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Race Tuning the MRRC Chaparral 2F

April 16, 2009

by Rex Easley

There isn’t an RTR slot car on the market that doesn’t have a lot of potential for increasing its performance. But where do you start to unlock all that potential? We get a lot of e-mails and phone calls from newcomers to the hobby asking just that question in one form or another. This article will take you through some of the basics of tuning an RTR car for better performance and help answer those questions.

The car we have chosen for this article is the MRRC MC0054 Chaparral 2F. Chaparrals have been popular with slot car racers since the full-sized cars’ glory days in the 60s. They continue to win thousands of new fans each year through their appearances at vintage races. MRRC’s 2F model does a good job of capturing the look and character of the 1:1 scale car and looks good on the track, but it needs some help in the performance department to allow it to race competitively with period-contemporary or near-contemporary cars such as Scalextric’s Ford GT40 and Ferra
ri 330P4
and Fly’s Ford GT40, Lola T70, and Porsche 908 and 917, among others.

The most basic step in tuning any RTR car is to make sure all the parts are fitting properly and moving freely with no binding, rubbing, or misalignment. The crucial areas are the guide and the axle assemblies. The guide should turn freely in its mounting and self-center readily without sticking at its limit of travel in either direction. The axle assemblies should turn freely with no binding or tire rubbing whether traveling in a straight line or cornering. First, make sure the guide and the axle assemblies are snapped all the way into their mountings. It’s not uncommon for the factory workers in Spain, China, or wherever to use a little too much force in screwing the car down to its case and pop an axle assembly out of place. In such cases the axle just needs to be snapped back in. Sometimes excess side-to-side play in an axle assembly can cause a tire to rub in the corners. Som
etimes this can be fixed just by pressing a wheel a little farther onto its axle. In most cases, however, you will need to put one or more spacers on the axle to reduce the slop and keep the tires off the body. Another thing that can cause problems is incorrect installation of some part of the car, such as a headlight bucket or the interior, which may rub on a tire or cause the body to sit incorrectly on the chassis. You may need to correct the fit of the offending part or do a little filing to provide the necessary clearance. Sometimes a lead wire will be caught between the body and chassis, causing the guide not to rotate freely or self-center properly or the body not to sit right on the chassis. Relocating the wire will usually solve the problem.

On our Chaparral everything was in its proper place and moving freely to begin with, so with a drop of oil in each rear axle bushing, motor bushing, and front axle mount the car was ready for its first run on our test track. The test track, by the way, is a 4-lane version of the 2-lane layout we will use in the Electric Dreams Slot Car Challenge #1.

Right from the start the car had good acceleration and top speed but suffered from a major lack of grip in the corners despite its two traction magnets. This is typical of most RTR cars and leads to the first and one of the simplest and most effective performance improvements you can make: sanding the tires. First, use a rubber band to hold the controller trigger on one lane of your track at full throttle. With one hand hold a piece of medium-grit sandpaper on that lane. 150 grit works fine, though you may want to finish the job with a finer grade. With the other hand, place the car on that lane and hold it as shown below. The rear tires will spin on the sandpaper. Keep doing this until the tires are sanded down to the point where the entire width of the tread is making full contact with the track at all points around the circumference of both tires. Since tire tracti
on with any given tire compound is a function of the “contact patch”, that is, the portion of the tire’s tread surface in contact with the track, this maximizes grip. It also makes the tire truer and more concentric for smoother, quieter operation and even lowers the magnet a bit. Before tire truing the best lap time we could make on our 56-foot track was 5.599 seconds. After truing, our best lap time dropped to 4.827 sec. with no other changes. This would prove to be the biggest single improvement of the entire tuning process.

Tire sanding

From there we moved on to trying different brands of aftermarket rear tires on the stock wheels, in each case using the tire designated for the car by the tire manufactuer. Here are the results:

Ortmann 28L: 4.701 sec.

Indy Grips IG1009: 4.742 sec.

Maxxtrac M6: 4.554 sec.

