Thanks for previous responses to my query, they helped a lot. my other question is: what has been people's experience with tough wheels for a tandem, given that i cannot find a disc specific rim in 48 hole drilling? i'm thinking my choice is between a 32/36 hole disc specific rim, or a 48 hole regular rim. given that this bike will be primarily on the road and i might demand occasional hard braking from it, 400lbs. of riders, and 2.5" tires, this combination seems to me that i'll be generating a good deal of tension on the spokes under hard braking (203mm rotors w/ hydraulic calipers, wide contact patch on road=decreased chance of skidding, braking hard from high speeds). so, which rim/spoke combo might hold up better? from what i've been told, the disc specific rims have a reinforced spokebed to account for the high stresses that disc braking can put on the rims, nipples and spokes @ that point.
also, is it possible to do a 5x lacing on a 48 hole rim? though i heard it somewhere... my take is that i might be better off with the 48 hole hoop and 4 or 5x lacing, as even though the rim wouldn't be disc specific, 50% more spokes, than 32, would create a sig. decrease in the per spoke load. love to hear from those out there who have any experience (direct or vicarious!) with this scenario, thanks!
The BikeForums Team
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Thanks for previous responses to my query, they helped a lot. my other question is: what has been people's experience with tough wheels for a tandem, given that i cannot find a disc specific rim in 48 hole drilling? i'm thinking my choice is between a 32/36 hole disc specific rim, or a 48 hole regular rim. given that this bike will be primarily on the road and i might demand occasional hard braking from it, 400lbs. of riders, and 2.5" tires, this combination seems to me that i'll be generating a good deal of tension on the spokes under hard braking (203mm rotors w/ hydraulic calipers, wide contact patch on road=decreased chance of skidding, braking hard from high speeds). so, which rim/spoke combo might hold up better? from what i've been told, the disc specific rims have a reinforced spokebed to account for the high stresses that disc braking can put on the rims, nipples and spokes @ that point.
also, is it possible to do a 5x lacing on a 48 hole rim? though i heard it somewhere... my take is that i might be better off with the 48 hole hoop and 4 or 5x lacing, as even though the rim wouldn't be disc specific, 50% more spokes, than 32, would create a sig. decrease in the per spoke load. love to hear from those out there who have any experience (direct or vicarious!) with this scenario, thanks!
Last year I converted over to disc brakes-- Hope Mono M4's with 200 mm discs. These brakes are very effective so I also changed over to 20 mm axle afterwards.
Total weight all up of 400lbs, on a mountain bike that is ridden aggressively. If a solo XC mountain bike can do it, then so can we, si it does take all the stresses and strains through the wheels that high speed offroad can give it.
We went to Hope Higun hubs on Mavic downhill rims with 36 spokes. Straight gauge is what was suggested to us and so far no problems. Theses rims are disc specific as we were were informed by a very good rider that he has problems using rim braked rims on disc set up. The disc specific rims are strong, but you could probably get away with "Freeride" rims if you are solely road use. We use Panaracer Fire XC in 2.1 and this is a tyre that works for us offroad.
I may have gone over the top on quality, but these wheels are still true after 2,000 miles of abuse, but a lot of that may have been due to the Builder. Get a "Known" good wheelbuilder to manufacture your wheels. The quality is far better than most LBS's and they will probably be cheaper aswell.
Brian
There is such a thing as overkill. We've got 36h Rhynolites, and they've held up well for us. That's with the 20mm thru-axle and 203mm rotors as well. Are you doing loaded touring? Planning a lot of high speed stops? Seems like you're overbuilding to the point of diminishing returns. You'll have wheels that will be near impossible to get rolling, and have extra rotating weight to stop.
prairie*boy
smh
Give Alex Nut a shout (www.mtbtandems.com). He has an assortment of combinations and experience to steer you straight.
