Improved Rear Bearing Holders

New Bearing Carrier Fitted

We have noticed that the kit rear bearing holders leave a little to be desired on the RC12R6.

The kit moulded inserts allow for both ride height compensation in steps of 0.25mm and give the option of running a slightly longer or shorter rear wheelbase.

We have found that the very simple moulded form of the kit insert allows the following issues

1. The bearing can rock and skew itself in the holder and..

2. The holder can rock and move around in the bulkhead.



The net result is that the axle has a tendency to move around a little, creating random issues with pinion to spur gear mesh and possible early wear and destruction of the bearings.

Enter Chris (Crisis) Kerswell from the UK Associated team.... Chris designed a new insert that fully locates into the full depth of the alloy bulkhead. This is stepped and locates in both the inner and outer oval sections within the alloy.

In addition to this, the standard flanged bearing fully locates within the holder also.

Rear axle spacing remains unchanged.

Flanged bearing fully locates

Bearing holder occupies all of the bulkhead

The part is 3D printed by Shapeways (link and info below) and is available in black or white.

We have fully tested the white material which we used for the prototypes. My black ones have just arrived and look to be very similar, fit perfectly and are.... black!

I think the white part is slightly finer in the granularity of finish so if you are bothered about that then go white and Sharpie them!

The holders come a a kit of 4 pairs identified by a number of "dots":


1 Dot: 0mm offset
2 Dot: 0.25mm
3 Dot: 0.5mm
4 Dot: 0.75mm

You can of course swap the inserts L/R to achieve long or short wheelbase just as with the kit parts.

Thanks to Chris Kerswell for taking the time to design these and go through the process of perfecting the fit. Long live "Crisis Industries".

RC12R6 Chassis Balancing

RC12R6 Chassis Balancing

On the whole, I think people worry too much about this but if you are going to worry about it then do it right:

You cannot/should not balance the chassis as a whole without thinking.

My RC12R6 using latest electronics and a (very light) Muchmore 17.5 Fleta ZX V2 and Hobbywing XR10 Pro 1S is 25 grams underweight (730g is our minimum).

What to do with that weight I need to add?


Rear Pod Errors

Most rear pods are balanced or not balanced based on the motor you are running.

Modified motors are lighter (in general) than spec motors and the latest generations of spec 13.5's or 17.5 or whatever are lighter than the old stuff. If you care, then balance your motor in your pod.

Be aware that you cannot (and should not) correct unbalance in your rear pod buy moving stuff around in the front part of the chassis by ESC and radio gear placement. If you drop your car on the balance pins and try doing the thing as one then you will unkowingly fall into the trap.

When the car is on all 4 wheels on the ground, weight placement in the main chassis has NO effect on the rear pod. Any weight correction is NOT passed through the side springs.

The front main chassis is supported in three places by the front springs via the king pins and the main shock spring via the rear centre pivot. Its a triangle with the single point at the back.

Balance the rear pod on it's own first. 

Here you can see I need 10g of lead strip over opposite to the motor to balance the pod.

So I chop that up and pop it on the back rear corner of the pod under the axle. I glue it directly to the lower pod plate. As low as I can get it without getting in the way of motor movement.






I will need to put 15g somewhere else to bring the car to minimum weight once the balance is done.

Update.... Now, one of our "longest serving" 12th racers in the UK is Fred Hatfield. His critique is this:

I don't think it's a good idea to add weight to the rear pod to balance it because the pod is the unsprung part of the car , better to shim the motor over if you can. Not being critical just a comment .

Well Fred I think is right.... I used to shim the motor over also: I just feel uncomfortable with it in the modern era of the "bottom only" motor screws. And its only 10g... and this motor is already 10g lighter than anything I have seen... and the COG is lower than it would have been with the heavier motor.... and ... I don't like the longer shaft length before pinion that this would cause. All excuses because I do think Fred is right.




















Balance the Front

Next I get the isolated front part of the chassis in balance. Our RC12R6 chassis has centre balance pin holes for both the pod and main plate to help with this.

The motor wires are lying in the right place(ish!) and the lose stuff is symmetrical.

The ESC position is tweaked lightly to the left of centre to get the balance. Job done.

Put it all together and check it as a whole (it must be right).

Finally. I cut another 15g of lead and popped it half and half either side of the battery front stop to bring the car to weight.

