42382 Tamiya TRF420X Build Review and Set up tips

When Tamiya announced the TRF420X there was a lot of expectation that it would follow the mid-motor chassis design that other manufacturers have adopted lately. Tamiya had other plans and decided to refine the layout they developed for the TA08 Pro with more advanced features that a pro level chassis would require. 

The goal has always been to innovate, to make a chassis that is both fast, and drivable. So has Tamiya succeeded with the TRF420X? .. let's take a look :)

The new TRF packaging is something that I am glad has been continued. The kit comes in a hard wearing plastic carry box, ideal for storing your chassis between races. 

The TRF420X prides itself on being a full option race package, there is nothing extra that you will need to purchase to unlock the potential of the chassis on a wide range of circuits, other than suitable springs and damper oil.  

For this kit I have treated myself to the Moody fools Titanium screw set, titanium droop screws and outer pins. This shaves off a good g of weight of the car. 

Also for this build I will use a few Blue Tamiya Hi Grade screws for aesthetics. I will also be replacing  the included steel ball ends with the hop-up Tamiya fluorine versions to shave off more weight and add a little bling. None of these parts are needed as the stock TRF420X is underweight when assembled anyway).

The TRF420X comes with both an Aluminium and Carbon chassis included in the box. This is a godsend to many TRF racers as it allows us to run at a range of tracks with no more than the initial outlay.  

The profiles of both chassis are the same, with a width of 85mm. The aluminium chassis still has quite a lot of flex, but with the added benefit of more low down weight. The most notable difference is that both chassis have no cut-outs foe the motor position. This is to provide a more consistent flex characteristic to the chassis. 
  • TRF420X 2.25mm Carbon Chassis: 70.6g / TRF420 Carbon chassis 69.5g (+1.1g)
  • TRF420X 2.0mm Aluminium chassis: 79.8g / TRF420 Aluminium chassis 84.1g (-14.3g).
As you can see, there is not a huge difference in weight between the carbon and aluminium chassis, only 9.2g! 

Compared to the TRF420 decks. The carbon chassis is 1.1g heavier probably because of the lack of motor cut-outs. The aluminium chassis is a whooping 14.3g lighter than the TRF420 aluminium chassis. This is down to it having many more cut-outs. 

For this build I will use the aluminium chassis, this is to help me compare the car with my TRF420 (Which also has the aluminium chassis installed), and I hope to have a test and tune day at Force Raceway, the only permanent indoor onroad track, with high traction. 

The lower bulkheads are a new design. The chamfered edges ooze quality. They have the same lower attachment points as the TRF420. The 4x7mm bearing retainers have been changed, although I cannot see what advantage these provide other than they may well be a little stronger.  

The bulkheads are not interchangeable like the TRF420, the rear ones have the facility to mount the 54887 Toe Control Rear Suspension Set. This makes the rear lower bulkheads heavier at 5.9g as opposed to 5.6g for the front. 

The motor mount is the centrepiece of the the new TRF420X. It is composed of two pieces that attach together perfectly. Its a very intricate piece, so it makes sense that it was not one entire CNC manufactured part. 

This distinctive shape is down to the spur gear being mounted in front of the motor. (Like the TA08). The assembled motor mount weighs in at  11.7g (Titanium screws).  The motor position is the same as the TRF420. 

The TRF420X's flex philosophy ensures that the motor mount is attached to the lower deck along its centre. You also have a selection of mounting points to adjust the cornering characteristics.  

Other than the central screw locations, the rest of the motor mount is raised above the chassis. 

Now we come to something that I have not seen included in any RC kit. The TRF420X features a floating RC deck for the electrics. This consists of a 1mm carbon plate that is mounted to the 20g centre ballast weight.

I found that there was a little movement when I attached the 3x5mm screws that mount underneath to hold the deck to the ballast. This was solved by adding a 0.3mm shims. 

The carbon plate weighs 3.7g. When you include the two screws you use to attach it to the centre weight, it comes to around 4.2g with the titanium screws. 

Here you can see how the plate floats above the lower deck, the gap is approx 0.7mm. The floating electrics plate is not entirely new, the excellent RC Maker has previously made a selection of these. 

However this is the first 1/10 touring car to have been designed with this in mind. It's obviously important to maintain the entire controlled flex philosophy behind the TRF420X, and it also shows how Tamiya's TRF kits are always full option, unlike some other manufacturers. 

The TRF420X also features an 2.0mm carbon adjustable stiffener plate at the rear of the chassis. Weighing in at only 1.1g, it provides a selection of different settings. I have always been a fan of rear stiffener plates, making a selection for previous cars. You can use the included blue stiffener nuts, or you could swap them out to bearings to change the way in which the car flexes. 

