42345 Tamiya TRF420 Build Review and set-up

The Tamiya TRF420 is here! After their decision to reduce their factory driver program at the end of 2016, some people never thought we would see a new chassis from the Tamiya Racing Factory.  Yes got an updated TRF419XR at the start of 2018 and have had a range of new hop-ups steadily released since this period, but now we have a brand new chassis in the form of the TRF420

The TRF420 is not a small update, just about every single component is new for this new car. It is the result of several years of development, so it will be exciting to see if it can improve on the already impressive TRF419XR. 

The first thing you notice is the package that it arrives in. Instead of a small cardboard box it comes in a plastic carry box that will comfortably house the assembled chassis. Ideal for storage and taking it to the track. It is a small touch, but even at this stage you get the feel that there has been a lot of thought put into every component of the TRF420 experience.

For this build I will be using a selection of the Blue Tamiya Hi grade screws, Moodyfools titanium screws and also replacing the kit steel ball ends with the Tamiya fluorine versions to save a little more weight over the kit steel versions. 

The carbon lower deck is 2.25mm thick, 85mm wide and 3mm shorter than the previous chassis plate. Weighing in at low 69.5g it is 4g lighter than the TRF419XR deck. It has symmetrical cutouts and holes for even flex characteristics,

Other than being shorter, the profile of the deck at the front is the same as the TRF419XR, but at the rear the inner section is more dramatic and narrower to provide more flex at the rear.

The nicely chamfered bulkheads are all new, gone are the three lower mount screws to a more conventional 2. They retain the 4x7mm bearing mounts for the roll bars and have a new fitting for the bearing eccentrics. The inner section that holds the top-deck is also lower by 2mm. As you would expect these smaller bulkheads weigh in at 5.5g, roughly one gram (0.8g to be precise) lighter than the older bulkheads.

The bulkheads are now 20mm apart, 2mm narrower than the TRF419X/XR. (I used a couple of droop blocks to make a 20mm jig to ensure they were perfectly straight). The TRF420 also comes with the new adjustable suspension mounts (Covered in detail in the article here). These have a range of different bushings that can help you tune the track width, toe and roll centre. The front comes with four of the E blocks (Providing C, D, E, F G) widths. I used the N4 bushing to set both of the front blocks (F) with the roll centre 0.35mm lower.

At the rear the TRF420 has a new motor mount that now has a removable centre section which is attached via a 3x5m screw. 

This centre section provides 5 different flex settings. There are some interesting options that this could provide in the future. 

The rear section with the lower bulkheads attached. The new motor mount moves the motor 1mm closer to the centre of the chassis. The rear chassis has the A block on the inside (XA, X, A, B, C), and the E block at the rear. I used bushing N3 in the Front Rear (XA) and Bushing N2 in the Rear Rear (D). This will give 2.5 degrees of rear toe-in.

For lots of info on block settings, check out the Tamiya Suspension Ultimate Guide (Click here)

The differential has also been revised. The internals are the same as the TRF419 unit, although the gasket is now a different material to the old version. 

The main difference is the actual case. It is still 37t but has has been re-designed to move the belts 1mm closer to the centre of the chassis, it is also 1.5g lighter and the precision of the two halves is much better, with better tolerances. 

The diff comes with different internal shims, and it is a snug fit, and a little bit of a struggle to get the pin in the outdrives.

An empty diff is 18.25g. I found that it was fine with 1.45g of diff oil. The actual movement of the differential is very smooth and easily the best one yet from Tamiya. 

The Centre pulley assembly is also all new. The 20t pulleys are hard anodized and now spin on two bearings each. They are attached either side of the pulley and you slide a plastic belt aligner onto each. These ensure the belt is always aligned perfectly as the drive train spins. The TRF420 brings the belts closer to the centre spur, so this is critical to ensure that it all runs smoothly. 

The kit comes with the Tamiya 116t 0.4mod spur, I use Axon spurs and they fit well, and the overall assembly is very precise.

The front spool is also new, gone is the beautiful blue alloy mount and now we have a plastic part. The outer rim is separate on the spool, I simply clicked it on without adding any glue. I have not experienced any issues with this part coming loose. The drive cups are attached with 3x10mm screws from inside the cup.

