25/9/2012 – I first wrote this article last year… well, after another year of running the car, I’ve tried a few more things, had a few more successes, and a few more disappointments – what I’ve learned is in red. I’ve also added a few new pics of the car as it is now…
Here is how I build and set up my M-05 for carpet at Chippenham club nights and the CWIC. I’ll try and keep it brief!
General build tips
- Follow the instructions – they put them in the box for a reason.
- Use quality tools. Tamiya screws are not standard Phillips, they are JIS pattern. Get a JIS screwdriver (eg Tamiya’s own Craft Tools – I use TOP tools) and the screw heads will not strip.
- Don’t overtighten the fittings, don’t force parts together, make sure all the parts that are designed to move do so freely under their own weight, and that all the parts that aren’t designed to move stay put.
- Bearings. Don’t even take the plastic bushings out of the bag.
- Oil shocks and short springs. More on your choices later.
- A steering upgrade. More on these later too.
- A tighter differential. More later.
- The right tyres for your track.
The good news is that the M-05 Pro and S-Spec kits come with a lot of these goodies in the box. My car started out as a normal kit. Run Tamiya parts if at all possible – they work.
The first time you put your newly built M-05 kit on a carpet track you are likely to notice two things. The first is that the car will not run straight. The second is that it will roll over as soon as you show it a corner. This can be frustrating (trust me, I’ve been there). But it can be solved. Read on…
The diff has probably the biggest single effect on the cars handling. An open diff will make the car stable but it will lose a lot of speed in the corners. A locked diff will make the car very unstable and prone to understeer but will carry a lot of speed through fast corners. For most of us the best setting is somewhere in the middle. I’ll run through the popular options…
- Kit gear diff with the standard grease. This setup is very open, and will “diff-out” easily mid-corner and corner-exit (“diffing-out” is where the diff transmits too much power to the unloaded inside wheel during cornering, spinning it up instead of driving the car forward) . Not only do you lose speed and acceleration, you can get some odd handling as well. Not recommended.
- Kit gear diff with thick grease. I have used Mugen Super Grease, others have used Tamiya AW grease. This is gives a very tight action at first (perhaps too tight), before bedding in to a nice feel, and then pushing all the grease away from the gears leaving you with an open diff again. All over the space of half-a-dozen races. So not a consistent setting and not one I recommend for that reason.
- Kit gear diff with extra shims. Not something I have tried, this will increase the pressure between the gears making the action tighter.
- M-05 Ball Diff (#54194). A very nice quality diff, built like the modern Tamiya touring diffs. Has quite a free action if built normally (normal greases, tightened by hand and backed off 1/8th of a turn). I like it, it gives a good balance between cornering traction and straight line stability. To make it tighter, you could use thick grease on the thrust bearing and/or the main balls. Experience suggests that even a fully tightened M-05 diff is a little loose for an M-05 (although OK in an Xevo) – not recommended either!
- TA03 (#53267) or Manta Ray (#53070) Ball Diffs. Tamiya’s old style of diff. I’ve never thought much of them as an actual diff, but they do have a much tighter action than the M-05 diff. I did use one in my old M-03 (many years ago) and don’t recall having any bother with it. Some people build them with thick greases or fewer spring washers to make them even tighter. Having bought and raced one since originally writing the article, this would be my recommendation for a foolproof and effective diff upgrade – build it according to the instructions to start with!