After that we loosened each of the three body mount screws about 3/4 of a turn. That allowed the body to “float” a little on its mounts without making it loose enough for anything to rub. It didn’t significantly affect all-out speed for one lap, but it did make the car easier and more consistent to drive over the course of a run. This is something we recommend for any car, as it will yield higher lap totals over the length of a race.

At this point we had explored all the readily available options for getting better grip with tires that would fit the stock wheels. However, MRRC’s Sebring chassis, used on the 2F and many of MRRC’s other cars, leaves plenty of room for wider wheels and tires. The chassis also has lots of clearance underneath on stock-sized tires, so we had some scope to go to smaller-diameter tires at the same time. The stock rear tires, after sanding, were .795″ (20.19mm) in diameter. After a little scrounging around we found original-equipment front and rear axle assemblies for a Slot It Porsche 956. The rear tires were .762″ (19.35mm) in diameter. The Slot It fronts were correspondingly smaller in diameter¬†than the srtock fronts. Best of all the Slot It rears were .395″ wide, more than a third wider than stock. We did not have on hand at the test site a Slot It crown gear small enough in diameter to clear the 2F’s rear magnet so we used a press-on crown from a cannibalized Carrera car we had lying around. This gear not only fit well but gave a smoother gear mesh than the original MRRC gear. We had to shorten the axles slightly to fit the wheels, with their BBS inserts that look almost exactly like the classic Chaparral wheels except for their gold-colored centers, within the car’s width. On the front axle we used a couple of old Scalextric plastic axle bushings as spacers. If you don’t have a junk Slot It car around to pull parts from the Slot It components are all available on our web site under Slot It parts.

With Slot It wheels

With the alternative axle assemblies snapped into place it was back to the test track. Right away our lap times dropped into the 4.2s and we ended up with a best of 4.174. However, with the chassis, and therefore the two magnets, now much lower to the track we were getting so much magnet downforce the car had only one braking point per lap and was bogged down on the straights and perhaps in some of the turns, also. Not much fun to drive, in our opinion, and not good for the motor either. So, we popped out the front magnet and tried again. This time the car was back to being quick in a straight line and much livelier all around. The best lap time improved only slightly to 4.170 sec., so we had clearly lost some speed in the corners as we gained on the straights. However, we were no longer overheating the motor and we had freed the car up to take advantage of the additional quar
ter inch (about 6mm) of available rear tire width on each side. We expect adding wider tires to deliver lap times under 4.0 sec., though we didn’t have an opportunity to explore it before the deadline for this article. Another avenue we didn’t explore was to test Slot It’s other tire compounds for these wheels. That would probably be good for another tenth or two, also.

Slot It guide

Our final demon tweak for this session was to replace the stock guide with a Slot It SICH07 guide. Slot It bills this guide as being for routed wood tracks but on this car at least it worked just fine with no trimming on our Sport track. The guide upgrade was a straight swap with no mods needed to either the guide or the chassis. The eyelet connectors on the stock lead wires are a perfectly snug fit in the new guide. With the Slot It guide the ultimate lap times did not change, but again we noticed an improvement in the consistency and drivability of the car. This indicates that the stock guide was doing a pretty good job, but anything that makes the car more drivable will pay dividends over a race or a season, and on cars with less effective stock guides this upgrade can make a
big difference. Depending on the kind of track you run on you may also want to try SICH06 or SICH10.

One good thing about all these changes is that they are all snap-in mods and completely reversible if we want to return the car to stock form. The only fabrication of any kind needed was the shortening of the Slot It axles, and one could probably avoid that simply by buying axles of the proper length to begin with. With these easy changes we took almost 1 1/2 seconds off the car’s lap times and made it a much more consistent and pleasant car to drive. You can use these modifications to make your car faster for all-out competition or you can use some combination of them to tune your car to a desired performance level and equalize its performance with other cars you would like to race it with. The techniques described in this article can be applied successfully to almost any RTR car in your collection.


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