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Discussion Starter · #1 ·
stupid question...when I'm trying to decide which size frame to buy, do I pay more attention to the Effective top tube length or actual length?

Also...most DH frame seems to have HT angles of 66 or 67degrees.
What is the slackest HT angle used out there (I can use as a benchmark).

Not many LBS's in my area carry high end DH/FR bikes so it isn't always possible to sit on one for sizing purposes. Before I plop $2,000 on a frame, I want to make sure I do my homework....

Thanks.
 

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I bike long tyme.
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Coma's got it nailed on the HA. As far as top tube length, I always base my decision on effective tube length. Especially since most DH frames don't offer a pure straight tube design to use for any real guidance. Keep in mind too that the seat tube angle will greatly play a role in the effective top tube length. My F1 has such a slack seat tube on it that raising it up a few inches from my normal DH height really lengthens out the cockpit from fairly compact to a very trail-bike feeling geometry. Great for when I gotta do any real pedaling of any kind.
 

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Discussion Starter · #4 · (Edited)
seat tube angle

Secace said:
Coma's got it nailed on the HA. As far as top tube length, I always base my decision on effective tube length. Especially since most DH frames don't offer a pure straight tube design to use for any real guidance. Keep in mind too that the seat tube angle will greatly play a role in the effective top tube length. My F1 has such a slack seat tube on it that raising it up a few inches from my normal DH height really lengthens out the cockpit from fairly compact to a very trail-bike feeling geometry. Great for when I gotta do any real pedaling of any kind.
Here is a comparison between a regular & Large Transition Gran Mal:

GEOMETRY (570mm axle-crown)
Regular Long
Top Tube (Effective) 22.5" 24"
Top Tube (Actual) 21.9" 23.3"
Seat Tube (center to top) 16.1" 16.1"
Head Tube Angle 66° (Adjustable) 66° (Adjustable)
Seat Tube Angle 74° 74°

so...I should also consider the seat tube angle in combination with the headtube angle?
there is no difference between the medium and Large in the above example. What would be considered slack for the seat tube?
I want to make sure that my next frame does not feel like a XC bike. I had a Bullit years ago that I had to throw a 24" rear wheel on to slacken it out.

thanks again....
 

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How come no one cares about down tube length? That actually determines where the pedals are in relation to the head tube.

When standing raising or lowering the seat has no effect on the cockpit.
 

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I bike long tyme.
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Rest-assured if you're spending major coin on a dedicated DH racing frame, its engineered not to feel like an xc bike. I doubt you'll find one that even comes close. The Bullit was targeted more for aggressive trail/freeriding which typically don't use geo quite so slack to enhance slow speed manueverability. True, standing and mashing will bypass the seat angle aspect of it all to an extent. But lots of racers (especially pros) will spend time on the seat from time to time be it blazing down a straight, cutting through berms or pedaling back home. Watch Peat, Romaniuk, Rennie, Hill, Minnar, etc. Those guys all shred with their azz planted when they can get away with it. Seat tube angles vary greatly by manufacturer. The largest part of the design of it is to keep your weight balanced between the wheels for optimal weight transfer. Not too far forward, not too far back. Be it glued to the saddle or hovering right above it or just ahead of it. Everyone has their own idea and angles they play with. Just another factor in the equation. I'd pay heed to the manufacturers' sizing charts and listen to their advice. They know best what numbers are gonna translate into your correct fit and performance value. Likely, whatever DH frame you get will feel much more controlled at speed than your old Bullit. Not Bullit bashing, just relating how the geo numbers will effect your ride. They're designed specifically to go fast on a slope. Good luck.
 
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