- 3Racing Gear Diff (#M06-06). The new kid on the block, a sealed gear diff. Quality is very good, and although I was very impressed with it outdoors in my Xevo Triumph, I haven’t found the right setting for it indoors yet. I’ve been using #7K silicone oil to date but it makes the car inconsistent on the tight indoor track, so I will have to try a few lighter weights over the coming weeks. Joe Keaveney (author of the Mini Racing blog which I highly recommend) has been running #5K in his and seems to be going well (although I hope Joe won’t mind me saying that he is a more talented driver than I am!). I’ve gone back to the M-05 diff for the time being. After running it for most of the indoor season with some success, the diff started to cause troubles outdoors, resulting in a disastrous result at the SPC. The o-rings on the outdrives are far too tight, and need a huge amount of running in – I only realised this after seeing how much better designed the gear diffs on my ARC R10 were. The 3Racing diff changes so much as the o-rings bed in that the #7K and #5K oil I started with ended up far too loose and the car would spin mid-corner – I now have #100K in it to get a similar feel. I’ll say it again – run that diff in (perhaps by using the car motor to run it in by holding one wheel with a dry diff and lightly oiled o-rings). The gear diff has no slip, which is an advantage over the ball diff, but it does need more work to get race ready. Spec-R have also released a gear diff but I have not seen it so can’t comment on the design.
Shocks and springs
It is not the shock oil or spring rate that is the most important thing here – it is the shock and spring length.
- The kit friction shocks and long springs should be kept well away from the car. Tamiya’s short springs are the ones to get (#53333) otherwise you will struggle to get the car low enough. The CVA Super Mini Shocks (#50746) are OK, the TRF Dampers (#54000) are much nicer.
- Droop is very important. Zero-droop (or even pre-loaded) settings should be avoided, especially on the front where they will make the car grip-roll suddenly due to the fast initial weight transfer. Large droop settings can make the car feel lazy and can also cause the car to grip roll mid-corner due to excessive total weight transfer. My basic setting is to have 0.5mm of shock travel over ride-height all round, with a ride-height of arms-level. I build my shocks to 56.5mm overall length to achieve this. Use a combination of internal spacers and unscrewing the shock bottoms to get the setting you want. I’ve since gone to 57mm shock length to get a more reliable ride-height with worn tyres.
- I’m currently running 3-hole pistons inside the TRF dampers, with Blue springs and Much-More #450 oil up front, and Yellow springs and Much-More #400 oil in the back. Sometimes I’ll run the Blue/#450 combo on the rear to get more steering. I’ve dabbled with the anti-roll bars too, and the rear one seems to make the car more planted.
The M-05 steering has too much slop with the standard parts, and won’t find centre again after a corner. You don’t need to spend much on hop-ups to sort it.
- The bare essentials are the Aluminium Steering Posts (#54193) and a High-Torque Servo Saver (#51000). The steering posts are the correct fit on the bearings in the steering cranks, the High-Torque servo saver is far more precise.
- Tamiya do aluminium upgrades for the cranks and rack as well but the standard plastic parts work well enough for me.
- Front-wheel-drive cars must run toe-out for stability, because the drivetrain forces are always trying to toe the wheels in. The kit setting of 2mm is not far wrong, I’m running 1.5mm, and I also run some spacers to decrease bump-steer. As long as the wheels don’t toe-in at any point in the suspension travel, I’m happy. I’m down to 1mm gap on the toe-out now which is very stable with good steering.
- Always run the right tyres for your track. If you don’t know the right tyre, copy the fast guys.
- Sweep’s pre-mounted mini slicks are very popular round here. Always 25s on the rear, 25s or 33s on the front. Sometimes 40s!
- If grip roll is a problem, run a bead of glue around the outer sidewall of the front tyres. This will take the edge off the initial turn-in. Experiment with the amount of glue, I feel that just up to the curved shoulder of the tyre is enough. Glue too high and you will end up with major understeer.
- On carpet, I usually run 25s at the rear and glued 25s on the front. Glued 33s were my preference at the end of last season.
Wheelbase and weight distribution
The long wheelbase build puts more weight over the front axle – this means more traction and more front end cornering grip. The car can be a little sluggish to change direction on very tight circuits though. I much prefer LWB outdoors, indoors I’m torn between that and MWB. If you need to add weight, try to put it in the front bumper or under the servo, lower is always better.
Now for some up-to-date pics…