Getting a good fit on your bike shouldn’t be tricky.
I have been a hardcore heavy bike rider riding a 19kg something MTB on-road and brevets. Recently I decided to switch my ride to a Road/CX bike. But finding the right frame size seems like a callous decision to make. If that is the case that you are struggling with, then you have indeed come to the right place since I just found the right, more mathematical solution to this problem to start with.
STEP 1: FIND OUT THE INSEAM/INSIDE LEG
Besides your body height, one more dimension is crucial to select the proper frame size: your personal inseam/inside leg. Depending on the desired bike type, the inseam/inside leg is the basis for an approximate calculation leading to the correct frame height for your dream bike. This is how it works:
Please stand with your back against a wall — barefoot. Your heels should touch the wall as well while your knees are straight, and your pelvic area is positioned towards the ground in a linear (paraxial) way. The inseam/inside leg can be determined best by pulling a water level horizontally and as high as possible into your crotch — the distance between the level’s upper edge and the ground is then measured via an inch centimeter rule. If a water level is not available, you can also carry out the analysis by using a book that is flush with the wall on one side. In all cases, measuring the inseam/inside leg works best with the help of a partner.
STEP 2: CALCULATE YOUR FRAME SIZE
Based on the so correctly measured step length, the proper frame size (individually different for each bike type) can be defined using an approximate calculation:
(inseam length in inches)x2.54 = inseam length in centimetres = Li
Lix0.67 = Correct frame size
For example, my inseam length is 30in, so my frame size would lie somewhere from 51cm to 54cm — — for an aggressive ride, I can go with 50cm/49cm and slightly relax more endurance rides, I can go with 52cm.
For sporty riding you rather choose the smaller frame size.
You want to ride more comfortable, choose a larger frame size.
If you use a suspended seatpost, you should subtract approx. 3cm (or 1 inch) from the calculated size.
STEP 3: CALCULATE YOUR SADDLE HEIGHT
Multiply your inseam length in centimeters by .883 to get your saddle height. The correct saddle height allows you to stretch your body out comfortably. Unlike your frame, you can adjust your saddle height at any time by merely loosening the nuts and raising or lowering the seat. If you ride with your toes down and your heels raised, you may find that you need to adjust your saddle so that it is slightly higher to match your riding style.
I hope this helps you a bit in killing all the confusion that surrounds this topic. Remember, most of the bike fit you are looking for can be done by yourself using simple tools at home.