REAR Smart Pie Vector on the front of a FAT TIRE BIKE?

[Slacker]

Hello,
I just bought a Mongoose Dolomite.  It is a WalMart  7 speed Fat Tire Bike.  The FRONT tire is 26 X 4.0 and the space for the front hub is 130mm. 
Two questions...
1)  Can I use a REAR Smart Pie Vector on the front wheel of this bike?
2)  Can you supply the proper spokes?

[Bikemad]

The rear Smart Pie should fit the 130mm dropouts but lacing the wheel using the existing holes in the rim is probably not the best way to do it.

The spoke holes on most rims are fitted along the centreline of the rim to give a greater angled spoke between the hub flanges and the rim to provide better lateral strength for the wheel:



The wide rims on the Dolomite have staggered spokes and a much wider distance between the flanges on the hub to produce a similar spoke angle to conventional rims.


If the rim was laced using the existing holes, the spokes would be exiting the rim in the wrong direction (dotted blue and black lines) and the nipples would jam and cause the spokes to bend. The spokes could well end up being more parallel than angled, which would provide very poor lateral support to the rim.

It would be better to spoke it like a conventional rim (as indicated by the the solid blue lines in the previous diagram) but new spoke holes would need to be drilled in the rim around the centreline as shown here:



The spoke length could then be determined by accurately measuring the difference between the internal diameter of the two rims (Standard 26" GM deep "V" rim and your 26" wide rim).

Alan
 

[Slacker]

Thank you for the prompt and thoughtful reply, Alan!   
And with pictures and graphics to boot!
I'm happy to hear that it can be done and will proceed as you have directed.
Thanks again,
Slacker

[Morgen 3Eman]

Hey, Alan, what do you think about cross lacing the rim?  By that I mean take a spoke from the left side of the hub to the right side of the rim, and from the right side of the hub to the left side of the rim.  Wouldn't that work well to stiffen the assembly lateraly?  I vaguely remember seeing Borrani? rims like that in a paddock in the 60s? ….

By the way, the fat tire bike I saw had really tiny diameter spokes that didn't look like they would last very long.

TTFN,
Dennis
 

[Bikemad]

Hey, Alan, what do you think about cross lacing the rim? 

Cross lacing is often used on spoked car wheels where the wheels are subjected to very high lateral forces on corners:



The severe angle between the spoke and the rim means that the holes in the rims have to be specially formed to allow the nipple to seat evenly with the spoke exiting the rim at the correct angle.

If you look carefully at the following picture, you should be able to see that the rim is actually angled on the portion where the original spoke holes are located:



This allows the nipple to seat correctly against the rim as shown in position "A" below.
If you tried to cross the spokes with this rim you would end up with the nipple being unable to seat itself against the rim properly, as shown in position "B" in the following diagram:

By the way, the fat tire bike I saw had really tiny diameter spokes that didn't look like they would last very long.

There is no logical reason why they should need to be any thicker than a conventional bike's spoke, as the forces being applied to the spokes should be the same. Having said that, the much larger volume of air within the fat tyres themselves will absorb a lot more of the impact forces on bumps etc. therefore the same thickness spokes should actually last much longer.

Alan
 

[Flipseth]

Here is my front rim drilled that I handed off to the wheel builder today, I will post more as I work it out.
I used masking tape and a 90deg straight edge and marked the holes then went back and drilled with a hand drill.

I went with a Smart Pie 4 rear motor.

Phill

[Bikemad]

If you fancy  drilling another 144 holes you could lose the original spoke holes by turning them into lightening holes as shown here:



This will involve a lot more work and require some very heavy duty rim tape to prevent the tube from busting through the larger holes.
I don't know how much weight this would save but if the holes were all drilled nice and accurately it might look very neat on the finished wheel.

Alan
 

[Flipseth]

I was going to just use some red rtv and fill those old spoke holes in.
That way it would match the front rim.

Thanks for the idea though.

Phill