Seatposts, layback, and a daft idea

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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 20 Oct 2010, 9:09pm

To all those talikng about steep seat angles on race bikes, yes, I agree entirely if you want to get an aerodynamic position, thats the way to go. But Horizon started all this off talking about Galaxies, not race bikes.

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horizon
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Re: Seatposts, layback, and a daft idea

Postby horizon » 20 Oct 2010, 9:25pm

Thanks for that Colin. What is interesting is that we (and others) have spent a fair bit of time posting on this, so it's a real but unrecognised issue. When I got my Super Galaxy back in the late nineties, I happened to be passing the dealer (a good one by the way) and mentioned the problem only to be met by bemusement and blank looks (though with concern as well, to their credit). I think it was CJ who flagged up the VK on here and changed my (cycling) life. I'm still of the view that it may be a "one size cannot fit all" problem rather than a deliberate design policy and give still Dawes the benefit of the doubt.

Whichever it is, a good dealer could have a few tricks up their sleeve: a stock of VKs, a few stem raisers, some large size toe clips etc: when the customer comes back for their one month free service, the dealer could check comfort/size issues as well which may not have been apparent at the time of sale. I have never had the luxury of a custom fitting but I would be interested to know what shape of bike the frame builder would come up with.
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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 20 Oct 2010, 9:44pm

Horizon
I dont understand why at 5 feet 10 inches I have trouble getting the Brooks far enough back - I would have thought 5 feet 10 was awfully average!
But its only in the last month that I did the KOPS (knee over pedal spindle) test. I found the bump at the top of my tibia was plumb above the pedal spindle, but I'm not certain thats the right place to hold the plumb line - anybody got a link??

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Trigger
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Re: Seatposts, layback, and a daft idea

Postby Trigger » 31 Dec 2010, 6:28pm

Sorry to bump this thread, but I just did a search as I'm having similar issues mentioned in this thread.

I'm 5' 10 and also can't get my B17 back far enough, although it's not far off, I find myself shifting back on the saddle quite often but this takes me onto the studded edge which I'm guessing isn't the best position for comfort?

Thanks to Horizon for mentioning the VK adaptor, I've just bought a shop soiled item from SJS on Ebay for £10. Hopefully this will sort the problem as I reckon I'm only 30-35mm away from being perfect.

I've no idea as to the dimensions and angles of my bike though so I can't comment on that, it's a steel framed Trek rigid MTB, I'm pretty sure the frame is the correct size, although I did have issues in getting the stem to the right height so maybe it's a bit on the small size (18" frame I think)

I'd say it's us whose dimensions vary from the average of people same height, I'll do some measuring when it arrives and it's set up, then I'll know what's going on.

Cheers again for the VK tip!!

Edit: I'm now concerned about the amount of extra leverage being placed on a single bolt, I'm a fat bar stool so I'm hoping I'm not going to break it and end up in a ditch with the bike on top of me!

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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 31 Dec 2010, 6:41pm

Hi Trigger, I just linked this thread to yours!
As you say, there is a bending force on "that bolt", long ago CJ recommended replacing with high tensile steel bolts in place of the common mild steel bolts.

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Re: Seatposts, layback, and a daft idea

Postby BigG » 31 Dec 2010, 8:04pm

Suntour used to make a seat post with a sliding mount point that allowed up to about 4 cm layback. Two were advertised on eBay recently and I think only one sold.

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Trigger
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Re: Seatposts, layback, and a daft idea

Postby Trigger » 31 Dec 2010, 10:13pm

531colin wrote:Hi Trigger, I just linked this thread to yours!
As you say, there is a bending force on "that bolt", long ago CJ recommended replacing with high tensile steel bolts in place of the common mild steel bolts.


Thanks for linking the thread, luckily it came up high in the search results though!

I may be wrong (not unheard of) bit aren't high tensile bolts only strong in one direction? ie it will take more pulling/stretching force but they will snap like a twig with a sideways tap from a toffee hammer. Like I say, I may be wrong.