Small tyres are on. Lightest shell I have (no clips!). I would rather be 5g over than lose a round in tech.

And another sad and final update on this subject!

Kit Associated Clamping Hub

My OCD did not like the stick on weight and I was thinking of other ways to get more weight opposite the diff side.

Then it occurred to me that I had an unused Zen Racing "spider" clamping hub. This is about 4.5g heavier and goes as outboard as you can get so its balance correction is maximised.

I tested the pod balance and with lighter ceramic balls in the diff side it all worked out "good enough". I ditched the stick on weight. OK... its 4.5g of more rotational axle weight but I think its a neater solution.

Would I bother with the Zen piece if I did not have one in stock? .... Nope!

This became one of those things you start that you wish you had not!

Zen Spider Hub

RC12R6 Front End Build Notes Part 2

Moving on to more build detail...

Decide your tyre diameter range

The new RC12R6 front end

The minimum front tyre diameter I will will run down to is in the order of 39.6 mm.  Starting the fronts at 40.8mm. This gives a tyre diameter range of 1.2mm .. which will be around 4-5 runs on 13.5 stock allowing for tyre wear. The ride height shim range will be half of the diameter range, around 0.6mm.

Steel shim kit and 0.5mm spacers will give the needed adjustment.

To facilitate this you will need to be playing with the 0.5mm blue shim washers in the kit and I have purchased the optional metal shims (part 4742) which are 0.2mm each (you get 4 of them in the pack).

The design of the low blue stand off mounting the lower carbon wishbone to the chassis will allow for very small front tyre diameter... down to and beyond the rim if you like!

The reality is that you will be always using the 1mm spacer so why not mount that on top so it is secured in place always.

1mm blue shim always on top of the standoff

The standoff is not deep and takes thread from both sides. The lower side against the chassis will see the most action as continuous adjustments are made for ride height.

Size the top screw correctly.

If you are not careful the screws will meet each other in the standoff before clamping down so watch out!

I ground 4 top screws to 8.25mm to allow enough thread free in the bottom when using a standard 5mm CSK to go up into the standoff from beneath the chassis. This length will allow the perminant location of the 1mm spacer as shown above. 

Consistent front ride height.

I have not changed the approach I have been using for years and this is well documented here. https://markpayneblog.blogspot.co.uk/2005/12/crc-carpet-knife-32r-total-tweak-guide.html

I suggest giving this a good read as I will still do all of this building a car for the first time.

I have already written all the words over 12 years ago (see the link!) so here it in pictures for the RC12R6.

Hold your wishbone / stand off assemblies against each each other on a flat (very flat) surface and look to compare the ball height.

Height error seen

Mine had an error of around 0.5mm (left is high). Not good. The standoffs+Shim arrangement was not true. It only takes a tiny angle error in the standoff - wishbone mount to make this a problem outboard.

I rotated the standoffs by 180 degrees (on the axis of the screw) on one side and tried it again. This was better. Fiddle with this till you get the best match.

Once mounted on the car. Block the chassis and check the axles are at the same static unloaded height.

Which Spring?

In the UK we run on various carpets but the "ETS" black rug is popular and setup notes below will assume the use of JFT S35 compound all round.

My preference backed up by testing the car at a couple of club meetings is to run the Associated .018 springs on the front end (Part 4144). The kit spring is the 0.020 which I think is a little too hard and immediate resulting in an aggressive immediate steering response followed by washing out a little.

Eliminate almost all front end Droop.

I would recommend taking nearly all of the droop out of the front end springs. I want the car to _just_ and only just sit into the front king pin springs. As recommended in the manual I run two 8425 shims (total 0.8mm) above the steering block.

I then shim above the top king pin ball, firstly to just take all the play out of the king pin so the spring is just touching. I then add a single 0.4mm shim in addition to slightly preload the spring such that static self-weight if the car only just parts the steering block from the lower ball when the car is sat on the pit table.

Finally I set appropriate ride height on a true set of wheels. I remove the rear springs and disconnect the rear dampers. 

I then block under the front axles with 20mm Hudy blocks and check the ride height is the same left and right. 

We really should be close to within 0.2mm. I may add or remove a 0.2mm shim to change the spring preload to make this right.

When you run the car for the first time the springs will compress and you will be chasing this for the first meeting. I use old springs!

