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2011 Yamaha YZ85 Project Bike

Wednesday, October 26, 2011


Although there haven’t been any major changes to the bike in several years, we came away very impressed with the little Yamaha YZ85 and its potent motor. Our 5’3”, 95lb test rider found the ergos perfectly suited for his stature during our initial test back in May. The suspension works very well in stock form with just a sag setting and a few clicks of the adjusters. We tested at a variety of practice tracks and were very happy with the overall performance of the YZ, but did run across a few things that we wanted to change if we were to actually go racing. We decided to hit the track and see how it stacked up during a few months of summer racing with only minor upgrades and standard maintenance.



With initial testing complete, it was time to go
racing with the 2011 Yamaha YZ85.
Upgrades

The YZ85 is a very competent machine right out of the box and can easily win races with the right rider. We decided to keep the mods to a minimum and focus mainly on improving durability to ensure the bike would hold up to the demands of racing. Our test rider also had some personal preferences for the controls, so we made a couple of upgrades there as well. Finally, we found the stock gearing a little tall, so we swapped sprockets to better suit the tracks in our area.

Our first upgrade was a set of Renthal 7/8” handlebars. The stock steel bars on the YZ are easily the bike’s weakest link. They bent during testing with only the smallest of falls. Our rider slid out in a low speed turn and the last thing you want after paying an entry fee for the day is to have a simple fall in practice that screws everything up. The Renthal bars provide a low-cost upgrade that will help ensure that your bars don’t end up looking like a pretzel. The Renthals are constructed out of lightweight 7010 T6 aluminum which gives them high impact strength and excellent vibration damping. The bars are available in a ton of different bends and dimensions to fit almost any bike and every rider preference. We opted to run the RC Mini bend and our test rider found them to fit his style perfectly. The 7/8” bars also come in a wide variety of anodized colors to give exact look you are craving.

As a testament to these bars, our mini test pilot suffered a massive practice crash after getting kicked sideways off the face of a jump and spit off the side of the bike in mid-air. The bike landed on its left side with the left bar end taking the majority of the impact. The bike and rider were then hit by the next racer, with the bars taking a major hit to the crossbar area. In the end, our rider was fine and the bars, with only a slight bend to the left side, were able to finish out the rest of the motos that day. Had we been running the stock bars, I can guarantee our day would have been over.

With new bars on the YZ, we then needed to outfit it with new grips as well. We stuck with Renthal for these and since our 12-year-old tester still has relatively small hands, we opted for the Renthal MX Full Diamond grips with the medium compound. While the Full Diamond grip can get a little slick in wet conditions, we like the narrow circumference, which enables smaller hands to cover more of the grip.

Levers are another component that can easily bend or break during a simple mistake and bring a quick end to your day of racing. We upgraded both the clutch and front brake to ASV F3 unbreakable levers. The F3 levers feature a pivot design that allows the lever to fold out of harm’s way. Instead of breaking or bending, the ASV levers pivot outward during impact, then spring back instantly. The F3 levers are top-notch. They are forged from 6061 aluminum and feature sealed bearings, stainless steel pivot and bushing parts. They are also re-buildable in the event the pivot bearing or spring wears out. The F3 levers also feature an adjustable reach to suit any hand size. Most importantly, ASV provide a three-year replacement guarantee should the lever ever break, no matter what the reason.

Improving durability with Renthal handlebars was important for surviving a season and the Tag sprocket improved performance.

Our test rider not only loved the adjustability of the ASV levers, but was also very impressed with how the lever actually made the clutch easier to pull. The stock lever on the YZ is a little stiff, but the bend of the F3 levers and angle of the perch lightened the pull considerably. After a summer of racing, and crashing, the ASV levers lived up to the company’s unbreakable claim.

In addition to upgrading the hand controls we decided to show some love to our tester’s feet as well by installing a pair of Pro Circuit Flow Thru Titanium foot pegs. While the stock pegs on the YZ decent in size, we prefer a larger platform and a little sharper bite. Anyone who has ever come up short on a big jump will always appreciate a larger platform to distribute the force of the impact over a larger area. The larger platform also makes standing more comfortable and provides added stability for the rider. The Flow Thru pegs are also designed to reduce mud from packing in the pegs, giving better foot traction and control. While we opted for the titanium pegs for maximum strength and less weight, Pro Circuit also offers the pegs in stainless steel for riders with a more conservative budget.



