onroule

Hi everyone,
Just wondering, is tandems are more sensitive to speed wobble than single bike? It happend to me once on a single and was not fun at all. Any of you had this bad experience on a tandem?

Bye,
Michel

Co-Mo

We drive a Co-Motion speedster. We've had it a tad over 50mph and had no wobble at all.

Steve Katzman

No it has never happened to me either. I would think that the likelyhood of it happening on a tandem would be much lower than for a single bike, due to the extra weight of the two riders and the sturdier structure required of a tandem.

TandemGeek

There are a number of different factors that can cause the front end of a bicycle to oscillate (aka, shimmy or wobble); frame frequency, a weak top tube, front wheel/tire problems, and of course road and environmental (cross wind) conditions.

With regard to pure and simple frame shimmy, as Steve notes, the likelihood of experiencing shimmy on a properly designed and built tandem in good repair is significantly reduced by three factors:

1. Given the length and mass of a tandem, it will have a natural freqency that is much lower than a single bike and less likely to matching the frequency of any road vibration on high speed descents.
2. The front-ends of most tandems produced today are very stiff and overbuilt often with the addition of a 3rd, internal tube running between the head and seat tube.
3. The captain's placement mind-frame acts as a vibration dampener which is even more important that merely the extra weight of a second rider.

However, there are still some double diamond frames running around out there that, if ridden by large teams, could easily exhibit a front wheel shimmy at even moderate speeds as would any tandem with faulty or weak welds at the head tube. A weak or mis-aligned fork could also cause a recurring shimmy condition is not corrected.

Other causes:

A front wheel that is out of true or fitted with a tire that is out of round could also create a "wobble" unrelated to frame frequency, but with similar handling implications and no on-bike remedy (e.g., a frame shimmy on a single bike can usually be stopped by a slight adjustment in speed or bracing the top tube with your leg). In some cases, it is the application of the rim brakes on an out-of-true rim at high speeds that will induce shimmy.

A strong oblique or cross wind gust could also cause the start of some momentary front wheel oscillation/shimmy that the captain must cancel with a strong steering input, less it continue unchecked. Again, the additional mass of a tandem team and the captain's "dampening" effect will mitigate some of the shimmy.

There are a few other causes but the above capture the most common.

Bottom Line: A modern, high-performance or premium grade tandem is inherently resistant to frame shimmy that will sometimes occur on personal bikes. However, there are other things that can cause a tandems front-end to shimmy that a Captain must always be alert for and respond to.

onroule

Thanks for your answers. At first, I was thinking that a longer frame will be more succeptible to oscillation but as you are saying. a longer frame will resonate at a lower frequency thus less likely to happend because od road induce vibration. Of course, other factor like out of true wheel could create some vibration problem but these are usually controlable element.

Thanks,
Michel

zonatandem

Howdy from Tucson!
Usually not an issue on a tandem. Longer wheelbase and extra poundage and re-inforced frames (internal lateral, twin laterals, extra uptube, etc.) make for non-wobble tandems.
We've blown a front tire at 30+ mph on a tandem . . . yes it was a bit scary and like riding a bronco, but it was quite controllable. Blowing or flatting a tire can cause momentary concern, but relax, don't panic, and bring tandem to a stop by using the brake on the opposite wheel of where flat/blowout occurs.
Pedal on!

TandemGeek

Yes, but be mindful that applying the rear brake on a tandem will still load-up the front wheel (damn physics) so a steady, controlled use of the rear brake is called for vs. an aggressive grab of the brake lever.

Trivia: If you've ever heard someone who rides motorcycles or who races automobiles talking about "trail braking" this is what they're referring to. It's used to help keep the front tire(s) loaded up as you approach the apex of a turn so that the front end stays "stuck" while limiting understeer. There's a lot more to it than that, but the point is, applying the rear brake on a tandem will still cause loading on the front wheel; the more you weigh or the faster you're going, the higher the loading that will occur.

stever

got whole tandem wobble with yak bob in poland last year

the side of the road sorta bevels up

lost concentration for a split second
wobbled front wheel then corrected it and the back end wobbled

it was a close one at about 25mph whew :-)

Trsnrtr

We've owned 5 different tandems (see list) and have exceeded 50 mph several times on all of them. None of them exhibited high-speed wobble.

1978 Motebecane
1979 Paramount
1991 Rodriguez
1992 Santana Noventa
2002 Santana Sovereign

Big H

Hi Zonatandem,

Hoe gaan dit. Hier by ons word dit nou wnter.

We blew a front tyre at 70km/h (44 mph I think). Verrrrrry scary. An important thing to rememer is that like with any other vehicle if you blow a tyre is that everything has to happen slowwwwwly!!!! Keep your line and do not do anything erratc or sudden. A damaged rim is less expensive than a mouth without teeth!!!! The blown tyre will in most cases fold under the rim and if you keep your line support the rim.

Keep yhose wheels spinning!!!

Big H

zonatandem

Hi Big H!
Alles gaat nog goed met ons! Het is hier a warme lente; Zondag wordt het 90 graden Fahrenheit (omtrent 33 C)!
For us non-Suid Afrikaaners or Dutch speaking folks: Everything is fine here. We are having a warm spring. Sunday will be 90 degrees!
We will be doing the Tour of the Tucson Mountains, a 58 mile event and expect 1,000 riders. It is one of our favorite rides in Arizona. Sunscreen and lots of water!
Glad you survived the blowout Big H! Yes, they are quite scary!
Back to hi-speed wobbles. On my Merlin single bike last August I was descending a paved curvy canyon road near Logan, Utah. Developed a hi-speed rear wheel wobble, felt like tire was loosing air. Sat upright to catch the wind and slow down while simultaneously clamping both knees to the top tube. Oscillation got worse. Lightly tapped front brake, and by then I was doing about 30mph. Bike swung violently and I lost control, rolled over the bars; rider behind me rode over me and crashed and cracked his helmet. I had shoulder broken in two places.
After crash, immediately checked the weel and felt like maybe lost about 10 lbs of air out of a 140 lbs inflated Vredestein tire. Pedaled home, quite a bit slower, and drove then to hospital.
Tire did not loose any more air; road surface was newly paved, ultra smooth, no debris, no crosswinds. I was in the drops and tucked in, when wobble occurred. Still can not figure out 'why.' Harmonics of course could be the culprit.
At age 70 (then) I was glad it was not any worse.
However, now I still have sort of a built-in reaction when descending hills and approach the 30 mph nark. Maybe in my 'old age' I no longer think I am indistructible!
Have had a couple other bikes do that but was able to pull it off without crashing.
Moral of the story: If you don't do nothing, you'll die anyway!
Pedal on TWOgether!
Rudy & Kay/Zona tandem