Of course I don't use 5.1mm ride height! (see right). This is the effect of blocking the front axles at 20mm.

Finally (finally) I sit the chassis flat on the board and offer up a camber gauge to the steering block to make sure the left and right castor is the same. The RC12R6 block is moulded with a nice straight edge tab that helps with this.

Of course, during this process I have set the camber to 1 degree as a matter of course. many of these steps are iterative. You get the thing built rightly and then progress the accuracy until dead right.

Finally... finally finally.... I did cheat a bit and ended up using a Xenon top ball carrier with a Roche ball in it. I fell out of love with the verticle movement of the Associated one. To be honest I am being way too picky here and would not have bothered if I did not have the bits.

RC12R6 Front End Build Notes Part 1

Ok, ok. I had some Yokomo blue turnbukles!

I am a little picky about front end build. For me it is one of the most important as the consistency of the way the car drives is very dependant on it's accuracy.

Lower Wishbones

First, something to get right. The front carbon lower wishbones are NOT symmetrical. There is no Left/Right to worry about but there is a front and back. This is not obvious from the manual.

Here is the manual pic below. Notice the inner mounting hole lower in the picture is more "meaty". This will be towards the front of the car. The thinner part is towards the rear. If you run it the other way around then you will have a longer wheel base than the kit setup.

We are running the kit setting here. Meaty/fatter bit forward. We are also running the kit setting for a narrow front track using the 3 dot insert as shown.

Orientate these correctly!

Thinner part to REAR of car





Fatter part to FRONT of car

Tight Ball Syndrome?

Next I feel that the lower ball carrier is too tight in the wishbone (tolerances will vary). Insert the ball and feel that it is free in the carrier. It's a nice fit and all is well but.... when I then inset this into the wishbone, the carrier is compressed and the ball becomes tight.

You don't want "tight ball syndrome" in your undercarriage, it will restrict your shaft movement later :-) Seriously. The king pin angle changes under spring compression in a reactive castor front end and this ball has to move to allow it. If the ball is restricted, it binds the king pin.

So I open it up a little with a file till the carrier is snug but not overly tight. Free your balls!

There is no way I am using the O ring supplied in the kit to secure the call carrier in place, it will move around. Follow the "racer tip" in the manual and glue it in there. I just dab a little super glue onto the flange (this is the lower side). It will capillary around and into the material joins.

At this point (before gluing!) really make sure you have orientated your wishbones so you know your left from right and top from bottom otherwise you are going to glue something in wrongly that is not coming out again without damage.

RC12R6 First Impressions and Build Tips.

Centre Pivot Genius

The first thing you are going to notice the the ingenious centre pivot. The pivot ball push-clicks into a holder that is then slides into an alloy surround that is bolted to the main chassis.

Associated Genius Centre Pivot

The alloy outer allows the ball carrier freedom to move forward and backward slightly without creating a locking force on the pivot. Now the rear pod has correct, unbinding rotation. The shortening effect of the side links can no longer lock the pod and a crash cannot tweak it.

David Spashett designed the Delrin "Zen Slot" for LMP cars that was a fair attempt at this idea. However I found that under a big hit this would pull itself out and damage the ball holder so I gave in on it.

The original Zen Slot

The new Associated push in ball worried me at first for similar reasons but once inserted into the alloy holder the flex needed to pop the ball out is eliminated and it is not coming out.

12th racers spend half their "sad pit lives" chasing pod tweak around so this is going to be a revelation for all.

Zen Racing have made a retrofit alloy outer that has the standard "Associated" hole centres, this is purchased with the Associated AS4728 carrier to make this solution available to most link cars.

New Zen carrier suits all cars with Associated spacing
Part ZENA118

Associated RC12R6

Well its been a long time since my last 12th scale updates.

The Build is about to start

I have been racing on and off since the last 12th posts and must admit the influx of new, young talent in the UK has had me on the back foot! Work commitments in 2015 and 2016 very much compromised the time I could give to racing racing but the 2017/18 season is approaching in the UK and I am raring to go.


We have lovely 12th community here in "Blighty" and I am privilidged to be racing with Zen Racing and CML Distribution.

Associated RC12R6

I get a lot of people still commenting that this blog has helped them with 12th setup even after all this time so I have decided to give it a set of updates as I learn and develop with the Associated RC12R6!

Happy reading!

Mark