13.5T Spec Top Force EVO
Build Date: 2022
You can learn more about the foundation of this build here - Top Force Evolution (58107)
Back Story
I, along with most North American Tamiya fan boys, waited nearly a full year for my Top Force EVO (47470) kit to arrive (thanks COVID). In my lack of confidence that resellers would ever take delivery of stock, I had placed multiple pre-orders hoping to get a single kit….. three ended up shipping to me on the same day 9 months later. I figured I would build one up as a shelf queen, but I didn’t know what to do with the other two.
I quickly got the work bench cleaned up and built the box stock shelf queen kit. Upon completion, I got to experience an “Evolution” for the first time. It is hard to explain, but it just felt different than any other Tamiya build I had built previously… it felt like a race buggy.
I quickly packed it up and took it to the track to show it off. There, it caught the eye of a few local top drivers. “This thing feels like a racecar” was the unanimous conclusion. I then knew what to do with the other two kits, build one into a top tier 13.5T Spec Class 4WD Buggy and use the other for spare parts. This would be the start of RetroRCBuggy.
The Build
Disclaimer: I was not sponsored on this build and I paid for every part with my own money. If I recommend a product below, it is because from my experience, the company provides high quality parts and/or top notch service.
To say this car is over the top would be an understatement, the Top Force EVO in stock form is impressive even by today’s standards. The dual deck carbon chassis with carbon towers, the “solid” A-arms (which are now a fad again), the 12mm diameter shocks (which perfectly work with Associated B74.1 springs - lengths match the front and rears respectively), and its insanely low weight allow it stand toe-to-toe with modern buggies. Let's look closer at the weight situation. A stock fully race ready Associated B74 weighs in at nearly 1800 grams, a stock race-ready Top Force EVO comes in at a laughable 1428 grams (that is with a Trinity 4100 shorty pack). Spec class rules has a 1588 gram minimum weight requirement. While most racers go to great lengths to put their cars on a diet, the Top Force EVO gets to start pounding protein shakes and building serious muscle mass.
The biggest motivation to this build involved stumbling on Custom RC Parts eBay story. This is family run machine shop in Serbia, and the owner is clearly a genius who has a love for the DF-01 chassis. Not only did Custom RC Parts convert known weak plastic parts over to aluminum - he also designed totally new parts to further strengthen the platform and also add tuning options. The most amazing aspect of Custom RC Parts’ DF-01 offering is the rear A-arm hinge pin assembly that adds “C” and “D” blocks that have indexable “pills”. This hop-up adds the ability to adjust both toe and anti-squat angles on the rear areas while also greatly increasing the strength of the hinge pin mounts.
I also sourced a few random aluminum parts from Xtra Speed via RC-Mart out of Hong Kong (if you pay for expedited shipping you can get parts from Hong Kong to your door in the USA in about 3-4 days, we live in amazing times people). Probably the most important aluminum conversion part not offered by Custom RC Parts that you need to acquire is the front lower differential cover. This part is a weak point on the DF-01 as it is the sole part that holds the front A-arms in place. I also threw in Xtra Speed front and rear aluminum hubs (why not) and a really nifty Xtra Speed shorty battery conversion. Another upgrade that you will want to make is removing the servo savor - you want a horn with about a 15mm to 16mm radius. The chassis, body, dampers, diffs, suspension components, turnbuckles, and drivetrain are all stock. I wanted to keep it as true to the original as possible while adding strength as this car sees far more abuse than 1992 was dishing out.
For the body work, I didn’t want to stray too far from its Top Force Evolution heritage. I created a set of paint masks that allowed me to retain the design of the original decal sheet but could give me more of a racer paint scheme. For the wing, I knew the sexy stock one would tear like tissue paper the first time I roll the car, I would need to run something more modern. I grabbed a trusty JConcepts S2 1:10 wing and noticed that I could trim the side dams taller and maintain the vintage look of the original. I also knew that no self-respecting Top Force would be caught dead with a clear wing, so it also received some paint and custom decals to keep its numbers impressive.
With the chassis and body complete there was another major issue to tackle before this thing could hit the track, wheel offset. The front of the DF-01 chassis is narrower than modern buggies and I did not want to hunt around to find special off-set wheels. I realized that stock +5mm Associated B74 wheel hexes worked perfect for the rear, and that the +8.5mm Associated T4/T6 wheel hexes work perfect for the front. With these hexes, you can run easy to find modern B74 1:10 4wd buggy wheels and have an ideal track width front and rear.
