This
paper helps explain how to set up a bike for general road riding then how to
modify the position for riding in a aero position using tri bars.
The paper also highlights the compromises that need to be considered when
moving away from a road to an aero riding position.
Much of the information comes from experienced cyclist and published
articles which seem to make logical sense to me.
I hope you find it helpful.
1.
Preparation
1.1.
Gather together the following equipment:
Pen
& paper
Calculator
Tape
measure
Sprit
level
Plumb
line
4mm,
5mm, 6mm Allan keys
Turbo
trainer
Large mirror and/or assistant
1.2.
Find a level floor preferably with a hard surface.
1.3.
Place your bike in the turbo trainer and set the bike level by measuring
the distance from the floor to the centre of the rear wheel spindle (assuming
both wheels are of the same size). Pack up the front wheel so the spindle height
from the floor equals that of the rear. Do
not use a sprit level on the top tube as they are a reliable way to set the bike
level.
1.4.
Make a note/sketch of all the key dimensions of the initial bike set up
using references that will allow you to re-establish this road/racing position
easily.
2.
Crank
Length
2.1.
Measure your inside leg length in mm (to the floor in bare feet).
2.2.
Multiply your inside leg measurement by 0.2 to get the correct nominal
crank length.
2.3.
Fit cranks that are within ±
2.5mm of the nominal value in 2.2.
Note: Powerful riders who
cycle with a low average cadence (< 85 rpm) tend to select cranks that are on
the plus side of the nominal value. Shorter
cranks encourage riders to cycle at higher cadences.
It is generally accepted that average cadences of 90 rpm or higher is
more efficient than pushing big gears at a low cadence. However, cycling at higher cadences is more demanding on the
cardio vascular system and pedalling technique.
3.
Seat
Level
3.1.
Place the spirit level on the top of the saddle and set level.
4.
Shoe
Cleats.
4.1.
Sit on the bike and clip in.
4.2.
Set shoe cleats so that the ball of your foot is over the
pedal spindle
5.
Seat
Height
5.1.
Wearing your cycling shorts and shoes sit on your bike in your natural
road riding position, with hands on the top of the brakehoods.
5.2.
Unclip one foot and with this leg locked out straight adjust the seat
height so your heel just scrapes the platform of the pedal at is bottom
most position. Take care to keep your hips level.
6.
Seat
Fore and Aft Position
6.1.
Sitting on the bike clip into your pedals adopt your natural road riding
position with hands on top of the brakehoods.
6.2.
Place the crank arms in the horizontal position with your foot level with
the floor.
6.3.
Drop the plumb line down from the front of your knee and adjust seat fore
and aft position until the plumb line bisects the pedal spindle. Take care to
sit in the saddle as you would if you were riding your bike. Do not slide
forward and back in the saddle or drop and raise your heel to bring the knee to
the correct position, do it by adjusting the saddle!
6.4.
Recheck your seat height and adjust if necessary.
6.5.
Recheck the seat fore and aft position if you adjusted your seat height.
7.
Drop
Handle Bars Fore and Aft Position
7.1.
Get off the bike and stand at the side.
7.2.
With your forearm horizontal place your elbow on the nose the saddle with
finger tips pointing towards the front of the bike.
7.3.
Check that the tip of your longest finger is three to four finger widths
from centreline of the handlebar as it passes through the stem.
Change the stem for one of the correct length if not.
Note: The distance of the handlebar from the seat is a down to personal
preference and this way of setting the handlebar fore and aft position only
provides a start position from which you can fine tune to your riding style.
Hence it is a good idea to borrow a stem of the length suggested by this method
first before buying. However
beware, stem length affects the way the bike handles.
Hence, it is not wise to fit extremely long (>>120mm) or short
stems (<<80mm) to correct for a frame that is too small or large for you.
If in doubt about frame sizes seek advice from a reputable cycle shop or
knowledgeable cyclist.
8.
Dropped
Handlebars Rotation & Brake Hood Position.
8.1.
Sit on the bike and adjust the handlebar rotation so they feel
comfortable when riding on the tops, the brakehoods and the drops.
Note: The top of the brakehoods should be level or slightly tipped up at
the front. The tips of the brake
levers should not be below the bottom off the bars. Brake levers should be
within reach when on the drops.
9.
Dropped
Handlebar Height
9.1.
Sitting on your bike with your hands on the brake hoods adjust your
handle bar height until your hip angle approximates to 90 degrees.
Note: Hip angle is shown in the sketch below. It is created by imagining
a line from your pedal spindle in the down position to your hip and from your
hip to your shoulder. In this
position you should feel well balanced with not to much weight being taken
through your hands.
10.
Record
Bike Set Up Key Positions
Make a
note/sketch of all the key dimensions you have just set using references that
will allow you to re-establish this road/racing position easily.
11.
Experiment
Each
of the three riders represented on the right are in positions appropriate for
Time Trialling / Triathlons. Which one you adopt depends on how much you are
willing to spend, comprise comfort and safety for the sake of speed and
efficiency. We will come back to these issues later when we consider the
advantages and disadvantages of adopting an aggressive aero position using a
Time Trial / Tri specific bike compared to a more neutral riding position using
a road/race bike.