Prairie*boy
Brian
I think we gave him that address in another thread. Alex hooked me up with some gear for our tandem. He's very helpful and really knows his stuff. I just don't understand what the motivation is here. Smh seems to want the most overbuilt wheels he can find, but doesn't state what they're going to be used for. If he's worried about beaking spokes, Alex can solve that too with a pair of these. (http://www.aerospoke.com/indexa651.html?id=402)
smh
i might have been too vauge in my description of intended use for the tandem wheels, sorry. the serious loads i plan on putting on these wheels stem from this scenario: high speed braking on hydraulc discs w/ 203mm rotors, on asphalt with a 2.5" slick tire. here's my rationale why this would be high stress (someone steer me straight if i've veered): 400lbs. of riders, and i'd like to have strong, predictable (miniaml fade, although i realize discs can heat up, hence the benefit of an arai, i'm just not into 'em), safe braking from speeds up to 60+ mph cuz we'll be riding this thing down mountain passes in cali where i've broken 60 mph on numerous occasions on a single. i've heard tell of doubles reaching 70+ and have no qualms about going this fast, just wanna make sure i have a braking system suitable for the job...i'm making the assumption that some people have achieved these speeds and that what i propose is not unsafe, but since i don't know for sure, i was hoping this forum would be a good place to air the idea and see what experienced tandemers thought. the high stress really comes in when one considers that this speed/braking scenario coupled w/ (and i've never seen tires this wide addressed here before) 2.5 slick tires on asphalt on a tandem could allow me to generate a good deal of spoke tension, wanting to rip spokes out of, or break nipples at, the rim. the brakes can be applied a lot more before a nose-wheelie (the tandem dynamic) and the tire isn't likely ('specially the front) to skid, so in a hard stop we could be putting spokes under serious tension.
also, i proposed this scenario to Alex Nutt and he said he wasn't comfortable recommending a wheelset for me for my proposed usage. He referred me to Peter Jon White who gave me some good ideas, but i still figured than ultimately, a large forum of tandemers, at least a few of whom i'm sure engage in this sort of bike use, would have some valuable input based on actual experimentation and usage... based on the help i've got here and thoughts shared, i'm convinced i'm right! thanks again for all input.
prairie*boy
smh:
Ok, I can understand Alex's (and an apology for the misspelling of his name) reluctance...
Tire width is basically irrelevant (so says my engineering background)...tire construction is what matters as it determines the coefficient of friction and that determines the force.
The force is not significantly different at 70 than it is at 5...stopping the wheel requires you to overcome the inertia of the spinning wheel but the mass of the wheel is small compared to the weight of the rest of the bike and riders. Which brings us to the big issue: a tandem going 70 has ~2.75 times the energy of a single doing 60... (end of physics lesson). I'm not sure that any set of disc brakes is up to that task....not even with galfer's 255mm discs.
Therefore, the issue is really not a issue of spoke/rim strength but of thermal capacity.
Prairie*boy
p.s. Also read the other thread so hopefully am not putting my foot in mouth...
p.p.s. I am interested in what PJW had for suggestions if you don't mind sharing.
TandemGeek
i might have been too vauge in my description of intended use for the tandem wheels.
There are a lot of missing details and conflicting requirements in your 3 posts thus far, including an unspecified off-road tandem frame with unknown rear spacing and an as yet undisclosed brand and model of tandem-rated disc fork which by themselves are enough to give me the heebeegeebee's. Add to that the initial desire to go cheap with something like a Shimano HF08 tandem hub & thread-on adapter vs. a Hugi HU0921 or HU0919 while, at the same time, wanting an absolutely bomb-proof set up.
The simple answer is, you use the more expensive Hugi disc-hubs -- 40 or 48 hole (frankly, for 26" wheels, 40 is more than enough) -- and the also previously mentioned Sun Rhynolites in 40 or 48 hole. Yes, a 48 hole hub/rim can be laced 5x; a 40h can be laced 4x and perhaps 5x if the flanges are large enough. Regardless, use double butted spokes. Of course, the short-cut to all this expense is to go ahead and just purchase an '04 NOS or '05 Cannondale MT which comes with this wheelset & the Avid BB7 discs from the factory; $2,250 at TandemsEast.com and other fine tandem retailers. That's not all that bad when you consider that the wheelset has a retail value somewhere around $500 + the two sets of Avid BB7's, 203mm rotors & special adapters, i.e., $750 not including the frame ($1,200) and the rest of the parts. Oh yea, and for anyone who uses the Hugi hubs just be sure to service them with the factory spec. lube per the instructions; if you don't they can and do fail... even the new ones.
