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  1. #1
    Gear Combo Guru Chris_W's Avatar
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    Tough touring wheel suitable for a road tandem?

    Hi all, I'm looking for some advice about wheels. I need a temporary replacement for our front wheel on a Co-motion Speedster (reason described below) and I have a candidate that is currently on my touring bike; it is an XT hub, 36-hole Mavic A719 rim (700c), DT Swiss Competition double-butted spokes (2.0 / 1.8 / 2.0 mm or 14 / 15 / 14 gauge). It's about two years old and has done about 3,000 km (2,000 miles), it was hand-built, and has never given me any problems. I'll be mounting a 28mm Continental GatorSkin tire on it.

    I want to check with you guys that this wheel is tandem-suitable because we want to do one or more rides in the Alps at the end of this week with some friends that will each include three BIG passes, and so 3,000+ metres (10,000+ feet) of climbing and descending. There will be some high-speed riding involved - I've hit 80 kph (50 mph) on these descents on my single bike before, and one of the descents is 1,500 m (5,000 ft) of vertical drop, and so can take 40 minutes to get down. Fortunately, our team weight is under 300 lbs and the Swiss Alpine roads are generally very good quality with few pot holes, but these wheels could still be tested to their limit. So I'd like to know if there is any reason not to use this XT / A719 front wheel? For braking, we have front and rear Avid SD-7 V-brakes with Swisstop pads controlled by the captain, plus an Avid BB-7 with an 8" rotor on the rear wheel controlled by the stoker (used on the straight sections only) to give us more heat capacity on these descents.

    The reason for needing a replacement wheel is that I wrecked our rear rim yesterday. While getting hopelessly confused riding out of Geneva, we ended up on a road meant for trams and pedestrians only. While deftly avoiding the two sets of tram tracks, I found a 28mm-wide drainage ditch between the paving slabs that both tyres managed to squeeze their way into and out of in less than a second.

    Despite a slight wobble, we never went down, which I still can't quite believe, but we then discovered that we had a slow puncture in the front wheel and the rear rim was quite badly damaged. The front tube was easy to replace and fortunately I had a spoke key with me and managed to make the rear rim true enough to continue the ride with but had to set the rear brake pads quite wide apart to avoid any rubbing (fortunately, we still had the rear disc for braking on that wheel). Upon closer inspection at home in the truing stand, the rear rim is certainly toast. I'm currently looking at my options for sourcing a replacement, but in the meantime my plan is to move the front rim (which escaped without any damage) to the rear wheel and use my touring wheel on the front. I want this to be a temporary measure, but it may end up being there for 4 weeks, which could mean 600+ km (400+ miles). When I buy the replacement rim, I'll certainly be buying two of them so that I can solve the problem more quickly if something similar happens again.
    Last edited by Chris_W; 06-22-09 at 10:13 AM.

  2. #2
    Senior Member Stray8's Avatar
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    Quote Originally Posted by Chris_W View Post
    because we want to do one or more rides in the Alps at the end of this week with some friends that will each include three BIG passes, and so 3,000+ metres (10,000+ feet) of climbing and descending. There will be some high-speed riding involved - I've hit 80 kph (50 mph) on these descents on my single bike before, and one of the descents is 1,500 m (5,000 ft) of vertical drop, and so can take 40 minutes to get down.

    In my opinion, if you're going to do high speed descents then perhaps a wheel off a single bike is not as suitable as a tandem-specific wheel due to the stresses involved. Why take the chance if you can avoid it? If you're getting replacement rims anyway, why not have them built right away, or is there not enough time?


    .

  3. #3
    Gear Combo Guru Chris_W's Avatar
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    Quote Originally Posted by Stray8 View Post
    In my opinion, if you're going to do high speed descents then perhaps a wheel off a single bike is not as suitable as a tandem-specific wheel due to the stresses involved. Why take the chance if you can avoid it? If you're getting replacement rims anyway, why not have them built right away, or is there not enough time?
    I would normally agree with you, but this is one of the toughest single-bike wheels you can get, which is why I'm wondering whether other people think it is suitable. Unfortunately, because we live in Switzerland, there is no way to get a replacement rim very quickly. I have considered going to my local Trek dealer and asking how long it would take to get a Bontrager Race Lite Tandem front wheel in, but I'm expecting that will be no faster than getting a replacement rim (Velocity Dyad, 40-hole) shipped to me from an online store based in the UK or US.

  4. #4
    hors category TandemGeek's Avatar
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    Quote Originally Posted by Chris_W View Post
    So I'd like to know if there is any reason not to use this XT / A719 front wheel?
    None that I can think of, so long as it's as you said, a low-mileage wheel in good shape and you have the spoke tension double checked.

