Thompson Elite "Tuned"

Discuss light weight issues concerning road bikes & parts.
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djconnel
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by djconnel

Where do you get just the yokes?

Epic-o
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by Epic-o

Not mine....

You can find the KCNC clamping parts in some German shops. Bike-components.de??

You are in the States...maybe Jason can help you

Dan, nice blog!! I learn a lot about physics reading your entries.

by Weenie


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djconnel
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by djconnel

Thanks!

This looks promising:
Image

So would it work with Thomson? It's for M5 bolts. I think the Thomson is M4 bolts.

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djconnel
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by djconnel

I'll attempt to answer my own question.

The Thomson bolts I measure at closer to 4 mm than 5 mm, and the KCNC yoke is available only in 5 mm or 6 mm. So I'd need new bolts as well as the yokes. But the Thomson Elite FAQ (which presumably also applies to the Masterpiece FAQ) says:

Q - I lost my bolts, and I can't find any at the hardware store. Are they special? Where can I get some?
A
- Our bolts have been specially designed to work with the Thomson seatpost.
First of all, there is a spherical radius under the head of the bolt, which allows the force to be evenly distributed across the bolt head, as the bolt swivels during seat adjustment. A standard bolt does not have this feature, and would be more likely to break. Our bolts are made of a high strength steel alloy, and go through and extra manufacturing process that increases their fatigue lives.
Finally, Thomson seatpost bolts are plated to prevent rust and corrosion. As you can see, bolts from the hardware store would be very poor replacements for Thomson bolts, and would cause failure and void the warranty. Contact your local bike shop for replacement bolts. The bike store may order bolts from our distributors. Only Thomson bolts may be used on Thomson seatposts.


Toronto Cycles, for example, offers Ti bolts specifically for the Thomson posts:

Image

So the answer is no, it's nontrivial to install KCNC yokes on a Thomson post. You'd need to replace the bolts with M5 bolts, and these won't have the shaped heads which the Thomson post really requires.

The KCNC has an alternate design in which the bolt doesn't need to rotate; rather they are attached to a rotating part of the post itself:

Image

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lancejohnson
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by lancejohnson

I've gone out and gotten Titanium M5 bolts and used them in my Thompson posts in the past with no issue, so I can't imagine that there would be an issue using those yokes and regular M5 Ti bolts...
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djconnel
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by djconnel

The KCNC yokes are listed at 5.8 grams each (total 11.6 grams). Toronto Cycles sells M5×30 mm Ti bolts. My Masterpiece hardware is:

clamps (2): 48.1 grams
cylinders (2): 9.4 grams
bolts and washers (2): 11.7 grams


The KCNC would get rid of the cylinders and one of the two clamps. I'll assume both clamps are the same mass. That makes the replaced clamp = 24 g. On the screw, assuming scaling in proportion to the square of the diameter times the mass density ratio of Ti to Fe, I get 10% saved = 1.2 grams. So total saved would be 24 grams + 1.2 grams + 9.4 grams - 11.6 grams = 23 grams. My post is presently 180.4 grams, cut. This would take it to roughly 157.4 grams.

Not bad. There's only the issue with whether the nonaxial load on screws without rounded heads pops off the heads. That would hurt.

Epic-o
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by Epic-o

Better with pics....

Standard Clamp: 69.2gr

Tuned one: Carbon rails seat 8gr + M5 Ti bolts (maybe too long) 12gr + KCNC M5 yokes 9.4 gr= 29.4gr

So the real saved weight would be 39.8gr....180.4 - 39.8 = 140.6gr
Attachments
Dibujo.jpg
dd.jpg
KCNC_Yokes_f__r_M5.jpg

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djconnel
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by djconnel

BikeComponents.de charges 29,95 EUR for shipping to the US. A bit silly on parts this small.

On the other hand, Clee Cycles has a nice collection of KCNC parts: yokes, clamps, and U-shaped shell (nice for those of us without access to machining).

Unfortunately they're out of the M5 yokes. I'd be worried about going to M6 (adds a bit of mass, but far more importantly the holes on the Thomson are designed for M4, so M6 would be seriously pushing it).

