Verifying Speedometer Accuracy (40.93.03)

Publication date: 1993-04-27
Reference number: 40.93.03

VERIFYING SPEEDOMETER ACCURACY

TECHNICAL SERVICE BULLETIN

Reference Number(s): 40.93.03, Date of Issue: April 27, 1993

VERIFYING SPEEDOMETER ACCURACY

Model(s): 1971-94 Alfa Romeo Vehicles

Group: 40 - Electrical

Bulletin No.: 40.93.03

Date: April 27, 1993

SERVICE INFORMATION

Speedometer accuracy may be verified in the field by one of two methods.

METHOD ONE SPEED VERSUS R.P.M. IN HIGH GEAR

164 SPEED VERSUS RPM IN 5TH GEAR OR DRIVE.

23.7 MPH per 1,000 RPM or approx. 2,500 RPM (2,526) = 60 MPH

1994 LS 5spd

24.2.MPH per 1,000 RPM or approx. 2,500 RPM (2,481) = 60 MPH

1994 LS AUTOMATIC

23.9 MPH per 1,000 RPM or approx. 2,500 RPM (2,510) = 60 MPH

1991 thru 1993 SPORT

23.0 MPH per 1,000 RPM or approx. 2,600 RPM (2,608) = 60 MPH

1991 thru 1993 BASE & L 5spd Models

25.6 MPH per 1,000 RPM or approx. 2,350 RPM (2,343) = 60 MPH

1991 thru 1993 BASE & L AUTOMATIC models

25.2 MPH per 1,000 RPM or approx. 2,400 RPM (2,380) = 60 MPH

NOTE: Vehicles equipped with automatic transmissions cannot be tested on a lift. Vehicle must be under a load during the test due to torque converter slippage.

MILANO SPEED VERSUS RPM IN 5TH GEAR OR DRIVE

3.0L VERDE

25.2 MPH per 1,000 RPM or approx. 2,400 RPM (2,380) = 60 MPH

2.5L 5 spd

21.1 MPH per 1,000 RPM or approx. 2,850 RPM (2,843) = 60 MPH

2.5L AUTOMATIC

21.3 MPH per 1,000 RPM or approx. 2,803 RPM (2,816) = 60 MPH

NOTE: Vehicles equipped with automatic transmissions cannot be tested on a lift. Vehicle must be under a load during the test due to torque converter slippage.

SPIDER SPEED VERSUS RPM IN 5TH GEAR OR DRIVE

1980 thru 1993 5spd

22.14 MPH per 1,000 RPM or approx. 2,700 RPM (2,710) = 60 MPH

1991 thru 1993 AUTOMATICS

19.71 MPH per 1,000 RPM or approx. 3,000 RPM (3,002) = 60 MPH

1971 thru 1979 5spd

19.71 MPH per 1,000 RPM or approx. 3,000 RPM (3,044) = 60 MPH

NOTE: Vehicles equipped with automatic transmissions cannot be tested on a lift. Vehicle must be under a load during the test due to torque converter slippage.

GTV-6 SPEED VERSUS R.P.M. IN 5TH GEAR.

1981 & 1986

21.78 MPH per 1,000 RPM or approx. 2,750 RPM (2,754) = 60 MPH

1985

22.17 MPH per 1,000 RPM or approx. 2,700 RPM (2,706) = 60 MPH

1984

26.99 MPH per 1,000 RPM or approx. 2,200 RPM (2,223) = 60 MPH

1982 thru 1983

26.14 MPH per 1,000 RPM or approx. 2,300 RPM (2,295) = 60 MPH

The relationships noted above will vary if tires of another brand or size are fitted or if the tachometer is inaccurate. Also, SPEED, LOAD. INFLATION PRESSURE, and WEAR substantially effect the rolling circumference of the tires and thus are a factor in R.P.M./ROAD SPEED ratios. Because of these factors NO conventional speedometer is 100% accurate. The most common variance in any speedometer accuracy is +/- 5%.

METHOD TWO CLOCKING THE CARS SPEED OVER THE MEASURED MILE

Maintaining a constant speed, time the car with a stop watch between mile markers (highway mile markers are found on ALL major highway's) and record the time. Then divide 3,600 by the number of seconds it took to travel one mile. The result will be the average speed of the car for the given mile timed.

Example Number 1: If it took 62.53 seconds to cover the mile, we divide 3,600 by 62.53 (3,600 divided by 62.53) the result is 57.57. This is the average M.P.H. at which the car traveled the measured mile.

Example Number 2: If it took 74.2 seconds to cover the mile, then 3,600 divided by 74.2 = 48.51. This is the average M.P.H. at which the car traveled the measured mile.

If a speedometer on a car under warranty is found to be inaccurate by more than +/- 5%, contact your local Alfa Romeo District Service Manager who will advise you what steps to take.