Here's some tech info from my stock racing experience at the Spanish Nationals last weekend! Anyone that's using the XRAY X4 platform on low to medium grip conditions in a spec class, will find this info useful!
The grip levels at Club ARCA actually resembled those of my hometrack in Monsanto, Lisbon. So I had a decent starting point going into the race. Here is the most important setup data to pay attention to:
Shocks - I ran a pretty soft shock setting, 300 cSt oil with 4x1.1 pistons. This setting not only kept tire overheating to a minimum, but also made the car very forgiving to drive, with a good flow, which made it easy for me to hit my marks lap after lap. I don't recommend using PSS for these kinds of conditions, since I feel that it just makes the car too loose, and too pointy to drive. The springs were the typical 2.5-2.8 front and 2.7 rear springs. You can't go wrong with this spring choice for any track or condition IMHO. In hot conditions like it was in Spain this time, it's important to rebuild the shocks for every race day, since fresh oil will give you more traction.
I ran a 40mm HUDY motor fan (#293111) which I soldered directly to the battery terminals on the ESC, to have the maximum power output to the fan. Make sure that you don't mount the fan too close to the motor.
Diff - For most of the race I ran a 6K rear diff, which is a good setting for low to medium grip. On the Sunday (main day) the grip was considerably lower, because of a bit of rain that had come on the Saturday night, also in combination with pollen in the air. Because of that, I switched to a 5K diff for the finals, to improve side bite and low speed steering on the slicker track conditions.
Roll centers - A bigger stagger between front and rear lower arm heights helped to stabilize the rear on corner entry, and made it possible for me to get on the throttle earlier coming out of turns. In the end, I ran 1.5mm under the front lower arms, and 2.5mm under the rear lower arms. The rear stayed nice and flat also on the fast direction changes on the right side of the track. For low grip conditions, it's important to not raise the hub heights above the kit setting (0.5mm). Doing so will just take away too much grip.
Anti-roll bars - I ended up fairly soft, with a 1.2mm thickness in both front and rear. A softer front bar is especially important on asphalt surfaces, to allow the front end to dig into the track more.
Caster - just like in the past, I preferred a bit more rear caster for stock racing. 3.5 degrees in the rear. This helped to put more initial load on the front tires on corner entry, which helped the car to get on the nose better in the right section of the track in particular.
Toe - The rear toe-gain was set at 6.5mm height with 2.0 degrees of static toe-in. The toe-in can be changed in 0.25 degree steps throughout the day depending on the grip level. For this class and track I would use anything between 1.75 to 2.5 degrees of toe. Less rear toe does increase top speeds somewhat, but it's barely noticeable in a class with an RPM limiter. The balance and handling of the car should be the main reason for changing the toe, and not the straight line speed.
Bump steer - I ran a lot taller bump steer shim that I would normally consider, at 5.5mm. It was a big improvement on this track. It made the car much more forgiving, and improved side bite. Most X4 drivers ran between 5-6mm of bump steer shim.
Flex settings - as usual on asphalt, a split topdeck, with a non-cut rear deck worked the best (only 1 screw at the end of each topdeck). The two front screws removed from the motor mount, and a T-brace installed with 1 screw only, for better stability mid corner.
Bodyshell - the Spanish TC nationals has a bit shorter bodyshell list than other events. The ZooRacing Wolverine was thus the given choice, mounted a bit forward, and with side dams on the rear wing.
Tire prep - The hot track temps in Madrid, in combination with the Matrix 36 tire made an oilier additive choice preferable. In the end I opted for the Solaris type C, which is the same additive that was a popular choice at the Euros back in 2014! It simply works the best on this track surface. I cleaned the tires with the additive, and applied it, warmed the tires for 12 minutes at 60 degrees. I then removed the warmers, and wiped the tires down thoroughly with paper. I then re installed the warmer cups to dry the tires completely for 1-2 minutes before walking to tech.
Drive train - For stock racing, I recommend the optional low friction belts (#305436). I run less belt tension than in modified, my eccentric bearing holders were in the center position in both front and rear. I ran Avid Racing Concepts LLC ceramic Aura metal shielded bearings, which spin very freely, with a thin bearing oil.
Electronics - The rules for this race featured the Hobbywing XR10 Justock ESC and 13.5T motor. The ESC was set to 20K RPM limiter, and the FDR was limited to 4.0. This can be achieved by a 47/99T gearing on the X4. The motor timing is fixed at 45 degrees. I had setup the ESC with punch level 9, and the drag brake set to 5%. The drag brake setting is highly dependent on your driving style. But personally I feel that drag brake, even in a stock class, helps to setup the car for the corner better, it simply helps the car to turn better. I also ran +30% of TH expo in my Sanwa M17 transmitter, to get a punchier bottom end feel.
Battery wise, for a stock class with an RPM limiter, you'll want as big of a battery as you can get, to have as little voltage drop as possible throughout the run, and thus, as little drop off in punch as possible. I ran the new Sunpadow RC 8200 HV packs, which worked great. The IR was really low, the lowest I measured was 0.4/0.4 at only 20A discharge! The packs are also somewhat light at 312g. The race rules only allowed 20A charge & discharge, hence why I discharged the packs down to 3.2V per cell before charging them back up, to try and make them as warm as possible (a warmer pack has more punch since the IR becomes lower).