Conversions: Axles, Hubs, Quick Releases and Adapter Brackets
Our conversion kits are designed to be versatile, fitting a variety of forks and accepting many wheel diameters. There are some subtilities to be aware of when using different types of hubs and axles for conversions.
Quick Releases and Axle Widths:
Our adapter brackets are made of 2.5mm carbon steel. These are quite strong, and making them thicker would make them unecessarily heavy. However, many quick release wheel stub axles are designed for aluminum dropouts, which are usually 5mm thick. An issue can arise where the quick release nuts do not have a deep enough relief, bottoming out on the stub axle before the QR can bite into the dropout (adapter bracket) properly. The QR will seem to tighten up very hard, but the nuts will not bite; allowing the axle to slide in the dropout slot on the adapter bracket. This can bend the bracket, as the differing loads on the wheel form the road and the bracket from the chainstay/pedaling combine to stress the bracket. Solve this by filing about 2mm off the hub stub axle on each side. Also, position the axle ahead of the rearmost point of the dropout slot. (This will also give your chain more operating clearance.)
This picture shows things done the wrong way:
The axle is all the way to the rear of the slot, and the QR has only bitten into the paint on the adapter bracket. Subsequent to this photo the axle was filed on each side and the front end of the bike became more rigid as a result.
MTB Hubs vs. Road Hubs
Bike wheel hubs are characterized by a measurement called OLD - Over Locknut Distance. MTB (and 29'er) wheels use an OLD of 135mm, and road wheels (650c and 700c) use an OLD of 130mm. The OLD is the same as the dropout spacing across the axle. Our adapter brackets change the front fork OLD of 100mm to an MTB OLD of 135mm.
If you use road hubs of 130mm OLD, you should place a 2.5mm washer between the fork and the adapter bracket (where the attaching bolt goes through) to match the bracket width to the hub width. The chainstay will still be looking for 135mm, but the nylon spacer washers that match the chainstay to the adapter brackets will tolerate this alignment in the front.
While bike parts tend to follow certain conventions, MTB and Road conventions are surprisingly different and it helps to understand these when mixing and matching parts to create your perfect Conversion Bike.
Sheldon Brown's site is a wealth of information about these small but important facts.