Is this something purely esoteric? Or is there a more tangible way to determine whether one brand of bike sized 56 cm is better suited to my dimensions than anther 56 cm bike?
First off forget the size number the manufacturer is using. One man’s 56 is not necessarily anothers. You really need to study the geometry charts. I just went through this excercise and last week bought my third bike in as many years sight unseen strictly off geometry charts. Never saw the bikes or test rode them. Seems strange but it can be done sucessfully if you know numbers you need.
if you have a specific bike in mind you should ask/PM cyclenutnz. i think he has the measurements for every bike manufactured since the invention of the wheel…
study the geometry charts.
Is there a standard resource that has many bikes’ measurements and geometry, where one can look up different bikes and compare them?
"where one can look up different bikes and compare them? "
You’ll probably have to go on the individual sites and look up the geometries. It’s a bit of work but I’m not aware of any single resource.
Finding the geometry of any given bike is no problem, but how do I go about determining which geometry is ideal for me?
I think this resource on this website may answer a lot of your (good) questions:
http://www.slowtwitch.com/mainheadings/techctr/bikefit06.html#Anchor-TRANSLATING-35882
And no, it is not esoteric. It’s pretty straighforward.
Go out and get yourself a good fit. In my opinion it’s critical. Once you’re measured, your feet are analyzed, your flexibility is measured, - then you are fit to a fit machine. Then numbers are spewed out and you have your perfect bike dimensions to match you. Then you buy a bike that matches those numbers. A road bike fit is different than a TT fit. My fit lasted nearly 6 hours with nearly an hour on my feet, and how I stand, versus how I pedal.
I’ve been fit for my road, tri, and mountain bikes. However, I’m still looking for that perfect fit on a tri. In a perfect world, I could go to any local bike shop and simply trust their opinion as to what bike would be optimal for my dimensions. But this is not a perfect world. Particularly regarding my local bike shops and their understanding of the sport of triathlon.
The last time I let a bike fitter choose my bike and set me up for a triathlon position he believed to be optimal for me, I found myself on a retro-fitted road bike in a slack, comfy position that saw my bike times consistently slower. The next bike I buy will not be for cool factor or because a bike shop guy thought it would suit me the best. It will be because I’m convinced it suits my dimensions better than anything else I can afford.
Then I’ll go about finding a good fitter.
Get the fit first. This puts your contact points in space. Use a computer graphics program (CAD if you’ve got it – I’ve used the design system where I work to do this) to lay these points in space (use a line for the saddle, another line for the aero extensions, and a circle – or centerpoint of that circle – for the BB axis). Now start laying the bike frame(s) on top of these points and see how much forward offset there is to get the saddle in the right place, how long of a stem you need, etc. One thing that will help GREATLY is to also do a weight analysis on a bike in that position – the bike doesn’t have to fit, just get you in very close to the right position. What you want to get from this is how far in front of the saddle is your center of gravity. Use this to then compute your weight balance on any prospective bike. If you’re getting anywhere past 55% of your weight on the front wheel, in my opinion you’re starting to get to where handling becomes less than ideal.
Picky, I know. But worth it, in my opinion.
"Or is there a more tangible way to determine whether one brand of bike sized 56 cm is better suited to my dimensions than anther 56 cm bike? "
Stack and Reach.
Haim
How does that apply when selcting a bike with different seat tube angles ? Surely a rider can be made to ‘fit’ a 74, 76, or 78 degree bike but on that feature alone, how do you know which to opt for ?
Precisely my question!
If anyone lives near VeloEuropa or Cadence Multisport in Philadelphia - I HIGHLY recommend the CYFAC PosturFit measuting system - they are global. I was firtunate and actually got the inventor Mathieu Pappin to do my fit. They measure everything - then quiz you on what you ride or want to ride (and can do both) - they even angle correct for if you ride only 3,000 miles or if you ride 25,000 miles a year!
I dropped 3 cm from my frame and added a longer top tube and my back has NEVER felt better - I am in the same position but my hips are open. It was the best money I have ever spent on a bike - PERIOD. They even give you cleat fore/aft and angle alignment.
It just so happens they offer a SWEET line of fully custom bikes that can be made to the measurements they take (absolutley not required but I am tempted for a road bike!)
If you have your bike - they also have an alignment system they can translate your measurement onto - or they give you a print out (the option I took) and it took me about 10 minutes and two straight rulers to implement. So thank you Matthieu!!!
Also in London at IBIKE for you UK Gear!
I think Tom has already sent you to this page to point out how to translate your position to a bike, but I would suggest reading the whole thing.
http://www.slowtwitch.com/mainheadings/techctr/bikefit06.html
Cyfac’s system is largely based on their philosophy of where a rider should sit.
Dan’s philosophy is based on where you want to sit.
There was also a thread about Cyfac’s system: http://forum.slowtwitch.com/gforum.cgi?do=post_view_flat;post=1182677;page=1;sb=post_latest_reply;so=ASC;mh=25;
Kinda like this…
On the last picture of just the bike I was trying to figure out just theoretical angles and measures and stuff.
Really ? when’s IBIke ?
Several years ago, I was set up using the Bikefitting.com system at my LBS, one of the co-proprietors happens to be a very experienced triathlete. It came up with some basic numbers, which were then put on the adjustable rig, postion tweaked a bit, then redo the numbers and fire them to the online system, which then spat out some numbers for ideal dimensions.
Basically, it said “Buy a Cervelo”
Heh! With how many Cervelos that passed me at my last race, I might just skip all the calculations and employ that strategy.