GT LTS Full Suspension KTM 50 Engine

[Wild Bill]

For those that dont want to read heres the Race/Crash Video posted below
http://www.youtube.com/watch?v=m_j5y9XD ... vEWedGWidg

Hi Im a Noob to this site. This is the second bike using a GT LTS frame I have built but on this one I used a KTM 50 engine with a claimed 9 H.P. (Seems more like 7-7 1/2 to me), and the first one I used a "China Girl". Both of them use a Sick Bike Parts shift kit.

This Is the frame I picked up off Ebay. At this point I had even picked up a KTM 50 fuel tank and pipe just to keep the KTM theme going.

[
I also found some cool dirt bike looking fenders made for mountain bikes, perfect!

 

[Wild Bill]

Then I mounted the Sick Bike Parts jackshaft & mount.



Then I used the SBP bracket to weld the rear motor mounts to.



Then I made up a front motor mount and pipe mount. I also had to cut the header pipe to clear the bottom tube and later weld an elbow to fit around the bottom tube.

 

[Wild Bill]

Then I made a chain tensioner for the primary drive chain.



And a tensioner for the secondary drive chain.



Then it was just about ready for the first test ride, the first ride happened before the disc brakes showed up. Normally on a KTM or Morini you set the centrifugal clutch rpm to lock up at a pretty high rpm to get into the engines power band but since this uses a shift kit I set the clutch rpm to grab at just above idle rpm. I did this so the power didnt hit so hard when you crack the throttle and 1st gear is a much lower ratio than a single speed bike would be so it accelerates much quicker and easier than a single speed and doesnt need to always be in the power band. This took the load off the bicycle chain and freewheel. Set up like this I can be in 1st gear at a stop and barely crack the throttle and accelerate. There was some worry that the bikes freewheel or the bicycle chain wouldnt handle the torque of a KTM engine, or the shifting itself would be a problem but I was very happy that everything handled the power no problem.



Then I put on the disc brakes on and we took both bikes out to race in a So. Cal Motorized Bicycle race at The Grange Motor Sports track in Apple Valley and I ran it in the Mid Range class. I was very surprised it handled as good as it did. In fact it handled great! I was about the only one running 26" wheels and my bike had a very high center of gravity compared to all the other bikes since I built it for dirt riding and we were racing on a road course.




The first heat race I started in the back and since its a shifter and all the other bikes are single speed I passed a lot of bikes before turn one and after about 4-5 turns I was in 5th place. But after about a half lap I got big time nervous since this was the first time in years that I had raced anything and I finally ended up about 7th-8th.

Race/crash Video http://www.youtube.com/watch?v=m_j5y9XD ... vEWedGWidg

Then in the second heat I told myself I wouldnt get nervous again and I started in the front row and had the lead breifly off turn one and got passed off turn 2. Then the leader pulled away from me and I pulled away from the rest of the pack and then I was going harder into the turns and braking later and harder until the front brake locked up and over the bars I went....There was a "Perfect Storm" of mechanical and physics related things that contributed to the front wheel locking up. I had just finished building the bike and had very little riding/testing time on it and the race day was a real trial by fire!

 

[Wild Bill]

Now that I have a race day on it I changed to 24" wheels to lower the center of gravity and give the bike a little quicker handling and I stiffened both the front and rear suspension, and shortened the pedal arms for more ground clearance. The bike handles better and has a much better feel. The bike before felt like you could hit any line, brake as hard as you wanted and hit the corners about as fast as you dared and the tires never slipped at all! Hard to believe its better than before but it is! I cant wait for the next race on October 19 !

 

[LukeTheJoker]

Wow! Some interesting stuff! I didn't know people ran motorized bike races!
Nice work on the bike!

Luke.

 

[Wild Bill]

Thanks Luke.

 

[mikeeebikey]

That is an awesome bike.

 

[wheelbender6]

Kool. Have you had time for some trail riding on it? Do you put the 26" wheels back on for dirt riding?

 

[Wild Bill]

Thanks Mike and Wheelbender, and I do put the wheels back on for trail riding. Even though I built my bikes for trail riding I have found myself doing mostly street lately.

 

[mikeeebikey]

I am usually the guy that hates on "motorized," bikes as they are built dangerous!
Using a Wallyland cheapo cruiser bike and a cheapo motor results in a lot of walking, and hopefully not an ambulance ride!
You used a top of the line bicycle and motor, good call! The jack shaft just iced the cake!

 

[wheelbender6]

Wild Bill - Do you shift using the KTM tranny or you shift with the derailleur?

 

[Wild Bill]

Thanks Mike, I studied the whole Motorized Bike thing and couldnt really see doing it any other way, although the first bike I built did use the cheapo "China Girl" engine but did use the same frame.

And Wheelbender, the engine is single speed and the bike does shift using the rear deraillleur, andf the rules dont allow the use of a motorcycle transmission. Before I built the bike I asked around a couple of Motorized Bike forums if anyone had used this engine with the Sick Bike Parts shift kit to see if the bicycle chain and freewheel could handle the torque but never found anyone that had tried it. I got a few opinions that the chain may not take it but I tried it anyways in hope that it would work because after watching videos of the KTM and Morini single speed bikes it just seemed really hard on the clutch slipping so hard for so long coming off of a standing start, and it seemed like the bike would accelerate quicker shifting.

It also seemed really noisy having the clutch rpm so high because of the gearing you need to run, but with the ability to shift and the lower gears you can set the clutch rpm very low and not have the engine screaming all the time. I also roll the power on a little slower and smoother after every shift to help lighten the load on the components.