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    2003 Speedometer Calibration

    I recently purchased a 2003 Protege LX with a 5 speed. I intend to put larger diameter tires on it to lower the engine rpm. This will be my daily driver commuter and I want to maximize mpg's. I want to make sure the speedometer reads correctly. I have read where folks us a GPS unit, but I'm just no interested in using something like that for tracking speed. Has anyone seen or used a Dakota Digital Universal Speedometer Interface with a late model protege to correct the speedometer signal? See the photo below. Thanks for any insight about this unit or any other digital speedometer calibration unit you have had success with, BradshawClick image for larger version

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    #2
    Folks, finally today I can give you an update on some changes I made to my 2003 protégé LX 5 speed manual tx, non-abs.

    I removed the factory struts and installed some coil over shocks to give me clearance for taller tires. The car had 195/55 R15's and I was able to fit 205/75 R15's with the coil overs, no rubbing and a "hands thickness" of clearance when the front wheels are turned lock to lock. The rear wheels are a little close at the rocker panel below the rear doors. My car has some bad rust in this area, but I used a ball been hammer to gently bend the inner fender around for a little more clearance. So far no rubbing, but that's with an empty car and no passengers.

    The BIG NEWS is that I was able to use the Dakota Digital calibration tool shown above to calibrate the speedometer to read correctly with the larger tires. I have driven on the interstate and checked a measured mile and that seems right on the spot.
    Now I cruise at 60 mph with the tach reading 2400 rpms and at 70 mph on the interstate at 2750-2800 rpms. Before I was revving 3000 rpm at 60 mph.

    I will run a couple of tanks of gas through it on my daily 52 mile round trip commute and report back with the fuel mileage.

    I'm hoping for 36+.

    Until later, Bradshaw

    Comment


      #3
      Glad to hear the calibrator worked. I'll have to remember that in the future once I finally start swapping wheels. How hard was it to actually recalibrate the speedo itself?

      Please do keep us updated on the mileage you're getting. I'm interested to see what the results are. Just to sate my own idle curiosity, what kind of tires did you buy?
      1995 626: daily beater, mostly stock. Future NASA racer?

      Next up: Speed6 or RX-8

      Comment


        #4
        Interesting concept going to a tire that large. I'd be worried the larger tires having a higher rotational mass will off set the lower rpms and either lower your fuel milage or you'll find no difference. There are 5th gear and final drive ratio swaps you can do in the transmission that I believe would have better affects.

        Comment


          #5
          Originally posted by crazycanadian View Post
          Interesting concept going to a tire that large. I'd be worried the larger tires having a higher rotational mass will off set the lower rpms and either lower your fuel milage or you'll find no difference.
          I was curious about this as well, but I was waiting to see the results before mentioning it. That's also why I was curious about the type of tire he installed. A larger, wider tire is going to have a greater rolling resistance than a smaller, narrower one, but with depending on how old the other tires were, the recent advances in tire technology could bring that rolling resistance down to the same level as the old tires had. If that is not the case, though, combined with the added weight of the larger tires the desired results may not be achieved. The weight penalty should be fairly minimal, as I presume the new tires are only a couple of pounds heavier, but that's still adding unsprung weight, which will have a negative impact on fuel economy. I'm interested to see how this experiment plays out.
          1995 626: daily beater, mostly stock. Future NASA racer?

          Next up: Speed6 or RX-8

          Comment


            #6
            The speedometer was very easy to re-calibrate. Finding the correct wire took the most time. I removed the air filter box, hose to the throttle body. Then reached down and unplugged the vss. Mine had 2 wires, one green, one off-white. I used a jumper wire plugged into each the green and then off-white pins along with a multi-meter that sets a tone when checking for continuity. After removing the gauge cluster, the wire was in the middle of the three plugs which is on the left side of the cluster. I cut the wire soldered in a jumper and plugged into the input on the calibration module. Another was soldered to the other side of the wire going into the back side of the plug and inserted into the Output1. Switch 3 and 4 are set to the ON or up position. Then you need a 12volt supply that is only powered when the ignition is on, and a good ground. Crank up the car, start driving. With this set up, the speedo was pegged way beyond 140mph, just push and hold the down button and slowly the represented speed drops until you get to where you want it set. I drove behind another vehicle and talked on the phone to check several speeds. Once you get it calibrated, release the down button, tuck the unit back under the dash and fasten securely. You are done. The tires are 205/75R15 Hankook's which google says weighs 19.6 lbs. A 195/55 R15 Yokohama weighs 18.8 lbs. If my math is correct, the new tires are 8.07" wide and 27.1" tall, the old tires were 7.67" wide and 23.4" tall.

            I didn't fill up today, but will tomorrow.

            I will keep you updated on mpgs. Bradshaw

            Comment


              #7
              Originally posted by crazycanadian View Post
              Interesting concept going to a tire that large. I'd be worried the larger tires having a higher rotational mass will off set the lower rpms and either lower your fuel milage or you'll find no difference. There are 5th gear and final drive ratio swaps you can do in the transmission that I believe would have better affects.
              Yes, the larger diameter tires will increase the rotational inertia of the wheel/tire combo which by itself will reduce vehicle acceleration. Couple that with the fact that the larger O.D. will effectively raise the gear ratio (effectively lower it numerically) and the vehicle should experience a marked decrease in acceleration compared with stock.

