1

I have a set of 26" Surly Rabbit Hole rims, which I need to build into a wheelset for a fat bike.

The Rabbit hole rims are unique in that the spoke holes are not in the center of the rim. The drive side holes are 5mm (approximately) offset toward the drive side brake track, while the non-drive side spoke holes are offset the same amount towards the non-drive side brake track.

I have physical measurements of the hubs & rims, as well as the manufacturers' stated specs for the rim, and used a couple of different calculators, including the one that is made by the rim manufacturer, but the spokes are not building up correctly.Specifically, they seem to be too long on the drive side, when the wheel is dished.

I'm looking for assistance in figuring out how to adjust the rim dimensions in a spoke calculators for the offset, to get the correct spoke lengths. It's unusual, because the offset is different for the spoke on each side of the wheel.

I'm happy to provide any extra information, if I know what you need to know.

3
  • Shouldn’t the drive side spoke holes be offset towards the non-drive side to make the spoke angle less steep? Maybe you are using the wrong holes and that’s where the discrepancy comes from?
    – Michael
    Mar 2, 2022 at 10:44
  • @Michael There are rims like that (usually called cross-laced, the worst name ever) and some people have built up Rabbit Holes that way (from looking around the internet). Usually it's an either/or choice because of the drill orientation through the rim, but these rims appear made to give the option, which is unusual. Mar 2, 2022 at 19:54
  • These rims give the option because they can be laced to hubs with a 135mm outside locknut diameter, if used in an older offset frame, or laced to modern 170/177/190 and 197mm OLD hubs, with a non-offset frame. With a modern build, the spoke alternate sides of the rim and the rim is centered on the hub. With an offset build, you would use a single row of holes, and the rim would be offset to the non-drive side, at least typically.
    – zenbike
    Mar 2, 2022 at 23:02

3 Answers 3

2

You can adjust the numbers in the spoke calculater by measuring the lateral distance of your spoke holes first. From your question, i assume that should be around 10mm. Now you can treat your hub as if it was less wide, by this distance. Be sure to remove those millimeters in the middle, meaning you measure your distances from the outside as you normally would, and substract the spoke hole offset from the overall width of your hub.

The geometrical reasoning: when the rim's spoke holes are in one line, a cross-section through the hub would show the spokes and the hub forming a triangle. with your offset spoke holes, you get a trapezoid. In your mind, you can push one side towards the other to again form a triangle (when the spokes "touch" in the rim) . You moved the triangle by the amout the rim's holes are offset.

2
  • This is what the manufacturer suggested, as well, saying to subtract 7.5mm from the center to flange measurement on each side. However, it doesn’t seem to produce enough of a change in the recommended length of the spokes to offset the amount of extra spoke length I’m seeing. I get the logic, and it does make sense, which is why I feel like I’m missing something else in the equation…
    – zenbike
    Mar 2, 2022 at 23:39
  • The final build ended up subtracting an additional 2mm from the spike length, after the 7.5mm correction for offset to each side.
    – zenbike
    Mar 31, 2022 at 16:16
2

My answer is a link to a calculator tool taht allows you to specify spoke offset for each side. Note you can input a negative number if you wish. I have put numbers into this tool to demonstrate that it will account for the offset, but you will need to update my pretend wheel figures with the actual measurements.

Please reply in comment if this gives you the difference in spoke length you think you need.

https://kstoerz.com/freespoke/?link=1&e=584&oL=5&oR=5&wL=30&wR=30&dL=50&dR=50&s=2.5&n=32&xL=3&xR=3

Your other option is to estimate how much shorter you need the too-long spokes to be and order the coresponding length. Generally you have a few mm to play with (packaged spokes come in 2mm increments) so you don't have to be decimal-places accurate to get a good wheel. You can also consider stacking brass washers between the nipple and the rim (1 or 2) to achieve a slightly shorter effective spoke length without spoiling your wheel. There is an argument for saying that nipple washers make a better wheel build, but hardly anyone uses them.

