Why are the wheels big? Why not tiny wheels?

on a mountain bike, how are you gonna clear obstacles? 🙂

"]news:[email hidden]...

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

You mean like Bike Fridays that are 20" x 20" or Dahons that may be even smaller?

The 'geometry' and 'physics' are trivially different unless you've a specific question.

My riding partner rode 1200 miles with me this spring, to Florida and back, on her Friday Air Glide
while towing Friday's hardcase trailer.

"]news:[email hidden]...

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

I have a Bike Friday (NWT) and have noticed 3 traits of the smaller wheels. They are very quick. You
can really accelerate on them. They make for very responsive steering. Some would say too
responsive, almost twitchy. You can really over steer and go down in a turn if you aren't careful,
ask me, I know. Last but not least, they do transmit more road shock than bigger wheels.

Andy

"]news:[email hidden]...

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm?

They seem to offer the best handling for non-smooth roads and trails. The higher rotational inertia
of larger wheels provides some steering damping, and a nominal amount of gyro effect (though this is
apparently not crucial for balance).

Quoted message said:

What would happen if the wheels on an upright were small like the wheels of a recumbent?

This is what Dr. Alex Moulton spent many years researching:

alexmoulton.co.ukalexmoulton.co.ukOpen ↗

Quoted message said:

Please explain the geometry and the physics!

Small wheels deflect off of obstacles at a sharper angle, causing a harsher ride.

I couldn't find any websites with good equations for you. Do a little Google searching - there's
plenty of information about bicycle physics to be had (though some of it is bunk, as I just
found out!).

Cheers,

-=Barry=-

=v= Bigger wheels get more forward rolling momentum, so it takes a little more work to steer them.

=v= I find that with 20-inch wheels (such as on my Bike Friday), are actually pretty nice for
everyday city commute riding, since I have to do a lot of maneuvering.

=v= If the wheels are *too* small, you get practically no forward momentum, so every anomaly, bump,
or gum wrapper on the road makes the front wheel turn, and you end up working hard just to keep the
bike going forward. This was one of the big problems with my first folding bike. <_Jym_>

P.S.: Here's a handy photographic reference:

bikesummer.orgview.phpOpen ↗

The Bike Friday I'm holding has 20-inch wheels. The woman in front of me is riding an early model
Dahon, the very model I used to own, with the difficult front wheels. (Newer Dahons with 20-inch
wheels are much better.)

I forgot to mention, after several years of the Bike Friday being my main ride, when I look at my
old bike, it reminds me of one of those old antique bikes with the one HUGE wheel. I'm just not used
to it anymore.

Andy

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

Smaller wheels absorb less road shock, unless the tires are inflated to lower pressure, which
increases rolling resistance.

The recent advancement of affordable, low-weight shock absorber components now make high-pressure
small-diameter bicycles more practical and comfortable. The Moulton bicycles are an excellent
example of fast, comfortable, high-quality bikes with small diameter wheels.

Steve Goodridge

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm?

Because those sizes are approximately the largest that will work with small frames and still allow
basic frame design principles to apply.

Quoted message said:

What would happen if the wheels on an upright were small like the wheels of a recumbent? Please
explain the geometry and the physics!

Small wheels rise and fall more abruptly upon hitting bumps, and descend much more deeply into holes
than larger wheels do. Damping out the additional vertical motion of small wheels uses rider energy
and causes vibration-induced fatigue.

Small-diameter tires flex more deeply to establish a contact patch than large-diameter tires do.
This causes significant extra rolling resistance. The shorter contact patch of a small wheel's tire
gives up some amount of traction compared to a larger wheel with a similar width tire, and
accelerates tread wear.

Most of the shortcomings of small bicycle wheels can be remedied at least somewhat by the use of
higher tire pressure along with effective suspension. Traction and wear shortcomings will remain,
though, and are exaggerated by higher tire pressure.

Small front wheels reduce steering trail dimension, which is proportional to wheel diameter. Within
normal limits, trail has a steering-stabilizing effect correlated to its length. To hold this value
at a normal figure with small wheels, a slacker head angle or shorter fork offset must be used, both
of which tend to increase wheel flop (the tendency of a bike's steering to "fall" into a turn under
the force of gravity), so one way or the other you wind up with a bike that requires more rider
intervention to keep under control than a large-wheeled bike does.

Small wheels serve to maximize wheel strength and minimize bike weight and physical size. Larger
wheels reduce rolling resistance and increase rider comfort and steering stability.

Chalo Colina

Kolaga Xiuhtecuhtli said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

It's not physics. You can test this by roller skating on a freshly chip sealed paved road or for
that matter on a dirt road. That ought to be convincing, considering that bicycles are commonly used
to ride on such surfaces regularly.

