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# Force from road on bump

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## Force from road on bump

(OP)
Hi Folks,
I have got a basic doubt here.I just want to understand the concept behind the (reaction) force from the road on the wheel and the vehicle when the vehicle crosses a bump.
When the tyre is still in contact with the road even on the bump, what causes the force from the road when the vehicle finishes the bump.

### RE: Force from road on bump

I don't understand what it is that you don't understand.

### RE: Force from road on bump

(OP)
Hi Brian,
I just want to understand the basic physics behind it. how is the reaction force created when the vehicle crosses the bump?

### RE: Force from road on bump

Umm, the roadway pushes up on the wheel and the springs and dampers in the vehicle push down?

Don't forget about momentum. If the upward side of the bump is steep enough then the upward-moving wheel may have enough inertia that it takes longer to reverse direction than the profile of the bump does, in which case the tire will momentarily lose contact with the ground.

### RE: Force from road on bump

(OP)
Hi Brian,
Excellent!Thanks a lot for your insights. will explore it and get back to you after enlightenment.Thank you so much.

### RE: Force from road on bump

(OP)
Hi Brian,
Can we say that when the speed is considerably low and hence when there is full contact of the tyre on the road,there is very less shock on the springs and the vehicle? Need your inputs please.

### RE: Force from road on bump

The tire is a spring between the road and the suspension.
Everything has inertia.
The force between hub and body is determined by spring and damper/shock, as function of deflection and suspension velocity.
The force between the hub and the ground is determined by the distance between them and the spring rate of the tire.
(not affected much by velocity, though some damping in tire carcass.)
Those are some of the basics, right?

Jay Maechtlen
http://www.laserpubs.com/techcomm

### RE: Force from road on bump

When the wheel is "finished" with the bump, it is no longer moving and the shock (damper) has no reaction force. The spring force (reaction) is the spring rate times its deflection at the top of the bump. Similar for the tire reaction force.

### RE: Force from road on bump

The body and the tire will still be bouncing after the bump is passed. How much and for how long depends on the masses, springs and damping in the tire and suspension.

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