Why does car understeer when going downhill?
 

Intuitively, I thought that when the car is going downhill, more weight is transferred to the front tires, leading to the front tires gaining grip and rear tires losing grip. However at the Thunderhill skid pad, I noticed that when going downhill, it is much more difficult to get the car to oversteer compared to level and uphill. And when I'm already drifting in the downhill portion, my car tends to go outward like in understeer. The test was just driving around in a constant-ish circle, progressively adding throttle. What's mechanics are happening that's leading to this behavior?

Is your speed the same in the uphill and downhill portions?

If you're going faster downhill it could be that you're going in too hot, which can be why it's pushing.

Technically you are off camber when you are turning on a downhill.

I don't think I'm scrubbing any speed on the downhill portions, if that's what you mean by "too hot". I drive around in a circle below the limit and then add throttle to start the drift.

Wouldn't it be harder to get the frontend to move due to weight transfer? i.e. the front weighs more, so it would take longer to react to direction changes :iono:

Is your trac control on or off?

I do not claim to know the exact reason or be an expert but I watched this video today and thought of this thread.

Could it be your applying more steering rotation when going down hill like in the beginning of this video? Since that guy was gradually gaining speed then turning the steering wheel more aggressively which pushed the car vs allowing the back end to slide. Up hill you may be just turning less allowing the car to slide more easily?

Just a thought.

Video: https://jalopnik.com/a-donut-is-actu...ift-1821270890

Weight transfer rate is different.

+1

Weight transfer.

You're probably asking too much of your front tires

Physics

Going down hill means gravity is adding to your car's momentum and increased momentum means a greater force upon the thing trying to resist or change that momentum (turning or slowing).

Therefore your car is understeering because the tires are overburdened. Either the moment of directional change needs to be reduced (turn in slower or with less radius) or your momentum needs to be reduced by further lowering your speed prior to turn in.

How a car handles directional changes in regards to track slope or pitch is what makes driving (or racing) on tracks with elevation change so enjoyable.

I have noticed the same phenomenon on track. You have made a correct observation. I get push on down hill turns and oversteer on uphill turns. This makes getting the car setup for perfect balance in all the turns basically impossible. There may be some way to lessen the effect but I have not discovered it.

You're overloading the front outside tire downhill and overloading the outside rear tire on uphill. Those are the tires responsible for the most grip in those circumstances