bike fitting, TTT and reach measurements
like many of you, i've become an internet armchair bike fitter. at least i try to get an idea. you see i'm 6'5" and live in a small center, so it's not like i can go hop on size xl, xxl frames at a whim and take them on the trail to see how they feel. hence- the genie in the box, the oracle, the net, the web, the problem, the solution, the alpha and omega as it were. the burning bush and so forth...
i like my bike and how it fits. however i'm looking for the next bike and checking out existing theoretical top tube lengths, and now reach. i'm surprised at how much it confuses me. there are bikes with shorter TTT and longer reach and some with longer TTT and shorter reach! what does it all mean? even when i know what the measurements are!
Banshee bikes all have long reach for example.
here's a Norco Sight Killer b: 647mm TTT, reach 464
Banshee Spitfire 640mm TTT, reach 477
so the spitty is almost a cm shorter in the top tube but a 1.3cm longer in reach.
if i could just go hop on these bikes i could get a sense for how that translates. try to find these guys in size xl. anywhere.
so any big thinkers, smart guys and or engineers willing to help translate how these number will feel? which cockpit will "feel" longer. which IS longer? i'm so confused...
Effective TT is the horizontal distance from the top of the head tube to the intersection of a line through the axis of the seat tube (since on a modern bike the HT is higher than the top of the ST). Reach is the horizontal from the head tube to a vertical line that goes through the bottom bracket shell.
So the Norco, with the longer TT but shorter reach, must have a slacker seat angle (and it does, if you look at the charts), since there is more TT behind the BB than on the Banshee.
On a downhill or jump bike, where you are basically never seated, the reach is what matters. On a bike where you will be climbing, the TT, or the seat angle depending on how you want to look at it, affects how far you shift forward/aft when standing or sitting.
seated, the Norco is going to feel longer, but when you stand, you will shift farther forward on it. The Banshee will have your weight closer to the same place seated vs standing.
I hear your frustration and pain in the lack of demo and test rides to sit on. Finding anything in XL or XXL anywhere is a losing proposition. All due to the % of the population that actually rides size HUGE - an LBS will rarely stock something that big.
Originally Posted by cunningstunts
How does it translate? You didn't give ST and HT angles (or what amount of travel in your fork you'll be using), but it could mean the Banshee will be a bit longer to the stem than the Norco as you sit in the saddle (depending on those angles). It will be a minute difference and all easily made up in terms of stem length choice to get on both bikes and fit them the same for you if you have the TT correct. The more travel you use for a fork up front, the shorter that reach measurement will get. What are the stack/reach measurements, TT length, ST and HT angles, fork travel on your current bike? How do they compare to the Norco and Banshee you are looking at?
As a tall guy, I pay more attention to HT length, ETT and fork travel. I do know that my JET 9 with a 100mm fork and the ST/HT angles has a reach of 450mm for the size XL. That would lengthen out to a reach of 461mm with an 80mm fork. I guess that information tells me my projected stem length I want to use and would be good to know if I was comparing it to another frame.
Did you plug your measurements into the Zinn calculator (great for big guys)? You can choose 3 different fits to see what is recommended for your size in a mountain bike (or road bike). It's pretty spot on as my size XL Niners match within a mm or two what the Zinn calculator suggested.
<a href="http://www.flickr.com/photos/7166535@N05/8976548985/" title="65193-medium_stackreach by BBcamerata, on Flickr"><img src="http://farm9.staticflickr.com/8263/8976548985_0495141c39.jpg" width="300" height="300" alt="65193-medium_stackreach"></a>
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