Caster mod??

[gareth231]

Is this mod only for people with coilovers? as I got gab with adjustable top mounts and was wondering if I could do this mod?

 

[Fast Guy]

It'll work with any that have camber adjustable top mounts, but that tends to be coilovers.

 

[campbellju]

With KPI set up to the max the steering feels more responsive, seems to give better feedback.

However the front does feels kinda softer (i don't know how is this possible). But i do know as an offroader sometimes we set up the dampers more an an angle (less upright) to get softer damping. Probably because of this and correct me if i'm wrong as per what i digested on the forums. More KPI increases the roll centre slightly. So i don't know if that could have contributed to the "softer" front feeling.

But what i don't like is that in the initial phase, entry into a corner it feels "precise", then mid phase it just washes, ploughs understeer.

End of the day i'm still curious how much roll does KPI plays in geometry/ alignment setup before i swap the top mounts around and dial in maximum castor. What was initially holding me back from the idea of dialing in more castor was the fear of fouling up the fenders as i'm runing 215/45 R17s (by right it should be 205/40 R17 by rule of thumb).

KPI sets your scrub radius, gives some wheel raise (in the same way as caster), gives some camber loss under compression and lowers your static roll centre a little. The main direct effect is on your srub radius. Fitting wider tyres or different offset rims will also change your scrub radius.

I've tried minimum and maximum KPI on my top mount. Maximum gives more scrub so more feel but more kick back as well (bad). Minimum gives less scrub. reduces kick back and gives a lighter feel (sometimes not enough feel). With a lowered car running wider track I believe the sweet spot is between the minimum and centre position on the top mount. If in doubt, just go with the centre position.

As an aside, when I first modified my strut tower to further increase the caster, I thought I'd gone too far and stuffed the handling. Tweaking the ride heights and damper settings made everything good again. Your mid corner understeer could be something else.

Jim

 

[BabyGodzillaGTi-R]

I've tried minimum and maximum KPI on my top mount. Maximum gives more scrub so more feel but more kick back as well (bad). Minimum gives less scrub. reduces kick back and gives a lighter feel (sometimes not enough feel). With a lowered car running wider track I believe the sweet spot is between the minimum and centre position on the top mount. If in doubt, just go with the centre position.

As an aside, when I first modified my strut tower to further increase the caster, I thought I'd gone too far and stuffed the handling. Tweaking the ride heights and damper settings made everything good again. Your mid corner understeer could be something else.
Jim

Jim, thanks for your feedback.
Yes I do concur the same with your observations. Max KPI, steering feeling was awesome, and a real blast around fast switch back corners (4th, 5th gear corners with a close ratio box).
But it was down right crappy on slow and bumpy corners. Like the steering just wanna pull my arms off at times.

As for my handling.... Ever since I've swapped tyres to 215/45 R17 Federal RSR semi slicks (Thread wear 140) and running 17x7.5 Ray Engineering Sebring ITC with -25 offset, the car just felt weird........... The outright grip is much better but the car doesn't feel balanced. It feels "STUCK" as opposed to "PLANTED" Argh... LOL Steering feel was crap too until i messed around with max KPi settings.

So i've been toying around with car setup to get back the handling I like with my previous tyres. 205/45 R16 on Hankook RS2 (thread wear 200). Doesn't grip as well but it was a real hoot to drive and i could induce lift off oversteer to my whims and fancies.

Next step is to reset back the KPi to centre and max out the castor. Maybe i should also dial in some rear toe in? For the record, the rear ARB is at its hardest now. sometimes i wonder is it because the rear inside wheel is not "lifting up" sufficiently.