Why all the steep seat angles for CX bikes?

[FastforaSlowGuy]

I'm eyeballing some CX frames (just window shopping for now), and I noticed that in my size the seat angles (74.5-75.5) are frequently steeper than on a comparable road frame (73.5-74.5). From my limited CX experience, having too much weight over the front of the bike creates problems, especially in sand, so I would have expected the reverse.

Is there a rationale here, or perhaps I'm seeing a pattern where one doesn't exist.

[Lewis Moon]

And I understand this not-at-all:

http://cx.cxmagazine.com/wp-content/uploads/2012/07/ryan-trebon-cannondale-superx-img_0767_11.jpg

[FastforaSlowGuy]

Wow. I ride a fair amount of drop because of my ape-ish arms, but that's ridiculous.

[thwart]

That's gotta be Trebon's bike.

Biggest drop I've ever seen. Yet he looks great riding it… and it obviously works for him. Note how high the brifters are mounted on the bars...

[Lewis Moon]

That's gotta be Trebon's bike.

Biggest drop I've ever seen. Yet he looks great riding it… and it obviously works for him. Note how high the brifters are mounted on the bars...

Guy's a giraffe. I wonder about how far forward his seat is on the SP. Almost a TT position.

[nooneline]

re: steep seat tubes - what size frames are you looking at?

Yeah, that's Trebon's bike. At 6 foot 6 inches, he's a total outlier. He has a ton of drop but it's because he has very long arms. If he didn't have drop, he'd be sitting completely upright. His position on the bike winds up being pretty conventional (below).

Guy's a giraffe. I wonder about how far forward his seat is on the SP. Almost a TT position.

Well, think about this - the seat tube is angled backwards. The higher a saddle is, the further back it is. With all his seatpost, he winds up having a saddle that's pretty far back by default. Having a standard-setback seatpost would give him pretty obscene setback, likely.

The real crazy thing is that he does cx remounts onto a Concor Lite. I tried it. Never again.

http://velocityresults.com/images/966.jpg

[shovelhd]

Paging E-Richie atmo.

[Lewis Moon]

re: steep seat tubes - what size frames are you looking at?

Yeah, that's Trebon's bike. At 6 foot 6 inches, he's a total outlier. He has a ton of drop but it's because he has very long arms. If he didn't have drop, he'd be sitting completely upright. His position on the bike winds up being pretty conventional (below).



Well, think about this - the seat tube is angled backwards. The higher a saddle is, the further back it is. With all his seatpost, he winds up having a saddle that's pretty far back by default. Having a standard-setback seatpost would give him pretty obscene setback, likely.

The real crazy thing is that he does cx remounts onto a Concor Lite. I tried it. Never again.

http://velocityresults.com/images/966.jpg

The taller you are, the longer your femur is. I'm 6'5" and I have my seat all the way back on a set back post, and I had 190 cranks too. Looks like his kneecap is a couple of cm in front of the pedal spindle (yes, I know this is old thinking). If I were in that position I'd be putting way too much weight on my hands.

[azrider]

Note how high the brifters are mounted on the bars...

Tim Johnson rides with his brifters in roughly same position.......don't want to guess as to why. Control?

http://cdn.velonews.competitor.com/files/2011/10/P1040708.jpg

[abalone]

Tim Johnson rides with his brifters in roughly same position.......don't want to guess as to why. Control?

http://cdn.velonews.competitor.com/files/2011/10/P1040708.jpg


His hoods look really high compare to some of the other pros that slam their stem. In fact, if you scroll down the page a little bit, you can use the browser's address bar as a line, and you can see that his Cannondale's saddle is about the same height as the top of his brake levers.

[FastforaSlowGuy]

I think TJ has had some chronic back issues, so slamming the stem might not work.

[pakora]

Even folks not even that tall do that because with three very recent exceptions there's no production bikes made with a tall st or long rt (over 60 c-c). And one is his team I'd guess making it because they had to make a mold for him.

I'm near Trebon's height and I have to run a 140 stem and more drop than I'd like. (I have short legs and a long torso though).

The high hoods though, I see many Cx racers (non pros alike) will do that, just to have more low speed control in the cockpit. I did with Shimano levers anyway.

[guido]

Johnson has chronic disc issues. If he can't get it straightened out soon he plans to retire...
I think TJ has had some chronic back issues, so slamming the stem might not work.

[false_Aest]

If my saddle setback is 47mm it is 47mm.

If my STA is 73* my saddle setback is 47mm.
If my STA is 74* my saddle setback is 47mm.
If my STA is 75* my saddle setback is 47mm.

If my STA is 73* my bike is a Serotta.
If my STA is 74* my bike is a Cannondale.
If my STA is 75* my bike is a CX.

If my STA is 73* my seatpost has 0 setback.
If my STA is 74* my seatpost has 0 setback.
If my STA is 75* my seatpost has 15mm setback.

I'm probably doing something wrong.

[sparky33]

I'm eyeballing some CX frames (just window shopping for now), and I noticed that in my size the seat angles (74.5-75.5) are frequently steeper than on a comparable road frame (73.5-74.5). From my limited CX experience, having too much weight over the front of the bike creates problems, especially in sand, so I would have expected the reverse.



Is there a rationale here, or perhaps I'm seeing a pattern where one doesn't exist.


A very smart builder once told me that his own cx bike has the saddle pushed forward a smidge because it gives him more power accelerating out of corners.

and I agree with you that cx seat angles seem a bit higher.

[pbarry]

If my saddle setback is 47mm it is 47mm.

If my STA is 73* my saddle setback is 47mm.
If my STA is 74* my saddle setback is 47mm.
If my STA is 75* my saddle setback is 47mm.

If my STA is 73* my bike is a Serotta.
If my STA is 74* my bike is a Cannondale.
If my STA is 75* my bike is a CX.

If my STA is 73* my seatpost has 0 setback.
If my STA is 74* my seatpost has 0 setback.
If my STA is 75* my seatpost has 15mm setback.

I'm probably doing something wrong.

With your lines of reasoning until the one I highlighted in bold. Seems like 7.5mm would be in order. If this was tongue-in-cheek, my apologies.

[false_Aest]

With your lines of reasoning until the one I highlighted in bold. Seems like 7.5mm would be in order. If this was tongue-in-cheek, my apologies.

You're kind've right.

IIRC 1cm for every degree difference. So if I had set it up right, I should have a 0, 10 and 20mm setback. But I have room on the rails and I'm a fan of using whatever is lying around not buying more.

But what I was getting at was that STA doesn't seem to matter all that much if your saddle remains in the same place.

And FWIW, my CX frame was designed for me (mega short femurs). I like the look of a seat post with setback and the rails centered so we pushed the STA steeper. I'm in the same place I just look better. :cool: