look worse than it is.
Assumming that the seat rails can be pushed all the way up to the portion of the clamp dimensioned on their drawings, you are correct about the clamp being 4mm ahead of the centerline of the post. Not a huge thing, but it could be significant to some.
My Colnago (ITM) post has the clamp positioned 7mm behind the centerline of the post. The 11mm difference between these posts is significant.
Dec 24, 2001 7:10 AM
|I was going to buy a thomson because of all the bad reviews of the chorus. If your calculations are correct it makes a big difference as my profile post clamp is behind the center of the post. Looks like the thomson will work as i like my knee in the classic position over the pedals . If I didnt it would not, by my quick measurement.|
|'Waddaya mean, not for road bikes???||dsc|
Dec 24, 2001 12:00 PM
|The straight-up Thomson post clamps right in the middle of my saddle rails, and puts my knees in the exact same position over the pedal axels as on my mtb (which by the way sports a straight-up design Ringle post).
This is what works, and is comfortable for me. What is always the prevailing advice to new riders on this board? It's all about the fit, that's what. Excessive setback won't work for everyone; I, for one, am glad that Thomson manufactures such a great post in a design that works for me. And yeah, I think it looks good, too ;-)
Jan 8, 2002 9:44 AM
|If you need that much setback you have a poorly fit frame and/or longer than average (i.e. not normal) thigh length. "Most folks" don't need that kind of setback. Ask any experienced frame fitter working in a LBS. |
The clamping mechanism is excellent and there is absolutely no "compatibility problem with standard road bike geometry." How do you make the connection between how (well) the clamping mechanism works and where it's actually located as being a design defect? Fact is their clamping mechanism design is one of the best out there. It's simple, percise, and easily allows for fine adjustments.
Learn to recognize personal bias and distginguish it from fact.
|Had the same problem until....||CT1|
Dec 23, 2001 11:55 AM
|I took some 320 wet/dry paper and scuffed up the part of the post inside the frame. No slipage afterward. :)
Dec 23, 2001 12:16 PM
|Hopefully your problem is isolated. I put 4000 miles on one and never had a single problem. No slip, no squeaks.
There is always a chance that part of the problem is with the frame. If you managed to break a seat clamp bolt, be sure that you haven't also squeezed the lug enough to deform it, which could cause the bolt to bottom out, or the "ears" to touch together, before applying sufficient clamping pressure.
Dec 23, 2001 2:52 PM
|as far as squeezing the lug, yes, it seems the threads on the frame lug are already misaligned.hmm... well, slightly used frames( as i bought it on a very good price. it's a pinarello vuelta!) are not new frames. the bolt doesn't bottom out though nor the ears touch together. the post enters nice and tight on the frame. |
what about the seat rails slipping on the craddle? the boilt on the craddle doesn't give enough pressure!
|You got to hate the slipping seat post||Bernie|
Dec 23, 2001 1:38 PM
|But I usually associate the seat post getting pounded into the frame as a mountain biking problem. I'd just try changing seat posts. I'm a big fan of Thomson also. I really don't understand the problem someone else on this post has with them a(the set back part), but Thomson is a good product and a good company.|
|No problems with mine. Doesn't do much for me or ag'in me,||bill|
Dec 23, 2001 6:07 PM
|just like a seatpost should.|
|re: i'm about to throw away this record ti post.||mackgoo|
Dec 24, 2001 6:01 PM
|Don't throw it away. I'll pay for the shipping, send it to me.|
|Try a Shaft||Texsun|
Jan 5, 2002 12:49 AM
|I bought a Salsa Shaft seatpost about two months back. To date I have nothing but good things to say. Doesn't slip, the separate cam adjustment for saddle tilt is SWEET, no squeaks, holds seat tight....what more can you ask in a seat post.
Can't go wrong with Thomson either...