E39 M5 Sway Bars

[vbhargava]

I currently have stock sway bars with PSS9 coilovers on a 2001 M5. The tail is a little happy recently but I suspect its due to bushing that are bad. 

Can someone help me understand the benefits of upgrading the sway bars considering the setup for WI back roads. I am concerned I will make the car too tail happy. 

Thanks

[m42b32]

With aftermarket (adjustable) sway bars you can use them to tune your handling. Stiffening the front sway bar relative to the rear will reduce oversteer, stiffening the rear relative to the front will increase oversteer. However, aftermarket bars are typically always stiffer than stock which will reduce body roll but also contribute to 'jostling' over rough roads as each side of the suspension is more strongly tied to the other. https://www.turnology.com/tech-stories/lateral-grip-sway-bars-actually-theyre-important/

If you are trying to reduce tail-happiness you can make changes to your coilovers as well: http://speed.academy/how-to-fix-understeer-or-oversteer-suspension-handling-setup-tuning/

[straight6pwr]

good points @m42b32

to add:

most factory cars with upgraded springs/grippier tires do positively benefit from sway bar upgrades. in general, it reduces body roll which in turn keeps the tire contact patch more consistent with the pavement. (less changes in camber) it also speeds up transition time in a corner (the less the suspension has to travel, the faster it can do it) 

if you want to maintain the safety factory of the understeer bias that comes factory with most BMWs, make sure you upgrade to sway bars with the same front/rear ratio of stock. most aftermarket kits (from my experience in the 3series world) tend to go too big on the rear and you lose the factory balance (they aim for a more neutral handling characteristic) 

i cannot speak to the e39 chassis itself, and its inherent handling characteristics.

[vbhargava]

Thanks guys. Very helpful. After reading the guide, I think I need to wait on the sway bar for now since I have exit oversteer. I'll try their suggestions around reducing ride height, reducing stock  compression. To be fair this did come about the same time I raised the car about .5 inch...

[straight6pwr]

upgrading just the front bar is one way to help correct oversteer.