I'll check back later to see if they get more M5 yokes.

Alternative is to just buy a KCNC seatpost. The kluged Thomson should be lighter, however. Maybe not, though: Clee claims 158 g for 31.6 × 350 mm[/url], and I'd maybe able to shave 10 g off that by cutting, which gets close to that 141 gram total with the home-brewed U-clamp.

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djconnel
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by djconnel

Okay -- I got the KCNC hardware from Kevin @ Bike Nüt (gotta love it when an LBS sells KCNC hardware. If in SF, definitely check that shop out).

The numbers:
Some data from my Thomson Masterpiece:

clamp diameter: 31.8 mm
original length: 350 mm (stated)
original mass: 190.3 grams
cut-section (3.9 cm): 9.7 grams = 2.5 grams / cm
final mass: 180.4 grams
sawdust: 0.2 grams (calculated)

clamp & cradle: 48.1 grams
cylinders (2): 9.4 grams
bolts and washers (2): 11.7 grams
cut post: 111.2 grams (cut)
uncut post (calculated): 121.1 grams

KCNC M5 hardware (clamps, bolts, spherical washers, cradle): 26.2 grams
replaced Thomson hardware: 69.2 grams
mass saved: 43.0 grams.
new post mass (calculated): 137.4 grams

That was a very worthwhile operation. I could get it a bit lighter if I went to a shorter rear bolt: it's clearly longer than I need. Of course the Thomson hardware seems a lot more secure. But compromises must be made in the quest for lightness.

Only issue: KCNC cradle is slightly lower diameter than recess in Thomson post. I put some foil in there to act as a buffer. Mass of foil = 0.0 grams.

BmanX
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by BmanX

Just received my Masterpiece layback post for the MTB which is a 31.6 post and was 191g so I am looking for some good weight saving on this post.

Also trying to pick up another 31.6 post with zero offset for my winter road bike. Should hopefully have that sorted out today.

Keep up the posts as I need to shed weight on these posts.
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AERO & LIGHT is RIGHT

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bikenerd
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by bikenerd

djconnel wrote:KCNC M5 hardware (clamps, bolts, spherical washers, cradle): 26.2 grams
replaced Thomson hardware: 69.2 grams
mass saved: 43.0 grams.
Of course the Thomson hardware seems a lot more secure.


So Dan, how would you feel about using this setup for cyclocross? 160 pound rider who rarely breaks any parts. Also, how much did all the KCNC bits cost, and can you provide any pics of how it all went together? Thanks for testing the concept!

MrRedRaider
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by MrRedRaider

Just something to think about if you are using the KCNC hardware, which is more apparent in the picture of the red KCNC post. The yoke ends are not lathed, so they only clamp down on the rail in a straight down manner. Other yokes (ax-lightness) have lathed ends so that the rails of the seat post can be at any angle. I would only worry about this if you are using saddles with all carbon rails, as the KCNC yokes could pinch or crush them. A similar argument could be made with the ax-lightness yokes also, since the contact area would still be very small. If you are confident in your post/saddle combination, I suppose you could file down the yokes to match the angle of the rails. I am going to tune an Easton EC70/90 once I find one. I already ordered the yokes from ax-lightness, and will get ti bolts when I find out which ones would suit it best.

Super_fast
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by Super_fast

How much do the yokes from Ax Lightness cost?

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djconnel
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by djconnel

MrRedRaider wrote:I suppose you could file down the yokes to match the angle of the rails.


Good point. The rear clamp has a nice angle. The front clamp is not parallel/normal to the rails. I suspect it would be difficult to file, as the relevant surface is curved: filing could well end up reducing the contact area rather than increase it.
Attachments
rear_view.jpg
rear view of the seat interior
00002.jpg
left-front-bottom view of the seat clamp

Super_fast
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by Super_fast

I don't think the clamping area is big issue as long as the torque is low, never heard of anyone cracking the saddle rail with a KCNC or AX post.
Filing the sharp edges from the KCNC yokes might be already enough to prevent them cutting in the carbon rail when they are slightly at an angle compared to the saddle rail.

by Weenie


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