The final spool is 10g, that is 2g lighter than the old design. If you use titanium screws you save nearly an additional gram, so that is 3g overall. The way that the cups attach is very smart and it will enable you to change them without undoing the bulkheads, it also does away with messy pins etc. 

The new bearing holders are made from a nice stiff plastic, they attach to the bulkheads in a much cleaner way than the old design. This precision will ensure the spool and diff spin really freely in the chassis.

The TRF420 comes with a 171t (513mm) front belt, the same as the TRF419X. The rear belt is 62t 186mm rear belt, one tooth more than the old chassis. 
The upper bulkheads are similar in design to the innovative TRF419X versions that allow you to just add spacers to shorted the upper arms to your desired length. Satisfyingly the upper arm mounts are now blue in colour. They look especially good with the Tamiya aluminium screws. The kit does not come with any spacers, you can just use shims or the Tamiya 42307 option parts. (Note the direction of the part and how it is mounted, the arrows need to be at different positions for the front and rear of the chassis).

The main drivetrain is now assembled. It feels very free with no binding.

Here you can see how well aligned the rear drive train is. 

The steering assembly again is a new design. The main difference is the steering bridge. It comes with a removable steering pivot bushing that allows you to change the length of the steering rods. The kit setting recommends the 8.0mm version, the 8.5mm version that is also included will provide more aggressive steering response. 

Once assembled the steering mechanism is really free with very little slop and movement, again the precision feels better than before. 

The steering mounted in the chassis with the new open face adjusters on the 42m turnbuckles. The steering posts are hex bolts, so easy to remove if you want to swap to the alloy lower deck in the future.

The suspension arms are new for the TRF420. They have a new design that has no cut outs and the plastic used seems to have more graphite in it. The result is that they are much stiffer, which will help with steering response.

The arms have bushings that allow you to move the lower damper mount position. The TRF420 kit comes with the standard (B) setting bushing. There are option bushings (Part no 54943) that provide you with the ability to set the position to A (Closer to the centre) or C (Further out).

The rear arms also sweep back 3mm, this allows the chassis to be shorter with less overhang. I covered the arms in a lot of detail in a previous post (here). They are great, but the only thing that I am not impressed with is how the roll bar mounts need some sanding to ensure that the ball connector is able to move smoothly.

The inner pins are now 3mm shorter at 43mm. They are still 3mm but as the arms now pivot around the pin as opposed to with the pin, you could use a reamer to ensure that they move as free as possible.

The outer pins are now 3mm, so will be stronger than the previous 2.6mm versions. I exploited this by mounting some titanium versions from Moodyfools. These save around 4g in weight.

The rear hubs are the same as the previous cars but have a larger 3mm hole for the new outer pins.

The front C-hubs are thankfully totally new. Anyone that ran the older car knows that the previous versions of these were the worst aspect of the car. The new versions are notably chunkier and also made from a stiffer material. They still offer 4 degrees of caster and also have a 3mm hole for the new outer pins. 

The uprights are a two piece design. The kit comes with plastic arm connectors along with the unique TRF420 carbon version. The carbon parts are stiffer and offer even greater steering response. Alternative versions of these arm connectors could offer different ackerman adjustments to change steering feel in the future.

The suspension kit is available as an upgrade for older TRF kits. For more detail check the article here (Click link)

The drive shafts are also updated. The front Double cardan shafts are now 44mm and come with a new axle that enables a 3mm thick inner bearing to be mounted. The 2mm bearings on the old axles would take a lot of load and would be the first to fail. Also they come with the lightweight optional Joint pipe that was released last year to help shave off some weight.

The rear driveshaft has the hard lightweight 44mm option shafts (These are actually a little heavier than the Blue aluminium shafts, but offer better durability). The axles have again been revised and have cutaways that shave off 1.5g of weight each :)

The rear upright assembly and driveshafts weigh in at an impressive 13.6g. The upper 2mm spacer can easily be changed to tune the roll centre.

The front upright assembly goes together well, one nice touch is that it now uses two identical 4.5 x 3.5mm flange tubes for the top and bottom of the kingpin with no 0.7mm spacer for the upright. Once assembled it all feels very good with no lateral movement on the kingpins, whilst it still rotates smoothly.

