STABLE vs UNSTABLE

[Homer W. Smith]

When I was young, 15, I had a rather large Schwinn, and this thing was
rock stable, I could ride and pedal it
no hands with out any problem.

Also a friend had a standard English race with undercurved handle bars
with same result.

Now I try to get on a mountain bike, and the instant
I let go of the bars it goes out of control.

Why?

Homer

[Frank Krygowski]

Bicycle stability is determined mostly by front end geometry, especially
the inclination of the steering axis ("Head angle") and the distance the
front axle is ahead of the steering axis ("Fork offset" or "fork rake").
Those combine with other detail measurements to determine the "Trail."
Here's a diagram that shows these dimensions:
http://www.bikequarterly.com/images/BQGeometryTerms800%201.jpg
Trail is often considered the predominant factor in bike stability,
although other factors do have an effect.

Mass market bikes in the '50s and '60s were designed to be rock steady.
Perhaps it was just fashion, when relaxation was preferred over sport.
Perhaps it was to reduce crashes, I don't know.

When performance-oriented "ten speeds" came on the scene, I think the
fashion changed toward "sportier" handling, which meant more agility, so
less stability.

But bikes are still available with a range of stabilities. If you shop
around, you can probably still find one you're comfortable with.
Advertising copy should give you a clue (perhaps words like "relaxed" or
"comfortable" vs. "nimble" or "sporty"), and a test ride should tell you
more.


--
- Frank Krygowski

[Sir Ridesalot]

Is it every mountain bike or is it just one you've tried?

Many mountain bikes today have geometry that's designed and built for quick handling so that when riding at high speed off road the rider can manouver quickly to avoid obstacles on the trail.

My 21 inches size frame 1980s Bianchi mountain bike had so much space between the rear fender and the seat tube that I was able to mount a water bottle cage and place a 500ml water bottle in it there. It had a much longer wheel base than most mountain bikes today have with the result that it was directionaly very stable but not so great where quick precise turns/movements were needed.

Cheers

[AMuzi]

Could be a problem with geometry (faulty design or 'modified
by impact'), could be an equipment problem (wheel bearing,
rim out of round, tire lumpy etc), could be a rider position
issue (some 'pedal forward' designs have just horrible
handling) or of course it may well be your own brain's wetware.

Do other riders have the same experience on this bike? A
quick perusal at a competent shop would spot serious or
safety-related problems with the machine.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[avag...@gmail.com]

On Friday, August 21, 2015 at 9:16:58 PM UTC-4, Homer W. Smith wrote:

on a classic 10 speed geometery, 1/8th" trail +/- with 1"3/8ths tires would bring a different handling feel over patchy surfaces and turn in response.

[Andre Jute]

Christ, who said you could be an engineer, Krygowski? Your momma? You're nothing better than than a funnel for street corner gossip, and rather low quality gossip at that. You'd do better if you checked your facts before you spouted the crap below. As just one example, David E. H. Jones proved, and it has been accepted by all serious bicycle engineers (which clearly will never include you) since he published his results In Physics magazine in April 1970 -- 45 bloody years ago, wakey, wakey Frank Krygowski -- that the stability of a bicycle is indifferent to the trail of the front wheel. Jones proved this very simply by demonstrating in the ICI parking lot (a place to which I have made pilgrimage, and you should too if you know what is good for your soul, if you have a soul of course) that a bicycle with the fork reversed would run untended as far as one with the fork facing forward in the normal manner. Go get your facts straight, sonny, then come apologize for spreading wretched lies so old, they're full of maggots. Just to stop you whining that you don't know how to look up a copy of a common magazine, here's a direct link to the seminal Jones article, complete with color piccies just for you: http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf

Bloody hell, Jobst is turning in his grave at the stupidities daily committed on RBT (which, perhaps ironically, stands for rec.bicycle.tech), 95 per cent of them by Krygowski.