Jobst Brandt [email hidden]

Chalo said:

Small front wheels reduce steering trail dimension, which is proportional to wheel diameter.
Within normal limits, trail has a steering-stabilizing effect correlated to its length. To hold
this value at a normal figure with small wheels, a slacker head angle or shorter fork offset must
be used, both of which tend to increase wheel flop

An extreme example of that were the old ('60s) bikes used for motor-paced racing on a track, with a
24" front wheel and 700c rear. They had reverse rake on the forks in order to have enough trail to
be ridable. The use of the small front wheel was to allow the rider to get closer to the motorcycle.

--

David L. Johnson

__o | I don't believe you, you've got the whole damn thing all wrong. _`\(,_ | He's not the kind
you have to wind-up on Sundays. --Ian (_)/ (_) | Anderson

The Moultons compensate for the small wheels with full suspension. Moulton was a pioneer in
this regard.

Even my unsuspended Bike Friday NWT, though, is comfortable enough to
me. Granted, it got more so after I bought a Brooks saddle with springs, but it was good even
before this, not a signifcantly harsher ride than my unsuspended 700c bikes.

I also have a Dahon Boardwalk D6, 20 inch wheels, no suspension. This is Dahon's cheapest
multi-speed bike. It's very comfortable, pretty much like any low end comfort bike with 26" or 700c
wheels. The low gearing and relaxed geometry mean it's best suited for laid back recreational rides,
but the wheel size isn't an issue.

[email hidden] (Steven Goodridge) wrote in message
news:<[email hidden]>...

Quoted message said:

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an
upright were small like the wheels of a recumbent? Please explain the geometry and the physics!

Smaller wheels absorb less road shock, unless the tires are inflated to lower pressure, which
increases rolling resistance.

The recent advancement of affordable, low-weight shock absorber components now make high-pressure
small-diameter bicycles more practical and comfortable. The Moulton bicycles are an excellent
example of fast, comfortable, high-quality bikes with small diameter wheels.

Steve Goodridge

In article said:

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm?

Because those sizes are approximately the largest that will work with small frames and still allow
basic frame design principles to apply.

Quoted message said:

What would happen if the wheels on an upright were small like the wheels of a recumbent? Please
explain the geometry and the physics!

Small wheels rise and fall more abruptly upon hitting bumps, and descend much more deeply into
holes than larger wheels do. Damping out the additional vertical motion of small wheels uses rider
energy and causes vibration-induced fatigue.

Small-diameter tires flex more deeply to establish a contact patch than large-diameter tires do.
This causes significant extra rolling resistance. The shorter contact patch of a small wheel's
tire gives up some amount of traction compared to a larger wheel with a similar width tire, and
accelerates tread wear.

Most of the shortcomings of small bicycle wheels can be remedied at least somewhat by the use of
higher tire pressure along with effective suspension. Traction and wear shortcomings will remain,
though, and are exaggerated by higher tire pressure.

Small front wheels reduce steering trail dimension, which is proportional to wheel diameter.
Within normal limits, trail has a steering-stabilizing effect correlated to its length. To hold
this value at a normal figure with small wheels, a slacker head angle or shorter fork offset must
be used, both of which tend to increase wheel flop (the tendency of a bike's steering to "fall"
into a turn under the force of gravity), so one way or the other you wind up with a bike that
requires more rider intervention to keep under control than a large-wheeled bike does.

Small wheels serve to maximize wheel strength and minimize bike weight and physical size. Larger
wheels reduce rolling resistance and increase rider comfort and steering stability.

Chalo Colina

Making too much sense, Chalo. Gotta stop doing that.

David L. Johnson said:

Quoted message said:

Small front wheels reduce steering trail dimension, which is proportional to wheel diameter.
Within normal limits, trail has a steering-stabilizing effect correlated to its length. To hold
this value at a normal figure with small wheels, a slacker head angle or shorter fork offset must
be used, both of which tend to increase wheel flop

Quoted message said:

An extreme example of that were the old ('60s) bikes used for motor-paced racing on a track, with
a 24" front wheel and 700c rear. They had reverse rake on the forks in order to have enough trail
to be ridable. The use of the small front wheel was to allow the rider to get closer to the
motorcycle.

The use of the reversed fork was to get even closer to the motorcycle than just the small wheel
allowed. After this became standard practice, the rules were set and the roller on the motorcycle
was extended to not allow the driver to get any closer to the bicyclist. The whole get-up is absurd
if you look at it closely. The motorcyclist sits rigidly upright so far back that he needs long
handlebar extensions with which to steer.

Jobst Brandt [email hidden]

Quoted message said:

Kolaga Xiuhtecuhtli said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

It's not physics. You can test this by roller skating on a freshly chip sealed paved road or for
that matter on a dirt road. That ought to be convincing, considering that bicycles are commonly
used to ride on such surfaces regularly.

