Choose the best tandem bicycle wheels for your tandem. Be sure to make an informed decision.
Just what makes tandem bicycle wheels so special? Lets look and compare them to standard bicycle wheels.
Your typical one person bicycle and rider will weigh in the neighborhood of 170-200#, depending on the rider obviously. Your tandem team can easily weigh 350#. This is a lot more stress on the whole wheel assembly.
Taking the super light carbon wheels off your road bike and putting them on your tandem isn't the greatest idea in the world. These wheels are not designed to stand up to the forces exerted by a tandem.
Tandem Wheel Construction
Foregoing the discussions on the merits of which way to lace your spokes (we'll look at one manufacturer's different approach later), a tandem wheel is not just a standard bicycle wheel. Let's look at the different parts of the wheel:
Built with a beefier flange and wider axle spacing the tandem hub is specifically designed to take the extra stresses that are generated by a tandem wheel. This is becoming more and more the case with disc brakes.
Rim brakes would exert the forces on the rim itself to slow the bike. The disc brake transfers that force to the hub and the spokes. These components must be even more durable to hand this extra force.
- RimDue to the extra weight put on the wheel and the extra spoke requirements (most cases with your exceptions), tandem rims are specifically designed to handle the stresses placed upon them. Not merely a re-packaged road wheel, a tandem rim has extra material in the places where it is needed most. Take a look at this cross section of a Davinci V-22 rim.
You see from the explanations that a lot of thought and time went into making sure the rim was just right for the use on tandem bicycle wheels.
I have these wheels in a 26" diameter on my Davinci Joint Venture. I have had the bike for about 6 years and have never had to true the rims!
The correct spoke tension on tandem bicycle wheels cannot be overstated. The number one cause of wheel failure is insufficient spoke tension. As a wheel rolls, the tension on spokes change due to the loading. If the tension on spokes is not correct, they will flex too much as loaded and can become brittle and break. Also they can deform at the end, either the hub end or the nipple end and this can cause failure as well.
The subject of actually building the wheels is beyond the scope of this page. If you want to learn everything there is to know about building a wheel, The Bicycle Wheel 3rd Edition by Jobst Brandt is what you need to read. He is a mechanical engineer (Stanford) with extensive experience, having worked for Porsche automobiles, Stanford Linear Accelerator Center, Hewlett-Packard and Avocet bicycle products.
26" or 700c?
Boy is this a can of worms. There is a raging debate on quite a few newsgroups about which is the best size for tandem bicycle wheels. Personally, I like the 26" on the tandem we ride. Besides fact that the wheels have never been trued in all the time I have owned the bike, let's look at a very well written article.
Condensed down from a long page here is what Bill McCready, president Santana Cycles, Inc. has to say.
"First, the physics of the 26vs700 discussion are only meaningful if we standardize the other variables: rim width, tire width, tread pattern and inflation. To perform comparisons here at Santana we used two diameters of otherwise identical Avocet tires mounted to two diameters of otherwise identical Sun rims. We installed these wheels in frames built from identical tubesets. The frame geometries differed only to the degree that the resulting bottom bracket heights were equal. Components other than the tandem bicycle wheels were identical. We inflated the tires to 115psi.
Between 700c and 26" there is no difference in the AREA of the contact patch. "Pounds per square inch" means just what it says. If we know the loaded weight of a tandem and the inflation of the tires we can accurately predict the area of the contact patch. Actually, if we know any two of three variables (weight, inflation and the size of the contact patch) we can calculate the third. Tire diameter has no effect.
Tire diameter does, however, effect the SHAPE of the contact patch. Because the 26" tandem bicycle wheel has a diameter that is 11% smaller (559mm vs 622mm bead seat diameter) the resulting contact patch or footprint of a 26" tire is both 11% shorter and 11% fatter.
The shape of the footprint affects handling. With all other things equal (especially fork rake and bottom bracket heights) the rounder contact patch of a 26" front tire dramatically improves low speed maneuverability. Conversely, high speed stability is enhanced by the longer and narrower footprint of a 700c front tire. While the two tires will feel different in a hairpin curve--the smaller tire corrects quicker and the larger tire holds a smoother line--because cornering speed is a function of area and grip, maximum speed through a sharp turn is the same.
If they both corner at the same speed, is either tandem bicycle wheel size more efficient? Yes. Because of its smaller diameter, the 26" tire is forced to deform more to apply its equal-area-yet-fatter contact patch to the ground. When we put the same weight on both bikes it's easy to observe more "bulge" in the sidewall where the 26" tires meet the ground. Greater tire deformation (sidewall flex and tread squirm) equals greater internal tire friction; the leading cause of rolling resistance.
Why not compensate for the extra rolling resistance by inflating 26" tires to higher pressures? While many of us fear blowouts, the leading justification for lower pressures (and wider tires) is COMFORT. Because the smaller tandem bicycle wheels start with a comfort handicap (smaller wheels are less compliant), higher pressures won't be a popular option.
If rolling resistance effects speed, why do leading triathletes use 26" tires?
For certain events (triathlons, track pursuits and time trials) rolling resistance is less important than the frontal area of the tire--in these no-slipstreaming events a solo bike with 26" wheels has an advantage. But for pack cycling events (criteriums, sprints and road races) the aerodynamic advantage of the smaller tandem bicycle wheel is not great enough to offset increased rolling resistance.
Is the wheel efficiency equation different for tandems? Yes. Compared to a solo bike, a tandem tire's frontal area is roughly half as important (twice as much power to push each tire through the wind). Further, a tandem's doubled weight can make sidewall deformation and rolling resistance twice as critical. Subsequently, there are no on-road races where a tandem with 26" wheels will be faster.
If a 700c tandem is faster, why does Santana offer nearly twice as many models with 26" tandem bicycle wheels?
Even though a 700c wheel is actually slightly heavier than a 26" wheel, the difference in "bash-strength" (the ability to survive impacts) is enough to render a 700c wheel damned near useless for rutted jeep trails and urban curb-hopping.
If you want one tandem that does it all, 26" is the only tandem bicycle wheel size that makes sense. While a 26" mountain tandem can easily be converted into a pavement scorcher that will keep you abreast of the fastest roadies on their solo bikes, a tandem with 700c wheels is too fragile for real mountain biking.
And even if you never plan to venture off pavement, the "bigger is faster" argument is limited by the size of the riders--tandems built around 700c tandem bicycle wheels are inefficiently tall for captains shorter than about 5'7"."
As Santana sells the same bikes in a 26" version and 700c version, I would say his comments have some real merit behind them.
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