When most folks think about California’s Mammoth Mountain they envision bundling up in thick winter wardrobes and zigzagging down the mountain blasting waist-deep powder on their skis or snowboard. But for 10 days each summer, this relaxed mountain resort is overrun by two-wheeled racing enthusiasts for the annual Mammoth Motocross event. This year, MotoUSA participated in the fun with its 2010 Kawasaki KX450F dirt bike.
Mammoth Motocross is one of the oldest continuously run races in the U.S. It started 42 years ago and has run every summer since. Over the years many racing superstars, including James Stewart, Ricky Carmichael and Jeremy McGrath, have bashed handlebars around its one-of-a-kind course carved out of the Sierra Nevada’s deep forest. The track’s spectacular rollercoaster layout, majestic landscape and relaxed mountain atmosphere have made this event one of the must-dos for any avid motocross racer.
Originally, both I and our ace test rider, Matt Armstrong planned on racing, however we both ended up breaking bones in separate dirt bike crashes (oops). I broke a bone and separated my shoulder in late April, then Armstrong fractured a bone in his heel six weeks later. Since both of us were out of commission, we recruited another test rider, Frankie Garcia, to man the helm of our project KX450F.
The Build Up
(Above) Not only does FMF’s Factory4.1 slip-on muffler look better it reduces sound slightly and increases power at maximum engine speeds. (Center) Ferodo’s latest SinterGrip SG-Plus pads have slightly more power and feel when used aggressively. (Below) Renthal’s Kevlar Dual Compound Half-Waffle Grips are both durable and soft which reduce arm fatigue during motos.
Perhaps the most amazing feature of contemporary 450 motocross bikes is how race-ready they are from the crate. With little more than a few simple modifications you have a dirt bike that is ready for competition and tailored to your ability and style of riding. We choose to race a Kawasaki KX450F based on its powerful, easily tunable engine and friendly chassis and ergonomics. Considering our KX had accumulated over 50 trouble-free hours there were a few wear and tear items that needed immediate attention.
First up were tires. While the OE Bridgestone’s complement the KX450F’s chassis, we were anxious to try Pirelli’s latest knobs – a set of Pirelli Scorpion MX tires. Pirelli offers five different compounds to choose from based on terrain, but we settled on the Mid-Soft compound on recommendation from the Mammoth Pirelli tire vendor’s, Pit Pro Cycles.
Next to tires, the OE chain and sprockets are the fastest wearing components. So we replaced them with a reasonably price setup from Renthal. We like the versatility of the stock final drive ratio so we selected a 13-tooth steel countershaft sprocket and 50-tooth black-anodized aluminum drive sprocket. The sprockets were mated to a more durable 520-pitch non O-ring R1 Works Chain with gold plates.
Having already replaced the rear brake pads once, both the front and rear pads were almost down to the backing plates again. Although we’re fond of the stock pads we wanted to see if we could get more performance and/or life out of an aftermarket set so we installed Ferodo’s latest SinterGrip SG-Plus pads.
One of our favorite features of the KX450F is its ergonomics. If you’re an average to above-sized rider you’re going to love the cockpit of the KX. The spatial position of the handlebar, seat and footpegs is balanced and open, making it easy to ply your body when riding. Our only real complaint are the rock hard hand grips.
Even with 50 hours on the bike the grips looked brand new, which is testament to just how tough they are. So we swapped them for a pair of Renthal’s Kevlar Dual Compound half-waffle grips. The cool thing about these handholds is that they offer the best of both worlds. The dual compound Kevlar design allows them to be durable like the OE grips, but then soft when touched which helps reduce hand and arm fatigue during motos. Surprisingly getting the original hand grips off isn’t the easiest thing to do as they are melted to the handlebar and throttle tube with a “vulcanizing” process. This means that you literally have to grind them off.
Without question the most important modification you can make to your bike is having the suspension tuned for your riding style and ability. As we stated in the 2010 Kawasaki KX450F Comparison the stock suspension spring rates and valving favor heavier and/or faster riders. But with time the damping performance of the suspension, especially the fork, had degraded. We also wished to modify the valving characteristic of the fork as there wasn’t enough initial or mid-stroke damping causing the front end to dive excessively during deceleration compromising chassis balance. To fix these problems we enlisted the help of RG3 Suspension.
(Above) RG3 Suspension revalved the Kayaba fork with its Smart Valves. (Below) RG3 Suspension revalved the Kayaba fork with its Smart Valves.
Considering the weight (170-180 lbs.) and skill of myself and our test rider, Frankie Garcia (novice-intermediate) RG3 recommended we stick with the OE spring rates (0.48 kg/mm fork and 5.5 kg/mm shock), saving us a bit of cash. After disassembling both components they fitted it with their proprietary valving. Additionally they installed the optional KYB Smart Valve in the fork. The Smart Valves are an aluminum valve piston that utilizes two fluid ports as opposed to the stock single port piston. This better directs fluid to specific sections of the valving for improved performance throughout the stroke. For the rear shock they retained the original piston but modified the valving shim stack for improved action.
