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pdunn13445 Samba Member
Joined: August 14, 2007 Posts: 78 Location: Zacatecas, MX/TX/CO/MD
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Posted: Thu Nov 22, 2007 12:48 pm Post subject: Speedometer accuracy |
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Have an '84 Westy Wolfsburg GL with the tachometer option and auto trans. In a reply to how tach was wired in I again confirmed that the speedometer is not all that accurate. I figure roughly 10 mph high at higher speeds. For instance at 4000 rpm reads 87 mph, but actually about 75 mph? Does anyone have a reference to engine rpm w/ auto tranny in top gear and actual mph? It would be nice to know what my speed is, even within 5 mph. |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50350
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Posted: Thu Nov 22, 2007 12:58 pm Post subject: |
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What size tires are you running? The speedometer works off the left front wheel, it is in no way affected by the kind of transmission you have or your gearing, just tire size. |
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0to60in6min Samba Member
Joined: November 27, 2006 Posts: 3416 Location: OR & CA (Oregon/California)
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Posted: Thu Nov 22, 2007 1:02 pm Post subject: |
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Given stock 14" rim.... 4000 rpm is 70 mph... give and take a few miles error due to wear and tear of the speedometer.. |
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tikibus Samba Member
Joined: July 07, 2006 Posts: 834 Location: Rochester, NY
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Posted: Thu Nov 22, 2007 3:43 pm Post subject: |
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The Speedo of the 84 is funky.
Tiki and I get to do math while driving. Running on stock rims and 14" tires gives a reading of 10 MPH higher on the Speedo. When doing 40, doing 30, etc..
Never Have I gone to muck about with the cables.
What I have done is to find a area ( construction or school) with a reader. Blinks or numericaly shows your speed and gauge off of that.
Hence my destain with NYS Thruway (90). I can only go so fast, Some get it, some don't. Much rather do the old school roads.
Puttin' along with a smile. Enjoy the ride.
_________________ Happy Trails!
Mark
______________
Founding member of the Empire State VW Camping Club.
http://www.empirevwcamping.org/
1984 Westy - Tiki
1997 Honda Civic -The Green Hornet
1971 Volvo P-1800E- needs TLC |
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msinabottle Samba Member
Joined: September 20, 2005 Posts: 3492 Location: Denver Area, Colorado
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Posted: Thu Nov 22, 2007 5:00 pm Post subject: Pleasantly Accurate... |
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Winston's '84 speedometer has also been funky--and it's the second one I've had in him, don't worry, CrimeStoppers, I left a note in the owner's manual. The huge Big O knobbies he'd had on him before undoubtedly screwed up the reading a bit, but he's been a LOT better since I put DogPilot's old 15" Audi rims on him and the Michelin Agilis.
Supposedly, those are just the same size as the stock rims. If you have one of those radar speed limit signs on a road you drive, check often and learn. Winston's quite on at low speeds. For faster speed, you could zoom... All right, amble... Past a State Patrolman and see if he gives chase, but more easily, get a GPS of any description and use it to compare its hyper-accurate speed reading with your speedometer.
Long the '84's! Yay for the Round-Eyes!
Best! _________________ 'Winston,' '84 1.9 WBX Westy
Vanagon Poet Laureate: "I have suffered in
many ways, but never, never, never in silence." |
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Perales Samba Member
Joined: May 07, 2007 Posts: 2046 Location: Nova Scotia
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Posted: Thu Nov 22, 2007 5:33 pm Post subject: Read it and weep! |
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Could be that VW was just trying to make us feel better.
Or was it the law just trying to be clever.
Here it is from the Bentley
It's a conspiracy man! _________________ -- 1987 Westfalia automatic (Captain Vino) |
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pdunn13445 Samba Member
Joined: August 14, 2007 Posts: 78 Location: Zacatecas, MX/TX/CO/MD
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Posted: Thu Nov 22, 2007 8:59 pm Post subject: I thank all of you! |
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First of all, I blew it by not relating rims and tires, which in this case are both stock. Second, the question involved the tach reading and speeds at specific rpm's, therefore the tranny, thus gearing does make a difference. So with all your input, it is still anybody's guess as to actual speed. I do like 70 mph at 4000 rpm, but I swear it feels faster in Shirley. Also love the clip about the speedo head. At 60 mph I think the difference was about 10 mph, or actually doing 50, so the clip is close. But my, like I said 4000 rpm indicates 87 mph. I will have to do my math and get a curve going. Here in Mexico my general rule is that the Federales on the toll roads will maybe stop you if you are on radar going over 100 mph. |
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tencentlife Samba Member
Joined: May 02, 2006 Posts: 10078 Location: Abiquiu, NM, USA
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Posted: Fri Nov 23, 2007 10:42 am Post subject: |
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I don't think you would be going 70 at 4k with an automatic unless your tires were fairly oversized. I have near-stock OD tires and a tall 4th in my standard, and that's nearly my speed at 4k. As I recall the automatic's final gearing is pretty low, but I don't have my book. There's an online listing of all the trannys in German (Getriebe), but I can't find the link either. Perhaps someone could chime in with the ratios, it's not hard to figure out your mph/rpm from there.
