The theme of this issue is to interpret some of the development concepts behind the unique model of Yamaha TDR250, to see the "crossover" and "multi-functional" in that era, whether there are still inspirations worth observing for today's use scenarios, and to find the residual value of revisiting the past and the new.
In 1988, Yamaha introduced the TDR250 (factory number 2YK), the "crossover" expedition vehicle of the time. The car was powered by a water-cooled, two-stroke, inline-two-cylinder engine from the 1985 TZR250 sports car, with a bore, 56.4 mm x 50 mm of travel (the same specification as the final 1990 TZR250R/3MA) of the final inline-two-cylinder car, with a displacement of 249 cc, a YPVS power valve, and a maximum horsepower output of 45 hp (the Japanese version). For the European and North American versions, the TDR250 is 46 hp and the TZR250 is 50 hp). The body is a steel-tube double-cradle frame, and the 18- and 17-inch rear diameter steel wire wheels are fitted with off-road tires as standard.
The TDR250 has a modest product life cycle, first released in 1988, last updated in 1990 in Japan, and last updated in 1993 in Europe and the United States.
Back in late October and early November 1987, Yamaha presented the all-new versatile TDR250 at the 27th Tokyo Motor Show in Japan. The car was already defined as a "reference car" at the time, and was officially launched in 1988.
At launch, the new TDR250 was said to offer users a "new riding experience": it combines the features of the TZR250 sports car, the RZ250 sports street bike, the DT200R and the XT225 Serow off-road bike. The power unit derived from the sports car, the sitting position of the street car + off-road vehicle, the chassis (frame + suspension system), transmission ratio, and tires of the off-road vehicle, this is the "crossover" in that era. Perhaps this kind of crossover is only to achieve the satisfaction of their respective functions (sports cars, off-road) to a certain extent, and cannot achieve a more thorough performance benchmarking, but for conventional drivers, it can meet the needs of most riding scenarios, and the meaning of multi-function may lie in this: let one car meet the needs of different road conditions, so that there is no need to buy a few more cars, go on a collective trip with different groups of riders, and use one car for multiple purposes, thereby reducing expenditure.
At the beginning of the TDR250's development, Yamaha took part in the Rallye des Pharaons in Egypt as a prototype car, and won the 16th overall 250 cc class in the 11-day, 4,815-kilometre race.
Note: The Pharaonic Rally, also known as the Pharaons International Cross Country Rally, was founded in 1982 and is held in Egypt, with the start and finish points under the pyramids in Cairo. The race has been a stop at the FIM Cross-Country Rallies World Championship since 2000 and the FIA Cross-Country Rally World Cup since 2005, when it was the second largest motorsport event after the Paris-Dakar Rally. And 2015 is the last edition of the competition so far.
The heavily modified TDR250 achieved a top speed of over 180 km/h, with an average speed of 140 km/h for most of the race, proving the TDR250's extreme performance and durability in the races.
Perhaps many young riders do not have a very clear impression of the performance of the non-competition two-stroke two-cylinder 250 cc class engine in the last century, but here are a few words: production models such as the NSR250R, TZR250R, and RGV250r with two-stroke two-cylinder engines used to perform slightly better than the 400 cc class sports cars with four-stroke inline four-cylinder engines, but slightly worse than those with four-stroke inline four-cylinder engines 600 cc class sports car. Overall, this is roughly the same as the power performance of current two-cylinder machines from 600 cc to 800 cc.
In addition, in terms of output characteristics, a two-stroke engine with a relatively simple structure will have faster acceleration performance than a four-stroke with a similar bore and stroke ratio. To some extent, it can even be understood as the acceleration characteristics of a two-stroke, between a four-stroke internal combustion engine and an electric one.
Pictured below, a TDR250 competing in the 1987 Pharaonic Rally (profile photo. Image source: Yamaha News No. 294, December 1987).
