Explanation of dishing, flange spacing, etc.
1. Preface
2. How Dishing makes the wheel narrower
3. Rim Center Measurements
4. Actual Measurements
5. Cold Setting a frame
1. Preface
The alignment of a rear wheel requires having the right number of spacers so it fits a given frame dropout. Eg: 135mm dropout. So if you are trying to fit a new wheel onto an old bike, you need to check that the axle length is correct (146mm), and there are the right spacers on each side so the rim ends up centered. What is tricky in rear wheels is the rim is not in the center of the hub flanges. Instead, the spokes on one side are shorter and more vertical than on the other side. This is called "dishing".
If you buy a new wheel, you need to check the rim alignment. When these issues often come up is when you are upgrading an older steel frame to a wider dropout width, so it will fit newer wheels. The old standard dropout width was 126 mm but these days a 135 mm spacing is much more common. So it may be desirable to convert your bike to use 135 mm wheels. Spreading the frame is called "Cold setting". To do it requires special tools. A good bike shop like OurCommunityBikes has the tools and some experience. But you should familiarize yourself with what needs to be done beforehand, so you know what's being done.
On my Miyata 1000, I bought a used wheel with 135 mm spacing, and then had the bike shop "cold set" my dropouts to that width. The original width was 126mm. It was tricky, because you have to bend each side of the frame the same amount, in order to keep the frame in alignment. An alignment tool is essential.
Another strategy I used in the past on my 126mm bike was to remove spacers from a wheel built for 130mm dropouts so it would fit in 126mm. But this also requires making sure the rim ends up centered.
In any of these wheel replacement projects, you want to have some basic knowledge of how any given wheel is dished and aligned with spacers such that the rim stays centered, and the chainline is still somewhat straight. The correct spacers you need on either side of the wheel depends on the dishing. I found that I ended up wondering about the dishing and spacers of the used wheel I bought. This document provides the necessary theory to understand dishing and spacers.
The structure of the document is first of all to talk about the general concept of dishing and spacers. Then a second chapter has some actual measurements.
The value of this document is to provide some theory so you can adjust the spacers in any given wheel to match the dishing.
2. How Dishing makes the wheel narrower
Although the distance between hub flanges is pretty standard at 56mm, different wheels can be constructed with different dishing and spacers. The purpose of dishing is to make the O.L.D. of the wheel narrower, and move the freehub closer to the center. The distance between hub flanges does not change, they are just pushed over. This chapter starts with a diagram of an undished wheel. I then copy this diagram and adjust the diagram to push the hub flanges over. In the diagrams, I ignore the part of the axle which projects beyond the lock nut. The wheel is facing ahead with the drive on the right side.
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|------|..........x..........|######|
1 2 3 4 5
In summary, the 4-5 distance is the width of the freehub plus the flange base, and distance 1-2 is the same.
Here is how I adjusted the copied diagram:
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|--|..........x..........|######|
1 2 3 4 5
- take out 2 spaces on the left. (the "offset")
- that moves the right 2 spaces in
- so take out two more spaces on the left to indent the locknut same distance
- now the O.L.D. is 4 mm shorter
AGAIN:
START:
The rim center is 6+1+10+1 spaces from the left locknut. And 6+1+10+1 from the right.
Count 18 spaces and you are lined up with the center.
Method of counting the spaces is to start at the locknut and count until you reach the position of the rim center.
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|------|..........x..........|######|
1 2 3 4 5
- take out 2 spaces on the left (the offset). That moves the flange center 2 spaces to the left of the rim center. 1 and 5 are the original dropouts. Now the rim center is 4+1+10+1+2 = 18 from left,and 6+1+9=16 from right. The rim is not centered, such a wheel would have the rim center over to the right.
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|----|..........x..........|######|
1 2 3 4 5
Now the distance from the left locknut to rim center is 2+1+10+1+2 = 16 and from the right locknut 6+1+9=16. The rim center is the 16th character from the locknut on either side.
|
|--|..........x..........|######|
1 2 3 4 5
3. Rim Center Measurements
Any given wheel you can always adjust the rim center by adding and subtracting spacers. But the rim has to end up centered. This depends on the dishing. The easiest way to inspect a given wheel is to use a dishing tool. It is just a bowed piece of metal that touches the rim at each end, and has a thumb screw in the center. For any given wheel, you screw in the center screw till the socket rests on the lock nut. You then check that both sides of the wheel are the same. Examples of this tool are the Minoura FCG-310 or Park tools WAG-4 Wheel Alignment Gauge.
