WHAT IS IT? The Steahly Yamaha YZ450F flywheel
weight comes in 7-ounce and 9-ounce versions. The
9-ounce version is designed to harness the power of cur-rent-generation 2014 to 2017 YZ450Fs. It is a bonded-on
weight, so it can’t come loose.
WHAT’S IT COST? $139.95 (flywheel weight kit),
$149.95 (installed on your rotor if you send it in); $299.95
(flywheel weight mounted on a Steahly-supplied stock
YZ450F rotor); $150.00 refund (if you order the flywheel
mounted on a rotor, but send your old rotor to them within
30 days); $19.95 (YZ450F flywheel puller).
CONTACT? www.steahlyoffroad.com or (800) 800-2363.
WHAT STANDS OUT? Here’s a list of things that stand
out with Steahly’s YZ450F flywheel weight.
(1) Construction. The Steahly weight is a CNC-milled-from-scratch flywheel weight that is added to the stock
Yamaha flywheel rotor. Steahly cuts a 9-ounce ring of
steel on a lathe. The ring is machined to close tolerances
for an exact fit on the stock flywheel rotor. Additionally,
Steahly cuts a groove in the ring to hold the special epoxy
that cements the two pieces in place. Nine ounces wasn’t
a magic number that Steahly discovered through testing
a wide variety of weights. It was simply the most weight
that they could fit into the space available.
( 2) Installation. You can install the Steahly flywheel
weight yourself (by following the instructions). Or, you can
order the flywheel weight already installed on a YZ450F
rotor, send in your rotor to have the weight installed
by Steahly or order the flywheel installed on a Steahly-supplied rotor, and then send them your stock rotor (in
good condition) for a refund on the price. The only other
cost is for a YZ450F flywheel puller, regardless of which
option you choose. Both Steahly and Motion Pro sell inexpensive Yamaha flywheel pullers.
( 3) Do-it-yourself. These are the steps you need to
take to install the Steahly flywheel weight yourself: (1)
Order the Steahly flywheel weight. ( 2) Pull off your stock
YZ450F rotor. ( 3) With supplied sandpaper and your own
contact cleaner, thoroughly sand and clean the flywheel
where the new Steahly weight mounts. ( 4) With the sup-
plied two-part epoxy, carefully apply the Steahly weight
to the flywheel. The epoxy dries rapidly, so immediately
wipe away any epoxy that seeps out. ( 5) Tighten the four
set screws in a cross pattern for equal pressure. Use the
excess epoxy to fill the screw holes, so the screws can
never back out. ( 6) Allow your newly modified flywheel to
cure for 24 hours. ( 7) Once the epoxy has cured, bake in
your oven on a cookie sheet for two hours at 250 degrees.
It can be done with a toaster oven. ( 8) Reinstall on your
bike and prepare to roost.
( 4) Acceleration. In stock trim, the fuel-injected
YZ450F is very aggressive at first crack of the throttle.
This leads to unwanted wheelspin on slick surfaces and,
conversely, jumpiness in tacky situations. Deep sand and
fast Pros may prefer that hit, but for most tracks the MXA
test riders wanted more throttle control. After racing with
and without the Steahly-modified flywheel, every test
rider was generous in his praise of the benefits of the
heavier flywheel. The YZ450F pulled more smoothly and
gained traction in places where it would previously spin.
The power was more manageable and usable. Flywheel
weights do not cost horsepower; they just change the way
the power is delivered by torquing up the low end and
carrying it further on the top end.
( 5) Braking. The extra inertia of a heavier flywheel not
only resists speeding up, it also resists slowing down. We
thought this might be a negative, but the heavier flywheel
helped under braking and transitioning through corners.
When chopping the throttle with the heavier flywheel,
engine rpm doesn’t drop as suddenly. This made for a
smoother transition from full speed to full stop, and it
reduced the chance of flame-out.
( 6) Options. You can choose between 7-ounce and
9-ounce flywheels, but MXA has always preferred the
9-ounce weight. Given the YZ450F’s abrupt powerband,
the heavier, the better.
WHAT’S THE SQUAWK? We would pay the extra
money to have Steahly do the work of installing the
YZ450F flywheel weight on the rotor and save the oven
for baking birthday cakes.
STEAHLY YAMAHA YZ450F FLYWHEEL WEIGHT
MXA TEAM TESTED
Performance-wise, the Steahly 9-ounce fly-
wheel weight is exactly what the Yamaha
YZ450F needs. Not only does it help the power
delivery, it calms the YZ450F chassis by keep-
ing the power hooked up.