Two-bolt seatpost designs

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fastpedaller
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Re: Two-bolt seatpost designs

Postby fastpedaller » 26 Apr 2018, 4:36pm

I've one of these on-one twelfy sports - seems a good design.

seatpin.jpg
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amediasatex
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Location: Sunny Devon! just East of the Moor

Re: Two-bolt seatpost designs

Postby amediasatex » 26 Apr 2018, 7:08pm

amediasatex wrote:
Brucey wrote:
amediasatex wrote:just brandished my verniers at one and I couldn't find any trace of a wedge shape. Maybe they are not all the same.

cheers


Could be there are different versions... of course It's entirely possible I am mis-remembering or have confused them with another post of similar design :lol:

I'll try and remember to check when I get home as I'm curious now...


So it appears I was confusing it with a similar design, the SR post doesn’t have the angled edge, but the Easton CT2 post which uses an adaption of the same design does, but the angle isn’t where I remembered it. The inner part of the two part clamps is the one that actually cradles the saddle rails from underneath and that is wedge shaped so that load on the saddle acts to effectively add tension to the bolt.

It appears Easton dong use that type of clamp any more on any of their current models though.

robc02
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Re: Two-bolt seatpost designs

Postby robc02 » 26 Apr 2018, 8:47pm

Many years ago, after trying other types, I realised that the Campag two bolt design was the best in terms of adjust-ability and security - the latter because even a loose bolt wouldn't result in the saddle abruptly tilting, unlike with single bolt types. When they became unavailable I used an SR equivalent followed by an ITM "Big One".

The ITM had a similar layback to Campag but the rear bolt was an allen key type easily accessed from below and the front one was a hex head accessed with an open ended spanner from the top of the post underneath the saddle rails. Both this and the SR model were anodised so didn't suffer the same level of corrosion (mainly due to sweat in my case!) as the polished Campag item.

BBB make a similar design but with very little layback:
https://www.sjscycles.co.uk/seat-posts/272-bbb-skyscraper-inline-seat-post-400-mm/

I currently mainly use Thomson inline posts They are expensive but well made, durable and easy to adjust due to both allen headed bolts being accessible from below. The saddles I use have long rails so the lack of layback isn't a problem for me - my saddles are as far back as many others would be on a Campag post. There is a layback version but this is achieved by bending back the post itself - effective but not to everyone's taste and not giving very much layback compared to traditional models:

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Cunobelin
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Re: Two-bolt seatpost designs

Postby Cunobelin » 27 Apr 2018, 6:16am

Randy_Butternubs wrote:I have a Deda Elementi RS01 seatpost that works in a similar way. Adjustment is done with allen keys from beneath.

Image



That was the one design thing that hit me with the original post, although they are hexagonal heads as opposed to Allen key ones, putting the head at the top where the saddle position makes tightening a fiddle was not the best option

Samuel D
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Re: Two-bolt seatpost designs

Postby Samuel D » 27 Apr 2018, 10:09am

Although accessing the bolt heads may be a problem with the Campagnolo posts, the design has the advantage that the pivot for the lower jaw has a small radius.

I haven’t managed to find photos of a disassembled Nitto, but I imagine the semi-cylindrical trough in which the lower clamp rests has a larger radius and crosswise length, both of which would increase friction.

Does this smaller radius in the Campagnolo bearing more reliably balance the load between the two bolts, ensure the bolts don’t suffer bending, and allow smoother saddle tilt adjustment? Perhaps lubrication would take care of any problem in the other designs.

I’d like to study these designs in the hand before getting one, although the shortness of the Campagnolo posts probably rules them out anyway.

alexnharvey
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Re: Two-bolt seatpost designs

Postby alexnharvey » 27 Apr 2018, 11:17am

What's the value option for a silver, offset, two-bolt post?

Randy_Butternubs
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Re: Two-bolt seatpost designs

Postby Randy_Butternubs » 27 Apr 2018, 12:39pm

Samuel D wrote:Although accessing the bolt heads may be a problem with the Campagnolo posts, the design has the advantage that the pivot for the lower jaw has a small radius.

I haven’t managed to find photos of a disassembled Nitto, but I imagine the semi-cylindrical trough in which the lower clamp rests has a larger radius and crosswise length, both of which would increase friction.

Does this smaller radius in the Campagnolo bearing more reliably balance the load between the two bolts, ensure the bolts don’t suffer bending, and allow smoother saddle tilt adjustment? Perhaps lubrication would take care of any problem in the other designs.

I’d like to study these designs in the hand before getting one, although the shortness of the Campagnolo posts probably rules them out anyway.


That's an intersting point. The semi circular bit on the Deda RS01 has a radius of 12mm and is 34mm wide. It does seem like it might have more friction than the riveted (?) pivot of the Campag seatpost.

As I alluded to in my post the Deda does seem to clamp up in a slightly uneven way which then loosens and evens out from the flex caused by riding. The friction between the bottom clamp and the seatpost might be part of the reason for that. Another part of the reason though is the way the top clamps tend to want to clamp up a bit skewed, which shouldn't be an issue with the Nitto.

alexnharvey wrote:What's the value option for a silver, offset, two-bolt post?


The Deda RS01 is about £25 but as I've posted I do have some issues with it.

The Nitto S83 is currently £50 in a sale on Planet X.

Edit: Also I've realised that the Nitto design with the single-piece top clamp means that the screws need to change angle slightly as you adjust the saddle angle. Does anyone know if they use cupped washers under the bolt heads like you get on v-brake pads?

Brucey
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Re: Two-bolt seatpost designs

Postby Brucey » 27 Apr 2018, 1:54pm

Randy_Butternubs wrote: .... It does seem like it might have more friction than the riveted (?) pivot of the Campag seatpost. ....


The lower clamps are not riveted in position in the NR/GS seat pin design, they just slide over the fitting on the seat pin head (which is why they are so often lost when the seat pin is off the bike).

The friction element is a bit of red herring, in that the saddle rails flex in service, everything moves, and the clamp always tends to settle a little anyway. The campag design minimises settling in that the parts are chrome plated steel, slide/move easily (without wearing) and therefore settle more quickly. Two-bolt clamps with more friction are just more likely not to tighten fully first time round, settle in the first few miles and therefore need to be retightened.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

slowster
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Re: Two-bolt seatpost designs

Postby slowster » 27 Apr 2018, 2:35pm

Also I've realised that the Nitto design with the single-piece top clamp means that the screws need to change angle slightly as you adjust the saddle angle. Does anyone know if they use cupped washers under the bolt heads like you get on v-brake pads?


Yes they do. The tops of the recesses in the underside of the top of the seaptpost into which the bolts go are correspondingly concave to accept the convex surface of the washer, and there is also a split washer between the washer and the bolt head.

Brucey
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Re: Two-bolt seatpost designs

Postby Brucey » 27 Apr 2018, 6:25pm

I've never seen it happen with my own eyes but even the M7 bolts fitted to campag NR/GS pattern seat pins can break; I recently found this picture of a Zeus seat pin (made to the campag pattern, possibly using campag parts, on pardo.net)

Image

which shows the front bolt after a fatigue failure; the bolt had cracked about 1/3 through (on the left side) via fatigue before the final failure. The rider must have asked himself what the heck was going on; apparently he sat down unusually heavily on the saddle and this prompted the final fracture. The reason he say down unusually heavily? -one of his (campag NR) cranks had just snapped.... :shock: :shock:

cheers
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alexnharvey
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Re: Two-bolt seatpost designs

Postby alexnharvey » 13 Mar 2019, 8:12pm

I thought this thread would be the place to ask about the other two bolt design, that is two bolts side by side rather than front and back. Do these also offer the same fine adjustment as those discussed above and how do they compare in terms of strength and ease of adjustment?

Brucey
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Re: Two-bolt seatpost designs

Postby Brucey » 13 Mar 2019, 8:46pm

they vary considerably; there are several discussed upthread.

cheers
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iandriver
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Location: Cambridge.

Re: Two-bolt seatpost designs

Postby iandriver » 13 Mar 2019, 8:58pm

fausto99 wrote:I bought this one, 3 or 4 years ago.
Image
It allows me to have the saddle further forward because my thighs are relatively short. It is very easy to adjust the up/down nose attitude.
I can't remember the make though and I haven't found the receipt so far...


That arrangement looks very similar to a type USE used to use https://www.bikeradar.com/gear/category ... -09-33996/
Not your seat post, but the head design is the same
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

alexnharvey
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Joined: 10 Jan 2014, 8:39am

Re: Two-bolt seatpost designs

Postby alexnharvey » 13 Mar 2019, 8:59pm

Oh, I didn't see any discussion of the side by side type I am thinking of, I will go through again more carefully.

Image

Brucey
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Re: Two-bolt seatpost designs

Postby Brucey » 13 Mar 2019, 9:02pm

apologies I thought that type had been discussed but in fact it hasn't.

FWIW anything with two bolts is better than one, even if they are side by side.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~