Driving Experience
This car just wants to maintain traction - it is pretty amazing. Keep in mind this was built for hard a packed dirt track - not an ultra-high grip prepared surface or carpet. We run on a track with a high clay content that generally starts out the day as slick/damp and then turns to a hard dusty surface that takes a little rubber around the double mains. This means that we are generally running on a relatively low traction surface compared to most modern “offroad” tracks. The winning driving style on this type of surface involves using the throttle to steer the car - just keep it pinned and let the front follow the rear. The Top Force Evolution/Evo does the complete opposite, it simply finds traction. The more throttle you apply in a turn, the more it seems to bite and steer tightly through the turn. While this technique is arguably not favored by the fastest of drivers, I am not the fastest of drivers, I prefer a car whose rear follows the front.
At 1600 grams, the power to weight ratio is not a problem. There is arguably too much power in this setup. I played around with multiple gearing setups but ended up on a 21/69 which seems to get enough rip on the throttle without punishing the ball diffs constantly. One of the first things that was discovered driving the car on the track was that the one-way bearing is a no-go. I can see it as an asset on a high grip track, but on a lower grip track it causes the rear to swing around under heavy braking and it can feel very inconsistent. Secondly, are the ball diffs inability to fully lock up. I was concerned how they might handle the torque of serious 13.5T motor, while they seem to not destroy themselves - they slip. This is most notable when you roll a larger jump and full pin the throttle as you load your suspension on the back side of the jump. You can hear the rear ball diff squawk. Unfortunately, there is not enough adjustment to tighten the differential enough to remove the slip, and instead you just have to drive around it and learn to roll on the throttle a little more than you would if you were running a gear diff (similar to running a slipper clutch).
A quick note on the ball diff build, I am using teflon tape on the diff outdrives to give them a friction fit rather than using the suggested synthetic rubber cement (RTV silicone). Epoxy them together. The re-re 47470 “EVO” kit actually has the original Evolution style ball diffs (I was expecting at TA01 style diff), I do feel the three piece, 6 ball thrust bearing is a weak point on this design. You can use the one-piece Tamiya thrust bearing 53136 which has more balls (both figuratively and literally) and in theory can help the smoothness and longevity of the diff. I built the rear with the one-piece thrust bearing so I can compare the longevity and report back.
The dampers required a little tuning but the overall geometry by the book was sound. With testing, 500 cst damper oil front and rear at 60 degrees F paired with Associated “White V2” springs felt great. We also added some fuel tubing to the rear shock shafts with just enough length to start to absorb some of the compression right before the chassis can slap. The suspension runs very soft, and this is key to its superior traction, removing all the chassis slap would most likely stiffen the car to the point where it would negatively impact its unique handling. While the Custom RC Parts rear hinge pin assembly allows for additional tuning, I have kept with the stock toe (roughly 2 degrees) and zero anti-squat. These adjustments require drilling out the stock hinge pin mount, my focus has been on increasing durability and I am hesitant to do this without some additional testing first, but there is no doubt that some addition anti-squat would improve things a bit.
Durability of the car his been very impressive and down right surprising. It has taken some hard smacks and tumbles, but has not broken any parts yet outside of the stock servo saver (TLR 22T aluminum horn is a perfect fit). I suspect the ball diff thrust bearings will be higher wear items (as noted earlier). Remember there are many reinforcements on this build that are not stock - a normal DF-01 would not be able to take the kind of abuse this thing has seen so far. Those paper thin damper stays look suspect as well, my guess they will cause a DNF at some point.
Conclusion
If your driving style is more focused on cutting the track down to the shortest possible driving line and not about just drifting around every turn - then the Top Force chassis is an excellent tool for the job. I have always found the most success with the “slower is faster” approach, keeping it clean and consistent - the TF Evo seems to thrive on this philosophy. While It isn’t for everyone, this DF-01 puts a huge smile on my face and really turns heads when it puts up Impressive Numbers.
Racing Setup
ESC: Hobbywing Xerun XR10 Pro G2
Motor: Trinity Revtech “X-Factor” tuned by Rotor Ron
Gearing: Optional “High Speed” Top Force Gear set 47393 - running 21/69
Battery: Trinity Shorty Low CG 4100 7.2v
Wheels: JConcept Associated offset
Tires: JConcept Ellipses (Green or Silver)
Wing: JConcepts S2 (custom trimmed)
Springs: AE B74.1 White Front/Rear (fuel tube bump stops on rear)
Shock Oil: 500 CST Front/Rear