Monthly Archives: May 2022

Tamiya TRF420X Correction

The battery post mistake made by Tamiya with the TRF420X kit, mentioned in the presentation last week, is getting a correction from Tamiya.

Sorry for the bad quality picture.

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As it’s now May 2022, quite a bit of time has passed since the last Tamiya TRF TC chassis release, with the TRF420 launched late 2019. Some even started to have doubts if there would be a follow-up to the TRF420, but as there had also been two years between the TRF419XR and TRF420 releases, there was no need to worry. Side-by-side with the TA08 development, Tamiya had been quietly working on an update to the TRF420 platform, and even though it took some time for them to release the car – the TRF420X is now finally here.

I’ll admit that my first reaction when details of the TRF420X surfaced was a bit tentative, as it seemed like quite a small and conservative change taking into account the time that has passed since the 420 launch. At the same time, Tamiya have always been quite conservative with the TRF cars, following a strategy of continuous refinement, and still each of the latest TRF cars has been a clear step forward on track from the previous one, so probably they know what they are doing. While on the new TA08 chassis Tamiya decided to go with a new style suspension, for the TRF420X they found that the TRF420 suspension still worked better. Both the TA08 and 420X share the same drivetrain though, with a longer rear belt, and the spur gear positioned in front of the motor.

Another point that we have to address is the price of the car, as it is now considerably more expensive. This is a worrying general trend in the TC market, although with significant worldwide increases in almost all prices and especially in many materials, it’s not difficult to understand why the top-end alu/carbon cars have suddenly got quite expensive. Long-tem I fail to see how it can be sustainable for the sport/hobby to have chassis kits costing 700-1000 € though, and it is something that needs to be considered for the future.

Tamiya can at least say that you get a lot in the kit though, with the usual almost “full-option” treatment given to the TRF420X, and taken even further with the inclusion of both a carbon fibre and an aluminium chassis – which is fairly unique to say the least! Tamiya also hold the advantage of significantly more affordable spare parts compared to most TC competitors.

The lowest advertised price for the TRF420X that I have seen in Europe is 649 €, while most prices are between 689 – 799 €. So for Tamiya the change has not been that big when you consider the additionally included alu chassis, but it still means that to buy the car (and many other TC’s) you have to have a spare 700 € lying around, and that is the more worrying part of the current TC market/hobby/sport.

Now it’s time to focus on the build of the 42382 TRF420X Chassis Kit though – after all that’s what we’re all here for! 🙂

To see what the box, manual, decals etc. looks like, you can check out my previous post from when the car arrived earlier this week.

I also need to mention that for the parts that are the same as on the TRF420, I will not go into any details in this presentation, as you can find them in the original TRF420 Presentation.

Like already mentioned a couple of times, the TRF420X kit includes both a carbon fibre lower deck, and an aluminium lower deck meant for high-grip racing surfaces like carpet.

The outer shape of the carbon lower deck is exactly the same as on the TRF420, but you’ll notice the lack of pockets under where the motor go. It is the same 85mm wide, and also cut from a 2.25mm carbon plate. The alu lower deck also has the exact same outer shape, but obviously with a lot of cutouts making it fairly flexible for an alu chassis.

Carbon chassis:
– 2.25mm thick
– 69.7g

Alu chassis:
– 2.00mm thick
– 79.6g

The lower bulkheads are all new, and while the front and rear bulkheads are almost the same, there is one small difference as the rear bulks have an extension downwards from the top deck mounting holes. This has been added to allow you to use it as an inner mount for the toe-link if you use the optional TRF420 Toe Control Rear Suspension Set.

Compared to the TRF420 bulkheads, the roll bar bearing holders have been redesigned, but overall they are obviously quite similar to the 420 bulks.

Front lower bulkhead: 5.6g
Rear lower bulkhead: 5.9g

The motor mount of the TRF420X is all new, as the spur gear has been moved in front of the motor for the first time on a TRF chassis. It is made from two separate pieces of beautifully machined and anodised aluminium, screwed together with two screws. Fitment is excellent.

