Tandem Cycling - xt hubs on a tandem?
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02-29-08, 05:41 PM
let me begin by saying that i like shimano hubs. i like the serviceability, have all the tools to rebuild, and only once had a failure (flange broke) in many miles. i'm also very loyal to what i know. that's a little background.
i just bought an early 80's santana road tandem, and i'm interested in building a set of wheels for it. i'm leaning towards 36h velocity fusion rims to be our lighter, faster touring and day tripping set (then later building something beefier for loaded touring). i definately want to use disc brakes on this bike, so when i noticed that shimano does not make a disc tandem hub, i'm looking at the white m16. then i stumbled upon a thread in this forum (i think) where the discussion was about the difference between this hub and their mountain hub. i digested my white industries literature and now believe that difference is 1. longer axle, and 2. more casting where the rotor attaches (corresponds to the longer axle). the distance between flanges is the same, just more centered ('cause the axle is longer).
so then i go looking at the difference between the xt shimano non-disc hubs and think i'm seeing a pattern. so for hundreds of dollars less than a pair of m16's, i'm thinking about buying a pair of xt m756 hubs, putting a longer axle in the rear, making a spacer for the disc rotor and using longer disc attachment bolts.
any thoughts about this?
02-29-08, 06:53 PM
Why not just purchase the Shimano HF08 tandem hubs (same guts at the XT) with the correct rear axle spacing, left-hand threading, and use a thread-on disc adapter?
No need to mess around with swapping axles, spacers, or other custom modifications? FWIW, even the $950 Rolf Prima Vigor Tandem use a left-hand threaded hub and thread-on disc adapter.
02-29-08, 07:31 PM
ah ha! thanks tandemgeek. that thought had occurred to me as a possibility, but never when i was at my computer doing research.
but, here's another angle. the hf08 rear is approx $145 whereas the xt m756 is $60. the corresponding front hubs are $72 & $44 respectively. so obviously to do a disc front i cant use the tandem hf08 front. if the guts are the same, what is the real difference on these hubs? why would anyone use the hf08 front? on the rear, if i go with the hf08 i have additional cost of the adapter (prob. not that much). if i go with the m756 then i have cost of axle and skewers (significant, but $85?). so i guess i'm back to wondering what gives. special juju with a "tandem" hub - or - smaller market, supply and demand, etc?
02-29-08, 08:12 PM
The only differences for the XT vs HF08 front hub are: flange size / strength & drillings. If you're a lightweight team, then a solid high flange isn't as important. For example, we're a 275lb team and I use 36° White Ind. MI5 / Racer-X front hubs which have relatively small flanges for a tandem hub and they do just fine, which is true of the XT non-disc front hub. However, if you're combined team weight begins to creep above 300lbs then those 36° smaller flanges and/or drilled-out high flange hubs may not be the best choice vs. a beefier solid high-flange hub and/or a hub with 40° or 48° spoking.
As for the rear hubs, obviously the axles and spacing is different and while the parts only bump your out of pocket cost for the hub a little, you time has a value. If I was a shop wrench making $18/hr, no big deal: a couple hours and you're still a little ahead. However, if you time is worth 2x - 5x that per hour, then your opportunity cost far out weighs the potential savings. From a design perspective, again... the HF08 uses a non-drilled, beefier high-flange, steel carrier, the correct axle, and comes in 40° and 48° models that can be used with an Arai drum brake or thread on disc adapter. So, as before, if you're a lightweight team then perhaps a modified XT disc hub will work just fine. However, if you're an adult tandem team of average or greater than average size and weight, you might be better served by a rear hub that was designed to deal with much higher weights than you'd ever encounter on a single bike. In fact, the HF08 is spec'd for quite few 3/4/5 seat tandems because it's so beefy.
Bottom Line: Lightweight and even some not-so-lightweight teams can get away with using all kinds of components that weren't designed for use on tandems. However, when doing so, it's best to find out what their manufacturer's max load ratings and limitations are before making a final decision on which components to use. If a tandem will only be used once in a great while and won't carry a demanding load when it is used, almost any hubs aside for the cheapest ones will work. However, as greater demands are placed on a tandem -- weight, riding intensity, or added durability / reliability -- the most cost effective solution may not always be the cheapest one.
02-29-08, 10:59 PM
thanks, once again, tandemgeek for excellent information. we are, in fact, not a light team - 340#, nor gentle riders. so the flange strength and beefiness is important to me. i'll continue with my research.
The idea of using longer rotor bolts through a spacer scares me.The bolts will be stressed more than a single,yet be supported less.I'm guessing they may shear off.
03-01-08, 06:39 AM
The idea of using longer rotor bolts through a spacer scares me.The bolts will be stressed more than a single,yet be supported less. I'm guessing they may shear off.
