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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 06-28-11, 03:51 AM   #1
PMK
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Tandems and Faster Wheels / Rims

A recent ride saw the demise of our Velocity Dyad 40 hole rear rim. The rim developed circumferential cracks adjacent to the spoke holes.

I ordered another of the same rim, just being lazy. It should arrive soon and will be an easy swap.

When I noticed the cracks, it was after the Saturday ride in Vero with the PANTHERS tandem club. Sunday morning, after lockwiring the spokes to prevent a possible drivetrain lockup, I was talking with Bob Thompson, and he recommended having some taller profile wheels built.

I do have another set of hubs, and am now wondering, without going the cost of specialty wheels, or the price of carbon rims, what is an optimum rim height for the 25mm or 28mm tires. Seems it's a weight vs aero tradeoff.

BTW, my hubs are 40 hole, so whatever I decide will still be 40 spoke wheels.

Veocity offers a few possible choices.


Having discs front and rear, we could run these 43mm tall, 19mm wide / 770 gram

http://www.velocitywheels.com/store/...?pID=20&cID=18



These were popular on some bikes at Vero 30mm tall, 19mm wide / 518 grams

http://www.velocitywheels.com/store/...?pID=23&cID=18



Another possibility and wider 32mm tall, 24mm wide / 650 grams

http://www.velocitywheels.com/store/...?pID=21&cID=18



Our current rims are these. 22mm tall, 24mm wide / 480 grams

http://www.velocitywheels.com/store/...?pID=24&cID=18

This is a balance of cost vs performance for recreation type rides, group events and training rides.

Also open to any good articles or links on this to save you folks some keyboard strokes.

Thanks
PK
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Old 06-28-11, 05:09 AM   #2
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I had the Velocity Dyad wheels and switched to the Velocity Deep V you have listed. I really like the deep V,s they are a solid wheel and they seem to roll better. I have them on White Ind. hubs.
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Old 06-28-11, 07:01 AM   #3
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IMHO, it's better to focus on durability than speed with tandem wheels. With that in mind, I believe the Deep V Velocity rims are supposed to be pretty stout.
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Old 06-28-11, 08:59 AM   #4
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We're a 350 lb. team and our daVinci is using the stock V-22 40h wheels. These are very affordable and seem bullet-proof.
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Old 06-28-11, 10:42 AM   #5
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It is interesting that you have disc brakes and have this rim problem. It is my belief that disc brakes add additional stress to the spokes and rim.
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Old 06-28-11, 11:01 AM   #6
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Deep V's on Phils

We've had Deep V's on Phil Wood hubs for the last year or so, after our Rolf's failed yet again. Liking them a lot, but way too early to claim anything about lifespan, etc. We also have a pair of daVinci V-22s on White Ind. hubs that were the originals on our Erickson, but these have a history of breaking spokes despite a complete rebuild. 330 lb team.

Last edited by 2frmMI; 06-28-11 at 11:04 AM.
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Old 06-28-11, 11:31 AM   #7
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Ditto on the Deep"V" and White Ind hubs. Roll fast and strong.
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Old 06-28-11, 03:26 PM   #8
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It is interesting that you have disc brakes and have this rim problem. It is my belief that disc brakes add additional stress to the spokes and rim.
No doubt the discs do add more stress. Some brake manufacturers specify how they want the wheel laced.

I have no babied these wheels, and I likely run too much tension but prefer no flex on the back.

I'll cut a cross section and see, maybe the spoke holes were counterbored too deep, then again, maybe not.

Any info about the aero benefits based on rim height? The Zipps get pretty tall in the name of speed, just curious how it all relates.

