Tall Cars, Is there such a thing as too much Front Grip?

[covertrussian]

I need new front control arm rearward bushings on my BR Outback, I'm really tempted to get the caster increasing bushings (+1 over stock). My only concern with more caster is this additional front grip will offset the natural understeer tendencies of the car to oversteer instead (wife's daily driver + inclement weather car, not a racer here )

 

So this leads to the next issue, if oversteer becomes an issue you could increase rear camber to dial out that oversteer. But at what point do you have to start worrying about rollover from having too much mechanical grip. I love increasing caster on my Sedans, but with low center of gravity this is not a big concern.

 

Stock BR Outbacks have 0* camber front and rear, so it's not like you can reduce negative camber like you can on Legacies, though we might be able to dial in positive camber (I'm not sure about static handling implications of this though).

[covertrussian]

To help visualize this here is a camber vs steering angle graph that I made with my spreadsheet that you can grab here.

http://legacygt.com/forums/attachment.php?attachmentid=258135&stc=1&d=1510594237

 

If you compare the blue line (stock setup) vs red line (+1.0* caster), you will see that that much caster has a tremendous effect on negative camber gain (~0.5* gain) at higher steering angles like 24*. But at more realistic 12* steering angle your looking at about 0.20* gain, which is not too bad. But, I do remember my legacy becoming much more neutral handling with only 0.5* more caster though.

 

Now the green line shows +1.0* caster with total of 0.20* positive camber (stock is 0.00*). This puts the green line right with the blue line at 12* of steering angle, and at 24* your looking at about 0.20* negative camber gain. Basically green line is good at negating the caster bushing's gain, if your fine with having 0.20* positive static camber all the time.

[MilesA]

The most common cause of rollover accidents is where one side of the car "trips" on a soft shoulder when the car leaves the road. Followed by the type where the car is involved in a collision that lifts only one side of the car. Then comes the type you are talking about, high cornering forces. For a standard car, the threshold of rollover for that type is supposed to be > 1.0 g. It could be less for a taller car, but I'm not sure about the Outback. The Legacy is extremely safe if you look at the statistics.

[whitetiger]

no worries about the Outback. I autox'ed my 3.0R some years back for a couple events, on R-comps and stock suspension. if there ever was a perfect storm for rollover that was it. yes its a 4th gen, but with that kind of ride height and high levels of grip still being safe, a regular OB on street tires will be more than fine regardless of roll stiffness changes.

[covertrussian]

Thanks for the feedback!

 

Looks like rear camber bushings are much more expensive for BM/BR's (~$170) since the design requires 4 eccentric bushings. So adjustable rear camber is out of question. Guess now the question is, how tail happy 1* of extra caster would make the cars. I enjoy the outback handling good (I do lots of mountain driving) but tail happiness in snow when you don't want it is not fun.

 

On the other side, extra caster does help straight line stability, so that might make the car be more stable on windy/inclement weather days.

[covertrussian]

On other news, SuperPro lists the TOTAL caster adjustment for both sides, not just one. So it's increasing caster by only 0.50* on each side and not by 1.00*. With that in mind I have much less reservations against the caster bushings for a daily and will be getting those instead.

[MilesA]

Do you know how those Superpro LCA bushings fit? Are those the ones that seem a little too large for the space available? I forget.

[covertrussian]

Do you know how those Superpro LCA bushings fit? Are those the ones that seem a little too large for the space available? I forget.

 

Not yet, I'm waiting for them to hit the vendors still. They just released them last month and they are on a boat to USA for most vendors. One vendor said caster should be arriving end of November and non Caster end of December. So I'm trying to patiently wait for them, getting tired of how creaky Prothanes got

 

Stock caster will be SPF4863K

+0.5* Caster will be SPF4865K