Schumacher Mi4CX: Full Build Review

Schumacher’s Mi4cx represents the latest iteration of their very successful Mi4 touring car platform, and just a few weeks after its arrival ‘down under’, I’ve had the chance to build up a CX to run in the forthcoming Tasmanian Championships.  Read on for all the details on Schumacher’s latest flat-track weapon.

The Mi4cx (I’ll call in the “CX” from here on in) is the third variation of the Mi4 platform.  The original Mi4 came out a couple of years back, and was followed closely by the LP version of the car (oriented around the now dominant LiPo battery configuration.  The CX builds upon the basics of those first versions, with some significant revisions in the drive train and transmission/suspension bulkheads.

The CX has emerged after another succesful race season in the UK, with Schumacher’s #1 driver Chris Grainger bringing his considerable experience to bear to sharpen up the package.

The principle changes for this version of the car are in the drive train.

All new high tensile steel driveshafts bring revised design, with the cup component of the universal joint now on the axle, thicker (and stronger) pins and much cleaner design.  The new shaft/joint design provides a much smoother joint in action, with driveshaft shudder on steering lock much reduced, and the car smoother and carrying more corner speed as a result.

The front spool is redesigned entirely, a one piece spool attaching to the carried over front pulley, and with completely revised outdrives. Gone are the driveshaft sliders of the old car, replaced with a full-length insert into the spool outdrive and a 7075 alloy sleeve to keep it all together. It’s a good looking bit of kit, and initial feedback from customers running the CX (including in the modified class) is that wear is almost nonexistent.

The rear diff internals are unchanged, but the diff picks up the same new outdrive/insert/ring arrangement as the front spool.

Two other significant changes can be seen on the chassis, a response to the decreased weight limits in operation in some parts of the world.

Newly revised 7075 alloy bulkheads front and rear are now beautifully machined, with plenty of material removed to reduce overall weight while still providing a strong basis from which the suspension can operate. The new bulkheads are anodized in black for that all important stealth look.

Complementing the new bulkheads are much smaller, simpler and lighter diff retaining posts.  They’re also easier to fit, and do nothing but enhance the Mi4’s already easy to work on nature.


Schumacher put together a kit that is super easy to build.  The CX is packaged in such a way that every individual construction step has a corresponding bag. The bag contains every part, every screw and nut, and even in some cases the tool required for that step. You’ll finish the build with a small mountain of plastic bags (environment….?), but the result is that you’ll never be left wondering where the right part, right screw, right anything is. There are plenty of other manufacturers who could take a leaf out of this book.

Schumacher provide basic allen drivers, and their own fibreglass turnbuckle tool. You need to bring nut drivers, and the usual assortment of pliers, hobby knife etc to the mix.

We’d of course recommend a set of decent quality metric allen drivers for the assembly task. There’s nothing like good quality tools to make the build process easier.  You’ll also need to bring some fine sandpaper (we used 1200 grade wet/dry paper), and we’d suggest some of Tamiya’s excellent anti-wear grease.  We can provide EDS tools if you need them.

With the CX being a race-oriented kit you’ll also need to provide motor, esc, battery, servo, body and wheel/tyre package.

We built our kit up using our normal race package. Speedpassion V3 4.0 turn motor, LRP TC Spec Sphere esc (old skool!), Futaba 9551 steering servo, IP LiPo batteries, Protoform Mazda Speed 6 bodyshell, and Schumacher revlite/Sorex 36 premounted tyres, controlled by our Spektrum radio.

Construction begins with the main 2.0mm carbon fibre chassis plate, and those stunning new black alloy bulkheads.  I took the time to prepare the chassis (and the other main c/f components) by sanding the sharp edges off the chassis plate (take particular care to clean up the battery tape slots if you’re planning on taping your packs into the car….sharp edges = cut tape = ejected battery!).  Some also like to run a thin bead of super glue around the edges of the chassis to strengthen and help prevent delamination.  Personally….I’ve been running Schumacher c/f chassis for many years now and have never delaminated a chassis….so I don’t bother (but it’s probably not a bad idea, and now that I’ve confessed this….I’ll probably strike trouble!).

The first major task of the build is the assembly of the transmission.  Schumacher’s floating layshaft installs easily with the standard 85 tooth spur gear. If you’re planning on running a spec class (say 21.5 or 17.5 turn brushless motor, pick up a smaller spur gear (something like Schumacher’s 70 tooth spur) to help you get the gear ratios you’ll need in that class.