PK
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Old 06-29-11, 07:56 AM   #9
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I have no babied these wheels, and I likely run too much tension but prefer no flex on the back.
Tension won't affect flex, as long as the spokes aren't going slack. (But if spokes are going slack, the wheel isn't going to last anyway).
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Old 06-29-11, 10:49 AM   #10
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IMO if you're not checking spoke tension with a tension meter, and keeping it at the rim manufacturer's recommended tension, no tandem wheel will last. I'm also a firm believer in using 14-15 double butted spokes, not straight gauge. I've never broken a spoke or had a rim crack on any bike. Of course I'm not running Rolfs on our tandem, though I've run Rolfs on one of my singles for many years. On our tandem we run ordinary 36H wheels, with a variety of rims. We're a 310 lb. team, and have toured loaded on the same wheels we use for sport rides, without any issues. We have rim brakes.
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Old 06-29-11, 04:03 PM   #11
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IMO if you're not checking spoke tension with a tension meter, and keeping it at the rim manufacturer's recommended tension, no tandem wheel will last.
Without coming off as a smarty pants, this Manufacturers Recommended Tension should be found where?

The rims were 700c Velocity Dyads

The US distributors site is here

http://www.velocityusa.com/default.asp?contentID=584

The Australian site is here

http://www.velocitywheels.com/store/...ies.asp?cID=18

I'll gladly use a tensiometer for the rebuilding of the wheel, could not find the spec on either site, could you please help?

PK
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Old 06-29-11, 04:37 PM   #12
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Tension won't affect flex, as long as the spokes aren't going slack. (But if spokes are going slack, the wheel isn't going to last anyway).
Not to cause a debate, but if the tension has slackened slightly, I can feel the back end sway. We are no powerhouse or hardcore riders, but for us it can be felt.

I did a bit of looking and this seems to note wheel flex and factors that can have an effect. If the report is flawed that's fine too.

http://www.rouesartisanales.com/article-23159755.html

Based also on disc brake manufacturers recommendations, they want high tensions.

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Old 06-29-11, 04:38 PM   #13
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Thank you all for the input, now I just need to decide what route to take.

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Old 06-29-11, 05:38 PM   #14
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Originally Posted by PMK View Post
Without coming off as a smarty pants, this Manufacturers Recommended Tension should be found where?

The rims were 700c Velocity Dyads

The US distributors site is here

http://www.velocityusa.com/default.asp?contentID=584

The Australian site is here

http://www.velocitywheels.com/store/...ies.asp?cID=18

I'll gladly use a tensiometer for the rebuilding of the wheel, could not find the spec on either site, could you please help?

PK
What I've done is email the rim manufacturer. I've always gotten a response. This is a response I received from Velocity:

Quote:
We build all of our wheels at the same spoke tension. Spoke tension is measured in Kilograms of Force (KGF). We build the front wheel between 105 115 KGF, and the rear between 110 120 KGF. I hope this helps, let me know if you have any further questions.

Thanks for riding Velocity.
MD
Matthew Dennis
Customer Service/Sales
Velocity USA
616.243.3400
md@velocityusa.com
On my CK rear hub I went ~115 KGF both sides, since it's almost symmetrical. I think I went 110 on the front. On an asymmetrical rear hub, you go 115-120 DS, and then whatever on the NDS that centers the rim. So it doesn't matter how many spokes, doesn't matter which rim. I don't know of a traditional rim that wants tensions different from these, though my knowledge is limited to Velocity and Mavic. In general, I've found taller section rims build up stiffer and stronger wheels. Hence we bow before the beauty of the Deep V for up to 28c tires.

These tensions will really stretch a 14-15 DB spoke, which is a good thing.
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Old 06-29-11, 07:56 PM   #15
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Since you live in Florida and probably seldom ride in the mountains or hills the Deep Vs make since. About two years ago Velocity got some bad aluminum and had several rims crack. I had one of those rims crack in 950 miles although mine cracked around the side wall. Velocity was very good about replacing the rims. They even replaced my front rim which was not cracked but bought at the same time. I took the wheels to Velocity USA in Grand Rapids and had the wheels rebuilt with new rims for no charge. The rear rim that I have had last the longest (by far) is a Velocity Dyad with a disc brake.
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Old 07-01-11, 03:05 PM   #16
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Quote:
Originally Posted by Carbonfiberboy View Post
What I've done is email the rim manufacturer. I've always gotten a response. This is a response I received from Velocity:

