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View Full Version : Chronometric speedo question...



bthompson
04-11-2010, 01:10 PM
I'm puzzling around with a project, and mebbe some of you bike guys could help me out.

I'm thinking of re-doing the dash in my Midget, with a more complete range of Smiths gauges. Why? I dunno...just for a change of pace. Getting tired of staring at the same four gauges all the time, and thought I'd try for a "period-customized" look.

Considering putting in a chronometric speedo. Again, the "why" is just 'cuz I think they're neat. Trouble is, I don't know exactly how they're calibrated, hooked 2:1 into the back wheel and all. With the magnetic speedos, they tell you the revs per mile right on the face. (Mine's 1000 rev/mile, so I have to match that somehow) How many revs per mile are chronometrics? Any way to tell just by looking at them?

Any info you can throw at me would be appreciated!

SilentUnicorn
04-11-2010, 05:39 PM
cant help you- but here is some info i found on the web.

http://velobanjogent.blogspot.com/2008/03/smiths-chronometric-speedometer-and_21.html

http://archives.jampot.dk/Technical/Speedo/Smiths_Speedo_restoration.pdf

bthompson
04-13-2010, 12:21 PM
Hey, SU; I didn't know you had bikes too. Good links, they definitely reinforce the "I gotta have one" vibe. Neither one of them say anything about how many revs per mile they register, though. :confuse:

<span style="color: #CC33CC"> <span style="font-weight: bold">--edit--</span>the magic of Google reveals some clues. </span>http://www.bmh.com.au/norton/index.php?id=data says: <div class="ubbcode-block"><div class="ubbcode-header">Quote:]The Smith's chronometric speedometer on my ES2s was a 85mph version...The speedo drive must turn at the ratio of 2:1....The drive must turn 1600 revolutions per mile therefore with an accurate drill at 800 rpm the speedo should register 30mph....[/QUOTE]
and from http://www.scooteristscene.com/news/Speedometer-Notes :
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]The D shaped unit...was offered in 55, 65 and 70mph versions...rated at either 1000 or 1600 revolutions per mile...[/QUOTE]
and most tellingly from http://www.ajs-matchless.com/article_read.asp?id=13 :
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]On the speedometer saga...The cable rpm at 60 mph is marked on the dial, <span style="color: #FF0000"><span style="font-style: italic">(unmarked dials are 1600)</span></span> ... [/QUOTE]
So I think I have my answer. If I'm off base, someone let me know before it's too late!!