Record-breaking time for the Waikato’s answer to Burt Munro

Matthew Martin

March 16, 2024

Karapiro’s Don Short has the fastest 50cc motorbike in New Zealand after hitting 149kph at a Landspeed NZ meet.
MARK TAYLOR / WAIKATO TIMES

Don Short hopes his dreams of visiting Bonneville’s salt flats will one day become reality, but for now he’ll settle for having the fastest 50cc motorbike in New Zealand.

At a recent Landspeed New Zealand event, Waikato’s answer to Burt Munro averaged 147kph over two runs, reaching a maximum speed of 149kph on the day – not bad for a bike with about as much power as a decent weedeater.

Speedsters on both four and two wheels have been using Goudies Rd, a former private forestry road near Reporoa (halfway between Rotorua and Taupō), to conduct their speed trials on its 7km of straight, flat tarseal for decades.

“My goal is 160kph, or 100 mile an hour, and I’m pretty sure I can reach that with a few changes to the set up,” Short said.

Short said the key to his bike’s speed was its aerodynamic cowling.
MARK TAYLOR / WAIKATO TIMES

“I didn’t take into consideration the altitude – about 550m above sea level – which took about 5% of my horsepower away.”

Short’s two-stroke KTM dirt bike with a six-speed gearbox produces 18hp at over 14,000RPM, but the key to its speed is its aerodynamic cowling, which was built by a friend of Short’s and adapted and refined by engineering students at the University of Canterbury.

The 55-year-old roading engineer said he always had a need for speed, but to keep his long-suffering wife happy he decided on using a smaller bike to achieve his dream.

“I picked the smallest class as it was the cheapest, and to convince my wife it was not as dangerous as riding the larger, faster bikes.”

The 50cc motor in Short’s record-breaking bike is no larger than one you’d find in a decent weedeater.
MARK TAYLOR / WAIKATO TIMES

Short literally dreams of hitting the ton (100mph) on the salt plains of Bonneville in Utah, and like Burt Munro, has pretty much done all the work himself, with some help from his friends.

“I’ve always had a dream to go to Bonneville to watch, I do actually dream about it, and then I heard they have a Bonneville event in Australia, so I decided I’d go there to race on salt.

“This was before the Munroe movie, but I did get some inspiration from it and have watched the movie, the doco and all of that.

“I want to have the fastest 50cc bike in the world … the fastest at the moment is 233kph – but that’s a fully enclosed streamlined bike with a parachute.”

There’s not a lot of room to move within Short’s record-breaking bike, but it’s only designed to go in one direction.
MARK TAYLOR / WAIKATO TIMES

Landspeed New Zealand Association president John Seccombe said Short’s record was “official enough” for them, but to have it internationally recognised it would need to be verified by officials from the Fédération Internationale de Motocyclisme (FIM).

“It’s a bit unique what we do, but we mimic what the FIM do internationally, we just haven’t been endorsed by those international organisations.

“It’s fantastic for Don, and he now has bragging rights that he has the fastest 50cc motorcycle in New Zealand.

“All credit to him, he’s been trying a long time,” Seccombe said.

– Waikato Times

We Get to Race

It’s been a long time coming. The new landspeed body was designed for the salt at Lake Gardiner, but then COVID intervened, canceling the event. In the interim, I relocated to NZ.

Excitement filled me as I planned to participate in an event in NZ, situated in Reporoa, running on tarmac. In 2022, brimming with anticipation, I set out. However, the day proved to be challenging. The bike refused to perform well, leaving me without a single successful run.

Time was spent diagnosing the issue plaguing the bike. Despite its prior reliability, it suffered from a fueling problem. My modifications had inadvertently restricted fuel flow to the fuel bowl. Rectifying this required a thorough fuel flow test and adjustments to accommodate the horsepower I was generating.

To confirm the resolution of the fueling issue, we participated in the Cliffhanger speed trial. The event’s course, starting with a sweeping corner, crossing a bridge, and onto a straight, showcased the bike’s flawless performance. Fuel problems were definitively resolved.

Fortuitously, I enlisted the help of students to assess my aero package, initially constructed on gut instinct. Their insights led to valuable suggestions for improvement. Implementing one significant fairing change proved beneficial, enabling me to adopt a lower position on the bike.

The next scheduled event for the bike was in December 2023. Despite our readiness, adverse weather conditions – rain and erratic winds – prompted me to defer participation for a more favorable day.

