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The one part nobody can see from outside, but it still plays a huge role in the car performance. First step is about the gear differential.
First of all, I start with replacing the kit case with the graphite one, as it provides better heat resistance and makes the diff work more consistent through the runs. The kit cases work all really well, but for the top notch performance and durability, the graphite version is a great option.
#324955-G
#324912-G
I then apply grease on the outdrives, put them in the diff case with the o-ring inserted. When I insert the big shims and pins, I first apply a drop of oil inside the diff, before inserting the first bevel gear. Then I put in more oil and then insert the optional alu diff pin with ONLY 2 gears. I am using the optional gears with o-rings, that work partly as a self locking diff.
#335081
#335031
Make sure not to overfill the diff, so fill it up just above the diff pin.
When you close the differential, make sure to tighten the screws in a cross order, as shown on the picture for proper function.
Quick & easy gear diff tip:
2 gears = more rotation
4 gears = more stability and grip
  
Part 2 - the shock absorbers in our XB2'26 build series.
When taking all parts out of the box and cutting out the white plastics from the mould tree, it is highly recommended to check the edges of these parts, and preferably sand them down with using a fine sand paper or brick like I do. This will ensure perfect fitting in the shock bodies of all those parts and therefore a proper shock function.
One quite common mistake while building these cars can be the pivot balls - make sure to separate the shock cap balls from the shock end balls. Even though they look similar, they have different shape. See the picture to recognize which balls belong where, or properly see it in the manual.
For my current carpet setup, I use the +2 shock ends in the front and +4 in the rear. The shock lengths I use is 21mm in front and 25.5 in the rear. Check my current setups on the setup forum to match the geometry with these shock lengths. Note that different shock length is needed when changing the front/rear hub height for example.
When all this is done and the shocks are assembled, it is time to fill them up with some silicone oil. My current setup for 2-hole 1.6-1.8 config is the 300-300 oils from the kit and for 3-hole 1.5-1.6 config it'd be 400-300 oils.
For holding the shocks while filling them up I use the HUDY car stand or the designated Shock holder:
#108160 or #109801
Closing of the shocks is step-by-step explained in the manual. I fill the shocks a bit over the top, put a drop of oil also into the cap, then tightening the cap onto the shock body. Press the shock rod in to allow the excess oil to bleed out. After this, I put the shock screw in the cap and I pull the shock in and out approx 6-10 times. Leaving the shock rod pulled out, then remove the screw again and press the shock rod in again to remove all excess oil left. Finally insert the screw back in the cap.
I always double check to have the same amount of rebound on the shocks on both sides. Then put the spring on with the spring cups - for the front I use -2 and for the rear -6 spring cups, to get to my desired ride-height with no problem.
Quick & easy shock tips:Softer springs -> more mechanical grip, better bump absorption on rough tracks, smoother landings, but the car can feel lazy and roll too much in corners.Stiffer springs -> sharper response, more stable in fast corners and jumps, but less overall grip.Softer oil or more/bigger piston holes -> shocks move faster -> more grip, more forgiving car, but body roll increases and the car may bottom out more easily.Thicker oil or fewer/smaller piston holes -> shocks move slower -> car feels more stable, precise, and "flat" through corners, but can lose traction on bumps.On high-grip tracks (carpet, glued dirt) -> go stiffer for more stability.On low-grip / dusty tracks -> go softer for more grip.
   
The rear transmission is what drives the XB2 forward, so let's take a look at what I do when building it on the '26 kit
On high grip, and especially carpet, I like to replace the kit gearbox with the graphite mixture one. It reduces flex on the rear end, that adds more stability to the car. But the material is also more heat resistant, so it helps with keeping the temp of all the moving parts more stable, especially while being close to the motor.
#323029-G
And yes - I choose to use the 3G front motor gearbox for carpet here in Europe, as it gives me more rotation. I would suggest the 5G for very high grip conditions, or if you are looking for smoother and more easy-to-drive car.
5G conversion: #329005
5G Graphite Gearbox: #323026-G
25T gears for 5G (special resistant): #324225-G
For carpet, I go with the kit setting of the diff height, that means 1dot up (dot facing down, diff up), as can be seen in the picture.
When inserting the diff into the gearbox, always apply some grease to prevent any damage on the gears.
IMPORTANT: Always put the diff inserts in the same height on both sides to prevent any damage to the parts and for proper function.
I use the included ventilated slipper plates with the kit yellow slipper pads, this combo works very well on most of the conditions we run on.
Quick & easy tips for the rear tranny:
3G = more rear grip, more rotation, more aggressive
5G = more flat, more corner speed, more calm and easy to drive
Diff higher = more corner speed, less grip
Diff lower = more rear grip
(Also depends on the ride height of the car)
  
On a 2WD car, the driven part is the rear drivetrain, together with the rear suspension assembly - Steps 4&5.
Let's dive into the build steps and take a closer look at some key details.
Starting with the rear shock tower, I use the "kit" (initial) settings for the wing height, that being the upper holes. This has been found a standard base for almost all tracks we go to.
Higher wing - more grip and high speed stability
Lower wing - more steering and rotation, less grip.
Toe - mounting the chassis brace and suspension holders on the car, I most commonly use 1deg or 1.5deg of rear toe-in. RF position (C block) up&out as well the RR position (D block) being up&out. This setting gives the car more stability I found, and is my go-to base setting for high grip tracks.
I recommend installing the shock adapters on the carpet kit (separate bag in the kit) before mounting the arms on the chassis, as this way it is much easier to access. I use the two inner arm holes, with the arrow on the adapters pointing out from the center of the car.
 