This is what the assembled motor mount looks like. One would guess that the main reason for not making it one-piece is cost, but precision is as mentioned very good, so there should be no problems.

The weight of it is 12.0g + 4.6g, and screwed together 17.0g.

Front bulkheads fit onto the chassis like on the original TRF420.

Do notice the beautifully chamfered edges on the front and rear lower bulkheads!

I also have to say that the anodising of all parts on the TRF420X looks really good. This obviousy vary slightly from batch to batch, but on this car it’s the best I have ever seen.

The rear of the car features this new adjustable stiffener plate made from 2.0mm carbon with special blue anodised alu stiffener nuts. These mounting points can be moved to fine-tune flex in the rear of the chassis.

The car comes with “E” suspension mounts up front, just like the 420. Also the steering posts are exactly the same.

Motor mount in the car – looking even more beautiful.

In total there are 5 holes for mounting the motor mount to the chassis – 4 at the rear and 1 in front – all on the centerline. When you build the car according to the manual, 3 screws are used – 2 in the rear part + the front screw. By using different amount of screws in different positions, flex can again be fine tuned here.

A rear ball bearing is used to lift the rear belt so that it cleares the motor mount. A 3x6mm bearing is used in the picture. A 3x7mm bearing is also included, to be used when you run the rear diff in its “high” position. Tamiya attention to detail 🙂

Referencing the TRF “full-option” treatment mentioned in the opening text, the TRF420X comes, just as usual for a TRF chassis, with a specially designed center ballast weight. On this car it is 20g heavy, but also adds a new feature; The special floating carbon fibre RC deck. This carbon plate is attached to the bottom of the weight, and is used to mount the receiver and ESC, making them easily removable and “floating” above the main chassis, therefore minimising any unwanted effects on the flex of the chassis.

The carbon plate weighs 3.6g, and is cut from 1mm carbon.

The weight is mounted to the chassis with two screws.

The plate is mounted to the weight with two countersunk 3x5mm screws. However, here I found that the plate would not mount solidly as the coned part of the screw would hit the weight, so I had to add thin 4mm diameter shims to take out the play.

Here you see how the RC deck “floats” above the chassis. You also see the shims I had to use, but there is still enough free space between the RC deck and chassis to allow wnough flex without them touching.

Tamiya is in no way the inventor of this system. I believe this was one of RC Maker‘s many inventions – as in the first to bring it to the market at least.

The rear diff is largely unchanged, but there some detail differences.

It now uses bearings for the outdrives instead of the brass bushings used before. The “new” 42374 VG O-Rings for Gear Differentials (40°) are also now included. And the shimming shown in the manual is a bit different.

Overall the TRF420 diff has always worked well, and probably now it is even more fine-tuned.

The TRF420X also get the new TRF rubber sealed bearings throughout. These are slightly cheaper bearings compared to the previosus TRF bearings, but give a good impression so far.

The upper bulkheads on the car are the same as on the TRF420, but all the upper arm mounts are new and narrower. This means that even with the included upper arm spacers, the upper arm balls are slightly closer to the center of the car compared to the TRF420 with no spacers. This obviously give more options for inner upper arm pivot points.

Here the rear diff is in the car, held by the upper bulkheads. The spur gear and pulleys are also installed, with a black anodised 2mm alu part doubling as a battery stopper (inwards) and a support for the middle shaft and pulley/spur assembly.

The front direct coupling or spool is the same lightweight unit seen on the TRF420 – obviously with aluminium outdrives included.

Here you see how the bearing lifts the rear belt to clear the motor mount.

The car uses the same belts as the TA08 PRO chassis from Tamiya.

