pitpup Posted December 29, 2006 Report Share Posted December 29, 2006 Is your odometer/speedometer off now that you have purchased the SCT X-Calibrator 2 for your Stang? If so, an easy fix. This is long, but worth the read. 1. When I got my Stang, I was too busy having fun with it to take it out to the interstate and see if the odometer consistently clicked off exactly one mile (or something very close) with every mile marker I passed. If anyone has a stock Stang, I'd be interested in hearing how they clock from the factory. 2. Enter the SCT tuner. When I got it, I uploaded the tunes and again, was having way too much fun to think about odometer/speedometer accuracy. The car just rocked. So I continued to enjoy it. 3. After reading the manual on the SCT-2, I learned that in addition to being able to program in the rear gear, you could also adjust for tire diameter. Our 235/50/18's are 27.25 inches tall when inflated to 32psi. 4. Because I'm a math freak, I decided to throw this adjustment in too, BEFORE CHECKING THE ODOMETER ACCURACY FOR THE STOCK SETTING. So! I found out from the Falken Tire website that our tires roll 740 revolutions per mile. TO CHECK THAT (I'm anal, remember), I did it the old fashioned way. 27.25 inches x 3.14 = 85.6592 inches. This is how far the tire travels in 1 revolution. 5280 feet x 12 = 63,360 inches per mile. Ya with me so far? 63,360 divided by 85.6592 = 739.675 revolutions in a mile. 5. So, math boy plugs in '740' on the SCT and does not give it another thought. Meaning, I never checked it! 6. Anyhoo, I was on my way to Maryland on Tuesday, 12/26. Mile markers out the wazoo, but did I even think about checking the odo? No. But here's how I found the snafu. I put my cruise control on 63 miles per hour and at the next mile marker, I click 'start' on my watch's chrono. I'm anticipating covering a mile in 57 seconds or there about. 60 mph is 60 seconds, a mile a minute remember. But what do I find? I cover the mile in exactly 60 seconds. NOT 57 seconds. So I realize I'm off by 3 mph! 7. So I reset the odometer at the next mile marker and it's game on! Well don't you know that as each mile clicked off on the car, the mile marker was appearing just a little bit further and further out front with each passing mile. After going 4 miles, the Stang was clocking 4.1 miles, give or take. I tested this over 3 separate 4 mile runs and was consistently overclocking. 8. I realize at this point that '740' in #4 above is not correct. My tires have only 7000 miles and are fully inflated, so it's not like I've worn them down. I get back from Maryland and immediately grab the SCT-2 and head out to Interstate 295. The tuner lets you bump the value for revolutions per mile by increments of 5. So I had to dial in either 745 or 750 or 755. Some value more than 740 to tell the 'puter that I had to go further down the road before it registered 1 mile. That value turned out to be '750'. I made two checks on I-295. Both times, as the mile marker came up, WldTang would click off a mile on the odo. It was dead on. 9. I then put the cruise control on 60 mph and hit the chrono at the next mile marker. When the following mile marker came up, my watch showed 60 seconds. Not 1:03 or anything else. I did this for 3 separate checks. All 60 seconds. But the story continues! 10. So now I'm curious as to what the 'stock' value is on the SCT-2. This is the value that is downloaded to your car if you don't play with this setting. It does not give you a value. It just says 'stock'. So I hit I-295 again and this time, instead of overclocking (4.1 miles clocked for a true 4.0 miles) IT UNDERCLOCKED! It registered 3.8 miles for a true 4.0 miles. Two tenths the other way. While this would understate your mileage, IT WILL BE OFF FOR THE SPEEDOMETER. This could get you in big trouble. Say you're on a highway with a 65 mph speed limit. You set your cruise for 74 mph, or 9 over. You would actually be moving somewhere around 79-81 mph (approximately). So now you're 15 over the limit when you think you're 9. In closing, I don't feel this is a 'Brenspeed vs. Bamachips vs. YOUR TUNER' thing. It's just something that you should be aware of. I'm not aware that the custom tuners even touch the 'stock' value from SCT, so SCT is off here. And for those of you with 17 inch wheels, the 235/55/17's have a height of 27.17 and travel 742.670 revolutions in one mile. This is very close to the stock 18's with 739.675 revs. Forgive me for being this anal, but when my car is telling me it's going 70 mph, I want it to be humming along at 70 mph. Not 67. Not 73. But 70! And I want the mileage to be dead on. Not that I'm worried about resale, but when I take a trip to Maryland, I want to run off 155 miles, not 159. To wrap it up, the stock value (unknown) is garbage and the calculated value of 740 is garbage. The value that works for me is 750. And even this may vary as the tires wear, so I'm going to make a point to check it once a month. Link to comment Share on other sites More sharing options...
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