[born2pdl]

I recently asked True Temper if it would make sense for their next tandem fork to be an aero fork. I thought I'd share the response. I also offered to share with him the forum's interest level on a new Alpha Q tandem fork.

"I do not know your aerodynamics background, but I can tell you mine. I am a mechanical engineer and studied fluid dynamics with additional coursework in aerodynamics. I have done work in the wind tunnel at Texas A&M (where John Cobb worked with Lance Armstrong in the early 2000’s) and more recently at San Diego’s Low Speed Wind Tunnel (where team CSC, Discovery, Phonak, and Cervelo did all their testing). As a Cat 1 roadie, and USAT triathlete, I also give a lot of thought to enhancing race performance through aerodynamics.

Enough background, now to your questions:
1) yes, aerodynamics are important for racing tandems, just as in single racers. But the importance on each individual component is less than on singles.
2) Yes, I am considering a fresh design for the tandem fork. It would be based on a shape that we developed with increased stiffness and aerodynamics. It is not specifically an aero fork though. It is a stiff, strong fork that happens to be more aero than the traditional fork.
3) The difference between forks is very small, aerodynamically. The worst modern fork I have tested measured .42 lbs of drag at 30mph, head on. The average fork (I have tested dozens of models from many manufacturers) is around .30 to .35 lbs at 30mph head on. Aero forks have been measured at as low as .175 lbs to .22 lbs. The current tandem fork has .32 lbs of drag at 30mph head on.

Because of the thin blades used on “aero forks”, they are not stiff laterally, so cornering performance suffers. Aero forks made for road bikes would not do well on a tandem, at all. No changes to the tandem will be made in the next 9 months or more. If a change is made, it will be the shape of the new stiff, aero fork, around .25lbs drag.

Fork drag on a tandem is about 2% of the total drag of two 150lb riders on a tandem at 30mph and no headwind. Switching to an aero fork would reduce total drag by less than ˝ percent. This is why there is not so much emphasis on Aero forks vs forks that handle well. Another way to say this is safe handling.

Feel free to post this information to the discussion groups as it may fuel further discussion and interest in future products which will be safe, and more aero as a bonus."

Bert Hull
Product Manager
True Temper Sports
(901) 746-2064

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[TandemGeek]

Classic Bert.... Gotta love it. It will be interesting to see what they come up with. The current X2 fork design is approaching it's 10 year anniversary.

[zonatandem]

And an excellent reputation it is!
17,500+ miles on our Alpha Q X-2 on our Zona tandem . . . and at ages 75/72 we are not overly worried about being more aerodynamic!
Thanx for a great product!
Pedal on TWOgether!
Rudy and Kay/zonatandem

[specbill]

Excellent letter, super specific and very educational. As a guy that enjoys the mechanical/ technical side of our tandem equiptment, is is great to see the aero numbers and the obvious degree of committed expertise on a part as critical as the forks on our twicers.
Needless to say, if they decided to build a new one, I would would not hesitate in the purchase of one as they certainly have their priorities and technical processes well in order.

Thanks for sharing this with our forum.
Bill J.

[aeroboy]

Fork drag on a tandem is about 2% of the total drag of two 150lb riders on a tandem at 30mph and no headwind

This really depends on the riders' positions. 2% seems unbelievably low to me. That is roughly equivalent of saying that the frontal surface of the bike as viewed from the front (+ drag for wheels and reduced drag for following tubes) is 1/50 the frontal surface of the riders as viewed from the front (+ reduced drag of the following rider) assuming similar coefficients of drag for the bike's tubes, etc. vs. the riders. Seeing as they're pretty upright on most tandems, the above statement might be true for some teams, but the figure for singles is known to be 10-30%. I used to think bike drag didn't matter much until I rode a Cervelo P3. For some riders, small ones who adopt very aerodynamic positions, the drag of a regular, round-tubed single bike with non-aero wheels can represent 30% of the total. I would guess that a typical road tandem under a pair of average sized riders with horizontal flat backs, could represent around 10% of the total drag. Cannondale = 15%:p

Also, the structures at the front of the bike are the ones that affect total bike drag the most. Aerodynamic drag is the main limiting factor of speed in most circumstances. In the future, as much or more attention will be paid to aerodynamics than weight, all frames will be aero, and components will be marketed on the basis of their aero properties as well as their weight. Changing just the forks by themselves won't likely produce a noticeable difference but everything helps when you're going against the clock.

[TandemGeek]

2% seems unbelievably low to me.

.... based on what you've read or personally seen in wind tunnel testing and computer models?

Seriously, the aerodynamic drag on a tandem team, tucked or not, is significantly higher than what you'd see on a single bike: 30% to 50% less aerodynamic as I recall. This is one of the reasons that component performance and marketing data for aero forks -- as noted by Bert -- as well as for wheelsets and other aero goodies need to be looked at with a critical eye when it comes to extrapolating that data as it applies to a tandem.

It's not to say that the aero goodies don't help, but the bang for the buck is pretty low because of the combined aero drag of the two riders. Money would be better spent on body wear and time spent working on a team's aero position and perhaps even the selection of stokers.

[aeroboy]

.... based on what you've read or personally seen in wind tunnel testing and computer models?

My mistake - I misread the original statement. I had it in my head that he was saying that the bike itself represented 2% of the drag and not the forks. 2% for the forks sounds realistic. BTW I didn't see him claiming to have tested tandem teams in the tunnel. He also doesn't state if the "worst modern fork" is a tandem one or not. Some tandem forks are huge in comparison to standard road forks.

The difference, though, between a good aero bike setup and a standard bike is astounding. Even if the difference between a tricked-out aero tandem, with NACA airfoil frame tubes and aero wheels, and a non-aero one is only half as noticeable as with a single, it would still be significant. The forks by themselves might be negligible, but it's like weight: if you were to cut the drag of every component and the frame, the sum of all the changes would make a significant difference I'm sure.