The first step in building a frame is to design the frame you intend to build. There are lots of different opinions, techniques and algorithms to sizing a bike frame to a specific rider. I will not go in to detail about bike fit.
There are many ways to draw your frame. You can use any old CAD software, bike specific CAD
or a drafting table. Doing it on a drafting table is convenient because you get a full scale 2-D model of the frame before you build it. You can use this model to lay actual tubing down on to see how things are shaping up.
However you decide to do it, you want an accurate drawing of your bike frame. You will be using this drawing to take dimensions and angles from so make sure it is accurate!
I will be breaking most of the parameters used in frame design in to two categories fit and feel.
The fit parameters are determined based on the body of the individual the frame will be for. The feel parameters influence how the bike will feel or perform. If you want to learn more than I discuss about how these effect the feel of a bike take the UBI class or do some research.
Fit parameters (basically, what size bike are you building):
ST length (measured center of BB to where the center line of the TT intersects the centerline of the ST)
TT Length (measured from the ST TT centerlines intersection to the TT HT centerlines intersection)
Feel parameters (affects the comfort vs. efficiency of the bike):
BB drop (how far the center of the BB is below the axle line); influences frame stiffness, less drop = stiffer but less comfortable.
ST angle (measured clockwise from horizontal); affects weight distribution, shallow angle = more comfort but less efficiency.
HT angle (measured clockwise from horizontal); influences steering quickness and shock absorption, steeper angle = faster handling at the cost of shock absorption
CS length; also affects shock absorption as well as tire/fender clearance, longer stays means more shock absorption and more clearance for bigger tires at the cost of efficiency.
Rear axle over lock dimension (how wide the rear axle is going to be)
The best way for someone new to frame building to determine these fit and feel parameters (unless you have a fit bike at your disposal) is to take measurements of the bike you ride that fits you the best. Because you have ridden it you know what feels good about it and what you may want to change, starting with your current bikes geometry is a good way to go.
Another option is to look up different bike geometries online. Most bicycle frame manufacturers give frame dimensions on their website.
Other parameters important to your drawing/design
Wheel size; What size wheels are you going to use? (the important quantity is the bead seat diameter (BSD) or the diameter of the bead of the tire)
26” (MTB) 559mm
700c (road) 622mm
27” (old road) 630mm
29” (29er) 622mm
Tire Profile (this is the diameter of the tire profile i.e. the distance the tire extends beyond the BSD)
This quantity is usually given the by the tire manufacturer. For example 700 x 23 tires have a tire profile of 23mm.
Front tire clearance (how much room the front tire will have, bead seat to the bottom of fork crown)
Lower headset stack (how much room do you need for the lower headset bearings default dimension is 13mm)
Fork height (I am not going in to how to build a fork so you will get this number from the mfg of the fork you are going to be using. It is the distance from the center of the front axle to the base of the crown race seat (also called “axle-to-crown”).
Now time to pick your tubing dimensions:
Bicycle tubing can be bought from a variety of distributers. I personally have bought and built with True Temper tubing from Henry James
. A great way to go for your first frame is to buy a kit that includes all the tubing for a frame. UBI sells Kasai tubing kits here
(click the steel tubing tab). The numbers refer to the alloy type. Oversize and Standard refer to common tubing diameters.
Standard Road/Track Frame Oversized Road Frame
TT 25.4 mm 28.6 mm
DT 28.6 mm 31.8 mm
ST 28.6 mm (27.2mm seat post) 28.6 mm (27.2mm seat post)
Head tube diameter is determined by the size of steerer you want. 1" threaded steerers are the older standard, 1 1/8" threadless steerers are the more common modern standard. The steerer you choose influences the internal diameter of the head tube but the outer diameter is determined by the wall thickness of the head tube. They make thin walled head tubes for bikes being built with the added support of lugs thicker ones for luggless bikes.
It is worth noting at this point there are many options for BB shells. If you know all about bottom brackets
, great, buy the shell you need. If you don't know much about bottom brackets get the most common 68mm bb shell.
Most bike tubing is butted. The wall thickness varies across the tube. The end of each tube has a thicker wall (stronger joints) while the center is thin (lightweight). For your first build I recommend you stick with thicker tubing like 1/.7/1 for example which has 1 mm thick butts and a .7mm thick center. (.9/.6/.9 is also a good option)
Tubing comes in different lengths and each piece can have different length butts. All this information is given by distributors and is important when selecting cutting your tubing. You want to make sure you don’t cut the butt off of one end of the tubing...
After you have selected what diameter tubing you will be using and have come up with all the necessary dimensions it is time to draw your frame. Compile the necessary parameters in to an easy to use list. This example is from the UBI frame building handbook given to me in the class.
Rim BSD: 622mm
Tire profile: 25mm
Tire diameter (BSD + 2 X Tire profile) 672mm
BB Drop: 75mm
Fork Length: 370mm
Chain stay length: 410mm
ST length: ?
TT Length: ?
Take your time and get it right. Draw a side profile and a top down view of the chain stays.
Precision is important.