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Earning the scars:
 Flatirons Tuning Rally Car



Playing with LSD

Limited-slip differential, or LSD, is a term applied to any non-open differential, but that’s a bit misleading. There are three types of non-open differentials: hypoid or torque biasing, viscous, and clutch type. Each of them behaves differently.

The CUSCO differentials that we use for gravel are clutch-type locking differentials. The reason they’re good for slippery conditions like dirt and gravel is that they act like a regular open differential as long as the driven wheels are spinning at the same speed. If the wheels start spinning at different speeds, such as in a corner, or, to a greater extreme, in a slide where all wheels would be spinning, the clutch packs will grab and force both wheels to spin at the same speed. Both wheels are pulling forward with the same force and at the same speed once the differential activates. That is what helps a rally driver hold and control the car in a slide when all four wheels are spinning.

The problem on tarmac with sticky tires is that they won’t lose grip easily. When the clutch-type differential activates because of the difference in speed between the inside and outside front wheels, it makes the car understeer severely.

The hypoid differential connects the two driven wheels by a series of planetary gears. Its advantage on tarmac is that, in a corner, it does not force the inside and outside wheels to turn at the same speed, so it has no understeer issues. It will apply force to both the inside and outside wheels proportionately so the driver can apply power earlier, and through more of the corner while still holding a proper race line.

 

 

 

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