The Turbo's History

Practice makes Perfect…

By Kurt Tuthill, Senior Moderator here at OS-DB.net, the online home of old school Diamond Backs.

The story of the development of what many see as the ultimate Diamond Back - the Harry Leary Turbo - goes back much further than you might imagine.

1. The grandfather of the Turbo - the “Large”

Legendary Pro racer, Harry “Turbo” Leary joined team Diamond Back in early 1980. At that time Diamond Back’s premium range comprised three frames; The Large, the Standard and the Small. The Large and the Standard were available as complete bikes, while the Small was only available as a kit. Frames and forks were available in three finishes: chrome, metallic red or metallic blue.

The grandfather of the Turbo was the Large frame. These frames originated in 1979 when DB production began in Japan and continued to be made through till mid 1981. They were an attractive, light and well made frame in full cro-mo. At the time Harry joined DB, they featured 1/8” thick dropouts, a comparatively laid back seat tube angle of 68* and one of the sharpest steering head angles around, at 75*. Top tube length was a roomy (for the time) 19 ¼”.

The forks fitted to the DB range at the time featured a stylish diamond cut-out, safety washer holes and a distinctive Speedo-inspired dual dropout design, allowing riders to select either a leading axle or centreline axle position. With such a sharp steering angle already, the centreline axle position was arguably superfluous - and as we’ll see, DB was soon to drop it from production.

In the January 1981 Bicycle Motocross Action (BMXA) test of the Large, changes were already in the wind, with DB Pros Harry Leary and Pete Loncarevich at the time riding new prototype frames featuring revised geometry and single dropout forks. At the time, DB’s reported plan was to steepen the seat tube angle by ¼” to improve starting geometry. In a number of pictures of Harry Leary taken around this time you can see that he is running with the saddle clamping mechanism reversed, to simulate the effect of a steeper seat tube angle.

Harry really was heavily involved in testing changes to the DB frames, and along with Team Manager Sandy Finkelman, was the driving force in the development of the bike which was to come to bear his name.

2. The father of the Turbo - the “Senior Pro”

The next generational change came about in June 1981. The entire eight rider DB team had been involved in development of a new range, based on the previous Large, Standard and Small frames. Along with refined geometry, the range was renamed; Senior Pro, Medium Pro and Mini Pro.

At the time, the Pro frames were only available from Diamond Back as kits, with a complete Pro bike not due until 1982. Many dealers did however assemble and sell complete bikes to meet demand. The Senior Pro continued to be sold as a frameset and as a complete well into 1983, before being replaced in the DB line-up by the Formula 1.

When released, the differences between the Large and the Senior Pro were far more extensive than planned back in late 1980, a result of thorough testing and feedback by Harry Leary and the rest of the team.

The dropouts were now 1/16” thick. The top tube length was 19”. The bottom bracket was lowered by ½” to drop the centre of gravity. The BB was also moved forward by ½”, creating a longer rear end and improved traction. The seat tube was brought forward ¾” to an angle of 73*. The sharp steering of the Large was slowed very slightly by de-steepening the head tube angle to 74*. Finally, the forks were all single axle and though still featuring the stylish diamond cut out, the safety washer hole was thankfully omitted.

As was very much the theme at DB at the time, development continued. In the December 1981 BMXA test of the Senior Pro it was mentioned that Diamond Back were experimenting with “a new refinement of rear end geometry involving power-to-the-ground leverage ratios.”

At the time, little did anyone suspect from this hint what a surprising and distinctive bike was in the wings for 1982.

3. The Wild Child - The Turbo (still a work in progress...)

In mid-1982 the Diamond Back Turbo was released. The bike caused a sensation on release and remains a much coveted and highly collectable vintage BMX today. The Turbo was an elite machine with top quality componentry, including an exquisite purpose built three piece cro-mo crankset manufactured for DB by Sugino . The Turbo wore a high (for the time) price tag of $495 USD.

The frame geometry of the initial batch of Turbos was identical to the existing Senior Pro, but the finish was nothing short of exotic. That finish was an exclusive “Turbo Smoke” black chrome.

