I normally ride a Specialized Sequoia Elite, carbon/aluminum road bike with 700x28c tires. It is slightly to tall for me so I use a short 90mm stem on it.

I am not good with riding no handed and even if I barely let go of the handlebars, the bike seems to want to wander,just doesn't seem stable. Rides nice and is nimble though.

I just finished another bike. It is a Giant TCX cyclocross bike with 700x32c tires. It is slightly too short for me so I use a longer stem on it. Seems to fit better than my Sequoia but time will tell.

I noticed today on its maiden voyage that it just seems much more stable. I even noticed that it felt like I could let go of the handlebars and it didn't want to wander.

Why would that be? I know it must be the geometry but I am not sure.

Geometry has a lot to do with it. Rake, length of stays, etc. all contribute to the balance between agility and stability.

Quality, condition and tightness of your headset is another factor. A worn headset can index or develop notches that prevent smooth rotation. If not severe you won't notice it with your hands on the bars but the bike will feel twitchy when riding no handed.

Wheel trueness, alignment, and dish will also affect how well your bike tracks without constant minute adjustments through the handlebars.

Very narrow, high-pressure tires have a tendency to follow small grooves or irregularities in the road surface where wider, softer tires tend to roll over them.

Last but not least, rider ability and what you are used to riding make a difference. Riders who get a new bike that is significantly different than their old bike often complain that the bike doesn't handle "right" until they tune and get used to the new configuration.

If you want stability and aren't concerned about speed and agility (quickness) ride a quality touring bike, with good headset and properly built and aligned wheels, with 32+mm touring tires. It will track like it was on rails.

My guess would be the wider tires. More contact makes it more stable

No, of all the various factors, this is probably among the least significant.

Steering forces on a bike are mostly from caster effect. Watch the entire video, and for those in the USA a shopping trolley is a shopping cart. The video cuts off fairly abruptly after briefly discussing bicycles, but the keys are there, the head tube angle combined with the fork rake determine the trail. More trail = more stability, less trail = more nimbleness. What's best is the designer's judgement call.
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Other factors, such as tire/ground friction can increase or decrease the forces involved, so tire pressure, and weight distribution are also factors. Then there all the factors listed in the first response, such as wiggly tires, or less rigid frames.

Neat video! That simply explained how trail works on a bike. I always was confused by how the wheel was in front of the pivot point but I now understand that doesn't matter since the steering angle is at an angle unlike a shopping cart.

And it explained easily how trail relates to the fork. I'm going to go compare my forks and see if I can see an appreciable difference.

All I know is that most people my age road without hands as a kid on a pretty regular basis. It was normal. But if we try to do it today we end up on our head. Some people think the bikes have changed. Some people think the riders changed....

Go back to the video on caster effect. It's about balancing stability vs. nimbleness. Most children's bicycles, and entry level adult bikes have geometries favoring stability. But you're now riding a sport bike who's design and construction favor nimbleness.

If you want to improve your ability to ride no hands, the easiest way (short of replacing the bike) is to increase front wheel rolling friction. Lower tire pressure 10-20%, and either use a stiffer grease or increase preload on the front hub bearings slightly, and you'll gain a measurable improvement in stability. Shifting weight forward also helps, but involves other trade offs.

Another factor is wheel/tire mass. The greater mass will be more reluctant to move (steer to a different angle). Most people will see the, often, larger tire width that is the common way to increase the mass of the same wheel. But go to a wider/heavier rim, a thicker tube (thorn proof), thicker casing/tread cap and for the same tire width the mass will go up. Many efforts to discern speed man's wobble has led me to this aspect of the picture. Andy.

FB, Thanks... that makes sense... As I remember, as kids we pumped air into the tires about once a year or so whether they needed it or not. But I think I'll pass on the "Look Ma! No Hands!" routine. I may not be as smart as I was back then (or thought I was) but I sure am wiser!

You may be referring to gyroscopic precession. With a spinning front wheel, leaning the bicycle to the right, will cause the wheel to turn to the right (without help from caster effect). This effect is speed and mass related, so it comes into play at higher speeds and reinforces the effects of the trail. A heavier wheel will produce this more pronouncedly at any speed, and so is easier to keep straight or steer by holding or changing the frame tilt.