You’ll be hard pressed to find a rider who thinks that the KX450F is lacking in terms of engine power. Even so, when the engine is revved out near maximum rpm it feels like the power flattens. Plus the packing in the stock muffler wears out quickly making it obnoxiously loud. In our quest for improved performance at high rpm as well as a more pleasing exhaust note we mounted a sweet-looking Factory 4.1 SL slip-on muffler from FMF.
Mammoth’s track is situated at an elevation of over 8000 feet. Fortunately the KX450F is fuel-injected so it’s always going to run properly regardless of elevation or atmospheric conditions. However, at this altitude the air is significantly thinner which reduces the quantity of air the engine can ingest. To compensate we added Kawasaki’s spectacular Fuel Injection Calibration Kit. This easy-to-use tool allows you to electronically tune the power delivery of the engine with a PC-compatible computer. Per Team Green recommendations we downloaded the Soft Terrain map which restored the KX’s snappy sea-level throttle response and helped negate the effects of the altitude.
To cap off the project and add a bit of style we purchased a set of special M10 Mammoth Motocross backgrounds from Dirt Digits. We’re big fans of Dirt Digits graphics as they not only look awesome but are simple to install.
Before making the trek north to Mammoth we did some testing and suspension setup during the REM motocross races at Glen Helen Raceway. Fortunately setup was minimal and all that was necessary was setting the rear shock sag at 100mm and making a couple adjustments to the compression and rebound on the shock.
The day before racing kicks off you have the option for a full-day of practice. Mammoth’s soil and layout is unique, so it’s important to get some extended seat time if you’ve never raced here as the practice sessions on race days are limited to just 10 or 15 minutes. Just getting parked and set up inside the track is an ordeal due to how limited paddock space is. Securing a good spot requires you to wake up at 3 a.m. and queue up outside the front gate until it opens at 5 a.m. If you decide not to get up that early then good luck finding a good spot inside the track.
The layout of the track itself has a bit of everything. It’s fast and flowing in some spots and tight and technical in others. It’s got a fifth gear pinned uphill straightaway, a steep downhill, a number of tight second-gear off-camber turns, switch backs and some really technical sections that look like something you‘d see on a mountain bike trail. Jump-wise there are a few tabletops, the biggest being a 75-footer, but overall no obstacle is really difficult or dangerous.
Equally as unique is the composition of the soil. Considering its volcanic past, the dirt has a dark brown/red hue to it. In some areas, it is very fine and almost silty. Below, however, the ground is the textbook definition of hard pack. So hard in fact that it’s almost impossible for ruts to form because the ground is basically rock. This requires a different riding style in which we square up corners. It’s also crazy how rough the track becomes.
For the last few years the races at Mammoth always sold out well before the event begins. This means that practice and each class is full. And when I say full I mean it was like full-on bumper bikes with all-classes running together. It’s basically like an open ride day which makes it awesome for testing because you’re riding the track during in the worst possible conditions. Halfway through the morning the track is already covered in huge braking and acceleration bumps, pot holes and all other energy zapping obstacles.
Considering how tight many parts of the track are it is important to have a bike that turns in sharply even if you have to comprise a bit of straight-line stability. To do this we adjusted the tension on the rear shock spring and adjusted the sag to 95mm. This sharpens the steering angle and makes the bike easier to steer.
Friday – Pirelli Open Junior Race
Garcia’s Open Junior class practice session was the first on Friday. A total of 48 riders had entered in his class split amongst two divisions with the top-12 transferring right to the main. His five-lap Division 1 race was the first moto of the day meaning he’d be able to race on a relatively smooth track.
When the gate dropped, our rider got a good jump and was in second place going up the hill, proving the effectiveness of a stock KX450F engine.
(Above) Pirelli’s Scorpion MX tire worked well on Mammoth’s unique terrain. (Below) Pirelli’s Scorpion MX tire worked well on Mammoth’s unique terrain.
“I love how easy the KX450F is to launch,” said Frankie. “You kind of have to be careful on the concrete because the engine has so much power right off the bottom. But if you can get off it without spinning the tire too much then get on the gas hard in the dirt the engine just rips.”
The pack poured around the first turn with the throttles pinned as they motored up the long uphill straightaway. Frankie maintained his position through Turn 2 and back downhill but was already under attack. Halfway through the first lap two kids got around him and he settled into position for new few laps.
One of the craziest things about racing Mammoth is the elevated level of fitness required to wrestle a 250-pound motorcycle. Since the air is much thinner, aerobic activity taxes your body much harder and it’s this type of scenario in which properly dialed suspension really pays dividends.
