David.....
....The 'diff effect' is where the inside wheel would 'naturally' rotate at a different speed than the outside wheel if it were free to do so.
In a kart, it's NOT free to do so becuase we have no diff. Having the wheels trying to rotate at a speed that is NOT 'allowed' by our lack of diff causes drag which slows the kart.
We are agreed on the above: Yes?
Let's call the speed at which the wheel would 'chose' to rotate if it was free so to do, the 'chosen speed'.
When a kart is on the straight, the 'chosen speeds' of both rear wheels will be IDENTICAL. The reason for that is because the direction of travel is identical to the centre line of the kart. Agreed?
Now tell me the 'chosen' speeds of both rear wheels in a kart that is passing through a circular corner with the 'centre line' of the kart at a tangent to the inside kerb. The 'circular corner' is an idealised corner for this discussion.
You can guess that I believe the 'chosen speeds' at that 'attitude' to be IDENTICAL and thus there IS no 'diff effect' mid-corner if that 'slip angle' is used.!
In the above case, the centre line of the kart is AGAIN identical to the direction of travel..... hence ZERO diff-effect!
Just tell me that's wrong!
If the kart was 'understeering', there WOULD be a diff effect because the outer-wheel 'wants' to rotate FASTER than the inner wheel.
BUT.... If the kart was 'oversteering' then there WOULD again be a diff effect. That's where the outer wheel 'wants' to rotate SLOWER than the inner wheel (think about it..... that *I*S* correct and counter intuitive). If you are having problems with this.... envisage a second set of wheels at the rear of a kart which are mounted on stub axles. Those extra wheels CAN rotate at their 'chosen speed'. Consider the 'chosen speeds' of those wheels!
An angle where we feel ZERO understeer and ZERO oversteer is when both rear wheel's 'chosen speed' is IDENTICAL !
We choose to go through a corner AT the 'slip angle' we chose to ELIMINATE the diff effect.... that's WHY we do it! The 'diff effect' would slow us..... so we have found a way to REDUCE it as far as possible...
... it's what we DO and it's WHY we do it!
Ian
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