Why do tandems have spacing that is considerably wider than regular hubs? What would be the pros & cons of using a 135mm spacing for a road tandem, light team (under 300lbs), with disc brakes and 9 gears in the back? (let's assume the frame already comes with 135 spacing)
I didn't find many clear answers by searching tandem@hobbes & bikeforums, at least not without spending all day reading 150 threads. I realize that for some this might be one of those flame-prone soapbox issues. I guess what I'm asking is this: is there a COMPELLING reason to avoid 135mm spacing, vs reasons that make wider spacing MARGINALLY or SOMEWHAT better, but not dramatically so?
Own a Colnago Super (1979), a Bridgestone road bike , circa 1985, and a Santana Arriva tandem (1997).
Santana has for some time (years) supplied their bikes with 160mm rear wheels for a couple of reasons: as it was explained to me, wider is more stable, both at the triangle and for the wheel itself; 160mm means wheel is symmetrical, not dished, which is inherently weaker, especially if being required to support 300-400 lbs with attendant lateral stresses. I'm not an engineer (I'm a humanities kinda guy), but this makes sense to me...
You could ride 126 mm spacing if you wish. But, the rear wheel will not hold up as long. 135 mm (standard mountain bike) is stronger than 130 mm (standard road bike). As stated above, the extra axle width takes some or all of the dish out of the wheel, resulting in a stronger wheel.
Same reason that mountain bikes use 135 vs. 130 for road bikes:
1. Wider rear spacing allows you to optimize bracing angles through the use of wider hubs or reduced drive-side off-set using axle spacers, such that the overall wheel strength and durability is increased.
2. Once you get to 145mm you can build a dishless or near-dishless rear wheel for 8/9/10 speed hubs and dishless wheels are even more robust than 135mm spaced rear wheels as you eliminate the asymetrical tension in right hand vs. left hand spoke tension.
3. The move to adopt 160mm remains a hot topic: there are as many pros as there are cons to the extra-wide spacing.
You'll find 135mm, 140mm, 145mm, 150mm and 160mm rear spacing on tandems and, so long as you don't have problems, then what ever you have is probably OK. The problem with the “theory” regarding 160mm rear spacing building stronger wheels is that it doesn’t necessarily pan-out in reality: 160mm rear spaced tandems seem to experience as many broken spokes as 145mm rear spaced tandems, etc… as the durability has more to do with the quality of construction (specifically proper tensioning & distressing), rider dynamics (bouncing stokers are murder on rear wheels), than just the spoke geometry. So, while Santana makes a compelling argument for 160mm, in practice it’s a moot point: both prevailing “standards” for tandem rear spacing (145mm & 160mm) work equally well for most teams.
As for your specific situation, your sub-300lb weight would suggest that 135mm may be OK, but not as robust as 145mm for a non-disc road bike. However, if you are planning on buying a 135mm rear hub for that tandem you'd want to patronize a tandem dealer or use one of the tandem hub manufacturers so that they'll know to use heavy-duty axles / cassette carriers / bearings in their MTB hub vs. using a stock MTB hub; the latter won't hold up for long. Moreover, you would also want to find a wheelbuilder who has experience in building wheels for tandems and let them know that the wheelset you are building was being spec'd for use on a tandem: it will influence decisions regarding rim selection, spoke patterns, and spoke gauge.
Regarding Disc brake installation: We (275lb team) ride an off-road tandem with discs, 135mm rear spacing and, while that works fine for us in that application, a 26" wheel uses shorter spokes and steeper bracing angle than a 700c wheel which mitigates some of the strength issues of super-narrow hub flanges. We also have some friends (265lbs) who ride a Litespeed Talini that has been respaced to 135mm for racing using super-light Campy Record-based wheelsets. When not otherwise engaged in racing, their tandem is fitted with a Chris King disc hub/Velocity Deep-V rims, and 203mm rotor which has worked fine. Of course, they are not what you’d call timid riders and, like us, rarely use the brakes except when absolutely necessary. However, unlike us, they have ridden their tandem up and back down Brasstown Bald (you’ll recall that Lance was even impressed with how steep it was during last year’s Tour de Georgia), and the rear disc system built around an Avid BB caliper worked like a champ. David is a pro wrench who builds his own wheels and they have held up quite well. I believe the deep section rims are once again a good choice here in that anything you can do to shorten spokes helps to stiffen the wheel. So, as I say, it is possible to get away with 135mm rear spacing & discs on a tandem; however, I’m not sure it would be my first choice or a recommendation. I believe the average team would have less trouble in the long-run if they elected one of the other, wider rear spacing standards. In that you indicate what you have is already 135mm, if discs were a must-have and if the frame was steel, I’d be inclined to have the rear triangle cold-set to 145mm rear spacing by a frame shop. If it's aluminum, you're stuck with what you have as respacing is cost-prohibitive.
