capsicum

I've heard and read many discussions that state things like "Bike x is really stable." or "Bike y is twichy.". Well I'm here to ask what makes bike stable. I don't mean geometry, I mean its handling. Do not start talking about rake, trail, center of gravity, or wheelbase, this thread is not about those things and most of the "informed" people are misinformed about those items anyhow.

In other words do you consider stability to be; a bike that tracks straight and turns slow, one that is neutral in corners, that fights to stand up in corners or tries to fall into the corner, a bike that does S turns quickly without loss of composure, low speed, cruising, or ZOOM down the hill, etc.?

Aaaand.... discuss!

[edit add] In other words, how would you describe stable handling or a stable bike?

F1_Fan

Stable to me is defined by my old Serotta:

1) I can ride it no hands without even thinking about balance
2) Lean it into a corner and it almost steers itself through the curve.

Damn I loved that bike. It was so stable in a corner... like it dared me to lean further.

capsicum

Just to clarify, how was it at turning corners no handed? By "steers itself through the curve" do you meen that it was neutral? Neutral in that it didn't want to stand up or 'fall' into the corner, without much handlebar input.

F1_Fan

Yeah basically.

The Specialized I ride now feels like you need to hold it in place when cornering... the Serotta just leaned in and stayed where you put it. I noticed it the first time I rode the bike. I felt like the bike did the cornering for me.

If you're familiar with how oval track racecars are setup with larger tires on the outside to make the car naturally turn then you've got the idea.

slvoid

The most stable bike's my daily ride to work. Specialized 04' hardrock with 1.95" hemisphere ex semislicks. I can go around corners at 15 mph no handed and can spin almost 130-140 rpm without my ass bouncing around no handed. Can also fly into potholes no handed.
My OCR2 however, seems to have straight forks and is very twitchy.

roadfix

I don't know if this is a criteria for slow speed stability.....
My most stable bike can be ridden no handed at 3 mph. My least stable bike requires at least 10 mph to be ridden no handed.

catatonic

stable to me is two factors

a) how well it can stay upright (minimal side-to side motion while in the saddle) while sprinting. i have one bike that it just cant be done with, it seems to just not work out...that bike's my commuter...my other bikes...you can go well beyond 100rpm on the pedals and still have that bike feel like you were cruising it at 60rpm.

b) the real important one -- how solid it feels around corners. A stable bike should not fight you around a corner. Once you get that ahndlebar and angle down the bike should pretty much steer itself. My commuter has some issues with this, but that bike is slightly malsized and, frankly, could use some upgrades..but it's a commuter...no upgrades for it. My Talus just loves hard corners...it takes corners and slalom duty with a very snappy and solid feel to it...even when I'm pushing the limits of the bike I still feel fully confident in the bike's ability to pull the turn off.

I dont ride no hands, so I dont use that as a factor.

wfin2004

I had always thought of the way a bike "handles" with no hands as a combination of various differences in the geometry of that particular bike. I was not even making the connection between great stability and one with not so good stability. This being the case, my Trek 4900 has less than acceptable stability as there is no way to safely remove your hands from bike without the bike going in every direction but the one you want. Can you go into more detail on this "stabilty" issue? I am finding this quite interesting. Thanks!! wfin2004

capsicum

Good my whole intent was to get the ol' gears a churnin'. That and find out how different people define stability and what their preference is.

Any fully loaded touring folks out there? I'm sure you have a unique veiw of stability.

MichaelW

For me its about handlling on a fast descent. If the bike feels neutral and has "thought control" steering, then descents are much easier. Ive had some really scary moments on big , fast, steep descents with twitchy bikes.
Its less about balance and weight distribution. I find that on a good bike, I can load up a single pannier and it stilll handles well.
I just had to switch forks on my nicest handling bike, and it feels a whole lot worse now. Maybe I just need to get used to the new feel.

roadbuzz

I don't see twitchy and stable as opposites. Twitchy is just a derogatory (sp?) term for nimble handling. Nimble or stable... either can be found executed poorly in a design. Either can be a liability in the wrong situation. I have 3 bikes that fall into 3 decidedly different categories... a Bridgestone RB-T, Litespeed Classic, and Cannondale R3000.

The Bridgestone has a low BB, and a long wheelbase. I think it's along the lines of a touring geometry. It's a land-yacht, just no fun to ride on the road. Dead-stable and boring. Since I can mount wider tires on it (700x32, 700x35), it's been relegated to commuter and ride dirt road use. It's good for that. Disclaimer: I'm not dissing touring bikes. This was an inexpensive, heavy bike... not a good example of a touring design.

