When reading the spring rate charts, I noticed some setups are the same rates in the front and back, some are stiffer in the front than back, and a few are stiffer in the back than front.

What are the advantages and disvantages of all 3 setups in an AWD car?

 

bump.

 

It has to do with the desired wheel rate and the desired handling of the car. The EVO in stock form has softer springs in the front and stiffer springs in the rear, BUT it has a bigger sway bar in the front and smaller sway bar in the rear. The rates are tuned to get the desired handling and balance. An STi for eg: has stiffer springs in the front and softer springs in the rear, BUT it has a smaller sway bar in the front and bigger sway bar in the rear (I think) to get the desire balance.

Springs/coilovers setups that are of either equal rates on both front and rears or stiffer springs in the front and softer springs in the rear usually require a larger rear sway bar to balance out the wheel rates front to rear. Suspension is all about balance and compromise, and no one is really better than the other, they are just different theories and solutions to the same problem. Hope that helps answer your question ...

 

wheel rates?

 

Think of it as the combined spring rate of springs, swaybars and shocks.

 

okay, I'm beginning to understand. Here's the scenario...

Stock evo understeers at the limit. Stock spring rates are 3.2/4
So if I want to car feel more neutral, I should consider just buying a thicker rear sway bar?

What if I decide to up my rates with new coilovers to say 10/10. To balance this out, would I need even thicker sway bar than example #1?

thanks.

 

wheel rate is the effective spring rate acting at the tire/road surface. due to suspension designs, you will never have 100% of the spring rate working at the actual wheel, only a portion of it. Suspension mounting position, spring angles, leverage of the control arms, these all serve to reduce the effective rate of the spring acting at the wheel, sometimes as much as half the original spring rate. Evo's are macpherson struts up front and multi-link rears, with macphersons typically having higher wheel rates, while multi-link suspensions usually give up more to leverage of the control arms. In other words, with a macpherson strut suspension, more of the spring rate will be effective at the wheel, while with the multi-link, you will get less rate acting at the wheel. This is part of the reason why the rates are lower in the front and higher in the rear. Also when mitsu designers chose the spring rates for the Evo's, they most likely took ride comfort into consideration, and were aiming for a somewhat reasonable suspension frequency - that is, the natural frequency of the car when it encounters bumps. There is a range within which humans might consider the ride comfortable, stiff, and uncomfortably harsh; the softer front rates/stiffer rear rates that Mitsu chose most likely resulted in a favorable front/rear ratio of suspension frequency. The swaybars are typically not calculated into wheel rate.

Swaybars and springs do not replace each others' functions in a suspension system. You should not be "making up" for soft spring rates using swaybars to stiffen one end, and vice versa you shouldn't be just jacking up spring rates to reduce roll.

Going too stiff with the swaybar (to compensate for lower rates) can reduce the effectiveness of an independent suspension, and not allow the shocks and springs to perform their functions effectively. Going super stiff on rates so that you don't need to run a big bar is not a viable option for street cars, because the ride will be uncomfortably harsh.

Generally, to combat understeer, you stiffen the rear end. Depending on how much understeer you're facing, this may call for just a more aggressive rear bar, or an overhaul of the suspension. The Evo's perform pretty well at the track with stock suspension, so make sure you're not just overdriving the car before you start dropping a bunch of money into suspension upgrades.