Test and Tune: Taming the Ultimate Hoss® 4X4 VXL
We went with a 3-cell 5000mAh Power Cell LiPo battery for maximum monster stomp, and the Hoss continues to impress with its 540XL motor. The extra-long can and equally-extended rotor inside give the truck a big high-torque kick, and it moves out with a wild roost off the Sledgehammer tires. However, Project Hoss squatted harder than we liked, and pitched forward just as aggressively under braking, which told us our springing and damping were too light. This also made the Hoss a bit of a handful in the turns, as the light setup allowed rapid weight transfer to the outside wheels when entering turns and then unweighted the tires just as quickly when exiting.
With the truck constantly shifting weight front to rear and side to side, causing each corner to rapidly gain or lose traction, smooth lines required slower speeds than a well-tuned suspension allow—even with TSM® turned up. Project Hoss was also diffing out easily as all that suspension movement made it easy to get a wheel light. Thick swaybars would have helped prevent that, but we had the thin ones on there. As the Hoss is the widest model in the 4X4 lineup and has the heaviest tires, we should have seen that coming. The Hoss was still fun to drive as the highly animated chassis dynamics were exciting to watch, but we were looking for hammer-down stability. Back to the workbench!
Drivetrain Tighten-Up
Our Ultimate Hoss build has the stock fluids and grease in the differentials, like so:
Front differential: 30k wt. silicone
Torque-Biasing Center Drive: 500k wt. silicone
Rear differential: Greased
The Torque-Biasing Center Drive is highly resistant to “diffing out” with its super thick 500K wt. fluid, while the front and rear differentials allow relatively free diff action. This contributes to the Hoss’ nimble handling feel with a side-benefit of reduced strain on the factory telescoping driveshafts. For our “Ultimate” setup, it was on the light side for the planted feel we wanted. Firming the suspension up will help, but we wanted to really lock the truck in with more restricted diff action. To achieve that, we cleaned the grease out of the rear diff and filled it with 30K fluid, then replaced the front diff’s 30K silicone with 50K. The 5136X Differential Oil Kit includes one bottle each 10K, 30K, and 50K, and is a powerful tuning tool for Traxxas 4X4 models and larger 4WD models.
A range of diff oils is an essential tool for tuning power delivery.Suspension Stiffening
To firm up our GTR shock setup, we swapped the 7444 and 7446 black springs for 7448 and 7449 blue springs (the springs are powder-coated white, “black” and “blue” refers to the small patch of color-coding on each spring). These are the stiffest springs offered for the GTR shocks, with rates of 0.892 and 1.004 versus 0.767 and 0.874 for the black springs—that’s a difference of 15-16%. Stiffer springs call for heavier oil, so we poured out the 30 wt. silicone fluid that came with the GTRs and replaced it with 50 wt. oil from the new 5038X shock oil set.
Percentage-wise, going from 30 to 50 represented a bigger jump in viscosity than the change we made in spring rate, but we decided it was better to err on the side of a less active suspension system. With that in mind, we also installed the stiffer black coated swaybars in place of the flexier, thinner swaybars. We also pushed the swaybar links a bit closer to the shock tower or maximum anti-sway effect. Back to the dirt!
Tuning the Stock Hoss Suspension
Out of the box, the Hoss is equipped with 50wt. oil in the factory-installed Ultra shocks. If you want to get stiffer suspension like we are aiming for in this build, step up to 60 or 70wt. oil.PRO TIP: Not sure what oil your favorite model is equipped with? You can find out in the Tuning section of your Owner's Manual. Hit up the Support Page for your model to download it.
The 5038X shock oil set includes a carousel rack. Already have a set of oils? You can get the rack by itself, 5038.Hoss Highlights, Round 2
Our Hoss 4X4’s stiffer springing and heavier damping was easy to feel when bouncing the suspension on the bench, and we had high expectations for improved handling. Back in the dirt, the truck still leaned on the rear suspension under acceleration—there’s no getting around physics—but it didn’t feel like it was falling into the shocks. The stiffer springs resisted deep squatting, and the heavier damping smoothed and slowed weight transfer after the initial burst of acceleration, which made the truck much more tractable and helped TSM do its thing. Now we could dive into corners harder with much more predictable handling, and slide or wheelie the truck only when we wanted to.
The tightened-up differentials were helping here too, and lifting an inside wheel mid-corner resulted in much less disruption to the attitude of the truck. Peak traction was no doubt lower with the stiffer suspension and swaybars, but the truck was much more predictable since weight transfer was better controlled and the amount of traction was consistent rather than swinging between highs and lows. The Ultimate Hoss still drove like the monster it is, with the arm-pumping suspension action and chassis roll that’s so fun to watch, but it felt more planted and easier to drive—kind of like a Hoss with a 2-cell LiPo on board, even as we enjoyed full force of 3-cell Power Cell horsepower.
Tuning FTW!
You know what? Not getting the setup exactly right out of the gate actually added to the fun for this one. It’s very satisfying to spin a few wrenches, put your suspension-tuning know-how to practical use, and see real before-and-after results. Having a range of differential oils and shock oils at the ready makes it much more convenient to experiment, so adding the 5038X and 5136X oil sets to your 4X4 tuning arsenal is highly recommended. (Added bonus: the carousel full of shock oil looks pretty sweet on the bench. Very professional.) Now that Ultimate Hoss 4X4 VXL is a wrap, we’re ready for the next project—watch this space!
