Linear pull brake levers???

Alex Rodriguez said:

Quoted message said:

What is bad about cantilever, V, or centerpull brakes is their
large vertical error in rim contact during pad wear. The
centerpull progresses into the tire sidewall while the cantilever
can pop under the rim with wear, its action angle being about 45
degrees to the plane of the rim.

Quoted message said:

XTR and XT V brakes have a linkage that gives them nearly horizontal
travel. So they should not pop under the rim like other cantilever
brakes.

That's not the case. These linkages do not address the problem of pad
dive. That condition is governed by the location of the pivot post on
the frame. The pad traces the same arc as a non-articulated pad
except that it the pad does not itself rotate with the brake arm.

Jobst Brandt
[email hidden]

Jobst Brandt said:

I used
centerpull brakes when they were the rave and found they performed no
different from side pull brakes except for the pad-climb toward the
tire and the lack of a good QR.

The advantage of centerpulls is the same as the advantage of
cantilevers, viz.: increased tire/fender clearance.

It is a widespread misapprehension that this type of brake gives more
braking force.

Quoted message said:

Quoted message said:

Quoted message said:

What is bad about cantilever, V, or centerpull brakes is their large
vertical error in rim contact during pad wear. The centerpull
progresses into the tire sidewall while the cantilever can pop under
the rim with wear, its action angle being about 45 degrees to the
plane of the rim.

I replied:

Quoted message said:

Quoted message said:

This can be a problem. It varies considerably with cantilever stud
placement and rim width. Tends to be particularly bad on mountain bikes
where wide forks move the studs outward, and narrow rims are commonly
used to reduce weight.

J.B.

Quoted message said:

Pleas consult your diagram and notice that the brake pads approach the
rim at about a 35 degree angle, the line from P to S and the rim.
This is not a good brake function and it is that way for the brakes I
mentioned above.

That's just a drawing, but I agree that it is often a problem,
especially in some installations as described above.

Quoted message said:

Quoted message said:

Shimano's "parallel push" linkage and Avid's "Arch Rival" are
"linear-pull" cantis that solve this problem, though at some cost in
added complexity.

J.B.

Quoted message said:

Parallel push does not alter the approach angle but merely keeps the
face of the par parallel to the braking surface. It has no useful
effect in braking. The pad still dives the same as the rigid one, its
path governed by the pivot point of the brake arm... which is the
same for either kind of brake.

I think we had this discussion before, and you originally made that
mistaken assumption, but subsequently actually examined a "Parallel
Push" canti and saw that it did indeed solve the problem.

It is true that Parallel Push V-Brakes move the pad in a circular arc,
like all cable operated brakes, however the center of the circle is
displaced inward, so that the active arc section is very nearly horizontal.

Quoted message said:

Quoted message said:

Quoted message said:

>Traditional sidepulls are also linear in response, but to refer to
>them as "linear pull" brakes would be sort of like calling an
>Ashtabula crank a "cotterless" crank: technically correct, but
>idiomatically inappropriate.

Quoted message said:

Quoted message said:

The cotter attached cranks to the spindle while the Ashtabula crank
was one piece. I think the parallel is wanting.

Quoted message said:

So does that mean you'd describe a Schwinn Varsity as having
"cotterless cranks"?

Maybe you didn't catch it but the Schwinn Varsity did not have
removable cranks so there is no method of attachment, cotters, square
taper, or otherwise (cotterless).

Now you're being deliberatly obtuse. I didn't say anything about
attachment. The fact remains that it would not be "technically"
incorrect to refer to these cranks as "cotterless" since they don't use
cotters--but it would be idiomatically wrong and would only cause confusion.

Quoted message said:

Quoted message said:

Quoted message said:

This is about linearity in braking response

Quoted message said:

No, it's about the standard, albeit colloquial, terminology used in
the bicycle industry.

Quoted message said:

We also commonly use the term "alloy" as a synonym for "alumin(i)um"
and everybody in the biz understands this.

That doesn't mean we have to talk bicycle jive to be understood. It
doesn't hurt use the proper terms and say aluminum or titanium rather
than alloy. I think as sources of information for bicyclists, the
industry could raise the level of technical jargon rather than pander
to the lowest common denominator.

"everybody in the biz understands this" =: "cosi fan tutte" or "they
all do it" so it must be good.