On my CK rear hub I went ~115 KGF both sides, since it's almost symmetrical. I think I went 110 on the front. On an asymmetrical rear hub, you go 115-120 DS, and then whatever on the NDS that centers the rim. So it doesn't matter how many spokes, doesn't matter which rim. I don't know of a traditional rim that wants tensions different from these, though my knowledge is limited to Velocity and Mavic. In general, I've found taller section rims build up stiffer and stronger wheels. Hence we bow before the beauty of the Deep V for up to 28c tires.

These tensions will really stretch a 14-15 DB spoke, which is a good thing.

Thanks for those specs.

Replacement Dyad rim arrived. Borrowed the tensiometer from my buddies shop. With both tire pressures at about 25 psi, I checked the existing wheel builds.

Front is spot on to the range you published, with an inflated tire it will drop some. Possibly to the lower end of the range or below that.

The rear wheel, which still runs true, with a deflated tire, was less than 10 kg above the specs you provided. Adding 120 psi to the tire will likely place those tensions in spec.

Good and bad, bad is the rim failed, but nothing serious. Good is that even though I don't always use a tensiometer, I can still get the spokes tensioned without one. I'll buildup the wheel this weekend. I'll compare as I go to see if what I like in regards to tension and how the bike rides compares to how the tensiometer reads them.

Not one complaint about the Dyad rim, and for all the wheels I have built for myself, wife and friends, this only the third to crack a rim. The others were high mileage MTB wheels with brake tracks almost worn through.

Thanks for those specs. BTW, did they mention if that is for Velocity hub with any particular brand of spokes.

Thanks
PK
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Old 07-01-11, 05:52 PM   #17
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Thanks for those specs.

Replacement Dyad rim arrived. Borrowed the tensiometer from my buddies shop. With both tire pressures at about 25 psi, I checked the existing wheel builds.

Front is spot on to the range you published, with an inflated tire it will drop some. Possibly to the lower end of the range or below that.

The rear wheel, which still runs true, with a deflated tire, was less than 10 kg above the specs you provided. Adding 120 psi to the tire will likely place those tensions in spec.

Good and bad, bad is the rim failed, but nothing serious. Good is that even though I don't always use a tensiometer, I can still get the spokes tensioned without one. I'll buildup the wheel this weekend. I'll compare as I go to see if what I like in regards to tension and how the bike rides compares to how the tensiometer reads them.

Not one complaint about the Dyad rim, and for all the wheels I have built for myself, wife and friends, this only the third to crack a rim. The others were high mileage MTB wheels with brake tracks almost worn through.

Thanks for those specs. BTW, did they mention if that is for Velocity hub with any particular brand of spokes.

Thanks
PK
That's the whole body of the email. My guess is that hub and spokes don't matter to the spec, just to the longevity of the wheel. I also go through brake tracks here in the PNW, so I've probably never had a wheel go over 10,000 miles, except maybe the Open Pro Ceramics on my rain single. Could be why I've never had a rim crack.
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Old 07-01-11, 07:31 PM   #18
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Agreed. Disc brakes on a tandem, with much higher bike and rider mass than on a single bike, will cause much higher stress at the rim-spoke juncture.
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Old 07-02-11, 07:15 AM   #19
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I'm not 100% convinced but pretty certain the rim failed from fatigue / use.

So now back on topic, I am rebuilding the original Dyad wheel assembly with a new Dyad rim.

For my other wheels I'll build up, I have hubs already, just need rims and spokes.

I have suggestions of a Mavic CXP33, Velocity Deep V's and I myself am considering a B43 possibly for the rear.

So anyone have thoughts about the trade off of aero vs weight. Hearing the trailing edge or rear wheel matters most, and also that the heavier rim on the back won't be noticed as much for weight initially but may after a couple of hours of riding.

