The Racing Factory Blog

Here’s a short article on how we prepared a Tamiya TRF415MSX MR Edition for the new EFRA rules that states that cars must use no more than 5 cells and the minimum weight can be 1350 grams.

The 5 cell part is easy, just unsolder one cell or buy 5 cell packs. 5 cells have also already proven to work quite well and with the latest brushless motors there’s really more than enough power anyway.

The 1350g part creates a few more headaches though. One cell of the latest types weigh roughly 70 gram, with battery bar and solder perhaps close to 75g. So that means the relative minimum weight has gone down 75g. Now with the brushed speedos this would not have been that hard to acheive but with the heavier brushless components it’s another story. Weight balance also has to be taken into consideration as removing 75g from the battery side will throw the weight balance off on most cars.

The TRF415MSX, especially in the MR Edition, is perhaps one of the cars best prepared for this rule as it’s fairly light already from the factory. This due to the many lightweight features like titanium screws and aluminium layshaft, lightweight spool etc.  However, this also means it’s quite hard to find ways to further lighten the car.

The starting point is as I said a TRF415MSX MR with the following equipment:

- Futaba 9550 slim servo
- Futaba R603 2,4GHz receiver
- LRP TC Spec speedo
- GM brushless motor
- IB4200WC 5 cell pack
- Protoform Mazda 6 body
- LRP VTEC27R pre-glued tyres

With all ballast removed from the car with the equipment above the car weighed 1415g.

Now let’s take a look at some of the steps to make it lighter and where we ended up.

The first step was to replace some of the light titanium screws on the MRE with even lighter aluminium screws. The countersunk titanium screws under the chassis were still retained as they can receive quite some stress, especially the suspension mounts, and they’re already as low as anything can be. It’s much more important to remove weight that is higher up.

Using Much More aluminium screws that come in extremely nice Tamiya electric blue we could shave off around 5 grams.

http://www.racingfactory.fi/shop2/cat/product_details.php?p=514

Next up I removed the post between the rear bulkheads, as on asphalt you certainly won’t need the extra stiffness that might bring.

I also decided to lighten the front bumper as it’s quite rigid anyway and this should not make it weak in any way.

As these changes were done now* in time for the summer asphalt season the setup of the car was as well changed. Removing the 6mm wheel hex is a setup change due to using longer arms, but also serves to lighten the car. (*the rules in Finland allow 5 cells/ 1350g from 1.5.2007, the winter races were run according to 6 cells / 1500g)

Next, removing the front belt tensioner/stabilisator and original antenna mount.

After these changes we move to the suspension. Now with a reduction of 150g from the car the relation between sprung and unsprung weight changes dramatically, so any reductions you can make in the unsprung weight, i.e. suspension, is worth a lot.

The major changes here are to the drive shafts.  At the front I removed the original steel CVD’s completely and replaced them with Square aluminium/titanium CVD’s that have been designed to also reduce the chatter usually found when running front spools. Testing will show if this is the case, but the quality of these look very good.

In addition they save you a massive 4 grams per side, a total of 8 grams.

For the rear driveshafts I replaced the steel wheel axle I have run during winter for durability with the aluminium axle that come standard on the MRE. Again a very big gain of 3 grams per axle, total 6 gram.

I replaced the original spool with a JP Products spool made completely out of delrin, saving just over 3 grams. This will only be used for racing though, as it’s more economical to use an aluminium spool with replaceable outdrives for testing.

Time to start putting everything together then. This also including relocating the receiver and transponder to the right side of the chassis, behind the battery.

Further small weight saving changes made during assembly include replacing the 4 steel 3×15mm screws on LRP TC Spec with 2 titanium screws (did not have alu screws that long).

As I mentioned the receiver and transponder were moved to the right side behind the battery.  This was found to even out the balance with the used equipment fairly well.

For this the antenna needed to be moved away from the original location. The best option found was to use a 3Racing antenna mount, http://www.racingfactory.fi/shop2/cat/product_details.php?p=1180, mounted to the rear bulkhead with a 3×10mm grub/set screw.

After installing everything it’s the mometh of truth.

The final change and quite a major and easy thing to remove weight is to use a lightweight body. With East Coast Bodies Tune having just recently released a number of very good looking bodies, all EFRA legal from now and all available in lightweight versions, these are an obvious choice. 

Compared to a normal weight body you can save 10-15 grams depending on the body and paint. Obviously there are small differences in weight between the different bodies and also the weight of the paint will affect things, as you can see on the pictures. Testing will have to decide which body to use but for sure the Mazda is a secure choice.

As you can see, depending on the body, we did get quite a bit closer to the 1350g limit. Around 1380g leaves around 20g left that could be removed while staying on the safe side.

As you will have seen some of the steps were so small that they might have seemed stupid, but in the end it all adds up. The 1350g limit is so low that to get close you reallly need to find every little detail you can make lighter. 

A few grams could have been saved during the electronics installation but a clean installation was prefered. A future option is perhaps to use thinner wires, at least the motor wires, as this would also clean up the installation and with 5 cells this should be ok anyway.

Finally a few photos of the complete TRF415MSX MR Edition at 1380 gram.