The new lower flex components all installed. Perfect left and right balance, superb design. 

Lower bulkheads are now installed, so now onto the drivetrain. 

The TRF420X rear differential has been slightly upgraded from the previous car. Now you get bearings to fit instead of the brass bushings. Tamiya has also included the hop-up 42374 VG o-rings for gear differentials. I have used these in my other cars and they are smooth and leak free. 

The kit comes with 3K diff oil, usable for smaller, or low grip tracks. I used 5k oil. The diff takes 1.45g of oil. The overall weight of the differential is 18.25g. 

The centre pulley assembly is the same as the TRF420, with the 20t hard anodized pulleys. The only change are the new blue sealed bearings. These new bearings are very smooth, smoother than the already excellent ones that Tamiya used in the TRF kits. I did not use the kit included 116t spur gear, I always use the excellent Axon 64dp spur gears in my race cars. 

The front lightweight spool from the TRF420. It is 9g with titanium screws (10 with kit screws). 

The TRF420X uses the same belts from the TA08, which is no surprise as it uses the same 57/43 pulley layout. This gives you a longer front belt (132t), and a shorter rear belt (101t). Tamiya derived this balance from extensive testing to find that it gave the best possible pitch response in the corners. This is something that has been developed since they first experimented with this concept with the TA05 in 2005 with the mid pulley design that is seen on many of the contemporary touring cars available on the market today. 

The upper bulkheads from the TRF420 are used, the upper arm mounts are new and 1mm narrower. As a rule the longer the upper turnbuckles, the more stable the car as it has less camber gain when it goes around the corners. 

When assembled with the included 0.5mm spacers, fluorine ball connectors and aluminium screws each upper bulkhead half weighs 3.9g. With stock parts they weigh 4.84g

The drive train is installed. There is a 2mm aluminium support brace that holds the spur gear in position, it also doubles ups as a battery spacer. 

The drive train is very smooth once assembled.

The motor mount features a rear belt guide. You swap between either of the two included (630/720) bearings depending on the height of the differential. I run my differentials low, so I installed the 630 bearing. The new bearings work well, the drivetrain is really smooth with very little resistance. 

The excellent, slop free aluminium steering set-up from the TRF420 is used again. You have two steering pivots that change the length of the steering rods. The 8.0mm version gives you a more smooth steering feel whereas the 8.5mm option is more aggressive. 

The installed steering is silky smooth, with zero slop when using the kit included shims. 

Tamiya has decided to not provide TRF versions of their TA08 arms. Instead they have decided that the TRF420 arms provided the best results for the TRF420X. These arms have performed well, and I really like the adjustability of the bushings provide. (I covered the arms in detail before Here). The roll bar balls seem much better now. I only had one that needed a light go with a file to ensure free movement. Although I still do not understand why this cannot be solved. 

42362 44mm driveshafts for low friction double cardan Joint shafts are now included in the kit. These have 10.8mm pins that lengthen the life of the driveshaft blades, they also help stop the front spool cups for splaying open on hard collisions. 

The assembled front cardans spin freely in the two-part uprights. You can choose to run the carbon arms for sharper steering response, or the plastic parts for a more refined ride. Tamiya clamp type wheel hubs (4mm) are an essential for pretty much any race car (5mm for a TT02 though), with the kit included 0.1mm shim they hold the axle tightly with very little lateral movement.   The front corners weigh in at a very light 20.3g

The rear universals are different as the std 44mm driveshafts have been swapped with 43mm versions. I have been running these on my TRF420, I found that they made the rear of the car respond better on tighter turns. It's great to see these now included.

The other change here is that the axle is attached with a grub screw instead of the axle rings. I prefer axle rings as I find them 100% reliable, I always worry that a grub screw will come loose. The included lightweight axle will still take the rings, so I will swap over to them in the near future.

The assembled rear shafts. Each corner weighing in at 12.1g. 

I used the lightweight Moodyfools outer pins for all four corners, shaving off around 4g in total.

The arms and hubs are attached. The front mounts are to the F-F like the TRF420. The suggested roll centre is now 4.75mm, not 4.4mm like the TRF420. The front stabilizer bar is 1.3mm, same as the TRF420.

The suggested kit rear suspension settings are X-D this gives 2.0 deg of toe in. Normally I would run 1X-D for 2.5deg. Luckily we now have adjustable blocks, so I used different pills to set the rear how I like it. Although I will try 2 deg at some point. 

The rear stabiliser is 1.3mm. The revised bulkhead mounts are perfectly machined as you would expect and the bars move freely with no slop. 