That is the descriptivist position on language, vs prescriptivist. A
minority viewpoint.

If you don't like the term "linear pull" what alternative name do you
propose the industry adopt to refer to this style of brake?

"Side pull" would be technically correct, but this term is alreaady in
use for a totally different style of brake, so that's not a suitable
alternative.

"V-Brake" is a Shimano trademark, so that's not available.

Assuming you do have a suitable candidate, what incentive can you offer
to the industry to change the generally-understood name to something else?

Sheldon "Linear Pull" Brown
+----------------------------------+
| What sane person could live in |
| this world and not be crazy? |
| --Ursula K. LeGuin |
+----------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Sheldon Brown said:

Quoted message said:

I used centerpull brakes when they were the rave and found they
performed no different from side pull brakes except for the
pad-climb toward the tire and the lack of a good QR.

Quoted message said:

The advantage of centerpulls is the same as the advantage of
cantilevers, viz.: increased tire/fender clearance.

Quoted message said:

It is a widespread misapprehension that this type of brake gives
more braking force.

That was the basis on which they were touted but then measuring it and
showed them to be no different in ME.

Quoted message said:

Quoted message said:

Quoted message said:

> What is bad about cantilever, V, or centerpull brakes is their
> large vertical error in rim contact during pad wear. The
> centerpull progresses into the tire sidewall while the cantilever
> can pop under the rim with wear, its action angle being about 45
> degrees to the plane of the rim.

Quoted message said:

Quoted message said:

Quoted message said:

This can be a problem. It varies considerably with cantilever
stud placement and rim width. Tends to be particularly bad on
mountain bikes where wide forks move the studs outward, and narrow
rims are commonly used to reduce weight.

Quoted message said:

Quoted message said:

Please consult your diagram and notice that the brake pads approach
the rim at about a 35 degree angle, the line from P to S and the
rim. This is not a good brake function and it is that way for the
brakes I mentioned above.

Quoted message said:

That's just a drawing, but I agree that it is often a problem,
especially in some installations as described above.

It's a good drawing although not necessarily representing any specific
brake. It shows what the dive angle is for those who don't have the
image in mind.

Quoted message said:

Quoted message said:

Quoted message said:

Shimano's "parallel push" linkage and Avid's "Arch Rival" are
"linear-pull" cantis that solve this problem, though at some cost
in added complexity.

Quoted message said:

Quoted message said:

Parallel push does not alter the approach angle but merely keeps
the face of the par parallel to the braking surface. It has no
useful effect in braking. The pad still dives the same as the
rigid one, its path governed by the pivot point of the brake
arm... which is the same for either kind of brake.

Quoted message said:

I think we had this discussion before, and you originally made that
mistaken assumption, but subsequently actually examined a "Parallel
Push" canti and saw that it did indeed solve the problem.

Thanks for reminding me. That is correct. The arc of travel is the
same but because it starts at the top of the arc where cosine error is
trivial in contrast tot the brake in your diagram.

Quoted message said:

It is true that Parallel Push V-Brakes move the pad in a circular arc,
like all cable operated brakes, however the center of the circle is
displaced inward, so that the active arc section is very nearly horizontal.

Minimizing cosine error.

Quoted message said:

Quoted message said:

Quoted message said:

>> Traditional sidepulls are also linear in response, but to refer
>> to them as "linear pull" brakes would be sort of like calling an
>> Ashtabula crank a "cotterless" crank: technically correct, but
>> idiomatically inappropriate.

Quoted message said:

Quoted message said:

Quoted message said:

> The cotter attached cranks to the spindle while the Ashtabula
> crank was one piece. I think the parallel is wanting.

Quoted message said:

Quoted message said:

Quoted message said:

So does that mean you'd describe a Schwinn Varsity as having
"cotterless cranks"?

Quoted message said:

Quoted message said:

Maybe you didn't catch it but the Schwinn Varsity did not have
removable cranks so there is no method of attachment, cotters, square
taper, or otherwise (cotterless).

Quoted message said:

Now you're being deliberatly obtuse. I didn't say anything about
attachment. The fact remains that it would not be "technically"
incorrect to refer to these cranks as "cotterless" since they don't
use cotters--but it would be idiomatically wrong and would only
cause confusion.

