MAC motor fit to 135mm fork - centering

We received a new motor and additional parts for our project. We are wanting to put this motor into a 20" fat tire front fork and rim. The fork has 135mm spacing between dropouts, as does the motor. Had a whole stack of emails back and forth on motor selection and other topics, but the truth is neither we nor the vendor knew for sure how this would come together until we started fitting up.
The present problem is that the wheel is not centered well, with about 19mm clearance to the fork on the 'freewheel' side - and about 9mm on the left (cables out) side.
To be centered then each side should be about 14mm or so.
The spoke holes are to the outside of the rim, in rows both 30mm from center. Since the spokes spread going away from the motor flanges, dishing and spoke head changes don't have much effect.

I could maybe get a special axle machined, that would likely cost more than the motor!
The cable side axle protrudes 35mm from base to end of threads. I might be able to get a 2 or 3mm spacer on and still get full nut engagement Maybe more.
The other axle end also is threaded and has flats for 35mm. I could, in theory, machine those flats additionally at least the 5mm and still get full thread engagement. The thickness of the dropout, washer, torque arm, etc. add up to more than 5mm anyway.

The rim is just drilled without eyelets. I have enough flat rim surface outboard of the present spoke holes to move them 6mm or so. On each row of spoke holes, the holes are 70 mm apart around the circumference. I would just split the difference if I drilled new ones offset.

Those are my newbie thoughts, but would sure like to hear from the experts. This wheel is low speed (15mph max) and quite low load and shock bearing....if that helps.
I can post pictures if that helps.
Thanks!
Wallypedal

You'll need a different set of spokes, longer on one side than the other.

Dogman - Thanks for your reply! I do know about dishing and spoke calculators and short vs. longer spokes. When I began this I had a stack of spokes from previous setups to experiment with. The rim itself, with the parallel spoke rows 70 mm apart, doesn't work in the spoke calculators I've tried. I therefore started trying to fit things together just to determine ERD and spoke lengths on my own.

I happened to have a set of 113 mm spokes which fit in a radial pattern and just tightened up (not enough) - meaning to me if I were go with a radial pattern I probably would need 111 mm spokes for proper tensioning. That of course, would be leaving the wheel off center in the fork.

Still in experimentation mode, I inserted the spokes with all the heads on the same side of the flange - when you look at the motor you can see all the spoke heads, both flanges. One website wheel guy cited this as an example of how to change centering by a couple mm. It didn't work. That's when I got to wondering if having the spoke rows so far apart might not negate any dishing effect - but that's just guessing on my part.

More questions then -
- is dishing to achieve 5-7 mm offset done frequently?
- if I go with radial and want that much offset, what length spokes should I get? (Again, knowing that 111mm spokes will center.)
- does that much offset affect strength or wheel function issues/
- isn't it always best to center a front fork wheel?
- can I now input parameters that will work into a spoke calculator and get good output?
- is a radial pattern OK with spokes this length, or should we use a cross pattern of some kind?

ERD is 391.48 at the spoke holes. The nipples I have will allow the spokes to thread on to where they are just flush or protruding a little.
Or can you or anyone on the forum just tell me spoke lengths I need for dishing, or guide me to a spoke calculator to put this into? The flange diameter is 172mm.

We truly want to get this right, thanks!
Wallypedal (Tom)

OK,
I went back to Grin's calculator, studied it and input everything. The drawing looks like my setup, and it is giving me a one cross pattern, hub offset, and spoke lengths to match. I have some confidence in the results - any reason why I should not?

Spoke vendors - any recommendations?
Wallypedal

wallypedal said:

We are wanting to put this motor into a 20" fat tire front fork and rim.
...
The spoke holes are to the outside of the rim, in rows both 30mm from center.

Click to expand...

I believe you have two issues:

1. You have a small wheel so even 1-cross lacing looks like a problem. Radial lacing seems to work for many, but structurally is not a good idea.
2. The spoke holes are too far apart: your spoke holes are 30+30mm = 60mm apart and the motor has only a 44mm flange. This may not dish using the normal lacing or have good lateral strength.

For the first, you might try spoke pairs. This would require drilling some offset holes in the flange, but not too challenging if you make a simple jig with a pin to locate an existing spoke hole and a hole to guide the new drill point (see images here). See this post for a discussion of spoke pairs. Again, people seem get away with simple radial lacing, so it's a call for you and perhaps a question of how much thrust you want to apply.

