Bump steer is the toe-in or toe-out of the
front wheels as the suspension goes from normal ride height through
full bump (suspension system moves up) to full droop (suspension
system moves down). Measurement is usually limited to 3" up and
3" down from ride height. It is specified either by a graph or
measurements at 1", 2", and 3".
Bump steer affects handling much as setting
toe-in does. All cars have a certain designed-in pattern of bump
steer. Check with your chassis builder for his normal pattern. If you
have a factory chassis, you'll probably want to try to minimize bump
steer as a starting place.
Due to normal manufacturing tolerances, the
actual bump steer can vary from the designed pattern and should be
checked on a new car and occasionally during the life of the car to
see if it has changed. Many professional racers even use bump steer as
a chassis tuning tool. Again, check with your chassis builder.
Checking Bump Steer
First you must determine the position of the
suspension system at ride height. This is a starting point as this is
where normal toe-in is set. Later you are going to put the car on a
ride height block and remove the front wheel and spring.
- There are two easy ways to determine the
front suspension position
Choose one and take the measurement with the
car at ride height. Also measure the frame-to-ground clearance at
- Measure the length of the shock
- Measure the angle of the upper A
- Make a ride height block from wood (or
anything solid) the same as frame-to-ground to place under the
frame when you take the front wheel off.
- Put the ride height block under the frame
and remove the wheel and spring. Also disconnect the sway bar.
Place a hydraulic (or floor) jack under the A frame and raise the
suspension to ride height by measuring the shock length or A frame
angle as before.
- Bolt the aluminum plate to the hub. If
necessary you can drill other holes for your particular car.
(After you're done, keep the bolts with the set for future use.)
Rotate the plate so that the small level shows horizontal.
- Lean the bump steer gauge (tubular frame
with dial indicator) against the plate at a slight angle (approx.
15º) so that the upper tube is parallel with the plate and the
dial indicator tip and roller bearing contact the plate. Loosen
the knurled knobs adjust the height so the dial indicator tip and
roller bearing are next to 0" on the plate scale. Rotate the
dial on the dial indicator to 0".
- Using your hydraulic jack move the
suspension system until the dial indicator is at the 1" mark.
Note which direction the dial indicator moves to see if the wheel
toes in or out. The reading you get on the dial indicator is
the actual amount of bump steer. It's that simple. Record this
and go onto to 2" and 3". If you want to make a more
detailed measurement, you can take readings every 1/4" or
1/2" and plot a graph.
Note: When you are taking measurements the steering must not move.
If necessary, lock the steering in place. Also, the hub and plate
must not rotate. If it does, turn it back to horizontal using the
- Now go back to 0" and take similar
measurements as the suspension systems moves down. Repeat this
procedure on the other side of the car. Keep the readings as part
of your records.
- To adjust bump steer refer to your setup
sheet or manual, or there are several good books on the market
that describe how to make adjustments. Because suspensions vary
widely, it is not practical for us to go into detail on actual
- When you are done with the adjustments,
re-check as before.
To Bump Steer Gauge