So we have caster effect and precession working to steer the bike, with caster effect working alone at low speed, as in when you walk a bike holding it by the seat, and precession reinforcing the tilt/turn ratio and adding some steering damping at higher speeds.

I don't remember where I first heard this, but, I remember reading a frame builder comment on how a "perfectly" square and plumb frame often seemed squirrellier than those that had a very slight misalignment. Something about the slight misalignment setting up a very slight steering tendency that the rider would subconciously learn to counteract. While the perfectly (or more closely, if we're being really padantic) aligned had no natural tendency and the rider was left adjusting back and forth across the neutral point.

Like I said, I don't remember who or when I first heard this. But, it made sense to me. I know that on racing yacht rudders we chamfer one side of the trailing edge more than the other in order to set up a natural imbalance that helps prevent oscillating turbulence that leads to flutter.

I'm not sure this is true. No matter how a bicycle is built we correct by tilting the frame so the tracking forces are straight ahead. This is a bit different than on a sailboat with a wheel. Here there's backlash in the steering gear (comparable to the free play in the steering of an old car), so you need the rudder held to one side when dead ahead or, as you point it flutters. We used to get some rudder flutter on a schooner I used to crew when the sails were perfectly trimmed and the bot was balanced. We cured it easily by altering the trim a bit so the helmsman had to bias the rudder a bit.

Of course, if there's any play in the bearings, on a bicycle, you might also see some of that flutter, but usually headsets and front hubs are set at zero play.

My analogy to the sailboat is far from perfect.

In fact, rudder flutter on racing yachts is more pronounced on tiller steered boats than those with a wheel, due to the inherent friction of wheel steered systems (there shouldn't be anymore play in a yachts steering system than in that of a car) and the imbalance you refer to is called weather helm and also helps a boat develop lift from the keel and rudder to counter act leeward forces from the sails as well as making it easier for a helmsman to steer. But, flutter most frequently occurs when sailing downwind, where achieving a neutral helm is the desired and fastest condition.

Back to bikes.

I think the originator of the notion I mentioned may have even been Richard Sachs. But, I'm not sure and hesitate to attribute something such as that without some assuredness.

We, the rider, are constantly adjusting our weight balance to maintain a straight course. However, it is not hard to imagine a situation where a bike with a bit of "weather helm" so to speak would actually be easier to maintain on a straight course than one with an exceptionally neutral center point that could very well encourage or allow one to more easily wonder either side of the desired mark. I'm not refering to flutter, shimmy or wobbles in the front end. But, simply a bikes very slight tendency to pull in one direction or the other during otherwise neutral riding.

However, as my memory slowly recalls this. I believe the proposed notion came from a thread or article somewhere on reducing or eliminated "speed wobbles" from bikes that where otherwise well adjusted and it was proposed that bikes which came off the alignment table truer than others sometimes seemed more inclined to suffer from the "speed wobbles".

I could also just be suffering from early senility.

Are you possibly thinking of this article by Dave Moulton? Anyways, he's always a good read.

Also, this slight misalignment is what happened to me recently when I overtightened my threadless headset, "locking in" a non-smooth headset to a not-quite-forward position.

When you have a caster angle on a car or bike,when you turn the wheel,it actually lifts the front of the frame/car up....That's why it goes straight.

When rolling straight,the weight of the vehicle is holding the front wheel straight,the more caster/weight,the more the wheel wants to stay centered.When rolling straight,the wheel is actually at the bottom of a slight upward arc.As you turn the front wheel the caster angle decreases,then wants to return to the lowest point.

Positive and negitive caster will both work to keep the wheel centered.....Until you hit a bump.....Then one is a little bit twitchy...to say the least....

So,the most caster angle and the more weight you have,the more the wheel likes going straight.

Racing bikes are light and have less caster angle to make them more "lively"...so they tend to be more twitchy then say,a beach cruiser.

I noticed that with my old boss's Gary Fisher Presidio cyclocross bike. I could ride no-handed loops in the parking lot with that one, a really sweet bike.

On cyclocross bikes, the slacker head angle slows reaction to steering inputs and the longer fork offset lets the front wheel weave and "hunt" through ruts and roots and rocks without significantly altering the line of a turn. The net effect is outstanding low-speed stability.