Now onto Part 5 - rear drivetrain:
Alu link holder has been updated to become even more rigid than ever before. Now, the titanium shock stand-offs are also included in the kit!
I switch the kit graphite hubs for the optional alu ones, as these provide better stability on high grip tracks. Nevertheless the included graphite is a great start for all racers no matter what level.
Make sure to properly check the inserts in the hubs, so the front matches the rear, therefore the pin goes straight through the hub, and not under an angle. My start position is pin out&up (hub in/low).
Hub higher (pin / outter arm pos. lower) - more stability
Hub lower (pin / outter arm pos. higher) - more grip and rotation.
Last important notes on the rear end - make sure the collar on the sway bar is tight well and centered, to prevent any bind, and assure proper function.
My initial shock position is the same as marked in the manual.
For more corner speed and softer susp. - lay the rear shocks down
For more support on the rear susp. - stand the shocks up
  
Moving towards the front, let's dive into a quick step, which is the front assembly.
For really high grip, I strongly recommend the optional Graphite side braces (side guards) that add a lot of stability to the car
#321255-G
Steering arms and plate - the kit plastic is a great start for most drivers, and I personally use it on low grip dirt or astro, but for high grip carpet racing, the Alu options are a must for me. I swap both, the steering arms and plate for these:
#322575
#322516
Front lower arm mount - a key factor in the setup of the car. We have overall 3 different kick-up options and 4 different weight options.
Plastic (0deg kick-up) weighs 6 grams,
Alu (0deg or -3deg/+3deg kick-up) without inserted weight weighs 13.5 grams,
Alu (0deg or -3deg/+3deg kick-up) with the inserted HUDY tungsten weight weighs 23.5 grams,
And finally the Brass mount (0deg kick-up) weighs 46 grams.
For my carpet racing, I usually choose the Alu + Weight option
These different options and settings can have a big impact on the car setup. The optional arm mounts are as follows:
#322316 - Alu 0deg
#322317 - Alu -3deg/+3deg + #321211 Susp. Holder Brace
#293085 - optional round HUDY tungsten weight with M3 thread
#322312 - Brass 0deg
Quick tips:
More weight in the front - the front end is more lazy, there is less weight transfer, the feeling is more calm
Less weight in the front - helps to make the car more reactive and give more steering
More kick-up - more stable in high speed, more stopping in the corners, better bump absorption
Less kick-up - more aggressive in high speed, carry more corner speed while cornering
  
We're getting close to the finish line with the XB2 kit build — next up, the front suspension!
First of, for high grip carpet racing I always equip my XB2 with the Alu front hubs set. The Alu set not only gives the front end more precision and stability, but also allows to use the lock limiting screw, which can come in extremely handy on very grippy conditions, or when using the 3 dot steering extensions. More on those later.
The alu set: #320904
If you're looking for more precision, great looks and rigid design, the optional alu front roll center holder is a great option to look out for.
#322046
The included graphite mixture hubs are a solid start for all conditions and all drivers, but as I mentioned above, for carpet I always switch mine for the alu substitute.
Now EXTREMELY IMPORTANT:
Make sure to properly check and insert the caster inserts in the hubs the correct way. If you flip these, you will actually have way lass caster on the front suspension.
My go to caster inserts are the 5deg ones. If you were to flip these, you'd have overall 10deg less caster, which has a huge influence on the behavior of the car. Once again, check the pics attached or the manual for proper inserting. The number should always face to the left side of the car.
Quick tip:
More caster - more stable in high speed, more stopping in the corners, better bump absorption, feels slower
Less caster - more aggressive in high speed, carry more corner speed while cornering, feels sharper
We have overall 3 options for the steering carbon extensions, 1-3 dot. The 1 dot makes the steering link the longest and the effect is more outside wheel turn, while the 3 dot does the exact opposite. Note that the inner wheel turn stays the same. While all three options are included in the alu set, you can get the 1/3 dot optionally for the plastic hubs also.
Quick tip:
1 dot - most aggressive, most outside wheel turn
2 dot - middle option
3 dot - most easy to drive, less stop in the corners, least outside wheel turn.
   
Let's wrap this up! XB2'26 final step - the final assembly
My servo of choice going into the XB2 is the TeamSavox SB-3262SG, which has been a part of my program for a long time, doing an amazing job!
I equip the servo with the HUDY extended clamp servo horn with 25T: #293422
When mounting the servo, make sure all parts are moving freely and there is no touching or bind between parts. Especially when running the Alu steering plate, check that there is enough clearance between the steering link ball stud and the servo.
You may either change the servo mounting position or change the ball stud length.
Nevertheless, with the Savox SB-3262SG, there is no problem, when mounting it in the frontward holes and using the alu steering, when using at least 1mm of ackermann shims.
Ensure the 90deg angle between the steering link and the steering plate, as is shown in the picture.
When putting on the top deck, double check that the anti-roll bar is properly inserted in the designated slot. Same as for the rear anti-roll bar, make sure the collar is centered and moves freely.
I like to mount the servo without the servo brace, as I get more flex on the front steering with this setting. If you aim for a more precise car and steering, keeping the servo brace is a great tuning option. (It is included in the kit).
As I am using the low-profile Savox servo, there is plenty of space for other electronics. I mount the steel weight in the frontward holes for more forward weight balance.
Mounting the Elceram RC G2 speedo and SANWA Electronic Instrument RX492 receiver on the steel plate is easy, as it fits perfectly together also with the transponder.
My start battery position is the same as the kit initial setting, having the battery holders in the 4th hole on the optional carbon backstops, attached in the 2nd hole from the front on the side brace.
Optional carbon backstops: #326178
Under the LCG battery, I use the optional 35g weight, to meet the weight limits and get better landings on jumps.
#326181
Also, to keep the motor temps low, I chose the Hudy alu motor fan, mounted on the included plastic mount in front of the motor, to keep the weight as much in the center as possible.
#293101
   
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