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Today's topics:
* Speedometer error - 3 messages, 3 authors
http://groups.google.com/group/rec.autos.makers.honda/t/dd0e0cb203486443?hl=en
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TOPIC: Speedometer error
http://groups.google.com/group/rec.autos.makers.honda/t/dd0e0cb203486443?hl=en
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== 1 of 3 ==
Date: Wed, Nov 18 2009 8:05 pm
From: Joe Sixpack
Charles wrote:
> Nasty wrote:
>> My 2000 Accord speedometer is off by about 8 mph according to my gps.
>
> Are the tires currently on the vehicle the same size as those specified by
> Honda?
>
> I did a calculation on my (off-size) tires. Honda specified 195/60 but I'm
> running 195/65. The calculation involves the static loaded radius and the
> rolling circumference. For my configuration the error is 7 percent at 70
> miles per hour. I just add 5 mph to the dashboard reading.
>
> My old Prelude had a recall on my speedometer that I never took advantage
> of. That would have corrected some of the error but I just do a mental
> adjustment and live with it.
10+% is an awful lot of error. You'd need to run several sizes over
before tire diameter accounted for all of it.
See: http://www.miata.net/garage/tirecalc.html
== 2 of 3 ==
Date: Thurs, Nov 19 2009 7:48 am
From: Nasty
Joe Sixpack wrote:
> Charles wrote:
>> Nasty wrote:
>>> My 2000 Accord speedometer is off by about 8 mph according to my gps.
>>
>> Are the tires currently on the vehicle the same size as those
>> specified by Honda?
>>
>> I did a calculation on my (off-size) tires. Honda specified 195/60 but
>> I'm running 195/65. The calculation involves the static loaded radius
>> and the rolling circumference. For my configuration the error is 7
>> percent at 70 miles per hour. I just add 5 mph to the dashboard reading.
>>
>> My old Prelude had a recall on my speedometer that I never took
>> advantage of. That would have corrected some of the error but I just
>> do a mental adjustment and live with it.
>
>
> 10+% is an awful lot of error. You'd need to run several sizes over
> before tire diameter accounted for all of it.
> See: http://www.miata.net/garage/tirecalc.html
>
I'd have to go to 225/65 to compensate with tires.
Isn't there a gear I could replace or are they electronic?
== 3 of 3 ==
Date: Thurs, Nov 19 2009 6:45 pm
From: "Charles"
Nasty wrote:
> I'd have to go to 225/65 to compensate with tires.
> Isn't there a gear I could replace or are they electronic?
Typically, they are electronic although you should confirm that with the
service manual. Honda is not likely to provide you with the schematic for
the speedometer, so you'll have to pull it out and reverse-engineer it. If
you have lived a pure and wholesome life, you'll find a set of switches or
jumpers in there clearly marked with the divider values. Often the design
engineers build in some adjustability for the various tire sizes likely to
be delivered with the vehicle.
On another point, as Joe Sixpack points out, your readings are off more than
the usual amount of a few miles per hour. Is that normal for that model? If
possible, find another vehicle identical to yours and determine whether
_that_ vehicle is off as much. I suspect that yours has another problem.
Usually there are magnets on the drive shaft that pass a reed switch. As the
drive shaft turns, a series of electrical pulses is sent to the speedometer
which counts them and converts that number into miles per hour. Perhaps one
of the magnets is missing or not quite in the right position. Perhaps the
switch or sensor is askew. Maybe there is a defect in the speedometer so
that it is missing some of the incoming pulses.
It wouldn't hurt to confirm the speedometer reading with a measured mile. I
went so far as to borrow a police radar gun to verify my speedometer. If the
GPS, the stopwatch and the radar agree, look at the pulse circuitry.
--
Chuck
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