Yamaha RD 125

Once opon a time, in the land of ele--one compression ratios and 75-interstates, real motorcyclists id 125cc roadsters with rude rs and Bronx cheers. Performance word which those tiddlers could whisper. Magazine testers pro-the gaspers by omitting perfor-: figures, and any machine which struggle past the quarter-mile lights nph after 25 seconds sorely needed id Most 125 owners, discovering
the fact of non-performance, stayed off the great concrete ways with their buzzers. Indeed, on the freeways and interstates an unconscious herd of Ken-worths could rub a little jasper into just another grease spot.

Welcome to low-compression America and the permanent 55-mph limit. While speed laws have raced down to meet the tiddlers, manufacturers have bucked up the performance and reliability of small street bikes. One-two-fives which will
break 70 mph and cruise at 55 mph without self-destructing are newsworthy. And the performance king of the bantam-sized roadsters is Yamaha's RD 125.

The raspy twin won't be trampled by modern freeway traffic. Most automobile drivers relax their pedal-muscles when speedometers edge over an indicated 60 mph. This new standard freeway pace allows the 125 Yamaha to flow with the mainstream, and the engine, though busy at 60 mph, hardly sounds frantic.

Zero-to-fifty comes up quickly enough so that the Yamaha can avoid harm. Clean-air automobiles really do not accelerate, as that word was used in the 1950s and 1960s. More accurately, the modern automobile merely gathers speed, somewhat like a nineteenth-century locomotive. Consider some automobile tour-times through the quarter-mile: Opel Manta, 18.1 sec @ 74.6 mph; Vega GT, 18.8 sec @ 73.2 mph; Mustang II, 18.5 at 72.9. And remember the Plymouth Road Runner? Well, its beep-beep has been throttled down to an asthmatic wheeze: 17.1 sec @ 80.5 mph. Then there's the diamond-luster Mercedes-Benz 300D: a genuine $12,000 stone-20.8 seconds at 64.4 mph. By comparison, the $700 Yamaha seems downright quick at 18.05 at 70.8 mph.

That kind of performance from a 7.5-cubic-inch engine produces an intense little motorcycle. The power curve has two bumps in it. The engine reaches its initial peak at 6000 rpm, then trails along a plateau until 7000 rpm, whereupon the power curve ascends sharply to 9500 rpm. You might think that such a power-plot results from very sporting port timing, but that guess would be wrong. The only remarkable thing about the port timing is the fact that it's unremarkable, considering the actual performance of the bike. Keen fellows armed with equal portions of determination and knowledge could jump the peak power up another 15 per cent, without seriously endangering the basic reliability of the engine. In stock form the reed valves (sandwiched between the carburetors and cylinders) improve the fuel economy (42-49 mpg) and beef-up low-rpm'power.

Given the five-speed transmission, the most important function of the reed-valve system is spreading out the power. Contrary to Yamaha claims, there's nothing close-ratio at all about the gearbox. The gearing chart shows an almost perfect wide-ratio enduro-type transmission. The jump from first to second covers a bit too much space for the engine. Even spinning the engine past 10,000 rpm in first, the revs fall below 6000 rpm on the up-change to second.

This gap momentarily catches the engine a little short; an instant later, the bike reaches 7000 rpm again and starts its rush through second gear. Upstairs, the breech between fourth and fifth is considerable. Since the engine plays out in fourth gear at 60-plus mph, fifth gear must normally handle the 60-to-80 mph slot alone. In lieu of a bonafide close-ratio six-speed transmission, the reed valves are Yamaha's 125 answer: if you can't close up the ratios, then spread the power.

All this power-plotting will pass right over somnolent riders who will neitherfind the second power peak nor miss a close-ratio gearbox. The RD 125 can be ridden casually around town, burbling gently (but loudly) under 6000 rpm. Putting the 125 in any higher, tighter state-of-tune could drive away easy-riding customers who don't know or care about TA 125s, or Kent Andersson, or Kenny Roberts. And a six-speed transmission would only squeeze the price of the RD 125 upward and raise buyer resistance. Yamaha already has a final solution for increasing the performance of the RD 125. The RD 200 is stronger than any six-speed 125 could ever be.

