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First... Let me say
that any 700C road tire works fine on Topolino wheels but in my opinion
you can take fuller advantage of the advanced design of Topolino wheels
with a set of 20mm tires.
The Physics:
There are several
inter-related factors working to limit your performance on a bicycle.
The three most important are aerodynamics, weight and rotational inertia. The first two are
self explanatory. Rotational inertia refers to the fact that moving
weight from the outside toward the center of a rotating part will
facilitate quicker acceleration even though the total weight doesn't
change. I won't get into formulas here but it is helpful to have a way
of deciding which of these factors is more important in any given
decision. On a scale of 1 to 100, with 100 being the most dramatic
effect, here is how they compare:
Aerodynamics = 100 points
Weight = 10 points
Rotational Inertia = 1 point
Two other factors are
friction (including rolling resistance of your tires) and handling such
as traction and stability.
Topolino wheels are
19mm wide at the rim. If you look at the front of a wheel you will see a
frontal area 19mm wide by 700mm tall. This area is directly proportional
to the aerodynamic drag of your wheel. Of course when you mount a tire
on the wheel, you change the frontal area. The 23mm tire has a 15%
larger area than a 20mm tire and a 15% greater aerodynamic drag. The
typical 20mm tire is 10% to 15% lighter than its 23mm counterpart. In
addition, a lighter tire reduces the rotational inertia of the wheel as
well. While the weight and rotational inertia are significant, it is the
aerodynamics that is most advantageous.
Objections:
Harsher Ride -
There is one primary objection to running 20mm tires on a road bike... They
cause a harsher ride than wider tires especially when you consider that
you should run about 15% higher air pressure in the narrower tires for
comparable performance. With typical wheels this is true but with the Topolino design, the spokes provide high frequency vibration damping
(like a mini-suspension system - see more below). The typical chatter
from rough pavement simply disappears providing a smooth
fatigue-reducing ride even with 20mm tires at 150 psi (my road set-up).
Higher Pressure
Equals More Rim Stress - Sounds right but not accurate math.
While it is true that the stress on the rim is directly proportional to
the air pressure, it is also directly proportional to the width of the
tire so since the air pressure is 15% greater and the width is 15%
smaller there is no net difference in rim stress.
Rolling
Resistance is the Same at the Same Air Pressure -
Again, this is true, but we are running 15% more pressure in the
narrower tire so rolling resistance is lower for the narrower tire.
Handling and Traction:
There are two profound
advantages of the Topolino design:
Wheel Stiffness
- This is not related to tire size but is significant so let's
take a look at it. When you enter a corner on your bike, you initiate
the turn by counter steering. You may not be aware of it but all turns
begin with steering in the opposite direction of the turn. (Being aware
of this fact will improve your riding and safety!) The steering and
leaning actions apply a lateral force on your wheels. If they are not stiff enough, they deflect under
the force which has the effect of causing you to over-steer (turn more
than you anticipated). Once you correct for the over-steer, the lateral
force is reduced on the wheel and it returns to a more normal shape
causing you to under-steer (turn less than you anticipated). As you
continue through the corner you continue to oscillate between over and
under steering. The severity depends on factors such as speed, rider
weight and wheel stiffness and can range from a general feeling of
insecurity to outright out-of-control cornering.
Topolino Carbon
Core/Kevlar spokes are stronger than 14 ga. stainless steel spokes and
because they are 60% lighter, they allow Topolino wheels to have a full
spoke count. This design is very stiff under heavy lateral loads and
significantly improves handling and cornering stability. My personal
experience is a 10% to 15% increase in cornering speed over my previous
set of wheels. That is speed I don't have to scrub off on corner entry
and, more importantly, don't have to accelerate back to as I exit the
corner.
Vibration Damping
Mini-Suspension - The Topolino carbon/Kevlar spoke design absorbs the vertical
forces applied to the wheels by small irregularities in the road surface
such as cracks and rough pavement. If these forces are not absorbed,
they are transmitted to the entire bike. With spokes that absorb the
up and down movements, the bike is isolated from the vibrations for a
smoother, less fatiguing ride.
In motorcycle racing we
refer to the weight that is below the absorbing device (shock
absorbers/springs) as "un-sprung weight". Higher un-sprung weight
reduces the ability of the bike to keep its tires in contact with the
road. With no shock absorbing spokes, normal wheels cause the effective
un-sprung weight to be the full weight of the bike. Because the Topolino
spokes absorb these small forces they allow the un-sprung weight to be
limited to the weight of the tire, tube and rim of the wheel on the
typical rough road surface. This much lower un-sprung weight of Topolino
wheels significantly improves cornering and braking traction through
improved contact and traction with the road.
The narrower and
lighter 20mm tires also reduce un-sprung weight and add to the overall
Topolino design difference in handling and cornering.
My Specific Tire Recommendation:
Which Tires? -
My personal preference is the Continental Grand Prix 4000 700c x 20mm.
Although the stated tire pressure on the sidewall of your tires is
probably set more by the legal and marketing departments of the tire
manufacturer than by their engineering department, this tire is rated
for 150 psi and it has the new Vectran belt. Vectran is the material
that was used on the large balloons that cushioned the landing of the
Mars exploration vehicle. Vectran is much more puncture resistant than
even Kevlar and has a lower rolling resistance than other materials.
Continental claims 75%
less flats with racing teams using the GP 4000's.
The Bottom Line:
My Experience
- I'm a heavier rider but love to "dive" into corners and push
the envelope. Since switching to Topolino's Revolution AC29 wheels and
Continental Grand Prix 400 700c x 20mm tires, I have been able to
increase my corner entry speed by a solid 10% to 15%. It may not sound
like much, but every mph you have to scrub off before entering a corner
is another mph you have to regain after exiting. At 15% on a 20 mph
entry, that is 3 mph!
Even with the 20mm tire
at 150 psi, I find myself riding over rough pavement that I used to
dodge. This can be a hazard for those riding behind you in a pace-line!
You will appreciate the
lower aerodynamic drag, weight, rotational inertia and rolling
resistance of Topolino wheels with either 20mm or 23mm tires.
The smooth ride and cornering ability are just gravy.
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