I still have some hope to do a bit more running with the car, but we have already been very lucky with the weather in late August/early September after a horrible July with 3 x more rain than usual. Even if there are no more opportunities to run the car now in late September, I still feel happy that I have managed to do more testing than expected.

As you might have read, I have run a couple of other cars this summer as well, but I decided to write about the TRF421 first as many have requested it for some time already + many have asked for my setup.

I have not shared any setup until now, as I never want to do that before I have some confidence in knowing I have properly tested a car. In my opinion it’s also in one way quite a useless exercise, as it does not matter what anybody else runs. Any racing car should be setup for the driver actually driving it and according to the conditions at that moment, so even though I now will share my setup I encourage everyone to find your own setup that works for you.

I mentioned that I have done more testing than I expected. As the car arrived a bit late for the summer season, it was only possible to start testing it in the second half of June, but despite testing several other cars as well, I have done over 150 packs of testing with the 421, which equates to around 3000 laps.

I was quite quick to state that I love the car, and that has not changed at all. With the kit setup the car was already fantastic, and the couple of people I have had try my car have been amazed at how easy to drive and precise it is.

This is curious as having run it many times back-to-back with two other 2024 absolute top level TC’s, it has always been significantly easier to drive and felt like it always has more grip. I have found the car very forgiving and situations which I have never been able to save with any other car have been possible to recover from with minimum time loss with this car.

On this note I will also say that I noticed that the TRF421’s taking part in the last ETS round were very quick in round 1 of practice… I was not surprised.

Easy to drive is one thing, but it was always fast as well, on several different tracks. Like 95% of the time it was faster than any of the other cars by a couple of seconds over 5 minutes. Not as much faster as it felt better, but still always faster.

Having run the MTC2 when that was released – and the 421 is of course somewhat similar to it, the difference on track is huge in the asphalt conditions I drive. That car always felt tricky as well, just sometimes super good, but more often it was a bit difficult. Like a very narrow window where it worked. The TRF421 is the opposite.

The 421 has also been super reliable for me. The only broken part was a steering block early on. I have since only replaced two wheel bearings. I have cleaned and re-lubed the driveshafts a couple of times, of course rebuilt the dampers, adjusted belt tension, but other than that – nothing. I will do a separate post later where I disassemble the car to look for wear.

During each of the approx. 150 packs of testing I have always tried something, and many back-to-back tests have been conducted.

In the photos here you see how the car looks now with the exception that I still prefer the one-piece upper deck. The split top deck setup seen here also works really well – more on that below.

As you can see I run a shorty setup, and I already mentioned that in this post. I have explained this previously, but the reason is that I wanted to test the car with a shorty, and since I have not done any races nor do I have any plans to attend a race (I have done enough TC races since 1997…), it does not really matter what power I have. I understand that if I was to attend a high level 17.5T race on a “fast” track, I would need the extra power from a larger battery during the later minutes.

Anyway, on my home track which is very technical I was actually faster with the shorty setup, and the car had more steering/rotation at the apex as well as beeing more stable in and out of the corners, so I continued running the setup.

I revised the weight placement a few times. The weight I added for the shorty is 28g in front and 28g behind the battery, as well as 10g between the servo and battery. I also run a 20g weight plate under the battery. The battery holders are in the front shorty position on the chassis.

A few weeks ago I cut the front upper arms to take away the slight resistance there. The suspension would always fall under its own weight, but the upper arms disconnected from the rest of the suspension would not always be 100% free. Cutting the upper arms removed this, and on track the car actually felt a bit more free in the corners, so it was a good change.

I tried moving the included ballast weigths around as well, but the car always felt the best with them in their ‘original’ front positions.

I switched to the minimalistic horisontal only body posts quite early as they workes perfectly with the RC Maker mounts I have been running. For next season I will switach to the lastest ultra-lite model.

Late on I tried the rear T-brace from the TRF420X. This worked well when using the split top deck, but you need to cut down the width of it for it to clear the roll bar mounts. The inner holes fit the TRF421 chassis. Also use only 1mm spacers below it as otherwise it will hit the belt if you run the diff in the low position. Part number for the flex plate:

13404138 Rear stiffener
19803402 Stiffener nut

With the one-piece upper deck I prefered it without the T-brace.

I run a 1.2mm rear anti-roll bar, with a 1.1mm front bar.

I always liked the car more with the front bulkhead brace removed, but I can imagine it being required in high grip conditions and/or with modified motors and higer speeds.

The new USBB dampers are really easy to build and overall I like them. There is the issue that the piston can stick a bit when the shaft is fully extended, and I assume this is a mistake in the production of the dampers. In reality I never noticed any ill effects of this on track, but during one rebuild in August I placed the pistons upside down and this removed the issue. I got this tip from someone in Japan as I was not clever enough to come up with it myself.

With the standard o-rings the dampers would leak, but after switching to Axon black o-rings (OR-SO-001) I had no issues with the dampers.

I spent a lot of time testing different springs, but always came back to Axon HLS C2.15 (Green/Gold) front springs and SLS C2.6 (Blue) rear springs as my favourites. The car works really well with other combinations as well though.

If you want blue larger diameter spacers to raise the lower arms, the Tamiya #53873 set is a good choice.

I also did a lot of roll centre tests, but ended up with a fairly ‘neutral’ setup. This is what I felt worked best (see setup sheet). Angling both the front lower and upper arms slightly worked really well on my home track.

I did several tests with diff/spool in high or low positions, but I was always faster on our track with the low diffs, even though the car felt really good with high diffs as well.

Quite a while ago now I already posted about my favourite flex setup. This has remained the same, as I feel this gives the most consistently good results.

During the last few weeks I found a setup with the split top deck that also works very well, and that is what you see in the photos.

First up, for this split top deck setup I removed the screw furthest forward in the motor mount (lower chassis in front of spur) only running the screws behind the spur gear. I also used the T-brace as mentioned above. I then cut the front top deck as seen above. This setup made the rear secure enough while the front had enough flex for it to work for me.

Above you see my home track, and that’s the reason I run 17.5T motors now. Any more power makes this narrow track not fun. But with how good the latest TC’s work and running 17.5T it is now finally sort of fun to drive on even with TC’s, not just FWD’s like has been the case before.

In the beginning of the summer I would describe the grip as low. However the asphalt is very rough making it quite aggressive in that sense. In July we had a lot of rain, and in August and September we would always have rain between the good weather days. This meant that the track was super clean and combined with the rough asphalt it provided medium grip. Most of it is fairly flat, but the there are a couple of bumps.

Test track number 2 which is again quite small but considerably faster, and with great smooth asphalt that always gives decent grip. Still it’s more low to medium grip as it gets used so little now. Too bad the track gets worse and worse for each year as it seems there is no-one taking care of it anymore.

And below you see test track number 3 for this summer. These are the three tracks closest for me (under 300km). Unfortunately the grip on track nr 3 was really poor, as it would be good to do more testing on a larger high speed track like this also.

Most of my testing has been done on Rush Vr3 32X preglued tyres (High Precision/Type A Yellow – part# RU0862) which I started using last summer, and I must say this is my favourite TC tyre probably ever. A great product!

I have also done a bit of testing with Sorex 32R.