On Sun, 23 Feb 2003, at around 07:11:18 local time, Greg Rowe
<growe58@hotmail.com> wrote:
>>From: "William Davies" <bill@rarebits4classics.co.uk>
>>There are certainly too many variables to start pulling things apart - only
>>calibrate against known measurrements. At the moment both of your
>>calibration benchmarks are unknown variables, not a good starting point,
>
>I didn't see any mention as to whether you were running stock
>tires; that could have an effect.
Dear All,
I bought a new toy this morning, and have been playing with it (and
other things) earlier this afternoon. I can now confirm the following:
My rev counter is not in need of recalibration - it is certainly much
better than width-of-the-needle accurate, according to a Gunson
electronic rpm tester.
My diff is a standard 3.63:1 UK-spec 1500 diff (18.1/6 turns of the
crankshaft pulley for 10 turns of the rear wheel).
My tyres are standard (or at least I think this is standard) at 155/80
R13. They are running at manufacturer's specified pressures.
This being the case, my speedometer *must* be accurate if it reads 18
mph per 1000 rpm in fourth - is this correct? Have I missed anything?
However, I had to tweak the speedo needle by quite a bit to get it to
read accurately. Even now, it is only absolutely accurate at around
60-70 mph, with accuracy falling off to about +10% at 30 (i.e., when I'm
doing about 1650 rpm in fourth, my speedo reads 33 mph).
> Do you have any measured miles
>on the highways? I checked my speedometer on one of those once
>and is seems to be dead on. The odometer, however is off almost
>5%.
We have very accurate mileage notices on our motorways - I checked the
odometer against a fifty mile stretch of the M5 in Cornwall/Devon last
week and found that it was reading about 8.9% low.
All this being the case, I believe I can draw two conclusions:
The Mazda's speedo is *very* over-optimistic.
My speedo/odo drive gear has too few teeth.
Am I right??
ATB
--
Mike
Ellie - 1963 White Herald 1200 Convertible GA125624 CV
Connie - 1968 Conifer Herald 1200 Saloon GA237511 DL
Carly - 1977 Inca Yellow Spitfire 1500 FH105671
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