- Schumacher MI4CXL: Built and Raced -


Action RC - Scott Guyatt


Just a couple of weeks ago we first heard that Schumacher were planning the Mi4CXL, the latest version of the Mi4 line of touring cars. Only a week later full details emerged, the car was available for immediate release, and now we’re delighted to bring you our full build/drive review of Schumacher’s latest track weapon.




What’s New?

It’s worth recapping the significant changes the CXL includes over the previous CX version of the car. The major visible change is the inclusion of a long top deck, together with the resulting changes to the lightweight anodized alloy transmission bulkheads. New steering geometry, revised suspension geometry, new rear shock tower, revised layshaft, new alloy layshaft pulley, inclusion of the (previously optional) soft-weave 2mm carbon fibre chassis, new anti-roll bars are the other major changes.


What’s Not New?

For those new to Schumacher, the Mi4 is one of the more unique touring cars getting around (outside the outrageously out of the box Awesomatix car!). The design of touring cars these days is very much about controlling the flex charateristics of the car. Flex in the chassis is one of the key ingredients in generating traction, and controlling that flex is critical in keeping the car driveable and consistent. The Mi4CXL incorporates everything Schumacher’s designers know about flex. The long top deck, chassis-isolated motor mount, layshaft bulkheads split from the main rear diff bulkhead, chassis cutouts are all about equalizing flex. The main chassis deck itself is 2mm thick, and is designed to generate side-to-side flex, while limiting front-to-rear flex under hard acceleration and braking. Flex control is king.

A spool front end, twin belt drive and Schuie’s well known ball differential rear end form the basics of the drive-train, with a 1.8:1 ratio and a floating layshaft mount for ease of maintenance additional features. High tensile steel CVD’s in what Schumacher call a “reverse cup” design combine with durable outdrive inserts to deliver the ponies to the wheels.

Shock absorbers are Schumacher’s respected items, featuring nickel-teflon plating, threaded alloy shock bodies and cnc machined pistons.

Fairly standard TC suspension layout includes a small (but important) change to roll centre, while steering is by single pivot.

Why a New Car?

One of the common questions is “why do manufacturers release new cars so often?” It’s true, the CX was only released a little over a year ago, and here we are with a new chassis already. Schumacher, XRAY and Tamiya regularly release updated cars, and Team Associated have followed suit in recent times.

From our perspective it’s simple. Schumacher (like the other manufacturers) are constantly refining and improving their cars. They regularly release optional parts designed to make the cars faster, easier to drive or work on, and more reliable. Over the past 12 months we’ve seen Schumacher release the soft-weave chassis, long top deck and a dual-pivot steering system (for example). Mi4CX drivers have had the option of adding these components to their standard cars – and many (us included) have, finding useful improvements in performance.

The CXL bundles up the best of the upgrades, and some new additions and puts them in a new kit. The release doesn’t mean the CX is immediately slower or outdated, in fact a CX driver might already have most of the upgrades in place. What it does mean is that a new Schumacher customer gets the best package of chassis and updates all in one go (and for much less than buying the CX and each of the optional parts). From our perspective it’s a win-win situation. We’d much rather Schumacher release an up-to-date kit every 12-18 months bundling the best of the improvements, than have to tell customers they need to buy a kit and a shopping list of optional extras.


The Diff

In an era when every manufacturer is moving from the ball differential that has served so well for so long, to sealed fluid-filled gear differentials for the rear of the car, Schumacher’s decision to stick with the ball diff is worthy of note.

Schuie do offer a gear differential as an option (the Spec R unit) but for now it’s the tried and tested (and in this version slightly refined) ball diff that appears.

On one level that’s just fine. Schumacher’s diff is as good as anybody’s, and when built well, will provide great performance in stock/spec motor classes, and will last as well as a ball diff can in the ridiculous horsepower world that is modified touring cars these days. If you haven’t already seen it, check out Chris Grainger’s diff-tutorial for a long-lasting ball diff in your Mi4.



We’ve built and installed the ball diff in our test Mi4CXL, and I’ll happily run it – but at the same time I’m hoping that Schumacher are working on their own sealed gear version, and I’m a little disappointed that the CXL doesn’t include one.


The Options

Before we get into the build, there are option parts that we’ve installed in our CXL right from the start – and we reckon it’s worth pointing them out to you.
  • U3516: Ti turnbuckle set (light, and purple!)
  • U3932: LiPo battery retainer (to protect the battery and hold it in a little better in my inevitible “very” high speed accidents
  • U3791: Central body post & front shock tower (supports the centre of the body better – particularly at high speed & if using lightweight bodyshells)
  • U3924: Bando Tuff belt (a little more durable in modified)
  • U2459: Carbide diff balls (a tiny little bit more durable in modified)


Partly we used these options because we had them floating around, and partly because we’re particularly building the car for modified. In spec class racing we wouldn’t change diff balls, belt or centre body post. There are optional grey belts available that are specifically designed for the stock classes.
The Build

The build quality of Schumacher cars match just about anything. Instructions are clear and simple, and the build process flows in a pretty straightforward manner. We had no trouble at any time during the build with fit and finish – always a good sign (and to be expected in any of the front-running chassis).

The build starts with chassis, those beautifully machined bulkheads, and then straight into the drivetrain.

Follow the Grainger diff tutorial on the rear diff. And take your time to make sure the pulley fences snap on and sit straight. It’s an annoying part of the build that can be eased by warming up the fences a little – or grit your teeth and squeeze…..

