Some Bottoming Out & Significant Understeer Issues While Tracking My Car

Hey Guys,

I recently made aero mods to my formerly stock 360. Installed a rear wing and modified the OEM front bumper in a manner that filled in the OEM "scoop" and constructed a 1' thick splitter that protrudes apx. 3". The mod to the front bumper lowered the ground clearance by apx. 2".

When tracking my car, I definitely feel much more planted since the aero mods were installed, however, I'm experiencing some bottoming out of the front end and, more importantly, a significant amount of understeer in tight corners.

The understeer is worst in tight corners that follow a high speed section of the track. For instance, running CCW at Willow Springs "Streets", I experience such understeer issues significantly in turn 1 (the skid pad), moderately at turn 5, significantly after turning in from the top of the Bowl, significantly turning into and up the hill at turn 12, and the same at 13.

NOTE: It's important to consider that the understeer issues continue even after removing the rear wing (although the understeer issues are slightly diminished after the rear wing has been removed).

Possibly, the bottoming out is partly (or entirely?) due to the apx. 2" less ground clearance, however, I see that Challenge and GT cars have very similar mods and they don't bottom out or push like my car does.

My car has apx. 26K miles, the original OEM suspension and I'm running RS-3's (235-40-18 in the front and 285-35-18's in the rear). West End alignment recently set up the car for a 2nd time, however, the understeer and bottoming out issues continue. I'm not aware of any mechanical issues with my car's suspension.

Has anyone else experienced the same sort of understeer and/or bottoming out issues while tracking their 360? If so, what can be done about it? Has anyone experienced such issues and then found a broken or worn out part(s)? Can such issues be corrected by making repairs/replacement/upgrades of the suspension? Possibly a stiffer sway bar in the rear to make the car rotate more easily? Although a stiffer rear sway bar won't do anything about the bottoming out.

Appreciate any helpful information/suggestions.

Bruce

 

Stock springs and car allows for a lots of body roll...

Do you have pics of the car?

 

Please post a pic or two of the overall car, pics of your front and rear tire wear patterns, your alignment settings, and height measurements.
What tire pressures were you running?

 

Bruce, as above, please give us more details.

It does sound like the combination of tyre and splitter are overcoming the springs and perhaps forcing the car to the end of suspension travel etc.

I assume, given the aero mods, that you must already have applied a more track focused alignment?

I run my 360 in relatively stock form (save only geo setup and brakes/fluid) and found that handling was favourably influenced by changing out the rear anti-roll bar for the CS item (also shared with Scud and 16M). Stock understeer was effectively banished with additional camber and a neutral toe setting.

 

Since you say you get the understeer in tight turns, I suspect the aero mods you made have nothing to do with it. You even confirmed that by removing the rear wing.

If you are still running stock springs and the car has been lowered a lot, then you will probably have to go to stiffer springs or raise the car a bit to prevent bottoming. If the front end is bottoming, that will certainly cause understeer. Step one is to eliminate the bottoming, then work on getting the balance right with alignment, tire pressures, and maybe different anti-roll bars.

 

Have you tracked the car prior to the suspension/aero modifications? Also what's your previous tracking experience on the same track? I noticed MR cars are a bit more prone to understeer compared to FR vehicles. Doesn't sound to me like a mechanical problem, West End would have caught it during alignment setting.