The slightly longer wheelbase helps, too.

Makes sense.

I got another frame to play with this weekend. I'm going to build it up with spare parts as well but this one is going to be unique to my stable.

Its an old KHS comp aero. Frame is identical to this one:

I'm going to set it up with a common 52/42 front chainring and a 12-26 rear cassette and bar end shifters and see how it feels. Will probably feel MUCH more skittish than the cyclocross bike that I just finished. Look at the rear wheel and how the seat tube has that s-curve in it. Much shorter wheelbase. I just wish the paint wasn't so messed up. Heck, if I love the biek enough, it might be fun to get it powder coated.

I weighed the complete frame with headset and fork, just a hair under 5 pounds. Should be decently light for a steel framed bike.

As said earlier, the basics are head angle, fork rake, and weight distribution. Then a bunch of smaller stuff. There are too many variables to discuss why one bike tracks better riding no hands than an other, unless we deal in specific differences.

Even little stuff that we never talk about can be important, for example a ture with a narrow center ridge can make steering incredibly unstable if it isn't perfectly straight. Small wiggles put the track at the edge of the ridge moving the point of contact to the side.

Anyway, if you want to know more here's a link to an article that might be a good place to start. After that search "bicycle steering geometry" or something similar. There's plenty of info, from easy to understand to highly technical, and you'll have a good sense of the basics. However nothing matches actually getting on a bike and riding it no hands.

Swap stems then compare. You'll learn something.

You mean put the long stem that is on my cyclocross bike onto my Sequoia Elite bike and compare the difference? Wouldn't riding no-handed render the stem size moot since you aren't touching the bars?

If you can ride each bike no handed then they are both stable, per se. Changing stem length changes the moment of inertia of the whole steering assembly, thus changing its response rate, thus changing the perceived stability. (BTW, changing the load on the front wheel also changes the steering response rate -- by a different mechanism.)

One well executed experiment crushes all "expert" opinion.

+ things are in alignment.. throughout?

---Castor angle (angle between the horizontal line and the HT intersection with the ground to axle line) exists whether or not the frame raises or drops as the bike is steered. In fact often the bike will have an initial rise(or drop) then drop(or rise) as the front wheel steers past 90*. I am of the understanding the slight raise or drop is of far less force then the leverages that the offsetting to one side that the ft tire's contact goes through as the bike steers.

I have read about and done the math for a few "steering indexes" that use castor angle as the focused factor. The problem with these formulas is that they don't take into accouninfluences influcences, as Francis mentioned. Weight placement along with stem length (or front loads), wheelbase, tire size/width/mass and more factors. Long ago I gave up on trying to use math as the path to a good handling bike. Andy.

Frame geometry is a bit of an art. Of course there's science to it, but achieving good handling properties is a matter of balancing trade offs, which is where the art comes in. We also need to accept that bicycle geometry is highly evolved, and reflects 100 years of accumulated experience. Good designers follow well established rules of thumb, and know that they can tweak within a general area, but going too far makes a bike handle poorly.

I think the effect of stem length on handling is overstated. I am not an engineer, so I won't try to argue like one. However, I have ridden my current bike with stems ranging from 80 to 110 mm, and have not noticed any difference in stability or handling. The difference in lever arm due to changing the length of the stems is less than the difference riding on the hoods vs tops vs drops. I realize that it changes weight distribution, but I have ridden another bike with panniers and, while a load made everything seem a little more sluggish, it did not seem to affect the basic stability.

It seems to me that we are pretty adaptable. We drive cars and trucks with radically different steering ratios all the time, and don't have to think about it. An experiment was done years ago where they reversed the steering on cars: turn the wheel clockwise to go left. Took people about a minute to be able to drive them. On the bike, turning the bars, except at very low speed, doesn't seem to me to be the primary factor in turning; I have seen many threads arguing that all turns should be initiated with counter steer (not sure I agree, but that is another conversation).

To the original question, my 2 cents, is a combination of trail, head tube angle and fork rake. I don't think the same trail will behave the same for all head tube angles (which would require different rake to get the same trail). At the extreme are choppers with very slack angles, and if you don't hold tight the wheel flops over!