Andre Jute
Relentless rigor -- Gauis Germanicus

[Andre Jute]

A mountain bike (and anything related to its, like the wretched short-arse Gunnar that Paramount makes), as Ridealot intimates, is the wrong sort of bike from which to expect stability. Its designer had deliberately made it quick to change direction, and therefore unrelacking to ride. What you want, if stability is your measure of goodness, is a bike which for a start has a longer wheelbase, an understeering geometry (that's a low head- and seat-tube angle like 68 degrees rather than a higher one like 72 degrees to go with the long wheelbase with a medium to long trail), no careless barbelling bits haphazardly arranged on the handlebars, fat tyres rather than thin, your seat well inside the wheelbase (none of these modern short-arse bikes with the saddle hung out almost over the rear hub will do), and so on. I have such a stable bike, capable of being ridden hands-off at speed through potholes. You can see it at
http://coolmainpress.com/AndreJute'sUtopiaKranich.pdf
Compare it to the other bikes on my bicycle page at
http://coolmainpress.com/BICYCLING.html
and you'll soon that it is a very different from them in almost every respect beyond having two wheels. The downside of such a bike is that many would consider it slow-handling but in fact on the downhill parts of my very poor roads nobody has ever passed me and those who try to keep up end the day with white brackets around their lips and knuckles whereas I don't even notice the road is bad; it's like having my old Bentley Turbo back, a steamroller on two wheels.

If you want to build a stable bike you can't start with mountainbike frame, and generally speaking most popular frames have too many insuperable difficulties, almost always starting with too short a wheelbase. So you have to design and commission a custom frame, pay for a semi-custom frame from Europeans who have designed touring bikes from the ground up (there are a few Americans too, but I suspect them of crept-in 10-speed influences); that leaves you at the pricey end of the market, with Utopia (my guys, known as the Rolls-Royce of Bicycles for many good reasons), Patria, Thorn and from there the prices hike north rather suddenly because now you're into one-offs.

Before you start looking into custome bikes, here's a simple question for you: where will you get double-butted bicycle-weight tubes long enough for this notional bicycle of yours? (Hint: the tubes on my bike were specially drawn by Columbus in Italy, the same people who draw pipes for Ferrari. Ask yourself what that will cost for a one-off.)

The smart alternative is to find an old Raleigh tourer frame, forget that it is a venerable antique, and get someone like Muzi to modernize it for you so it takes modern components (bottom bracket, headset, frame- and fork-ends, bracketry) and, most important, to spread the forks for you so that you can fit minimum 50mm tyres, preferably 60mm low pressure Big Apples. (Or maybe Muzi can somehow make that Indian Raleigh copy that he sells into a lasting, smart proposition with a bit of Waxoyl and paint.

Anyway, a stable bike isn't impossible, but it will be long, it will definitely be clumsier than a road bike or a mountain bike, if you want to ride it fast you will have to learn new skills (if you're into big, fast transcontinental tourers you already have four-wheel skills and attitudes that transfer whole). On the other hand, my big stable bike is in fact the cheapest bike I ever owned. The tyres aren't worn out yet at over 8000km (and anyway, Big Apples are cheap), and the rest of the maintenance is new oil for the hub gearbox once a year, less than twenty dollars for the entire kit, plus a shot of Teflon grease once a year. That's it for seven years now. The brake blocks are still good too. A stable bike will almost by definition be a big bike, with more of everything to spread your weight, and the wear, across.

So, no, the lack of hands-off stability isn't a plot, it isn't even deliberate, it just happened for other reason.

If you're in reflective mood, you could consider that the most stable bike you ever owned or rode was probably a beach cruiser, the first of the fat bikes of which the Big Apple tyres I consider so stable are the direct inheritor. Those first beach bikes also gave birth to the mountainbike craze...

Andre Jute
What goes round comes round

[avag...@gmail.com]

an MTB geometry supplies a different vehicle platform for the operator than a standard road frame geometry.

This fact by itself does not establish criteria for judgments in scaling 'stability' as when claiming MTB is less 'stable' than road geo.

There are several unstable geometry videos

Forgive me for not reading the material herein.

The MTB is designed to pivot with the riders weight center, the road frame is designed to move rider's weight forward not pivot.

The rider can pivot stably or not pivot stably, move forward stably or not.

[Andre Jute]

On Monday, August 24, 2015 at 6:17:19 AM UTC+1, avag...@gmail.com wrote:
> an MTB geometry supplies a different vehicle platform for the operator than a standard road frame geometry.
>
> This fact by itself does not establish criteria for judgments in scaling 'stability' as when claiming MTB is less 'stable' than road geo.
>
> There are several unstable geometry videos
>
> Forgive me for not reading the material herein.

