When purchasing a bike, the best money spend in my opinion, is on a professional fitting. Over the course of years working and learning under John Cobb I have build up a lot of knowledge and experience, which expanded even more once I became F.I.S.T. certified. Below I'll list some generalized principals of fitting a road bike, though realize that optimal performance will be impacted, one way or another, by millimeter adjustments of saddle tilt, height and fore/aft position; height and reach of handlebars/stem. In case we are fitting you on a tri bike also the aerobars have to be take in consideration.
Needless to say, all this after having decided on the right size of frame. Often it's a case of "yep, seems OK, off we go". An hour later your back is in agony, shoulders and arms aching, bumb sore in places you didn't realise you had and upon arrival back home - bosh, road bike is chucked in the corner, until further advice is given and adjustments are made.
Tip 1 - Frame fit
There are many theories around. The two simplest are either, whilst barefoot, to measure your inside leg measurement from crotch to floor and take two thirds of that measurement or easier still ensure you have an inch of clearance between the top tube and your crotch.
You then need to know how to measure a frame. The frame size is determined by the distance between the top of the seat tube (a) and the middle of the bottom bracket (b). My suggestion however is measure it yourself, rather than take manufactures measurements as these can vary.
Tip 2 - Saddle height
Sit on the bike in the position you usually adopt. Set the saddle height so that your leg is just short of fully extended at the bottom of the pedal stroke and your hips don't rock from side to side as you pedal. This is often only a very rough guide as professionals at the start of the season will spend weeks adjusting this until they get it as perfect as they can. If you are into long distance riding many who do this set up with a centimetre or two lower than this to aid comport. Spend time getting this one right.
Your knee should be slightly (a) with your heel on the pedal (b) and the cranks in line with the seat post.
Tip 3 - Saddle position
Move your saddle back and forth until your knee is directly over the pedal axle when your cranks are horizontal. Recent changes in the geometry of some bikes designed for triathlon have brought into question the real need to concern yourself over this theory but better to start here and be safe than be sorry and ache.
Make sure it's the centre of your knee (a) that drops a plumb line down to the pedal.
Tip 4 - Saddle tilt
Ever felt you were slipping forward all the time - check your saddle tilt. This adjustment is vital to prevent you from putting too much weight on your arms and shoulders as you struggle to keep you bum back on the saddle. Your seat should be level or some riders prefer it set with the nose tilted slightly upwards ( I said slightly).
Check this adjustment by using as straight edge balanced on the saddle whilst the bike is on level ground. Daft statement you may say, but I have seen people checking this whilst the bike was in a repair stand!
Tip 5 - Handlebar reach
The old neck protector, get this wrong a you can get a real life pain in the neck. Again it's largely down to what feels right. Ensure you don't feel too cramped or too stretched. There are many ways of getting an initial feel. Try setting the stem one or two inches below the saddle. Then use a stem that puts the bars just ahead of a vertical line dropped from your nose whilst riding on the hoods. On the drops the handlebars should block your view of the front hub.
Many text books say your back should be at a 45 degree angle to the top tube (a) whilst riding on the hoods. Certainly use this as a start point to get comfortable then adjust to suit your style of riding.
Tip 6 - A special note
Often overlooked by many cyclists. Once you've achieved your ideal sizing - record it. Particularly if you are in the habit of removing seat posts etc. to maintain your bike. Use a tape measure to record key dimensions and don't be afraid to mark seatposts, stems etc. with magic markers before removing them from your frame. Believe me it makes sense.
Bryce Cain being fitted at Precision Bikes.
There are only two F.I.S.T. Certified people in Louisiana,
Mark Miller at Precision Bikes is one of them!