Yamaha SR-V: The Indy Killer
As the dawn of the 80’s was fast approaching, the sport of snowmobiling was to be exposed to a number of factors that would shape the industry in terms of the number of brands that would survive, as well as the evolution of the snowmobile itself.
In the late 70’s Yamaha was one of eight brands still available and (while not the leader) had made huge strides in capturing market share with the success of the GPX free-air stock race sleds in 74/75, followed by the liquid cooled SRX stock racers in 76/77. These race winning sleds drove customers to their local dealers where, in 1977, they could purchase a new introductory sled called the Enticer. Yamaha marketing had created a snowmobile that offered the best of what the industry had to offer at the time (forward mounted engine, aluminum chassis, slide rail suspension and oil injection) and built an adult size snowmobile that was reasonably priced for a first time buyer or as a second sled. Yamaha sold thousands of them and created a new generation of brand loyal Yamaha customers.
Interest in independent front suspension (IFS) had also captured the imagination of many snowmobilers and Yamaha built their first version of a trailing arm IFS on the 1978 SSR oval race sled. What we did not know at the time was that Yamaha’s R & D group was also busy developing a more “consumer friendly” IFS that was less complex but adaptable into a more traditional snowmobile chassis.
Speculation amongst the “tech driven” consumer in the spring of 1978 was all about the adaption of IFS onto a trail performance consumer sled. Arctic Cat was the first to the dance with their 1979 Trail Cat which lays claim to being the first consumer trailing arm IFS chassis built for the trail. Polaris however had been testing a liquid cooled prototype IFS chassis built for cross country racing during the winter of ‘79. The other sleds builders continued development in ‘79 with conventional chassis models.
Yamaha had kept their cards close to their chest in ‘79. Yamaha was not a threat in cross country at the time so no prototype sleds were competing like Arctic Cat, John Deere and Polaris had been doing all winter.
Yamaha turned heads when their new 1980 SS440 had the covers pulled off at the fall snow shows. While not an IFS sled it featured a new chassis that mounted the engine low and featured a jackshaft mounted secondary to further lower the center of gravity. The styling was derived from the ‘78 SSR oval racer but there was no trailing arm IFS. The coil-over mono shock rear suspension flew under the radar.
The 1980 Yamaha model line up was set at four models; the entry level Enticer, Luxury model Excel V and performance models Exciter 440 & SRX 440, which were getting long in the tooth. The new SS440 and SR-V models were built around a new reed valve fan cooled motor. Yamaha had one of the smaller product offerings in 1980 but they also were well positioned with arguably the best low cost introductory sleds available in the early 80’s. The Enticer would drive brand loyalty and sales as the market recovered and Yamaha Telescopic Strut models took the brand to number one in sales in the mid 80’s.
Telescopic Strut Suspension (TSS) – Keeping it Simple
Yamaha introduced the SR-V with TSS in mid September 1979. The introduction caught the industry by surprise. TSS had not been race tested prior to its introduction like the Polaris Indy trailing arm IFS but Yamaha’s reputation of not bringing a new technology to market until it has been thoroughly tested is well known. While there were no rumors that Yamaha had been working on an IFS performance trail sled, a search of the U.S. patent website revealed Kawasaki and John Deere had also been working on a strut type suspension at the same time.
The Yamaha TSS was advertised as having been inspired by the landing gear used on most aircraft. The “OLEO Strut” was designed to cushion the impacts of landing and dampen vertical oscillations. Yamaha chose TSS over the dual radius rod IFS for three reasons:
1. Eliminate bump steer (ski alignment change as the suspension moves through it travel)
2. Caster and camber change not effected as suspension cycles through travel
3. Less drag in deeper snow with less exposed moving parts
The first TSS design incorporated a nitrogen gas-over-oil shock system, which used 300 psi of nitrogen pressure under a floating piston to control oil cavitation (and the resulting loss of shock dampening) under high speed front suspension travel. The location of the floating piston was exposed to the cooling effect of the snow, which helped keep the nitrogen pressure consistent. Suspension travel was 6” which was nearly double that of a conventional leaf spring suspension at the time.
The early TSS preload could only be adjusted by replacing the shock spring. Not being able to easily adjust the preload for changing conditions limited the TSS performance in the early years. The nitrogen pressure really did not change the preload force and if it was reduced too much there was a chance for oil cavitation. Increase the pressure too high and the free piston friction became a problem.
Steering was through a steering arm connected to a torque (scissor) linkage that attached to a lower end bracket. As the suspension cycled through its travel the scissor linkage would pivot – not deflecting laterally like a trailing arm suspension which created bump steer. The Yamaha steel skis utilized a unique double wall reinforcing as opposed to the open bridge design used by Polaris which could trap snow and ice increasing unsprung weight. The system sounds like a suspension engineer’s dream come true but TSS had its problems also. With the steering and suspension loads handled by the strut itself, there were high loads placed on the sliding strut bushings. Owners report that when cornering hard the strut would resist sliding on these bushings and restrict the vertical movement of the strut. The scissor linkage bearings were also prone to wear causing sloppy steering.
