Watchdog Posted February 17, 2023 Share Posted February 17, 2023 (edited) With ForScan, the tire size was 2437mm in the system ... the original tire oem is 265-65-18 and is supposed to be 2517.... wth......??? Also, if you change the tire size, it will send a DTC code for AWD... You will need to relearn the PCM and then, delete/reset the AWD dtc code... Am I the only one with a improper tire size registered? Is this normal or I should change it to proper size for the oem tire? Edited February 17, 2023 by Watchdog Quote Link to comment Share on other sites More sharing options...
akirby Posted February 17, 2023 Share Posted February 17, 2023 Strictly a guess but would the weight of the vehicle at recommended pressure reduce the effective circumference? Quote Link to comment Share on other sites More sharing options...
ohsown Posted February 18, 2023 Share Posted February 18, 2023 Tire size was a great frustration when picking winter tires for my 22 Explorer Limited (20" rims) when I decided to switch to 18" rims like on the XLT. I went with Blizzak DMV2's. On line sites would show they would not fit. Costco would not warranty or install them. When compared to the 20" DMV's there is negligible difference. The 18" diameter, (P255 65 18) is 31.06" with 671 rotations per mile v/s the 20" (P255 55 20) 31.02" with 672 rotations per mile. When these numbers are close how could there be a problem. Of course load and speed ratings need to be close as well. The dealer I purchased my Explorer from ordered and installed the DMV's for me on some aftermarket wheels I supplied. There was never any concern over fit or computer recalibration. If there is a larger difference in the numbers for revolutions per mile it could make small difference in your speedometer reading but just a few mph. Hope this helps clear it up some for you. 1 Quote Link to comment Share on other sites More sharing options...
Watchdog Posted February 18, 2023 Author Share Posted February 18, 2023 4 hours ago, ohsown said: Tire size was a great frustration when picking winter tires for my 22 Explorer Limited (20" rims) when I decided to switch to 18" rims like on the XLT. I went with Blizzak DMV2's. On line sites would show they would not fit. Costco would not warranty or install them. When compared to the 20" DMV's there is negligible difference. The 18" diameter, (P255 65 18) is 31.06" with 671 rotations per mile v/s the 20" (P255 55 20) 31.02" with 672 rotations per mile. When these numbers are close how could there be a problem. Of course load and speed ratings need to be close as well. The dealer I purchased my Explorer from ordered and installed the DMV's for me on some aftermarket wheels I supplied. There was never any concern over fit or computer recalibration. If there is a larger difference in the numbers for revolutions per mile it could make small difference in your speedometer reading but just a few mph. Hope this helps clear it up some for you. I have the same tire however, when I look with ForScan, the original setting shows 2437mm circumferences but the original tires are 2517. Is this a Ford Tire gate?????? Were these specs done with the spare tire? How come, when I try to add, it says maximum tire size, This means the tire I have 255-70r18 with a 2558 circ. is to big, speed and mileage wont be proper! Quote Link to comment Share on other sites More sharing options...
ohsown Posted February 19, 2023 Share Posted February 19, 2023 You may have the same tire, a Blizzak DM-V2, but, you do not have the same size. You show you have a 70 series, 255/70/18 where I have a 255/65/18. Your size has a 1.07" larger diameter, requiring only 649 revolutions per mile. This will change you speedo slightly, 23 tire revolutions over a mile shouldn't be that big but I dont know the math for how much. It will show you going a bit slower than you actually are. As for the forscan system, computer and drive system I don't know impact on them. Quote Link to comment Share on other sites More sharing options...
Watchdog Posted February 19, 2023 Author Share Posted February 19, 2023 3 hours ago, ohsown said: You may have the same tire, a Blizzak DM-V2, but, you do not have the same size. You show you have a 70 series, 255/70/18 where I have a 255/65/18. Your size has a 1.07" larger diameter, requiring only 649 revolutions per mile. This will change you speedo slightly, 23 tire revolutions over a mile shouldn't be that big but I dont know the math for how much. It will show you going a bit slower than you actually are. As for the forscan system, computer and drive system I don't know impact on them. Yes, I knew there would be a slight speed difference but in ForScan, the tire size in circumference is not even close to the original tire size. 2437 vs 2518. That's who I was wandering where does this size come from? In summer, I will put back the original tire Dueller 265-65r18 but in winter I prefer tinner tire. Quote Link to comment Share on other sites More sharing options...
akirby Posted February 19, 2023 Share Posted February 19, 2023 I was right - the circumference of the loaded tire is slightly less. https://www.ranger5g.com/forum/threads/forscan-tire-size-wiki.10139/ Quote Link to comment Share on other sites More sharing options...
Watchdog Posted February 19, 2023 Author Share Posted February 19, 2023 6 hours ago, akirby said: I was right - the circumference of the loaded tire is slightly less. https://www.ranger5g.com/forum/threads/forscan-tire-size-wiki.10139/ Great info.... Si if I get it straigt, my new tires are 255-70R18 = 2558mm * 0.967 = 2473mm to input in Forscan. And when I will put back the OEM tire 265-65r18 = 2517 * 0.967 = 2434 instead of 2437 original settings. S Quote Link to comment Share on other sites More sharing options...
ohsown Posted February 20, 2023 Share Posted February 20, 2023 Squash factor, well I've been schooled! Am I ever glad I didn't know about this when I was looking for winter tires. I'd still be looking. I would have liked a narrower tire for winter as well but even the ones I bought show as not fitting my vehicle. Phone calls to Bridgestone were of no help either. Quote Link to comment Share on other sites More sharing options...
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