Front belt is 132T or 396mm 51670 TA08 Front Belt (132T)
Rear belt is 101T or 303mm 51671 TA08 Rear Belt (101T)

Here you also see clearly the lack of a cutout under where the motor goes – done to have a uniform material throughout the chassis for more consistent flex characteristics. It also slightly raises the motor, so as with all things it’s compromises and which ones to go for. Lengthwise the motor is in the same position as on the TRF420.

The suspension is exacty the same as on the 420 – this is unfortunately also true for the too tight (big) roll bar balls moulded into the suspension arms. The arms are obviously manufactured in batches, but I really think Tamiya should have made the effort to correct this at least on the arms included with the 700 € car kits.

An “E” rear suspension mount is again included, although the recommended choice of bushing is different in the manual. The recommended setup in the manual is X-D for rear, giving 2 deg of toe-in.
The manual recommendation for the front is F-F.
All at the neutral 4.75mm pin height, which is one step higher compared to the 420 box setup of 4.4mm.

On the pictures here that is not the setup you see, as I plan to start with the TRF420 setup I have been running so I can back-to-back test the two cars to understand them better. Later I will then try the standard 420X setup as well.

Front arms, here with optional suspension arm damper bushings. The “B” bushings are included front and rear.

The steering has stayed exactly the same as on the previous car.

More refinements when it comes to the driveshafts of the car, as the 42362 44mm Drive Shafts for Low Friction Double Cardan Joint Shafts (2pcs.) are now included for the front. The major improvement of these is that the pins are longer at 10.8mm, making the swing caps or more commonly called driveshaft blades last much longer.

For the rear of the car, new 43mm driveshafts are included. These were previously 44mm and a carryover from older cars, but the slightly shorter 43mm shafts will match the TRF420 suspension geometry better.

For the rear driveshafts the axle rings have after a few years been abandoned in favour of classic cross joints secured with a small set screw. Since the wheel axle is the same, you can of course still use the rings if you wish.

Rear suspension complete. Do remember that the blue alu TRF screws seen in the photos are option parts – steel hardware is included with the kit.

Front complete suspension with the new LF DCJ driveshafts. Standard 4mm wide wheel hexes are included as on all TRF cars for a long time.

The damper towers are new both front and rear. Still using 3mm CF, they now have 3 damper mounting holes instead of 4, and have been machined thinner in the middle to allow a bit of flex, which is said to give more grip and making the car easier to drive.

The 3 damper mounting holes are spaced in the middle of the old 4 holes, meaning that the positions are new. In terms of height, they’re the same.

Continuing the familiar theme, the SSBB Super Short Big Bore Dampers are very similar to what they have been, but with a few refinements.

The biggest change is the move to a shorter piston rod, which is roughly 1mm shorter than before, and will move piston lower in the cylinder. The piston rod is the same as used already on the TA08 PRO chassis. Unfortunately that means that it is no longer ti coated, but has a polished non-coated surface.

Another change is to the o-rings, which are now the latest dark blue TRF versions – 42359 VG O-Rings for Oil Dampers (30°). These feel very good so I hope they will make for a well working and more leak-free damper. While the TRF dampers are good, Tamiya know that the SSBB dampers so far have not been perfect. The SSBB dampers have been around for 6 years already, and although they have been updated and improved a few times, perhaps it would soon be time for a more solid damper design, as other’s have also made big improvements.

Both the black 13mm o-rings and bladders included felt excessively soft this time and made building the dampers slightly more work than usual. But obviously there can be slight variations between batches depending on manufacturing and storage conditions etc.

Front dampers and roll bar on the car. Green springs are again included – these are the softest from the 42306 Touring Car Large Diameter Short Spring Set.

The manual now suggests 1.5mm of spacers behind the front upper mounting balls, and 2mm on the arms, so the dampers are spaced out a bit from the tower and arms.

The front roll bar is 1.3mm thick – i.e. the same thickness as on the TRF420.

The rear gets the same green springs and also a 1.3mm roll bar – just like on the 420.