“The thing that stood out most to me was how much better the suspension felt as compared to stock,” said Frankie. “By the time my main came around the track was worked. There were huge bumps everywhere but the suspension made it way easier to ride. It felt like the bike sucked up a lot of the impacts instead of your body. It was plush initially but firmed up with a quickness as it moved deeper in the stroke. The rear end felt really planted too it didn’t hop around or kick when bombing down that steep downhill.”
Garcia was also impressed with the improved braking performance. When the brakes are initially applied they provide a similar level of feel as the stock components however they are a hair grabbier. But as you get deeper into the lever, the amount of feel increases as does stopping power.
“As you grab the lever the brake felt more responsive compared to stock,” notes Garcia. “It isn’t a dramatic change but considering the pad cost around $40 it’s a worthwhile upgrade.”
With only a lap to go two other kids barely got by him when he made a small mistake, but he managed to hang on and finish sixth meaning he’d transfer directly to the seven-lap main event.
Spectacularly, in the main Frankie pulled off a holeshot.
“The Soft Terrain map made the engine feel much more responsive,“ he said in comparison to the previous tuning. “It still didn’t feel quite as snappy as it does at sea-level but it definitely helped. I think the muffler made a difference too. The powerband didn’t seem to fall off quite as hard toward the rev-limiter. It wasn’t a huge difference but it was noticeable.”
Frankie lead most of the first lap before one guy passed him. By Lap 2 he had more riders on his rear fender. Two more guys got around him relegating him into fifth position but he still looked strong. He managed to maintain his position until a few laps later when he officially dropped anchor letting a steady stream of riders passing him. He eventually huffed and puffed his way to 17th position out of 38 riders. This wasn’t the result any of us were looking for considering that he was actually leading the race at one point, but it proves just how competitive and in-shape you have to be to race at Mammoth.
Sunday – Dirt Digits 450 Junior Race
A whopping 107 racers had signed up for Sunday’s 450 Junior class. Given the high number of entries the class was split into four divisions. The top-seven finishers from each of the four heat races transferred to the main. Once again Frankie was the first practice session of the day, but based on how tired he got during Friday’s main he elected to only run a couple of laps.
Frankie’s qualifying heat race was the seventh moto of the day meaning the track would be rough but tolerable for his race. At the start of the race it looked like he might pull of another holeshot until a small group of riders on the inside stole his glory. Still he was inside the top-10 through Turn 1.
But as he maneuvered through the narrow section before the downhill, a rider lost the front end going through the turn and crashed. Frankie was directly behind him when it happened and had nowhere to go causing a massive pile-up.
It took him some time to get his bike untangled leaving him dead last. He charged forward through the pack picking off riders, but eventually ran out of laps. He finished 14th out of the 21 riders. This meant he’d have one more shot at making the main if he could finish inside the top-three in his LCQ.
His LCQ was the fourth from last race of the day, and by then the track was totally hammered with humongous bumps that would make Chad Reed wince. Amazingly the holeshot master lived up to his reputation once again – his second of the weekend.
“Gearing-wise we could have probably gone one or two teeth smaller on the rear sprocket,” said Garcia when asked how the Renthal gearing worked. “I mean, I got two holeshots so it couldn’t have been too bad. Still, I wish I could have held gears a bit longer, but overall it wasn’t bad and something to remember for next year.”
One of the benefits of running Pirelli’s Scorpion MX tire is how soft the carcass is as compared to other off-road tires. This works in unison with the suspension helping to suck up heavy hits. The tires hooked up well though they did look pretty worn out after two days of racing. Many of the shoulder knobs peeled off, no doubt due the combination of high-speed load and rocky terrain.
(Above) Frankie failed to make the 450 Junior main on Sunday after crashing in his heat race then tweaking his back in the LCQ. (Below) Each summer for 10 days Mammoth Mountain hosts motocross races at its epic natural terrain track.
Frankie was doing well and looked like he was going to make it to the main until his bike started swapping down the steep hill. The bike was still out of control as he reached the bottom but he tried making the right-hand corner anyway and somehow tweaked his back in the process. Our rider continued to ride but the pain built up enough that he decided it wise to pull off, effectively ending his weekend.
“The braking bumps were beyond gnarly. It was like a whoop section down the hill that’s how bad it was,” said Frankie. “I wish I could have done better because overall the bike worked well. Everything from the engine’s power delivery, to the suspension, tires and brakes all worked great.”
Even though the weekend didn’t go quite as well as we wanted… Heck, we failed to even make the main on Sunday there were plenty of positives. Two holeshots, zero mechanical meltdowns, no big crashes or broken bones, plus we had a lot of fun. After our first time competing at Mammoth we learned some important things like how extremely fit you have to be to be able to run at maximum speed for 15-20 minutes at 8000 feet plus how a little bit taller gearing would have made the bike even more friendly to ride.