When slipping in the outdrive inserts it’s helpful to moisten the o-rings a little, and be sure they “snap” into place. We were surprised (and happy) to see that Schumacher included an optional set of delrin outdrive-sliders with the kit. The stock (grey) sliders are reliable, but wear more quickly, the new delrin inserts last longer, but can crack in a big accident. We’ve opted for the new delrin inserts on the front, and the standard grey inserts in the rear (the rear inserts last much longer anyway).



The spool is unchanged – relatively light and strong. We’re yet to see one damaged in use – the slider inserts taking the wear and tear and easily (plus cheaply) replaceable.

The layshaft arrangement reverts to something like the original Mi4 layshaft. It screws in from one side, is supported on the opposite side, but is easily removed for servicing. A full CNC alloy layshaft pulley looks great for durability.



From there its the new long top deck (an easy fit, though slightly complicating the diff installation and access) thus completing the central chassis of the car.

The single pivot steering system goes together easily, a revised geometry changing the ackerman angles, and retaining the forward-facing centre mounted balls to make ackerman adjustment quick and consistent.



Suspension assembly is all pretty straightforward and traditional. Drive-shafts are preassembled, the “reverse cup” format and materials strong and reliable. All our driveshafts were assembled perfectly and free with no binding. It might be worth a little Tamiya anti-wear grease to ensure longer lifespan. One change we’d love to see Schumacher make is the addition of bushes into the castor blocks – and through which the kingpins can insert. The current system is pretty much unchanged since the Mi2 (or even earlier) and while it’s robust enough, a bushing might be just a little more refined.

The suspension mounts for the Mi4CXL enable easy adjustment of track width, arm sweep and toe, but are fixed for major roll centre. Schumacher’s team drivers say that’s because for most drivers, in most conditions, the standard roll centres are spot on (and they’ve revised the suspension mounting points from the Mi4CX to make sure of it). There are optional two-piece alloy suspension mounts available for those of us who just have to have the adjustment. Me? I’ll be sticking with the standard mounts thanks. I’m more than happy for Chris Grainger and Martin Hofer to do my roll centre research for me!

Shocks are a treat to build, and easy to get consistent. We noted that while Schumacher supplied 35 weight oil with the car, the recommended setups usually suggest running 45 weight. We’re in the middle of switching over to Schumacher’s Core R/C line of cst rated fluids, so built up the shocks with 550cst Core fluid (similar to 45 weight). We built with the supplied springs (blue front, white rear for the record) but we’ll keep a set of HPI silvers close at hand for tarmac running. We’d love to see Schumacher upgrade their standard spring range.

Chassis build finishes with the all new anti-roll bars front and rear. They’re higher mounted for more linear action, and easier access with the new long top deck mounting arrangements.


Our Gear

We finished the build with the installation of our standard running gear.

A Speedpassion V3 4.0 turn motor and GT2 ESC will provide the horsepower.

Spektrum DX3R radio gear, combined with KO servo (for which we chose to bypass the steering servo in favour of a solid arm) provide the control.

We’ll start with the trusthworthy standard weight Protoform Mazda Speed 6 bodyshell, and Sorex tyres pre-mounted on Schumacher Revlite rims.

It’s a package we know well, and an excellent basis for testing.

In terms of setup, we used the base settings in most cases, only occasionally picking up some ideas from the Chris Grainger test setup, and Martin Hofer’s regular setup. For the record, here’s my build/starting setup: MI4CXl Scott Guyatt Start Feb 2012

Weight-wise, the Mi4CXL still isn’t the lightest car on the market. As described above, and with only a transponder to be added, my car weighed in race-ready at 1395 grams. There’s definitely some excess wire that could be removed, and lightweight parts like hinge pins and a ti screw set would shave some more grams if required.


The Testing Fail

My nearest track is 2 1/2 hours away. I was headed in that direction for work and so loaded the car, a couple of packs and snuck by the track in between meetings for an initial run.

While setting up the steering trims on the front straight I discovered a broken RX aerial and severly limited range curtailed my planned test runs. With all my spare electronics at home, I didn’t have much in the way of options and will get back to the test circuit in a couple of weeks.

The Racing

Fortunately for us, our team mates Chris and Gary Sturdy had been simultaneously building up their own car, and hit the track this last weekend for the first runs on the car at Brisbane’s Bayside circuit. Here’s their starting setup (notably using the Spec R gear diff): mi4cxl chris sturdy bayside 05022012

Here’s what Chris had to say after the first day’s running:
Right away in the first practice run, the CXL felt considerably different to our previous CX. The car felt sharper, and more responsive, and carries more corner speed without getting loose. The car feels stable through the corners, more consistent from corner entry through to exit. It’s smooth to drive and just generates more grip. I am very happy with the car on its first day out, and know that the more I get used to it, it’ll only get better. Lap times are going to drop for sure.

We’d love to report a dream win on debut…but the competition in Brisbane is super hot in modified right now, with one tiny mistake having big consequences. Chris ran right at the front all day, finishing just behind Corey Broadstock and Jason Dorn – two of Queensland’s very best.

Gary reported his delight with the build, and with the performance of the car and shares Chris’s conviction that it’s a useful step forward from the Mi4CX, delivering improved traction and more accessible performance.

What’s Next?

The Mi4CXL is now available worldwide and in Australia through Action R/C. We’ll continue our testing in a couple of weeks and report it here, before getting on track for the Tasmanian Championships in mid-March for our first full assault with the car.

We’ve seen enough to be sure that we like what we see. There are still some changes we’d like Schumacher to work on (springs, gear diff top the list) but there’s no question this is a better car than the CX and will keep Schumacher right at the front of the TC field.

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