Toy Civic

Regarding speedo and odometer accuracy……………………

I don’t know if this has ever been covered in previous posts. If you already are aware, or don’t give a ****, then disregard. But for those who are unaware, do care, or are new to Hondas and Acuras, then please read on.

When our Civics and Integras were stock, they came with 14 or 15 inch wheels with multiple tire sizes depending on model. I am here to tell you that the speedo and odometer MAY NOT BE ACCURATE with the stock tire sizes…………………between 3-11% depending on the stock tire size that came on the car. The only way to verify is by taking the car to a speedo calibration shop.

As many know, the whole system runs off the electronic vehicle speed sensor in the tranny and is driven by the supplemental ring gear on the edge of the differential and the gear attached to the speed sensor itself. Unless I am mistaken (95% sure that I am not), both those gears have the exact same ratio regardless of which Civic or Integra B or D series manual tranny you have. I cannot vouch for speedo gears in the automatic trannies. With the stock tire sizes, the only real variable is how the speed sensor electronic voltage signal itself is performing. Swapping speed sensors may or may not solve the problem. Chances are though that the vehicle speed sensor is functioning AS DESIGNED.

I bought my 1995 Civic EX coupe new and immediately noticed this flaw. When my gauges were reading 70mph, I was really doing 64mph. That 9% difference was also consistent at other speeds as well. The odometer was registering 1.1 miles per every mile driven. I had this verified by a speedo calibration shop. I had the stock 185/60/14 tire size. I took the car to the dealer and they replaced the speedo cluster, which didn’t solve anything. When I later went to 195/50/15 tires, the accuracy stayed the same. I drove the car like that for a few years and mentally compensated. My mileage accumulated a few extra thousand miles more than it should have.

In 2001, I switched to my current tire size of 205/40/17. With my original D series manual tranny, my speedo accuracy increased to 99-100% depending on my speed. My odometer has been perfect ever since.

In 2006, I swapped in a B series with an ITR tranny with factory LSD. I had the speedo and odometer checked again and it was exactly the same as my D series tranny.

So in summary, assuming that all B and D series manual tranny vehicle speed sensors are operating as designed, the only true fix is to use a tire size that has a total properly inflated external diameter of 23.5 inches to achieve 99-100% accuracy. Here is a rundown of some of the popular 92-00 Civic and 94-01 Integra tire sizes and their external diameters. These numbers were derived from Toyos website. There may be very small deviations in tire size dimensions from one tire manufacturer to the next. Smaller overall diameters mean more revolutions from point A to B, and vice versa for larger overall diameters. If all you do is race, then smaller is the way to go for most. But of you want accuracy for your street car, then follow this chart next time you decide to go with a new wheel and tire size:

205/40/16..........22.5 inches..........70mph=60.9mph.............87% accuracy
175/70/13..........22.7 inches..........70mph=62.3mph.............89% accuracy
185/60/14..........22.8 inches..........70mph=63.7mph.............91% accuracy
195/50/15..........22.8 inches..........70mph=63.7mph.............91% accuracy
205/50/15..........23.1 inches..........70mph=65.8mph.............94% accuracy
205/45/16..........23.3 inches..........70mph=66.9mph.............95.5% accuracy
195/55/15..........23.4 inches..........70mph=67.9mph.............97% accuracy
205/40/17..........23.5 inches..........70mph=69.3mph.............99% accuracy
225/50/15..........23.9 inches..........70mph=74.2mph.............94% accuracy