🛠️ What did you do to your Tremor today? [2026 edition]

[Blade420Play🔪🏆]

Confirmed that a 37x12.5R18 T/A KO3 will fit in stock spare location when aired down to 15 psi and forscanned the truck to let it know that it has larger tires.

The tire fit is TIGHT, but it is resting on all four of the plastic pucks underneath the bed. The factory tailpipe just kisses it, so it will get wrapped with exhaust wrap today and I’ll swing by my muffler shop next week. I believe a tweak to the rear-most exhaust hanger will give it a 1/4 inch of clearance or so. Not very worried about it as truck is a vegan and after running down Highway at 90mph I could put my hand on that section and leave it without burning myself.

I can recommend the procedure at the link posted below for the Forscan mods. No issues after following his guidance and speedometer tracks gps perfectly up to 90mph.

So, need to chalk test it, tweak exhaust hanger, and wrap exhaust pipe to be done, but we are getting there. Pretty happy with it now that Speedo matches and tire fits under the bed. Truck rides better, definitely looks better and hey, I have always loved me some All Terrain T/A’s.

View attachment 268614

https://www.thebakeradventures.com/post/forscan-speedometer-recalibration-37-inch-tires-ford

So, I am getting 37s next week. I have been watching my speedo vs my Google GPS and my speedo is under by 2 mph. How much of a difference between the 35s and 37s mph wise? I can and will use forscan to fix it, but I am fine being a mile off either direction. I assume I am running more like a 34 with the wear on my tire now.

 

[MrFancypants]

.How much of a difference between the 35s and 37s mph wise?

Circumference - Wikipedia

en.wikipedia.org

 

[Apples]

When we search "FORScan 37" tire speedo correction" one number is commonly tossed out: 2799 [mm circumference].

That worked a treat! for me after fitting my nominal 37" Nitto Recon Grapplers. Those measure 36.5" inflated, but unloaded. When we place the truck's axle weights on two each of our tire choice, the actual radius [axle centerline to ground] shortens considerably, affecting the dynamic circumference of the tire.

IOW, the circumference of an inflated but unloaded 36.5" tire is greater than when the same tire has it's axle weight on it.

2799 seems to be the sweet spot, and put my truck's speedo to 40 MPH = 40 MPH, 50 = 50, 60 = 60 and 70 = 70 which is close enough for my numbers' OCD!

 

[Apples]

I will add, too, that the effective final drive gearing (our axle gearing when considering our tire diameters) change when fitted w/ 37s acts just like if we had kept a fresh set of Duratacs and their 35.1" actual diameter and then had 4.10 geared axles instead of the 4.30s

So, not much at all. It's actually better for my tastes as the effective 4.10 gives my Godzilla a little more something to "lean against".

The only detriment I can conceive of for my truck is that I have made any ultimate Low Range + transmission 1st gear's gearing a tad taller for uber-slow crawling, but then again my Tremor's wheelbase is too long for those shenanigans anyway.

70 MPH used to be 2150 and now it's 1850. Perfect for my 10th gear cruise, and better everywhere else, too. I'm not concerned with any additional unsprung weight, either, since my 37 X 11.5 X 17 weighs 71 lbs, the Vision Flow 351 aluminum 17 X 8.5" wheel weighs 29 lbs putting the assembly at an even 100 lbs. That's about what the factory Goodyear/Tremor aluminum road wheel assembly weighs.

/blah blah blah

 

[MrFancypants]

2799 seems to be the sweet spot, and put my truck's speedo to 40 MPH = 40 MPH, 50 = 50, 60 = 60 and 70 = 70 which is close enough for my numbers' OCD!

Since I have a FX4 my truck came with 33’s. When I installed 35s I used the unloaded circumference spec and, big surprise, overcompensated the speedo adjustment. I then noticed the factory circumference setting was smaller than the calculated unloaded circumference (duh). I think I used the same % offset to adjust my calculation for the 35s. I updated FORScan and ended up with a 2 mph variance at 80 mph. I left it this way because I like to speed so a little safety buffer keeps me under the 9 mph get out of jail free threshold.

This is all to say there is not an exact science here. The specific tire, age (treadwear), tire pressure, and payload all play a role in changing the actual circumference of the rolling tire.

 

[Blade420Play🔪🏆]

Since I have a FX4 my truck came with 33’s. When I installed 35s I used the unloaded circumference spec and, big surprise, overcompensated the speedo adjustment. I then noticed the factory circumference setting was smaller than the calculated unloaded circumference (duh). I think I used the same % offset to adjust my calculation for the 35s. I updated FORScan and ended up with a 2 mph variance at 80 mph. I left it this way because I like to speed so a little safety buffer keeps me under the 9 mph get out of jail free threshold.

