Advantage of an Offset Rim

[SRock24]

I am wondering what the advantage of an offset rim is such as the Large Marge Offset Rim. Surly says it is to get more dish to the disc brake side but what does that do mechanically for the bike? Does it better offset or compensate for the force of the disc brake?

thanks

[TrailMaker]

Hey;

As far as I know, it was simply to get tire clearance and chain line using the components available at the time. There were fatter 3.8+ tires before there were 170mm rear hubs or offset ring cranks. Offsetting the rim was the only way to get the chain past the tire, coming from a #1 cassette cog on a 135mm hub to a front ring. The only "advantage" may be that you can build and run two rear wheels, which could prove useful in extreme adventuring environments.

[Andy FitzGibbon]

Offset rims create better spoke angle and more even spoke tension in an offset-built wheel, which makes for a stronger wheel.

[vikb]

Zero offset rim in a Pugs.



Large Marge offset rim in a Pugs.

The components aren't exactly the same in these models, but they are close enough to show the impact of the offset rim.

[dfiler]

What surly is referring to is that an offset rim provides more dish on the brake side when using an offset hub. A symetrical rim on an offset hub would be weak because the brake side spokes would have no dish. When wider hubs became available, a symmetrical rim could be made with good dish on both sides.

The reason for offset in the first place is that wide hubs were not available or were too expensive. With the fat bike market growing and components coming down in price, it is likely that offset setups will almost entirely disappear. The only remaining justification will be reliability for extreme touring. A rear wheel can be used up front, providing a spare should the cassette free hub fail.

[vikb]

The only remaining justification will be reliability for extreme touring. A rear wheel can be used up front, providing a spare should the cassette free hub fail.

IGHs like 135mm offset frames.

Using standard parts is also nice for repair/replacement on short notice. Any LBS has 135mm rear hubs for sale.

Having standard parts in your fleet allows stuff to move around from bike to bike. Quality parts last a long time and can be swapped to a different bike if they use the same standards.

Offset wheels are holding up to abuse fine. The biggest downside I see with them is that the offset requires you to decide if you want to go really big 100mm/5" tires or stay smaller with a max 5" tires on 82mm and the option to go down to 29er wheels if you want 'em.

It will be interesting to see if Surly holds firm on the offset design.

[dfiler]

The non-quoted part of my post shows that we are almost entirely in agreement about the justification for offset 135mm hubs. ;-)

As for offset rims, it depends on how and what you ride. For most people it is fine. Summer riding at high speed over rocks leads to untrue rims for some people. Symmetrical builds give you a better chance of truing those lighter weight single wall rims.

[vikb]

I've also noticed folks building up Krampus-esque Surly Rabbit Hole rims for symmetrical frames/forks using the offset holes to get even spoke tension.

[pbasinger]

What program is this? I think I've seen screen shots of it before on here, maybe from you. Seeing bracing angle and tension distribution is pretty cool.

Zero offset rim in a Pugs.



Large Marge offset rim in a Pugs.

The components aren't exactly the same in these models, but they are close enough to show the impact of the offset rim.

[vikb]

What program is this? I think I've seen screen shots of it before on here, maybe from you. Seeing bracing angle and tension distribution is pretty cool.

Hi Pete - it's freespoke:

Freespoke

With all the funky frame/rim/hub options on fatbikes it's nice to be able to see possible wheel builds and compare them this way.

[Fat_Burnman]

G'day Gents -
Interesting thread. I understand the logic behind offsetting the rear wheel predominately for chain clearance on the Moonlanders. However after buying my 2013 Moonlander (my other is a 2012) I was surprised to see the front fork now has a radical curve in it as well!

(Right hand bike in photo is offset fork)
Surly's sales pitch is it "allows the front and rear wheel to be interchangeable". I'm not entirely convinced however.
The look is strange (on the front specifically) it limits the ability to bolt on any front rack (its lost the bolts on the left hand fork side) and sticks out dramatically on the right hand side as you ride it - a nominal 30mm proud of the rim edge.
Its not a big issue, but I think I prefer my "old" fork being traditionally straight.
I thought it interesting aforementioned comments stating it would be phased out - if the 2013 model is anything to go buy, Surly clearly feel that the offset presents other benefits?

