Suspension Geometry and Total Travel in Bump and Rebound

[nocturnal005]

Hello everyone,

I've done some searching and didn't find much information (actual measurements) on bump and rebound travel, camber gain curves, bumpsteer curves etc. on our evos. I wanted to create a spot where all actual measurements could be compiled.

The information should prove useful in deciding how to modify the vehicle.

For starters, does anyone have information on: (stock vehicles only...please state year and trim of vehicle)

Bump travel before bumpstop is engaged
Rebound travel to full droop
Total travel (sum of above)
stock ride height from pinch weld on chassis to ground (measured at jacking points front and rear)

From here we can move onto measuring camber curves, bump steer curves, etc.

thanks,
Norman

[ustcc evo]

This is a great question. Quite a few people have this information, but I think most are race teams like us who spend lots of time and money to get that info.

The front suspension is a simple strut. Take the spring out of the car, reassemble the suspension, and then run it through its travel with a jack. You can measure stroke, camber, etc. with a tape measure and a simple camber guage. If you then measure the length of the lower control arm, etc., you can easily calculate everything you need to know (roll center, etc.) with geometric calculations that are well explained in many race car engineering text books availble at Amazon. Bump steer is also easy to measure simply by attaching some type of toe guage while running the suspension up and down with no springs in it. Shim the ends of the tie rod ends up and down until changes in toe are minimized. Usually the goal is to get the tie rod parallel to the lower control arm on a strut type suspension.

The back is a little more complex. You can measure stroke and camber curves like the front, but calculating roll center, etc. on a multilink is usually not a simple calculation like with a strut. The easiest way to find roll center on a multilink is to use an automated machine that has those capabilities. Modern alignment racks may have the ability to do this, but I've never used one for this purpose. The nice part is that the Evo rear suspension is pretty well designed, and the roll center doesn't move nearly as much as on the front in response to changes in ride height.

Keep in mind that racers have developed a lot of tricks to figure this stuff out without expensive machinery or difficult math. The is one of the many ways that a real suspension expert can save lots of time and money in the long run.

[nocturnal005]

Dave,

thanks for chiming in. I'll be starting to take some measurements and hope to update in the near future. Knowing all of the numbers and having them written down somewhere is really helpful in terms of remembering what changes were made last season for example =)

If I get ambitious I may generate a CAD model of both front and rear suspension.

-Norm