              Although I realize the OP is primarily interested in improved fuel mileage and less concerned about performance and handling.

              Happy Motoring!
              02 DX Millenium Red - The Penultimate Driving Machine
              MP3 Strut Tower Bar kit; Cusco Front Lower Arm Tie Bar
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              Comment


                #8
                Bradshaw: thanks for the walkthrough on using the calibrator. It does seem really simple. I will definitely be looking into one of those units once it becomes necessary, since it seems to be incredibly difficult to find a shop that will do it for you.
                1995 626: daily beater, mostly stock. Future NASA racer?

                Next up: Speed6 or RX-8

                Comment


                  #9
                  Update: Pre-modification I was getting approximately 30 mpg.

                  On one tank of fuel I travelled 508.3 miles. This was mixed city with some idling time, 70mph interstate cruising, but mostly rural 2 lane roads and a 4 lane divided highway at 60mph and 2400 rpm. I keep the tach below 2000 rpms in all gears and creep up to the 2400 when out on the main road.

                  I topped off the tank all the way up the filler neck till it was about to run out, it took 14.651 gallons. My math says that's 34.7 miles per gallon. Comparing the original tire circumference to the new tire circumference I get a 13.5% increase in circumference. Using 30mpg and 34.7 mpg the math works out to a 13.5% increase in fuel mileage. I am not suggesting there is true 1:1 relationship between tire circumference and the increase in mpg, its just a co-incidence.

                  I am going to run this second tank of gas out and fill the tank back up till its just about to spill out of the filler neck as this is the only way I know that I have replaced as close to the same amount of gas I used. I am also going to borrow a measuring wheel and measure exactly 5,280' on the road so that I can re-set the trip odometer, drive the measured mile and record the difference between when the trip odometer clicks exactly one mile and where the measurement is on the road since my method of calibration was to drive behind another vehicle, pace it, and set the speedometer accordingly. This should tell how close it really is to the indicated speed and distance.

                  I am considering the 5th gear swap that I have seen online. While the difference in the ratio is very minimal I wonder if it would help me get an additional couple of mpgs?

                  Considering that I plan to keep this car as long as I have the 94(currently 330,000 miles), I'm hoping fuel mileage improvements will pay in the long run. With the current price I paid for gas(2.05/gal) constant over that mileage, I will have saved more than the modifications cost. If gas goes to $3.05 per gallon, I would recover the cost of the car(what I paid) in savings.

                  Has anyone on here done the 5th gear swap?

                  Thanks for comments and suggestions.
                  Bradshaw

                  Comment


                    #10
                    I have done a 5th gear swap. As well as a final drive swap (not as well documented).

                    Don't fill the tank till it spills out. The evap system will draw in the extra gas, flooding and ruining the charcoal canister over time. The only way to measure fuel economy increases is based on an average over multiple tanks. Total gallons vs total miles driven. I'd look at 5 tanks as a min for an average. From there you also have to consider the time of year. Fuel consumption naturally goes up in the winter. If you are up north in the snow belts it'll be due to winter blended gas and colder weather.

                    Comment


                      #11
                      Thanks for the advice about topping off the tank. Do you remember how much your tachometer dropped after the 5th gear swap for any given speed?

                      Comment


                        #12
                        Update on the 03 protégé...

                        Previous owner said they had replaced driver's side wheel bearing. Terribly loud noise in front end, almost unbearable to drive at higher speeds. Replaced passenger side first, no change in noise level, but bearings were in bad shape. Replaced the driver's side about 2 weeks ago. Problem solved, noise gone, at least for 25-30 miles, then a new bearing crapped out on me. Went back to auto parts store with the pieces in hand and was given a full refund. Purchased another brand, Federal Mogul, and so far 250+ miles with no problems.

                        On to the gas mileage. Last fill up was 14.437 gallons and 564.1 miles. 39 mpg by my calculation.

                        I wonder if those bad bearings were holding back the mpgs that much?

                        Hopefully this next tank, with new wheel bearings up front and less friction will show the same or better results.

                        Seriously considering the 5th gear swap to get those 70 mph interstate rpms lower.

                        Will keep you posted on the next tank of fuel usage and miles traveled.

                        Bradshaw

                        Comment


                          #13
                          I know this is reviving an old thread.
                          I completed the fifth gear swap.
                          100k miles later, no problems with consistent 39-40 mpg running the 205/75R15 tires. On the second set of tires. Coil over shocks are stiff and make for a bumpy ride, but I can live with it. I've added a trailer hitch and was even able to tow an 02 Protege5 with a bumper bar. Gets the job done, reliable setup. Time is due to replace timing belt and water pump.

                          Next project may be a P5 with similar tire/shock setup, and may try shoehorning in a V6-auto from same year MPV?

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