Kyosho ST-RR Build / Run Review
ST-RR Build / Run Review
The Kyosho ST-RR has been in the wild now for a few months and is starting to make some serious inroads into the top spots across the racing scene. I personally have been using an ST-RR less the big bores since middle of June last year, having received the long chassis conversion kit. I subsequently ran it for half the summer season. Now the full kit has been reworked to include, and also omit, some bits and pieces, it's the right time for a proper review, with a few hints and tips along the way.
Length: 22.64 in. (575mm)
Width: 16.85 in. (428mm)
Wheelbase: 14.68-14.88 in. (373-378mm)
Track width: 13.90 in. (353mm)
Approx. weight: 151.7 oz. (4300g)
Final drive ratio: 16.54:1
Required for operation
Engine/21-28 class engine (P type) with Rear exhaust
Exhaust manifold & tuned pipe
Racing tires & foam inserts
Fuel and starting equipment
R/C system w/2 channels, 2 servos
Receiver battery for R/C system
Paint for body
HG Air Cleaner Oil (Part no. 96176)
The first thing you notice when you open the relatively small box are the build bags. Each one usually contains a full step within the manual for the build process. The screws for the majority of the build are all in one big bag, it's important at this stage to make sure you keep a good hold on all of these fixings. I usually put them all into a bowl and then sort them by type, size and length. This may seem like a over the top exercise but it pays long term as you won't be searching for screws you may have accidentally used in the wrong place earlier in the build.
The build process begins with the construction of the diffs. The ST-R was known in many circles for being a diff destroyer, I personally found this not to be a problem if you correctly shimmed the diffs to begin with. But Kyosho have addressed this issue be changing the crown and pinion gear teeth size. The teeth on the crown and pinion have been made thicker as can be seen in the comparison images below. This will make the shimming not so much of an issue. The old ones were okay if you shimmed correctly, the problem was when the gears stripped people were replacing the gears and re-shimming but not replacing bearings and gear box housing which would also be damaged when the breaking of the teeth was taking place! They would the same problem in a shorter length of time!
Using the recommended method of re-shimming after some use, these diffs haven't shown any signs of wear on the three ST-RRs I have recently put together. The rest of the ST-RR front and rear diff assemblies go together relatively quickly with the only other noticeable difference in the manual being the diff oils used. The ST-R used 4-7-3 and the ST-RR using 7-10-3 giving more drive to the front of the truggy.
The left hand Pinion is the IS008 old type. The other is IS102 new type that comes with the new ST-RR kit. You can tell the difference by the cut grove around the shaft. You can see that at the teeth are longer and will fit deeper in to bevel creating more contact area, also on the IS102 you will notice extra cut outs on the inside at the top to allow particles to escape easy.
The left hand Bevel is the IS007 old type. The other is IS101 new type that comes with the new ST-RR kit. You can tell the difference by the cut grove around the outside of the gear. You can see that at the base of the teeth it is a lot thicker to give support and extra strength.
All of the plastics in the new kits seems to be a little stiffer, especially the suspension arms which seem to have a higher fibre content to increase the rigidity and reduce the weight. The alloy parts are all very business like but beautifully finished. The radio plate and steering top plate are perfect examples of when less is more. They are there to be light and functional and not overly complicated or machined above and beyond what is necessary. The shock towers are also anodized blue and offer plenty of adjustments. The new extended wing mount now comes with 4 plastic braces instead of the the 2 blue alloy ones supplied with the original wing in the ST-R kit. The actual wing mount itself is longer than the mount on the ST-R by almost a centimetre and has adjustment for height in two positions on the wing cradle itself as well as having two angle adjustments at each of those height.
The nicely milled and anodized chassis itself is now longer in the rear portion by a full 25mm which changes the whole balance of the truggy. Moving the weight forward by only extending the rear portion between the engine and the rear diff assemble gives it a better weight balance and increase the truggy's steering ability by positioning the weight over the front wheels more. The overall effect of the lengthening is to make the truggy more stable over the rough stuff at speed and making it faster and more stable through the corners. Kyosho have also addressed the issues with the torque rods, otherwise known as chassis braces. The ST-R's single bolt fixing at the rear couldn't take the constant pressure it was under through the chassis flex and would invariably come loose. The rear brace now has a new mount that uses two hex bolts instead of the single fixing on the ST-R. The new arrangement eliminates this problem completely while still allowing the whole thing to flex and gain the extra grip that the flex is intended to generate.
The centre diff has not changed at all between the two versions and still uses the excellent steel rotor and semi metalic brake pad material from the ST-R. This brake setup has served me extremely well over the last year with the same set of pads offering great braking with no fade and very little wear. When mounting the centre diff to the chassis for the first time it is a good idea to use a little grease on the thread of the screws as the plastic used for the diff mount is extremely tough so the grease will help cut the thread smoothly .
The Fuel tank arrangement has not been altered either but does need some work to make bomb proof. The problem, if you landed hard enough upside down or had someone land on top of your truck the tank would be depressed enough to tear off the mounting lugs that attach to the mounting post thus pouring your entire fuel tank contents away. The cure, just put self adhesive foam between the tank and the chassis to eliminate the gap. I use the same foam to line the radio box to protect the battery and receiver.
