In the following, I will explain the build-up process and will also mention the differences and specialities compared to the TRF421 #42384.

As already anticipated, the suspension arms are now made from harder PA-CF material. Driveshafts have been upgraded to “ball bearing type“, which aren’t too complicated to assemble, BTW. Just use proper pliers and enjoy!

All other changes are most probably suited for tracks with higher grip levels. With that in mind, please keep your “old” TRF421 – as it might still be your choice for low-grip tracks.

Used Hop Ups / Tweaks:
– Square STM-90 TRF421 Alu / S-Flex Titanium Screw Set Sakaguchinetshop Special Edition (some sizes were replaced by other sizes)
– Axon ST-HL-013 “Red” Springs on Front & Rear (for more easy setup I still recommend ST-HP-013 on front and ST-SL-013 on rear).
– Tamiya #13404136 Carbon Battery Holders (2 pcs.)
– Prototype Alu Battery Holder
– Tamiya #19803493 Front Knuckle Plates from TRF421 (for shorter Turnbuckle length)
– Square NAR-314TB (2 pcs.) Alu Screws for Body Lift on front upper suspension arms
– Axon PG-BS-001 Front Lightweight Body Mount Spacers
– Axon DB-NB-105 Precision Shock Bladder V2 Type Flex NBR (better fit than #51738)
– Tamiya #42248 Alu Servo Horn
– Axon GS-T6B-111 Spur Gear (for Modified 4.5T Motor)
– Axon GP-A6-028 Pinion Gear (for Modified 4.5T Motor)
– Axon AC-BS-001 Clear Battery Tape (more friction between battery and main chassis)

Starting with an initial setup with many good points taken over from my last TRF421 testing at Arena33 in Andernach, I will see on Monday how the setup will work. For sure, I will tweak it here and there. The most interesting point for me will be the Axon HLS-SS Spring Series with shorter springs. Even though the stiffness is rated the same, they feel pretty different.

Generally speaking, the time for carbon main chassis is over! With loads of back-to-back tests on the TRF421, I came to the conclusion that Alu is always the better way. Regarding steel, I am still not 100% convinced. On some tracks, it might have some benefits – while on others, with Alu, everything is fine. In the end, it’s a matter of personal taste.

Relating the build-up: The first thing I noticed is the changed damper mounting position on the lower arms. They went quite a bit more towards inside. That matches also the fact that the upper damper stays to accommodate the dampers more close to the chassis. In my opinion, the outer 5.8mm ball fittings in the lower suspension arms are a bit too tight. With a Square TRX-430V 5.8mm Ball End Reamer, I have ground just a bit of material off, and the fit was perfect. With the help of #42276 TRF Damper Pliers, it was a bit more easy to press in the 5.8mm Balls into the suspension arms, as they have some 3mm holes to accommodate the balls perfectly. 

As always, please take note to assemble the front double cordon joint shafts in the proper way so you don’t risk losing the C-Clamp Clips. I have marked them left and right in the gallery.

After many tests on TRF421, I came to the conclusion that Axon DB-NB-105 Shock Bladders fit way better than the original #51738 ones, which occasionally are a bit too small and were soaked into the main damper body after some runs (this happens only on some dampers!). The Axon ones are higher and fit the USBB dampers just perfectly! Don’t forget to make the 1mm air bleeding hole into the top shock caps. Like on the TRF421, I recommend turning the rear damper pistons to prevent a suction effect when riding low droop settings on the rear (below 4mm). Damper length was adjusted to 7.4mm on the front and 9.0mm on the rear using the kit-recommended lower eyelets.

Further points that I had noticed:

– Underneath the centre pulley, there is now a ball bearing preventing a slip of the rear belt. So in general (especially for stock racers), the rear belt tension can be set to lower settings and have less drag.

– With new bodies to be adjusted, I will take advantage of the wider rear carbon body mount. For now, I am using my TRF421 bodies, which are all set to go.

– Topdeck settings give you now more possibilities to set it to your personal preference. Generally, I am a fan of split top decks, which always give an extra bit of steering. For amateur racers, I recommend using the single topdeck, as it makes the car less aggressive on steering.