Ah yes, but cotters and the like are references to removable cranks
and that is why it doesn't apply.

Quoted message said:

Quoted message said:

Quoted message said:

> This is about linearity in braking response

Quoted message said:

Quoted message said:

Quoted message said:

No, it's about the standard, albeit colloquial, terminology used
in the bicycle industry.

Quoted message said:

Quoted message said:

Quoted message said:

We also commonly use the term "alloy" as a synonym for
"alumin(i)um" and everybody in the biz understands this.

Quoted message said:

Quoted message said:

That doesn't mean we have to talk bicycle jive to be understood.
It doesn't hurt use the proper terms and say aluminum or titanium
rather than alloy. I think as sources of information for
bicyclists, the industry could raise the level of technical jargon
rather than pander to the lowest common denominator.

Quoted message said:

Quoted message said:

"everybody in the biz understands this" =: "cosi fan tutte" or
"they all do it" so it must be good.

Quoted message said:

That is the descriptivist position on language, vs prescriptivist.
A minority viewpoint.

Quoted message said:

If you don't like the term "linear pull" what alternative name do
you propose the industry adopt to refer to this style of brake?

I think we have had some suggestions already. I find the wordsmiths
at some bicycle hardware firms unimaginative. Mavic comes to mind
first.

Quoted message said:

"Side pull" would be technically correct, but this term is already
in use for a totally different style of brake, so that's not a
suitable alternative.

Quoted message said:

"V-Brake" is a Shimano trademark, so that's not available.

Quoted message said:

Assuming you do have a suitable candidate, what incentive can you
offer to the industry to change the generally-understood name to
something else?

I thought V-brake was poor to start with, there being no "V" in the
action or design. How about "cross-pull".

Jobst Brandt
[email hidden]

Tom Sherman said:

Sheldon Brown said:

...
We also commonly use the term "alloy" as a synonym for "alumin(i)um"
and everybody in the biz understands this....

The word "alumin(i)um" should always be accompanied by "alloy" unless
one is referring to a material that is of at least industrial grade
purity, since the mechanical properties of aluminium and aluminum alloy
differ greatly.

Since we use the word "alloy," it's not
applicable.

Sheldon Brown said:

...
We also commonly use the term "alloy" as a synonym for "alumin(i)um" and
everybody in the biz understands this....

The word "alumin(i)um" should always be accompanied by "alloy" unless
one is referring to a material that is of at least industrial grade
purity, since the mechanical properties of aluminium and aluminum alloy
differ greatly.

--
Tom Sherman

[email hidden] wrotr:

Quoted message said:

Sheldon Brown said:

The advantage of centerpulls is the same as the advantage of
cantilevers, viz.: increased tire/fender clearance.

It is a widespread misapprehension that this type of brake gives
more braking force.

That was the basis on which they were touted but then measuring it and
showed them to be no different in ME.

Mechanical advantage is only one element in delivering braking force.
Stiffness is at least as important.

Centerpull calipers have shorter, stiffer arms connecting the pads to
the pivots, so they are better able to resist fore-to-aft flex and
torsional flex in the pivot. It is flex, and not lack of mechanical
advantage, that limits the maximum braking force available from a
caliper brake. All else equal, centerpulls can deliver more braking
force than sidepulls because they flex less and can be pulled harder
before the lever runs out of travel.

Chalo Colina

g.daniels said:

and as i broke into a big grin drifting the fiat 128 into a series of
s-turns cut into the woods above Pennsylvania fields.
the salesman said: "well, this is one car you don't want to buy."

ROFLMAO!!!

--
Phil, Squid-in-Training

Pizza Man said:

I am considering upgrading my V brakes from entry level Tektro to SRAM
9.0 Linear pull brakes (or some other quality mid level V brake).

Ouch... not a good idea. If the Tektro levers have a lot of friction, then
I would upgrade, but the SRAM 9.0 levers are plastic. They aren't as bad as
one might think, but they are pretty poor unless you can use them with GOOD
disc brakes.

The Avid Single Digit series, including the 7, is an excellent choice.

