Originally Posted by Tablo .
.... So I was wondering, what's the difference between a track bike and a fixed gear?...
Gearing as pointed out above is different though not quite as dramatic as what Mojo posted. Racers on the track have to accelerate frequently and even accelerate quickly from standing starts in some events so typical track racing gears aren't all that high compared to top end road gears. For mass start track racing typical gearing is in the range of 90 gear inches or a 50x15 combo of front chainring and rear cog, on the road that would be considered fairly low road race gearing but as Mojo points out that's still a pretty big gear to be starting up from stop signs or pushing while riding uphills, something you don't do during actual track racing.
So yeah, you'd want to gear a road fixie lower than a dedicated track racing bike but there are other differences.
Fixies often (but not always) retain a front brake or sometimes both brakes but brakes are prohibited during track racing and all speed control on the track is done with the legs through the fixed gearing. If you're going to ride a fixie on the road I'd strongly recommend at least a front brake although many die hard hipsters shun the front brake.
Dedicated track racing bikes have more aggressive geometries which increases responsiveness for quick maneuvering during track racing and often have higher bottom brackets for additional pedal clearance since you can't ever coast on a track bike so pedal strike can become a concern with low bottom bracket road bikes in certain situations on the track. So you can't really convert a generic road bike into a true track racing bike since you can't change the geometry of the bike, it's handling will always be a bit sluggish in actual track racing situations even if you gear it appropriately and remove both brakes.
But the big issue you'll face if you decide to convert the bike in the photo to a fixie is achieving proper chain tension with the rear wheel road style dropouts. Track bikes and even dedicated urban fixie frames use long rear facing 'horizontal' fork ends which allow you to set proper chain tension for various combinations of front chainring and rear cog. That's pretty important for track racing bikes as racers select their single gear choice depending on the specific event and slide the rear wheel forward or backwards in the long horizontal track fork ends to take up chain slack. Too much chain slack and you can drop your chain which is a really bad deal if it happens during a fast track race or an all out sprint. Too little chain slack and the overly tight chain will bind which can also cause big problems.
It looks like your Raleigh has sloping dropouts which is good in terms of converting to a fixie as it gives you some limited chain slack adjustment range. Not as much as real track fork ends but a lot more than a newer bike with vertical dropouts which have no adjustment range. The late great Sheldon Brown has some good advice on fixie conversion and dealing with chain tension here: http://www.sheldonbrown.com/fixed-conversion.html
He also has info on fixies in general that you might find interesting: http://www.sheldonbrown.com/fixed.html
-Dave
