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Discussion Starter · #1 ·
I am looking at new bikes and saw the higher-level Treks have a proprietary seat post. The saddle is fastened onto the pre-length post that drapes over a seat mast integral with the frame. BMC also have proprietary streamposts. These ones even have different shape and diameters along their lines.

I read this is all for aerodynamics as the seat clamp creates turbulence. Really? How much time will you save in the real world by these?

With these frames, you cannot switch anymore your favorite post/saddle quickly. :cryin:
 

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It's a marketing exercise that allows them to create a look not otherwise achievable with a standard, round seat post. The transition between the relatively small, round seat post and the wide aero tubes is not visually appealing.

There may be a theoretical aerodynamic improvement that will also help them sell bikes to techie people like myself (my bike has a 27.2 post though), but the real world impact of this would be questionable at best
 

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off the back
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If there's turbulancee around a seat clamp, surely it must be less than the turbulance generated by two pumping thighs?
 

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Matnlely Dregaend
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I generate more turbulence in that area by eating beans for dinner!

I had a regular seatpost on my Kestrel for a while, but I have to admit the aero seatpost looks way sexier.
 

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Anphaque II
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I am looking at new bikes and saw the higher-level Treks have a proprietary seat post. The saddle is fastened onto the pre-length post that drapes over a seat mast integral with the frame. BMC also have proprietary streamposts. These ones even have different shape and diameters along their lines.

I read this is all for aerodynamics as the seat clamp creates turbulence. Really? How much time will you save in the real world by these?

With these frames, you cannot switch anymore your favorite post/saddle quickly.
:cryin:

My question is can one cut said seatmast to accommodate one's leg length/saddle height?


I have short legs but a long torso. I can easily fit a frame that's 61-63cm with said seatmast but it's for a rider with a saddle height of 800+mm.
 

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With these frames, you cannot switch anymore your favorite post/saddle quickly. :cryin:
That's why I'll never buy one, as soon as frame builder uses proprietary parts it's off the list. There are plenty of other manufacturers that stick with the basics.
 

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Your saddle is always pointing straight ahead, not cocked a little to one side. It saves so much frustration!

I think this is the only real-life advantage.

There are some very thin aero carbon frames that would have a profile like this, it's necessary in that kind of application. But on your Synapses et al, ???
 

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I do not even like 31.6. I shim everything down to 27.2 so everything is interchangeable. I also always buy braze on front derailleurs for the same reason.
 

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'brifter' is f'ing stupid
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calm down people...

firstly, the trek system has NOTHING to do w/ aerodynamics. it has EVERYTHING to do w/ ride quality. you DO NOT EVER cut the trek seat mast. there are 2 different length caps (135 & 175mm) w/ 2 different amounts of offset (5mm or 20mm) to cover pretty much every fit need.
the seat mast is round, why would you think it's an aero thing?
'carveitup'...sorry, but you don't know what you're talking about. it's not marketing hoo haw, it's engineering. the seat mast allows the frame to have the ride quality the engineers want that is in no way affected by the seat post you install. some seat mast systems are pretty much useless, but the trek system is not one of them.
 

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calm down people...

firstly, the trek system has NOTHING to do w/ aerodynamics. it has EVERYTHING to do w/ ride quality. you DO NOT EVER cut the trek seat mast. there are 2 different length caps (135 & 175mm) w/ 2 different amounts of offset (5mm or 20mm) to cover pretty much every fit need.
the seat mast is round, why would you think it's an aero thing?
'carveitup'...sorry, but you don't know what you're talking about. it's not marketing hoo haw, it's engineering. the seat mast allows the frame to have the ride quality the engineers want that is in no way affected by the seat post you install. some seat mast systems are pretty much useless, but the trek system is not one of them.
Or it could be a marketing reason to get that purty integrated seat mast look. Tires, saddle, and shorts probably have more to do with feel than the seat mast. On top of that, feel is very elusive and individual.
 

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Discussion Starter · #11 ·
calm down people...

firstly, the trek system has NOTHING to do w/ aerodynamics. it has EVERYTHING to do w/ ride quality. you DO NOT EVER cut the trek seat mast. there are 2 different length caps (135 & 175mm) w/ 2 different amounts of offset (5mm or 20mm) to cover pretty much every fit need.
the seat mast is round, why would you think it's an aero thing?
'carveitup'...sorry, but you don't know what you're talking about. it's not marketing hoo haw, it's engineering. the seat mast allows the frame to have the ride quality the engineers want that is in no way affected by the seat post you install. some seat mast systems are pretty much useless, but the trek system is not one of them.
Am talking about the BMC Streampost devoid of seat clamp which suppose to create turbulence.
 

