1989 Honda RC500M
1989 Honda RC500M
The most powerful Motocross bike ever built
In the 1980's Honda was the most dominant force in Grand Prix motocross. Their effort was financed by an almost unlimited budget and they produced by far the best bikes and had the best riders. Especially in the 500 class. It wasn't a question as to who would win the title, it was a question of which Honda rider would win the title. Eric Geboers is one of the greatest motocross riders of all time. He is a five time World Champion and has been World Champion in all three classes. This alone is a testimony as to what a talented rider Eric was. 1988 reigning 500cc World Champion Eric Geboers campaigned this bike in the 1989 500cc grand prix's. This was Honda's last attempt at an all out 500cc 2 stroke grand prix works bike. The bike appears to be production based, but in actual fact very few parts are production. Only the plastic and a few engine parts are production. The rest of the bike is hand made. The 1989 RC500 also known as an NT8, sits today in unrestored condition as Eric last rode it.
1989 Honda RC500M Photos
Eric Geboers' comments:
This 1989 RC500 is a bike that I have produced a lot of sweat on. I was successful at convincing the Japanese engineers to come to Europe to develop the bike here. From prior experience we knew that testing in Japan was much different than testing in the environment where the bike would be raced. Honda of Japan's strategy for 1988 and 1989 was to start with a production style frame and engine cases. Starting like this makes it much more difficult because you are limited in some key components. In prior years frames were custom made just for my size. For this bike the frame had to remain the same size as the production one, although it was modified. We put more hours in research, more man hours in engineers, more engineers at the track and more hours in track testing than any other bike before. No other bike had consumed so much attention as this one. The direction I went in, more than any other rider, was to make the power usable. I wanted all the power converted to acceleration. If I opened the throttle 20%, I wanted 20% of the power to the ground. This is very difficult to do with a 500cc two stroke. It is very easy to have so much power that it is impossible to control. With a 125 or even a 250 this is not such a big issue. But a 500 with uncontrollable power makes the chassis and the suspension bad as well. I wanted the shape of the powerband to be very linear. I got in many conflicts with the engine engineers at first. They wanted more compression and bigger carburetors for maximum power output, but this produced uncontrollable power. In theory it looked like the way to go. In reality on the racetrack it resulted in slower lap times.
Just before the Finnish Grand Prix, I suggested we do a blind test. I said," Build me three bikes and don't tell me what is on each bike. I will ride all three bikes during practice and I will tell you which bike has the smaller carburetor and low compression". They agreed. After riding all three bikes in practice I told them which one it was and I was right. My lap times were several seconds a lap quicker on that bike too. I opted for that setup on the Grand Prix bike. What really threw them out of their chairs is when I got the holeshot in both motos.
I was working at perfecting the powerband all year long. I even went as far as testing 24 different crankshafts. David Thorpe and I were allotted 12 crankshafts each for the season. Even though each crank was new and within the specified tolerance, I tested each one separately. You could feel the difference from one to the other. There were three that were so good that there was no engine vibration at all. This made the bike feel well balanced. I kept the best ones and put the rest back. David Thorpe will not be happy to read this! (laughter) So I had three good cranks for twelve Grand Prix's. The problem was that Honda demanded that we change the crank every three Grand Prix's. Since the three were better balanced than the others, we cheated a bit and used them for four races each. I didn't win the title in 1989. That was kind of a strange year for me. I carried the number one plate, but the biggest mistake I made was the choice of tires. For ninety percent of the year I used Bridgestones. They provided excellent straight line traction and were very good for cornering, but on any other part of the circuit that gives quite a bit, the Pirelli moose set up was far superior. I tried the moose set up in 1988, but that was with the 18" rear rim. On the 18" rims they felt kind of floating and were not as stable as the conventional set up. 1989 was the first year for the 19" rim and that provided a lower tire profile. With the lower profile, that removed the floating feeling and was a much better set up. I completely underestimated the performance on the 19" moose set up. My main competitor David Thorpe made the right choice by going with the Pirelli moose tires. By the time I realized it, it was already too late. The Championship was already decided. I had the bike working so good. The motor was perfect, the suspension and frame geometry was perfect, I just made the wrong tire choice. It was a shame to spoil the year after so much work and to disappoint so many people, but this was my mistake.
Much of the technology learned in 1989 was carried over into 1990 and beyond. My 1990 works bike was very similar to this one. I pretty much dominated that season. And was World Champion again.
Getting behind an RC500 at full throttle would be taking ones life in his own hands. The 1989 RC500M is probably the most powerful motocross bike ever made.
In 1989 it wasn't a question of who whould win the 500cc world championship, it was a question of which Honda rider whould win. Eric Geboers and David Thorpe at Namur Belgium.
- The top of the seat cover is suede and this does a good job of keeping you on the bike during acceleration.
