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Do the current floating seat stays in GT frame design really work?

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Do the current floating seat stays in GT frame design really work?

Old 06-22-20, 09:06 PM
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CaptainPlanet
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Do the current floating seat stays in GT frame design really work?

The current GT frames don't have the 2 rear triangles welded to the seat tube any more except Palomar.
So the seat tube is just being held in place by the top tube and bottom bracket, and every time you sit, your body weight applies a force and pulls against the top tube welds. Is this a good Hellenic stay design? Wouldn't the seat tube eventually break off because there's nothing else supporting it from the back?
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Old 06-22-20, 11:27 PM
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30 years of marketing down the drain.

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Old 06-23-20, 07:36 AM
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If GT has done the engineering well and if the production follows the design then the frames will last as long as any other design. But those are a couple of big ifs. Not mentioned is the weight of the frame...

Wasn't this design done by that company that Specialized battled with a bunch of years ago? Bowflex or some name like that for the design or model? Andy
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Old 06-23-20, 07:48 AM
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It seems like a very small a deflection. On aluminum, I'm not sure you'd notice. On carbon, it seems like those stress areas could happily be reinforced.

I think the carbon Grade is a shade under 1000g, not sure what size. No idea on the aluminum.

I love the adjustable rake fork too.

I'd personally love to have and would not be scared to hammer a carbon Grade. In aluminum, given work hardening, my own rough style, and how long I keep a bike, I wouldn't buy.

I think it would be good in Ti also, like the pivotless Moots of yesteryear.
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Old 06-23-20, 12:47 PM
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The seat stays on a bike don't see high loads so that design may be okay. They have to have something new and improved to market.
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Old 06-23-20, 12:57 PM
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The Trek Domane has implemented (in gradually more radical steps) something called isospeed couplings between the seatpost and the rear stay/top tube assembly. I have an older one (2014) and it sure seems to work nicely.
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Old 06-23-20, 08:40 PM
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Originally Posted by WizardOfBoz View Post
The Trek Domane has implemented (in gradually more radical steps) something called isospeed couplings between the seatpost and the rear stay/top tube assembly. I have an older one (2014) and it sure seems to work nicely.
The Trek Isospeed fulcrum is a bit different from the GT design. How the seat stays are tied into top tube and how both are coupled to the seat tube are not the same. The goal of Isospeed ts to promote ST bowing/flex from road forces and the seated rider's load. The GT design has no pivot between the TT and the ST. All I see are longer SS and an attachment in mid tube in the GT design. Andy
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Old 06-24-20, 05:18 AM
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Originally Posted by Andrew R Stewart View Post
The Trek Isospeed fulcrum is a bit different from the GT design. How the seat stays are tied into top tube and how both are coupled to the seat tube are not the same. The goal of Isospeed ts to promote ST bowing/flex from road forces and the seated rider's load. The GT design has no pivot between the TT and the ST. All I see are longer SS and an attachment in mid tube in the GT design. Andy
Thanks, Andy. One of the disappointing things about companies today is their total failure to explain stuff like this. A lot of companies fail in this regard, but Trek is notable for its lack of documenting stuff. I don't get it: A complete, well-maintained library of technical documents highlighting service methods and tech advantages increases the value of all Trek bikes. And doing this gives Trek a sales advantage for new bikes. Kind of like the Mercedes claim about their cars retaining value. It seems to me that the lack of Trek documentation is them giving away money. Sigh.

In any case, I found the diagram below. If I translate correctly (ST = Seat Tube and TT = Top Tube) then I understand better why my tuchus doesn't hurt after a long ride on the Domane. There is no bending moment induced by the seatstay/top tube combo on the seat tube. And when I look at the GT design, the seat stays fasten to the top tube forward of the seat post (this is all exactly as you say). So there might be a bit less shock transmitted by the seat stays to the seat tube, but the top tube CAN transmit such forces. Perhaps a better way for me to say this is that the seat stay/top tube combination does not add any bending stiffness to the seat tube, allowing it to be springier than a classic diamond design. I have an earlier version of this, so my bike doesn't have the sliding collar in the seat tube assembly that allows for variable flexibility in the seat tube.

Still, with longer seat stays and the less direct couple to the seat tube, the GT design may have some merit. Probably would be helpful for anyone with experience riding this design to add to this thread.

Both Trek and GT designs are a far cry from the old "fast back" seat stay design of the Raleigh Professional Mark II through IV. That design seemed to have a goal of transmitting the maximum shock lock to one's perineum!



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Old 06-24-20, 08:33 AM
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JIm- Trek does have a tech and sales library of sorts. They have an online series of brief "courses" for their dealers and staff to learn from (and they offer better discounts off Trek products as one "passes" more courses). What could be claimed is that Trek's model is to better inform their dealer network and service techs but not so much for their customers. (BTW Shimano does much the same). I think this is fairly common in many industries, the manufacturer focuses on their dealers and thus the dealers can better deal with the ultimate consumer. I'll add that as bikes become more complex there are more and more reasons to have a well trained service staff and to discourage the home mechanic from doing some levels of service. Whether one agrees with this is another issue. Andy
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Old 06-24-20, 09:24 AM
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Andy,

This all makes sense and aligns with my experience. I think the model is to give the customer an incentive to visit the Trek LBS. So this addresses part of my kvetch. (and thanks for clarifying this).

The other part was more a marketing complaint (I'm the son of a VP of Sales and Marketing). That point would be to show cutaway drawings like the one I shared, above, in sales materials. Explain the Isospeed design advantages (or the unusual GT design advantage for that matter). Easy for the customer to see the design difference. Easier for the Trek story to sell a bike. I had to find that drawing on a Spanish website, of all places! The marketing materials all made it seem like there were magic linkages in that joint. Not in the habit of buying promises of magic. A cutaway would have been a more solid sales tool.

But as usual, I am more educated after reading one of your posts. Thanks!
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Old 06-24-20, 10:39 AM
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Originally Posted by Andrew R Stewart View Post
I'll add that as bikes become more complex there are more and more reasons to have a well trained service staff and to discourage the home mechanic from doing some levels of service. Whether one agrees with this is another issue. Andy
This is not unlike how automobiles have become so imbedded with electronics that the backyard mechanic has pretty much disappeared, well so have backyards...lol.

I can see a time when high end bikes have electronics that allow for wifi adjustments on the fly through an onboard app. Change geometry or dampeners for different aspects during a ride not unlike car suspensions; climbing mode, crit mode, etc.

There could also be maintenance sensors, that provide feedback on chain stretch, trueness, brake wear, etc.

It will be a far cry from stingrays and banana seats.

John
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Old 06-24-20, 04:41 PM
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Originally Posted by 70sSanO View Post
This is not unlike how automobiles have become so imbedded with electronics that the backyard mechanic has pretty much disappeared, well so have backyards...lol.
I can see a time when high end bikes have electronics that allow for wifi adjustments on the fly through an onboard app. Change geometry or dampeners for different aspects during a ride not unlike car suspensions; climbing mode, crit mode, etc.
There could also be maintenance sensors, that provide feedback on chain stretch, trueness, brake wear, etc.
It will be a far cry from stingrays and banana seats.
John
Some cool ideas.
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Old 06-24-20, 05:20 PM
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I believe it's Shimano that already has applied for a patent on the e data collecting idea, with the initial application to be service announcements. Much like the car's dashboard will indicate when the car needs it's 15,000 mile service. Andy
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