Anyway, all DOT-approved speedos have to read correct or high, as has ben pointed out, and the early Vanagon speedos typically read really high. The same applies to those roadside radar guns; they add the same 3mph a cop has to subtract from his radar gun, to give the 3mph error in your favor. Having a GPS is probably the best and easiest way to confirm your actual speed.
If you don't mind a lot of trial and error tweaking, it's not hard to recalibrate your speedo to read correctly with whatever trans/tire combo you're on. You end up doing it several times unitl you get it dialed in. I got so good at it, I could have the head out, tweak the spring, and reinstall in 11 minutes! _________________ Shop for unique Vanagon accessories at the Vanistan shop:
https://intrepidoverland.com/vanistan/
Please don't PM here, I will not reply.
Experience is kryptonite to doctrine. |
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Christopher Schimke Samba Member
Joined: August 03, 2005 Posts: 5391 Location: PNW
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Posted: Fri Nov 23, 2007 11:00 am Post subject: Re: I thank all of you! |
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pdunn13445 wrote: |
... the question involved the tach reading and speeds at specific rpm's, therefore the tranny, thus gearing does make a difference. |
I don't know anything about the Vanagon automatic gearboxes but isn't there some torque converter slip even in high gear? If so, would the amount of slip change depending on the various driving conditions, ie; headwinds, steep hills, etc? Therefore, the amount of slip would make using the tachometer, in an automatic gearboxed Vanagon, to judge your speed somewhat inaccurate?
Just thinking out loud. _________________ "Sometimes you have to build a box to think outside of." - Bruce (not Springsteen)
*Custom wheel hardware for Audi/VW, Porsche and Mercedes wheels - Urethane Suspension Bushings*
T3Technique.com or contact me at [email protected] |
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UH60Driver Samba Member
Joined: August 02, 2007 Posts: 51 Location: Clarksville,Tn
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Posted: Fri Nov 23, 2007 11:27 am Post subject: |
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Just use a GPS to verify where you are at speedwise. If you dont have one or cant afford one(because you spent all you money on your van), certainly you know someone who has one that can go on a van ride with you to take a few readings at different speeds. |
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j.a.c.auto Samba Member
Joined: January 25, 2006 Posts: 68 Location: Ramsey,MN
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jackbombay Samba Member
Joined: October 19, 2007 Posts: 2723 Location: Eastern Idaho
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Posted: Fri Nov 23, 2007 12:32 pm Post subject: |
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UH60Driver wrote: |
Just use a GPS to verify where you are at speedwise. If you dont have one or cant afford one(because you spent all you money on your van), certainly you know someone who has one that can go on a van ride with you to take a few readings at different speeds. |
A stopwatch and some mile markers beside the highway works just as well, drive at as constant a speed as you can and time a mile, divide 3600 by the number of seconds it took you to drive a mile, the result is your speed. |
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tencentlife Samba Member
Joined: May 02, 2006 Posts: 10078 Location: Abiquiu, NM, USA
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Posted: Fri Nov 23, 2007 12:43 pm Post subject: |
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http://brickwerks.hostinguk.com/VehicleSpecific/T3/info/gbx.htm
Yeah, that's it. I also found a pdf I saved which is the German version of that same data.
If an '84 auto has the 4.09 FD x the 1.0 3rd gear, the effective ratio is 4.09. Most late wbx 4 speeds are 4.83FD x .85 4th for 4.10. So the auto is actually top-geared pretty much the same as a standard, all else being equal. I do remember in the book that with stock-sized tires, you get 18mph/1000rpm, or 72mph at 4k. If you're reading 70 at 4k, then your speedo is pretty much on target. For stock tires, that is. _________________ Shop for unique Vanagon accessories at the Vanistan shop:
https://intrepidoverland.com/vanistan/
Please don't PM here, I will not reply.
Experience is kryptonite to doctrine. |
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Perales Samba Member
Joined: May 07, 2007 Posts: 2046 Location: Nova Scotia
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