Yes and no. So long as you used a proper donut-style disc rotor spacer you'd probably be OK. But, for this application, it's almost a moot point as installation of a rear disc on an older tandem that never had a rear disc is going to require a frame modification. Therefore, the only place a disc could be used would be the front so long as a proper disc fork was used. Because of the vintage of this tandem, I'm not even sure it has a 1.125" steerer so that disc fork would most likely need to be custom made to get the correct steerer, rake, fork length, and added robust features for a disc caliper installation.
With respect to a rear disc, I focused my attention on the rear hub in the first two replies but let me now expand to the other challenges with that aspect of the OP's proposal....
Given the drop-out spacing and design of the rear stays on older tandems, I suspect the OP would quickly discover fitting anything larger than a 160mm rotor between the hub and stay may be a challenge. In fact, in this respect, the more inboard mounting configuration of the XT's disc rotor would probably be a good thing as I suspect the correct size rear tandem hub with thread-on adapter would need to have the thread-on adapter machined down by several mm's to get the needed clearance for even the small disc. In either case, the disc brake mount is going to be an add-on and that could only be fabricated after the rear wheel and disc were sorted out and installed on the frame.
Frankly, this is a lot of work for almost no real benefit compared to a good set of cantilever brakes and a rear drum "as required" for touring. Moreover, the rear stays really weren't designed to deal with the loads generated by a rear disc. Thankfully, the rear stays on most Santana's produced since the late 80's have always been beefy and took into consideration the installation of a rear drum (also a hub brake, but one that does not generate the very high loads that a larger disc rotor can). Therefore, the smaller disc rotor -- assuming it could be squeezed in -- would not be as big of a problem as a larger 203mm tandem-rated disc brake installation, but then again the performance of the smaller brake would also be just marginally better than a well-adjusted set of cantilevers. V-brakes are probably not a good solution for this frame either as the brake bosses even on Santana's produced in the mid 90's were too narrow for proper set-up of linear pull brakes.
Bottom Line: It's an interesting project idea, but I think it may be ill-advised. Just my .02.
03-01-08, 07:03 AM
I think the OP was referring to a thread I started about upgrades to our tandem. I wrote a story on the hub conversion along with pictures for my blog:
Tandem Hub Conversion (http://blog.hammerton.net/2007/12/05/tandem-hub-conversion/)
The conversion was easy and inexpensive and resulted in a wheel with virtually no dish. We came to the same conclusion as the OP, the only difference we could see between a Shimano MTB hub and the Tandem hub was price and axle size. I also figured that if people in the Clydesdale forum could abuse these hubs with no ill effects then our super-clyde (by weight only) team riding on smoother surfaces could also expect good service from the MTB hub conversion.
We are the same size team as the OP but we were trying to eliminate the discs not add them. We also went 32 spoke and after a couple of hundred miles have not had to touch the wheel in any way other than replacing the 23mm tires (I had those laying around at the time of the wheel build) with 25s.
We do not "tour" on our tandem (I know that is sacrilege for tandemers <sp?>) so the most we carry is a seat bag with a multi tool, CO2, 2 tubes, a few emergency goo packs, and a bit of cash.
03-01-08, 07:40 AM
I think the OP was referring to a thread I started about upgrades to our tandem.
Just a couple quick points... and then I'll go away.
There are things that I'll do with my own bikes, tandems, motorcycles, etc... that may or may not follow conventional wisdom and may, in fact, push the design limits of certain components or use them in ways not originally as intended.
However, when it comes to giving out advise on public forums and such, I use a different standard and will invariably go with more conservative recommendations given all of the unknowns. While I'm not surprised that WheresWaldo hasn't had any issues with a low-flange 32° XT rear hub so far, I still would not recommend it to a complete stranger. Moreover, I'd still caution WW to keep an eye on the flange area of that hub as the miles begin to pile up (5k, 8k, 10k) relative to stress cracks around the spoke holes and the rim if the miles are being piling on with two large adults as the primary team. After all, the concern with road bikes is fatigue life, not just tensile strength. Mountain bikes with their 26" wheels running on fat tires that can take big hits on 5 mile off-road loops do not replicate the same stresses or numbers of stress cycles that a 700c wheel running a narrow, high-pressure tires sees on 25 mile road loops.
