MX Racer Magazine YZ125 Test

Ivan Tedesco and his Yamaha of Troy YZ125 are favored to win the 2003 THQ Eastern Region 125 Supercross Championship. Now in his second year with one of the winningest 125 factory-supported satellite teams, Tedesco is considered by many industry insiders as a top pick to take the championship this season, and after putting in several stunning performances on a 250cc machine in the earlier west coast rounds, it is easy to see why he will be a front-runner.Now, we all know that it takes a great rider and a great team backing him to pull off an AMA championship, but it also takes one hell of a bike. In today's highly competitive world of supercross, the machine that takes the rider to the podium is a giant part of his key to success. While many think that, as good as today's production motocross machines are, all they would have to do is bolt on a stiff set of suspension and head to the stadium, that is certainly not the case in this day and age. Besides being in tip-top physical condition and having Superman-like riding skills, a rider needs a highly tuned race weapon.Today's supercross machines start out as production motorcycles (which for most of us are already way too much bike) and are transformed through hundreds of painstaking hours at the test track and back at the race shop into special one-off race bikes. Teams like Yamaha of Troy (YOT) are given all kinds of trick factory and aftermarket parts to test and develop for their race bikes. Yes, even with the production rule in effect, these bikes do use some trick parts that are available only to top pro riders. Most of you are probably saying that this is unfair to the privateer or are even wondering why your new bike doesn't come stock with some of this trick stuff. Actually, your bike does come with trick factory parts, just a year or two later, as many of the parts that these riders are privileged enough to use usually end up in future production. However, not all of the trickery is one-off factory exotica; many of the parts used on Tedesco's YZ125 are aftermarket and can be purchased from your favorite shop.We would have to be crazy to turn down the offer to ride a factory bike, so when Yamaha's Terry Beal invited us to burn a tank of gas through Tedesco's bike before the first round of the series we naturally jumped at the opportunity, figuring that our readers would want to know what one of these cycles is really like and how well it performs. With this in mind, we headed out to our secret testing facility to meet Beal and the YOT boys for a morning of test riding and brain-picking. These factory technicians are really nice guys when you are asking them the basics, but they sure do get tight-lipped when you get a bit more technical and start asking for port dimensions and ignition curves. All kidding aside, this was a very informative morning for our testing team.The Yamaha of Troy YZ125 begins as a stock machine but is stripped down to the bare frame as soon as it's peeled out of the crate. The frame is checked over and welds are strengthened, as these bikes take quite a bit more abuse at this level of competition. Modifications are also made to bolt on trick DSP carbon fiber frame guards, skid plates and case guards to the frame. With the motor out of the frame, YOT's Dean Baker and factory technicians from Yamaha Motor Corp., USA (YMUS) modify the already potent stock mill to provide each rider his own personal supercross powerband. First, the motor is torn apart and inspected for any flaws. The cylinder and head are YOT/YMUS-modified to each rider's personal taste. Many cylinder and head combinations are tested during the off-season to find the perfect setup. The crankshaft is stock, while a Wiseco piston and ring replace the OEM parts. Crankcases start out as production units (per AMA rules) and are then modified to YOT/YMUS specs. The stock Yamaha YZ125 transmission is inspected and placed back in the cases for final lower-end assembly. To improve clutch action and longevity, a Hinson billet clutch hub and basket replace the stock unit. YOT forces air and fuel into the powerplant with the Moto Tassinari V-Force two-reed block, which is fed VP MR2 race fuel mixed with Yamalube 2R premix by a Mikuni TPS power jet carburetor. Fuel and air are sparked by a YMUS programmable ignition and an NGK BR9EG spark plug. YOT uses Twin Air filters to keep fresh, dirt-free air flowing into the motor. Exhaust gasses are expelled and power is made by using an FMF Factory Fatty pipe with an FMF Titanium Power Core silencer.Now that this fire-breathing supercross motor has been built, it is time to put the power to the ground. YOT prefers to use Renthal sprockets for performance and durability to channel the power to the rear wheel, while a Dunlop rear knobby provides the grip. Dunlop tires are used in front and rear and many different rubber compounds and lug patterns are used during a supercross season, depending on track conditions. Also, gearing may be changed to accommodate a different track configuration or rider's preference. YOT mounts those Dunlops to Excel rims with stock hubs and spokes.Aside from a good motor package, a key ingredient in making any supercross bike even remotely rideable on today's brutal tracks is the suspension. With that said, YOT utilizes the services of Enzo Racing Suspension in Santa Ana, California. Enzo is a Kayaba specialist and sells AMA-homologated works suspension