PK

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Old 07-02-11, 12:13 PM   #20
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Rodriguez says they run heavier rims and more spokes on tandems with disc brakes. Now just because a rim is heavier, doesn't mean it has more wall thickness at the nipple. Obviously the rim can be just wider or taller. We ride with another tandem with a rear disc that has cracked a Dyad. I think it's worth more research. Another thing that might be in favor of the Deep V or similar for this application is that the rim shape might act to prevent flexing and thus cracking. Of course those two rims are designed for different tire widths, so that will be a factor. I put on a CXP33 rear rim recently, because I needed a rim that day and that's all I could find locally. It's an eyeleted rim. Maybe the eyelets spread out the stress, maybe not.

I don't think rim weight is as important on a tandem as it is on a single, at least for us. We never accelerate the bike quickly, so it doesn't seem like an issue unless the team is strong and climb a lot out of the saddle. I'm very happy with rims which don't need much spoke adjustment and which don't come out of true when I have some little issue on the road. So far, the CXP33s and the Deep-Vs have been the best at that. Haven't run Dyads. Since a Deep-V is 40g heavier than a Dyad and narrower, I'd sure think it would be stronger. The aero is a bonus, IMO. On a tandem, I'd guess that you're mostly faster with a heavier aero rim than a lighter flat rim, since a tandem is often faster on the flat than a single. Be interesting to hear what others think.
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Old 07-02-11, 01:36 PM   #21
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Often heard...

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Agreed. Disc brakes on a tandem, with much higher bike and rider mass than on a single bike, will cause much higher stress at the rim-spoke juncture.
Do you mean higher stress than rim brakes? I have often heard this, and it seems somehow intuitive, but I would sure like to see it explained in diagrams, numbers, vectors, forces, etc. I have tried to think through the fact that when braking, the friction that stops the bike is between the tire and the road. The weight is almost entirely the riders who connect to that tire/road interface via their saddles, handlebars and pedals, through the frame and fork to the hubs, to the spokes, to the rims. So how can there be more stress on the rim spoke junction for one brake over another? Can an engineer or physicist give a lesson here? Curious minds need to know.
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Old 07-02-11, 02:50 PM   #22
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Originally Posted by Carbonfiberboy View Post
Rodriguez says they run heavier rims and more spokes on tandems with disc brakes. Now just because a rim is heavier, doesn't mean it has more wall thickness at the nipple. Obviously the rim can be just wider or taller. We ride with another tandem with a rear disc that has cracked a Dyad. I think it's worth more research. Another thing that might be in favor of the Deep V or similar for this application is that the rim shape might act to prevent flexing and thus cracking. Of course those two rims are designed for different tire widths, so that will be a factor. I put on a CXP33 rear rim recently, because I needed a rim that day and that's all I could find locally. It's an eyeleted rim. Maybe the eyelets spread out the stress, maybe not.

I don't think rim weight is as important on a tandem as it is on a single, at least for us. We never accelerate the bike quickly, so it doesn't seem like an issue unless the team is strong and climb a lot out of the saddle. I'm very happy with rims which don't need much spoke adjustment and which don't come out of true when I have some little issue on the road. So far, the CXP33s and the Deep-Vs have been the best at that. Haven't run Dyads. Since a Deep-V is 40g heavier than a Dyad and narrower, I'd sure think it would be stronger. The aero is a bonus, IMO. On a tandem, I'd guess that you're mostly faster with a heavier aero rim than a lighter flat rim, since a tandem is often faster on the flat than a single. Be interesting to hear what others think.
The additional rim weight is not in regards to added strength around the spoke holes. My current thoughts are to run the 43mm tall B43 rim on the rear, and this is disc specific with no brake tracks, and run a non machined (no machining for the brakes just anodize) Deep V up front with a front disc setup. The additional weight is probably mostly in the height, but the 43mm tall rim is disc only so maybe the spoke bed is beefed up.

This would give a 770g 43mm tall rear rim, and a 518g 30mm tall front rim, both are 19mm wide.

