The first Sherpa T (M10) was unveiled to the public at a bike show in the UK in late 1964 and was soon a big hit with riders keen to win after Sammy Miller and many others showed it was a winner and easier to ride than the British bikes available at the time. Development continued at Bultaco and one of the big things happening there was the San Antonio 2 motor which was quite different mechanically to the previous (4 speed) motor. The M27 Sherpa T was released in 1967 with many refinements, the main being the new 5 speed motor and a longer wheelbase. The next year saw the first series of the M49 and the main difference to the M27 was that the tank was made much slimmer for improved rider ergonomics. There were two more in the M49 series, with the main improvements being the removal of the central frame tube under the motor, and a minor relocation of the top shockie mounts. This takes us to 1971, and the world had seen that Mick Andrews had been doing extremely well in top level competition on an OSSA development bike for a few years, and many riders eagerly awaited a bike from OSSA to compete with the Bultaco Sherpa T (since 1965) and Montesa Cota 247 (since 1968). That chance came in 1971 when OSSA released the Mk1 MAR.
We have seen 38 years of bike development since then so have a good look at the photos and try to see what people saw when the OSSA first appeared. Compared with the M49, the OSSA frame was much simpler and neater and many things like the side stand, kickstart, exhaust and brake arms were better tucked-in.
Of course, what you see in the photos is not two 1971 bikes, but a 1975 OSSA and a 1968 Bultaco. A 1971 Bultaco would have only side tubes under the engine and not the central tube as well as seen on my bike, while a 1971 OSSA is almost mechanically identical to the bike in the photo. However it is reasonably fair to compare how they feel to ride.
Context
When these bikes were new, trials was nothing like what it is nowadays. Back then, continuous forward motion was required because a momentary stop within a section meant failure of that section. Today, the rules are different and stopping is allowed and is often used to regain balance in turns and before obstacles. Because of the rules being the way they were, these bikes would not have seen section difficulty anything like what they would be ridden over at a modern trial, even in Twinshock class.
Motors
The 1968 Bultaco has motor performance that is very well suited to the way sections were set and trials were run in the 1960s. It has a very strong flywheel effect, and relatively strong performance in the midrange. People never pulled in the clutch in a section, and sections were much more open and straight than today. The bike was developed for muddy climbs and ruts and long uphill runs following the beds of rocky mountain streams. Nowadays, this motor requires the rider to maintain momentum at all costs. If the RPM gets below a certain point, throttle response suddenly gets very weak and control is lost. It feels to me like a non-reed trailbike motor that has had flywheel weight added.
The OSSA motor is at the other end of the performance spectrum. It has strong throttle response right down to extremely low RPM and this continues right through the rev range. Flywheel effect is similar to the Bultaco but the OSSA motor is so strong at low RPM that the flywheel effect never becomes an issue under accelleration, but remains there for when you need it in mud and on slippery rocks and logs. The response and peformance of the OSSA motor makes it well suited to modern sections and is complemented by having a light and relatively rapid clutch engagement. The Bultaco also has a light clutch action, but is slow to engage, which makes it poor for stop-start riding techniques.
Suspension, steering, handling
Both have Betor-designed forks and as such have a similar damping action (state of the art for the time). The OSSA has a more progressive springing effect which works well everywhere while the Sherpa tends to pack down at the front on steep downhills, which sometimes causes bottoming (and loss of traction).
The original shockies on both bikes were close to being the best available at the time, but neither was anything like the performance of good shocks available today. I've ridden the OSSA with its original Betor shockies and the springs feel hopelessly soft, but damping is in the ballpark. Maybe the springs have sagged. I haven't tried original shockies on the Bultaco but know that they had thin shafts that bent very easily.
They both are quite limited in ground clearance under the motor, so on either, the rider has to take care to take a line that avoids grounding out. The Bultaco is a bit worse in that having a centre frame tube, it tends to fall over if the bike rests on a log while the OSSA will stay more upright.
The steering is the main difference between them in the handling department. The Bultaco has steering that lies at the slow end of the spectrum, so corrections take more room to achieve. It also has a longer wheelbase than the OSSA so the turning circle is slightly bigger. While it has slow steering, the Bultaco has a wonderfully refined feeling to the steering, like it is on rails. Best results come from careful management of the front wheel path. The rear wheel seems to follow without conscious attention. The Sherpa steering is very responsive, light and well balanced in all but the most extreme of turns.
The OSSA steering is at the quick end of the spectrum, similar to a TY250 Yamaha, and has a wheelbase on the short end of the spectrum. This makes it a great tool for modern sections, and is also quite at home in rocky stream beds, but you always seem to need to be conscious of where the rear wheel is going to go, and work to ensure it follows. The steering effort is at the heavy end of the spectrum for bikes of the era, which is a bit contra-intuitive, because the front comes up very easily when required. The front can be placed with great precision, due to the quick steering, light front end and responsive motor.
Brakes
Both have an unjustified reputation for having poor brakes but in reality they both have brakes that are as good as the amount of effort put into sorting them. Having said that, many other bikes require less effort to sort out.
Which one gets ridden most? Well they both get about the same (not much). Most of the trials I ride are of a competitive nature and Twinshock class is open to bikes made before 1987 so both these bikes would be hopelessly outclassed by the likes of Fantics, SWMs, Honda TLRs etc which were made in the 1980s. Because of this, I tend to ride the OSSA or Bultaco when the event is of the type where the older bikes are featured and appreciated, like the Brooweena 2 day, and the Twinshock Masters at Conondale.
Theres probably something I've forgotten to say about the bikes so if I think of anything else or if someone asks, I'll write some more.
Photos to follow - there is some problem with my photo resizing tonight.
