Isenhour Motorsports has been racing Ultra4 with Crown Race Gears in their GM 14 Bolt axles since 2015
The Ultra4 Racing Series and the King of the Hammers, known as the toughest on-day off road race in the world, pushes 700hp, tube chassis buggies on 1 ton axles and 42" competition compound tires over rocks the size of cars and through the desert at speeds over 100mph. Not only is this extremely tough on drivers, tires, and suspension systems, it is absolutely brutal on gears.
Every time a tire impacts a rock or obstacle in the desert, the drivetrain and axles bind up to apply torque to the tire. Then, when the tire drops off the other side, the drivetrain temporarily unloads before binding up again when the tire comes back into contact with the ground. These shock loads happen tens of thousands of times each race.
The reason Ultra4 racing destroys gears is that each race subjects the ring and pinion gears to extreme shock loads, followed by long, high speed and high power runs, making for the perfect storm for gear failure. In the rock sections, climbing waterfalls and steep ledged, the vehicle will hop as it tries to gain traction, pushing all of the vehicle's weight (multiplied by the leverage of the tires) onto just a couple of ring and pinion gear teeth. These shock loads cause the ring and pinion teeth to flex and if the gears are not engineered for toughness, micro-fractures will begin to form and with continued use will grow to become cracks and lead to gear failure.
Crown Race Gears are specifically engineered to withstand this type of abuse by starting with a steel alloy that is heat treated and then cryogenically treated to be as tough (flexible) as possible so that it can absorb shock loads, yet have a very hard case (surface) to ensure a very long wear life and reduce friction at high speeds. This ideal gear case hardness transition is difficult to achieve, yet it is the key to making a ring and pinion set hold up to years of Ultra4 racing.
Because micro-fractures are the main cause of gear failure in off-road racing, Crown Race Gears go through two separate shot peening sessions that increase the gear density in those critical areas. This process has shown to improve the usable life of gears by about 75%, and has become a standard requirement for most aerospace components.
In addition to heat treatment and shot peening, Crown Race Gears are cut using 5-cut helical gear geometry that uses a sliding motion to transfer power through the gears instead of a pushing force that stays at the center of the ring gear teeth where it increases the likelihood of pitting and micro-fracturing.
To take full advantage of the 5-cut gear geometry, Crown Race Gears are REM ISF finished for an aerospace grade smooth surface that, when lubricated with the correct race-weight full-synthetic gear lube, reduces friction and power loss by almost 40%. This means that more power gets transferred to the tires allowing for a higher top speed and faster acceleration, and the reduction in heat allows for significantly longer high speed runs without overheating the axle bearings and seals.
By increasing gear toughness, creating a desirable case hardness transition, shot peening the tooth roots, and using an aerospace gear finish, Crown Race Gears are stronger, tougher, and more efficient than any other off-road racing ring and pinion gears available today, making them the top choice of Ultra4 racers.