PK
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Old 07-02-11, 03:59 PM   #23
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Do you mean higher stress than rim brakes? I have often heard this, and it seems somehow intuitive, but I would sure like to see it explained in diagrams, numbers, vectors, forces, etc. I have tried to think through the fact that when braking, the friction that stops the bike is between the tire and the road. The weight is almost entirely the riders who connect to that tire/road interface via their saddles, handlebars and pedals, through the frame and fork to the hubs, to the spokes, to the rims. So how can there be more stress on the rim spoke junction for one brake over another? Can an engineer or physicist give a lesson here? Curious minds need to know.
Engineering background here, not a PE. With rim brakes, the only braking force on the spokes is that forward pressure on the hub caused by the bike's deceleration. That's maybe .5g max? So half the weight of the bike, riders, etc. Not so much really, because you'll pull more g's than that hitting a big bump. And all the spokes on the trailing edge of the wheel are involved in that deceleration, both leading and trailing spokes.

But with a disc, you have that same deceleration force with the added stress on the spokes cause by the hub "winding up" the wheel. The force of the caliper on the disc has to be transferred to the hub and then to the rim by only the trailing half of the spokes, before the rim can transfer it to the tire and thus to the road. Because only half the spokes are involved in preventing the wheel from winding up, it seems to me that the deceleration force on the spokes could be twice as high with a disc as with rim brakes.

To put that in perpective, say we add a total force of 1g to the spokes, half distributed among all the trailing spokes, and half among all the spokes on the trailing edge of the wheel. From this earlier discussion, we see that manufacturers spec ~110 KGF or over 240 lbs. preload on each of the 72 or more spokes involved in the deceleration. So it's not that great a percentage increase or decrease in tension. So we shouldn't break steel spokes. However we might deform the aluminum rim slightly, and aluminum is sensitive to fatigue There is great resistance on the part of cyclists to the manufacturer adding a lot of extra weight to the rim to prevent fatigue.
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Old 07-02-11, 04:04 PM   #24
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The additional rim weight is not in regards to added strength around the spoke holes. My current thoughts are to run the 43mm tall B43 rim on the rear, and this is disc specific with no brake tracks, and run a non machined (no machining for the brakes just anodize) Deep V up front with a front disc setup. The additional weight is probably mostly in the height, but the 43mm tall rim is disc only so maybe the spoke bed is beefed up.

This would give a 770g 43mm tall rear rim, and a 518g 30mm tall front rim, both are 19mm wide.

PK
The Velocity sections show the spoke bed being heavier in the B43 and Deep V. The Dyad also shows thickening, but that area looks narrower on the Dyad. Just for fun, I bought my last Aeroheard front rim unmachined and sanded off the anodizing myself, hoping to save some rim material, my guess being that they anodize them all then machine, hence $5 cheaper for unmachined. BTW, don't try that yourself unless you have professional sanding equipment like I do.
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Old 07-02-11, 09:50 PM   #25
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I do have another set of hubs, and am now wondering, without going the cost of specialty wheels, or the price of carbon rims, what is an optimum rim height for the 25mm or 28mm tires. Seems it's a weight vs aero tradeoff.

This is a balance of cost vs performance for recreation type rides, group events and training rides.
Check the Zipp or HED sites, I believe one has some data relating rim height to drag. IIRC, aero benefits kicked in at 30mm rim height and modestly improved as rim height increased. Below 30mm rim height didn't play a significant role in reducing drag.

Assessing the trade-off of weight vs. aero is highly dependent on individual riding demands/goals: Weight is pretty unimportant for pure time trial applications, but becomes more important for climbing or pack riding/road race applications (where the ability to easily accelerate is prized).

You must be routinely riding at about ~ 22 MPH on the flat for aero benefits to start to kick in. At 25+ MPH they will become substantial (Just my rule of thumb, FWIW).

Typically recreational cyclists overemphasize aero and underemphasize weight in making equipment decisions (again, FWIW).
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