Signing Back On 2010 Itinerary (or How To Calibrate Speedo)

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Amskeptic
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Signing Back On 2010 Itinerary (or How To Calibrate Speedo)

Post by Amskeptic » Sun Nov 07, 2010 5:04 pm

See, ya just can't be tidy about it when you are subject to crazy ideas.

I am in Katy Texas, happily warming up in the midday sunshine [last night was some sort of crazy frost (!?) in the bayou outside of Boca Raton Louisiana] for the brief few hours allowed by the stupid tilt of the Earth away from my sunshine.

As I was driving along I-10 at 75mph, I thought "no . . . they can't all be in such a stupid hurry?" so I timed my progress against several mileposts. This required algebra, by the way.

If a mile goes by in a minute at 60mph, how many seconds does a mile go by at 70mph?

Well, my rusty brain was in no mood to figure this out, but I had to.
So what I did in my head was to multiply 5280 feet by 60 (316,800).
That is how many feet you drive in an hour at 60 mph.
Then I multiplied 5280 by 70 (369,600).
Now, if 60mph is 88 feet per second, you can check by multiplying it times 60, and there is your mile.
OK.
But I wanted to know exactly how many seconds it would take to travel one mile at 70mph.
So 369,600/60/60/60 is 102.6666666 feet per second at 70 mph. Excellent says I, let's divide 5280 by 102.6666666,
and I get 51 and a half seconds.

Well. The BobD apparently had the famous VW Bus weak speedometer hairspring, because it took almost an indicated 65mph to get my mileposts at a minute. It took a good 75mph plus a little more to get a true 52 seconds between mileposts. And since mileposts are driven in at convenient-for-the-contractor spots, I had to quintuple-check my indicated speeds for many miles on end.

Thus it was that I found myself once more on a dirt path off the interstate with my poor car in pieces once again:

Image

Removed the gauge cluster from the instrument binnacle and carefully rotated the speedometer needle drum to an indicated 75 mph:

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Made a sharpie marker stripe from the speedometer needle drum to the stationary surrounding metal with the needle indicating exactly 75mph:

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Twisted the needle head on the spindle carefully yet firmly CCW to 70mph:

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Reassembled the . . . no wait!
Detour! Brake warning light was all pale and pinkishly irritating:

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Removed warning light assembly and disassembled:

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Hit the inside surface of the brake warning lamp lens with a GumOut-thinned coat of dipstick red fingernail polish:

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Very nice, glows with an authoritative red now!

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OK, so I reassembled the instrument cluster (no more little lint speck from Tyler TX September in speedo, yay!) and clocked myself between mileposts from east of Houston to Katy Texas. At an indicated 60 mph, the mile markers are showing up consistently at exactly one minute.
That is how I calibrate my speedometer.

I am sorry to report that this car which I thought was so fleet of foot was actually being optimistic with those quick hits of 30 mph in 2nd and pulls to 55-60 in 3rd gear and effortless cruising at 75. Noooooo, it gets a little winded at those numbers with the recalibrated speedometer, but at least my fellow motorists don't seem so frenetic now!
ColinToIrvineCaliforn-I-A
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 121,400 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 92,435 miles

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Re: Signing Back On 2010 Itinerary (or How To Calibrate Spee

Post by glasseye » Sun Nov 07, 2010 5:50 pm

Amskeptic wrote:...
If a mile goes by in a minute at 60mph, how many seconds does a mile go by at 70mph?
Reminds me of the time droning along between Alamagordo and Albuquerque when I decided to calculate how long it took the Asstro to drink a regular coke can's worth of fuel.

About ten minutes, if I recall correctly.

By the way, the defense rests on the photography kidding. Superb work. :cheers: Macro, even.
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Post by vwlover77 » Sun Nov 07, 2010 6:21 pm

I've been wanting to adjust my speedo too but didn't know how. Thank you!! I've checked mine with a GPS to get a true speed indication, and like yours, it reads 5-7 mph high. I can't wait to get home to try this!

(I'm in your home state to visit Cornell University with my daughter tomorrow!)
Don

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"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Re: Signing Back On 2010 Itinerary (or How To Calibrate Spee

Post by Westy78 » Sun Nov 07, 2010 6:33 pm

Amskeptic wrote:
Image
Is that a bit of dust on the dash? For shame. :geek:

I've found my speedo to be 3-4mph fast via GPS. Seems to be exponential as speed increases.
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satchmo
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Post by satchmo » Sun Nov 07, 2010 6:50 pm

What do you expect from a speedometer that, sitting stone cold still, says you are going 10mph!

Tim
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First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Post by bajaman72 » Mon Nov 08, 2010 7:20 am

Uh.. what are you doing with nail polish?? :blackeye: looks beautiful though.

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Post by sped372 » Mon Nov 08, 2010 7:28 am

Hmmm. I've gotten pretty used to cruising at an apparent 70mph to be actually going 57. I think my brain rewired itself. Nice to know you can adjust it though.

