Going bigger? Run the numbers first. Pick your year, make, and model to auto-fill your factory tire size and stock axle ratios, then compare tire sizes, see your speedometer error, find the right regear, convert wheel offset to backspacing, and estimate ride height. A live side-view of your truck updates as you go.
Don't know your axle ratio? Pick your truck and we'll fill in the factory tire size and stock gear options for you.
Diameter change
+3.39"
+10.7% — 31.61" → 35"
True speed @ 60 indicated
66.4 mph
Speedo reads 10.7% low
Revs per mile
576.2
was 638.1
Effective ratio (new tires)
3.09
feels like 3.09 with your 3.42 gears
Regear to restore
3.73
exact 3.79 → nearest common 3.73
Cruise RPM @ 65 mph
2328
new tires + 3.73 gears
For reference at 65 mph: stock (31.61" tire, 3.42 gears) ≈ 2364 rpm · new tires on 3.42 gears ≈ 2135 rpm.
New backspacing
4.53"
current 5.21"
Poke (sticks out)
+1.68"
further out than stock
Inner clearance
+0.68"
more room
Total ride-height increase
≈ 3.7"
2" lift + 1.70" tire radius
Ride height rises by the lift plus the tire-radius increase. Whether a given tire actually clears — at full stuff and full lock — depends on your specific truck, backspacing, trimming, and lift type. Use this as a starting point, not a guarantee.
A taller tire travels farther per revolution, so your engine spins fewer times for the same distance. That effectively raises your gearing — numerically lowering the ratio your truck feels — which softens acceleration, hurts towing grunt, and can drop cruise RPM. Regearing the axles to a numerically higher ratio restores the factory feel. The calculator gives you the exact target and the nearest ratio you can actually buy.
Offset (in millimeters) is the distance from the wheel's centerline to its mounting face; backspacing (in inches) is the distance from the mounting face to the back lip. A lower or negative offset pushes the wheel outward ("poke"); more backspacing tucks it in toward the suspension, where you can run out of clearance. The tool converts between the two and shows how far a new wheel/tire moves in each direction.
Your truck rises by the lift height plus half of any tire-diameter increase. But whether a tire actually clears at full compression and full steering lock depends on your specific platform, backspacing, and how much trimming you're willing to do. Treat the estimate as a starting point and confirm fitment for your truck.
Taller tires effectively raise (numerically lower) your gearing — the engine turns fewer times per mile, so you lose low-end torque and acceleration. The calculator shows the effective ratio and the regear needed to get your original feel back.
It depends on your stock tire size and axle ratio. Enter both into the calculator and it gives the exact regear to restore your factory gearing, then snaps it to the nearest commonly available ratio (e.g. 3.73, 4.10, 4.56).
Yes — a larger tire makes the speedometer read low (you're going faster than it shows) and the odometer under-count miles. The calculator shows your true speed at an indicated 60 mph and the percentage error.
Backspacing (inches) = (wheel width + 1) ÷ 2 + offset ÷ 25.4. The calculator does this both ways and also shows how much further a new wheel pokes out and how much inner clearance you lose.
There's no universal answer — clearance depends on the truck, backspacing, trimming, and lift type. The calculator estimates total ride-height change, but confirm real fitment for your specific truck before buying.
Pick your year, make, and model in the calculator and it loads the factory axle-ratio options for that truck and fills in the stock tire size. If you've done an axle swap, choose 'Other' and type your ratio. You can also check the door-jamb sticker or the axle tag.
Talk to a diesel technician about gearing, towing, and fitment for your exact truck before you spend on parts.
Find a SpecialistEstimates for planning only — confirm fitment, gearing, and load ratings for your specific vehicle before purchasing or installing parts.