If you respond to the RD 125's basic character, you'll still long for a close-ratio box. The 125 twin is a mini-RD 350 which unfailingly says "racer," not "cruiser." The 125 Yamaha demands the rider's attention. The engine will not start from cold without using the choke knob. A couple of kicks (no electric starter) swats the engine into life, whereupon it falls into a discordant idle. A brief stationary warm-up may be followed by a half-mile of choke-on running. Further choking will only dirty the electrodes and require a hard burst through the gears to clear off the spark plugs.
Squirting the Yamaha in first gear lofts the front wheel. In common with other lightweight motorcycles, the 255-pound bike steers quickly and reacts to all body movement of the rider. The bike instantaneously mirrors sloppy inputs. The RD 125 seems more sensitive than other small roadsters in part because the Yamaha is impressively strong through its first four gears.

Any tiddler must have an extra capacity for abuse if it is to survive. Moto-mites lend themselves to flogging. In the case of the Yamaha, brisk departures from stoplights begin by dialing the engine up to 7000 rpm or so, and then feeding in the clutch. Staffers usually ignored the clutch on three-four-five upshifts, preferring to roll back the throttle and click into the next gear. This type of abuse used to frag old 125cc bikes, which, after an indecently short period of hammering, would expire with the finality of a hand  grenade. Our test Yamaha absorbed all manner of enthusiastic riding. The clutch refused to slip, and never required adjustment. No ominous clanks issued from the transmission.

Treated to a short break-in period—rough enough to have any dealer shredding warranty cards—the engine gave not the slightest hint of apocalyptic seizure.
Part of this bulletproof nature results from over-engineering which, in turn, stems from production rationalization. The RD 125 shares a number of engine and chassis components with the RD 200 twin. Crankshafts and upper-end assemblies are different of course, and the RD 200 mounts a heavier front fork and a larger front brake. The RD 200 also has additional luxuries, including an electric starter and tachometer. The lack of a tachometer on the 125 is unfortunate, since its absence can only result in a greater thrashing of the engine. Power-seekers will be encouraged to spin the 125 until the power fades, and then catch the next gear.

Like the "missing" sixth gear, the absent tachometer reminds the enthusiast that Yamaha wanted a sporting 125 which was also inexpensive. The speedometer proved to be a laggard; it ran up-and-down the scale slowly. Heavily damped against vibration, the needle would still show 30 mph after the bike came to a dead halt. And the speedometer does not have a reset tripmeter.
There are other cost-conscious areas. The 5.5-inch headlight is a bit small considering the kind of speed which the Yamaha will generate. The stick-on tape-stripes—common now on many Japanese machines—do not bespeak quality finishing. Nor does the foggy paint which ripples with orange peel. When fully depressed, the kickstarter would catch on the right foot peg and fail to return.
Care must be taken when handling the key. It works fine in the main switch located by the speedometer. The key works marginally well in the locking gas cap (which weeped fuel). The lock tumbler turned stiffly and this pressure was nearly enough to twist off the lightweight key in the lock. We never snapped the key, but we did exercise caution.

Construction economies not only repress price surges, but they also hold down the weight of the motorcycle. And weight certainly becomes an important consideration with 13.8-horsepower engines. At 255-pounds wet, the Yamaha still outweighs Honda's CB-125 S1 (Cycle, May 1974) by 35 pounds, though the two-stroke twin has 25 per cent more power than Honda's tiny four-stroke. Riders who break the six-foot barrier or bend scales past 175 pounds should skip over the RD 125. Most six-footers will find sufficient space to allow reasonable comfort. As rider weight cHmbs, the acceleration of the RD 125 wilts. The gross vehicle weight rating of the bike would permit a 175 pound rider to carry a 185 pound passenger, but this kind of payload would overtax the engine (turtle-type acceleration) and the small drum brakes (longer stopping distances). Passengers should be avoided.