Once the larger sprocket was installed, the YZ has enough grunt to pull out of corners and can still run with anything on the track.
We love the power of the little YZ. While it basically lacks any kind of bottom end or midrange, the top end pulls like there’s no tomorrow. Most of the tracks we race at provide fairly wide-open and flowing layouts which suited the power characteristics of the YZ very well. We did find, however, that the top-end-biased delivery and tall stock gearing make it difficult to keep in the power when exiting tight corners. To solve this we made a slight gearing change by going up one size to a 48-tooth TAG Metals 428 Aluminum rear sprocket. While the change was small, the extra tooth is noticeable and gives the pull out of the corners that we were looking for.

Results

We raced the upgraded YZ at a variety of tracks including a trip to the Washougal Loretta Lynn Area Qualifier. The bike performed flawlessly at Washougal and we were able to qualify in the 85cc 9-11 stock class. Our test rider was impressed with the engine, especially up Horsepower Hill where a weaker motor will quickly show its flaws. Our stock suspension also performed exceptionally well, even as the track deteriorated and the braking bumps at the bottom of the ski jump turned to mini whoops.

We also contested a few races at our local track, Rogue Valley Motocross. RVMX allows both stock and modified bikes to race the 85cc class. While most of the mini dads have decked the 85’s out with pipes, reed blocks and motor work, our stock YZ held its own and if the bike was lacking any power, it didn’t show. As long as our test rider was able to keep the engine revving in the sweet spot it had as much pull as anything else on the track.

The component upgrades we made proved to be a wise investment. Our rider encountered numerous falls during the course of testing which ranged from small tip overs to big, gnarly cartwheels. The bars and levers maintained their shape after each fall and enabled us to always line up for that next moto. Our gearing change also proved a smart move and gave the YZ enough torque to pull hard out of even the tightest corners.

Maintenance

Maintenance on the Yamaha is simple and the two-stroke proved to be a capable mini racer all season.

Probably the best things about two-strokes are the reliability and ease of maintenance. We made sure to clean and oil the air filter after every ride with PJ1 filter cleaner and filter oil. One thing we really like about the YZ is the roomy airbox and how easy it is to get the filter on the cage to get the air filter screwed into the airbox. We also kept fresh oil in the transmission by changing it out every three to four races. Finally, we made sure to keep the chain lubed and properly adjusted at all times. We were impressed with the design of the chain adjusters and how easy they are to accurately adjust which enables young riders to take part in this simple maintenance. We didn’t quite rack up enough time to warrant a top-end rebuild, but would have replaced the piston and ring with a few more hours on the bike.

Overall

We knew after our initial testing that the YZ85 is a very capable bike right off the showroom floor. The YZ features a strong motor with good suspension and rock-solid durability. We wanted to prove that you could go racing with the YZ85 and do so with limited modifications. In the end we were very impressed with the performance and reliability of the YZ. With just a few components the YZ held up to the demands of racing and gave us the performance we needed.
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Yamaha YZ85 Technical Specifications
2011 Yamaha YZ85
Engine: 85cc liquid-cooled two-stroke; reed-valve inducted
Bore x Stroke: 47.5 x 47.8mm
Compression Ratio: 8.2:1
Fueling: Keihin® PWK 28
Transmission: Constant-mesh 6-speed; multiplate wet clutch
Final Drive: Chain
Front Suspension: Inverted fork; fully adjustable, 10.8-in travel
Rear Suspension: Single shock; fully adjustable, 11.1-in travel
Front Brake: Hydraulic single disc brake, 220mm
Rear Brake: Hydraulic single disc brake, 190mm
Front Tire: 70/100-17-40M
Rear Tire: 90/100-14-49M
LxWxH: 71.7 x 29.8 x 45.7 in
Seat Height: 34.0 in
Wheelbase: 49.5 in
Ground Clearance: 13.8 in
Fuel Capacity: 1.3 gal
Wet Weight: 156 lbs (claimed)
Warranty: 30 Day (Limited Factory Warranty)
MSRP: $3850
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Comments
krg   October 21, 2012 05:12 AM
Can i ask was the front sprocket left standard 14 and rear one changed to 48 teeth Thanks Alan
pyiphoeaung   November 5, 2011 11:50 AM
i like this