At the same time as the TDR250 was introduced, Yamaha also revealed some of the car's design concepts in the form of technical documentation. The following is an excerpt from the July 1988 release of Yamaha Tech Conference No.6:
1. The background of development is the two-wheeled motorcycle market in Japan, which is gradually weakening and declining from the perspective of the whole market. At that time, the only thing in the market that was still growing was the light (under 250 cc) sports category;
2. Under such a market background, the sports fun of the product will be expanded to expand the area suitable for riding (extending from conventional paved roads to non-paved roads), so as to provide new driving pleasure for riders. The analysis object selected by the manufacturer, with TZR250R as the representative of road racing style and DT200R as the representative of off-road vehicles, how to combine these two relatively monofunctional models to develop exquisite aesthetics in addition to function has become the core issue of new car development.
3. After removing the two extreme parts of the road-type track and the off-road track, most of the riders mainly face the use environment/road conditions every day only On-Road (meaning paved road) and Off-Road (meaning non-paved road), the regular public road is the primary setting, and then there are streets, suburban forest roads and dirty roads in the wild. The TDR250 was developed with the goal of enjoying sporty riding no matter which road conditions the rider chooses On-Road or Off-Road.
4. The problem at the beginning of the design is how to meet the two functions of On-Road and Off-Road in one component. After comparing the engines of the TZR250R and DT200R, the in-line two-cylinder engine of the TZR250R was chosen because it has more powerful performance and can provide more exciting running fun for on-road riding;
5. In terms of overall performance, the engine of the TDR250 is basically the same as that of the TZR250R sports car, by adjusting the gear ratio of the first gear, the secondary reduction ratio, the change of the air filter, CDI ignition and the exhaust system of the cross design, the rear-wheel drive force of the TDR250 and the walking performance in the medium and low speed range are improved. After its launch, the TDR250 market evaluation received by the factory found its outstanding acceleration ability to become the core charm of the car;
6. In order to improve ground clearance, the exhaust system layout of TDR250 cannot be placed underneath like the TZR250 sports car, and it needs to adopt a top-mounted design like an off-road vehicle, and in order to keep the engine performance the same as that of the TZR250R, the size of the exhaust system needs to be kept the same as that of the TZR250R, but if the original design of the TZR250R is directly adopted, the width of the TDR250 will become too large. As a solution, Yamaha ended up with a crossover design (the exhaust port of the left cylinder corresponds to the exhaust pipe on the right side of the body) so that the expansion chamber of the exhaust pipe does not interfere with the riding position.
7. Adopt a pair of double cradle frame made of high-strength (marked STKMHT60, SAPH45, etc.) round steel tubes. For the material of the frame, the factory had considered using aluminum alloy, but was forced to abandon it due to cost constraints and the design of the top-mounted exhaust system, which did not have enough reserved space for the car body;
8. The suspension system with a stroke of 160 mm in the front and 150 mm in the rear is adopted, while the stroke of the suspension system of the common 250 cc sports car is generally only 120 mm - 130 mm. In order to balance the handling flexibility and cope with different road conditions, the TDR250 uses a standard wheelbase of 1385 mm, which is slightly shorter than the 1395 mm of the TZR250R sports car.
9. The mainstream specification of sports wheel frames is 17 inches, and the mainstream specifications of off-road wheel frames are 21 inches in the front and 18 inches in the rear. In order to balance the stability of handling and the passability in off-road conditions, the TDR250 opted for 18-inch diameter wheels at the front and 17 inches at the rear. Initially, there was the idea of adopting the front 19 and rear 17 inches, but considering the user's personal preferences in the future and the need to replace the tires, the variety of products on the market finally chose the first 18 inches.
10. Corresponding to the 18-inch front rim, in order to reduce the risk of breakage of the handlebar structure during off-road riding, the rake angle of the TDR250 has been adjusted from 26 degrees in the TZR250R to 27 degrees, and the towing distance has been extended from 100 mm in the TZR250R to 114 mm in the TDR250.
The image below is an excerpt from the Yamaha Technical Conference No.6 released in July 1988 (Image source: Yamaha Motor).
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