# Trying to calculate vertical wheel travel after hitting a bump

• ace-card
In summary, Ranger Mike suggests that you use the bottom ball joint as your reference point for vertical wheel travel.

#### ace-card

Hi everyone,

I'm studying Motorsport Engineering and am trying to do an in depth analysis of a vehicle double wishbone suspension system. I have been using Excel to model the behaviour of certain aspects, and I am currently trying to analyse the effect of a wheel hitting a bump and it's affect on camber change.

What I'm wondering is what reference point for the vertical wheel travel do you use? Is it the bottom ball joint in relation to the ground or the top ball joint? Obviously, this would be the same if the wishbones were of equal lengths and equal angles to the chassis, but what happens if they are not? This would mean that the hub and wheel would now be traveling in an arc and not straight up/down, making the ratio of travel between top and bottom different. It is this which is ultimately confusing me!

One last question...if I were to use wishbones of equal length, mounted at different angles to each other, how would this affect the motion of the wheel?

I hope I have made sense! Any suggestions would be much appreciated!

Thanks!

Welcome to the forum
i suggest you look at post on this mech eng forum
race car suspension class Jul22-09, 12:03 PM
tells about checking for Bump Steer and you arte correct..it is all about tire contact patch and camber change..get back to me ifin you got any questions

rm

ace-card said:
Hi everyone,

I'm studying Motorsport Engineering and am trying to do an in depth analysis of a vehicle double wishbone suspension system. I have been using Excel to model the behaviour of certain aspects, and I am currently trying to analyse the effect of a wheel hitting a bump and it's affect on camber change.

What I'm wondering is what reference point for the vertical wheel travel do you use? Is it the bottom ball joint in relation to the ground or the top ball joint? Obviously, this would be the same if the wishbones were of equal lengths and equal angles to the chassis, but what happens if they are not? This would mean that the hub and wheel would now be traveling in an arc and not straight up/down, making the ratio of travel between top and bottom different. It is this which is ultimately confusing me!

One last question...if I were to use wishbones of equal length, mounted at different angles to each other, how would this affect the motion of the wheel?

I hope I have made sense! Any suggestions would be much appreciated!

Thanks!

.

## 1. How do I calculate vertical wheel travel after hitting a bump?

The formula for calculating vertical wheel travel is: Vertical Wheel Travel = (Initial Velocity^2 * sin^2(impact angle)) / (2 * Gravity * Stiffness).

## 2. What is the impact angle in the calculation for vertical wheel travel?

The impact angle is the angle at which the wheel hits the bump. It is measured from the horizontal plane.

## 3. What is the significance of initial velocity in the formula?

Initial velocity is the speed of the wheel before hitting the bump. It plays a crucial role in determining the vertical wheel travel.

## 4. How does stiffness affect the calculation of vertical wheel travel?

Stiffness is a measure of the resistance of the wheel to deform under pressure. A higher stiffness value will result in less vertical wheel travel.

## 5. Is there a specific unit for vertical wheel travel?

Yes, the unit for vertical wheel travel is meters (m) or inches (in), depending on the unit used for initial velocity and stiffness.