Most 37s are not 37 inches

Nominal 37×12.50R17 means 37.0″ overall diameter. Measured, they run under it, and by different amounts: the BFGoodrich KM3 is 36.5″, the Nitto Trail Grappler, Toyo Open Country M/T and Maxxis RAZR MT all 36.8″, the Falken Wildpeak M/T 36.7″. Only the Toyo in 37×13.50R17 actually measures 37.0″.

So a “37” is realistically a 36.5 to 37.0 inch tire, and the most popular one is a half-inch short of its own label. If you are calculating clearance to the tenth of an inch, use the model’s measured diameter.

LT315/70R17 is a 35, not a 37

This one costs people money. LT315/70R17 measures 34.4″ on the KM3 and 34.6″ on the Trail Grappler and Falken. Jeep itself markets LT315/70R17 as the 35-inch tire in the Wrangler Xtreme Recon package.

Anyone told that LT315/70R17 is a 37 is being misled by about two and a half inches. Our 35-inch guide covers that size properly.

There is also no mainstream metric equivalent of a true 37 on a 17-inch wheel — you would need a 254 mm sidewall, which no volume mud-terrain is built in. In this size class, 37s are a flotation-size-only proposition.

Going up can cost you load capacity

This is the least intuitive part. Most 37×12.50R17 mud-terrains are Load Range D with a 50 psi maximum, not Load Range E at 80. The 37″ KM3 carries 3,525 lb, but only at 50 psi; the LT285/70R17 version of the same tire carries its rating at 80.

The exceptions are the Maxxis RAZR MT, which is a Load Range E at 3,970 lb, and the Toyo in 37×13.50R17, an E at 4,300 lb. If you tow or haul, check the 37’s max load at its max pressure against your door-jamb placard before assuming bigger is stronger.

What they weigh

A 37 in this class runs 74 to 91 lb per tire. Against the same model in 35×12.50R17 the step up adds about 2 lb on the Falken, 4.4 lb on the KM3, 5.9 lb on the Maxxis, 9 lb on the Toyo and 15 lb on the Nitto Trail Grappler — which at 88 lb is the heavy one here.

That is unsprung, rotating mass at the end of a longer lever. It is the reason the gearing conversation exists.

Which models are actually made in 37s

All six of the main mud-terrains offer 37×12.50R17. Maxxis has the widest 37″ range overall. Falken is the notable gap: no 37×13.50R17 and no 37×12.50R20, just the 12.50R17 and a 13.50R20. Milestar is the cheap route in at $477 per tire, less than a KM3 costs in 33s.

What else has to change

Here we have to be careful about what is published and what is folklore. On a Jeep JL, AEV — which develops and publishes fitment limits for its own kits — rates its 2.5″ DualSport RT for 37×12.50R17 on a Rubicon and only 35s on a Sport or Sahara, because the Rubicon has the wide-track axles. For its 4″ kit AEV publishes a hard number: maximum wheel backspacing of 5.2″ or less for a 37×12.50. That is the one manufacturer backspacing figure we could source.

On gearing, the honest answer is that the commonly quoted 4.88 or 5.13 for 37s has no manufacturer or engineering-body source we could find — it comes from retailer tech pages and forum consensus. The only manufacturer figure in this territory is Jeep’s own: the Xtreme Recon package pairs a 35-inch tire with a 1.5″ lift and a 4.56 axle ratio, with 4.88 offered on Rubicon for a 100:1 crawl ratio. That is the maker conceding that one size class up from stock already needs a numerically higher final drive. Draw your own conclusion for two size classes.

Speedometer and TPMS recalibration is real and cheap by comparison — AEV’s ProCal SNAP is $225 and handles tires up to 42″ plus gear-ratio changes on 2018-and-later JL and JT.

The budget, honestly

Five 37″ KM3s is $2,930 against $2,025 for five 33s. Then wheels with correct backspacing, a lift, probably gears, possibly trimming, and the labour on all of it. The tires are the line item people plan for and the smallest one.

One outlier worth knowing: the Maxxis RAZR MT’s 37 costs only $37 per tire more than its 33, making it by far the cheapest premium-brand route to the size.