The ultimate wild card remains how you intend to use those brakes since most mega high speed descents are just that: speed runs where brakes are hardly ever employed except when approaching turns since just sitting-up and catching air in your chest will scrub off 10 mph in short order. I say this as the captain of a team who is notorious for blistering fast descents with hands on the bars at the stem, chest on hands, head over the front wheel, pedals level & knees touching, and butt in front of the saddle with my stoker tucked in behind. On those types of runs, you either know the road or you don't bomb the hill because there aren't any ways to make short panic stops at those speeds; you just head for lowest risk way around an obstacle. Managing speed is as already stated; you sit up and catch air and carefully modulate the brakes front to back to manage the heat in your braking components and run out the speed at the bottom of the hill.
For those who are looking for controlled descents with lots of brake input, the aforementioned drag brakes remain the only game in town. Now, you've made it clear that you're not turned-on by the drag brake approach and that's fine and dandy. But, if you want to play in the disc brake game then you need to pay to play AND get real about their limitations. Yes, you can subject them to far more abuse / heat build-up than rim brakes which makes them ideal for aggressive descenders taking on switchbacks where you let it fly between the turns and then thrown on the hooks just in advance of the turns. But, if you're predisposed to "riding the brakes" on descents to keep things in check you'll burn up a lot of brake pads and rotors and perhaps discover that you can, in fact, melt those little red plastic adjuster knobs.
Anything's possible, but not everything. Figure out what you're willing to compromise on, i.e., budget, performance, or technology and then go for it.
Just my .02.
Brian
Thanks Mark. I couldn't have said it better. Titanium rotors will stay cool under these conditions, but you'll have to replace the pads each day.
smh
thanks TG, a lot of good info. other stuff i forgot: Raleigh coupe tandem, 26" wheels, 145mm rear spacing, aluminum, w/ rigid steel fork, has disc tabs and i called raleigh to make sure it was OK to use a disc brake f/r and they said it was. i heard something somewhere about one of the cannondale tandems, older, that had disc tabs on the fork, but that the fork somehow wasn't rated for discs... this spurred the admonition for tandem owners to consult their manufacturer to be sure about disc fork.
as far as my intended uses, i do not anticipate having to use the brakes much, if at all, on high speed descents, like you said, the only drops suitable for this type of bombing are typically very straight, little need for brakes save an emergency. also, i'm fine w/ using the brakes a bit between curves on something steep and curvy, letting 'em cool before using them again, i have no intention of using them as a drag brake.
as for the rear hub, gosh, i just wish there was something a little less expensive than hugi, although i realize that the shimano cheapie tandem hub is likely asking to go a little too low-qual for the heavy duty paramters i've set forth, point well taken. are there any other brands you know of that might make a lesser pricey disc rear hub than hugi, phil, hadley, etc?
what do you think about the adaptor from arai threads to disc? are these hokey? something tells me thay once i mount it, it'll never come off... i permanently mounted a suntour 13-32 7 spd freewheel to an old phil huh on my mountain bike, and i installed it with loctite and used a 4 prong removal tool secured w/ QR. we ended up having to cut it off with a grinder, 4 hours later... so i'm thinking that a disc adaptor of this type, with a lot higher clockwise screwing force from slowing descents than my climbing legs put on the freewheel, would just end up living on the hub, no? also, are there spacing hassles using this thing, as far as getting the rotor properly spaced from the caliper?
also, prarie*boy noted that tire width wouldn't affect my braking load. i realize that the increased tire width in and of itself only contributes a little more to angular momentum, but what i meant (someone correct me if i'm wrong) was that the radically increased tire width would allow me to lay down harsher braking force before skidding the tire, due to increased width (2.5" tire vs. typical 1-1/4" or so)=higher coef. of friction. does anyone know, will this wider tire offer me any more braking ability on the road over a narrower tire, or is tire contact area not the limiter in this equation? i'm still pretty sold on these tires for bombing speeds though, as they're dang near slick and handle very well. they're maybe 1000 g. each, extremely burly, almost took moped levers to mount 'em! i'm thinking they'll be good insurance against the kind of damage that even the smallest road debris could cause @ 60 mph.
i'm leaning towards the 5x 48 hole w/ rhyno lites, just to have it as stout as possible. i guess one good thing is that i have no illusions about light weight... it'll just be better training for me... my primary road training bike is an 89 fisher cross bike from water pipe steel with 40c wtb cross tires & TR tubes... over 30 lbs! i like 'em heavy!
oh yeah, one last question: as far as spokes, most have said go for some type of butted spoke as this will allow the spokes to give a bit, thereby reducing breakage. some said use staright 14's as these would be stronger... what's the scoop? would any good tandem wheel builder know for sure which is better? and when you say butted, do you mean 14/15/14 or some type of 13/16/15(4) or something like that?
this tandem stuff is a bit new to me, but again i'm extremely thankful for everyone's time and responses! :)
smh
yeah, he recommended a velocity deep V rim, there was also one other designation about the rim, forgot it right now. he said that rim is plenty stout, although it's not disc specific, its spokebed area is reinforced quite a bit to make the hoop strong. he told me that hoop in a 40 hole (highest drilling in that rim) with a hugi hub would be the call, of course 4x lacing.