kits for AMA 125 pro riders. This is about as close to full factory suspension as a 125 rider can get while staying AMA legal. The forks are 48mm in diameter compared with the stock 46mm units. The larger diameter fork is more rigid and thus flexes less, reducing friction within the forks. A special gold titanium nitride coating is also used on the inner fork tubes to reduce friction. While the internal workings of the forks remain basically stock, they too have special coatings to keep all of the moving parts nice and slick. Along with much stiffer springs, stiffer, more aggressive valving is also used. Enzo outfits all of its works kitted forks with its carbon fiber sub tank assemblies, which are also made available to the masses.The rear shock is also an AMA 125 pro class-homologated unit, which uses a two-piece body rather than the stock cast body. The shock body is treated with a special coating to reduce friction and help dissipate heat. Over the years, Enzo has developed several trick parts for use in shock assembly. Billet shock spring preload collars, reservoir bladder extenders and heavy-duty bumper kits are just a few items that come on the works kit shock that are also available to its customers.With plenty of motor, works Kayaba suspension and a finely tuned chassis, all that is needed is a way to slow it down. YOT utilizes stock master cylinders and stock calipers in front and rear, but replaces the stock brake pads with Ferodo aftermarket pads. The front brake rotor is a floating factory YMUS unit, while the stock rear rotor is standard on its race bikes. Fastline brake hoses are also used for rider preference and a DSP carbon fiber disc cover protects the front disc.Hosts of other factory and aftermarket parts are used to complete a YOT YZ125 race bike. Renthal bars with soft dual-compound grips are mounted to YMUS special triple clamps. A very trick Genuine Yamaha Technology-Racing (GYT-R) easy-adjust clutch lever and perch are installed, which makes clutch cable tension adjustment a breeze when on the fly. The throttle assembly is stock and uses an aluminum throttle tube for durability. An array of trick titanium and aluminum hardware is used everywhere on the bike, in an effort to shed some pounds and make working on the bike an easier and quicker task for the mechanic. Many of the bolts used have the same size head, so the mechanic doesn't have to change tools as often. This really comes in handy when it is crunch time at the races. Fenders, side panels and other parts are stock Yamaha and decorated with N-Style and Yamaha of Troy graphics. For grip, an N-Style seat cover wraps around the stock seat foam, and GYT-R Titanium (wide) footpegs are installed.Now don't head out to the garage to tear into your bike just yet, because we saved the best for last. After spinning several laps on this factory one-off, we came away from our experience surprised to find that, aside from a few details, a stock YZ125 doesn't feel too different from this exotic machine. Yes, the motor is really fast, but so is the stock YZ. Power delivery, however, was a bit different from stock, as with most pro-level bikes that we have ridden; the motor makes most of its power up top. Granted, the YOT YZ125 had plenty of bottom-end to go around, but it also pulled long and hard up top, which is surprising for a supercross bike. Most would expect a supercross motor to be nothing more than an arm-jerking bottom-end monster, but a top pro rider can go far and beyond the lower RPM range.As expected, the suspension was plush during the initial part of the stroke, but very stiff as the stroke gets past its first couple of inches. Big hits and flat landings were a dream, as the Enzo Kayaba works suspenders sucked up the big stuff like a Cadillac. Suspension is so crucial in supercross, as it not only absorbs the big hits but allows the rider to spring off obstacles like a pogo stick. For instance, take those gnarly step-on, step-off combos that are so common on today's SX circuits. The area that a rider has to land, transition and jump to the next obstacle is often only about a bike length in width, so not only is great timing required to get through those sections unscathed but also a great suspension setup. A rider would not be able to clear the monster jumps out of the corners or get through the whoops without the perfect suspension setup. Supercross setups are designed to be less absorbing and stiffer to help lift the bike over the obstacles.The most notable thing that sets a factory bike apart from a new production model is the attention to detail. Every nut and bolt is turned and massaged to perfection. The fit and finish of every component is darn near perfect, down to the butter-like pull of the clutch lever, and if it's not, it is tested until it is. So many hours are put into these machines, from their inception through the racing season, that it is easy to see why factory riders have the edge over their competitors. These bikes are completely torn down, inspected and rebuilt every week after a race. Hours of use on components are logged and parts are changed as needed. The information is sent back and forth among the factory in Japan, Yamaha Motor Corp., USA and Yamaha of Troy. All of this is in an effort to win races and build a better bike for you to buy each year. The old saying still stands true today: What we race is what we sell, only in this case it is sometimes a year or so later.