One-up, the RD 125 could be turned up to an indicated 60 mph for long (35 mile) stretches. At a sustained 60 mph (7500 rpm) the 125 twin exhibited no ill effects whatever. Long freeway upgrades necessitated a drop back to fourth gear, which allowed the bike to accelerate slightly going uphill. Screaming the engine in fourth gear produces some fearful vibrations—the rider's feet are literally buzzed right off the ends of the pegs. In fifth gear, where the engine spends almost all its freeway time, the bike stays in a calm state. No vibration comes coursing through the running gear and rider. Though top-gear acceleration is hardly dazzling, you can pass slower traffic on the freeways, and you'll not be tattoed on some Diamond-T's bumper.
By no means does the RD 125 offer a velvet-cushion ride on its 49-inch wheelbase. The short wheelbase leads to some choppiness in the ride, though it pounds less than you might imagine. Front and back, the suspension has very little travel, and none of this movement has any perceptible damping. The combination of soft springs, short travel and near-zero damping gives a surprisingly civilized freeway ride. Were there stronger springs, or harsh damping or even longer suspension travel, the ride might get rough and unpleasant.

This strange combination of suspension characteristics should produce positively diabolical results on winding back-country roads. It doesn't most of the time. The bike's good handling rests on other factors. First, the basic chassis is fairly rigid. Second, the suspension doesn't move much: two inches of perfectly sprung and damped movement may not be greatly superior to two inches of indifferent travel. With so little suspension movement, the running geometry isn't changing every millisecond, so the RD-125 doesn't slide into a deathly pitchroll-yaw routine. Third, the RD 125 hasn't enough power to get its running gear in real trouble. With a 175-pound rider, the bike has a power-to-weight ratio of 38 pounds per horsepower. With so little power relative to its weight, the chassis can handle all loads without distorting.

The nimble Yamaha has lightning-fast responses which allow the rider to flit the bike easily through a series of left-right-left combinations. Cornering clearanceon the left side suffers, thanks to the side-stand, but the RD 125 can be hooked over in right-handers until the stationary right peg begins scuffing on the asphalt. Since a rubber-mounted bar holds both pegs, there's a certain amount of play in the peg. While not as good as fold-up foot-rests, the cushioned peg won't immediately dig into the pavement and upset the works. By dropping off the sidestand you can get just as much clearance on the lefthand side as on the right. The lean angles established by the pegs mark a sane limit for the OEM Bridgestone tires.
Riding the RD 125 quickly is contagious. You simply charge up to a road-kink, clamp on the front brake lever, rapidly snick down a gear or two, sail deeply into the corner, smoothly flick the bike over and feed the power right back in.

Real shortcomings in the braking and handling department don't surface until you start going downhill on mountain roads. Going up steep mountain grades limits the top speed to about 50 mph, and tends to obscure the brake fade. Running hard on the downside of a mountain road hints at those characteristics which a 30-horsepower RD 125 would possess. The thing would terrorize the fainthearted. When the RD 125 gets rushing along, the 28mm front fork tubes, the small brakes, the lack of damping, the soft springs, and the minimal suspension travel create a genuinely breathtaking experience.
Try plunging toward a 60-mph corner at an indicated 80 mph. Heavy last-second braking makes the front fork tubes feel as they're flexing. That might be imaginary, but the brake fade isn't. Remember, the RD 125 responds quickly to inputs, and the faster you go, the faster its handling gets. So you have to concentrate on being smooth; just cough coming out of a corner and you can literally move over to the opposite lane. Sweeping right at 60 mph over a set of bumps will remind you that the suspension is truly flaccid. The bike no longer feels as if it's plugged together tightly. You avoid bumps, because there's no such thing as steadying a 14-horsepower motorcycle by feeding the rear wheel more power at 65 mph. If you get uneasy with this sort of riding, you need only wait for the grade to flatten out. The RD 125 slows down, regains its composure, and lets the rider return to an enjoyable afternoon swinging through endless curves.

Threading your way down a winding road, accompanied by the sharp rasp of that willing little twin, fifty-five seems like seventy. And that's a good feeling in fifty-five-mph America. ®

Source Cycle 1975