The Classic is an all-around recreational design. The handling is not boring, but it's not in the realm of 'if you sneeze, you'll run off the road'... sort of like you don't have to be concious of it. I can get on this bike and motor away for hours happily and comfortably. In cornering, it has what the NASCAR community would describe as a "push." Lean into a sharp corner, you feel like the bike wants to straighten out again. I'm not comfortable 'pushing the envelope' on this bike through sharp turns.

The R3000 is nimble. Analogous to a sports car. The handling is significantly better than any of my other two bikes. A long descent at 50mph, the bike is rock-solid... no resonant vibrations. Lean into a fast turn, it stays neutral, it gives me confidence to take the turn faster next time. It's more comfortable in fast groups, because the handling responds faster. You *do* need to pay attention to where you are going, but it's not like it's a problem. It's all good, so the handling is nimble, not twitchy. Stable, but lively. This bike is wayyyy light, and the ride is plush, which help make it fun and invigorating to ride. But, this bike, more than either of my others (past or present) is designed to have the rider further forward, weight more centered. That probably helps the handling. It's also a downside for me, since it requires more front-of-the-leg strength. I prefer a balance of front, back, and glutes, which I get from the Classic.

I guess what I'm getting at is that I think stability can be had in any geometry... it's not just a matter of, e.g. wheelbase. My preference? Well, the Classic and the R3000 get about equal time. If the RB-T were a better execution of it's design, who knows, maybe I would find more recreational uses for it as well.

photojtn

Having been touring for 30+ years on only two bikes, (1st is a Schwinn Le Tour Luxe, and 2nd is my current Trek 520) I haven't been plaqued with bike stability, only BODY stability. i have learned that the body posture is paramount when fully loaded touring, when we tour (wife and i) i usually carry the heavest loads (anywhere from 55-70 lbs) and here in NC we do the Blue Ridge Parkway every other year in segments. On the downhills (mountains) where speeds can approach the TDF speeds you have to be always on guard of your body posture on the bike on the downhills, ex. leans on the curves, down on the drops for lower center of gravity, etc... Not once have we observed wobbles or shimmys that others have described. I deffinetly disagree with the idea of taking your hands off the bars when your touring or for that matter anytime because of unexpected road hazzards. When we're on the flatlands the same is true, the bikes are always comfortable. This is just a tourers point of view, we're not racers, and our bikes are set up much differently.

jukt

Trek 4900 is a MTB, Dude.

Differant animal.

TandemGeek

I don't believe there is a universal definition of stability since it depends on how a bicycle will be used and what a given rider "expects" in terms of how a bicycle should handle throughout the speed and cornering envelope.

Some riders will define a bike as stable based on its slow-speed handling characteristics whereas others have a bias towards high-speed handling characteristics. Therefore, good or bad is relative. And, of course, what constitutes stable for an off-road bike may be of little consequence to a road bike, just as much as what is stable for a comfort or leisure bike vs. a road bike optimized for criterium racing.

All that said, I define bike stability as being what works best for each individual rider. If a bike "spooks you" with the way it handles then it is not "stable" (generic). I have been "spooked" by bikes at both slow speeds and high speeds.

My preference is for having road bikes that handle more predictably when ridden in an aggressive manner; slow speed handling can be mastered with experience. The same cannot be said for a bike with a lot of understeer at high speed.

redfooj

stable = slow steering
i can bomb down my local hill at 50mph without the fear of death in me... like on my old 87 Trek 400

my fuji is more sensitive to steering input... seems like steering is more sensitive... gotta concentrate on keeping the bike straight or kerplow

capsicum

This is all good stuff. Gotta keep them brains a burnin if Anyone thinks of a better way to describe their prefered or dreaded handling then feel free to post again. I'm trying to get to the base of how the different veiws of stability affect handling.(I think... I don't feel tired but I haven't had a lot of sleep either.)

Yes yes good point. I'm not looking for a universal definition, but rather what different folks "expect" stable or good handling to be.

So what, this is general cycling. MTBs need to handle well too.

HereNT

Mines pretty stable, but it is really nimble, too. That's the nice thing about track bikes. I like that I can just zip around anything with a really brief turn of my wrist. It tends to stay upright through the corners, which is good because I can't stop pedaling through the turn. I can bring it almost all the way to a stop no-handed, too...

Don't know if that helps much...

Maj.Taylor

I agree. My bike might be considered by many to be twitchy. But, is it stable? Well, it turns on a dime, but is a mother to ride with no hands in a decent crosswind. Others have commented on my/its ability to do a sharp no-hands ninety-degree turn. It can turn very sharply with no hands, if the rider has the skills. Without good handling skills, good luck. I've seen more than one person I've let ride it almost fall off because any lateral input is immediately translated into lateral movement of the bike. People simply don't expect it to handle as quickly as it does. Conversely, it's one of the easiest bikes on which I can do track stands.