For the second, you probably need to use cross-over lacing to lace the drive side of the motor to the brake side of the rim, etc. This will get you the angle you need to get some lateral strength and proper dishing. See this post for an discussion/example.

Caveat: These are just some thoughts.... I am not a wheelbuilder - in my case this advice is based entirely on reading with no practical knowledge beyond truing wheels, so some added research or a few words from a truly knowledgeable wheelbuilder (Chalo) would be a good plan (maybe a PM to him linking to this thread).

What motor flange diameter? Large 233mm DD motors rarely work well 1 cross in 20” wheels so I’m assuming you’re working with something 110-170mm diameter? ***EDIT*** I should read thread title more closely. MAC motor.

I often dish my wheels 3-7mm and a simple way to help gain a little extra shift is the in/out of spoke heads in the motor flange. If you do one side in and the other out that will often gain a few mm dish to one side of the axle.

I’m not experienced with these fat rims or bikes so I’m not really following some of your descriptions?

However, my self-taught bottom line about motor wheel dishing is that when one side approaches near vertical, that’s about all it can reasonably do. Opposite side spokes will be pretty loose by that point and the wheel not very strong.

As far as sourcing custom spokes? Danscomp - and not everything’s on their website. My go to 13/14ga single butted Sapim Stainless spoke isn’t listed but I buy a lot of ‘em for about 50 cents each w/nipples. Gotta call and ask but they do a good job and easy to deal with if you’re USA?

We dunno where you’re located, so???

Ykick said:

What motor flange diameter? Large 233mm DD motors rarely work well 1 cross in 20” wheels so I’m assuming you’re working with something 110-170mm diameter?

Click to expand...

Using MAC drawings from a few years back, I get a flange diameter of 172mm and an offset of -7mm.

wallypedal said:

The spoke holes are to the outside of the rim, in rows both 30mm from center.

Click to expand...

wallypedal said:

The rim itself, with the parallel spoke rows 70 mm apart,...

Click to expand...

A moving target....
Plugging in the restated spoke hole offsets, seems to indicate that a regular non-swapped lace looks workable... (tension ratio = 66:34)

Justin_le said:

Spoke Angle Measurement Finally, for any of these arrangements it shows the actual angle between the spoke nipple and the tangent where it enters the rim, so that you can quantify the feasibility of a build. I'm not sure what rules of thumb there are for acceptable angles, but my experience is that with eyeletted rims and tight nipples it can often be tricky when this angle is less than about 75-77 degrees, while with rims that don't have eyelets you can usually get away going down to 70, though it's not always pretty.

Click to expand...

Using your 1-cross pattern the spoke angle is about 75.4 degrees -- so probably workable...

Teklektik, thanks for replying and giving it some thought. Sorry about any confusion from my verbal description. Yep, the spoke calc says 75.4 degrees on a one cross pattern. I put in 6mm of hub movement. I ordered spokes from Grintech; if it doesn't work out I'll tell them it was their calculator's error! :lol:
Wallypedal

Are you going to use a disc brake or a rim brake?

Gregor said:

Are you going to use a disc brake or a rim brake?

Click to expand...

Disc for sure, we've got clearance. BTW for those wondering, I edited the profile to show my Wyoming location.
Wallypedal

Success!! Thanks to all who responded on here, and to Grin and EM3EV - we got the motor laced in. The spoke calculator was spot on, the spokes were shipped fast, fit correctly, and the wheel is centered in the dropouts.

Great looking wheel! Be sure to check your spoke tensions every ride for the first 5 to 6 rides. With the wide rims, you can't really do much to "true" your rim, but to keep even tension on them will prolong your spokes' lives.

When you off-set the rim, the tension in the spokes from one side to the other is different. For a small off-set, there's not much difference, but the difference accelerates upwards the further you go. Your spokes on the long side are probably looser than they should be, so they have a tendency to come loose in use. You need to check them regularly in the beginning until they eventually stick in position.

I think that it's best to use the biggest spacer you can on the left side, and then dish the remainder. Even a 1mm spacer can make a big difference in the tension if you have a big dish.