--
Phil, Squid-in-Training

In article <[email hidden]>,

(Chalo) said:

Centerpull calipers have shorter, stiffer arms connecting the pads to
the pivots, so they are better able to resist fore-to-aft flex and
torsional flex in the pivot. It is flex, and not lack of mechanical
advantage, that limits the maximum braking force available from a
caliper brake. All else equal, centerpulls can deliver more braking
force than sidepulls because they flex less and can be pulled harder
before the lever runs out of travel.

The pad to pivot distance is shorter, but there is also the pull point to
the pivot point distance, and whether more or less of the arm is pulled
more or less directly around that pivot point. On sidepulls one arm is
definitely shorter and the other longer in that way, but depending on the
design of the arms and the quality, even the longer one might be stiffer on
bottom than a centerpull is on top. That certainly is the case for several
I have compared, e.g. my CLB Racers versus my Weinmann 500s. I don't know
if either is forged although I believe the Weinmanns are.

However, cantilevers beat all on this score.

--
TO WHOM IT MAY CONCERN

Please excuse the inconvenience allegedly caused by our son. Send
us the bill for all the damages, and we can settle this to your
satisfaction, without any need for a public record of the incident.

Most Sincerely, George and Bar

"Phil, Squid-in-Training" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Pizza Man said:

I am considering upgrading my V brakes from entry level Tektro to SRAM
9.0 Linear pull brakes (or some other quality mid level V brake).

Ouch... not a good idea. If the Tektro levers have a lot of friction, then
I would upgrade, but the SRAM 9.0 levers are plastic. They aren't as bad as
one might think, but they are pretty poor unless you can use them with GOOD
disc brakes.

The Avid Single Digit series, including the 7, is an excellent choice.

Phil,

I did not realize the levers are plastic. I'll pass. I spent a while
reading the reviews of the Avid SD7 at MTBR and it looks to be a great
brake at a great price. Thanks for the tip.

Tracy.

Pizza Man said:

"Phil, Squid-in-Training" <[email hidden]>
wrote in message
news:<[email hidden]>...

Quoted message said:

Pizza Man said:

I am considering upgrading my V brakes from entry level Tektro to
SRAM
9.0 Linear pull brakes (or some other quality mid level V brake).

Ouch... not a good idea. If the Tektro levers have a lot of
friction, then I would upgrade, but the SRAM 9.0 levers are plastic.
They aren't as bad as one might think, but they are pretty poor
unless you can use them with GOOD disc brakes.

The Avid Single Digit series, including the 7, is an excellent
choice.

Phil,

I did not realize the levers are plastic. I'll pass. I spent a while
reading the reviews of the Avid SD7 at MTBR and it looks to be a great
brake at a great price. Thanks for the tip.

Tracy.

I've got a set of SD7s brakes , recently outfitted w/ Kool Stop pads. I
love 'em. I do prefer XT levers, but the SD levers almost as good and I'd
have no problems using 'em if I could get a good deal.

You might want to head down to the LBS and pull a few levers and see what
you think.

Tom

Tom Sherman said:

Quoted message said:

We also commonly use the term "alloy" as a synonym for
"alumin(i)um" and everybody in the biz understands this....

Quoted message said:

The word "alumin(i)um" should always be accompanied by "alloy"
unless one is referring to a material that is of at least industrial
grade purity, since the mechanical properties of aluminium and
aluminum alloy differ greatly.

Oh? So all metals used on bicycles must be referred to as alloys,
alloy steel, iron alloy, copper alloy, tin alloy, etc. You're pulling
my leg aren't you. This sounds much like the cement, asphalt, and
concrete discourse. There's much too much liturgical turgidity there.

Jobst Brandt
[email hidden]

Chalo Colina said:

Quoted message said:

Quoted message said:

The advantage of centerpulls is the same as the advantage of
cantilevers, viz.: increased tire/fender clearance.

Quoted message said:

Quoted message said:

Quoted message said:

It is a widespread misapprehension that this type of brake gives
more braking force.

Quoted message said:

Quoted message said:

That was the basis on which they were touted but then measuring it
and showed them to be no different in ME.

Quoted message said:

Mechanical advantage is only one element in delivering braking
force. Stiffness is at least as important.

Quoted message said:

Centerpull calipers have shorter, stiffer arms connecting the pads
to the pivots, so they are better able to resist fore-to-aft flex
and torsional flex in the pivot. It is flex, and not lack of
mechanical advantage, that limits the maximum braking force
available from a caliper brake. All else equal, centerpulls can
deliver more braking force than sidepulls because they flex less and
can be pulled harder before the lever runs out of travel.

