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  #1  
Old 03-24-2006, 04:38 AM
LarryIII LarryIII is offline
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Misc. Ramblings----Optimistic Speedo

Many of you who live in the Phila. area know that construction season has started on the Blue Route (I-476). I take that road every day to work in SVXY. On the northbound side, they have blocked off the right hand lane so we go from 3 to 2 lanes in a 'cattle chute'. The speed limt is 45 mpg thru this zone and there is one of those radar signs which flashes your speed just as you enter the 'cattle chute'. I usually pass it around 5:00 AM and the road is emty. I have been using it the last 2 weeks to test my speedometer. It seems that my speedo in SVXY is 2 mph optimistic. When I am exactly at 50 mph the sign flashes 48. Like at 70, the sign flashes 68. This morning I was at 60 and the sign flashed 58. I always thought that speed error is a fixed percentage so that as you go faster the variance increases. Either the sign is off or my speedo is off. Next week I'll increase speed to 80, 85, then 90 mph, conditions permitting. I'll report back my findings. I just hope that they don't put cameras on the the sign.
PS: SVXY has stock rims ad tires.
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  #2  
Old 03-24-2006, 04:57 AM
Bipa
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We've got those kind of "check your speed" signs over here. My SVX consistently thinks it is going about 4 km faster than the sign says I'm going. I've always thought of it as just another "safety feature", which in this case helps protect my wallet!
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  #3  
Old 03-24-2006, 05:15 AM
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b3lha b3lha is offline
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I think the percentage error idea goes back to the days of cable-driven speedos.

Our speedo is driven by a digital electronic signal and could potentially measure your speed accurate to a fraction of a mph. IMHO the only reason the speedo reads optimistically is because it has been designed to do so. I think that a constant error would be easier to engineer than a percentage error because it's just a matter of moving all the numbers back a little on the scale.

When I drive through those signs I find that my reads 5mph over and it's a constant 5mph, not a percentage.
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  #4  
Old 03-24-2006, 08:02 AM
PDSides PDSides is offline
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Larry, I don't think FHI ever intended to alter the SVX's speedometer reading for any reason. Any discrepancy is, in my opinion, the result of unintended variables in the system. A car's speedometer need not be totally accurate, but is intended to display the car's approximate speed, within a targeted and acceptable range. Even our Texas Highway Patrol cars are prone to have a variance in their speedometers and for that reason they are equipped with a more accurate instrument that can be easily re-calibrated for conditions. The SVX speedometer is no better and no worse than any other, on average.
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  #5  
Old 03-24-2006, 10:33 AM
Clydesvx Clydesvx is offline
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"Our speedo is driven by a digital electronic signal"

So this must be why I can't go throught an automatic car wash that has an under carriage wash on days when the temperature is below freezing!! Every time I do my speedometer stops working until the temperature goes above freezing for a few days. Hey, that must mean I really have over 264,000 miles on my '92!!
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  #6  
Old 03-24-2006, 12:19 PM
ItsPeteReally ItsPeteReally is offline
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Quote:
Originally Posted by b3lha
I think the percentage error idea goes back to the days of cable-driven speedos.

Our speedo is driven by a digital electronic signal and could potentially measure your speed accurate to a fraction of a mph. IMHO the only reason the speedo reads optimistically is because it has been designed to do so. I think that a constant error would be easier to engineer than a percentage error because it's just a matter of moving all the numbers back a little on the scale.

When I drive through those signs I find that my reads 5mph over and it's a constant 5mph, not a percentage.
I concur, there does appear to be a consistent 5mph. measurement error. I wonder if this error is carried over into distance measurement too. If it is, then the fuel consumption might turn out to be something that I'd rather not know about
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  #7  
Old 03-24-2006, 01:19 PM
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b3lha b3lha is offline
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Quote:
Originally Posted by Clydesvx
"Our speedo is driven by a digital electronic signal"

So this must be why I can't go throught an automatic car wash that has an under carriage wash on days when the temperature is below freezing!! Every time I do my speedometer stops working until the temperature goes above freezing for a few days. Hey, that must mean I really have over 264,000 miles on my '92!!
I can't imagine why you would want to cover the underside of your car with ice.

Maybe you should check the insulation on the cable to the speed sensor.
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  #8  
Old 03-24-2006, 01:44 PM
Clydesvx Clydesvx is offline
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Covering the underside with ice reduces friction!!!
Just kidding.
I'll start by checking the insulation. This is my 92's third transmission. No telling what it looks like under there.
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  #9  
Old 03-30-2006, 05:11 AM
LarryIII LarryIII is offline
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After a long time parked, I finally took out the 'garage queen' SVXes. Yesterday I drove SUBYDOO to work. Coming home on the Blue Route, last night, the radar sign flashed 25 mph and the speedo read 20 mph ( notice, the slow crawl speeds going home). That surrised me. The only thing that is not stock is the tire size. The tire size on the car is the '92-'96 SVX stock SVX size while the '97 stock size is slightly taller and narrower. I think it's 215-16-55 series, I can't remember the exact numbers.

This morning, I took in PEARLY, '94 SVX. The sign flashed 65 mph while the speedo indicated 70 mph. No surprises here. There are 17" rims and tires on PEARLY.

All this tells me, is that I better put the good radar detector in SUBYDOO and the cheap ones in the other SVXes.
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Larry III & The Beautiful Naviguesser
'19 Tungsten Pearl Outback 3.6R Ltd...."AISHA"
'08 Harvest Gold Outback 3.0L. L. L. Bean...."AIJOU"
'07 Gray Diamond Pearl Outback XT Ltd..."AH SO"
'05 White Pearl & Silver BAJA Turbo..."AH HA"
'97 Bordeaux Pearl SVX LSi..."SUBYDOO"
'94 White Pearl SVX LSi..."PEARLY"
'92 White Pearl SVX LSL w/touring pkg..."SVXY"
'92 Teal SVX LSL w/touring pkg..."ALCYONE"
'96 Polo Green LSi ... "MIDORI"
'00 Black Dodge VIPER RT-10... "VINNIE"

Engineers do it with precision.
English teachers are novel lovers.

Home: larrysingeriii@comcast.net


SVX FEVER, CATCH IT AT A MEET NEAR YOU !!

Last edited by LarryIII; 03-30-2006 at 05:13 AM.
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