I know it’s been awhile coming, but I just simply haven't been happy with the recent changes I've made to the one-way setup and the results they produced.
But...
I've finally figured out the setup black hole that I had fallen into. All it took was looking back to my old FK04 setup that was pretty dialed before switching to the FK05. What I found is that with a one-way high traction setup, tied with the 2mm front anti-roll bar at the top of the list of key ingredients needed is the need for a lot of caster.
In the last month, I had changed my front arms bulkhead positions to produce 1.5 degrees of anti-dive, which also reduced the overall caster to 4.5 degrees. Before then, I had always run the front arms flat with an overall caster of 6 degrees from the c-hubs. The reason that this is critical has to do with the inside front tires camber and resulting contact patch on corner exit. With the 2mm front anti-roll bar, the front end stays pretty flat while cornering and
the inside tire has more load on it to provide both front end traction and steering. The key for increased corner exit steering is to get the inside tire to gain enough positive camber to where its contact patch is on the outer edge of the tire. This part of the inside tires tread is closest to the corners apex and therefore has the tightest steering arc of any part of the car touching the ground.
Simply put, 4.5 degrees of caster is not enough. In the past month with the 1.5d anti-dive, I had to make a few setup changes in order to cure the front end push. The changes included raising the rear ride height, standing up the rear shocks one hole and increasing the steering EPA/dual rate 5 points above my preferred setting to minimize mid corner scrubbing of speed. However, I soon found that these changes also caused the car to "plow" through the corners. The motor had to work harder, the gearing had to be reduced for less rollout/top speed, the front tires were wearing faster than normal and I was loosing too much speed mid corner (costing me 2 to 6 tenths per lap, depending on how smooth and consistent I drove).
Our latest track layout is pretty technical, although not too tight, and with stock motors you are almost always turning the steering wheel and on the gas, except down the front straight. However, at the end of the front straight there is a tight chicane that emphasizes hard deceleration (notice I didn't use the word braking
) and corner entry turn-in. For this reason, I decided to reduce the anti-dive from 1.5d to .75d instead of eliminating it totally. This fine tuning change can only be accomplished by using the .75d suspension holders and the resulting overall caster was therefore increased from 4.5d to 5.25d.
Before I made the changes and hit the track, I performed a cornering simulation test on my setup station to record the camber settings of both front wheels while the steering was at full lock. I tested corner entry, mid corner and corner exit and the results looked great. Full lock with my preferred transmitters steering EPA/dual rate and using ackerman position #3 on the steering blocks comes out to 16.5d on the inside wheel and 14d on the outside wheel. The static camber was set to -0.25d as I am also using the shortest front upper link position at a steep angle for a lot of camber gain. Corner simulation test results:
Front wheel camber at full lock with 4.5d caster (inside wheel / outside wheel):
Corner entry: -0.5d / -1.5d
Mid corner: 0d / -1.5d
Corner exit: +0.5d / -1.5d
Front wheel camber at full lock with 5.25d caster (inside wheel / outside wheel):
Corner entry: +0.25d / -2.0d
Mid corner: +0.25d / -1.5d
Corner exit: +1.5d / -1.5d
As you can see with the little bit of added caster, the inside wheel is always leaning into the turn. And what’s impressive is that its positive camber gets really aggressive as the front end lifts up when the power comes on and the car squats down on the rear outer tire at corner exit. An added benefit is that the outside wheel has a little more aggressive camber on corner entry where it’s needed as the cars weight is shifted forward.
On to track testing...
A little side note: At the beginning of testing, I mounted standard purple compound tires on the front and magenta's on the rear. The result was a lot of over steer from the middle of the corner out, although without any loss of rear end traction. I had expected this, and my goal was to see if the front inside tires outer edge contact patch was indeed affecting the steering arc. I then mounted plaid (purple/orange) tires on the front and the results of the front tires outer edge compound change from purple to orange were very noticeable. Not only did the on-power over steer go away, but the difference in steering arc from off-power to on-power disappeared. The car's steering became very predictable to where I could blip the throttle anywhere throughout the corners and the car would stick to its line and not push or over steer.
With the car's front end tamed, I worked a little on shock positioning/dampening, rear droop, and dialing in the right amount of neutral throttle trim for forward roll at mid corner. The results were a slightly softer rear end with the shock angle brought down to the same as the front shocks, a quicker transitioning front end with only one hole open on the pistons, greatly reducing the rear droop to be equal with the fronts at 1.5mm, and a ton more mid corner speed as I had both the ESC's minimum throttle setting, and the transmitters throttle trim setting, at maximum. This provided a pretty fast roll with the throttle trigger at neutral, but the car never pushed around even the tightest corners and just ate up every corner exactly on the line that I put it.
By the end of the day, I was able to stay on the gas a lot more during each lap and ended up increasing my pinion gear by two teeth. The motor never came off the track over 180F and didn't fade until the batteries started dumping after the last three 7 to 8 minute runs with IB3800's.
Now I reserve the right to stating any actual on track performance increase, until after I've proven it on an upcoming race day.
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On race day, the tire change worked ok, but I felt the car was not loose enough with the stock motor in and the front tires were wearing quite fast for a stock setup. I have a feeling that the stock setup would fair much better on corner speed and tire wear if I switched at least the fronts back to purple/orange. I'll be testing the stock setup with a full purple/orange & purple combination this week.
The effect was definitely noticeable on race day as the car didn't dive as much as it used to, but mid corner steering also suffered. I didn't want to take the time to change the holders again, so I removed the 1.5mm shim under the outer camber links to lower the roll center some. It worked to give just enough mid corner steering (could have used a little more though), but the car was a little slow to react on turn-in coming into a large sweeper at the end of the straight. Opening all holes up on the front shock pistons cured that. The last problem of the day had to do with a little too much on power steering. Lowering the rear ride height to be equal to the front cured it.
