Is Big Caster Necessary?

[260DET]

Having moved the front X member 15mm forward, the max caster that could be obtained was 1.2 degrees with the existing adjustable tension rods. So it was set up with 3 degrees negative camber and 2mm toe in. On a sealed racing circuit and using Toyo RA1 tyres the car handled beautifully. Turn in was good and there was no instability down the straight or otherwise. In fact I got her into a controlled 4 wheel drift at 140kph once. So, rather than get another set of adjustable tension rods for more caster, I'm thinking of leaving it as is. Anyone else had a similar experience? Comments?

[RB30-ZED]

Hi Richard

Well id say they you sound very happy with the settings you have now. The only case for running more caster is that it will give you more negative camber on the out side wheel in turns, which could let you reduce the static negative camber of 3 degrees to perhaps improve grip for braking.

Steven

[Mikelly]

YUp, We found that running crazy amounts of positive caster required much LESS static negative camber. Our car is one of the fastest in Northern California's SOLO2 racing ranks and we're running 6.5 degrees to 7.0 degrees positive caster with less than a degree negative camber (I think it is .8 negative!)

 

Mike Kelly

[johnc]

Mike...

 

I might be mistaken, but I think your guys are running bias ply slicks. If that's so, they work best with 1 to 1.5 degrees of static negative camber. Radial slicks and DOT-R tires prefer more static negative camber regardless of the camber gain in the suspension.

 

On the early Z suspension caster controls the amount of camber gain in bump. More positive caster, more camber gain. I think the stock suspension will pickup about 3/4 of a degree negative camber in bump. With a lowered car and modified caster/camber you can increase that to about 1 degree.

 

But, getting the driver comfortable is important too. If Richard is happy with the way the car handles and the tire temps look good, there's no reason to change it.

[Mikelly]

Oh I agree John. What works for him IS best, particularly AFTER relocating the rack 15mm which is a fair amount... My guys JUST switched over to some Goodyears, so we'll see how they compare to those worn out Yokohamas.... Those things wouldn't hook up for anything... So far the setup is still consistant and they took TTD and 2nd TTD in the last event!

 

Mike

[260DET]

The reason why I specifically mentioned the Toyo RA1 tyres is because the factory say that these tyres work best with around 3 degrees negative camber. Certainly going from 2.2 to 3 made a lot of difference, although there were other changes made as well at the same time.

 

Now I have to work at using more accelerator input during the steering process. Hell this is fun

[Dan Baldwin]

My caster is about 2.5 degrees, and I like the way the car handles for the most part. Effort at the helm is very light, there's an almost servo-steer effect. However, it does seem way more "oversteery" at fast tracks like Mosport and Watkins Glen, while at NHIS it seems about neutral. More caster should give relatively more negative camber in slower turns (more steering wheel angle). So I'm thinking of dialing in additional caster.

 

I *thought* increased camber change with steering angle was the big effect of increased caster, along with increased self-centering of the steering wheel. I don't think I quite understand the increased camber change with bump John mentions. Comments?

[johnc]

Dan you're right. With the wheel striaght ahead the stock Z suspension does gain camber in bump. With the wheel turned you get that normal camber gain plus any additional camber gain inhernet with positive caster.

 

In my mind I guess I never separate the two because I'm always thinking about what the suspension is doing in a corner. But, the built in bump camber gain and the steering angle camber gain from caster are two separate items.