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Bike size croosreferance.(17 posts)

Bike size croosreferance.Len J
Apr 2, 2002 10:12 AM
Reading the response below re Colnago sizing to bottom of seatcollar reminds me of some earlier posts (I think by TJeanloz) where he compared the actual sizing of various frames one to another.

Does anyone know of a place to get actual comparitive sizing, one bike model to another? It would be a really valuable tool to be able to plug in a standover height & get the "best" sizing in various brands, or plug in Top tube sizing & get the same.

I'm not suggesting that this would be the end of the fitting, but it sure would whittle down the choices & take some of the noise out of the process.

I think it would be a hell of a tool. Go ahead flame away, tell me why I'm nuts.

re: Bike size croosreferance.Jekyll
Apr 2, 2002 10:47 AM
I've though many times about building an on line tool to do this. It really would be pretty easy to build just take a ton of time to compile the data. If someone would want to suggest a list of frames and do the research I would built it and publish it to the web. Ok, so I'm a computer geek...
Apr 2, 2002 10:50 AM
One would have to decide on the scope of the tool - do you worry about just the frame size or about actual contact points (saddle position & stem length)? A lot of questions to answer to do it right and actually make it worth using...
Apr 2, 2002 10:55 AM
I think the only measure in question is the seat tube, and I propose a center of the crank bolt to top of the top tube as the standard. This will take into account varying tube diameters, and add consistency to the process.
Areed but....Len J
Apr 2, 2002 11:04 AM
If we were going to do it right wouldn't you want some other consistantly measured data in the database to allow for bike comparisons? I'm thinking things like seat tube & head tube angles, Top tube length center to center etc.

That's agreed duh. In addition........Len J
Apr 2, 2002 11:12 AM
I would propose the following data:

Manufacturer's size
Center of crank to top of top tube measurement in MM
Ground to center of crank measurement in MM
top tube length center to center in MM
Seat tube angle
Head tube angle

Any others?

Issues with some of those...TJeanloz
Apr 2, 2002 11:16 AM
Head tube and seat tube angles are difficult to measure accurately, and I don't think they merit inclusion.

Ground to center of crank will be effected by tire size/profile.
You're more experienced, two questions.....Len J
Apr 2, 2002 11:21 AM
1.)Are published head tube & seat tube specs usually correct? & if so, is there a benefit in including?

2.) do tire profiles affect overall standover height enough to worry about? I see your point about tire size 700 vs 650 but how much different is a 20 from a 23?

The devil really is in the detail isn't it?

You're more experienced, two questions.....TJeanloz
Apr 2, 2002 11:56 AM
1) They usually are correct, but there isn't a compelling argument about why they need to be included. I could see including the STA because they vary so much at the extremes.

2) The profiles really are pretty different, even among 23's from different manufacturers. Enough to measure in mm anyway.
I can think of one ...tarwheel
Apr 2, 2002 12:38 PM
Aren't the top tube measurements pretty meaningless without the seat tube angle (and perhaps head tube)? It's my understanding that a bike with a 55 c-c top tube and 74 seat angle is effectively the same size as a 56 c-c top tube with a 73 seat angle (assuming the same knee over pedal position). That can make a big difference when trying to determine proper fit, particularly when many people say the top tube length is the most important dimension in assuring proper fit.
Yes and No,TJeanloz
Mar 29, 2002 9:37 AM
Mathemeticians who frequent internet forums like to point this out, but differences in seat tube angles can (ALMOST) always be accounted for by moving the saddle foreward/aft, or utilizing a seatpost with different setback. On a custom bike, you would definitely take STA into account, but where you know there are going to be some adaptations, it isn't necessary.
Compact vs. non-compact frameslaffeaux
Apr 2, 2002 1:04 PM
I ride a compact Bontrager frame, and have no idea what my seat tube length is nor do I care (as it's a superflous measurement). The manufacturer's size is "XL" and the effective top tube length is 59cm (who knows or cares what the real TT length is). You need some way to account for non-standard geometries. I can't imagine what a someone that rides a "soft ride" frame would do with those measurements.

It's a hard problem to solve, especially when you try to serach the data for results. For my frame, if you search under standover height or ST length, you'd not find a frame that fit you. The effective TT length is the only accurate size measurement in my case.
Compact vs. non-compact framesDave Hickey
Apr 2, 2002 1:17 PM
I think most compact manufacturers state their effective top tube lengths. I agree, real top tube length on a compact is useless.
That's agreed duh. In addition........O
Apr 2, 2002 8:03 PM
Head tube length, I think, is a pretty critical measurement. Using 6 cm of spacers on an ouzo pro does not seem very like a very appealing idea to me.
It's really not,TJeanloz
Apr 3, 2002 5:05 AM
Headtube length could vary by quite a bit simply by bike design, and there's really no way to know from that dimension how it will work for you. The information you need to know how many spacers is how much seatpost you will extend and how much drop you want from seat to handlebar.

I could see, maybe, giving a dimension of how far the headtube extends above the top tube (a top-of-top-tube to top-of-head-tube), that might be helpful, but headtube length itself, isn't so helpful.

It is my opinion that anybody using 6cm of spacers is probably on a poorly fit frame in the first place. If people would stop pretending they're pro racers and buy a bigger frame in the first place, the problem wouldn't be an issue.
Anyone think that data accumulated on this site.....Len J
Apr 2, 2002 11:09 AM
would be adequate for this purpose?

I mean, with all the cyclist we have here we have to have a pretty good crosssection pf bikes, maybe we could set up something for people to input a simple series of measures that Jekyl could use to create a database that could be used.

Maybe GREGG could create someplace on the board to enter the data.


Anyone think that data accumulated on this site.....Jekyll
Apr 2, 2002 11:16 AM
you'd probably want to use manufacturers' data and then make sure with a real life example that the data correlates as expected. The odds of people here having lets say a C-40 in every available size is pretty low.
Like I said above, manipulating the date to provide results is not rocket science - getting the data and setting up a reliable set of questions to validate against the collected data presents a much larger problem - I guess this could be a class project :-)
If you guys have serious ideas about this feel free to email me and we can see how we can go forward.