I’ve been trying to tune AWD cars for the first time this week and fighting the understeer beast. Aside from soft front springs and ARBs, I imagine the differential will have the biggest impact on this. How does the front differential impact handling on an AWD car?
My best tune so far has something of a ridiculous differential setup that seems to work pretty well. My Ferrari 250 GT beats everything but the Prowlers in b600 Ghost League.
Front Accel : 5%
Front Decel: 0%
Rear Accel: 55%
Rear Decel: 0%
Torque 95% Rear
Rear grip is not a problem, the goal is reduce understeer mid-corner and exit. How does Front Accel and Decel impact cornering grip?
My default settings (starting point) for AWD"s are 45/0, 65/25, with a 70 balance. And, I only go about +/- 5% (in some cases a max of 10%) on all of these except Front Decel which I keep at 0.
The biggest problematic settings that I have encountered for AWD’s include the springs/ARB’s and damping (mainly bump)…plus, you can use aero (based on the F-2-R ratio) to provide more rear end “following” versus holding you back from turning. Mid-corner and exit understeer is usually the ARB’s.
In the Ferrari 250 GTO, your PI actually goes down when you put more rear tire on the car. My rear ARB is set to 38, rear springs are ridiculously stiff (bumps suck) and It still has more rear grip than I want or need. Basically I’ve built a RWD car that I can drive in the AWD leagues and it works pretty well outside of some very strange results over bumps and high speed, hard braking.
I don’t really understand what the impact of front Decel is in a AWD car. Front Accel should increase oversteer, but the decel setting does not seem to impact much in my testing.
Here is an usual setting that can work as well…set your balance at 45%…i know its not the norm but give it a go and see how it feels, also 45/0 and 75/30 split diff. This is simply just a different approach…good luck.
Have you tried lowering the caster? Works wonders sometimes to get the front turning in harder. Then you might want to stiffen the rear roll bar in conjunction. As far as the differential goes, you’re going to want enough front accel to pull the car through the corner, in a way that complements your rear accel, which pushs the front. Try at least 25% front accel.
Front Decel should probably be zero. When you downshift, or let the drivetrain drag mid-corner, you are engine braking with your front inside wheel. Transferring any of that braking to the outside wheel will just steal grip for no reason.
Its different in a RWD car because you gain stability by letting off the throttle and transferring your engine braking from the inside wheel to the outside wheel a bit. It straightens you up mid-corner so you can exit. It also eases up the tire temperatures on the inside tire leaving more grip for accel. So a touch of Decel on the rear is good. The desirable amount depends on how much under-steer the car exhibits in a low gear mid-corner.
For AWD I would do something like
F Accel 50-60%
F Decel 0%
R Accel ~70% (60-80%)
R Decel ~30% (30-50%)
Balance ~85% (80-93%)
All can be tweaked within those ranges generally depending on the car.
If the rear slips power is sent to the front. Excessive power sent to the rear will actually cause understeer IIRC without TCS unless actually pegged to 100%. Inefficient balance WITH TCS steals corner exit oomph.
My setup is usually around
Front
65-75 / 0
Rear
70-90 / 10-30
mid
55-75
Driving style tip. Brake before the turn, get the car turning, floor the throttle, and you will accelerate trouch the corner with tiny oversteer (Does not need countering)
How ever there is few cars where this just does not help, 92 and 94 Celica’s being the ones that I just cannot get do anything else but understeer.
I’ve said this before but, for me, the more experience I get in tuning the more “unusual” settings I find myself trying. Especially with the leagues and finding myself in a lobby full of AWD Prowlers and Shelby Daytonas I’ve even built some AWD cars I’m not proud of, most of which have not left the garage because…4 wheel drive muscle cars, seriously?? I have had more success with stiffer ARB’s and spring rates with AWD cars and 20-50% accel front 0% decel and 40-60% accel rear and 20-40% decel. The decel depending on how stable the rearend is on lift throttle.