With the front and rear uprights mounted to the car everything fits very well. I did find that the rear uprights needed a very gentle file to move freely. The front was a perfect fit. 

The anti-roll (Stabilizer) bars now spin on bearings mounted in the bulkheads (Introduced on the TRF419XR). Both front and rear bars are 1.3mm. The TRF420 comes with the optional 54870 Stabilizer end Adjusters. These are easy to set-up.

As mentioned earlier, the main issue is that the mounting balls on the arms are too big so you have to file / sand them down to ensure they move smoothly. 

Once attached the rollbar system is really free and very easy to set up. It is starting to look like a car now. 

The dampers are the Super Short Big Bore (SSBB) type but with the new 54878 upgrade set included. The new parts include high precision plastic connectors to allow 5.8mm ball connectors for a smoother action, and importantly blue aluminium caps. The kit comes with the green rated springs (2.5 approx). 

As expected they fit together very well, the kit comes with blue o-rings which ensure the shocks are very smooth. The kit has done away with the aluminium lower retainers. I have to admit I usually run these plastic ones nowadays but if you want the bling (and extra weight) they are available to buy (Tamiya 42192 TRF Damper Large Diameter Retainer)

The shock towers are new to compensate for the narrower (20mm) bulkheads. They are still 3mm thick with 4 mounting holes. The towers are now attached with four 3x6mm button head screws instead of the flat / button head combo.

Very close to being finished now.

The servo mount is back to being a great looking one piece blue anodised aluminium part. It moves the servo 2mm more forward than the old part, and you attach it the servo from the rear. Tamiya provides the 54862 Aluminium step screws in the kit. The fit and finish of these is superb and they hold the servo much better than a standard screw. 

The servo mount is attached with three screws without a locating pin. There is no provision for an aerial mount, if you run a receiver that uses an aerial, you can mount it on the chassis.

Tamiya also provides a 52g centre weight and two 5g front weights in the kit. The centre weight also acts as a battery stop to ensure that the lipo will not rub against the belt. You can see how well aligned the drivetrain is. It is not touching anything whilst working in very tight tolerances.

The TRF also comes with aluminium battery retainers. These are much lighter than the steel versions found in the XR and TA07MS, weighing in at 12g. With these mounts you still need to use tape to attach the battery to the chassis. I don't really like that, and I would have liked Tamiya to provide us with the same option as the TA07MS to be able to use posts and a carbon battery retainer. I will make my own version of this at some point.

The top deck is made from 2mm carbon fibre and weighs 7.4g. The main difference is that it is wider around the rear pulleys. 

There is a good amount of clearance now,  so no chance of the pulleys rubbing (This could happen on all of the older TRF419 cars). 

The bumper parts are also new. The actual bumper itself is larger to compensate for the longer overhang of modern touring car bodies. The mounting parts are made from a different plastic to the old parts. The carbon bumper brace is also new as it has two different mount options. This is because you are able to move the body 2mm forward by adjusting the front and rear posts. The front involves swapping around the lower post mounts. 

The rear you simply have to swap the posts around.

The final part is the clever little fan mount that was introduced via the TRF419XR. It is secured with a grub screw from underneath the chassis. It allows you to mount either 30 or 40mm fans. I did find it a tight fit with a 40mm fan because the new top deck is wider in that area, but I still managed to fit one without it touching the upper deck and affecting the flex characteristics.

Here is the finished Tamiya TRF420. The final weight of this assembled chassis is 467g (529g with the included weights).  I can honestly say that despite building TRF cars since the 414, this feels like the most refined version yet.

Track test

I pitted with TRFUK guys Dan Booker and Tony Watts, all of us have the new chassis. This was going to be the first proper run of the TRF420 for all of us, but at least we could help each other out when trying different set-ups.

The EWS ICC track is one of the largest in the UK. The layout was not as open or sweeping as some of the previous years but it looked like it would be a good all around test for the driver and the chassis.

The field of 80 drivers featured many of the top international stock drivers who come down for this three day racing extravaganza.For me it is always good fun, although it is my only time I use the control tyres and additive so I always find it a bit of a steep learning curve. 