From this, I assume the long reach Campagnolo side pull brakes on my
bicycle don't work at all. They have a lower ME than dual pivots and
they are too flexible to work, having excessively long arms. I think
you are selectively exaggerating as though you were a user of
centerpull brakes defending your crummy brakes. You must be aware
that the centerpull was discontinued because it had no clothes,
offering no functional advantage over other brakes while having a pad
sweep that endangered the tire as its pads wore. Besides, it never
has a good QR.

Jobst Brandt
[email hidden]

Quoted message said:

Tom Sherman said:

Quoted message said:

We also commonly use the term "alloy" as a synonym for
"alumin(i)um" and everybody in the biz understands this....

Quoted message said:

The word "alumin(i)um" should always be accompanied by "alloy"
unless one is referring to a material that is of at least industrial
grade purity, since the mechanical properties of aluminium and
aluminum alloy differ greatly.

Oh? So all metals used on bicycles must be referred to as alloys,
alloy steel, iron alloy, copper alloy, tin alloy, etc. You're pulling
my leg aren't you. This sounds much like the cement, asphalt, and
concrete discourse. There's much too much liturgical turgidity there.

Jobst Brandt
[email hidden]

No, he said "alumin(i)um" should always
be accompanied by "alloy..." If my
element table is correct, steel, iron,
copper, tin are not "alumin(i)um."

Richard Tack said:

Quoted message said:

Quoted message said:

> We also commonly use the term "alloy" as a synonym for
> "alumin(i)um" and everybody in the biz understands this...

Quoted message said:

Quoted message said:

Quoted message said:

The word "alumin(i)um" should always be accompanied by "alloy"
unless one is referring to a material that is of at least
industrial grade purity, since the mechanical properties of
aluminium and aluminum alloy differ greatly.

Quoted message said:

Quoted message said:

Oh? So all metals used on bicycles must be referred to as alloys,
alloy steel, iron alloy, copper alloy, tin alloy, etc. You're
pulling my leg aren't you. This sounds much like the cement,
asphalt, and concrete discourse. There's much too much liturgical
turgidity there.

Quoted message said:

No, he said "alumin(i)um" should always be accompanied by "alloy..."
If my element table is correct, steel, iron, copper, tin are not
"alumin(i)um."

Yes, he said "unless one is referring to a material that is of at
least industrial grade purity, since the mechanical properties of
aluminium and aluminum alloy differ greatly". I guess you missed that
part of the rule which applies to most pure metals.

I take it you believe in bicycle jargon even when unambiguous English
words exist for the concepts.

Jobst Brandt
[email hidden]

Jobst Brandt said:

Tom Sherman said:

Quoted message said:

We also commonly use the term "alloy" as a synonym for
"alumin(i)um" and everybody in the biz understands this....

Quoted message said:

The word "alumin(i)um" should always be accompanied by "alloy"
unless one is referring to a material that is of at least industrial
grade purity, since the mechanical properties of aluminium and
aluminum alloy differ greatly.

Oh? So all metals used on bicycles must be referred to as alloys,
alloy steel, iron alloy, copper alloy, tin alloy, etc. You're pulling
my leg aren't you. This sounds much like the cement, asphalt, and
concrete discourse. There's much too much liturgical turgidity there.

To be pedantically correct, yes. 😉

Cement is an adhesive material, asphalt [1] is an adhesive derived from
petroleum, and concrete is a composite material consisting of an
aggregate matrix in a cementituous binder. The terms are not at all
interchangeable.

[1] Not to be confused with tar, which is a coal derivative.

--
Tom Sherman - Pedant

Quoted message said:

Richard Tack said:

Quoted message said:

>>We also commonly use the term "alloy" as a synonym for
>>"alumin(i)um" and everybody in the biz understands this...

Quoted message said:

Quoted message said:

>The word "alumin(i)um" should always be accompanied by "alloy"
>unless one is referring to a material that is of at least
>industrial grade purity, since the mechanical properties of
>aluminium and aluminum alloy differ greatly.

