Andrew R Stewart
Join Date: Feb 2012
Location: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder
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Replacing a fork has a few deminsions that need to match or be really close for things to work out well. unfortunately the new supply of forks is less then it was a number of years ago.
The steerer spec needs to be the same, unless the headset is also replaced. Long enough length and if threaded (as yours is) the threads also need to be long enough and of the correct spec (unless the headset and maybe the stem are changed) , diameter (to fit the frame, headset and stem). The fork crown race seat can be cut smaller but not the other way.
The drop outs need to have a wide enough slot width for the ft axle (this can be filed larger). The axle to brake hole (or canti/vee bosses) length close to the original so the stock brakes can be adjusted so that the pads still contact the rim well, or the brake will need replacing. This also includes any clearance for a fender be still present. If the caliper has to be of less reach said fender space could be lost. Will the drop outs need a fender eyelet or rack mounts?
The crown controls three factors that usually don't have a lot of variation but still can come into play. First is the mentioned crown race seat. For a 1" steerer this is either 27.0 or 26.4. Second is the crown seat to brake hole. A small range of common deminsions here so usually not noted. Third is the width between the blades. Again not usually a concern but if you're running a 32mm tire and find a race fork check this deminsion or suffer from possible tire/blade rub.
The last deminsion of concern is the fork's rake. This can be measured (don't trust a bike's spec chart) by supporting the fork's steerer level on a raised block (vee blocks are best), level the blades and drop outs, measure up from the table to the axle and the table to the underside of the steerer then subtract the steerer's height off the table and half the steerer's diameter from the axle height.
Outside of the steerer's fitting the head tube diamener and length wise all the other deminsions can be fudged some. Changing headset, stem, ft brake, cutting race seat, filing drop out slots can all be done to make a fork otherwise work. Having said all that getting as close a match is the first choice. Andy.