You and Krygwoski both. You'd rather mouth off the comforting, wrong platitudes of cycling "wisdom" received on the nearest street corner.

> The MTB is designed to pivot with the riders weight center, the road frame is designed to move rider's weight forward not pivot.
>
> The rider can pivot stably or not pivot stably, move forward stably or not.

And then you have the cheek to complain when I open tech conversations elsewhere than where clowns like you and Krygowski derail every tech discussion with your willful ignorance.

Andre Jute
It's one thing to wear one's learning lightly, quite another to have none

[avag...@gmail.com]

under power, a Beetle oversteers...is this unstable ? For a Mustang owner...is a Mustang unstable off course for a Beetle driver.

but market an unstable vehicle ?

500000 unicycles ?

https://www.google.com/#q=definition+unstable

[avag...@gmail.com]

.........................

Total 1,786,243

[cycl...@yahoo.com]

There are many points here and it appears to me that those trying to answer your question are correct but not very helpful.

The Schwinn was stable for many reasons. First and foremost as Franks was describing - the front end had a LOT of trail to make the steering very slow. The Schwinn also had a long wheelbase that also made the handling slow. And third - the steel frame was dead solid and you couldn't hit a manhole and have the frame wiggle. Schwinn were built in this manner to make them extremely predictable at the low speed young people are likely to be capable of.

Modern full suspension mountain bikes have a small amount of trail and a relatively short wheelbase because you want to have relatively nimble handling AT HIGH SPEED which these bikes are astoundingly capable of. Because of this, at low speeds you will find at low speeds there is insufficient trail to hold the front wheel straight and it will try to flop from side to side without a strong hand on the bars.

You have different problems with road bikes. Because these are meant to be "forgiving" in their handling when riding on the bad roads that have become part of riding in America, the frames flex and can change the direction of the bike. Ig you get a well make steel bike they will still give you nice predictable handling because the flexing is minimal.

As a minor problem - because everything is using threadless headsets, if the stem isn't properly tightened so as not to move it can slide down and gradually tighten the headset until it seizes and you crash because the fork won't turn.

[Roger Merriman]

Andre Jute <fiul...@yahoo.com> wrote:

> On Saturday, August 22, 2015 at 2:16:58 AM UTC+1, Homer W. Smith wrote:
> > When I was young, 15, I had a rather large Schwinn, and this thing was
> > rock stable, I could ride and pedal it
> > no hands with out any problem.
> >
> > Also a friend had a standard English race with undercurved handle bars
> > with same result.
> >
> > Now I try to get on a mountain bike, and the instant
> > I let go of the bars it goes out of control.
> >
> > Why?
> >
> > Homer
>
> A mountain bike (and anything related to its, like the wretched short-arse
>Gunnar that Paramount makes), as Ridealot intimates, is the wrong sort
>of bike from which to expect stability. Its designer had deliberately
>made it quick to change direction, and therefore unrelacking to ride.
>What you want, if stability is your measure of goodness, is a bike
>which for a start has a longer wheelbase, an understeering geometry
>(that's a
>low head- and seat-tube angle like 68 degrees rather than a higher one
>like 72 degrees to go with the long wheelbase with a medium to long
>trail), no careless barbelling bits haphazardly arranged on the
>handlebars, fat tyres rather than thin, your seat well inside the
>wheelbase (none of these modern short-arse bikes with the saddle hung
>out almost over the rear hub will do), and so on.

hard trail MTB's tend towards 70 degrees but full suspension frames
differ from 63 to 72, ie from downhill bikes to XC race. trail bikes
tend to be 67 to 69, with reasonbly long wheelbases, my MTB has a
wheelbase of 114cm which is not unsually long for a trail MTB by any
means


big snips

> Andre Jute
> What goes round comes round

roger merriman

[avag...@gmail.com]

well that should clarify meanings of stability. Predictable handling under pre determined conditions is stability ?

yeah we could go with that for example this would denote acceptable or unacceptable that is unstable handling in the class: unicycle.