View Full Version : Bottoming out

18-05-2015, 17:50
Quick question, what suspension parts should I be tuning to help with bottoming out? I know I'm probably not going to get rid of it entirely but I'd like to help it some.

The car/track combo that has me asking this is the C9 at Road America. I always seem to bottom out around the kink for some reason and it sometimes throws the car off. It looks like the back left side is scraping but I'm not entirely sure.


18-05-2015, 17:51
Ride height - > bump stop

18-05-2015, 17:56
Higher ride height, stiffer springs and dampers.

19-05-2015, 01:09
Bump stop, spring rate, and ride height will all have an affect on the height of the car.

Bump stop will be the end all of ground clearance. A car cannot go past it's bump stops. You can give these a higher number to increase the length of the bump stop to keep the car from touching the ground, but the downfall is that if the spring rate is too low and the car hits the stops violently, balance can be thrown off in a hurry, and it's into the run off (or the wall) for you.

Ride height is obvious, it's the height of the car above the ground. Raise it and the car sits higher, but so does the center of gravity. The cars handling is very COG dependent, that's why you see race cars sitting low.

Spring rate is obvious too. Higher spring rates are harder to compress, and thus keep the car off the ground better than softer springs. However, they also affect tire compliance, which is the suspensions ability to keep the tire on the road over bumps and into dips.

That said, it's all about BALANCE (as is all tuning really). Too high of a spring rate and your car may become twitch, especially on bumpier tracks like the Mulsanne straight at Le Mans. Too high of a ride height and your car will want to lean outside too much, overloading your outside tires in a corner and causing a slide. Too long of a bump stop, and your bottoming out car will defect off of them and bounce around. Have you ever seen a car with cut springs bouncing around on the streets? That's the bump stops.

Mess with them all, but remember what setting they were at before your adjustments. Take note of how the car reacts. Maybe a bit higher of a ride height is the answer, but maybe that needs to be supplemented by a stiffer sway bar rating. Maybe you just need to adjust your bump stops, but the springs need to be stiffened a bit to keep off of them.

Trial and error is going to be your one of your biggest tools in all of this. You won't know what works and what doesn't until you find out the hard way.