FWIW, here are some flange-width dimensions from different manufacturers to keep in mind when shopping for hubs; note that there is a lot of variation. In many cases, spacers fitted outside the flanges are all that distinguish one size hub from another.
Spacing = Left / Right-Drive Side [Flange Dist. from Center (mm)]
My problem with most tandem specific hubs is the exhorbitant cost, except for Shimano, who doesn't make their tandem hub in a disc version. I've got to keep this project on a budget! I've heard that the shimano tandem hub can be converted for disc if it's threaded for a drum brake by using an adapter. So, given the advice so far, maybe I should go that route, go with 145 spacing, and a high spoke count. It would be kind of nice if someone came out with a reasonably priced tandem disc hub. But there doesn't seem to be a market for it, since tandem parts are already a small niche, made even smaller by the fact that many tandem owners--more, uh, prosperous than I--can more readily shell out big bucks for a Phil Wood, a White Industries, or a Chris King. I simply don't need those kind of high level components. Other tandems do just fine with quality mid-level parts, but it hasn't seemed to reach the tandem disc hub market yet.
I know DT/hugi hubs are a little more affordable, but they are cartridge bearing hubs, I believe. I'm already having problems with a set of high end cartridge hubs on one of my single bikes, and I like cup & cone bearing designs for the ease of finding replacement parts.
My problem with most tandem specific hubs is the exhorbitant cost, except for Shimano, who doesn't make their tandem hub in a disc version... I've heard that the shimano tandem hub can be converted for disc if it's threaded for a drum brake by using an adapter. So, given the advice so far, maybe I should go that route, go with 145 spacing, and a high spoke count.... I'm already having problems with a set of high end cartridge hubs on one of my single bikes, and I like cup & cone bearing designs for the ease of finding replacement parts.
Shimano's hubs are hit or miss in off-road applications, but seem to do just fine on the road so the Shimano + Dimension disc adapter "should work". However, I'm not sure how close the tolerances are with regard to matching up against an Avid BB on IS disc mount. I've got one of the adapters at home but haven't played with it much, other than confirming that it's not compatible with the current caliper installation on our Ericksons. I'll likely press it into service if and when I have the travel tandem's rear triangle modified for the Avid. Anyway, you might want to check with one of the tandem specialty dealers like Mark Johnson at PrecisionTandems.com who does a lot of fiddling around with rear discs on tandems, more so than some of the other dealers.
Back to the hubs, White Industries hubs are no where near as expensive as Phil or Chris King and they do offer a disc version. Get in touch with Alex Nutt at MTBTandems.com as I suspect he would be able to give you your best deal. Mark Johnson @ Precision.com as well as Mel Kornbluh at TandemsEast.com also sell the White hubs. Mark, Mel, and most of the other guys like Rich Shapiro at gtgtandems.com sell the Shimano hubs & thread-on disc adapters.
Cartridge bearings can be hit or miss, depending on which ones the manufacturers use, just how well they are sealed, and if the manufacturer calls for maintenance and relubrication: not all cartridge bearings are maintenance free. Phil Wood & Chris King's sealed cartridge bearings are, as you'd expect, top shelf. White Ind. uses pretty low-end models that will last about 1/3 as long for 1/3 of the cost of the better bearings. On the bright side, when a cartridge bearing goes bad, you pop it out and press in a new one. No worries about damaged races or cups or getting the preload "just right". I thought I had a bad bearing on our White Ind. front hub a while back. However, it turned out to be a tolerance problem with the end-cap that, in turn, did-in one bearing. White sent out a new end cap and two new bearings and I haven't had a lick of trouble with it ever since. Seemed to affect a bunch of hubs produced back in 2002.
Basically it looks like the Shimano rear tandem hub with an adapter is my most affordable option. If I want to go with 40 spoke wheels, White Industries is the best option. You are right that they are much less than King or Phil hubs. It appears that no one besides White (and the unobtanium ones from Phil, King, and Hugi) makes a front 40H disc hub.