The front and rear towers are new for the TRF420X. They are made from 3mm thick carbon and feature cut-outs between the bulkhead mounts which provide more overall grip because of the change in flex characteristics. 

The 3 mount holes are set into the middle of the previous 4 holes, so they are new positions. With that in mind, I have decided to run the kit included suspension arm bushings (B) in the lower arms, as opposed to the 54943 Suspension arm bushings (A,C) that I run on the TRF420.   

There is a difference with the recommended set-up here over the TRF420. Previously there were no spacers suggested,  now the manual suggests 1.5mm spacers behind the upper shock mounting balls, and 2mm on the arms. 

The TRF engineers also decided that you need 1mm spacer on the rear upper shock mounting balls and  0.5mm on the arms.

Tamiya's Super Short Big Bore shocks (SSBB) have been slightly tweaked for this kit. The new 1mm shorter suspension shaft from the TA08 Pro is included here, along with the inclusion of the excellent 42359 VG 0-Rings for Oil dampers (30 deg). Tamiya has again included the Green springs (Super soft) from the 42306 Touring car large diameter set. 

The kit oil is 400cst, so quite usable on a range of tracks. I filled the shocks with 450 as it is my go to for carpet.

The floating servo mount is new to the TRF420X. It looks very similar but moves the servo 0.5m more forward than before. It is also lighter, weighing only 7.8g. The quality of the machining is amazing as you would expect, Tamiya also includes 54862 Aluminium Servo Step screws, providing extra support for the servo and importantly.. more blue bling. 

We are getting near to the end of the build. Now we get onto the distinctive top deck  It is made from 2mm Carbon Fibre and has multiple flex adjustments and weighs only 6.8g.

You can change the amount and flex characteristics of the deck by adding the included nuts and screws, and the front belt tensioner. There is a larger rear hole that provides even more flex control. 

Here you can see the maximum amount of screws attached to the top deck.. In reality you will never fit this many, instead you will choose one or two at different points on the top deck to help optimise the flex to best suit your current track conditions. 

The top deck is attached to the front of the motor mount with just one screw. Again you can add more flex at this point by swapping the screw for a grub screw, or the Tamiya 42294 TRF3x5mm Step hollow Screw (Pictured above). 

At the rear there is also only one mount point. This is not a screw hole, but instead a large cut-out. This provides two main tuning options. 

The first option is to fit the 6mm flanged bearing. This allows the top deck to flex sideways whilst still keeping the longitudinal flex perfectly rigid. This option will give you lots of rear grip. 

You can swap the bearing out for the included upper deck holder. This is a solid blue aluminium bushing that eliminates the side flex to make a much more reactive rear end. 

The new battery holders are the first to not require the use of tape.. at last! They are aluminium so do not add a lot of extra weight. The front is 6.1g and the two piece rear part us 6.9g (13g). The carbon battery holders are nicely bevelled and look great. 
It must be noted that the included battery posts are really tall posts to accommodate Tamiya Life batteries. These are much too high for those of us not racing in Japan, and using standard hard cased lipos. Tamiya has since supplied the kit with a second, shorter set that seem a perfect fit for my LCG lipos. If your kit does not come with them, contact your local Tamiya stockist for the part.

The final new feature is the floating fan mount that fits into the motor mount. A nice little detail. I am going to be interested to see how efficient a fan will be when mounted here, as the esc and motor wires will obscure it a little. 

The chassis is now complete

It's really hard to to beat the look of the Tamiya blue anodising ๐Ÿ˜Ž

The front bumper and body mount system is the same as the TRF420. This allows you to move the body 2mm forward if you need more steering. 

The floating electrics plate also benefits from you being able to securely stick down the electrics without worrying about the gaps in the chassis

The chassis looks stunning once built. There is nothing quite like Tamiya blue so I thought I would fit the TRF setting wheels to complete the look. 

The aluminium chassis has more flex than the TRF420 aluminium chassis. 

The TRF420's drivetrain is so free it kept rolling around when trying to take photos

It looks fast! Let's hope it's looks translate into quick lap times..

The final built aluminium chassis weighs in at 510.7g  This includes:
  • 20g Centre weight
  • 2x 5g front weights

Some of the option parts I used did lighten the chassis. Above shows the weight difference, it must be noted that the chassis is underweight with the stock parts, I just prefer to add my own weight later. 

With that in mind here are the adjusted weights for geek value :)

I've built many of the Tamiya TRF kits over the decades. They have always been high quality, but with the TRF420X Tamiya have taken the whole experience up another level. The only gripe was needing to file one of the roll bar balls on the front arm. 