[vikb]

Surly's sales pitch is it "allows the front and rear wheel to be interchangeable".

Surly changed the ML recently to allow front to back wheel swaps like the Pugsley. It's a good feature if you ride far enough from help that walking back would be a problem. Which makes sense given the MLs floatation and usefulness as an exploration machine.

I've gotten so used to my Pug's offset fork I don't really see the offset anymore and there is no impact on how the bike rides.

If you ride the bike like a MTB on short day trips it's not a feature you probably care about, but if you ride a long way from services on a fully loaded bike it's nice to know you can swap in a FG or SS front wheel and keep going no matter what.

Surly does sell non-offset ML forks for something like $99 if it's something you really want to change bad enough. It will require a wheel rebuild as well.

[dfiler]

In the picture it appears that the fork has retained at least some of the mounting bolts despite being offset. Are some of them missing?

I too found the move to an offset front to be curious. Perhaps they're catering to the touring crowd for which running an actual rear wheel up front would provide a backup free hub. Strangely, the complete build uses a cassetteless hub up front. (Edit: is that correct or does the standard build include a cassette hub up front?)

Given the weight of the moonlander compared to the competition, it does seems likely that touring is one of the primary goals. It is the only reason I can think of for an offset front. Also, the surly moonlander page refers to those "long days grinding out miles in the saddle", which doesn't really seem like marketing toward the trail bike crowd.

[Fat_Burnman]

The offset fork is not a dealbreaker for me, just noting that I have both now so can see the pro's and con's of each. Conceptually its a nicety to swap the wheels, but when it comes to crunch time on a long trip as you say and wish to swap them, how does this benefit you when you only have two wheels? Ride in a wheelie?
The front hub has thread exposed on the right hand side so I can only assume the freewheel assembly threads onto this. Given I have broken 2 freewheel hubs on my moonlander (std XT hub) I have since thrown them in the bin and replaced both front and rear with Hope Evo hubs. Its more likely to break the freewheel vs the hub in my opinion..
As for mounting points, yes the straight fork (on the right) retains the mid screw and 3 lower screws. The bent (left) fork has only one mid screw now.

[sparlinx]

Though the offset allows a rider to swap the front and rear wheels in case of cassette failure, you can do practically the same thing on a symmetric wheel. One can purchase a bolt on cog for the six bolt standard disc brake. You can get one from here: VeloSolo Shop - Disc Hub Mount Cogs and Accessories Add the bolt on fixed cog to the brake rotor. In the event of cassette failure, remove the brake rotor, flip the wheel, shorten the chain and ride. You will not have a rear brake but a rear brake is not necessary on a fixed gear. I have never had to use this but I believe it will work. . In fact, one reason I never purchased a fat bike was because of the odd offset. As soon as I saw the Salsa Mukluk, I purchased one and I LOVE it. There is nothing inherently wrong with the offset design but, I like symmetry. Just a matter of preference.

[vikb]

Conceptually its a nicety to swap the wheels, but when it comes to crunch time on a long trip as you say and wish to swap them, how does this benefit you when you only have two wheels? Ride in a wheelie?

My Pugs is setup with a fixed cog up front and an Alfine 8 in the rear. If the Alfine fails I swap wheels and keep rolling. The FG cog is mounted and ready to roll.

I have seen some folks who have a single wheeled trailer that uses a wheel they can cannibalize for the bike. Important if you are travelling somewhere with real consequences to a gear failure.

[vikb]

You will not have a rear brake but a rear brake is not necessary on a fixed gear. I have never had to use this but I believe it will work. .

That's cool... I hope someone tries one out to confirm it works.

For a loaded fatbike in the backcountry I'd rather have both brakes if there are any serious downhills, but if the choice is between walking all the time or riding at least a bunch of the time I'll take the later...

I've also seen a symmetrical fatbike with two rear wheels for swapability without the offset.