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The impact of suspension changes on vehicle dynamics

Based on a few recent posts, I thought this list might be useful to some folks who are thinking about chassis changes.

Quote:

Originally Posted by BonzoHansen

Guide To High Performance Handling

Code:

Adjustments                 Decrease Understeer         Decrease Oversteer 

Front Tire Pressure         Higher                         Lower 

Rear Tire Pressure         Lower                         Higher 

Front Tire Section         Larger                         Smaller 

Rear Tire Section         Smaller                 Larger 

Front Wheel Camber         More Negative                 More Positive 

Rear Wheel Camber         More Positive                 More Negative 

Front Wheel Toe         Toward Toe-Out                 Toward Toe-In 

Rear Wheel Toe                 Toward Toe-In                 Toward Toe-Out 

Front Wheel Caster         More Positive                 More Negative 

Front Springs                 Soften                         Stiffen 

Rear Springs                 Stiffen                 Soften 

Front Anti-sway Bar         Soften (Thinner)         Stiffen (Thicken) 

Rear Anti-sway Bar         Stiffen (Thicker)         Soften (Thinner) 

Weight Distribution         More Rearward                 More Forward

Front Track                Decrease track                Increase track        **

Rear Track                Increase track                 Decrease track  **

Front Toe-in                Reduce                         Increase

Front tire downforce        Increase                 Reduce

Rear tire downforce        Reduce                         Increase

understeer = the nose pushes
oversteer = the tail gets loose

good call on this post

Nice post, just one concern. Its seems to me that the first 2 rows are backwards?

Quote:

Originally Posted by BarneyMobile (Post 698660)

Nice post, just one concern. Its seems to me that the first 2 rows are backwards?

I had the same thought. :scratch:

I'll do some more research. But I know with my civic it would oversteer when pushed hard and bumping the back tire PSI up absolutely helped. In any event I believe the concept is based on starting with PSI on being within an ideal range. So we’re talking maybe +/- a few psi, just fine tuning. IMO it’s tweaking after you’ve already set ‘ideal’ PSI via reading temps across the face of the tire. It’s not saying drop the tire to 10 psi or raise it to 60 psi.

I have read where if a car understeers entering and oversteers exiting a corner, raise all pressures. But I’ve never done that.

Taken from How To Make Your Car Handle by Fred Puhn

To Reduce Understeer:
Increase weight transfer at rear by increasing rear roll stiffness
Reduce weight transfer on front by reducing front roll stiffness
Reduce front toe-in
Increase aero downforce on front tires
Reduce aero downforce on rear tires
Wider front tires

To Reduce Oversteer:
Reduce weight transfer at rear by reducing rear roll stiffness
Increase weight transfer on front by increasing front roll stiffness
Increase front toe-in
Reduce aero downforce on front tires
Increase aero downforce on rear tires
Wider rear tires

He states the old rule of thumb was to increase front PSI to reduce understeer and increase rear PSI to reduce oversteer. He goes on to say this really applies to road cars where PSI is often too low to begin with. Best bet is to get PSI correct via temp readings via skidpad testing and changing psi only limits grip.

In Herb Adam's Chassis Engineering, he also does not appear to get into PSI other than working off temperatures to get to ideal and is generally in the same vein as Puhn.

So that jives with my gut that PSI is just fine tuning and Puhn talking about only going up on road tires matches my experiences.