What are these models with a serial starting VM

Investigation on these started way back in 2009 and early suggestions pointed towards them being prototypes which was soon quashed when word got out and people started contacting me and providing pictures. As with all my articles, I'm compiling from historical conversations so information can or will be tweaked as time permits

Here's what I do know. Popularity of BMX was rapidly growing in the very late 1970's, especially in the US and Diamond Back was looking for a cost effective way of increasing output and mass producing their up an coming models (more so the frame-sets) which inevitably meant moving away from Jere. This exercise was being driven the strength of the $ which sought them to seek alternative manufacturers in the far east. 

Several companies were investigated but with Japan's techniques and experience in vehicle 'parts' manufacturing, it was Koizumi that was chosen since they already had relationships in the country with various fabrication companies and offered a relationship Diamond Back preferred....(enter the Koizumi/Tange relationship)

By the end of 1978 and early into 1979, design and fabrication had already starting at Koizumi

The new Pro (aka large) was a far cry from the MX and introduced various design changes such as the box section (aka match-box) which replaced the brace, curved brake bridge at the seat-stays and altered dropouts. Diamond cut-outs had been introduced the the forks and the frame-set was also 100% Chromoly compared to the previous Tri-Moly material.

Other noticeable areas to check on these early Pro's were the rear dropout thickness which are approx 1/16" or 2mm, the same went for the forks. The forks also had a different tig weld position on the inside of the dropout where it met the fork leg.

There is also evidence that the geometry followed that of the MX but at some time it was adjusted (this being the angle of the seatpost/headset tubing, fork rake) and mild steel 3mm dropouts replaced the existing Chromoly.

Early Pro's were also stamped differently on the frames (format wise), starting with VM on the inside rear dropout (non drive side), what these two letters referred to I'm not sure and neither did my contacts but it might have referred to Vehicle Manufacturing. It was then followed by numbers (below you can see the list serials I've compiled over the years). The forks were not stamped and I will be adding some pictures at some point of the rear drops and forks.

The numbering format follows a continuing count and was not split into months which Koizumi changed fro January 1980, which also followed their stamping format to include month separation

Known VM serials

VM 00 23

VM 00 64

VM 00156

VM 00164

VM 00390

VM 00431

VM 00455

VM 00471

VM 00524

VM 00547

VM 00605

VM 01257

VM 02346

VM 02400

VM 02489 (3mm)

VM-02973

VM-02895

Last updated 10th April 2023