Update: upon further investigation I believe the calcs on the blog post I link to are in error or at the very least they don’t apply to the offset Large Marge rims I have. The offset of my LM rims is ~13mm [measured hastily so it could be +/-1mm] this should be entered in the wheel calculator as +/-13.0…the Phat Divide Blog uses +/-6.0 which would be correct for a 6mm offset rim. I have redone some calcs using what I think is the correct offset LM value and published them in them in this post. If you are motivated look at this and confirm I’m correct.
If you ride a Surly Pugsley or an offset 135mm 9:zero:7 fat bike your rear wheel uses a standard 135mm wide MTB hub, but it’s moved 17.5mm to the right to clear the big fat tires you ride on. This is an unusual situation for wheel builders and worth considering as you plot your next wheel set. There is a great post over at the Phat Divide Blog discussing this exact topic that is worth a read.
Since we are on that topic Joe over at the Pedaling in Place Blog has an interesting post about experimenting with Pugsley wheels/tires trying out a number of “What If?” scenarios you might have been pondering, but like me been too lazy to actually try out.
Above and below are offset and symmetrical Large Marge rims with XT 135mm hubs – which demonstrates why you’d want to use an offset LM on a Pugs with an IGH or a normal MTB hub.
Sorry for not checking these calcs out before linking. Everything looked good until I punched in an offset LM with Alfine and the results didn’t match my wheel so I went out and measured the offset on my LM rims.
Above you’ll see the results for a 170mm fatbike hub with a symmetrical Large Marge rim. I also tried an offset LM rim with this hub with the offset going left and right – neither option was as good as using a symmetrical rim which makes sense
Just an observation if you look at the symmetrical LM rim shown above the spoke holes are actually offset to both sides of the rim. This needs to be entered into Freespoke as +3mm/+3mm [I’m guessing as I don’t have a symmetrical LM to measure]. I used +0/+0 which gives the same % spoke tension results, but the spoke angles will be different so if you have symmetrical LM rims measure them and use the actual value.
- 135mm IGH in Pugs with offset rim provides most even spoke tension
- 135 MTB hub in Pugs has approximately the same spoke tension as a 170mm MTB hub with symmetrical LM in a non-offset fatbike
- flange spacing is also a factor in wheel strength [170mm MTB hub has widest spacing followed by 135mm IGH]
- offset spoke holes may not result in as strong a wheel a symmetrical rim, but this doesn’t seem to be an issue in practice
- measure any spoke offset of your rims to confirm these results apply
- if my calcs are correct than an Alfine offset LM Pugsley wheel is stronger [better spoke tension balance] than a normal Alfine MTB wheel with a symmetrical rim.