As already indicated, I know of teams who weigh upwards of 500lbs who have ridden on an older C'dale RT3000 tandem that came with a 32°/36° Shimano XT hubset. The only reason that the hubs (and rims) didn't show sings of cracking sooner was because they rarely rode their tandem, putting perhaps a couple hundred miles on a year at best, despite conversations and comments that would have suggested mileage numbers and performance feats several magnitudes greater that just weren't in evidence. I gave them a new rear wheel as a retirement present -- 48h Shimano HF08/Sun RhynoLite XL laced 5x -- which is what they should have always been using. I believe the original front hub gave up the ghost a short time later and they may or may not have gotten the mate to the rear wheel as a replacement. Conversely, there are lightweight teams that you'd think could get away with riding just about any hubs and wheels that they so choose but who, after a time, found they even they were not immune from fatigue taking its toll on lightweight components.
A properly designed tandem hub will last 10's of thousands of miles with not more than perhaps a sealed bearing replacement around 20k miles if no one bothered to pull the seals and regrease the bearings as part of periodic maintenance. Flange failure on these types of hubs is rare and when it has occurred it's been quickly (a few thousand miles) on short-lived models that used material removal techniques like machined openings or additional drillings between the spoke holes to reduce weight, e.g., White Ind. Rocket front hubs and some of the early Rolf front hubs come immediately to mind. These are my observations based on a decade of intense interest, reading, research, and 10's of thousands of miles of road riding and several hundred off-road miles on tandems.
In closing, you can put any wheels you want on a tandem so long as you adjust your expectations for performance, durability, and perhaps safety... although the latter is usually not an issue as the former will manifest themselves as issues first. So long as you do your homework and are comfortable with what the people who design these products can provide in terms of the design limits, knock yourself out. However, be mindful about applying and reading the caveats and qualification of recommendations as WW did, e.g., a couple hundred miles to date.
03-01-08, 09:54 AM
wow, tandemgeek, you know my tandem/situation pretty well. yes, the rear stays are fairly close to the wheel. if i can't use 203mm rotors, then i'm not going to do disc brakes, but i'm optimistic about that from my initial observations. my plan is to not only braze disc mounts onto the seat stay, but an additional support connecting the seat stay and the chainstay.
the cantilever bosses are currently barely useable. they are set fairly close to the wheel (narrow spacing) and also designed around 27" - which i'm moving away from. so while i'm into frame modifications, i've been planning on moving those too. they currently are useable with the original canti's that are the old mostly horizontal style. i can just barely adjust the pads to hit the 700c cyclocross wheels i'm testing with. correct, linear pull brakes come nowhere close to working, nor do modern narrower canti's, like avid shorty.
i wouldn't be doing all of this if i hadn't gotten the bike for very little money and i didn't enjoy these sorts of puzzles
the front is also a puzzle. i would discribe the fork as petite-looking. i could add brake tabs for little effort, but i do have concerns about the fork holding up to the additional stress of hub breaking. interestingly, in my mind, the larger rotor helps by moving the breaking closer to the head tube. i've also considered adding metal to the full length of the fork for stiffening. i'm also considering having a custom builder make a new fork for me - here in portland oregon we are lucky to have many. with a new fork, i could have a longer threadless steerer, braze on tabs for a rack, etc. correct, that none of the commercially available forks work - 1" steerer, longer distance between hub and head (27" again).
i'm off for a club ride this moring, but i'll post back with progress updates on my project.
Rear facing dropouts on a disc brake fork are not as good an idea as forward facing dropouts: Lawyer tabs help, but I would not do it on a tandem. Nor would I modify a fork.Too scary to think about.
03-06-08, 07:35 AM
Slightly off the xt hubs topic....buy why not add the disc mount to the chain stay (like Santana does on its current tandems?)
Does your Santana have the current 1-1/8" headset (or the 1-1/4" headset that you can get the reducer to 1-1/8)? If so, the easy, safe (and probably less expensive) solution is one of the current disc forks - Winwood Disc Cross fork has been reviewed here a couple times.
I'm pretty aggressive but I wouldn't braze disc tabs on my half bike fork let alone on the tandem...
Back on topic...how much riding do you do?(be honest) Tandemgeek with his 1000s of tandem miles is different from my 100s of tandem miles (and I divide my 1000s of 1/2 bike riding across several bikes). How often are you willing to repair / replace your hubs? How far from home do you ride? Failed hub for me in the Canadian Wilderness could be 2 hour walk to cell phone coverage and then same more time to contact someone to pick me and the bike up (and the husband points I would lose.)
03-06-08, 02:30 PM
I've been using Shimano's XT disc hubs on my tandem for a few years with no problems. It had disc brakes, but I've sinced ditched those, while keeping the hubs. Buying the regular XT disc hubs and swapping the axle (if you have 140 or 145 spacing) will still be cheaper than buying the XT tandem hub.
03-06-08, 03:04 PM
I've been using Shimano's XT disc hubs on my tandem for a few years with no problems.
Just curious: About how many total miles do you have on these wheels, what kind of terrain (flat, rolling, hilly, mountainous) and what was the average & heaviest team weight?
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