Finally, on March 9th, we seized the opportunity to race as the weather cooperated. With only two return passes for the day, one north and one southbound pass, we achieved impressive speeds. Clocking in at 149kph and 145kph respectively, we averaged a remarkable 147kph (91.875mph). This surpasses the current New Zealand record by 18.6kph (11.665mph).

Regrettably, Motorcycling New Zealand’s absence means I cannot officially claim it as a record. Nonetheless, it’s widely acknowledged as the fastest 50cc in New Zealand, verified by Tag Heuer timing gear.

Building some Streamlining

So we did pretty well with our long low bike.  A lot of our horsepower is being consumed with air friction.  So the plan is to build a fairing.  But where do you start?

First is tried to work out what size I needed to be able to be inside and fit around my bike

I got a size and proceeded to see how it would fit around the bike.   It seemed like it would work in the computer and in reality.  Now all I had to do is work out a way of translating it to something I could build and attached to my bike.

I took some inspiration from Hiro Racing out of the USA who built a wireframe and then a fairing around that

I went back to CAD and played with some ideas

Then it was a matter of trying to turn that image into reallity.  So I purchased a box of welding wire and turnd the hot glue gun on.

Once I worked out I could fit into the shape I wanted I proceeded to firm up the shape and see how we could build it from fiberglass.  I showed Warren from Coopertech Composites what I wanted to do.  He didn’t run for the hills.  We decided to build it using a sandwich foam construction for strength and weight

It turned out pretty good.  There was approx 3kg of wire inside the form holding the shape we were after.  Once the bottom was formed it was time to try it on the bike.

So it all fitted fine.  Next was to work out how/what to build the rest of the fairing out of.

Warren had some parts of various things.  I had some parts from last year so we started to blend it all together to make it into one homogenous unit.  It was not easy and took a lot of time, swearing and heartache but we got there.

Inspiration was taken from Alp Sungurtekin for the riding position

We got published

Speed Week 2019

Race day comes and we line up for our place. Everything is going well and we move up to the start line. Still a little nervous on how the bike is going to handle. I have only ridden it twice. Once on a back street in Queensland and a second run yesterday out the back of the pits. I was a little concerned with the ride out the back of the pits. It was really rough so I move the clip on bars out a little to give me some more leverage.

It was our turn. I had filled up the bike back in the pits and we were ready to go. Moved the bike to the start line (there are 3 positions beside each other at the start so we still have 5-10 mins) and proceeded to start the bike to warm it up. It wouldn’t start. What was going on. Every time on the dyno it started first time. I kicked and kicked and kicked the bike. It would not start. I couldn’t work it out. Thankfully John had an idea after looking at the plug. He said we were not getting any fuel. How could this be I had filled it up back at the pits. We pulled out of the line so others could run. John quickly went back to the pits and retrieved some more fuel. After putting more fuel in it and replacing a spark plug I had now killed the bike ran again. It wasn’t till later that day I worked out what had happened. I had filled the bike on the paddock stand. The top tube is our gas tank so on the paddock stand with the rear of the bike raised it had created a vapor lock and we had almost no fuel in the bike.

Leaving the start line was interesting. Had to be like a tripod but laying down. So into gear. One foot on the foot peg and drag the other foot until I was moving fast enough and the lift it onto the other foot peg

The bike ran perfectly. I had to hold it back a little on the 2 mile run up. The unknown this year is we were doing two way runs over one mile (previously one way 1/4 mile runs). The max hp on the bike is around 14,000 rpm so this is a lot of rpm to be holding for 45 sec plus a little run up. She held together, didn’t miss a beat and handled perfectly.

I know it had gone well but didn’t know how well. John came and picked me up in the van and we headed back the pits to get our timing slip. Out of the box, first run after the dyno tune we did 81.718 mph. We were pretty happy. Off to impound until we could complete our back up run.

The second run did not happen until the next day. Choose not to change anything even though I thought the bike should be able to pull some more gearing. Do fix what isn’t broken.

We ran 83.414 mph on the back up run so things were all good. Now we had to go off to tech to have the bike measured. I was not worried about the size being right but I was a little nervous about the fuel I was running. I had got the fuel from Power Plus Fuel and they had supplied me with a Non Ethanol 102. He had assured me that it would pass the organisations dialectic reading but until the tech officer confirmed it I a little worried. Worse case I would have had to move to the Fuel Class.

These two runs gave us an average of 82.566mph

The rest of the week was a bit of a bust. We didn’t break anything but there was a head wind and when you have less than 20hp any headwind makes a difference. We did another three runs but could not move the record up any more.

We know there is still more in the little bike.

We made it to the salt

So John and I flew down.  Picked up a van and then the bike.