4. Actual Measurements
The first chapter described how dishing affects the size of spacers on either side. But in those diagrams, I just used character spaces to communicate the idea. In another chapter I describe how the dishing can be checked with a dishing tool. In this chapter I will give some actual measurements at the hub.
6 left axle Projection
4 left locknut
15 left spacer
12 left flange base
57 flange pair
3 right flange base
37 freehub
1 right spacer
4 right locknut
6 right projection
----
145
But the actual
WHAT MEASUREMENTS TO CHECK
Measure from flange surface to the locknut. All wheels intended for 135mm dropouts should match because the rim must be centered.
Right Left ---------------------------------------------
Shimano C201 39 30
Shimano Deore 39 30
FH-2400 Malaysia
Black Noname (DX18) 45 30
The value of all this is to determine if a given wheel has the rim centered between the locknuts. Eg:A wheel intended for 135mm dropouts should have certain measurements for left and right.
Any wheel with a proper length axle (146) should have the same number of spacers.
5. Cold Setting a frame
In order to upgrade an older steel frame bike to use newer wheels it is necessary to permanently bend the rear triangle so the dropout distance is wider. For example the old standard from 1980-2010 used to be 126mm, but nowdays the standard is 130 for road bikes and 135mm for hybrids or touring bikes. the 135 width is probably what you want, it is more common and is a stronger wheel with less dishing.
Cold setting a frame is something I would rely on a bike shop to do. And you might want some assurance they have the necessary tools. The tools are expensive: And even then it is tricky, and so it pays to know in advance what is going to be done. And ask to be present when the bending is done so you know what was done. On my Miyata bike they were unable to get the frame exactly aligned, but when I thought about it afterwards, I realized we could have done things differently. A frame alignment tool is essential.
First, a general introduction. See this video:
What tools are involved in cold setting a frame?
1. Tool to check alignment of frame
2. Tool to bend the frame (threaded rod, and Wooden Pry bar)
3. Tool to align the dropouts at their new position.
If you get a shop to do the alignment, they should have the following tools:
Example: Park Tool FAG-2 (~$100-$150) or Super B Dropout Alignment Tool (retractable pointer for dropout distance comparison).
Examples: Park Tool FFG-2 (~$100-$150, chrome-plated steel, for dropout-equipped frames/forks, not thru-axle).
Hozan (HKC) Dropout Alignment Tool (Japanese-made, vintage, for 100mm front or 130/135mm rear).
Cyclus Tools Dropout Control Gauge (for precise geometric alignment, adjustable for various widths).
DIY Alternative: Threaded Rod Setup: Use two 3/8" threaded carriage bolts or all-thread rods (100mm or longer) with coupling nuts and washers. Insert into dropouts, adjust nuts until nearly touching, and bend dropouts to align the nut facets (indicating parallelism). This method achieves ~1mm tolerance.
Surplus Hub Axle: A spare hub axle (9mm front or 10mm rear) with cones, locknuts, and a large adjustable wrench (12" or larger) to grip the dropout’s neck and bend it. Check parallelism with a straightedge.
Additional Tool: Derailleur Hanger Alignment Gauge (e.g., Park Tool DAG-2.2) Function: Ensures the rear derailleur hanger is aligned with the frame and wheel for proper shifting. Screw into the hanger, check rim-to-tool spacing at multiple points, and bend gently if needed.
Note: Dropout alignment is critical after cold setting, as spreading/compressing the frame can slightly alter dropout angles (e.g., 0.3°-0.5° for 120mm to 130mm). Only steel frames with a narrow neck between the dropout and frame tube can be safely bent. Thick or bonded dropouts (e.g., carbon fiber) may not be repairable.
Process OverviewCheck Alignment: Use a frame alignment gauge (FAG-2) or string method to assess rear triangle centering and measure dropout spacing with a caliper. Confirm hub width for the target spacing. Bend Frame: Secure the frame in a vise (via bottom bracket cups) or use a support (crate/ladder). Apply controlled force with a 2x4, threaded rod, or FFS-2 to spread/compress one stay at a time. Check alignment and spacing after each adjustment to avoid overbending. Align Dropouts: Install a dished wheel or use an FFG-2 to check dropout parallelism. Bend the dropout’s neck (not the face or tube) if needed, ensuring a gap of <0.5mm. Recheck derailleur hanger alignment with a DAG-2.2. Final Checks: Verify frame alignment, dropout parallelism, and wheel centering. Ensure the wheel slides in smoothly with no axle stress.