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I'm thinking about having a custom Titanium/Carbon gravel frame made.
I would like the design to be a bit special, and therefore I would like it to come with a ISP in carbon, dropped seat stays, and with mono/wishbone seat stays.

I would like to hear what the opinion are on the three details, and if its a bad idea to combine all three in a frame.
The dropped stay's and mono stay might work against each other, since the dropped stays will allow the ISP to move more backwards, and the mono stays will make the rear triangle more stiff? Can anybody advise me?
And will the dropped seat stays be critical if they allow the carbon tube to twist more backwards?

I have attached a picture of my first iteration together with a reference picture of a mono stay:

enter image description here

For reference, a photo of a frame with monostays is below.

NEW additional approach for the frame geometry What are you guys viewpoint on a triple triangle geometry (GT Style) together with the dropped stays and Carbon ISP?

enter image description here

enter image description here

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    Are there any particular ride or performance characteristics you would like to design for? What kind of riding do you anticipate doing? Do you have any physical characteristics to take into consideration? - tall / short / heavy / light
    – David D
    Aug 31, 2022 at 16:35
  • "Mono stay" is an interesting phrase. The sample bike definitely has two stays on each side, but taper to a single tube above - it would be a "steerer" if it were a fork (does that mean it has a crown, or an aft-crown?. Might this short tube be called a "tailbone" or a wishbone as per your other comment. Great question and welcome to the site.
    – Criggie
    Aug 31, 2022 at 19:37
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    The bike will primarily be used for training on the danish roads and bike packing around northern Europe. That means flat gravel and pimple roads. Sep 1, 2022 at 8:45
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    @Criggie The stiffening could also be achieved with the gusset, but once again I'm also designing for the aesthetics. I just wrote a mail to the frame builders, and now I'm waiting for their response. thanks for your comment. :-) Sep 1, 2022 at 10:13
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    I'm just an infrequent visitor to this site, but this seems like far too many questions in one and would be mostly opinion based. I'd VtC, but, as noted, I'm just stopping by...
    – FreeMan
    Sep 1, 2022 at 17:59

2 Answers 2

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I’m not a frame builder, I don’t have any real world experience with designing these things.

I think the benefits of dropped seat stays are super small. The idea is basically to make the rear triangle less stiff in the vertical direction. But how much flex is there actually in a rear triangle? I’d really love to see some good slow motion footage of a modern gravel frame going over rough ground.

It should be possible to make a mono seat stay no more stiff than normal seat stays. I think it’s just a neat way of combining a seat stay bridge and the seat stay <-> seat tube interface. But with disc brakes I’m questioning the benefits of a seat stay bridge anyway.

Why not go for a sloped top tube to allow the seatpost to flex more?

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    Hi Michael, Thanks for your comment! :-) I think mono stays might be canceled in the design. I'm not a big fan of the appearance of a sloping top tube, and therefore I have used a horizontally aligned top tube geometry. I find it really hard to decide if it's the aesthetics or performance I'm designing for.... XD Aug 31, 2022 at 12:45
  • @FrederikSølver Concur - sloping top tubes are ugly, and curved ones are worse. Both remind me of a dog dragging its backside on the carpet.
    – Criggie
    Aug 31, 2022 at 19:32
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    @Criggie Hahaha I can only agree with you! Sep 1, 2022 at 7:27
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  1. These are questions for your framebuilder, not a bunch of Internet strangers.
  2. Since you asked a bunch of Internet strangers, a carbon-fiber integrated seatpost seems like a bad idea for a gravel bike. You want more flexibility there, not less, which is what a relatively large-diameter tube is going to give you. I am dubious about integrated seatposts in general, since they limit adjustability and transportability, and lock you into using a non-standard cap.
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  • It should be possible to make an integrated seatpost flex more, not less. Since you get rid of the crack-prone seatpost-clamp area and should have more nice, straight steatpost sticking out which can flex evenly over the full length (especially when combined with a sloped top tube). With a custom frame it should be possible to build it precisely for the rider's weight and leg length. If you use all those possibilities I think it’s even possible to get an annoying amount of flex.
    – Michael
    Sep 1, 2022 at 6:27
  • @Michael From the CAD diagram provided, I imagine the top of that lug would also serve as a seat clamp-like stress concentrator.
    – MaplePanda
    Sep 1, 2022 at 7:36
  • I haven't yet delivered my first design iteration to the frame builder, but I guess they will probably also be able to analyze the frame construction with their know-how. I already asked if they were able to build frames with Carbon ISP, but I think they will just use straight carbon tubing with uniform wall thickness. Sep 1, 2022 at 8:43
  • @MaplePanda: The lever arm is much shorter and therefore stresses are much lower on the top of the seatpost.
    – Michael
    Sep 1, 2022 at 9:02

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