chfong

Hello,

What makes riding one bike hands-free possible, while on another
bike the hands-free is very difficult if not possible. Could it be the saddle,
the bike geometry like the seat and steering angle , rake ,
bottom bracket height, etc.. ??

CHF

krome

Well, a bike with the fork installed backwards in inherently unstable, and cannot be ridden hands free. It has to do with the rake of the fork. I believe it is the way the geometry is, such that as a bike is moving forward, as the bike leans, the front wheel turns into the lean, getting underneath the center of gravity and correcting the lean. Then the bike would lean the other way and again the front wheel turns into the lean and corrects. A properly made bike will be dynamically stable, due to the gyroscopic action of the wheels and the geometry of the fork/head tube. There are other variables which make a bike more stable or less stable, but the fork rake and the rotating wheels are the key.

I'm sure someone can explain it better than me, but this is my observation.

hillyman

A combination of bravery and stupidity

2manybikes

It depends on how good the wheel alignment is.

Could be the fork, the frame, a wheel not on straight, etc.

flyingscotsman

+1

same time

Headset needs to be adjusted properly - no binding and no play.

bmclaughlin807

I think it's mostly just experience with the bike in question. After the last thread like this, I went out and tried to ride my commuting bike hands free (on a weekend) and couldn't do it. I was puzzled for a while, but the next week on the way to work, thinking nothing of it, I grabbed my water bottle, leaned back and took a nice, long drink. No hands on the bars.

That's when it hit me: 95% of the time that I'm on that bike I have my laptop strapped to one side of the rear rack. I'm so used to it I didn't even notice, but I compensate automatically for the weight of the laptop. So much so that I had a VERY hard time riding without hands when the laptop wasn't on there.

zowie

I could easily ride hands free when I was a teenager, cornering and everything, but now I can't. I assumed it was something with me, but now I'm thinking maybe it's the change in the bikes.

Eatadonut

+1. I learned to ride hands-free on a bike with a dying headset, and the wheel always tilted slightly right when I wasn't holding it straight. When I tried to ride my roadie, I realized that I was leaning to the left to compensate when I took my hands off. Several times, it nearly landed me in oncoming traffic.

NoRacer

Rider balance and "steering trail", according to this:

https://www.diablocyclists.com/bicyclescience.htm

Apparently, some grocery carts do not abide by this "steering trail" phenomena.

fillthecup

It's been a long while since I studied physics, but rotational inertia plays a role. The faster a wheel is spinning, the harder it is to turn. This is why it's hard to balance when riding very slowly, but easier as you are moving, the wheels help stabilize you as you go faster. Wheel diameter also factors into rotational inertia and stability, larger wheels should provide more. My old Schwinn ten-speed is MUCH easier to ride w/o hands than my MTB, and it's larger wheels play some part in that.

The other part I believe is the rake and head angle, although I can't explain this well. Adjusting the angle of the front forks can make for a 'responsive' or 'twitchy' bike (for trail riding perhaps), or a bike made for stability on long rides (touring). My MTB is very twitchy, which makes it feel almost alive when I'm riding, but makes it sketchy riding w/o hands. Check out what Sheldon has to say... (https://www.sheldonbrown.com/rinard/forklengths.htm).

AndrewP

Extra weight in front of the bars can make no hands riding much harder. One bike I had was impossible to ride no hands when I had the front carrier on, but perfectly easy when the bag was removed.

lima_bean

True statement about this, but It doesnt it plays into account here on why the bike is easy to stay upright.
This is a common physics fallacy actually. I believed this at one time as well having learned about gyroscopic force and rotational inertia in highschool physics and having bikes used as an example. But later (i was a physics major in college) learned that this isnt true, and even ran an experiment to prove it. You can add counter-rotating wheels to the bike to completely cancel out the gyroscopic force of the rotation you mention. Do this, and the bike is still JUST AS EASY TO RIDE (straight)!

now this force does play a large role when you try and turn your bike, but not reallly in keeping it upright and balanced moving forward.

Cool article on it on wiki actually: https://en.wikipedia.org/wiki/Bicycle...cycle_dynamics

Eatadonut

You know, many people have told me this, and they all present useful arguments.

However, none of them can explain why it is that I can ride a bicycle for hours at a time, but can only trackstand for a minute on a good day.

lima_bean

Good point, and I cant explain that off the top of my head either! Which means obviously I dont understand it well enough to preach about it here, BUT you got me curious as well, so Im going dig deeper and find out (after work) and ill let you know =)

Eatadonut

You would be my hero.

But only for the week - don't get too cocky

Allen

If I have my Brooks B33 saddle on my Giant, I can't ride it hands free. With my B66 saddle mounted I can ride it hands free. I don't think my center of gravity changers more than a centimeter or two between the two saddles. Haven't tried swapping saddles on my Salsa yet.

--A

krome

I don't think it is the gyroscopic force directly, but the force caused by precession.

Read this: https://www.wiskit.com/marilyn/bicycle.html

specifically, I believe that Jeff Kaylin's explaination is the correct one. The gyroscopic force combined with the geometry of the fork/head tube angle cause the bicycle in motion to be self correcting.

Edit: here is more info to chew on: https://howthingswork.virginia.edu/bicycles.html

and this: https://hyperphysics.phy-astr.gsu.edu...s/bicycle.html

HardyWeinberg

What about frame geometry like was being discussed in the mechanics' forum recently? Chain stay length, seat tube angle, etc... one person's 'responsiveness' is another person's 'jittery'? I couldn't ride my current bike hands-free when I got it (after being plenty comfortable hands-free as a teenager), but can fake it now, though still not leisurely about it, so acclimation does play an additional role, I guess.

itsIRIEpat

Isn't that referred to as Procession?

Grampy™

Tire size matters. at least to me. My Cyclocross with 32's on it is extremely easy to ride no-handed. put some 23's on it and it's not nearly as stable, I can still do it, but it's not as stable.

Black Shuck

My heavy, lumbering hybrid is remarkably stable, even with 25kg of touring equipment and a 100+ kg rider. I have run tires ranging from 28 to 47mm in width, mostly Nokian Rollspeed. I think it's the relaxed geometry and sturdy(unfortunately heavy gas-pipe) steel frame that does it. Even when my front wheel was way out of true i could ride around no-handed.