It was then the drive to Port Agusta

We stayed the night here, got all the food we needed for the week and had our last meal/beer at a real pub.  Tomorrow we had a good 4hrs drive to get to the lake.

We got our camp all set up, down to the lake and set up our pits.  Then there was a little time to get the bike ready for technical inspection the following day.   I mixed up some fuel and started the bike.  We are good to go.

Every competitor also has to do a session of volunteering.  I was down to help set out the race circuit.  This required us to put in track edge markers by drilling 19mm holes in the sale and erecting the flags.

Time for technical inspection.  This all went well with a few people surprised about what we had built.  Now we just had to wait till racing started on Monday morning.

 

Ready to see what this bike can do

We were still finishing the bike on the weekend before tech and didn’t really know how it would go.  It was booked in on the dyno on Monday morning and at the freight company Monday night to take to it, Adelaide.   Although I had done one test run this was before the engine was rebuilt, ported, new ignition and carb.  Who knows what it’s going to run like.

The only way to really test it was back on the dyno.  So it was off to Bevan at Euro Twins.  It took a morning but we were able to get something that we liked.  Given that it was leaving that afternoon we didn’t want to blow it up so the tune was kept conservative.  It pulled well in all gears and was ready for the salt

Need a Smoking Pipe

To make a Two-Stroke go well you need the right pipe.  And when you make a custom bike/engine your not going to find the right pipe on the shelf.  I had been looking at pipes for a while and the techniques to make them.  Most pipes you buy are two pressing halves welded together.  There is another method where you weld two flat sheets together that has a shape.  You then pump up with water and get this nice looking pipe.  This method needs some black magic to come out looking nice.

The most common method for custom pipes is cones.  This means welding and a lot of welding.  This is the path we decided to go down.  But until you have a pipe design you have nothing to weld.

Shane the engineman worked some magic and somehow did the calculations to design a pipe to do what we needed it to do and to fit the bike.  The hardest part is I had the bike in Brisbane and Shanes in Melbourne.

Somehow he did it and I received a file to send to the laser cutter.  I dropped the material off and a few days later received and a handful of components.

Now I just had to make them cylindrical.  Andy Corrigan helped with some advice and rollers.  I rolled and beat all the flat material until it became round.  Then took it to a welder who welded up the seams.

After the seams are welded you get some deformation.  So it was back to making them all round again.  Then it could be fully welded into a pipe.

It came out great.  Just tacked together here but very close to the finished product.  It also has a stinger tube that could be replaced to change its size.

Bodywork complete

So the bodywork came back great.  All painted up in the KTM orange, all we had to do was fit it to the bike.  It took a little work to get it mounted.  I decided to use the rear subframe.  This took a bit of work to get the rear seat to mount to it.  And I messed up a little with the captive nuts I had.  They were designed for bodywork and not to attach to metal so would move a bit.  It was a real pain to get the bolts lined up to mount.

It’s starting to look like a saltracer now.  Warren did a great job from Coopertech Ind.

What am I going to sit on

The class I choose to run in is called A class. This meant you could build the frame I wanted and use the engine I wanted. Because it’s what they call a bare-bones class you are not able to run any aerodynamic fairing. The rules do allow you to have a front guard that covers almost half the front wheel and a seat.

My longer-term plan is to run the Honda RS125 bodywork. Two reasons for this. Reason one – in Tony Foale book on chassis design he has the Cd of a number of fairings. The RS125 came in as pretty slippery. Reason two – I purchased a set of RS125 molds.

Of course, they were not going to just bolt-on and the front guard is much smaller than I wanted. A friend Michael from Hand Held Dyno put me on to his guy Warren from Coopertech Ind.

Warren has been in the fiberglass industry since before he left school. He’s an old surfer who’s built everything from surfboards to superyachts.

What impressed me about Warren is what he was able to make out of very little. I turned up with mold and he made the green part in the above picture. He then went about extending the nose from a section of a Suzuki A100 and filling in the sized with some sheet he made.

It was all tacked and taped together. He then joined it all into one guard in such a way that you would never know it’s made of five parts.

Now Warren didn’t need much arm twisting to get involved. He’s ridden bikes all his life and has been working on his own land speed bike.

Next came the seat.

Again there was cutting and tucking required to make it fit. It didn’t take to long and Warren had it all shaped up and fitting nice.

Now he doesn’t claim to be a painter, he didn’t want me taking his work to anyone else. I contacted KTM who was really helpful and provided me the KTM Orange paint code so the fairings could be painted.

I think you will agree that it came out pretty good.