The two real changes to the ST-RR come in how it distributes the power and how it handles bumps. The new big bores are certainly a step above the already great shocks on the ST-R. The 16mm internal bore and massively increased shock oil volume of the big bores means you won't be experiencing any changes to shock perform in long finals through temperature increase thinning the oil out. The only issue I found with the build process was that no shock oil is provided or even recommended in the manual. This meant that for a while it was hit and miss when trying to dial the shocks. I invested in sets of the Blue, Red and Purple tuning springs as soon as they were available to give me other choices apart from the lime green springs in the kit, which i found too soft for my setup. In the end I went for 700wt Kyosho oil with red springs at the rear and blues at the front. This set-up is perfect for my local club (DRT).
The new thin cvds supplied with the kit are a real joy. Not only are they thinner and lighter than the original drive shafts, reducing your rotating mass and increasing your drive train efficiency, they are also stronger being made from cro-moly steel like the diff gears. The only disappointment for me on the drive train is the omission of Kyosho's lovely CNC knuckles from the kit. It comes supplies with cast alloy knuckles, but these are supplies with all of Kyosho's top kit's including the 777 WC buggy. Through experience I replaced these items with the CNC versions straight out of the box, removing these as a weak point in the drive train.
The new body shell is a clear improvement over the old kyosho offering, I would even go as far to say it's better looking than the crowd pleazer shells! It is still a racing body and as such is made of very thin lexan so long term durability for bashing about with is dubious but it is form fitting and looks stunning and does keep the weight down which is a big consideration when it comes to racing. The kit comes complete with some very sexy chrome Kyosho sticker with 2 sets of decals for doing the grill/light area.
The kit comes with 9mm axle extenders which widen the trucks stance an extra 18mm total. This is more to keep the trucks overall dimensions square and help it's stability as the 25mm chassis extension would have otherwise made for a stretched looking truggy. There are other axle extender lengths available but I have found the stock length to be the best area to settle on. The kit doesn't include tyres of any sort but comes with a set of zero offset ten spoke wheels for you to mount your choice of rubber.
The radio tray and receiver box has not changed at all from the original ST-R but really didn't need to be as it is functional and well sealed against moisture and dirt. The ability to remove the whole radio tray/box arrangement for cleaning with just 8 screws is very useful.
The only other changes to this version of Kyosho's flagship truggy are the omission of the blue alloy ball end retainers on the upper arms at the rear and a new front suspension plate at the front of the truggy. The change to plastic braces and the removal of the ball end retainers is something I wasn't expecting but it all saves weight without compromising functionality so is more than welcome if it helps the truck go faster. Quite a few of the U.S. Pro drivers are actually replacing the alloy radio tray posts with plastic ones to reduce the weight even further.
Living with the ST-RR
The ST-R was no slouch when it came to handling but the ST-RR is a step above and beyond it's predecessor. Powered by my Sirio .21B STI and soon to be O.S. Speed, the longer chassis and wider stance gives it a far smoother, more stable, run at speed over any blown out and rutted areas of a track. The big bores are supremely capable of soaking up knocks that would otherwise have put the truggy out of shape. They allow you to keep on the power in situations you would otherwise be rolling across.. Jump handling is predictable and smooth, especially on landing. Having the ability to get back on power quickly after landing is extremely important and the big bores allow you to get the truck back in control faster than the previous setup. The braking, as I mentioned before is awesome, I have been waiting for an excuse to upgrade to a set of Cradocks for months but have had no reason to buy them with the stock brakes being extremely good and hard wearing.
The thicker diff set-up means the truggy pulls more through corners. I have had some understeer issues mostly whilst using the Proline Badlands but with a set of Proline LPR wheels and tyres or a set of GRP Grips its a different ball game. With the newer generation of lower profile tyres the truck handles like it's on rail.
Working on the truggy is extremely easy with everything easily accessible and open. Some people don't like the use of e-clips but with a tube of Tamiya thread-lock you can stop the clips from disappearing easily. The use of Philips head screws has been an annoyance to many, but I have found them to have their advantages. Clearing a dirty Philips screw head is simply a case of using a Stanley knife blade to clear the debris and then using a number 2 Philips screwdriver.
Overall the ST-RR is an evolution from the original truggy and as such it improves upon the already good attributes of the Kyosho truggy. The changes that have occurred are all positive steps forward that keep the brand fighting at the front of the pack. With the improved durability of the new truggy and the proven race pedigree the Kyosho kits provide I think we will be seeing a few more of these being driven next season and driven fast.
It isn't the cheapest kit out there and yes there are some things that I would like to see included in the package as standard but it is a supremely capable, quality kit that deserves to be considered if you are in the market for a top flight truggy.
I would like to thank the following people for there assistance with this review as without them it would not have been possible.
Mike Cradock Kyosho Europe
Added: Thursday, January 24, 2008
Reviewer: Site Admin