peterw_diy

My Yuba Mundo needs a new rear wheel. The stock wheel is a 48h 26" with a 14mm solid axle and 7s freewheel. I routinely have 300+ pounds of rider + passenger + cargo, on good roads. Sometimes 450#.

I would like to hear opinions on switching to something like an XT 756 hub in 36h, 14ga straight spokes, and a Halo SAS rim (36mm wide, 785g, marketed as a downhill/jumping rim). I would buy Yuba's adapters to make the 10mm standard axle fit the 14mm dropouts, and a spacer to allow a 7s HG cassette on the 8/9s freehub body.

I would like the standard hub for easier maintenance. Not only does the stock Mundo hub have oddball 19mm nuts, but standard freewheel tools don't fit over the 14mm axle, so pulling the freewheel to rebuild with a new hoop (which was my plan 12 hours ago) is a real hassle even in my own garage -- completely removing the axle & cartridge bearings is required and an axle vise is practically needed. Field repairs beyond a flat tire would be awful. But is a 36h standard hub up to this challenge?

Thanks in advance for your insight,

Peter

(FWIW the current rim is failing at the DS spoke holes, looks like factory or dealer over-tensioned.)

JohnDThompson 

I would keep the 48h wheel. Perhaps you can bore out your freewheel tool to fit over the oversize axle? I did this for my tandem, which has a 12mm axle, and it worked fine.

Bill Kapaun

I definitely would use a butted spoke. Something like a Sapin Strong would be much better than a 14 ga. non butted spoke.
Sapim Strong Single Butted Spoke - Wheelbuilder.com

A DT Swiss Alpine III would probably be better yet.
DT Swiss - DT alpine III

The XT 756 hub doesn't have the most favorable CTF offsets. According to Spocalc, the NDS spoke tension is 58% of the DS tension.
IF you can find a hub with the CTF's "more equal", that would help even the tensions.

Using a 4 mm offset rim would result in spoke tension ratio of about 80%.
Velocity Synergy OC Rim - 26" x 2.00, 32H, Silver NMSW


IF you could find a "genuine" 7 speed FH Body, that would reduce the dish by about 2mm, that would make things about 9% "more favorable.
Using both would give you a ratio of ABOUT 92%

EDIT-
Thinking about this some more and I have to agree with John about more spokes.
With the set up you have, you'd have a higher than normal % of the weight on the rear wheel.
A "conventional" bike has about a 40/60% F/R weight distribution.
I would expect yours to be maybe as bad as 20/80%?
That all depends on your weight vs the "other" weight.

fietsbob

Aarons bike shop in Seattle drills out 16 more holes in a 32 hole large flange IGH and laces it "crow foot" in 3s to a 48 spoke rim ..

wide braced dishless makes a stronger, lateral-radial, wheel ..

I toured a (pretty heavy) Solo load touring bike for a decade 48 hole Phil Freewheel hub, QR, 10mm ends .. 14 ga straight spokes because I was buying 88

Shimano type freewheel extractor splined, Their thin wall splined remover interface is common amongst the business now .


XT is aiming for light weight , XC Racing cashe' rebuilding a Shimano tandem Freehub with a shorter axle is more to the haulage goal.. & 48 & 40hole ..

though the Base is narrow , the 2 flanges are narrow spread , to make room for that stack of sprockets ,Aka "speeds".


FWIW .. a 36 hole IGH may be OK , Rohloff hubs now offer a 36 hole hub shell since their 32 hole became Popular in tandems ,
and the web pictures of a cracked flange on someones bike tandem touring the Andes made news.

peterw_diy

Thanks everyone, especially fietsbob for the encouragement re: tools & the 14mm axle! The local coop's Park BBT-5 fit over the axle and got the freewheel off pretty easily.

Spoke tension looks high. The coop's TM-1, which seemed to be well kept so no reason to doubt it, measured the NDS tension around 110 Kgf and the DS tension around 175 Kgf. Looks like the builder based everything on NDS tension and ratcheted the DS up as needed. :-(

I'm feeling encouraged about rebuilding with the existing hub. I'd love to find a wide OC 26" rim in 48h, guess it's time to start looking. Initial web searches are not encouraging -- I'm only seeing traditional drillings in 48h (and even 40h).

nfmisso

Here is an alternate 48H cartridge bearing hub for you: HUB RR WM MT1110 QR SF 9sCAS 48x135 SB SL

And a wider 559 48H rim: Velocity Wheels

peterw_diy

An LBS over here that sells a fair number of cargo bikes is suggesting Rhyno Lite. Also when I tried putting a standard 26" wheel in (mostly so I could roll the bike around), it seemed pretty clear that the frame OLD is significantly more than 135mm, so I think I'll measure and see if adding spacers on NDS is an option for improving dish & tension balance... maybe get to 140mm or so.

fietsbob

O.L.D. of 140 puts you into a Tandem Hub category for rear hubs .. and makes 48hole a common part of the mix. https://images.jensonusa.com/large/hu..._40___drum.jpg

Bill Kapaun

Obviously the extreme spoke tension is the problem.

Without knowing the CTF and exact OLD, you may find that an OC rim might NOT be desired.
I built a rear using the Velocity Synergy OC (4mm offset) with a Shimano RM-30 hub.
Using spokecalc, I determined that an OLD of 142MM would have resulted in a symmetrical wheel.
Let's say (just for purposes of discussion) you had the same hub as I used and a 145mm OLD. That would result in a wheel that was past symmetrical.
Using your 175 & 110 kgf figures, I think you still have "room" for an OC rim, but I don't think you'll find one.
The theory behind 40-48 spoke rims is to make a stronger wheel.
The theory behind OC rims is to make a stronger wheel.
I would venture they don't feel you need both.

I would try to find one of the "stronger" rims that hopefully has the same ERD as your current rim if you want to reuse your spokes.

fietsbob

OR Steel hub shell spoke holes bored out to take a 12 gage spoke then 36 may be fine ..

MoPed spokes and a heavy duty rim (or just be OK with replacing the rim Occasionally. )


All Weather sports Is a Fairbanks Alaska shop , I got a set of their Snow Cat 45mm wide rims in 1990, they may do a custom drilling

Its not a particularly heavy duty rim , its a single wall , and for lighter weight like the fat bike rims, they even make big holes between the spoke holes

CliffordK

I believe that many of the solid 10mm axles are made of pretty cheap metal, so a good 10mm QR may be stronger than a straight axle. But, of course, you have an oversized axle.

Also, the Cassette/Freehub combination may be stronger than the typical freewheel (less axle sticking out).

If I was you, I'd find a cheap used 36 spoke MTB wheel and try it out. If you don't have one, your co-op should have a few (plus longer axle?). That would at least get you a spare. Then, perhaps tinker on the Yuba.

Can you talk to your Yuba vendor about getting a replacement rim? Or perhaps contact the company directly?

Have you looked at the Through Axle hubs? I think 12mm is getting more common.