Steeljunky

Hey guys!

I've been a rider for many years, and am at the point where I want to try my hand at building. I'm currently in the process of learning how to weld, braze, etc, and in the meantime gobbling up any info I can find. One thing I am struggling with is frame design. I know my basic measurements and what feels good as far as frame fit, but I'm finding that designing a frame from scratch is much more complicated than I could have imagined....or maybe I am overthinking it. My question is, does anyone know of an online program where I can input my measurements and desires and it will spit out tube lengths and joint angles? I have done the online frame size calculators, but that just tells me numbers that I only pseudo understand. It would be nice if there was something that would give me exact specs for each component. Am I asking to much? Thanks for any input...

repechage

There is bikecad.

From the read of it I would measure what you have and note what you like and don't. Thee is a wide range of possibilities as you have figured out. Where it gets more problematic is where you say, want a bike with 650b wheels and you don't have one yet. So you will be guessing.

duanedr 

I've had good luck with RattleCAD. it's free. I think bikecad is a bit expensive - for a hobbyist. if you search for it, you'll find it. Rattlecad is a bit fiddly to install etc but once up and running, it's pretty intuitive. It outputs to PDF but you should use the measurements to draw a full size rendering you can compare against.

Scooper

The on-line version of BikeCAD is free.

BikeCAD Pro, the standalone application, is $350 Canadian.

Andrew R Stewart 

If all you need is the math calculations to complete a design then a simple understanding of Trig and proper formulas will do. If this is the OP needs, then PM me and I'll mail you such. If you need help with the dimensions that are the inputs of any calculations then the Op needs to both do more research as to what a bike design comprises of and should consider a program like Bike Cad. Or do a drafting, the closer to full scale the better. Andy.

JohnDThompson 

I've used "Bicycle Geometry 101," an Excel spreadsheet you just plug in your measurements and it calculates tube lengths, miters, etc:

https://www.os2.dhs.org/~john/Bicycle...try/index.html

Steeljunky

Awesome, thanks for the links and info. I will give these a shot and see if I can pin down my design a little better. My plan is to build up a fixie frame for this first one. I figure a stripped down simple triangle frame would be best for my learning. Maybe ill try and post some pics of my progress. Hopefully I will habe a ridable bike by summer! Thanks again! Oh, and any unsolicited advice on fixie frame design would also be welcome

Happy trails e'rybody

MassiveD

I don't use bike cad, but many pros do, so that has to be a way. At the other hend of the spectrum is the Paterek manual, free download on his site. He describes a simple method of doing the design on paper.

Bike design is technically easy, you are not developing the surface of a boat hull. The bulk of it consists of four lines. For this reason I am not really sure, presentations to clients aside, why one needs some fancy CAD.

You say you know your fit, OK, so what is holding you up from measuring your current bike; your current wheels,;etc... To do custom, you have to understand your body, your rides, and the actual components you will use to build the actual bike. You need to do some work, and actually start measuring the world. I have been through this in lots of projects, I am currently working on a jeans pattern. Like you I am reading everything, but I am also measuring my body; making up a genral trial pattern called a sloper, and then I will make a trial pant, and taylor that, then return to the pattern, and so forth. It is pretty easy because all I need at the end of the day is a design that fits me. But it would be a bit delusional to think there is someone or some program that will actually do it all for me. I need to do some work. Accept some initial uncertainty.

It's great if BC will pump out some bike, but if you intend on fabbing your own drops, you need that actual stuff in your drawing. You need the actual wheels you will use, not generic wheels actual wheels. we have guys measuring frame straightness to the thou, but I am supposed to use some generic parts list from a computer menu?

When it comes to taking stuff off, you just measure it with a protractor from a drawing, or in my case I use 2D CAD I have been using for a long time, then either cut on machines, or enter the dimension into a tube coping program, and get it to spit out a template to cut to.

JohnDThompson 

The easiest thing would be to copy the geometry of a bike you've ridden and liked. Then make a few tweaks, like tightening up the wheelbase by shortening the chain stays, raise the bottom bracket a little for better clearance in corners, etc.

duanedr 

That's what I did. Then, once I found it rode pretty nicely (surprise!), I added cable stops and a derailleur hanger and canti posts and bottle bosses and rack mounts. I just painted it with rattle can so I can sand off spots quickly to add new braze ons where I want. I'm done adding stuff at this point. I may try to re-do the derailleur hanger as it's slightly askew and affects shifting. I will send it off to the powder coater with #2 when I finish that.

And absolutely post pictures!
Good luck!

repechage

I lean the other way now, increasing the chain stay length to make fitting 28 mm wide tires easier... Dropping the bottom bracket to help handling as with most modern pedals, in comparison to the ubiquitous Campagnolo record of decades ago, one can have a lower bottom bracket today and still have more cornering clearance than with a 75 mm drop got you in the 70's..... 73-75 mm was pretty common on Italian bikes back then... For criteriums I had a special purpose bike where the bottom bracket had like 60 mm of drop, great for that purpose with 165 mm cranks but not my favorite descending.... But it also had a 37.125" wheelbase, those were the days... Toe clip overlap? Plenty.

Live Wire 

Not sure about that.
I have found a fixed gear specific bike will always benefit from a higher bottom bracket.
The handling improvements you're looking for by lowering the bb are negated by the fact that the rider is always pedaling.... whereas a higher bb increases cornering confidence and feels snappier in a sprint.

79pmooney

My custom fixie has a 66mm drop, 175 cranks and Shimano 600 semi-platform pedals. With 24c-25c tires, it is a good compromise. I don't race it but it is quite able in corners and works as an all day bike as well. (Crank length is dictated by my knees. They really don't like changes. 175s are on all my bikes.)

Ben

repechage

I missed the line in post 7 where he mentions a fixed gear. Even so, the comments here are notable that one needs to understand what you need, if its a specific crank length, or setback or use, those things need to be taken into account and help define the geometry.

PithyBikes

I'm currently in the beginnings of designing my own frame. This thread is very useful, thanks! I heard that when building your first frame, it's good to design on paper. Can't remember where I heard this. I'm exploring a little of both. I purchased Bike Cad about a month ago. I've also messed around in Rattle Cad a bit. I found Bike Cad to be way more intuitive. Cheers.

ksisler

Steeljunky... not sure it is yet so in Alaska, but the local Walgreen's stores in the CONUS are now equipped with a large format plotter that would suffice to get you a full scale drawing without having to go to a Kinko's (a very spendy place)... Just be sure to add some confirmation lines to the edge of your file so you can confirm the output to correct 1:1 scale with a good meter stick.