Giving your old wheels a boost

Bicycling
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This is mainly a question directed towards @supercraig that I thought others may be interested in hearing his answers to, but if anyone else has helpful info, feel free to share it.

Lets say you’ve bought a nice set of wheels, back before there was this thing called ‘boost spacing’. Now after a few years, your old frame is getting tired and you want something newer, but most new frames have boost spacing and you don’t want to buy a new rear wheel to suit. Yes, a proper boost spacing wheel should be a little bit stronger/stiffer, but for the added price of it doesn’t seem worth the small benefit.

There are options for certain hubs to change them from 142mm width to 148mm. Some kits add 3mm to either end cap, and a 3mm rotor spacer to position the rear rotor in the right place. This keeps your wheel centered in the frame and doesn’t require re-dishing of your wheel.

Some other options add 6mm to the non-drive side of the hub, as well as a 6mm rotor spacer. This option requires the rear wheel to be re-dished by 3mm to center it in the frame. The manufacturers of this option claim that this will bring spoke bracing angles closer to symmetric, creating a stiffer, stronger wheel. The non-drive side spoke length will be reduced by 0.4mm, the drive side by 0.1mm - both minimal changes and well within typical spoke length tolerances according to them.

Is re-dishing a rear wheel to the non-drive side by 3mm truely not a big deal?
Generally that won’t affect spoke length enough to require different length spokes?

What about on a front wheel, using a non-boost wheel in a boost fork, utilizing a longer end cap on the drive side of the hub and re-dishing the wheel by 5mm to center it?

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There’s a lot to unpack here, so forgive me if it gets wordy. I’ll start by explaining some of the reasoning behind boost spacing (hint: it wasn’t to sell you more shit), then I’ll answer your questions.

148x12 mm rear axle spacing, aka Boost 148, first appeared around five years ago. It was developed to solve a few problems and address the shortcomings of 142 mm spacing. When 142 mm spacing was developed it was simply a longer through axle on a 135 mm hub shell, the freehub, flanges, and rotor mount all remained in the same location as on a 135 mm rear hub. This caused a few issues with chainline and didn’t provide any increase in wheel stiffness via spoke bracing angle that was theoretically possible. The rising popularity of 1x11 and then 1x12 drivetrains necessitated a change to improve drivetrain performance. Simply pushing the flanges outward on a 142 mm hub would have caused a whole fanny pack full of problems. Can you imagine the nightmare of two different and incompatible rear hub standards with the same spacing?

Q. Is re-dishing a rear wheel to the non-drive side by 3mm truely not a big deal?

A. In my opinion it is a big deal. There’s two factors at play here: thread engagement and spoke tension. The actual threaded portion inside of a spoke nipple is pretty small as is the threaded portion of a spoke. Dishing a wheel 3mm means tightening the spokes on the side you are dishing to and loosening the threads on the opposite side, possibly to the point where very few threads are engaged. Spoke tensions can also change as you dish the wheel, sometimes drastically. Rims, spokes, nipples, and hub flanges all have maximum tensions. A properly built high tension wheel will already be near those tensions, by altering the characteristics of the wheel in a way it wasn’t designed for decreases the margin for failure. Messing with spoke tension and thread engagement are both recipies for catastrophic wheel failure.

Q. Generally that won’t affect spoke length enough to require different length spokes?

A. I disagree, see my answer above regarding thread engagement.

Q. What about on a front wheel, using a non-boost wheel in a boost fork, utilizing a longer end cap on the drive side of the hub and re-dishing the wheel by 5mm to center?

A. Five mm is a lot of dish on a built wheel at final tension. One could do the math based on the wheel’s geometry to see how many mm of spoke movement that would be, but you are likely going to need new spokes to ensure safe thread engagement.

Once you start looking at the costs surrounding adapting a set of non-boost wheel for a boost spaced frame, and the fact that it won’t be performing optimally, it just makes sense to go with properly spaced hubs.

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Great job @supercraig. Very informative but it might be easier and more simple to just chek yur cabels

:slight_smile:

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That level of detail is why I stray from some mechanical jobs on my bike.

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Thanks @Jetter for asking and @supercraig for the thorough explanation. I learn something new everyday.

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