Seat tube angles on DJ bikes!
Lee, was checking in and read How seat tube angle affects bike character. Have you ever ridden a Cannondale Chase 1 DJ? Both small and med frames have a 77 degree seat tube angle and 69 degree head tube angle. What would be the purpose of such an extreme ST angle unless perhaps it does not matter if you don’t use the seat as a peddle platform. BTW love my Chase!!!
Enjoy those kids- they grow up too fast.
Thanks for the interesting question. I have not ridden a Chase.
For the sake of comparison, we’ll compare the Chase to another popular DJ bike, the Specialized P.3. (BTW love my Mighty P.3!!!)
The Chase has a 77-degree seat tube angle. The P.3 has a 72-degree seat tube angle. Otherwise, those bikes have very similar geometry. For a DJ/pump rider who doesn’t sit on the seat, these are the key measurements:
Bottom bracket height. Almost identical.
Chainstay length. Almost identical.
Front center (the distance from bottom bracket to front hub). Almost identical.
Handlebar location. Given the right stem/bar, they can be identical.
Standover clearance. Comparable.
Ignoring material and component variables, these bikes should jump, pump and jib like brothers.
So why does the Chase have such a steep seat tube angle? I’ve asked a smarty-pants at Cannondale. Until I hear from him, it’ll be fun to guess:
Shorter chain stays? The older Chase has a 74-degree seat tube angle, and its chain stays were an inch longer. By angling the seat tube forward three degrees, Cannondale was able to tuck the rear wheel farther forward. Seems like a slick way to shorten the rear end without drastically re-working other aspects of the frame design.
Better tricks? Maybe the farther-forward seat helps Aaron Chase-style tricks? Maybe you can grab the seat in your teeth? (Dude, that was a sick Superman Incisor!) I am a trickless fellow, so I have no idea there. But Jeff Lenosky is a very tricky fellow, and his STP has a pretty normal 74-degree seat tube angle. Dunno.
Until someone tells me different, I’m going with the shorter chain stays.
Know more. Have more fun!
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I second the chain stay aspect Lee. From the frame stand point, the P.3 seat tube is offset forward of the bb (straight line through the seat tube is forward of the bb) to allow the rear wheel closer (short stays) and then slack the seat tube back (cleaner lines maybe, the P.3 does look sweet.) The Chase looks to be straight to the bb so in order to get rear tire clearance ( for super short stays) it has to be pretty steep. This is easier and more cost efficient to produce, one less tube to bend. Not sure on the STP, I haven’t seen one up close. My 2 cents.
All this talk about geometry trigged me to wonder what would make a good winter/snow commuter frame. Medium height bottom bracket? short wheelbase? steepish head-angle, slack seat angle? short stays? Maybe an undersized XC mtb frame with Frankenstein like stems and seatposts??
You need something that won’t be all floppy when grinding it out in some snow/slush but, something that won’t have you dragging your feet in that same slush or too twitchy at speed.
Maybe you can’t have it all… but i’d like to try 🙂
Hi Lee, How’s the twins?
I have a question regarding comparatives between bikes.
When you want to compare the geometry of a number of bikes, What’s the starting point? Let’s say I want to align those 3 bikes. Should I align them by the BB? by the rear hub? or the head tube maybe?
Also, it looks like every brand gives the geometry specs in slightly different ways. What’s the more appropriate way of present a bike geometry? (not only dj, I’m talking about mtb in general)
ps: bought your book and I love it. I had to buy in in English from Amazon because the morons from Spain that sell the Spanish edition didn’t care to answer any of my mails…