Edit: this is my current seatpost http://www.chainreactioncycles.com/Mode ... elID=33162

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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 31 Dec 2010, 11:13pm

Trigger wrote:
I may be wrong (not unheard of) bit aren't high tensile bolts only strong in one direction? ie it will take more pulling/stretching force but they will snap like a twig with a sideways tap from a toffee hammer. Like I say, I may be wrong.

Edit: this is my current seatpost http://www.chainreactioncycles.com/Mode ... elID=33162


I dont think thats the case with high tensile bolts, but hopefully somebody who really knows will comment.

Your seatpost has some layback, maybe marginally less than the 2 posts I showed at the start of this thread. The VK adapter will show how much layback you need, you might then choose to buy a more elegant solution, if applicable.

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Trigger
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Re: Seatposts, layback, and a daft idea

Postby Trigger » 1 Jan 2011, 2:20am

That might be the way to go, although from a quick look some of the reasonably priced layback seatposts cost nearly as much as I paid for the whole bike!

Pity you can only find high tensile bolts in packs of 100/200 as that would be a cost effective safety measure. I suppose I could always lose some weight :lol:

I'm sure high tensile only refers to the strength of the material under pulling/stretching force, sideways or shear isn't improved. We used to use high tensile bolts on some of the tooling where I used to work. We always used to change out the HT stuff for regular bolts because when lifting the tooling off with the crane the slightest bit of sideways force would snap the bolts where as the cheap stuff would just bend. For a bike saddle though it may just be ok!

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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 1 Jan 2011, 8:28am

I got a handful of high ten bolts from the local bolt stockist.
I guess seatpost bolt failure is fatigue, rather than a single "overload"....?

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Re: Seatposts, layback, and a daft idea

Postby reohn2 » 1 Jan 2011, 9:25am

531colin wrote:To all those talikng about steep seat angles on race bikes, yes, I agree entirely if you want to get an aerodynamic position, thats the way to go. But Horizon started all this off talking about Galaxies, not race bikes.


Its always been my understanding that steep seat tube angles were more to do with shorter chainstays making for a stiffer frame for racing from the days when steel was really the only material used and more or less everything was lugged.
What really annoys though is seeing,Audax and touring bikes with the same steep angled seat tube and a 30 to 40mm gap between tyre and s/tube.Chainstays on a touring bike are longer to facilitate the use of panniers without catching the riders heels but a slack (70 to 72 deg)s/tube angle doesn't affect that at all.
I never heard of anyone complaining the s/tube angle to be too slack as to not allow the saddle to be positioned far enough forward, but out of a handful of tourists on here some five or six have complained that they can't get the saddle back far enough, so cycle frame makers have a problem that needs solving and we all know the answer!
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531colin
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Re: Seatposts, layback, and a daft idea

Postby 531colin » 1 Jan 2011, 9:50am

My opinion of cycle industry "bike designers" has been on here often enough!
Putting my reputation where my mouth is, here is my design (from Spa's website)...http://www.spacycles.co.uk/smsimg/uploads/touringgeometry.jpg

As to why they put steep angles on touring frames, I think its just blindly copying racing.
Or its a "who can get the shortest top tube" contest - although as this thread shows, all that happens is the rider finds a layback seatpost to get comfortable, a short top tube doesnt get the bars closer once you fit a layback post.

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frank9755
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Re: Seatposts, layback, and a daft idea

Postby frank9755 » 8 Mar 2011, 12:21pm

I'm sure you're right Colin, Horizon, about it being a fashion thing amongst designers.

I've just enjoyed reading this thread, and am trying to decide whether to go for a VK adaptor or VO seatpost to meet exactly the same need...

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Re: Seatposts, layback, and a daft idea

Postby yello » 17 Mar 2011, 11:52am

tour59 wrote:I have a VO post on one bike, and a CLB on another. The CLB has a longer layback.


Thanks for that info Tom, exactly what I was looking for! CLB ordered.

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Re: Seatposts, layback, and a daft idea

Postby island girl » 24 Jul 2012, 11:11pm

This is a year old thread which I have been reading as I have a B17 saddle that I would like to move back a bit,
I have tried to resource a VK Adaptor but it doesn't appear on their website now. Has anyone any idea
where I could buy a saddle extension/adjustor.