You’ll also at this point choose which of two options you want to take when assembling the transmission.  The whole transmission can be flipped to enable you to move the heavier electronics (motor, esc, receiver, servo) more inboard, getting closer to an even weight distribution.  Option 1 gives you this inboard weight distribution, while Option 2 is the more “standard” setup.  I have relatively light weight electronics, so opted for the second build option.

Attention then moves to the all important rear diff.  The differential has a huge impact on the handling of your car. If it’s crunchy or gritty, or has tight spots, the car will suffer for it. Before you build the diff, take five minutes to watch Schumacher’s factory driver assemble a perfect diff….and follow the tips Chris Grainger gives.  It’s worth taking the time to prepare the diff properly.  I also opted to replace the standard ceramic balls with carbide balls. I think in modified they help the diff last a little longer.

The video covers a standard Mi4 diff. The one suggestion I have to add for the CX diffs, is that it’s worth moistening the o-rings before attempting the slide the oudrive “inserts” over the diff outdrives.  The inserts slip over an o-ring set into the outdrive, and will click into place faintly. A little moisture helps make that process easier.

As you start to assemble the car, from time to time you’ll have setup choices to make (suspension mounting locations for instance).  Schumacher provide a range of sample setup sheets at the rear of the manual, and I built my car according to the “Cotswolds Test” setup provided by Grainger.

The new spool builds up simply, to complete the central transmission of the car.  It’s a lighter overall transmission, and the new outdrives really do look like they’ll enable smoother power delivery than previous versions of the car.

Attention then turns to the suspension, and here the CX carries over most of the Mi4LP’s suspension components.  Carbon-fibre composite is used for the suspension arms, together with fixed suspension arm mounts. Two piece alloy options are available to give a much wider range of roll centre adjustments, but we’ve found the standard settings right for just about every track we’ve visited…so we’ll be sticking with the one-piece composite units.

One quick note when assembling the suspension. It’s probably worth running a 1/8th inch arm reamer throug the suspension arms – the goal being to remove any tiny traces of debris from the moulding process, to ensure smooth and free suspension action.  We also found the need to ever so slightly file down the quick clips used to alter wheel-base to ensure the suspension arms could pivot freely on the inner hinge pins.

One other specification change for the CX sees Schuamcher include the “Flex” versions of the four degree front castor blocks. There is a firmer “Medium” option available if you’d like to experiment a little in this department.

Otherwise, suspension on the CX is reasonably conventional, following class norms.

Attention then turns to the excellent shock absorbers provided with the CX. These are carried over unchanged from the Mi4LP, and rightly so.  Assembled carefully, the result is a smooth shock, easy to build consistently, and delivering excellent on-track performance.

Once again, Chris Grainger’s shock assembly tips are worth taking the time to study and replicate.

We built up the shocks using standard (supplied) 35 weight fluid, three hole pistons and the kit supplied springs. We’ll start our test with that specification, but will also experiment with thicker shock fluid (particularly on a warm Australian day), and will have on hand a set of HPI Silver and HPI Pink springs to trial.

Schumacher also offer an optional ‘big bore’ shock tuning kit. The Big Bore shocks follow much the same build process, but hold a larger volume of fluid, and incorporate a different range of springs. We’ll definitely trial a set of the Big Bore shocks during our test process, with Schumacher claiming they’re worth trying particularly on bumpy and low traction surfaces (a description that fits many Australian race tracks).

Last finishing touches include anti-roll bars, front foam bumper, body mounts and electronics.

The Mi4CX carries forward the clamp-style motor mount unique to the Mi4 range. The motor is clamped in place by a wide alloy ring, rather than bolted into place from the front face in the manner of most other cars. The clamp mount has proven very effective and reliable, and delivers some improvements to the way in which chassis flex occurs around the motor-mount area.

Our Thoughts

We don’t sell Schumacher cars just for the sake of it. We like them, and have done for years. The Mi4CX is no different in that regard.

It is, in a sense, a chassis that has “grown up” and been refined immensely in this version of the car.  The changes introduced to the CX, while individually small, combine to produce a much more refined, smooth, but robust transmission. That combined with the rest of the chassis that is well sorted, high performance, and uses compoments of the highest quality.

We’ll be back in the coming weeks with the next part of the story….the part that matters most. The Track Test.

If you’d like to build your own Schumacher Mi4cx, contact Heavy and we’ll get one headed in your direction. Great quality, at an excellent price.

EDIT: The track test is up.  Find our first impressions from the race track here.

2 thoughts on “Schumacher Mi4CX: Full Build Review”

  1. Excellent vids, learnt a few tips and confirmed some I already do.
    Schumacher is my first touring car brand, have only started late 2010. So far very pleased!

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