Nothing to say, other than ๐Ÿ˜

Installing electrics

Always a job that I find a bit stressful. Made even worse because I have to post pictures here once I've done the job. 

The motor is still in the same place as the TRF420, this helps quite a lot to ensuring the installation can be quite neat. 

I installed a Hobbywing XR10 Pro Stock Spec Esc. Its got a lot of punch, the brakes are great and it's also very tiny and neat. 

I swapped out the capacitors to the nonpolar capacitor (Stock version). It looks neat, and it have a nice little extra bit of protection.

The Hobbywing G4 is new, it will be interesting to see how this performs. 

One of the advantages of running lower profile batteries is that I was able to run the wires from the esc under the top deck. this ensures the wires are kept low, and also looks very neat.

After a lot of swearing and nearly cutting the ESC wire too short.. the electrics are neatly installed. 

Now it's time to go racing :)

At the track

I was really excited to give the Tamiya TRF420X it's first race. Luckily a local club had a tune and test day followed by an evening of racing.. A perfect set-up.

Well it would have been if I hadn't been working on the electrics through the night.. I was still soldering at home when the club opened. I arrived late (Standard).. I missed all of the practice and tuning session as the club had decided to start racing earlier to get in more rounds.. 

Q1 started and I was still setting the car up on the bench.. so not much to report there..

Q2 the first time the TRF420X had turned a wheel as I drove it up to the starting line at least it seemed to be going in a straight line. I started off last and slowly got to grips with the new car. The first thing I noticed is that it was really, really stable. Even with the used tyres the car had lots of grip from the first corner. I was initially was very careful driving the car as I just wanted to check that it felt ok to push.. as I continued through the 5 minutes I pushed harder and harder and the TRF420X just took everything in it's stride. 

Q3 I decided to adjust the rear droop a little as the car was so stable for my taste and the circuit had quite a technical infield. The car felt incredible, I couldn't believe how good it felt with so little tuning. I pushed harder and took TQ in this round.

Q4 I moved to a stiffer rear spring, primarily because the car was still very locked in the rear. I was really starting to push the car now and try to see how far it would go before it would let me down. The car would eat the corners, I could be much more aggressive into the corner than with my TRF420, but it was out of the corner that really took me by surprise. the car doesn't seem to pitch as much when applying power. This combined with the rearward motor ensures the grip is superb, but I also have a good amount of steering. I only wish I'd have got to do more practice, as I was being more aggressive into and out of the corners than I usually drive. Unfortunately I had a couple of issues with back-markers so I didn't TQ the round. This put me in second place overall in the 17.5 blinky class. 

Final 1. I always prefer races to qualifying, and whilst it's best to be on pole, it is always fun to battle to the top. I had made a gearing change to the motor (The Hobbywing G4 seems to run very hot). On the tone we raced away and it was a clean start. I slowly got into a groove chasing my rival around the track. I was down on the straight thanks to my gearing change. On the infield though the car was able to easily claw back the difference.  I maintained this for a few laps, there were a hairpin by the drivers podium that I could noticeably see that I had a grip advantage. I knew that this would be a good place to pass. On the next lap the leader went wide so I took my chance. I went in hot, with less brakes than normal.. I now had to put all of my faith in the TRF420X to hold on around the corner. I got a nose ahead and instantly opened the throttle. I launched ahead and claimed the lead. The car felt like it was on rails as I still kept a lot more speed than normal into the next group of corners and then entered the final sweeper into the straight with enough of an advantage to compensate for the top speed difference. I manged this to take a good victory. 

A quick lap at a small club (Not the race venue)

Final 2. I went back up a tooth on the pinion to try to level the speed difference, and was ready the second final. The race followed a similar pattern to the first one. There was still a good speed difference on the straight (I should have gone up more teeth). I was still able to easily follow on the twisty parts. This time my rival was really keeping their car close to the apex, not giving me much opportunity to sneak in. I started to get creative and look at more bold lines. This was only possible as the TRF420X was so responsive and grippy. I tried a couple of audacious moves, grazing the apex's to get as much speed as possible before using the speed to try to pass on the outside. Every time I had to pull out, sometimes costing a bit too much time, so I would have to wait a lap to catch back up. I was loving the thrill of the chase. It was a battle that was going down to the wire, then the lead driver made a costly mistake entering the straight and I was able to pass with no drama. I then managed a good gap and got into a rhythm and the Tamiya TRF420X crossed the line to take the flag and ensure I won my category. 

I was really happy with the result. (And the new set of tyres I won for first prize!). I was at a disadvantage from the start, with no practice and even missing the first qualifier. The car had been fantastic from its first run and it only got better. I was buzzing, the car felt great, and I loved every single lap I drove with it. 