I asked Greg Marier (former Yamaha R&D engineer during the time of the SR-V introduction) on his thoughts of the TSS vs. trailing arm IFS. “The TSS had advantages in going thru snow and the ability to have 100% shock travel along full ski travel, which was a major advantage when it was first developed. However, as the travel increased and the ski stance increased, using struts also meant the hood design had to be much larger than the trailing arm system – that means more weight and greater wind drag.”
Greg added, “As the travel increased, the strut side loads increased and the strut wall thickness had to go up also (adding more weight). Bearing tolerances all along the steering system had to tighten up to control ski movement (especially along the main large bearing located at the bottom of the frame and across the steering scissor), which added more cost. In addition, all vertical TSS systems have the roll center at ground level, whereas the trailing arm allows the designer to have the roll center closer to the center-of-gravity height. The closer the roll center is to the center of gravity the flatter the sled will corner.”
Yamaha offered an anti-roll stabilizer kit for the SR-V that was originally designed by Tim Bender. Bender built 50 kits for the 82/83 race season which included a front end widening kit and stabilizer bar. The production SR-V would not incorporate this kit but several production stabilizer designs were used on future TSS models including the Phazer.
Mono Shock Suspension
Yamaha had been designing innovative track suspensions for years utilizing nitrogen gas charged shocks. This design allowed the shock to be mounted in novel positions that reduced unsprung weight. The lower the unsprung weight the more reactive a suspension is over bumps. The SR-V was built with the same suspension originally designed for the SS440. This new suspension had enough unique features that Yamaha patented the design. Yamaha engineers were looking to increase suspension travel within the confines of the track and not increase the ride height of the snowmobile. The ‘81 SR-V used a 15” x 116” Yokohama rubber track. Yamaha had the shock mounted horizontally and replaced the rear scissor torsion springs with a straight rate coil spring, reducing weight by 10 pounds. Utilizing a crank lever on the rear scissor arm allowed the shock to compress at a higher speed to improve damping.
In real world conditions it soon became evident that the new skid was not adequate for the higher speeds the TSS allowed – up to 15 mph faster was Yamaha’s estimate. This original coil over suspension later evolved into the (rising rate) Pro-Action Link suspension introduced on the 1983 SR-V. Racing again highlighted the need for an improved track suspension to compliment the new TSS front suspension that engineering analysis failed to identify.
Fan Cooling, Reed Valves and Smart Clutching
While chassis /suspension development was high profile entering the 1980’s, engine cooling development to improve performance and reduce noise emissions was also a priority. The industry was using liquid cooling in 1980 on high end trail performance machines. Free air engines were nearing the end of their life cycle as noise regulations and the need for higher power levels was quickly ushering in their demise. Fan cooled engines were still the highest volume engines in service typically producing less than 50hp. Yamaha had built a new reed valve 535cc axial fan cooled twin for the luxury trail sled market in 1979 and that same engine would be de-tuned to 55 hp allowing the SR-V to meet HP regulations to compete in a number of race circuits. The over-square motor was a cylinder reed valve design that was not common in the day but enabled these motors to have excellent bottom and mid range performance.
The Yamaha primary clutch was a flyweight design where by changing the position and quantity of removable rivets the shift characteristics and operating rpm could be changed. This unique tuning capability is still used even today on the YSRC primary clutch used on the Sidewinder!
From Nurturing the Consumer to Sales Leader
The SR-V design would take 2 years before it became a consistent winner on the cross country and snow cross circuits. The 1983 version with a Bender wide front kit and torsion bar in combination with the Pro Action link suspension (finally) ended the dominance of the Polaris Indy. What’s more important is that the SR-V led the way for other manufactures to respond with their own fan cooled IFS models. The SR-V also paved the way for the 1984 Phazer which put Yamaha as the #1 sales leader in the mid eighties.
The tough economic times of the early 80’s combined with low snow in the majority of the Snowbelt across North America was a tough time for manufacturers to invest money in IFS sled development. It was clear that to stay in business, long travel suspension design was the future that had to be invested in. Yamaha had sewn the seeds early on with the Enticer, which a generation of future Yamaha faithful grew up on. They responded by purchasing the Phazer, V-Max, Vector, Apex, Nytro and Sidewinder models of today. In the 1980’s Yamaha was an exciting company with new model introductions coming fast and furious. They believed in the industry when it was at its lowest and rode the wave to its highest. Yamaha faithful are waiting for the next unique Yamaha product that will renew that passion once again.
By Hal Armstrong
SnowTech Canada
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