"Like to try a couple of Penthouse pets?" said the man.

Now offers like that don't occur every day of the week, even to a bike journalist. So with visions of grappling with a pair of busty beauties, I agreed.

Then came the catch. "Actually they're motorcycles." He added, realising I had jumped to all sorts of wicked conclusions. "A couple of BMW-Gus Kuhn racers in fact." My face lit up again - now that's a bit more like it, I thought.

Now if your idea of a BMW is a rather pedestrian touring motor cycle being pottered through the lanes by elderly enthusiasts, think again. They are very fast, durable, light and handle remarkably well, as has been shown over the years by Hans-Otto Butenuth in the Isle of Man and by the works machines at the Bol d'Or in France .

Gus Kuhn Motors, the South London dealers, have been entering Nortons in production and F750 racing for several years, but now they have switched over completely to Penthouse magazine-supported BMWs, initially in endurance races and eventually with a very special racer Gary Green and Dave Potter, who last week finished a fine second on the R90S in the Le Mans 1,000 km race, are spearheading the Gus Kuhn team of riders.

The plan started when Gus Kuhn boss Vincent Davey met the top brass at BMW in Munich . "I got to know BMW's Technical Director, Von der Marwitz, and he showed an interest in racing," he said.

The factory have been producing the occasional works racer and are very successful with them. What this means for Gus Kuhn is that they can enjoy the spin-off from the factory's experience. Several parts have found their way to the Kuhn workshops as well as one of the complete machines for cannibalisation.

One feature of the whole effort has been the riders' enthusiasm. They have all been agreed on the fact that the big Bee-Emms are among the most relaxing and forgiving racers on the tracks today.

But I wouldn't have thought so from the moment Dave Sleat fired up the production racer at Brands Hatch. Otherwise the same as the production bike, the long-distance racer has a megaphone exhaust and bigger inlet and exhaust valves.

Dave pulled the plunger ignition switch mounted on the new alloy top yoke and pressed the starter button. The silencers were from the old /5 series but the sound was certainly very un-Bee-Emmish.

More like a Rennsport, it had an evocative rasp, and out on the track it became immediately obvious that there was more to this BMW than met the eye. Thanks to the lighter flywheel and no air filters, the throttle response was immediate. The revs screen and crash with a blood-curdling blare on the overrun.

The handling is vastly changed as well. With a low riding position you fit into the bike comfortably when you're flat on the 5½ gallon Sports tank. But there is none of the bobbing about normally associated with the long-action standard suspension. The bike sticks dead on line and, thanks to the increased ground clearance as a result of using one inch longer top mounts for the rear suspension and modified internals in the front forks, you can crank it over to fantastic yet safe lean angles.

Even so, the tyres, a K81 front and the new K91 endurance rear cover, work very well on the BMW and at the tight Druids hairpin it was still possible to touch the rocker box covers.

Riding the flat twin is more akin to riding an old Manx Norton or Matchless G50. It still weighs a fair amount, so you have to set it up properly on the right line. Nevertheless, there is still some room for slight trajectory modifications.

What you must get right on the BMW however, is the gear changing and braking. The gear-lever is swopped to the right, one up and four down in the classic style, and perfect for easy changing up when you're really cranked over. Contrary to what you'd expect, the action is very slick, mainly as Brands Hatch requires only the top four ratios.

Brakes are standard R90S and perfect. The rear is still the drum unit but, because of the weight of the drive unit, it is necessary to co-ordinate smooth changing down and braking for a corner otherwise the rear wheel chatters badly. And if that starts there's no stopping it.

Otherwise the bike is typically BMW: smooth, plush and secure. It wriggled only on hard acceleration coming out of Clearways and even then that was only very slight. Remarkably, the gearing was bog-standard R90S, a fraction on the high side, but the bike was flying up to well over 115 mph in fourth with 7,500 rpm showing on the Krober rev counter.

The engines rev up to 8,000 rpm and then cut out with valve bounce. Trouble was, you'd find yourself coming quicker and quicker out of corners thinking there was plenty to come from the motor. Then it would cut out, as there was no indication from the super smooth engine that it was being taxed.

After a dozen or so laps, I got down to a fraction over a minute for the short circuit, which pleased me immensely as Martin Sharpe had earlier clocked 57s, giving an indication of the potential of the bikes. Shame was that the pukka megaphoned racer hit a gearbox snag and the test had to be curtailed.

But it's great to see some new blood in the production class.