- The three number ones on Eric's radiator shroud signify that Eric has been World Champion in the 125, 250 and 500's
- This is the best two stroke motor Honda has ever produced. The acceleration of this bike is absolutely unbelievable and yet the powerband is very linear. The power feels like there is no end to it. It just pulls and pulls. It is like controlled violence. Under acceleration the front wheel is always about a foot off the ground and wheel spin is minimal. It is hard to imagine not getting the holeshot with this bike regardless of how poorly you timed the gate. Off the bottom there is no hesitation whatsoever, the throttle response is instant. The motor has no short comings at all. Everything feels perfect. Riders had their choice of different pipes for different powerbands. Pistons are a special HRC parts with two rings that are very thin to reduce friction. Tolerances are kept very tight. The crankshaft can be tuned by changing the weights in it to alter the inertia (see works parts). Due to the extremely linear powerband, the bike uses a hand machined four speed gearbox. The gears themselves are massive and need to be to handle the tremendous load. There is so much power at hand that you can start this bike in third gear without slipping the clutch! The clutch basket is surprisingly out of a production bike. It was replaced every race. A decompressor is added to the side of the cylinder for aid in starting.
- The decompressor is covered by a magnesium cover and is operated by the lever above the clutch lever. Titanium bolts with dished out heads are used at the lever perches. Eric used stock Honda grips glued and safety wired. This would probably be the last bike that you would want the grips to come loose on!
- The air box is a production item with added holes to help the motor breath better.
- A massive set of three core radiators are used to compensate for the heat generated by all the extra the horsepower this bike puts out. Temperatures were constantly monitored by the use of heat tape as shown in the photos.
- NT7 is the code for the works 250 and the RC500 shares the same coil as seen in the gallery above.
- The front forks are works showas that cost about $17,000.00 a set in 1989. Their performance was superior to anything at the time. This style of front fork went well into the nineties. Below, the top triple clamp is a cast magnesium unit that has an eccentric insert at the steering stem that can be changed to provide different offsets. The handlebar mounts are rubber mounted to reduce rider fatigue. There are two mounting positions in the top clamp so the rider had a choice of mounting the bars more forward or rearward as seen here. They are tied together with a one piece magnesium top bar clamp to add to the rigidity. The entire front end is very solid. Below, you can still see the control technique sticker (MUL FIM) from the the bikes last race, the Luxemburg Grand prix.
- Up front a very light machined magnesium hub is used and attached to it, is the front brake rotor made from a very special steel that provided superior braking. Replacement rotors were nearly $1000.00 each! Riders had their choice of several different brake pad compounds. The stopping power on this bike is incredible. The master cylinder is a works Nissin sand cast magnesium unit that has a larger capacity than stock. The front brake lever is also adjustable for positioning unlike the stock one. In the photo below you can see the friction tape around the brake lever is as it was when Eric last rode the bike.
- Eric's brake pedal was custom made for his boot size from a standard HRC brake pedal. The brake pedals themselves are much thicker and more solid than stock. The rear brake pedal attaches to the master cylinder via a heim joint to prevent any binding. This is barley visible in this photo. The green foam was provided by Tecnosel and was used to keep mud from building up in-between the frame and the brake pedal. The frame guard is made from heat treated aluminum to keep the riders boot from hanging up on the rear master cylinder. The rear master cylinder is sand cast and extra capacity. Rear shock spring coils are further apart than stock for less weight, with a large variety of spring rates to choose from. Riders had several different types of footpegs to choose from, Eric opted for the standard HRC one. You can see at the end of the peg, it is stamped STD. The swingarm pivot hole and the hole in the swingarm for the linkage bolts are filled with rubber plugs to prevent mud build-up. The extra precautions and details on the works Honda's is amazing.
- 1989 was the year that brought the 19 inch rear tire. The rim on this bike is an extra wide 2.50 DID with a raised section in the middle to provide extra strength. The idea here is to get a much tire contact with the ground a possible. The original HRC sprockets were machined from billet aluminum and cost a whopping $350.00 each. Later the French sprocket company AFAM sponsored the team. The muffler is a works HRC unit that resembles a cannon. Although hard to see, the green paint from tech inspection is still on it.
- The rear suspension linkage is the Delta design and the dimensions of the links are much different than stock. Each piece is hand machined from aircraft aluminum, they ride in needle bearings and are held together with steel bolts. You can see the extra gusseting at the frame for extra strength. Also notice the adjustment bolt on the rear brake pedal to adjust the pedal height.
- The rear brake rotor is made from the same special material as the front and it is fastened to the hub at five points instead of four like the stock one. This is to help prevent warping under braking. With a rider of Eric's skill and the speed of a works 500 Honda, a lot more heat is going to be generated from braking. Notice that the team was monitoring the rotor temperature by the heat strips on the rotor. Steel is used to fasten the rotor to the hub, also to help prevent warping. The chain guide block and axle nut are machined aluminum. Check out the diameter of the rear spokes...they look like pencils!
- Everyone that had a CR Honda in 1989 wanted a swingarm like this. It is a work of art and very strong. It would only fit the works bike though because the linkage parts were a different dimension. It is tapered toward the rear to reduce weight and in doing so it became known as the coke bottle swingarm. This is a very expensive part, taking days just to make one. In the above photo you can see the heim joint that attaches the rear brake pedal to the rear master cylinder.
- A special chain guide made from heat treated aluminum keeps the chain on and the nylon blocks interchangeable. It is held to the swingarm with machined titanium bolts. The rear axle is high strength steel and machined to act as a chain adjuster.
- A steel glide plate is welded to the bottom of the frame and there is a heavy duty aluminum guard bolted to the right side of the frame to protect the engine cases and rear brake pedal when going thru deep ruts. The rear brake pedal also has a wire attaching it to the frame to prevent the brake pedal from bending out. Notice how thick the brake pedal material is.