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'brifter' is f'ing stupid
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Or it could be a marketing reason to get that purty integrated seat mast look. Tires, saddle, and shorts probably have more to do with feel than the seat mast. On top of that, feel is very elusive and individual.
you've never seen a Madone or Domane seat tube flex i take it? tires definitely make the biggest difference but there is a considerable amount of seat tube flex designed into those 2 frames.
 

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Anphaque II
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you've never seen a Madone or Domane seat tube flex i take it? tires definitely make the biggest difference but there is a considerable amount of seat tube flex designed into those 2 frames.
I saw a write up of Cancellara's Domane at Paris-Roubaix.


A donut made of some gel that isolates the seatmast from frame vibrations. I look at it like a vehicle engine mount in that a rubber material separates the engine vibration from the vehicle chassis.

Is that about right?
 

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'brifter' is f'ing stupid
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I saw a write up of Cancellara's Domane at Paris-Roubaix.


A donut made of some gel that isolates the seatmast from frame vibrations. I look at it like a vehicle engine mount in that a rubber material separates the engine vibration from the vehicle chassis.

Is that about right?
not even close. there is a pivot w/ 2 cartridge bearings, just like a suspension pivot on a mountain bike frame. there is no 'gel donut'. it's a pivot that allows the seat tube to flex more than on a madone.
 

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Anphaque II
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not even close. there is a pivot w/ 2 cartridge bearings, just like a suspension pivot on a mountain bike frame. there is no 'gel donut'. it's a pivot that allows the seat tube to flex more than on a madone.
O.K. I just watched Trek's vid of the IsoSpeed Decoupler.


I see what you're talking about. Thanks for the clarification.

Here is what I don't get: Usually a pivot involves two different pieces joined at the pivot. Isn't the seatmast one long piece with those 2 cartridge bearings at the TT and ST junction? And I guess the seatmast is designed to flex at the 2 cartridge bearings.

But why bearings? I guess that's what's throwing me off. It's flexing past that point, not rolling. :shrugs:
 

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you've never seen a Madone or Domane seat tube flex i take it? tires definitely make the biggest difference but there is a considerable amount of seat tube flex designed into those 2 frames.
I just looked at it. Why would it require a proprietary post? It looks to have a regular seat post binder on it.
 

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'brifter' is f'ing stupid
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O.K. I just watched Trek's vid of the IsoSpeed Decoupler.


I see what you're talking about. Thanks for the clarification.

Here is what I don't get: Usually a pivot involves two different pieces joined at the pivot. Isn't the seatmast one long piece with those 2 cartridge bearings at the TT and ST junction? And I guess the seatmast is designed to flex at the 2 cartridge bearings.

But why bearings? I guess that's what's throwing me off. It's flexing past that point, not rolling. :shrugs:
rolling? what are you talking about? it just allows the seat tube to flex more freely. the top part of the seat mast flexes backwards when you hit a bump, the lower part (between top tube and bb) flexes forward. the seat can mover over an inch.

I just looked at it. Why would it require a proprietary post? It looks to have a regular seat post binder on it.
on 5 and 6 series frames...look at them again. 3 and 4 series use a normal seat post.
 

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Anphaque II
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O.K. I just watched Trek's vid of the IsoSpeed Decoupler.


I see what you're talking about. Thanks for the clarification.

Here is what I don't get: Usually a pivot involves two different pieces joined at the pivot. Isn't the seatmast one long piece with those 2 cartridge bearings at the TT and ST junction? And I guess the seatmast is designed to flex at the 2 cartridge bearings.


But why bearings? I guess that's what's throwing me off. It's flexing past that point, not rolling. :shrugs:
rolling? what are you talking about? it just allows the seat tube to flex more freely. the top part of the seat mast flexes backwards when you hit a bump, the lower part (between top tube and bb) flexes forward. the seat can mover over an inch.

If you would have read my poast a little more carefully you would have noticed why I mentioned rolling.
 
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