The September 1982 BMXA test of the Turbo explained: “The black chrome look took some doing. Diamond Back had introduced chrome frames with black components in 1980 and seen them become instant faves. They decided to reverse the look for 1982. Black, but a different kind of black, with chrome components. Seven months and twelve prototypes later they had it. A high quality paint, applied by a mysterious process over the chrome-plated frame and then clear-poly coated. Far out without a doubt.“

In reality the finish was the result of significant testing and was created using six coats of blue-black paint and four coats of clear! Decals were printed in chrome on a clear background. Although undoubtedly stunning to look at, Turbo Smoke has not lasted the test of time - scratching and chipping very easily. Original examples in good condition are very scarce and attract prices many times higher than the original cost of admission.

Notable BMX collector, Jeff Haney, knew DB Team manager Sandy Finkelman well and from their many conversations, recalls the following regarding the development of the Turbo and the Turbo Smoke coating; “In the beginning they were sending Turbos in all colors. Some black, some dark, some light, even some in chrome. They wanted him to evaluate, test and give feedback on what color it should be. The testing was very good. Harry loved the frame as it was already a proven design. So when they got the color right they started production. He said it wasn’t until they were a few races in that Harry discovered that with the dropouts and rear end like they were, he was slipping the rear wheel out of the gate.”

As we will see, development of the Turbo was still ongoing…

4. The Turbo “Leverage Ratio” dropouts

As you will recall, back in 1981, Diamond Back were experimenting with “rear end geometry involving power to the ground leverage ratios.”

The initial batch of Turbos (thought to be those with serial numbers beginning 2F) were identical in geometry to the existing Senior Pros. Soon after release however, following Harry’s experience with rear wheel slip, a refinement was made.

Jeff Haney continues Sandy’s story; “This is what led to the redesign of the dropouts. With the change it helped keep the rear tire from slipping.”

The September 1982 BMXA refers to the improved geometry; ’They modified the Pro frame (tested in the December 1981 issue) with a rear section leverage concept that was two years in development.” See below for photographs detailing the differences.

Below is a photograph of a genuine 2F serial Turbo dropout. As you can see, the bottom of the dropout runs parallel with the chain stay.



Below is a photograph of a genuine 2J serial Turbo with “leverage ratio“ dropout. You can clearly see that the bottom of the dropout drops noticeably towards the straightedge. The angle of the dropout acts as a lever to improve traction.



Work is continuing at OS-DB.net to determine exactly when the dropout change took effect. It could be as early as 2G. What is clear is that the new dropout geometry was also introduced to the Senior Pro frame, very likely at the same time. The Senior Pro continued to be manufactured and sold alongside the Turbo, generally as a frame kit, well into 1983.

This is another clear example of Diamond Back’s ongoing testing and refinement of their product and is a tribute to the commitment of Sandy Finkelman and Harry Leary, not to mention the responsiveness of the Koizumi factory in Japan, who manufactured both Diamond Back and Kuwahara frames.

I’ll leave the last word on the Mark 1 Turbo to Jeff Haney;

“Harry really put them through the ringer so you can feel good about buying a Turbo knowing that it is truly battle tested to be one of the best to ever ride.“

Coming up in the future, we delve into the ongoing development of the small diamond gusset 1984 Mark 2 Turbo and the amazing history of the Turbo crankset.

Kurt Tuthill, September 2008.

Sources:
Bicycle Motocross Action, January 1981. Bicycle Motocross Action, December 1981. BMX Action, September 1982. BMX Torque, January 1983. OS-DB.net. Email from Jeff Haney, September 2008.

I’d like to acknowledge the people who have either inspired or assisted me in the creation of this brief history. All errors and omissions are mine. Firstly of course, the late Sandy Finkelman as well as legendary BMX racer Harry “Turbo” Leary. The rest of the DB team of 1982: Jimmy Smith, Jason Wharton, Mike Horton, Doug Davis, John Copeland, Rich Farside, Pete Loncarevich and Eddy King. I couldn’t fail to mention the great Bob Osborn, Editor of the mighty BMX Action magazine. Mark “Sparky”, creator of OS-DB.net and DB collector Lew Schramm were great helps over a long period of time. It was a pleasure to receive the valuable input of legendary BMX collector Jeff Haney. Finally, thankyou Tim Jenkins who first inspired me, 27 years ago, to get my own DB...