Handling characteristics of the FFR Roadster on-track

[Logan]

The Coupe, and by the sound of things the Challenge Car also, has a rear weight bias...even if only by a few percent. Quite a bit different than a lot of the "typical" American sports/muscle cars.

So this rear weight bias has thrown a wrench in my research for track brake setups. Can I run the same 14"x1.25" rotors at all four corners? Probably yes. Can I run the same 6-piston calipers at all four corners? Possibly...but not likely to be an ideal solution. I wanted to run the same brakes all around for parts commonality, simplified spares (only one or two rotors and calipers in the trailer instead of all four individual). But we all know street cars shift weight forward when they brake, so larger front brakes are the norm. Track cars shift even MORE weight forward, and I don't think the slight rear weight bias of the FFR is enough to overcome this. All that said, I'm pretty sure John George ran equally sized brakes all around... wish I knew all the details of that setup and how effective it was. More research is in my future....

As for the overall handling, I hope it raises the bar set by the S550 Mustang chassis which I've been pleased with for the past year or two.

[mike223]

I wanted to run the same brakes all around for parts commonality, simplified spares (only one or two rotors and calipers in the trailer instead of all four individual).

But we all know street cars shift weight forward when they brake, so larger front brakes are the norm.

Track cars shift even MORE weight forward, and I don't think the slight rear weight bias of the FFR is enough to overcome this. All that said, I'm pretty sure John George ran equally sized brakes all around... wish I knew all the details of that setup and how effective it was. More research is in my future....

Lots of hardware variables - but the biggest variable is the driver's approach to coming off the throttle and on to the brakes.

I was originally strongly inclined toward a lot of rear brake bias - but as I've gotten better with the car I found I needed less + less.

I'm back close to an OEM brake bias of 75/25 front/rear - but that is for autocross where I come off the throttle at 6000 rpm in 2nd gear and on the brakes - hard, quickly.


I find it difficult to imagine successfully, reliably using the same violent approach on track in 3rd or 4th gear (there's a lot less room for error).

[GoDadGo]

The Coupe, and by the sound of things the Challenge Car also, has a rear weight bias...even if only by a few percent. Quite a bit different than a lot of the "typical" American sports/muscle cars.
.

Being the only Chevy Guy in the room and Big Camaro Fan, we've owned four (1980, 1989, 1990 & 2000) plus having a C-4 Corvette from 1995 until 2018 makes leaving that 50/50 distribution mind set a bit tough. The 1989 and 1990 Camaro's were stupid nose heavy while the 1980 and 2000 Camaros and C-4 Corvette were much more balanced. Both the 1980 and 2000 lost some nose weight when we ditched the steel hoods and moved the batteries rearward to the trunk. The C-4 and the 1980 Z/28 were my favorites.

Again, leaving the 50/50 weight thing behind is not an easy change for this guy.

C-2 47/53 Small Block
C-3 52/48 Small Block
C-4 51/49 LT-1 & LT-4
C-5 52/48 Base
C-5 53/47 Z06 (Lightest C-5)
C-6 51/49 Base & Gran Sport
C-6 50/50 Z06
C-6 51/49 ZR1
C-7 51/49 Z51
C-7 52/48 Z06

[Jim1855]

On brake bias.

Last "cobra" replica had 6-piston Wilwoods in the front and the then owner had the original 1-3/4" front 4-piston calipers moved to the rear. Braking was unbalanced. I swapped the original 1-3/8" piston calipers back to the rear and the balance improved.

It doesn't take much to affect brake balance. The car didn't have the means of adjustment with balance bar or pressure balance so the method was either caliper/piston size or pads.

Once I made the caliper switch the brakes became much more predictable and manageable.

Just my few pennies worth of contribution.

Jim

[Jcdata]

When we just easier just to get an adjustable brake proportioning valve?

[Logan]

There will be a brake bias adjuster. This is a sheathed cable that connects to the balance bar of the Wilwood pedal box on one end, and has a knob on the other end that mounts inside the cockpit which the driver uses to adjust balance on the fly. This works due to the pedal box having two master cylinders for brakes (one front and one rear). No fluid-type proportioning valve is necessary.

Now, I wouldn’t rely on this bias adjuster to magically make ANY brake system perfectly balanced. Think of this as the fine tuning device that is used in the final stages of brake tuning (literally while racing the car). The coarse/rough tuning should be done first by sizing the rotors and calipers appropriately, then secondly by sizing the master cylinder bores accordingly, and lastly using the remote bias adjuster to fine tune a fully functional system while on track (or street to a lesser degree).

[AdamIsAdam]

Well this was an interesting reading thread. As I posted elsewhere yesterday and today, I took my car to the auto-x for the first time and was quite surprised by the handling. Bottom line is that I did expect it to handle more like a Mustang or any front engine/RWD car as opposed to a 911. I still say it handles better than a 911, but I understand the comparison.

I was already planning on installing softer springs all around to make the car more enjoyable on the streets of NY (Eiback 425lbs up front, 250lbs in the rear) before I took it to the auto-x for the day and had one heck of a time keeping the rear IN THE REAR as I went faster. So I'll install those springs and then take it from there.

The car was so quick and precise in the slalom that I was shocked at how loose the tail felt later in the course. And when I did finally spin it, it spin very quickly on me as expected with the short wheelbase, but I didn't think it was going to come around like that at that moment with ZERO chance to try and correct it. I was honestly surprised when it came around at that moment.

I posted it before, but I'll post it again here for your viewing pleasure. After all, this short video took me a few hours to string together. I hate video editing!

https://youtu.be/XeZ0zhI_3PQ