2
  • I’ll check this out as soon as I get to a PC.
    – zenbike
    Mar 2, 2022 at 23:44
  • @zenbike it's probably the best calculator and gives you a visual representation of the spoke angles so you can see if your wheel looks like it makes sense.
    – Noise
    Mar 3, 2022 at 13:02
2

This answer build's on JoeK's; I think he points out the problem but what went wrong may not be obvious.

Rims can have offset holes for different purposes, but the rims in question here have them for potentially all the purposes depending on the build choices. An average, holes-running-down-the-center (or nearly so) rim will frequently have some small amount of offset side to side to match the side of the hub the spokes are intended to run to. Usually the amount of offset in rims like this is negligible for spoke length calculation purposes. But, if you are building your Rabbit Holes (or other 64-hole Surly rims) such that the drive side offset holes are going to the drive side flange and vice versa for the non-drive-side, you are building a wheel where the effect on spoke length won't be negligible.

The confusion point can be that "normal" offset/asymmetric rims that still only have one set of spoke holes are doing something completely different. On a rim like that, all the holes are offset from the rim centerline in the same direction, whereas on your rim they are offset in alternating directions.

There are three ways you can build up 64-hole choose-your-own-adventure type rims like yours, and each could make sense depending on the application. Using a calculator such as Freespoke that accepts a different offset value for each side of the wheel, the options would be:

  • The DS flange spokes go to the DS rim holes and the NDS flange spokes go to the NDS rim holes. This would tend to be the choice that goes along with the really wide fatbike rear end spacings. You would enter both offset numbers as positive values.
  • The DS flange spokes go to the NDS rim holes and the NDS flange spokes go to the DS rim holes. This a way of maximizing the bracing angle and I see some people have built their Rabbit Holes this way. For this you would use a negative offset value on both sides. enter image description here
  • The DS flange spokes go to the NDS rim holes and the NDS flange spokes go to the other NDS rim holes. This would be done for the same reason as using an asymmetric rim; to get a better bracing angle on the drive side spokes and more even spoke tension, usually on a non-fatbike-specific rear end. (Where my working knowledge ends is where the cutoff is in rear end spacing for the different modes to typically make sense, but the good spoke calculators nowadays all will show you with the bracing angles and the L-R tension balance so you can see for yourself which option does what). To do this you would enter the DS offset as a negative value and the NDS as a positive. (For a front it would be the opposite, non-brake-side positive and brake side negative.)

If your DS spokes are coming out too long, likely what's happening is that you've done the calculation for that side using a negative offset value where you needed it to be positive. A likely way you could have gotten to that problem is you're building the wheel using the first of the above options and you used a spoke calculator that's not set up to handle alternating offset rims. If the calculator you used has just one single "offset" value to fill in, then what it's doing is assuming you're building a normal offset road or mountain wheel with an asymmetric rim (a WTB Asym for example) and it invisibly calculated the DS spokes as though their holes were offset to the NDS, not the DS.

You can use calculators like that to build alternating offset wheels, but you do it by running the calculation twice, once with a positive offset value entered and once negative. I believe the main way of adapting the classic spoke length formula to the situation would be similarly running the calculation twice, and spoofing the "hub width" variable differently each time (I could be wrong about this).

3
  • The calculator I used was one provided by the manufacturer of the rim. It doesn’t let you input any rim characteristics, instead using the part number of the rim and the characteristics stored in their database for that part number.
    – zenbike
    Mar 2, 2022 at 23:43
  • @zenbike spoke calculators of that sort have limitations, and rims that give you options are one of them. Try doing it in on that lets you go under the hood more and see if the result lines up with the issue you were having. Mar 4, 2022 at 1:01
  • That’s what I am trying to do. But I needed to know what measurements to use, and how to enter them correctly in the calculator.
    – zenbike
    Mar 4, 2022 at 2:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.