    The low flange isn't ideal, but I've got 12,000 miles on a low-flange White Industries Racer-X hub which is on par with the XTR front hubs for lighterweight teams, e.g., under 300#. The rim is basically what the old MAVIC T217 Trekking rim spec'd for tandems back in the late 90's evolved into so it's more than adequate, as is the spoke count at 36h.

    I only mention the spoke tension because it probably was built by someone who never expected it to be used on a tandem and it likely has lower spoke tension that would be more appropriate had it been built for a tandem. While I don't think you'd have any durability issues on your trip I think the handling could easily be a little sloppy UNLESS the wheelbuilder just had a habit of building extra robust wheels with tension set a the upper limits. If latter would the case, then you'd be golden.

  5. #5
    Gear Combo Guru Chris_W's Avatar
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    Thanks a lot, TG. What spoke tension would you recommend? I have a Park Tools spoke tension meter and have built several wheels myself (previously only for our single bikes), so I wouldn't mind tweaking it a little myself if necessary.

  6. #6
    hors category TandemGeek's Avatar
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    Quote Originally Posted by Chris_W View Post
    Thanks a lot, TG. What spoke tension would you recommend? I have a Park Tools spoke tension meter and have built several wheels myself (previously only for our single bikes), so I wouldn't mind tweaking it a little myself if necessary.
    You can go the easy route and make it consistent with the tension on your current front wheel (which is to say, go get a reading BEFORE you remove the rim).

    If your stock front wheel is 40h, go with a little higher tension on the 36h, but not in excess of the MAVIC spec. If you still have the Park tables, just figure out what type of spokes you have and go for the upper end of the tension range.

  7. #7
    Senior Member zonatandem's Avatar
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    Have used single bike front wheels more than once on tandems throughout the years; while we do not llive in Suisse we do have some big mountains here in Arizona (9,000+ feet). With 3 brakes and a decent wheel, would not cancel plans. We are a bit on the light side (+/- 250 lbs) and do credit card tours (about 22 lbs of stuff); however have never used more than 36H wheels on our tandems in the past 34+ years.
    Do recall that Swiss roads are usually in great shape even with some tough winters.
    May behoove you to order 2 rims so that you'll have a spare rim in stock; stuff sometimes happens . . .
    Enjoy the ride TWOgether!
    Rudy and Kay/zonatandem

  8. #8
    Gear Combo Guru Chris_W's Avatar
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    Once again, your advice has all been very useful, thanks.

    The 36 spokes on my XT / A719 touring front wheel were at about 100 kgf, and on the 40 spokes on the original tandem wheels (both front and rear) it was about 110 kgf. Although Mavic's web-site didn't provide the information, I found elsewhere on this forum that the A719 can take 110 kgf, so I took the touring wheel and evened up the tension a bit while increasing it to 110 kgf. I've now done a bit of stressing and fine-tuning and it looks like it will be good to go.

    Switching the front rim onto the rear was obviously a much bigger task. I took it slowly and built up the tension steadily. It now appears to be well dished, round, and true, and the spoke tension is again around 110 kgf, some final stressing and re-truing and it should work well.

    We'll take it out for a test ride this evening, and hopefully everything will be fine.

  9. #9
    Gear Combo Guru Chris_W's Avatar
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    A quick update. The 110 km (70 miles) and 3,200 m (10,500 ft) of ascent and descent went extremely well. The climbing was easier than we both expected it to be; even the second of the three passes, which averages 9% for the last 9km, and gets up to almost 2,500m altitude (8,200 ft) was OK. We used a lowest gear of 24 teeth front - 26 rear, which allows us to use a cadence of about 80 even when doing just 9 kph / 6 mph. We entertained ourselves and our three companions with our new stereo system (iPod nano plus a basic battery-powered speaker pack attached to the stoker's bars). My stoker can also be quite entertaining herself:



    The descents were a bit more chilly than the climbs (as you can see by our clothing change in the photo below). We touched 80 kph a few times, hitting 88 kph at one point (55 mph). Both rims stayed true and tight, no complaints whatsoever. It was nice to have the rear disc brake as well as the two rim brakes. We used all three intermittently, but the braking wasn't that intense because these major passes are fairly wide, generally straight roads (with some exceptions, as shown below). I think we would have been fine without the disc, but some of the more minor passes that we do require almost constant braking during the descents and then the rear disc is far more essential.

    Last edited by Chris_W; 06-30-09 at 03:21 PM.

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