quemazon

As I was going through the mental gymnastics of how to upgrade an old tandem, I came across "boost QR" hubs, which are used on some new mountain bikes. They are regular skewer quick release axles with a hub spacing of 141mm. I don't know what the axle diameter is, so I'm not 100% sure they'd work on older tandems. Has anyone here tried it? They seem like the answer to the prayers of all owners of pre-2000 tandems.

OneIsAllYouNeed

I think a modern boost QR hub could give an old tandem new life. Specifically, steel tandems with 140mm QR should readily fit a 141mm QR hub. The axle diameters are the same. The DT Swiss 350 Hybrid hub is a tandem-friendly hub that's a good candidate for conversion from 148mm TA to 141mm QR. There may be workable hub options from Chris King, Industry Nine, White Industries, Hope.

Another option is replacing the axle on a relatively modern QR hub. We're using a Shimano SLX rear hub with Wheels MFG axle (and 10mm of spacers) on our 145mm QR tandem. I built a wheel with than hub three years ago as a low-cost way to try out 650b wheels and tires on our 1997 Trek tandem. That frame is gone, but the wheels are still going strong.

Alcanbrad

I would think that if the hub was 1 or 2 mm wider than the dropouts, mounting the wheel in the shop will be possible, though will require some elbow grease, and roadside maintenance requiring removal of the wheel would be a real pain.

A better option might be a standard 130mm TA hub with a custom QR adapter that provides 140mm dropout spacing. Such an adapter could offset the hub to more closely match hub spacing for maintaining the chainline and could be a single or 2 piece affair. Machining would be relatively straight forward on a lathe.

quemazon

I would think just the opposite. I doubt the spacing is held to better than +/- 1mm on the frame. Basically 141mm is likely well within tolerance. If anything it should create very minor interference. And you get the benefits of the increased stiffness of the wider hub. Using a 135mm hub with spacers may require weird dishing and be weaker.

jim_pridx

I tend to agree. A 1mm difference will likely feel a bit tighter than it probably should, but not by much. I remember having this same issue long ago (don't remember which bike it was), but it didn't present any problems at all.

Darth Lefty 

Fitment? Mmmmaybe. We are talking tandems, they are usually not very wimpy in the rear triangle. But people cram 130 hubs into 126 Cannondale single frames without too much worry.

The funny thing about that DT Swiss 350 Hybrid hub is that they apparently no longer sell a 36h rim to build it with. I couldn't easily find anyone stocking them for mail order, maybe you have to go through a shop to get access to the distributor. Edit - Universal has them. But $276, ouch. Hard to look at that when CRC has complete 240-hubbed 142TA wheels on clearance for less.

Alcanbrad

If your frame's dropouts fall to the wide side of tolerance it shouldn't be an issue. If if falls on the narrow side, it won't be fun.

Your comment about the 135mm spacing is the issue. Frames that support the 141 or 142 Boost are in fact 135mm spacing so the dishing issues are the same as using 135mm hubs.

If I understand it correctly, TA hubs can be configured as QR with end caps as i described. Using custom QR end caps opens up pretty much the entire market of available hubs and gives better spacing. All other issues are the same.

quemazon

Standard rear boost spacing with the through axle is 148mm. When you change out the end caps to QR, it goes to 141mm. So, it is truly a 141mm hub, which is better than, essentially a 135mm hub. I have a marin pine mountain which has boost QR. The dropout spacing is 141, not 135.

Alcanbrad

You may be on to something. I would be interested to hear how it works as I have an old Santana and I am looking for a low cost rear wheel replacement option.

quemazon

I was was considering an old santana but ended up with a newer burley, so I won't be doing this upgrade. (I kind of wish I had an old Santana to fix up now, just for fun.) I measured my pine mountain (new 27.5+ mountain bike) and the spacing is indeed 141mm.

There are a few bikes that have gone to this hub recently--most commonly the Trek Roscoe. People are really hating on it because they consider it yet another hub standard. But as far as I can tell, most TA boost hubs (148mm) should be ok for conversion to 141 QR. This is explicitly the case for the higher end Hope, Chris King, DT Swiss, etc. They sell end cap conversion kits.

If you want something less expensive I'm sure they are out there. The hub on my pine mountain isn't anything special. But I've had a hard time finding them. I have a feeling that you could convert pretty much any TA boost hub, but I don't have any to play with.

LV2TNDM

If by "old Santana," you mean steel, then this should be an optimal solution. A 6mm difference in dropout spacing is a mere 3mm change at each dropout. Steel stays and dropouts will accommodate this change without much problem. Assuming crank and heel clearance isn't already at the limit. Dropout tools, muscle and a long piece of string is all that's needed to respace an old steel frame and maintain frame alignment. Newer (air-hardening) steel takes a LOT MORE MUSCLE to respace, but can also be done. Aluminum shouldn't be cold worked or respaced.