TandemGeek
Interesting... Yes, the newer Coupe's come with the Avid BB7 discs so this frame sounds like one of that particular pedigree.
The Shimano HF08 hubs are actually quite durable and you'll even see them on triplets sold by Tandems East. The thread-on adapter isn't all that hokey and they work quite well. In fact, we've been using thread-on disc rotors since '98 and I'm in the midst of updating our '02 tandem with an Avid BB7 which will be mated to a Phil Wood hub with left hand threading that will use a tread-on Dimension disc adapter. Minor adjustments in alignment can be made with the caliper or using cassette spacers. Removal is only a pain if you don't use the leverage of the wheel to "back-off" the adapter: basically, you lock up the rear brake and counter-rotate the rear wheel or back up the tandem which loosens the rotor/thread-on adapter. If it's really stubborn you an stick a metal rod through a rotor hole or the spider and carefully brace it against the rotor and rear chain stay and rotate the rear wheel backwards to loosen the adapter. However, you'd still need to use a conventional front disc hub.
The point in focusing on the Hugi hub & Rhynolite rims was to set a benchmark for bombproof at a reasonable mid-point, noting that using a Phil Wood or Chris King disc hubset with the same Rhynolite (or similar eyeleted rim) would be the high-end. Velocity's rims are a personal fav. of mine; however, having a few sets of them in our fleet -- two sets of 700c tandem road wheels built on Deep-V's and our 26" tandem off-road disc wheelset built on Aeroheat rims -- I'm pretty pleased with their durability and reliability. However, when looking for bombproof I look for eyelets.
Finally, on spokes, double butted 14/15/14 (2.0/1.8/2.0) properly tensioned and distressed will tend to outlast straight gauge spokes on tandem applications.
prairie*boy
Smh:
Why so hung up on the threads to disc adapter? Why not get the hugi disc hub (although the pictures of it on the web, look suspiciously like it is a threaded hub with an adapter).
Engineering lesson:
The ideal spoke is a triple butted..using your example 13/16/15(14). The 13 guage fills the hole in the hub to the maximum, the 16 guage provides flexibility in the center and the 15(14) guage threads are smaller which allows them to pass through the hub but larger than the 16 guage which provides the nipples more metal to be in contact with. This is the engineered - expensive - solution that provides strength where required and flexibility where stress is less.
The straight guage spoke is at the other end. The hole in the hub is no entirely filled as it needed to be large enough to allow the threaded end through (Rolled threads, as found on all quality spokes are larger than the base material). The center section is overly stiff which produces higher stresses at both ends...
but it is much less expensive to produce a straight guage spoke and if it is large enough (heavy enough) it won't fail.
The double butted spoke is the intermediate compromise....more expensive than the straight guage/less than the triple...has the flexible center of the triple which avoids the stress concentrations at the ends (which are the usual failure points)
Assumption: using same material and manufacturing process.
Personally, I have the double butted on one set and straight on the other set of wheels (but they are Shimano Sweet 16s and don't really count....)
Hopefully, I have answer some of your questions.
Prairie*boy
TandemGeek
The ideal spoke is a triple butted..
Just a side note: When DT introduced the Alpine III (2.34 / 1.8 / 2.0) the folks who build tandem wheels rejoiced. However, in many cases the 2.34mm spoke elbow is a tight fit for some hubs which has led to increased spoke breakage instead reducing it due to the elbow being overstressed (bent) during the wheel build or tensioning process. Spoke breakage at the elbow normally results from having play between the spoke and hub flange which is usually remedied with small brass washers placed under the spoke head during the build.
Again, the better wheelbuilders are usually aware of these subtle nuances and can advise on which combinations of hubs and spokes will provide the best results. Tell them what you're looking for in terms of how you intend to use the wheels and they'll usually be able to suggest the right combination.