Quoted message said:

Quoted message said:

Oh? So all metals used on bicycles must be referred to as alloys,
alloy steel, iron alloy, copper alloy, tin alloy, etc. You're
pulling my leg aren't you. This sounds much like the cement,
asphalt, and concrete discourse. There's much too much liturgical
turgidity there.

Quoted message said:

No, he said "alumin(i)um" should always be accompanied by "alloy..."
If my element table is correct, steel, iron, copper, tin are not
"alumin(i)um."

Yes, he said "unless one is referring to a material that is of at
least industrial grade purity, since the mechanical properties of
aluminium and aluminum alloy differ greatly". I guess you missed that
part of the rule which applies to most pure metals.

I take it you believe in bicycle jargon even when unambiguous English
words exist for the concepts.

Jobst Brandt
[email hidden]

You may need to have it become an all
inclusive "concept" for your own ego.
However, the specific subject matter was
and still is a single element:
"alumin(i)um" and not "all metals used
on bicycles."

Quoted message said:

Chalo Colina said:

All else equal, centerpulls can
deliver more braking force than sidepulls because they flex less and
can be pulled harder before the lever runs out of travel.

From this, I assume the long reach Campagnolo side pull brakes on my
bicycle don't work at all. They have a lower ME than dual pivots and
they are too flexible to work, having excessively long arms.

If you never require more braking than they can provide, then they are
fine for your use. If you require more braking than that, a stiffer
brake (like a centerpull or better yet a stud-mounted brake) works
better, all other factors equal.

In the same way that 36-spoke wheels with Mavic MA-2 rims are perfect
for you but inadequate for my use, a sidepull caliper may provide you
enough stopping power but would never suffice to stop me safely in my
usual riding conditions.

I have drum brakes that are as weak as sidepull brakes and more
fade-prone, but solve the problems of chatter, tire sidewall rub, rim
wear, filth, inadequate tire and fender clearance, and poor wet
braking that afflict sidepulls. Likewise I have cantilever, linear
pull and disc brakes that offer me better stopping power than
sidepulls but have their own tradeoffs.

The fact that you prefer sidepulls to all other brakes indicates that
you value their benefits of simplicity, compactness, infrequent pad
adjustment and light weight over the qualities they lack, like
stopping power, tire clearance, and weather tolerance. You make a
valid judgment, just as do those who place more importance on strong
braking or the ride quality benefits of fat tires.

Chalo Colina

On 27 Sep 2004 19:54:10 -0700, [email hidden]

(Chalo) said:

Quoted message said:

Chalo Colina said:

All else equal, centerpulls can
deliver more braking force than sidepulls because they flex less and
can be pulled harder before the lever runs out of travel.

From this, I assume the long reach Campagnolo side pull brakes on my
bicycle don't work at all. They have a lower ME than dual pivots and
they are too flexible to work, having excessively long arms.

If you never require more braking than they can provide, then they are
fine for your use. If you require more braking than that, a stiffer
brake (like a centerpull or better yet a stud-mounted brake) works
better, all other factors equal.

In the same way that 36-spoke wheels with Mavic MA-2 rims are perfect
for you but inadequate for my use, a sidepull caliper may provide you
enough stopping power but would never suffice to stop me safely in my
usual riding conditions.

I have drum brakes that are as weak as sidepull brakes and more
fade-prone, but solve the problems of chatter, tire sidewall rub, rim
wear, filth, inadequate tire and fender clearance, and poor wet
braking that afflict sidepulls. Likewise I have cantilever, linear
pull and disc brakes that offer me better stopping power than
sidepulls but have their own tradeoffs.

The fact that you prefer sidepulls to all other brakes indicates that
you value their benefits of simplicity, compactness, infrequent pad
adjustment and light weight over the qualities they lack, like
stopping power, tire clearance, and weather tolerance. You make a
valid judgment, just as do those who place more importance on strong
braking or the ride quality benefits of fat tires.

Chalo Colina

Dear Chalo,

I don't mind you being so sensible and courteous, but do you
have to write so much more clearly than the rest of us, too?

Enviously,

Carl Fogel

Chalo said:

...
I have drum brakes that are as weak as sidepull brakes...

Are these drum brakes used on larger (ISO 559-630 mm) wheels? Drum
brakes are best used with small diameter wheels, since the shorter lever
arm from the contact patch to axle greatly increases their effectiveness.

--
Tom Sherman