Perhaps one of the most important upgrades — by replacing all bushings in the kit with twelve 5mm×11mm and two 5mm×8mm sealed ball bearings, friction is reduced. This means less energy is spent fighting friction which can mean higher speeds and longer run-times.
A 3-step mechanical speed control is included with the M roadster kit. This is analogous to driving by pressing three switches; one for 5mph, one for 15mph, and another for 30mph. A 2nd servo is normally used to manipulate this mechanical speed control. Upgrade to an Electronic Speed Control so it replaces the hardware along with the 2nd servo. This eliminates some bulk and weight. In addition, an ESC provides a smooth, stepless acceleration curve. When finessing your way around a corner, this is essential. For an in-depth article on Electronic Speed Controls, visit RC Car Action's ESC Guide.
Just like the real thing, adding swaybars (anti-roll bars) prevent the chassis from leaning excessively during heavy cornering. (part #53382)
Tires are available in all sorts of compounds and tread patterns. HPI makes a number of racing tires that will fit the M roadster's 26mm-wide wheels (part #50844). The standard foam inserts included with most HPI tires are way too large and bulky. This causes the tire to look and perform as if it were overinflated. Replace them with molded foam inserts to restore a better contact patch between tread and pavement. Looking for "aftermarket" wheels? Those are available too. The hex-hub design of R/C cars is mostly universal, so most of the aftermarket wheels will fit onto the Tamiya M roadster without problems. For genuine Tamiya wheels and tires that fit this M04L chassis, take a look through Tamiya's pages. Still need more choices? Try Pro-Line, RPM, Hammad Ghuman, RadTechRacing, or EndLess Wheels.
Tamiya offers a hop-up Touring Spring kit (part #53333) consisting of three pairs of coil-over springs with firm/medium/soft rates. In addition, oil-filled aluminum shocks (part #53280) from Tamiya's TA03 series should fit the M-04L M roadster. These shocks use actual hydraulic valving like the real thing. Experimenting with different spring rates and shock oil viscosity weights provides a level of tuning that's on-par with the real thing. For additional information on these shocks, check out Dave's detailed procedure page.
The motor in the kit is a Mabuchi RS-540. This is known as a "stock" motor. There are stock motors and modified motors in the R/C world. Some simple key points differentiate the two — stock motors are 1.) those constructed with 27 turns of wire wrapped around the spinning armature, 2.) has it's timing advanced and fixed at 24°, and 3.) uses bushings inside the metal housing to support the armature. Modified motors are those that fall outside of these constraints — they typically feature ball-bearings, adjustable endbell timing and are sold with armatures wound for considerably faster speeds. Trinity, Reedy, Orion and Kyosho are some of the companies that manufacture stock and modified motors. Decreasing the turns of wire wrapped around the armature increases the speed of the motor; sometimes at a cost of less torque. Stock motors ($20-$35) have 27 turns... often referred to as "27T". Modified motors ($35-$75) generally feature armatures that range from 19T to 8T. ESCs are rated on how low of a turn it can handle in a modified motor. The inexpensive Futaba MC230CR ESC shown above can handle a motor down to 20 turns (20T). Whereas Racing ESCs can handle everything down to an 8T modified motor (sometimes even lower) without frying itself but can cost $100-$150; more than the Tamiya kit! Aside from outpowering the handling envelope of a car, modified motors cut the battery's run-time drastically and do require constant maintenance. Most modified motors are designed to barely finish a 4-minute race. For those of us just wanting to have fun, the low-maintenance stock Mabuchi is a great fit as it gives about 10-15 minutes of hot-dogging per battery charge. (TIP: get additional battery packs) One other way to alter the speed of the Tamiya M roadster is to change the pinion gear. The kit supplies a 17tooth gear (48 pitch) providing a 6.82:1 drive ratio, but using a 19tooth or 21tooth gear will give 6.10:1 and 5.52:1 respectively. (the closer we get to a 1:1 ratio, the more top-end speed is gained at a loss of acceleration) At the end of a run, if the motor outfitted with a larger pinion gear gets too hot to touch, it's overgeared. Drop back down to a smaller gear or risk a shortened motor lifespan. Roughly speaking, a stock Mabuchi motor under the load of this Tamiya M roadster should spin a ballpark 18000-20000 rpm. A quality stock motor from Reedy or Trinity might do 21000-24000 rpm. Higher maintenance modified motors can push 35000 rpm. With those figures, it's theoretically possible to power the Tamiya M roadster beyond 40 mph but understanding the fundamentals of modified motor maintenance will be key. The most authoritative resource on that subject is The RC Motor Blackbook; written by one of the designers of the hobby's most popular stock and modified motors.
The standard differential in the kit uses three planetary bevel gears to provide it's differential action. It matches fairly well with the humble stock 540 motor and works without any restrictions. However, that very lack of restrictive movement can mean the chassis tends to oversteer as the car is tossed into a corner. To dial down some of the oversteer that often seems the embodiment of rear-wheel drive cars, it's necessary to limit that differential action. This "limited slip" is achieved with the TA03 Ball Differential. Considerably more advanced in it's construction over the standard diff unit, the #53267 upgrade includes tiny items like pressure plates, thrust bearings, disk springs and ball bearings. Toward the end of the intricate assembly, there's a crucial 4mm bolt to tighten. How much this bolt gets torqued down determines how much slip exists in the whole unit. Once this differential is installed it's a bit cumbersome to adjust the slip so try to guage the preferred amount before sealing up the gearbox.
