Frame
The frame determines a bike's type and geometry.
Frames have attachment points that allow or limit which parts you can use.
Frames come in different materials and designs, which determine rider position and tire clearance.
Headtube size
Determines the headset, fork, and stem options.
VIntage bikes: 1"
Modern bikes: 1 1/8"
Seatpost diameter
Various sizes.
Rear dropouts
Fork
Wheel size
Frames are designed for a specific wheel size, but you're free to experiment.
If you're using rim brakes, make sure they can reach the wheel rim.
Tire clearance
Narrow road forks will limit allowed tire sizes, and you can find all kinds of forks for various sizes.
Rake
The angle of your headtube and fork.
Trail
The distance your front axle is from a straight line from the headtube (the rake). Think of a fork that's curved or angled forward.
This affects the handling of the bike. More trail will make the bike more stable going straight, but will add some "flop" as you steer from left to right. Less trail will be less balanced but more agile, turning faster with less input.
Steer tube length/diameter
The fork needs to fit inside the headtube with room for the headset.
1" steer tubes are common on vintage bikes.
1 1/8" tubes are common on modern bikes. Some are tapered, meaning the lower tube is larger and must be fit to the heaset and headtube.
Axle to crown distance
Distance from the bottom of the headtube to the axle.
The crown is the bottom of the headset, which attaches to the fork and supports the bearings in the headtube.
Using a fork with a different axle to crown distance could elevate or lower the handlebars and change the bike's handling.
Suspension bikes have various compression distances, which change the axle to crown distance.
Axle type and size
Quick release or Thru Axle?
Rack/fender mounting
Bolt on points.
Eyelets near axle.
Brake mounting
Disc mount - ISO or post.
Cantilever.
Caliper.
Post mount.
Bottom Brackets
The bottom bracket has to work with the frame and the crankset. If the frame is threaded, it is usually BSA or english. If the bearings are held in place by the frame, it's a pressfit. There are different sizes and standards though, so make sure you know what you have.
You can use spacers to adjust the chainline. Some older bottom brackets have different spindle lengths.
Vintage bikes used square taper bottom brackets. Then a bunch of new things came out and some became standards.
Cranksets
Most crankarms use the same pedal thread - 9/16” x 20 tpi (14.28 x 1.27 mm). But check it if you're using something vintage.
Check for clearance with the frame, especially for 1x systems where you want to use a larger ring closer to the frame.
The distance between pedals is called Q factor. It's larger for gravel and mountain bikes to allow larger tires, disc brakes, and more gears on the rear axle.
Chainrings
Check if BCD matches the crankset.
1x drivetrains require a narrow wide chainring.
Check for clearance between large chainrings and the chainstay. Especially for 1x systems.
Chainring options can be limited depending on your drivetrain. Front derailleurs can have a min/max tooth gap, or have brand specific shifting patterns.
Friction shifting can be more flexible for chainring choices, where STI systems are very sensitive.
Front Derailleur
Speed
Double and triple speed front derailleurs have different cage shapes.
Cages are narrower for higher speed chains.
Attachment types
Braze on
Bolts on to a fixed point on a frame (brazed onto steel frames).
You can use a clamp adapter for frames with no brazed on front derailleur mount.
Clamp
May come in different clamp sizes for different frames.
Downtube diameter affects the derailleur adjustment, some derailleurs specify which clamp need to be used.
Direct mount
Some mountain bikes have a direct mount attachment.
The mount point may be attached to the bottom bracket if the frame doesn't have one.
Chainring sizes
Front derailleurs are designed for chainrings of a certain size.
Max tooth difference
Front derailleur max capacity (large gear - small gear). For example, 46/36T is 10T.
This number is often conservative and you may be able to use a smaller inner ring.
Min difference between top an intermediate
The minimum tooth difference between the largest outer ring and the second or middle ring.
Handlebars
Vintage drop bars are 25.4mm or 26mm. Modern bars are 31.8mm.
A 25.4mm bar will fit a 26mm clamp using a shim.
Stems
Modern bikes are 1/18" clamps on the fork, and 31.8mm for the bars.
Vintage bikes have 1" threaded forks, with a quill stem and 25.4mm or 26mm clamp.
You can use a threadless stem adapter to clamp a modern stem onto a threaded fork.
Wheels
Vintage road bikes have 27" wheels. Modern road bikes are 28"/700c.
Gravel bikes use 27.5"/650b
The sizes in inches are approximate, depending on the tire and pressure. The real measure for a wheel is BSD, or bead seat diameter - the diameter of where the tire seats in the rim.
To swap wheel sizes, check for frame and brake clearance. Disc brakes make it much easier. Be careful to chose a tire that fits.
Wheel compatibility
If you have disc brakes, you can swap wheels if the hubs are the same width.
If you have rim brakes, be careful that they can reach the new wheel rim.
Road
27" - Vintage
700c - Modern
650b - Gravel
Mountain
26" - Classic
27.5" - 650b
29" - 29er
Tires
Slick, narrow tires are great for smooth roads, thick knobby tires are for traction in loose dirt. There's a whole range of options in different sizes and tread patterns for where you want to ride.
Your options are limited by the space available in the frame and fork, and the width of the rim. Keep in mind that the wheel will deflect in corners and over rough terrain, so ensure you have enough clearance to account for that without getting wheel bite on the frame.
Fenders
Fender types
Full fenders
If you commute or ride in the rain, these are a must for keeping your clothes clean. Many cyclists in wet places will cut plastic bottles to add fender extensions and direct all water back down. This will help keep your feet dry and the person behind you.
Clip ons
There are quick race fenders for road bikes, or foldable butt flaps for fixies and commuters.
Mtb
MTB specific fenders fit around the forks and have wider coverage.
Fender size
Fenders are made to match your wheel size and tire width.
Recommended to have at fenders at least 10mm wider than your wheels. But you can try running larger tires and test clearance/coverage.
Fender clearance
Fenders need to fit between your wheels and the fork or seat stay.
Race frames will have very tight fits between the frame and wheels and may need clip on fenders.
You may be able to use long reach brakes if you can't fit a fender through them.
fender installation
Many frames will have eyelets near the axles to attach fenders.
If you don't have these eyelets, there are adapters that attach to your axles to provide mount points near the dropouts.
In the front, take off your brake and reinstall with the fender bracket in place.
In the rear, the fender will bolt to your chain stay.
Brakes
Brake types
- Caliper
- Dual pivot caliper
- Cantilever
- Disc (hydraulic)
- Disc (cable)
Disc Rotors
Rotors come in 6 bolt and centerlock.
Adapters are available to mount 6 bolt rotors on centerlock hubs.
Chainline
Measure the front as 1/2 the diameter of your seatpost + the distance to the middle chainring (1x, 3x) or between rings on a double.
Measure the back as 1/2 OLD - 1/2 cassette width - distance between cassette and chainstay dropout.
Shift to your middle gear and look down the chain from the rear, it should be straight. If it is slightly off, you want it to be a little wider in the front so that the chain is angled away from larger sprockets it might rub on.
Front chainline can be adjusted with different bottom brackets, bottom bracket spacers, spindles, cranks, chainrings, and chainring bolt/spacers.
Rear chainline can be adjusted with wheel spacers and redishing the wheel.