Just like at the front, the dampers are spaced out a bit, with 1mm on the tower, and 0.5mm on the rear arms.

A new servo mount has been designed for this car, although very similar to the last one. If nothing else, it’s super beautiful! 😍

The new servo mount weighs in at 7.9g, which is actually lighter than on the previous car.

Another example of the “full-option” theme is the special alu step screws included to mount the servo to the servo mount.

And as we continue on the full-option theme, these special screw-on 5g ballast weights are again included, just like on the TRF420.

The upper deck is all new, as the new spur gear position requires a new design.

The upper deck is 2mm CF, asymmetrical, and with multiple options for flex adjustments.

In the phto above you can see 4 holes in the front cental cutout, and 1 hole in the rear cutout. Screws and nuts are included which you can use here to adjust flex / change the flex points. You could also move the belt tensioner for the same effect.

The bigger hole in the rear part of the top deck is elongated, with several flex options available here (see later photos).

Top deck on the car, mounted with 2 screws per bulkhead, 1 screw in front of the spur, and 1 behind.

Closer view of the front of the upper deck, and how the belt tensioner is mounted.

This is the standard setup of mounting the upper deck to the rear part of the motor mount. It uses a 3x6mm flanged ball bearing in the elongated hole of the top deck – a setup which allows quite a bit of sideways movement but no front to back movement.

The second option is the included blue alu upper deck holder, which really removes a lot of flex from the rear of the car. Great to see these options included.

The new battery mounts mounted to the car, with new black anodised alu lower holders which look quite similar to the old parts but are all new. These are quite sturdy, and weigh 6.2g for the front one, and the two-piece rear holders weigh 5.7g + 1.2g = 6.9g.

The rear holder allows front/rear adjustment, while sideways adjustment can be done with screws like on the old car. However, for most this won’t be needed, as a normal size pack just fits in with a little bit of play. The black lower holders are a bit too high though, as they make sliding in or out a normal size lipo battery unnecessarily difficult. Of course, Tamiya also have to think of fitting their own LF battery packs which are used in Tamiya racing classes, but still they have to make sure the system is good to use for normal lipos as well.

Nice carbon upper holders are finally included, but Tamiya must have made a mistake with the length of the blue posts that these mount to, as they are too long for anything but a full size 25mm high lipo. No problem if you have boxes full of old parts (and posts) like me, but still they should correct this. According to some reports Tamiya are already preparing to give new shorter posts to customers, so hopefully that will be the case everywhere, not just on any particular market.

This super beautiful and minimalistic fan mount is included with the car (full-option!), again mounted ‘invisibly’ like on previous TRF cars.

This is what she looks like then – the completed Tamiya TRF420X Chassis Kit.

She’s a beauty! 😍

As you can see, the (excellent) front bumper has remained the same, just as the body mounts introduced on the 420. Of course you can also run horizontal rear body mounts if you wish, but Tamiya also have to think of their own racing classes with their own bodies, so keeping the vertical option makes sense.

As photographed here (with alu screws), the chassis weighs 535g.

Overall a very pleasant build, just like with any TRF car. The TRF420X certainly has a lot of very nice features and is beautifully designed and made. It’s not a car that follows every latest TC trend, but what matters in the end is how it consistently performs on track in he hands of normal drivers. If the last few TRF cars are anything to go by, the 420X promises to be another good improvement. It’s no perfect car though, and there are still improvements that can be made with TRF’s continuous refinement philosophy. Or perhaps next will be an all-new generation TRF421? Who knows…

But for now and the coming months I will be (hopefully) enjoying the TRF420X, and finding out how it compares to the TRF420, as I still have that car. This makes proper back-top-back testing possible, and you will be able to read about that here later in the summer. I might also make some follow-up to this article once I install some electronics in the car.

For the TRF420X presentation though, this is it. Hope you have liked it and felt that it was a worthwhile read. 🙂