The
aero position with its low frontal area should not be created by making the 90
degree hip angle (established in the previous section for a neutral road/race
riding position) more acute. Instead
the aero position is created by rotating the rider about the bottom bracket.
There are several ways of doing this, namely: pushing the seat further forward,
by sitting further forward on the seat (“sitting on the rivet”), or by using
a bike frame with a steeper seat tube angle (which effectively pushes the bottom
bracket back further under the rider). How
to modify the neutral road riding/racing position established in the previous
section is explained below.
1.
Fitting
Tri Bars
1.1.
Fit the tri bars to your bike and adjust so they are at their lowest
possible position. Ensure this position places the bottom edge of your hands
level or slightly
above your elbows when in the aero-position.
Note: Some riders (even professionals) ride with their hands lower than
their elbows but this is not the most aero dymanic position.
1.2.
If converting a road bike for Time Trialing then the front of the bike
(relative to the saddle height) may not be low enough to achieve a good aero
position. Special stems (such as
the Look “Ergo Stem”, see picture insert) are available that allow the
handlebars to be mounted lower than a traditional stem.
2.
Seat
Fore and Aft Position
2.1.
Sit on the bike and clip in and adopt the aero position.
2.2.
Adjust the fore and aft position of the seat in order to preserve the
90-degree hip angle. Note: The position of the knee may now be in front of the
pedal spindle when the crank arms are in the horizontal position, this is ok.
2.3.
Check and readjust the seat height as before. Note: Pushing the seat
forward will require you lift seat to maintain the correct seat height over the
pedals.
2.4.
If you can’t achieve the 90 degree hip angle by pushing the seat
forward then raise the tri bars so you can. Note: Special ‘fast forward‘
cranked seat posts are available that allow the seat to be placed much further
forward then that achievable with a regular seat post.
Take care not to push the nose of the saddle past the centre line of the
bottom bracket. Such a position
would be too extreme and will adversely affect rider comfort and the safe
handling of the bike.
3.
Tri
Bar Fore and Aft Position
3.1.
Sit on the bike and adopt the aero position.
3.2.
Set
the fore and aft position of the tri bars so that the angle created by drawing a
line from your hip to your shoulder and from your shoulder to your elbow is 90
degrees. A different length
stem may be required to achieve this fit.
Note:
This 90 degree angle between your back and upper arm allows you to support your
body weight by your skeletal structure. Departing from this angle places more
work on your shoulder and arm muscles and so is not efficient.
3.3.
Set the fore and aft position of the arm rests so they are on the fleshy
part of your forearm.
3.4.
Check that any adjustments to the tri bar fore and aft position has not
changed your 90 degree hip angle. If
it has then readjust the tri bar height or seat fore and aft position or a
combination of the two.
3.5.
Check the position of the tri bar grips relative to the tri bar arm pads
also create an angle between your upper arms and your forearms of about 90
degrees. If it is the bottom of
your hands should be above your elbows.
4.
Tri
Bar Width Position
4.1.
Sit on the bike and adopt the aero position.
4.2.
Set the width of the arm pads so your elbows are as close together as
comfort allows. Note: Arms close together improves the aero dynamics but
restricts breathing. Experiment to find your preferred width position.
5.
Record
Bike Set Up Key Positions
6.
Experiment
Try riding in your new position for several miles. Consider tweaking it to suit your preferences. Pointing the nose of the saddle down slightly may improve the comfort of an aggressive aero position. Consider the trade-offs between the high torque neutral road/race position and the aero dynamic riding position. A hilly TT course would favour a less aggressive position. What ever position you finally decide upon take care that it does not to depart to far from the 90-degree hip and shoulder angles shown in the sketch above.
Higher
average speed for a given power input
as a result better aero dynamics combined with correct pedalling
cadence, helped by the ability
to finesse the gear selection when riding on the tri bars fitted with bar
end gear shifters.
Disadvantages
of the Aero Position:
Limits
ultimate peak speed
& ability
to climb very steep hills. This
is a result of departing from the high torque neutral road riding
position.
Ridding
on the tri bars can be uncomfortable and unsustainable.
This
because steep seat angles and low front end forces the rider to sit on part
of the bottom not designed for sitting on!
Cause
of crashes into stationary vehicles.
This is because the low front end requires you to lift your head (and
eyes) back further to see ahead. This head up position can be difficult to
maintain and riders let there heads and eyes drop down and refocus on the
tarmac a only few metres in front of their bike!
Slow
braking response. This
due to the extra time required to reach the brake levers when riding on the
tri-bars. Hence, the aero
position is dangerous when riding in a group, taking a draft from a rider in
front or riding amongst traffic.
Poor
stability. The
aero position makes negotiating tight bends or twisty roads or riding at
speeds lower than 15mph dangerous.
Difficult
to change gears
whilst climbing or sprinting out of
the saddle. This because
the rider will be out of the aero position and holding on to the horns of
the tri bars with the bar end gear selector out of easy reach.
Expensive. Expect to pay in excess of £1,500 for a tri specific bike.
Easy to get lost if your name's Eric!