Jobst Brandt [email hidden]

Roller skating has nothing to do with it. I have just measured the rolling radius of a 26" tire at
24.5" and the rolling radius of a similar profile 20" (406) tire at 19" then calculated the the
height of the tires in each case above the next peak if they were being ridden on coarse agregate
roadway with the peaks 0.5" apart, which is rough enough in anybody's language. The 26" tire will be
.005" above the next peak and the 20" tire will be .0066" above the next peak, which in the whole
scheme of things is insignificant.

The above is armchair theory at its best. The proof of the pudding is in the eating. Having had the
experience of riding an aluminium alloy framed 26" wheeled tandem and owning a 20" wheeled tandem, I
am of the opinion that there are so many other factors to consider that the ride quality and
efficiency of a 20" wheeled bike versus a 26" wheeled bike each shod with the same type of tires is
so far down the list as to be not worth consideration.

Like others before us, my wife and I are so impressed with our 20" wheeled BF tandem that we are
considering scrapping our "good" solo bikes in favour of 20" wheeled solo bikes. We have only days
ago returned from a tour of the UK on our 20" wheeled tandem, where we commenced riding in the
Orkneys and ceased in Cornwall. But what would we know about it, we are both over sixty and
shouldn't be messing with bikes should we?

Alan.

So you don't topple over., think gyroscope

On Wed, 29 Oct 2003 04:01:51 -0500, Kolaga Xiuhtecuhtli

Quoted message said:

For what reason are bicycle wheels 26-inches/700cm? What would happen if the wheels on an upright
were small like the wheels of a recumbent? Please explain the geometry and the physics!

Alan Hutchison said:

But what would we know about it, we are both over sixty and shouldn't be messing with bikes
should we?

Wonder if thats a reference to my other post .... don't mind me 🙂 i just dont know a heap of older
people, my own grandpareents cant run let alone cycle

Quoted message said:

Alan.

Quoted message said:

Small wheels rise and fall more abruptly upon hitting bumps, and descend much more deeply into
holes than larger wheels do. Damping out the additional vertical motion of small wheels uses rider
energy and causes vibration-induced fatigue.

A friend of mine has an "ordinary". You know one of those bikes with the enormous front wheel?
It has some very interesting characteristics that illustrate the difference between big and
small wheels.

Even though it has solid rubber tires, it has a smooth ride. I suppose the big ol spokes flex some.

Another thing is it handles bumps and pot holes well. Shoot it is so huge that it sort of spans most
pot holes.

I guess it doesn't turn really well - rather stately.

Also, with solid rubber tires, who cares about broken glass?

You can do things with these bikes that one would not want to try even with a modern mountain bike.
I recall reading about someone who rode across the country in the 1890s on an ordinary (or maybe
even earlier). They did a lot of riding down railroad tracks and on dirt roads. That big wheel sort
of smoothed out the bumpy ride down the tracks, but I would not want to try that on a mountain bike.
One could do it, but why would one want to?

[email hidden] (Chalo) wrote in message
news:<[email hidden]>...

Quoted message said:

Small wheels serve to maximize wheel strength and minimize bike weight and physical size. Larger
wheels reduce rolling resistance and increase rider comfort and steering stability.

Chalo Colina

Well said. It may be of interest to note that 29" mountain bikes are now out there. Gary Fischer has
several models including a Sugar. These were evedently of some advantage off-road as they were
origianally outlawed by racing organizations.

I think the reasons most bikes have larger tires are pretty easy to see in other posts on this
thread. For recreational riders, smaller tires should be fine, but I don't think I would call
them ideal.

"Phil" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

[email hidden] (Chalo) wrote in message

news:<[email hidden]>...

Quoted message said:

Quoted message said:

Small wheels serve to maximize wheel strength and minimize bike weight and physical size. Larger
wheels reduce rolling resistance and increase rider comfort and steering stability.

Chalo Colina

Well said. It may be of interest to note that 29" mountain bikes are now out there. Gary Fischer
has several models including a Sugar. These were evedently of some advantage off-road as they were
origianally outlawed by racing organizations.

There probably is a small advantage in ride quality and being able to roll over bumps. But the
real reason for outlawing stuff like this is to prevent a perceived advantage from leading to an
arms race.

There have been several attempts at marketing mountain bikes with 700c wheels -- Klein did it in the
early 90s, and so did Diamond Back. Others too, I'm sure. The problem was getting tire companies to
produce good tires for such a small market. Also just plain old marketing, selling the idea and the
bikes. It's taking off now that a big company (Fisher/Trek) is behind it. And they've done it
because it's a good "new and improved" marketing ploy to revitalize sales -- many people will think
they need this latest, greatest thing.

Quoted message said:

I think the reasons most bikes have larger tires are pretty easy to see in other posts on this
thread. For recreational riders, smaller tires should be fine, but I don't think I would call
them ideal.

Bigger wheels roll better for everyone, but there's a practical limit that works well with most
frame sizes, which is the size we have.

Matt O.