89 244 DL with Virgos on stock sized 195 tires, 3.31 rear, and m47 5 speed.


What RPM are you guys running @ 60MPH? 70? 80?


My calculations show that I should be running 80MPH@3000 RPM. My speedo shows lower than that. So either I am doing faster than what my speedo is showing, or my tach is showing higher revs that what I am really turning.

Idle is steady@950RPM, so I know it is good at idle. Both needles rest at the zero mark properly.


When I am doing 70 on the interstate, it just seems like I am passing people right and left.

Thanks!

Andrew
195x60 is the correct tire on the Virgo for the sedan (195x65 for the wagon), this is probably the small error you are noticing due to tire circumference differences. Find a measured mile on the highway and see what the odometer reads, it should be 1 mile. Also at 60 MPH you are going one mile a minute so a stopwatch could also be used to test your speedo's accuracy on the measured mile. Dan

'86 244, 3.31 rear, M46 4spd+OD manual. Cable driven speedo.

I get 2300 at 60, 2500 at 65, 2700 at 70, and ~2900 at 75. It's hard to tell exactly, but when I hit 3000 the speedo shows maybe 77 or 78mph. 80mph gives me just over 3000rpm on the tach, maybe 3100-3150 or so. The 500rpm increments on the stock VDO tach don't help here. :-)

Once the tach is calibrated properly (at the factory or when you install it in your car later), it should be set for life. It is fed by the coil and simply counts the number of ignition pulses per second.

The speedo in an '89 is fed by a speed sensor on the rear axle that can get flaky and will eventually fail. The speedo also develops mechanical problems as it ages, although this usually means broken gears in the odometer.

I'd say that your speedo is off, but then I don't know what your tach shows at the above road speeds. Whatcha got?

Just read your post again....The Virgos are a non-standard wheel size for a DL. That probably accounts for most of your speedo error.

3000 RPM at 80 MPH on level highway is what I usually see. 4 speed automatic with new 185-70-14's.
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 248K looking forward to 300K badge (or sticker??). >>You haven't really worked on a car until you draw blood<< :-}

I am running non-stock wheels, but I have a set of 195/65 tires on the Virgos. I am unsure of the original size tired, butdo you my tires could make a 10MPH difference at speed?

The speedo unit has been cleaned up, has a new odo drive gear installed on it, and the 1/10ths counter keeps right up with the mile markers on the interstate. The speedo needle is rock solid at whatever speed. Very seldom though, the needle will sometimes blip for a split second when I have just come to a complete stop.

I guess I will make myself a sticky for now that says 70=80 so I remember!

Hi Andrew,
If you go to the following site and put in your standard wheel size the car was made with and your current wheel size then you will know the speedo error as it calculates it for you. http://www.miata.net/garage/tirecalc.html
Cheers,
Checkpoint Charlie

Andrew,

You need to determine your stock tire size first. Their is a sticker in the door jam on the passenger side of the car that should have that information. Once you have that information you can use the Miata site suggested by Checkpoint Charlie or,

http://www.wickedbodies.net/Tire-Size-Calculator.htm

I used the wickedbodies site because I was converting from 185rx14. I ended up with 215/65/15 for my 93 245 with Virgo's.

Hope this helps,

RonJ

"I used the wickedbodies site because I was converting from 185rx14. I ended up with 215/65/15 for my 93 245 with Virgo's."

You ended up with that size because the wickedbodies conveniently plugs in 82 as the aspect ratio when none is entered. I've used the wickedbodies calculator many times and have also taken apart its code to find the formulas within.

My best efforts have shown that the correct aspect ratio for a tire such as 185/R-14 is not 82 but 80. If you go to tirerack.com and find their 185/R-14 tires, you can go to the specs for them and find the diameter, section, and other dimensions. From these you can reverse-calculate the aspect ratio, and I found it to be 80. For what it's worth.

Using 80 as the aspect ratio I ended up with 205/65-15 for my '89 245 with 15" steelies. You may find that your actual speed and distance are slightly greater than stated on the instrument cluster; 65.89 mph when it says 65.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

So do not have Virgos on my DL, still looking. But with the steel rims 3000 rpm on the tach is about 83 mph.

Not that I would ever drive that fast you understand. This is only ment for a scenario of what would happen if you were to drive that fast someplace where that speed would be allowed. 65 is the posted limit in town and of course the limit is strickly followed.

Regards,

PT

Sven,

Thanks for the info. I will definitely take it into consideration next time I need tires. It seem no matter how we cut it though, where going to be going a little faster or slower than indicated on the speedo. That's assuming the speedometer in correct in first place. This made me think though, is the spare tire (donut) the same circumference as a stock 185? If it is then we could measure it and maybe come up with something closer. Maybe I'll get mine out tomorrow see if I can come up with something.

Thank,

RonJ