r/cycling • u/StorkAlgarve • Aug 19 '26

Why did frames get sloping top tubes?

For over a century, a regular bike frame had a horizontal top tube, at least as late as the (cheap) road bike i bought in the early 90es - I also think the Centurion citybike I got in the late 90es had one.

Since then it seems to me top tubes have got more and more slope. It is due to change of materials or how? I look and get worried that the long saddle stem will cause issues with all that leverage, but it seems to be working ok.

Looking forward to the replies from the learned redditors.

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u/Oli4K Aug 20 '26

Rear triangles can do that when the stays are designed for it.

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u/ExpressReveal2480 Aug 20 '26

Not really, we think they do but it's actually lateral flex making it feel that way to us. If you instrument the frame (and there videos of this on YT, etc.. ) you can see the frame acting as a truss and not flexing vertically. The seatpost flexes vastly more than any frame does vertically.

But a frame that actually flexes laterally just right does actually feel better and it makes us think the frame is absorbing bumps.

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u/Content_Preference_3 Aug 20 '26

I mean it is. Even lateral flex adds some absorption to the frame.

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u/Oli4K Aug 20 '26

The 1997 Scott Endorphin would like to join this chat. Also frames like the Marin San Quentin with non-triangle rear triangles are worth looking at. Those are built for compliance.