You had better be very careful taking your very first turn, at speed, on it. You're likely to find yourself headed straight for the inside curb. Again, you think it will turn later, but it turns NOW! However, there is not another bike I trust as much going downhill through sharp switchbacks. The sharper the switchbacks, fewer and fewer riders will be able to follow its line. (I love downhills!) My bike goes exactly where I tell it to go. It will take that last millisecond correction without any negative consequences.

So, is my bike stable? I think so. A less experienced rider would probably think not. Is my bike twitchy? One of my instructions to its builder was: "Build me a bike just short of twitchy." They could not have done a better job. My bike is stable, but only if you like a very nimble bike.

jukt

So what, this is general cycling. MTBs need to handle well too.

Yes yes good point. I'm not looking for a universal definition, but rather what different folks "expect" stable or good handling to be.



Differant animal. Sorry, but they are not the same. Steering is differant, Genuis.

So, well is a universally deep subject.

Try riding a MTB with no hands off road, please ?

Say you will.

capsicum

I do. Ride offroad no handed that is.



This is general cycling. For good reason, I did choose here, to put this thread. It's not a road bike thread, it's not a 'no handed' thread. That mostly road bikers replied, is just happenstance.


Now get out of my thread if your going to be a beatle headed chode eater.

bkrownd

Labels, labels, labels... There's a whole spectrum of bikes out there. Isn't this issue relevant to all of them?

capsicum

Yes.

Now thats the end of that. Lets all get back to issues of countersteering, osillations, and sub trans-sonic fluid flow. or something of that nature.
Maybe somefolks will be willing to describe their prefered handling in terms of the forces they experiance rather than generic terms like neutral or push or understeer.(Try it, it'll get ya pondering for sure.)

khuon

I think people define stability differently because there are different axis of stability. In the world of aviation, dihedral angle of the wing effects roll-axis stability of an airplane such that when something causes it to roll away from its neutral position, it will attempt to right itself by side-slipping in the direction of the lower wing. This causes a lateral flow across the wing and thus produces an increase in relative lift because the dihedral forms a positive angle of attack relative to that lateral flow. The lower wing will then rise until the relative lift is equalised. For a "stable" bike, much the same thing should happen. The bike should try to resist movement about the vertical plane (parallel to the angle of the wheel) and hold its roll-axis such that with no steering input, it will not want to increase or decrease its angle to the road. Likewise, stability in yaw can be thought of as the bike's tendency (assuming once again a neutrally stable bike) to not want to steer itself such that the front wheel will have a tendency to try and track the longitudinal forward vector of the bike's motion rather than the other way around. Both of these forms of stability, while independent, are also tightly coupled and tend to effect the overall stability of the bike.

capsicum

You make it to hard. Dihedral makes an aircraft stable do to the lift force vectors of the wings' relative to the center of gravity and to a lesser extent by raising the center of lift relative to the cg. In a roll the lower wing has more horizontal area and thus resists the pull of gravity better than the upper wing. Side slip will have negligable effect and will actualy have a slight destablizing effect if the roll angle exceeds the dihedral angle, which is most rolls as dihedral is only a few degrees normally. (Highwing planes don't need positive dihedral because c of lift is higher than c of g, some even have negative dihedral because they are too stable, like c-17 cargo planes.)https://www.edwards.af.mil/gallery/ht.../c17-1_072.jpg

You forgot that it needs adaquate resistance to harmonic low frequency vibrations in the steering assembly within the operational envelope of the bicycle lest it suffer the wrath of the head shake and shimmy dance.

khuon

The displaced CG/CL is a factour but the the statement that the lower wing has mor horizontal area is somewhat false. It has more effective lifting area due to the slip. If there was no additional lift due to lateral flow then the aircraft is in a neutral bank angle.


I think you need to model this and you need to do it as a full fuselage structure and not just the wing structure alone.


Many high-wing have a fuselage structure which tends to provide effective dihredal as you've said but it's still the shape and not necessarily the CG/CP relationship. And given that, it is not true that all high wing planes are straight wing or have anihedral wings. The heavy lifters may have anihedrals because of the fuselage shape for the same reason. Other reasons are that when fully loaded, the wings will form a dihedral on their own due to the shape and large amount of upward forces generated because of the high lift coefficient relative to the stiffness of the material.



Ahhh... well yes, that is another matter too. But if you go that far, you need to also consider the inherent (or possibly lack thereof) stability of the rider (both physical and mental).