Oldairhead 

I've got this "known to be" 1992 RB-1 road bike on my stand right now. I've got the catalog for that year and it all checks out except for one thing. The frame number does not match the resources I have seen for Bridgestone bikes. Maybe I didn't get the right resource to consult. Any thoughts?

IAmSam

Yeah that's a '92 paintjob and yeah starting with an X like your number does throws all the B'stone SN decoders stating A-L tells you the month it was made out of whack. My '93 has 7 digits after the letter to tell the day it was made and such. So yours differs from the norm there too. But I bet you've heard this all before. Have you been to the Bridgestone Owners Bunch on Facebook? There's a couple guys there who know this SN stuff in and out. Good luck...

T-Mar

While Grant Peterson is on record as stating that the alpha characters, represent months, I believe that they are actually fortnights. That would make make the frame manufacture during weeks 47-48 of 1991, which is certainly late enough in the calendar year to be a 1992 model.

Oldairhead 

So far the experts over at the BOB group on Facebook agree that it was a "built in 91" as a 92 model but are confused by the rest of the number. Here is an excerpt.

"The 1 means it was made in 1991. No doubt it’s a 92 model but it was likely made in late 91. The first letter is usually an A-L which signifies the month however there were frames stamped X or M and I’ve never seen an explanation."

If the X means it is a custom order then that likely puts the rest of the number as a non standard method, except for the second digit (1) which indicates 1991.

rjhammett

The '92 RB-1 I used to own had a serial number of X124108.

Oldairhead 

Was your bike a custom order?

T-Mar

I've been collecting Bridgestone serial numbers for quite some time. I've seen a lot letters beyond L, besides M and X, probably around 18 different letters in total and about 8 beyond L. The first numeral does appear to be the calendar year indcator. That would make the letter prefix a fortnight indicator. The remaining number string, typically 5 characters, is likely a sequential frame numbering for the fortnight.

It's possible that at one time the letter prefix was a month indcator but they may have converted to a fortnight indicator once the monthly volume started exceeding 99,999 frames.

Oldairhead 

Thanks @T-Mar, I will consider the mystery solved.

rjhammett

I was not the original owner so I don’t know.

bikingshearer 

I am not aware that Bridgestone ever made customs. The 1992 catalog discussion of the RB-1 touts their geometry, but certainly doesn't say anything about doing custom builds. It does say you can take their geometry to a custom builder if you want to. FWIW, that sounds to me like customs were not on the menu, at least not for 1992..

And as usual, my opinion is worth exactly what you are paying for it . . . .

Oldairhead 

Okay, here is a follow up. I inquired to the folks at Rivendell to see if someone would ask the "big guy" if he could shed light on this frame number. This is the response that I received today.

An "X" means it was part of the Fall production run.

I suspect that production during the fall and into the holidays was a little sporadic and work that was started in one month may have carried over into the next so they just put them into an X batch. This might lend credibility to the letter = month version as explained by GP in an earlier document as opposed to the fortnight theory. @T-Mar

Cheers!

Hummer

That is quite an assumption that the letter is a fortnight indicator. Do you have any other support for this assumption?

The fact that more than 12 different letters have been used does not necessarily mean that the time period for the letter is a fortnight

I have catalogued more than 140 Bridgestone serial numbers, with a broader range of letters for the time period indicator, 21 different letters and 10 beyond the letter L. The distribution of the letters in may data show that most frequent letters found are X and letters before the letter M. I would not assume that the letter is a fortnight indicator.

There is a blog which proposes a decoding of Bridgestone serial numbers. The writer of this blog, Demo Tori-san, is a Bridgestone bicycle owner in Japan.

Here are a link to the blog and another to a google translation of part of the blog.

BS frame No.

Bridgestone serial numbers decoded.


From the findings in the blog from Japan, the X is for the month of September. X was used for September instead of the letter "I".
The findings are consistent with Grant Peterson.

Demo Tori-san also researched the Bridgestone custom order bicycles and the findings are in this post:

BS frame No. (Granvelo)

Oldairhead 

Wow, amazing research! Educated guesses are great but confirmation is even better. Your rationale seems to be confirmed by Grant Peterson's statement (to me) that X was a fall production date. Along with the fact that letters I and O could easily be confused for digits and so were replaced with other characters. This seems to be a very plausible explanation. Along with the fortnight theory this bike was built in the fall of 1991, end of story. Thanks again to all!

nlerner

I have no dog in this fight that you seem to continually picking with T-Mar (other than finding it quite annoying), but I do have to say making any claims from a sample of 140 out of the 10s if not 100s of thousands of frames Bridgestone produced is in the realm of wishful thinking, not statistical evidence. I mean, you could be right, but that would be because you got lucky, not as a result of your analytical method.