How do other speeds measure up now? Does it seem to have worked fairly proportional throughout the entire range? Time to find one of those traffic/speed measuring signs.
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1984 Westfalia - 1.9 WBX

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whc03grady
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Post by whc03grady » Mon Nov 08, 2010 9:59 am

Your formulation is needlessly complicated. Just remember that distance=rate times time (great Pixies song, incidentally), and flip around the numbers as necessary.

Okay, maybe that's complicated too. Buy one of these instead:
http://shop.nordstrom.com/S/3092854?cm_ ... erralID=NA
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Post by sped372 » Mon Nov 08, 2010 10:12 am

Just remember that distance=rate times time
I always liked the little triangle memory device, cover up the one you want to solve for and use the spatial relationship of the other two to help you get there... here's a writeup I found after a quick search:

http://www.bbc.co.uk/scotland/learning/ ... rev1.shtml

Make sure you keep track of units! Man, I sound like a teacher.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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Post by BellePlaine » Mon Nov 08, 2010 10:26 am

Now that your speedo is correct at 70 MPH, are you confident that it is correct at 30 MPH? Did you make a static adjustment on a dynamic spring system?
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Post by dtrumbo » Mon Nov 08, 2010 10:31 am

sped372 wrote:How do other speeds measure up now? Does it seem to have worked fairly proportional throughout the entire range? Time to find one of those traffic/speed measuring signs.
The speedometer in my Beetle is very non-linear. At indicated 37mph, I'm really only traveling 25mph. However, indicated 60mph is spot on. GPS and the neighborhood traffic speed signs are in lockstep.
- Dick

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... as it turns out, it was the coil!

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Post by Hippie » Mon Nov 08, 2010 5:10 pm

You could just buy bigger tires.
Nice job with the brake light thingy

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Post by Amskeptic » Tue Nov 09, 2010 7:02 pm

I am in El Paso tonight, briefly. I am planning to drive all night because the night time temperatures look sleeplessly chilly to me as I traverse the root of the Rockies.

Needlessly complicated, Mitch, but note that it was easy to do in my head one little carryover number at a time. I couldn't figure out how to build the formula from intuition. But, I now know that 70 is 102 ft/sec.
I do not know if the speedometer is calibrated all perfectomundo down the scale, but since I spend most of my life at 60-70, that is where I want it to be good. The speedometer is actually dead-nuts accurate at 60, and a little bit slow at 70. I will try to check the calibration at 40 if the interstate is good and abandoned later tonight. (lessee, 211,200 feet per hour/ 3520 feet per minute/ 58.666666 feet per second hey! 90 seconds per mile!)

Spent the afternoon down a dirt road I had no idea that it was two miles from Mexico. I was glorying in the sunshine and the heat in my shorts with more little wires strewn about than you can imagine (I cut airkooledchris' LM-1 harness in half, see, and was splicing and soldering eight 2 foot extension wires so I can read the LM-1 while driving without the usual death-teasing sideways-and-down glance at the too-reflective read-out. Had to double-wire splice my hack power cord extension to meet the gauge of the power cord.

Who dya suppose just had to visit to TELL me that the Mexican border was just down there a ways?
Mr. Border Patrol of course. I had my license out, shirt back on, and back to the soldering job in a split-second.
"What are you doing way out here?"
"I have to solder these twenty wires and heat-shrink 'em too, to get the LM-1 to reach my line-of-sight while I am driving."
. . . . well, it seemed like a pretty precise explanation to me anyway.

Now I know why my fuel economy has been suckish. 7.3 gallons to get 100 miles down the road?? I'll be broke by Gila Bend.
16.5:1 at idle, but 11.5 at cruise, 10.5 under full throttle acceleration?
Now I am 13.3 at cruise, 12.5 at full throttle, 14.7 at idle.
Three clicks CW on the cog, 1.25 teeth CCW on the static adjustment, and just crank that mixture screw in all the way then back out to 14.7, stochiometric, why not?

Out into the cold go I, yuck. What kind of moron works his tan all afternoon just to get walloped at sundown? Someone said, "get a sleeping bag." I just might.
ColinToLasCruces&Beyond
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 121,400 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 92,435 miles

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Post by Vdubtech » Tue Nov 09, 2010 9:27 pm

vwlover77 wrote:(I'm in your home state to visit Cornell University with my daughter tomorrow!)
Damn Don that's 45 minutes from my house!! Wish I had known you were comin this way!How was Cornell?

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bajaman72
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Post by bajaman72 » Tue Nov 09, 2010 10:28 pm

Ironic. I own a 20 acre ranch in Texas pretty close to the border (Fabens) I have to go out there once in a while to kick the "pallet houses" down. (although never would I kick a VW Bus down ;)

California is pretty cold right now Colin... I suggest the bag :geek:

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