The TRFUK racers all race prepped.. although I forgot my wheels :)
Practice was first up and I was not only driving a new car but also new electrics so I just gently got to grips with everything. The first thing I noticed was the amount of steering that the TRF420 exhibited in the corners. The older car was good but it could sometimes be a little too stable on corner entry. The new car was much more eager. I found it easy to go onto power and follow the tight sweeper into the chicane.

Even after the first couple of practices all three of us were picking up on the new characteristics of the TRF420. It just felt much more responsive.

In the third practice I started to push the car harder as I was becoming more confident. As I started to ride the curbs the TRF420 just soaked up the bumps and felt very settled.

After the first three runs I had just started to build up my confidence with my base set-up. I felt good about seeded practice and whilst I was eager to tweak the setup I thought I would eliminate risk and not change anything for my seeded practice.

Unfortunately it all went very wrong for practice. I was unable to get a good sequence of laps as it seemed that either people were blocking me or just taking me out by returning on the track right in front (or sometimes into) me. To cap it all off I was shunted really hard by a car rejoining the track and the car felt a little odd at the end of the run. Removing the shell I noticed the rear turnbuckle was bent, and on closer inspection the hard hit had smashed the bushing in the suspension mount. Luckily there are loads of spares in the box so I just swapped it out.

For the first qualifier I was determined to have a clean run. I had made a few small changes to the car but this was mainly to tweak the droop to work with the taller tyres, and also reduce the front camber as the grip was already coming up quickly and cars were grip rolling already. The car again felt good, but I was unable to get a clean run.

I suffered a few more scrapes and bangs in the qualifiers. The car was great and the amount of T-Bones that it survived at least made me feel confident that it was durable. I proceeded to improve my best lap time buy over a second over the three runs. The car felt great, and as it was more robust it made me more aggressively hunt tighter lines. The great thing is that the TRF420 just responded to anything I demanded from it on the track.
Then it happened, on the straight I was ‘Clipped’ and the car launched at full force into the barrier. It tore a hole in the shell and also snapped an arm. As you can see it snapped around the area where the bushing is mounted. I had a spare arm so started the repairs. This did involve me having to sand down the roll bar mount on the new arm.. Just my luck the one part that is a faff and it was the one that I broke :) Importantly, despite the huge crash the C-Hubs were fine and intact.

Dans TRF420
Dan Booker was setting some great times with his car and one of the things he tried was to remove the spacer on the steering bridge to change the ackerman. This softens the car up a little more as it entered the corner. This was to compensate for the high grip and the fact that the carbon chassis on the TRF420 is already reactive, so just making it a little calmer was a good call.

In the end I qualified 51st overall, this put me in the F final. Not exactly where I wanted to end up but sometimes that’s racing.

Race one, I just wanted a clear race and being able to start at the front of the grid allowed me to race off to a comfortable lead. The car was superb, I just wanted to ensure that I would at least bag one win so I drove steadily and managed to still pull a larger gap. I still managed to get a love tap from a back marker 20 seconds from the end,  yet I had a comfortable lead so was able to resume back at the front and win the first final.

For the second final I caught myself out by chatting in the pits whilst looking for some parts for another racer’s TA05, so totally messed up my tyre prep.. Not very professional (ahem!). Despite this I again managed to get away well at the start, however after a few minutes I noticed a lack of power. The car felt good but I could tell that it was not pulling away well. Second place started to catch me up and I was caught in a great race with them chasing me down in their T4-20. I made the most of the precise handling and hugged every apex for the last few minutes, closing the door at every opportunity and also exploiting the extra apex speed to just pull enough of a gap to give me a small cushion on the long straight. We had a great close battle and I managed to take the second race with only 3 tenths of a second.

When I got back to the pits I inspected the TRF420 and couldn’t see any problems. I was genuinely confused as to what was the problem.. Only once I put the second battery on charge did I realise that I had actually fitted the used battery when I was rushing in the pits and not the fully charged one.. Embarrassing, but at least it explained the lack of power.

