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I recently upgraded road bikes from a heavy one (25lbs+, 25mm) with thick tires to a very light one with skinny tires ( 16 lbs, 22mm ).

One thing that changed noticeably was the loss of the ability to ride without hands, which I like doing on LSD [long, slow, distance] riding so I can stretch out my spine every once in a while.

What are the factors involved with whether or not a tire starts to wobble when riding a road bike without hands?

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    Theres the whole geometry of the bike that affects twitchiness. For example, if you took a touring bike (which has different wheelbase, chainstay lengths, etc.) than a race bike, it'll be a lot more stable. – Batman Apr 12 '17 at 22:16
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    Consider changing your stretch library. I keep one hand on the bars, on the curve between hoods and tops, and I work the other side of the torso, then pedal a bit more, then stretch the other side. For a lower back stretch, steer with both hands but slide your pelvis forward and off the seat while either pedalling or coasting. 10 seconds of that helps immensely. – Criggie Apr 13 '17 at 2:05
  • Mainly stability is a function of the front fork geometry -- the angle and "rake". The length of the frame is also a minor factor, as is your center of gravity on the bike. Tires have a minor effect on stability. – Daniel R Hicks Apr 13 '17 at 2:15
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    As an aside, even most professional riders now use 25mm tires tires as it's been shown that they are more efficient on regular asphalt roads than smaller 22mm tires. This is because they absorb the imperfections in the road better and create a smoother ride. You probably should be using 25mm tires unless you are riding around a velodrome. It will both be much more comfortable and will actually be easier as well. – Kibbee Apr 13 '17 at 13:25
  • A factor that is probably not at play here but worth knowing about: If you run with front panniers, they can flop around on their rack and cause a lot of problems. They need to be somehow cinched down tight so they don't flop. – Daniel R Hicks Apr 14 '17 at 19:00
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A big cause of a high-speed shimmy-shammah is a mis-balanced wheel. You could also have an ovulated wheel from having the spokes tightened too much in a particular direction.

Another could be your headset bearing not being up to scratch with a lot of play. This also causes it quite often. Also, a bent frame will almost always make it impossible.

Also check your calipers are centred, as this rubbing on the wheel can cause unusual behaviours. Another thing to check is that the quick-releases are tight and that the wheels (front and back) are perfectly centred inside the frame dropouts. Check also that the fork itself has no kinks and hasn't got any play.

Also, make sure your body position on the bike (saddle height, angle, fore-aft adjustment and your handlebars) is optimal for you, as this will help your balance greatly. And, check the frame size is suitable for you. For example, I ride a frame-size smaller than I'm recommended to so that I have a high seatpost, and I can run slightly shorter cranks for faster speed, yet lower acceleration. (However, I can still achieve dank wheelies! :3 )

Forks are designed with a slight spring to them to absorb road vibrations, just like a leaf spring on old cars and vans. If a fork is made too stiff, it can be a challenge to do no-hands on a frame.

Honestly, it should merely take a bit of practice to do no-hands again on this bike, as I found out from going on a road bike to a criterium bike.

  • Funnily enough of my two bikes, the one with rubbish wheels is that one I can balance no hands for a short distance. It's got a huge amount of trail though, and the other also has a D-lock carried on the (stiff) fork. All these factors interrelate – Chris H May 12 '17 at 12:10
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  • Bike geometry will be the biggest factor

  • Head tube angle is a big factor

  • Tire and rim weight is also a factor

From physics you have less angular_momentum with lighter tire + rim. The vector points out from the axle and magnitude is based on velocity and weight. So if the tire is 1/2 the weight you have 1/2 the stability. Conservation of angular momentum is what lets a top spin.

  • Load on the front wheel is another factor. Riding hands-free takes load from the front and increases likelihood for high-speed wobble or shimmy. – Carel Apr 13 '17 at 8:16

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