Importantly, I was staggered at just how easy to drive the car was. This was proved in how consistent the car would be, I always feel good if my average is around a tenth from my best, but look at how close my average was in the last final. I also put in my fastest time in that round, so I was not driving conservatively.. Really impressive. 

Here is the final set-up that I used on the car.

I am very excited about the new TRF420X, but here are some views from other drivers who have recently raced the new TRF420

Andy Travis (UK),
In April, I decided to leave my current chassis sponsor & became a free agent to choose any chassis I like. The TRF420X looked very innovative & took to plunge to use this chassis

Compared to my previous mid motor chassis, the 420X has a lot more rear traction, allowing me to apply the power earlier & has a lot more stability. 

The only thing I have changed has been springs, every other tuning option is already included in the box. I have gone nearly 3 laps faster at my club with minimal setup changes. I am really excited to see how much further I can push this new chassis! 

Maurizio Basile (Sicily,Italy) 
I had the opportunity to test my TRF420X model car in two different circuits, and on both occasions it performed well, one of the things I noticed was the temperature of the tires: the front ones heat up 1/3° more than the rear ones, this leads to greater insertion into the curve and greater consumption; it feels a lot when you loosen the upper deck, the car grabs the asphalt, so it is very useful when the track is dirty;  it should be noted that I have not made many changes yet and comparing it to the TRF419XR model, but it much more balanced and already 2/3 tenths faster per lap.

The model is very nice and I embrace the idea of ​​the spur gear moved forward leaving the motor in the rear. My model is equipped with Esc Team Power electronics and PRT 13.5 engine, Bitty Design "Hyper" body and Marka batteries.

I will participate in the next 21-22-23-24 July test of the Italian Championship in the city of Gubbio. I hope for a decent result, and I will try to keep you updated on the next race or tests I do.

James Davis (UK)
Fantastic chassis! 

My first full run beat my old PB by a lap at my regular track with the kit settings and my spare ESC! The car has more grip and speed out of the box than any of my previous TRF cars.

As you can see the car is working well in a wide range of different tracks at the hands of many drivers. 


There is never really a time that I will not be excited about a new TRF release from Tamiya. I was initially surprised to not see a copycat mid design, but also quite happy to see that the Tamiya Racing Factory had decided to go with a trend, but with the design that they found faster at the track. 

The resulting TRF420X is a very competitive car that can compete with any of the other top chassis out on the market today. There are a good amount of new parts for this car, even those that have been carried across have been tweaked in little ways to improve the reliability and handling of the chassis. 

The quality is superb as you would expect with any TRF kit, although I think they have upped their level even more with this release. 

The kit isn't cheap. In the UK it's £675 price tag puts it is up there with the most expensive competition touring cars on the market. The difference here is that Tamiya supplies a 'Full option' kit. You do not need to purchase any parts to make the car more reliable or perform better. 

Another thing to factor in with the cost is that you get both the Carbon and Aluminium chassis in the box. This ensures you are able to compete at any track you decide to attend without any additional outlay. 

The most frustrating element is that the battery mounts make fitting a standard height lipo awkward. In reality you need to loosen the rear battery mount, fit the lipo and then tighten the screw. It's not a big deal, but it is frustrating that Tamiya's designers didn't just reduce the height of the lipo holders 1 or 2 mm to eliminate this issue. 

I've now raced the TRF420X at several clubs, and the car has been victorious on a range of carpet tracks. It really is the most easy to drive TRF I have ever owned, but more importantly it is also really consistent and fast.

I personally like the fact that this car has a strong design philosophy about having even flex, and providing the racer with loads of options to adjust it. This is the first competition kit that has really delivered in that respect, Tamiya has not compromised with this aspect, even raising the motor to ensure there are no cut-outs in the chassis, and including unique parts in the box such as the floating electrics deck. 

The most exciting thing to me though, is the wealth of tuning options I have available with the TRF420X chassis, I know there is even more speed to unlock. I'm looking forward to booking a test day soon to really understand how the different flex options influence the handling and will report back soon. 

So in summary, its blue, its quirky, its fast yet consistent, and importantly it puts a smile on my face when racing.. what more could you want from a TRF๐Ÿ˜Ž

Useful links 

Tamiya suspension set-up guide (Click Here)
Editable TRF420X setting sheet (Click Here)
TRF 420 Set-ups (Click Here)
Moodyfools (Click Here)
TRF Onroad Facebook group (Click Here)
Dai Sakaguchi Video Review (Click Here)
Kentech Blog TRF info (Click Here)

TRF420 5252741710674972047

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