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Aev Procal Settings - 35" Nitto Recon Grapplers on 20" wheels

Electronut

Electronut

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Thought I'd put out a lending hand for those of you running this tire/wheel size setup and using the Procal for speedo adjustment.

These tires measured 34.6 inches mounted and on the truck. Putting this value in the Procal resulted in +3-4 mph error still. Not sure why but is what it is.

Sweet spot to get it it calibrated spot on was 33.5 value on the Procal. Ran against my JBV1 Radar App and Google Maps.

TPMS adjustment worked great too!

Cheers!
 
Im a bit surprised to hear that 35s measured that close to 35" while mounted and on the truck. What PSI are you running? I have 37s on mine that measure closer to 35" on the truck currently.
 
tchur1 said:
Im a bit surprised to hear that 35s measured that close to 35" while mounted and on the truck. What PSI are you running? I have 37s on mine that measure closer to 35" on the truck currently.
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Pretty much spot on the spec Nitto provides for them and physically measured as such on truck with it's weight.

I'm at 54 psi fronts and 49 psi rears. Contact patch pretty darn good. Could go little less than this but the edges on these tires are slightly tapered so I don't see it being necessary. Don't want to lose more gas mileage either.
 
What was your measuring method? I, too, have 37's that measure 35. My method was a level on top of the tire and measure from the bottom of the level to the ground (parked level surface).
 
ClawSS said:
What was your measuring method? I, too, have 37's that measure 35. My method was a level on top of the tire and measure from the bottom of the level to the ground (parked level surface).
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Exactly how I did it but instead of a level I used a straight section of 2x4 lumber.
 
you should measure from the ground up to the center of the hub. That number will be less than half of the total height I bet. :cool:

To get a true circumference, mark a spot on the tire with a corresponding mark on the ground. Move the truck for 1 full rotation of the tire and mark the ground. Then measure the distance between the two marks. That will give you the most accurate measurement.

My BFG 35's came out to just a little over 33" when at running pressure of 45/35 PSI.
 
Electronut said:
These tires measured 34.6 inches mounted and on the truck. Putting this value in the Procal resulted in +3-4 mph error still. Not sure why but is what it is.

Sweet spot to get it it calibrated spot on was 33.5 value on the Procal. Ran against my JBV1 Radar App and Google Maps.
Click to expand...

Electronut said:
Exactly how I did it but instead of a level I used a straight section of 2x4 lumber.
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This is why, because of the method you used. The BCM is looking for the rolling circumference (which procal converts to diameter). You would measure from the ground to the center of the wheel, then multiply by 2. That gives the closer (and smaller) diameter for the true rolling circumference.
 
Honestly we are splitting hairs here guys. Your talking maybe 1/16 to 2/16 of an inch variance using the rolling wheel method to measure.

I did the way AEV said to measure in their instructions and even that didn't work to calibrate correctly is the bottom line.

I ended up having to use 1.1 inch less as the data input into the Procal than from my original measurements to get the speedo on the money. I'm sorry that no way my measurements are that far off. Going to hub is subjective too. How would you know your measuring smack in the center of the wheel cap as well?

Measurerment of the tire also jives with the spec Nitto lists for it right on their website.

Cheers!
 
I dont think we are splitting hairs here since your initial measurements still resulted in a 3-4 MPH difference after adjustment. And finding that 33.5" was correct, not 34.6" shows the difference was a lot more then 1/16".

My personal experience would verify the methods outlined above. When I initially tried to update mine via procal i was way off until I did the rolling test that @Crusty old shellback and @Jimmy07 are referencing. I cant remember exactly but my 37s measured to like 35.5" and that was accurate with the procal, not the 36" or so that I measured the first time via the method you outlined.

Either way, glad you got yours dialed and hope youre enjoying the truck!
 
You guys are all debating your measurement methods assuming the GPS speed you’re seeing on your phone is 100% accurate all the time. Get it close and don’t worry about it!


Sent from my iPhone using Tapatalk
 
mountainears said:
You guys are all debating your measurement methods assuming the GPS speed you’re seeing on your phone is 100% accurate all the time. Get it close and don’t worry about it!


Sent from my iPhone using Tapatalk
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Lol. Agreed. This has quite blown up and was to be a helping thread not one where my measurement methods are critisized but I have thick skin Lol. Issue here and the point is that AEV needs to have different instructions for measurement as their method doesn't work and appears my measurements were off but I was only using their instruction guidance so I learned a few things now while at it.

I can confirm 100% my speedo is spot on because GPS apps I use jive spot on when in my 2016 Jeep GC Overland that has a stock setup.

These Nitto tire specs are 32.52 inflated so even using that for setting would have produced likely a 2 to 3 mph slower recording to correct speed.
 

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Electronut said:
Lol. Agreed. This has quite blown up and was to be a helping thread not one where my measurement methods are critisized but I have thick skin Lol. Issue here and the point is that AEV needs to have different instructions for measurement as their method doesn't work and appears my measurements were off but I was only using their instruction guidance so I learned a few things now while at it.

I can confirm 100% my speedo is spot on because GPS apps I use jive spot on when in my 2016 Jeep GC Overland that has a stock setup.

These Nitto tire specs are 32.52 inflated so even using that for setting would have produced likely a 2 to 3 mph slower recording to correct speed.
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What's the fun in a forum without a little back and forth on seemingly benign stuff like speedo calibration lol.

