Single Speed Wheels: Axle Issues
We sometimes get customers coming to us telling us they have fitted the rear wheel and it is great but:
With the front wheel, the axle is too thick to fit in the fork dropouts
Some frames, especially older ones, are designed for a smaller front axle. I'm not totally clear what sizes different vintages/designs are designed for but it certainly happens.
Also most of our wheel sets have 3/8" axles on front and rear. 3/8" is about 9.5mm and some modern track bikes run 9mm front and 10mm rear axles so these also have this issue sometimes.
This answer applies to similar (but less frequent) issues with rear wheels and dropouts.
The two stage answer to the issue is: 1. file, 2. probably file the wheel because you'd rather maintain the integrity of the frame.
If you look here there's an image shown of a filed down axle, http://bmxmuseum.com/forsale/gt_hub_5_blowup.jpg. Note two things:
1. Instead of being filed all the way round this has simply had two 'flats' (as they say) filed on 180 degrees away from each other. This is all that's needed;
2. Also, unlike what they've done with this axle, you only need to file the bit close to the lock nut where the wheel will actually be within the frame... so you don't need to file where the nuts will be screwed on and wonder if that's going to cause issues.
To File Wheel or Frame?
As pointed out above your frame is likely to outlast your wheels and may have a really nice paint job, so we'd usually think you'd want to keep the frame intact.
However there is one good reason to go with the forks instead - it's easier, specifically easier to get it done evenly. For filing forks I'd get your file and put it all the way through both fork ends (basically in the same position the axle will later take). This means you can file both sides at the same time - quicker and more even than going at one side and then the other. Filing four different sections of a wheel axle reasonably evenly is a bit harder than this! But it's not too hard if you're methodical.