full speed ahead! - General - VWDiesel.net The IDI, TDI, and mTDI source.

• full speed ahead! by Dr. Diesel on 26 Feb, 2005 21:26
• I've been enjoying my extra long ratio tranny since november. coupled with the slightly taller than stock winter tires, it makes for a noticeably inaccurate speedo reading. Matched up to Chris-pl's passat, I'm reading 10% low, meaning to hold 100, i'd have to drive roughly 91 on my dial.
  According to the scirocco.org caluculator, with my tires and gearing, i should drive at 2343 rpm to hold 100. This calculator also says that at 4500 rpm, i should be doing 190km/h, and at 5500 (haven't tried that yet. hehe) 206km/h! Had a long open stretch hwy the other day, and had 4500 rpm. Speedo read 165, which according to the chris test should actually be 181 km/h. I guess there's no telling how accurate chris's car is though. I've changed the ring and pinion and 5th gear in this tranny. I'm using the original speedo cable. Does anyone know if speedo cables and pinion gears are matched sets? I'd like to have an accurate speedo.
• #1 by cheng on 26 Feb, 2005 23:36
• I know that in the older A1's there are three different speedometer drive gears.
  
  I dont screw with any of those
  I put the taller tires on my 84 and it was reading aprox 10% slow as computed on a 100 mile trip in a straight line with no stops
  I took it down to the speedo shop and they ran it on their dyno and put a gearbox in line and now it reads perfect
  
  all the guess work gone for only $100 bucks
• #2 by Patrick on 27 Feb, 2005 05:38
• My 84 gasser read high by about 8% according to the dyno on the etest machine.  Just ran it that way anyway!
  
  My truck (3/4 ton 4 door GMC powered by Perkins) Read about 30% slow when I first put it together. There's a shop in London that can do what Cheng was talking about, at least on bigger stuff. Don't know if they can do volkswagens. They put a counter on instead of the speedo and drive a measured course.
  
  Other way of checking (assuming the odometer works) is use km markers on the 401(or 403, you're in Hamilton right?) and compare to your odometer.
• #3 by Dr. Diesel on 27 Feb, 2005 06:13
• a speedo shop..... who'd have thought! I wonder if A2's have different drive gears as well... I'll ask my pal at the dealer.
  thx!
• #4 by QuickTD on 27 Feb, 2005 07:23
• The greatest speedo calibration tool is a handheld GPS. Very accurate. Like cheng said, you can get little gearboxes to correct the readings, your gears should be factory supported though. I expect there is a pinion available that will get you close and you probably have it in your junk pile...
• #5 by Hammy on 27 Feb, 2005 16:23
• Ok, I'll ask. What is a gearbox, other than the one asking this question so don't say it's me!, LOL!
  
   Also, Dr.D, what tranny are you running that lets you only turn 2300 and change at 100Km/h. I'd love to do something like that, since I do alot of highway driving.
• #6 by QuickTD on 27 Feb, 2005 16:31
• The little gearboxes that cheng and I are referring to are installed inline in the speedo cable to correct a speedometer error. Usually they are screwed onto the fitting on the trans where the cable hooks up, the cable is then screwed onto the gearbox. They are available in a wide variety of ratios from your local speedo/instrument shop.  
  
   A 3.67 final drive, a 0.71 fifth gearset and 195-205/50-15 tires will get you the same gears as the Doc. Check one of the many 020 tranny charts online, I think this gearing was offered stock in a few early 80's gassers. I had to build my own. The stock final drive is 3.67 in the A3's, I added the 0.71 fifth gear set.
• #7 by Hammy on 27 Feb, 2005 16:57
• Thanks for the 411, Quick TD. I'm gonna look into it tommorow. BTW, does anyone think this will be worth it for the sake of fuel mileage?
  i usually drive around 120Km/h, and currently turn around 3500 rpm. I get about 800Kms/tank. Your thoughts are welcome.
  
  Thanks
• #8 by QuickTD on 27 Feb, 2005 17:05
• VW diesels love to scream. They often get worse fuel mileage after being geared up, unless you  like to drive fast. 2500-3500rpm seems to deliver the best economy. If you are always at 120km/h you may see some gain. In my experience, it would likely take about a million years to pay back in fuel economy.  More than anything it will help preserve your sanity, thats why I did mine. I like to drive fast and the noise drove me nuts...
• #9 by Hammy on 27 Feb, 2005 18:02
• Funny, you mention the noise, and driving fast. Last fall, I was working in Pickering (at the nuke plant), and I was driving it back and forth daily. It was over 300Kms per day round trip. I would leave just after 5AM and get there around 6:30AM or so. I was usually travelling around 150Km/h for most of the trip, lol. Talk about loud. I wasn't running a muffler at the time, just straight pipe.    Drivin' it like I stole it  Still got 750/tank!
• #10 by SMOKEYDUB on 02 Mar, 2005 15:49
• If you think your speedo is out try mine at 5500 in 5th my speedo goes right to the reset button WOW! im running p185/70r14's on it i think its pretty weird also i am running a different tranny but with the same gear ratios. How weird is that!
• #11 by Dr. Diesel on 02 Mar, 2005 18:24
• with a stopwatch and the highway KM markers, I found i have to drive an indicated 90 km/h to actually be doing 100. No wonder everyone else was always driving so slow. hehehe. at that speed, the car's so quiet, and just sips fuel... too bad now I'm the traffic bottle neck.
• #12 by BlackTieTD on 07 Mar, 2005 10:27
• Quote from: "Dr. Diesel"

  with a stopwatch and the highway KM markers, I found i have to drive an indicated 90 km/h to actually be doing 100. No wonder everyone else was always driving so slow. hehehe. at that speed, the car's so quiet, and just sips fuel... too bad now I'm the traffic bottle neck.

  
  
  lol, i've got mkII-size tires on the rabbit with the same gearing as you doc...... i know what you mean! i get a little flustered when i'm doing 10 over and a cop drives by. :lol:
  
  i read about an adjustable gear box a while ago that is used by harley guys moslty. apparently they use it so that when they are going 100, it says 50... and their odo racks up half the milage. i'd like to find an adjustable one so i could tweak it as i change tire diameters.