Speedo adjustment
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Lead Driver
Joined: Oct 2014
Posts: 5,940
Likes: 1,355
From: NY/Canada border
Speedo adjustment
If I were to go a size or 2 bigger to fill the wheel well more like I did with my 2016, is there any way to adjust revs per mile in FORScan to keep the speedometer accurate?
Before I had a 5 Star tuner and there was a provision to make that adjustment. I've decided not to mess with tunes on this truck.
I haven't purchased tires at this time, I'd like to have this information beforehand.
Before I had a 5 Star tuner and there was a provision to make that adjustment. I've decided not to mess with tunes on this truck.
I haven't purchased tires at this time, I'd like to have this information beforehand.
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Lead Driver
Joined: Oct 2014
Posts: 5,940
Likes: 1,355
From: NY/Canada border
No tires purchased yet, also do not yet have FORScan in the regular version - only have Lite currently as all my stuff is Apple. Been considering a cheapo $130 Windows box from Best Buy to use strictly for FORScan. I've got one or two ELM27 adapters laying around. Just not sure if they're correct for the app or not. I understand the low budget adapters don't necessarily work.
Fleet Mechanic
Joined: Sep 2016
Posts: 1,613
Likes: 156
I have 37s. I used Forscan and programmed for 285/75-18s (35s), which appears to be the largest value that can be used before the CEL is illuminated.
at 70 mph on the dash, I am actually doing 74mph per GPS
at 70 mph on the dash, I am actually doing 74mph per GPS
Junior User
Joined: Aug 2017
Posts: 50
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From: Texas
Would this still be the case for dually's? I just put on 285/75-17s 33.8"
Freshman User
Joined: Jul 2017
Posts: 36
Likes: 0
From: Orlando
I put 37's on my truck, I went with the hypertech. I'm the type that wants things to just work the way they are supposed to. My numbers are all spot on.
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Lead Driver
Joined: Oct 2014
Posts: 5,940
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From: NY/Canada border
Current tires are LT275/65R18E, which shows as 32.1 inches high. To move up to a 34 inch tire (actually 33.9) would require an LT305 by the site I'm checking out. Not really looking to go wider. In my experience, which is quite lengthy in snow driving, a wide tire will ride up on top of snow. Then if the wheels spin you're suddenly buried to the axle. Learned this the hard way many times as a 20 year old kid with Goodyear Wrangler R/Ts on a 1979 GMC plow truck.
From what I've gathered here, a 34 inch tire should be within the range of FORScan to compensate the speedometer. Am I on the right track here?
I put BFG KO2s on my last truck and liked them. But most pricing I'm finding right now is a shade under $350 each. Not quite ready for that at this time.
From what I've gathered here, a 34 inch tire should be within the range of FORScan to compensate the speedometer. Am I on the right track here?
I put BFG KO2s on my last truck and liked them. But most pricing I'm finding right now is a shade under $350 each. Not quite ready for that at this time.
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Fleet Mechanic
Joined: Sep 2016
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although the size I used is not a factory option, i think it works because it is within the threshold perameters.
my truck came with 275/70-18 tires which are 33.2" tall.
trucks with 20s have a 275/65-20 tire which is 34.1" tall
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Lead Driver
Joined: Oct 2014
Posts: 5,940
Likes: 1,355
From: NY/Canada border
I don't know, maybe post in the forscan section? i think it will work because i believe forscan will allow changes to be made that were options from the factory. I don't know if it is vehicle specific.
although the size I used is not a factory option, i think it works because it is within the threshold perameters.
my truck came with 275/70-18 tires which are 33.2" tall.
trucks with 20s have a 275/65-20 tire which is 34.1" tall
although the size I used is not a factory option, i think it works because it is within the threshold perameters.
my truck came with 275/70-18 tires which are 33.2" tall.
trucks with 20s have a 275/65-20 tire which is 34.1" tall
Hypertech is out of the question at $229 to use basically one time if I buy the tires. Maybe one more if I traded the truck and put stockers back on.
I've found the tires I like for considerably less than my original search. But trying to make the speedo right for a tire 2 inches taller than my stock tires is becoming not so fun research.
Logistics Pro
Joined: Apr 2017
Posts: 3,674
Likes: 51
From: SoCal
Yeah, this is all starting to make my head hurt. So far, I've only found that FORScan can program up to a limited tire height (max specified by factory) without setting a DTC. I don't know if this still holds true or not. Also, the search hasn't turned up a specific step by step on how to do this particular procedure. Just pages & pages to surf through.
Hypertech is out of the question at $229 to use basically one time if I buy the tires. Maybe one more if I traded the truck and put stockers back on.
I've found the tires I like for considerably less than my original search. But trying to make the speedo right for a tire 2 inches taller than my stock tires is becoming not so fun research.
Hypertech is out of the question at $229 to use basically one time if I buy the tires. Maybe one more if I traded the truck and put stockers back on.
I've found the tires I like for considerably less than my original search. But trying to make the speedo right for a tire 2 inches taller than my stock tires is becoming not so fun research.
Once FORscan and your adapter are talking, its as simple as changing a couple digits and hitting save.
Mountain Pass
Joined: Jun 2010
Posts: 185
Likes: 3
From: Scenic Vermont
There’s only one very small change for recalibration in the FORscan spreadsheet. Where did you get your info? I’ve been waiting for the list of values to be published but nothing yet I can see. I need the O.E. values for the 17’s on my stripper XL and the values for the O.E. 20’s which are essentially the same as 35’s. Curious to know! You’re running the same tires I am.
Mountain Pass
Joined: Jun 2010
Posts: 185
Likes: 3
From: Scenic Vermont
Where are these values on the spreadsheet? If you still have them will you share? How did they disappear from the spreadsheet if that’s where you got them?
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Lead Driver
Joined: Oct 2014
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From: NY/Canada border
Its pretty easy once you wrap your head around it. Just go to the FORscan thread, click on the Google Doc, and flip through the tabs there. There's great instructions on all the steps you need to do to set everything up.
Once FORscan and your adapter are talking, its as simple as changing a couple digits and hitting save.
Once FORscan and your adapter are talking, its as simple as changing a couple digits and hitting save.
Then, I'll see if someone comes up with answer's to Dan B's questions before I spend the dineros on tires.
Logistics Pro
Joined: Apr 2017
Posts: 3,674
Likes: 51
From: SoCal
Speedometer Recalibration for Different Tire Size
BCM 726-12-01 xxxx xx00 xxxx --> xxxx xx4C xxxx
Forum comment: "Original tire size 275/70r18, New size 285/75r18. No DTC codes after 900 miles. This is a small change. Larger tire size changes do calibrate the speedometer but a check engine light will persist."