Weight Transfer Under Braking: Why the Front Brakes Are Bigger

Brake hard and the nose dips: load moves from the rear wheels to the front. A tyre can only grip in proportion to the load on it, so in a hard stop the front tyres can do far more of the braking than the rear. Ask the rear brakes to do their static share and the rear wheels lock, and a car with locked rear wheels turns round. This practice rung works out the load on each axle at several decelerations, and shows how to find a vehicle's centre-of-gravity height — the number the whole calculation turns on — with two scales and a block.

مبتدئ

About 2 hours

التعليمات

Axle loads and centre-of-gravity height

جارٍ تحميل دفتر Jupyter…

Measure a cart's centre of gravity

Build or take a wheeled cart — the dynamics cart set, or a board on the axle-and-wheel kit — and load it with weights. Stand its front wheels on the kitchen scale and its rear wheels on a block of the same height; read the front load. Weigh the whole cart too. Raise the rear wheels by 100 mm on a stack of books and read the front load again. Put your numbers into the notebook in place of the example inputs. Now move the weights higher on the cart and repeat: the front load changes MORE when the cart is tilted, and the notebook gives a greater height. A high centre of gravity means more weight transfer — the reason a tall van pitches so much more than a low car.

المواد لهذه الخطوة:

ثقل1 طقم

الأدوات المطلوبة:

ميزان مطبخ رقمي

طقم عربات الديناميكا (منخفضة الاحتكاك)

مسطرة

Context

A practice rung: the statics of a braking vehicle, which set the proportions of every brake system — bigger front brakes, pressure-limiting valves to the rear, and today anti-lock systems that keep each wheel just short of locking. **Honest limits of the model.** Rigid body, no suspension movement, level road, and constant deceleration. Suspension geometry can resist the pitch (anti-dive); a slope changes the static loads; and a tyre's grip is not exactly proportional to its load.