Now that I have my exterior design model complete, its time to start on the suspension.
Design ApproachI will be using the suspension from a Yamaha Raptor 700.
- The rear suspension should require very little modification. I will start by simply angling the entire Raptor chassis down in the front to pull out some of the angle in the rear trailing arm. I plan to leave a little bit of angle in the trailing arm to provide some anti-squat characteristics. The driver will be placed well forward in the chassis, so the rear spring load should be about right.
- The front suspension will use many of the parts from the Raptor, such as the spindles, brakes, ball joints, A-arms, and steering linkage. However, the Raptor suspension will be completely redesigned to provide good road manners.
Tires and WheelsATV Wheels and TiresSuspension experts always say you should start with the tires and work your way back to the wheels, suspension, and then chassis. The Raptor comes with knobby dirt tires on very small 9" and 10" rims. There are ATV street tires available, but the selection is very limited. I wanted to use a DOT auto tire on a 14" to 15" wheel. There are aftermarket ATV 14" & 15" wheels. So I called tech support at one of the major ATV wheel manufacturers (IRC). They told me that a DOT tire will fit the ATV 14" & 15" wheels, but flange that the tire bead seals against is not as wide as a auto rim, so the tire bead could slip off on hard cornering
That news sent me down the path of using an auto rim and an adapter to fit the Raptor bolt pattern.
Auto Wheels Since the overall vehicle will be very light, it is even more important to keep your unsuspended and rotating weight to a minimum. I looked many different lightweight racing wheel sets, but they were thousands of US dollars. Then I discovered the Mazda Miata "Hollow Spoke" wheel. 1994-1997 Miatas came with the hollow spoke wheel, and they only weigh about 4.98kg (11lbs)! There are lots of Hollow Spoke wheel sets on ebay at very reasonable prices, so I bought a set. After a good cleaning I mounted the lightest tires I could find from Khumo. This wheel and tire combination weighs only about 7.71kg (17lbs) in the front and 10.43kg (23lbs) in the rear.
Adapters After an exhaustive search, there is really only one supplier of ATV to Miata wheel adapters "Adapterking.com". The adapters they sent me were one-offs. The Rear adapters fit well, but the front adapters did not. The Raptor front hubs has a wheel centering tab that required some additional machining to fit. See attached photo of hub. All of the adapters were very heavy, so I decided to do even more machining to lighten them.
- Rear Original: 1.79kg Lightened: 1.16kg Difference: 0.63kg (35% lighter)
- Front Original: 2.45kg Lightened: 1.36kg Difference: 1.09kg (44% lighter)
Note: I just checked and Adapterking.com webste no longer online.
Wheel backspacing is important when choosing the wheel/adapter combination. I will cover backspacing in my next post as part of the suspension geometry design.