This inexpensive upgrade is molded to hold both rear half-axles at a -2° toe-in. The enclosed upgrade sheet itself claims that this "makes the car more stable, controllable in high speed and sturdy." The stock uprights are supposed to already have around -1° toe-in, but after building a few kits a disturbing observation was made where the chassis would hook to the left during heavy acceleration. Once at speed in the straights, this dog-legged performance would disappear. Adding a limited slip differential and higher traction tires didn't solve the problem. The diagnosis was finally evident when the individual toe-in of each rear tire was scrutinized. One measured -1° while the other measured -½°. A skewed thrust angle of the combined drive wheels was effectively pointing the rear like a rudder. Adding the toe-in upgrade only to one side fixed the problem as the car now tracks much better during initial acceleration and stays that way at top speed.
"Slop" is simply a term to describe the looseness of a suspension and steering system. Grab a front wheel and wiggle it. That amount of free play is slop. For most beginners, their driving skills outfactor any amount of inherent slop, but as those skills sharpen the slop interferes with steering accuracy. Part of the problem stems from the suspension arm assembly. This can simply be fixed with a set of washer shims like those from Kyosho. Set #96643 consists of shims in three thicknesses — .1, .2, and .3 . Insert one or more greased shim in the suspension areas wherever there is some play noticed. This may be in the suspension arms, the kingpins, or the half-axles at the hub. Do not add so much that it causes binding though. Shims alone can remove around half the amount of slop in the system.
A Servo Saver acts as the last line of defense in case the car bashes hard into a wall. A strike on the front wheel would otherwise transmit through the steering tie-rod and onto the servo crown and ultimately destroy the servo's inner plastic gears. A Servo Saver is an open plastic collar at the servo crown that's simply designed to "give" on a hard impact. Unfortunately, the one included in the M04L kit contributes to a large amount of slop. Thankfully there's a better solution; Tamiya's Hi-Torque Servo Saver #50473. This upgrade features precision molded nylon parts and uses metal ring collars instead of plastic. Once assembled, it's a very precise wiggle-free unit. The combination of shims and an upgraded servo saver has all but eliminated the initial slop in the system. Steering turn-in is dramatically more noticeable and straight-line tracking seems more stable.
This upgrade doesn't really require buying anything but is invaluable in the process of race-prepping the M04L chassis. One minor flaw in the kit's original instructions occur when the assembly calls for positioning the Receiver and ESC on the top platform of this chassis. Letting the components sit that high only means that the overall Center of Gravity is shifted higher than necessary — and that in turn may cause the chassis to roll over during high-speed corners. Sometimes this is referred to as "traction roll". Rummage through the kit's unused pieces (presuming nothing's been tossed out yet) and an extra plastic item should be easy to spot on parts tree lettered "A". Part #2 on that tree was initially meant to house a second servo for owners opting to use a Mechanical Speed Control over a recommended Electronic Speed Control. In light of this, it should prove perfectly acceptable to relocate the Receiver here instead. Just use extra 3x8mm tapping screws to fasten it into place. With a sliver of ingenuity, the ESC can be relocated on the other side by creating a simple mounting plate that screws onto a couple unused chassis holes. This method ensures the ESC can be cleanly removed to provide access to those other screws underneath belonging to the chassis. Another benefit is that these relocated components now provide some marginal improvements to the front-rear balance of the chassis. Optimal front-rear balance promotes a more neutral-handling car.
Not exactly a speed modification, but for those who seek even MORE realism, a light kit can be added to the M roadster with some hobbyist ingenuity. The lighting kit from RC Neon uses some really bright LEDs powered by a 9v battery. If lights are desired, it's best to plan ahead and mask-off the headlamp shields on the body prior to painting. Other lighting kits and gadgets can be found from RAM Electronic Devices. The ultimate lighting kit is perhaps the one shown on the concours page.
Can't decide which color to paint the Polycarbonate Body? Get a few additional bodies (part #50848) and have it all! Polycarbonate Bodies sit on the chassis via bodyposts and clips, so changing one for another is a snap. Hardcore racers prefer to spray only a few light coats of paint on their racing bodies to shave off that little extra bit of weight. Some colors don't require a lot of coats to result in an opaque look from the exterior.
Pactra RC287 => BMW 314 Bright Red
Pactra RC264 => BMW 405 Imola Red
Pactra RC262 => BMW 309 Arctic Silver
Pactra RC280 => BMW 303 Cosmos Black
Pactra RC250 => BMW 668 Black
Pactra RC251 => BMW 300 Alpine White
Pactra RC293 => BMW 335 Estoril Blue
Pactra RC272 => BMW 448 Laguna Blue
Pactra RC257 => BMW 337 Dakar Yellow
Pactra RC266 => BMW 358 Evergreen
Pactra RC273 => BMW 328 Violet Red
Pactra RC285 => BMW 351 Kyalami Orange
Other colors can be achieved by mixing their jar paint and applying with an airbrush.
Absolutely. I recently found out a parts list has been posted online in a PDF version. Grab it directly from the source. A portion of that document contains part numbers of Tamiya upgrade parts that will fit the M roadster. If you're having difficulty obtaining the parts locally, Tamiya actually has a customer service number where the parts can be ordered directly: 1-800-826-4922