This is all to say there is not an exact science here. The specific tire, age (treadwear), tire pressure, and payload all play a role in changing the actual circumference of the rolling tire.

Yeah, I like the reading faster than I am going too. I tend to get up to the 80s on the interstate (70 top speed here).

 

[Blade420Play🔪🏆]

Circumference - Wikipedia

en.wikipedia.org

Ew. I don't want to do math. It's Saturday.....

 

[Godzilla/Tremornator]

Ew. I don't want to do math. It's Saturday.....

"hey google"

what's the circumference # i need to put in forscan to correct my speedometer for tires with a diameter of ??

isn't that the way it should be done?

 

[Blade420Play🔪🏆]

"hey google"

what's the circumference # i need to put in forscan to correct my speedometer for tires with a diameter of ??

isn't that the way it should be done?

More like this....

 

[MrFancypants]

Ew. I don't want to do math. It's Saturday.....

 

[DTX2023Tremor]

More like this.... View attachment 268640

That's interesting that Google says the difference is that much. I haven't dealt with changing my tire size in Forscan. At 73 mph, my gps has me at 75 mph - only 2 mph faster than the 4 - 5 that google seems to think I would be driving.

 

[Blade420Play🔪🏆]

That's interesting that Google says the difference is that much. I haven't dealt with changing my tire size in Forscan. At 73 mph, my gps has me at 75 mph - only 2 mph faster than the 4 - 5 that google seems to think I would be driving.

This is the real world number I was looking for. So, I probably will even out with the new tires. At least if my Saturday math works out

 

[Modman]

With tires that are exactly 35" and 37" diameter it's (37/35)-1 = .057

Depending on the brand some tire diameters measure slightly less than nominal and some are a lot less. Props to Google for identifying a range!

If you're staying with the same tire but just up sizing it's probably pretty close to the 5.7%. Maybe Google's lower number (5.4%) is accounting for a bit more deflection with the increased sidewall but lower pressure of the 37?

 

[Explorerinil]

Confirmed that a 37x12.5R18 T/A KO3 will fit in stock spare location when aired down to 15 psi and forscanned the truck to let it know that it has larger tires.

The tire fit is TIGHT, but it is resting on all four of the plastic pucks underneath the bed. The factory tailpipe just kisses it, so it will get wrapped with exhaust wrap today and I’ll swing by my muffler shop next week. I believe a tweak to the rear-most exhaust hanger will give it a 1/4 inch of clearance or so. Not very worried about it as truck is a vegan and after running down Highway at 90mph I could put my hand on that section and leave it without burning myself.

I can recommend the procedure at the link posted below for the Forscan mods. No issues after following his guidance and speedometer tracks gps perfectly up to 90mph.

So, need to chalk test it, tweak exhaust hanger, and wrap exhaust pipe to be done, but we are getting there. Pretty happy with it now that Speedo matches and tire fits under the bed. Truck rides better, definitely looks better and hey, I have always loved me some All Terrain T/A’s.

View attachment 268614

https://www.thebakeradventures.com/post/forscan-speedometer-recalibration-37-inch-tires-ford

I love your videos btw!

 

[Blade420Play🔪🏆]

With tires that are exactly 35" and 37" diameter it's (37/35)-1 = .057

Depending on the brand some tire diameters measure slightly less than nominal and some are a lot less. Props to Google for identifying a range!

If you're staying with the same tire but just up sizing it's probably pretty close to the 5.7%. Maybe Google's lower number (5.4%) is accounting for a bit more deflection with the increased sidewall but lower pressure of the 37?

I will be going from the duratrac which is what ~34.8 new (mine are obviously smaller with wear) to the different rto1 which says online it is ~36.8.

 

[Avslash]

Somebody might have mentioned it already, but be aware, supposedly 2799 is the highest circumference the truck will accept.

 

[Apples]

I will be going from the duratrac which is what ~34.8 new

No.

Unlike most "nominal" 35s, especially those in flotation sizing, the Duratracs measure a true 35.1" when new.

Somebody might have mentioned it already, but be aware, supposedly 2799 is the highest circumference the truck will accept.

It is the sweet spot, too, and when fitting a nominal 37" that measures 36.5. It's right on the money, in fact.

One thing folks seem to be overlooking is the "loaded radius"/dynamic circumference being physically smaller than the tire's actual inflated but unloaded diameter/circumference.

2799 works.