With 2024 coming to an end, I thought it would be interesting to have a look at Tamiya's latest TRF421 against the TRF414X. These cars were released 25 years apart, so I thought it would be fun to do a brief overview looking how Tamiya's competitive racing chassis have evolved over this time. It's also an excuse some nice photos of these two tasty looking Tamiya chassis.
The TRF414X was released in July 1999. The small development team of of Takahiko Yasui (Design), Masayuki Miura (Test driver, project lead) and Takanori Aoki (Test driver, platform geometry). Thus started the development of the TRF404X.
The chassis design was focused on having the heaviest weight along the centre of the car. It is really evident here with the motor position being centre rear. The TRF421 has the motor to the left of the car (Albeit only 7mm offset from the centre). It also has the motor positioned much more forward in the car.
The batteries we used on the TRF414X were saddle pack nimhs with three cells either side of the belts. You can see here how wide the chassis has to be to accommodate this. The TRF414X chassis at it widest point is 110mm, The TRF421X is 84mm at it's widest point. The weight of these chassis is also quite different. The 414X has titanium screws as standard and weights in at 538g. The TRF421 with titanium screws weighs in at 473g with no additional ballast.
Here you can see one of the reasons why they layout changed in touring cars. The TRF414X has high layshaft / pulley drivetrain. In fact at its highest point (not including the pulley it is over 80mm). This isn't great for high grip technical corners.
The TRF414X even has a higher profile bumper than the TRF421 :) The 414X had a lot of shock tower holes. These provided you with not only different upper damper positions, but also provided the racer with different upper turnbuckle positions to change roll centre and camber gain. The TRF421 has done away with carbon shock towers all together and has aluminium 'horns' that allow you to simply add or remove shims to change the position. You can also see how short the dampers are on modern touring cars compared to the originals.
Symmetry a key part in modern touring car design as can be seen on the TRF421. Whilst it was a consideration on older cars it can be evidently seen with things such as the asymmetrical upper deck (Which was changed on the TRF414). Centre mounted floating servo mounts and the motor mount that is also attached along the centreline of the chassis.
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The drivetrains are quite different. The TRF414X has a 32t front oneway pulley, a 15t centre oneway and a 32t rear ball differential. This was the preferred set-up for quite some time, it did help steering for these older cars. The internal ratio was 2.133
The TRF421 has 37t front pulley, 20r direct centre pulley and a 37t oil filled gear differential in the rear. This is the defacto set-up for touring cars for the last decade. It provides you with much better braking into the corner. The gear differentials also robust and require less maintenance than ball differentials, especially with high torque brushless motors. You do however loose the ability to quickly tune a differential by tightening a nut, now you have to swap oil.. which is messy.
The TRF414X chassis is set up to be stiff. Flex was the enemy in older touring car designs. The goal was to make the chassis solid and rely on the suspension arms to deal with the bumps. Much like a real car. This philosophy has changed a lot over the years and now modern chassis has so much flex that they are almost a separate 'spring' in themselves. This approach basically provides modern cars with a potentially wider set-up window. With the chassis providing flex and some mechanical grip it lessens the precision needed to get the actual suspension geometry perfect. Whilst this wont find you the ultimate best time, it will help you put in the laps.
This approach does make sense, as you will never has the same level of feedback from a RC car as opposed to a real one because you are not actually sitting in it. This change of design shows how the world of RC has matured and understood some of it's own nuances to improve it's design process.
The TRF414X has the classic C-Hub suspension geometry which has decades of race wins. The TRF421 has followed the trend for A-Arms suspension. It can be argued that this set-up will give more flexibility when tuning the car for the track, certainly you can adjust caster more simply (Especially with the way that it is implemented on the TRF421). Like all things though, it can also create more set-up issues so it does require more maintenance in the pits between races.
The TRF421 has adaptive rear toe control. This is now common in most high level touring cars. One of the benefits is that the modern cars can reuse suspension components at the front and rear of the car. You can also see that the TRF414X doesn't provide any outer roll centre adjustments on the hub.
It's great to see how far forward these cars have evolved. To me though I still get the same amount of enjoyment out of any of these era's. It's great to just go to a club and race toy cars :) I will do a more indepth look at the TRF414X at some point, including a track test (Although I dont have many spares)..
So what innovations have you noticed over the years? or where do you think cars will go in another 25 years..