My goal isn't to criticize your method of measurement, especially if thats how AEV says to do it, more so just to highlight for those that do care about absolute accuracy how to get there. Not everyone needs their speed dialed in perfectly but plenty on here do, so why not share that info for those that want it.
 
The specs on the tires are when they are inflated, but not under load. Found that out the hard way.

The reason measuring the tire height doesn't come out right is because the load is actually only on the lower half of the tire. That's why Jimmy and I said to measure the bottom half, then double it. That's gets you about as close as you can, without actually doing the rolling measurement I mentioned. I didn't invent it, just passing on knowledge I've learned from others.

The reason to use the actual rolling measurement is because that is exactly what the computer is using to determine speed. How much ground did the vehicle cover for one revolution of the tire.

And if you want to get real nitpicky, it will change depending on the pressure in the tire. Higher pressure will make the ground covered more. Lower pressure will be less. ;)

Not trying to be a A hole. Just want to make sure correct info is being put out.

I watched a youtube video last night about installing a split AC system. Guy seemed to know what he was talking about. he even showed that his system needed 12 gage wire and a 15 amp 2 pole breaker for 220 power as per the manufacture. All is good right? At least to that point.

Then the guy shows he has some 10 gage 3 wire that he's going to use instead of going out and purchasing the correct size wire. No big deal as he had it on hand.

And the 10 gage wire is rated for 30 amps. So he goes and puts in a 30 amp breaker. :eek: Well the manufacture spec said 30 amp breaker for a 10 gage wire, so whats the problem?
But that was for a system more than twice the size of his. If that system has a issue and draws more than 15 amps, he's going to burn stuff up, possibly even his building.
 
Crusty old shellback said:
The specs on the tires are when they are inflated, but not under load. Found that out the hard way.

The reason measuring the tire height doesn't come out right is because the load is actually only on the lower half of the tire. That's why Jimmy and I said to measure the bottom half, then double it. That's gets you about as close as you can, without actually doing the rolling measurement I mentioned. I didn't invent it, just passing on knowledge I've learned from others.

The reason to use the actual rolling measurement is because that is exactly what the computer is using to determine speed. How much ground did the vehicle cover for one revolution of the tire.

And if you want to get real nitpicky, it will change depending on the pressure in the tire. Higher pressure will make the ground covered more. Lower pressure will be less. ;)

Not trying to be a A hole. Just want to make sure correct info is being put out.

I watched a youtube video last night about installing a split AC system. Guy seemed to know what he was talking about. he even showed that his system needed 12 gage wire and a 15 amp 2 pole breaker for 220 power as per the manufacture. All is good right? At least to that point.

Then the guy shows he has some 10 gage 3 wire that he's going to use instead of going out and purchasing the correct size wire. No big deal as he had it on hand.

And the 10 gage wire is rated for 30 amps. So he goes and puts in a 30 amp breaker. :eek: Well the manufacture spec said 30 amp breaker for a 10 gage wire, so whats the problem?
But that was for a system more than twice the size of his. If that system has a issue and draws more than 15 amps, he's going to burn stuff up, possibly even his building.
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Dude you nailed this explanation. Makes absolute complete sense. So much so I went in the garage to re-measure. ;) Still doesnt come out correctly but better. I got hub center exactly too since cap on stock 20" night edition wheels is exactly 1-3/4 inches to center. Came to 16- 2/16 for half wheel from ground to hub center. Doubled up obviously is 32-1/4 inches. Still 1-1/4 inches short of correct value the Procal required for spot on speed calibration. Still doesn't equate but this is what I got.

Yeah mentioned in another post you have to take YouTube videos with a grain of salt. I do a bunch of wiring at home. Including rewiring of 2 x 200 amp panels in the basement to add a generator subpanel. Talk about nerve wrecking. Also did a near $12k solar/lithium battery upgrade on our Airstream Travel Trailer a few months ago. That's just the cost for materials. I did all the labor. You can always upsize wire but can never downsize. You run greater risk of fire and frying things. Good example there though and makes alot of sense.

HD trucks are new to me but I'm not new to handling mechanical functions on cars etc. Hell..... Just installed leveling kit, shocks, and bunch of other stuff on this rig. I'll post up when I get all done. Thuren sway bar on the way along with Putco Blade light bar. Window's getting tinted Saturday. Getting down to the last of it. Happy with the build outcome thus far. :D
 
I measured mine the way AEV says to in their instructions same as the OP did. I can’t remember the exact measurement but I followed their instructions. I haven’t ever had to manually “tune” a tire size in a computer before since I’ve always had old sh!tboxes so I figured I should follow the instructions to get the computer set right.

I found their method to be off as well. My speedo is ~3 mph fast at 75 mph (actually moving 72) I never bothered to adjust it any closer. Been that way for three years. So, I guess my truck has 4% less miles on it than the odo thinks it does but it’s not that serious to me.
 
Rockcrawlerdude said:
I measured mine the way AEV says to in their instructions same as the OP did. I can’t remember the exact measurement but I followed their instructions. I haven’t ever had to manually “tune” a tire size in a computer before since I’ve always had old sh!tboxes so I figured I should follow the instructions to get the computer set right.

I found their method to be off as well. My speedo is ~3 mph fast at 75 mph (actually moving 72) I never bothered to adjust it any closer. Been that way for three years. So, I guess my truck has 4% less miles on it than the odo thinks it does but it’s not that serious to me.
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You walked my walk.

Lower the Procal setting 1 to 1.1 less than your current setting and you should get dialed in pretty darn good but depends on your wheel and tire size.
 
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