With the two victories I had already sealed the win for my final, however for the final just tried a few crazy set-up changes to see how the chassis would react. Again this involved roll centres and moving to only 2 degrees rear toe. 
For the third final I again took the lead and managed to retain a decent gap. The rear end was still very planted, but the tweak of the roll centres also made the car feel responsive, especially in the slow chicane. I was able to take it quicker than I had done before. There was a largish pile up behind me so I was able to coast home claiming another win. So despite not getting into a higher final, I at least capitalised on it and achieved a clean sweep of final results.

It was a good event for us to experiment with the TRF420. All three of us were really impressed with the increased performance of Tamiya's latest chassis. We all had our fair share of bad luck over the event but none of it was down to the new TRF420. It would have been good to run it with the aluminium chassis on this track as the grip was really high, but its release date was just after this event.

Another week, another race.

I took the Tamiya TRF420 for a race at one of my local clubs. This was going to be a much easier way for me to compare the TRF420 to my TRF419XR as it was a track I was very familiar with, and knew what lap times I would normally achieve. The TRF420 was running the same electrics, same tyres (Sorex 28) etc so I was excited to see what it could achieve. 

Even after a few laps I could tell the new car was quick, the extra steering and responsiveness of the chassis struck me straight away. I was able to drive hard into the fast sweeper, hit the brakes later towards the apex without needing to scrub as much speed as before as the TRF420 would still steer calmly around the corner. The car excelled on this medium grip technical circuit. I held the previous track record in the TC class, and I smashed it by over 11 seconds with the new car. This was on old tyres.. To be honest this made me really buzz with excitement. I still feel that there is more speed to find in this car.


The above is a base set-up for the car for high grip carpet, although I will be trying the aluminium deck in the near future.


TRF racers have been waiting patiently for a new car and that faith has been rewarded with a fantastic, fast race car.

Tamiya has always made a big change between chassis numbers and the move from the TRF419 to the TRF420 has seen one of the most dramatic changes for a long time. 90% of the components used have been re-designed or tweaked. Yes it does look similar from a casual glance, but look closely and you see a chassis that has taken the conventional TC design but optimised it to a totally new level. 

The drivetrain is precise and free. The TRF420's low and narrow central core really comes alive when on the track. Left and right transitions are very quick, especially in technical sections on the infield.

The revised motor position and lower bulkhead attachments have given the car with much better corner entry, apex speed and exit. All seemingly without the expense of stability and rear end grip.

This is combined with the weight savings on the drivetrain. ensuring great throttle response, more precise cornering control, acceleration and braking

The revised plastics for the C-hubs have provided the car with much better durability. This in turn promotes more driver confidence, I have increased my speed as I am not worried about an innocent clip causing a breakage and ruining my race. I have four spare sets of the new C-Hubs in my pitbag and I am confident it may be a long while before I need to buy more.

There are a few things that could be better. My biggest gripe are the plastic roll bar mount balls that need sanding down for a good fit. I would have also liked the car to have plastic battery retainers, battery posts and battery stops to hold down the lipo instead of having to use tape. These are minor quibbles, but I do hope they are addressed in the future. 

The price of the kit is actually competitive compared to many of its rivals. It also comes with better specification parts such as alloy steering arms, lightweight drivetrain parts etc whereas many of the other brands these are sold as options.

The TRF420 is the TRF that gives you the most tuning options. You do not need to buy different suspension mounts, you can adjust the upper arm length, lower suspension mounts and even change the steering pivots. All you need is a set of springs and you will be able to compete at any track out there.

The TRF419XR was great, probably the best TRF since the 416, and after several races at different clubs, I am confident that the TRF420 is better in every conceivable way. It is also great to see Tamiya providing the aluminium chassis so close after launch along with other key spares (Top deck, lower deck and pulleys etc). It really feels like Tamiya has listened and is providing its racers with the things they want.

As you can tell I am impressed, I feel that this kit has been worth the wait and importantly it has also helped quell any fears that Tamiya has abandoned the TRF project after scaling back its factory driver program. Going forward it looks like us TRF racers can be assured that Tamiya is still supporting us with some excellent cars.

Thanks to the TRFUK guys
Tonys Tamiya parts
Editable set-up sheet PetitRc (Here)
TRF420 Build manual (Here)
TRF420 1611143598044506978

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