KYOSHO INFERNO ST-R

There’s no doubting the truggy scene has really exploded this year and we’ve been riding the tidal wave of new releases every month but we’ve pulled out all the stops this time with reviews on two of the highest quality truggies on the market at the moment.

There are several brands in this industry that always seem to fight it out like cat and dog on the race track, Losi and Associated have battled in the 1:10 electric class for years and closer to home, Kyosho and Mugen Seiki have always been at the forefront of the 1:8 rallycross buggy market and now these two companies revive their skirmish in the world of outlaw monster trucks with the launch of the Inferno ST-R from Kyosho and the MBX5T from Mugen.

Kyosho’s offering

The ST-R has been around for a few months now and we took a look at UK rep and Kyosho sponsored driver, Mike Craddock’s very own truck a while ago.  Now however we’ve got a kit for ourselves and have had a great opportunity to see how it builds up and goes together.
To make things a little more interesting, Nobby and I sat down to build these two truggies up side by side.  It gave us chance to compare them at every stage and of course brag to each other when one of our hop-ups were nicer than the others, unfortunately Nobby seemed to be doing a lot more of that than me.

The build

Like most Pro kits, you need to build the ST-R, not normally my favourite job and nine hours into it, I really started to appreciate the concept of ready to run. But I remembered, with this kit in my hands, I was going to be unbeatable on the race track (I was a bit delirious by this stage, fortunately the Chinese take away turned up).
So there we were bright and early one morning with two new kits and all the other bits and pieces we needed sat in front of us.   The instructions for both had us building the diffs first, there’s a set up sheet from Yuichi Kanai, designer and top guru at Kyosho recommending the use of 4000 weight diff oil in the front, 7000 in the middle and 3000 in the rear and these are all supplied with the kit.  It seemed a little light to me but I’m not going to argue with a multiple world champion, not until I’ve tried for myself anyway.

As you might be aware the diffs in the ST-R are a new spiral cut design which has been developed especially for this model.  Spiral cut gears offer the advantage that more teeth mesh at one time giving you better traction and less chance of the gears slipping.  43 tooth spiral cut crown gear marries up with a ten tooth spiral pinion gear giving you a higher gear ratio of 4.3:1.  Increasing this ratio means you have a more normal 50 tooth spur gear in the middle instead of something resembling the London Eye. A smaller centre spur gear means the centre drive shafts don’t run at an exaggerated angle which puts them under more strain and also keeps the overall centre of gravity lower and gives you a final gear ratio of 16.54:1.  Attention to detail in areas like this proves that the ST-R has been designed as a kit in its own right and is not just a buggy with an extended chassis and arms.

With the diffs built you move onto building up the rear and then front sections, all this goes together pretty easily and while most of the parts for each section are separated into their own bags, a few bits are randomly placed in different bags just to confuse you.  I coped with that, the thing that plagued me most during this build was finding the right screws to use.  These are all split between two bags which I dumped into two plastic containers to rummage through more easily.

While this is the first Kyosho kit I have built up from scratch, I have often heard people moan about the cross head “wood screws” Kyosho use.  The self tapping wood type screws I don’t have a problem with although you do need to keep an eye on them as they have a tendency to back out but after the first few stages I was getting rather hacked off with the cross heads, and when it came to attaching the rear end to the chassis I resorted to using an electric screw driver, after all four lots 20mm of self tapping screw is more wrist action than even a single bloke like me can handle!

As you would expect, there is a full array of set up options with the ST-R, these include front and rear sway bars, a two degree gold anodised anti squat plate on the front and a choice of 2, 2.5 or 3 degree plastic toe plates for the rear. Camber adjustments are possible all round with the turn buckles in the upper suspension arms. Four metal shielded bearings pad out the suspension system which also has a 7075 Ackerman plate with three lots of holes for mounting the turnbuckles to.

Inferiority complex

Building this kit up next to the 5T meant we really did have a good chance to compare every part as we went through it and it wasn’t long before I was starting to feel slightly hard done by.  With the rear end all built up and screwed to the chassis, I felt a little embarrassed to pull out the cast aluminium front knuckles.  These really didn’t look the part and the casting was so imprecise that it took a considerable amount of effort to get the metal shielded bearings in both sides and the drive shaft to sit in there properly.   Still I suppose the cast knuckles on the front are better than the plastic uprights on the rear but when Nobby showed me the anodised machined aluminium equivalent parts on his Mugen, I ducked out to crack open a can of beer!

Build Tip

When screwing the knuckles in to the C hubs, don’t over do the thread lock as the screws seize in the collars.

I was usurped by the chassis braces as well, although originally Nobby installed the standard plastic ones, not noticing the upgraded ones he had in a separate pack, he’ll deny that though of course and claim he was seeing what they looked like or something else highly implausible. 
The ST-R uses aluminium tubes with the Kyosho logo boldly imprinted in them, which indecently make it slightly more tedious to line up if you want it to look good.  I can’t decide if these are good or not.  They certainly look the part; the tubes themselves are nice and tough and end with sturdy ball ends which pop onto a ball on the chassis.  With it not being a completely solid structure it will give a little more chassis flex which Kyosho claim will aid stability and handling but I couldn’t help but think they are likely to pop off after a hard landing but again am I going to argue?  Well actually I would have done at this point as I’d had a couple of cans of Stella.
The only other area where I was left slightly humbled was with the hinge pins as all the ones on the ST-R use the traditional E clips to secure them in place.  There’s nothing wrong with this but they are vulnerable to popping off mid race and in reality virtually all the top spec kits on the market nowadays come with captured hinge pins and it would have been good to see them included on this.

Bragging moments

One area where the ST-R did stand out was the quality of the chassis, it really is one of the nicest truggy chassis I’ve come across, made from 3mm 7075 aluminium with a hard anodised coating, it features some serious milling to make the ST-R the lightest truggy on the market (yes we weighed them all) and gives you a wheel base of up to 350mm, some 20mm longer than the normal Inferno buggy.  Both shock towers are pretty impressive as well, made from 5mm 7075 aluminium and anodised in blue, they, like the chassis are cleverly milled to keep them lightweight but tough and offer a huge variety of shock mounting positions.

I didn’t have many opportunities to point out the superiority of the ST-R over the 5T but I did relish the fact that the CVDs used throughout this kit were all pre-built and saved me a considerable amount of time and effort, which was handy as Nobby was cruising ahead of me in the build.  In early versions of the ST-R, we’d seen the CVDs pop out of the drive cup but it would appear these have now been ever so slightly extended as the ones in this kit had no hope of popping out even with the suspension at it’s most extreme articulation.

Nearly there

With the centre diff mount and brakes added to the chassis the truggy is starting to take shape, the 150cc fuel tank is mounted off the chassis and padded out with rubber grommets to reduce vibrations and reduce air bubbles.  The instructions get you fitting the engine and pipe next but I’ll come onto that in a moment as the penultimate stage of the build is installing the radio tray and electrics.  The radio tray and battery box are bolted together and attached to the chassis to add more rigidity to it.  I used a bit of a combination of servos in this, a Hi-Tech digital 5945MG for the steering and Futaba S3050 for the throttle / brake.  I also used a Peak Racing 1400NiMh pack, Spektrum receiver and my Futaba 3PK transmitter.

And finally

One of the last stages of the build is the shocks, these go together like most shocks but included sturdy 3.5mm shock shafts and are virtually the same length front and rear, this long travel complements the extended A-arms perfectly although do make sure you set the droop screws to avoid too much rebound snap after some big air activities.