Tech Corner: Going from 35s to 37s—Bigger Tires is a BIG Investment

Is there ever a time when we don’t crave more? Bigger, bolder, grander, flashier. In the battle of man’s ego, we all know that a few extra inches on a tire can make a world of difference. And that prized ride sitting in your driveway? It’s an extension of yourself. Your hard work, your willpower, your audacious spirit. So if you really want bigger and badder, it’s time you start thinking about 37s, my friend.

Bigger tires open up a range of possibilities, giving that 4×4 a meaner, meatier aesthetic and an undisputed boost in performance. This upgrade transforms a vehicle from off-road capable to off-road dominating.

Naturally, we turned to someone with experience in extreme off-roading—Dan Guyer, the Category Manager of Wheel & Tire at Keystone Automotive. “The difference between a 35 and a 37 is whether you make an obstacle or you don’t. When you go out in the woods, you want to feel challenged a little bit—and 37s makes everything pretty doggone easy,” says Guyer.

But chasing bigger tires in the name of off-road performance demands some genetic reconfiguration. Tuning 37s is quite the job for most vehicles, and the upgrade can be a bit of a rabbit hole. Before you make the snap decision for bigger and badder, there are a few things you need to take into consideration.

Are you sure you’re up to it?

Will Your Rims Cut It?

First things first, what kind of wheels are you running? Some 37s will work with the rims used for 35s. After all, the use of a 17-inch rim is pretty common for both tires. However, this won’t be the case for everyone’s project. Remember, 37s are usually much wider tires, and this will have an effect on the demands of the rims’ width and offset. So, the width of those current rims just may not cut it.

Do your homework and determine if the wheels you’re currently running will work. And if not? Well, while wheels can be expensive—trust me—this is only one of many aspects of the platform you’ll be addressing.

Pain is gain, right?

Do you have enough lift height?

Alright, ya lifted your truck or Jeep just to fit those 35-inch tires. Now, it’s only natural to think back to when you moved up in tires sizes in the past and how it wasn’t a deal breaker. “The difference between 31s and 33s is two inches—but nobody ever notices it,” explains Guyer. “But when you go from 35s to 37s, it’s a big deal. You go up so much in weight and leverage.”

That means, the lift kit you’ve got for those 35s probably won’t do the trick for 37s. According to Skyjacker Suspensions’ Wheel and Tire Guide, most full-sized pickups will fit a 35-inch tire with about a 6-inch lift, while Jeeps will accept them with just a 4-inch lift. And while these numbers can vary across builds and supplier kits, you can’t change facts: these bigger tires are beasts. What fits 35s won’t fit 37s properly, especially if you only have the bare minimums. Ergo, you need an upgrade.

But that’s not all…

Guyer explains that many people will fit 35s under a JK Wrangler with only a small lift, meaning they’re not changing control arms. But that bigger lift kit? Well it complicates things. “With a taller lift, there’s more—adjustable control arms, so you can change your pinion angle and your caster. It’s not just adding more lift. You’re probably going to need new shocks to make them longer.” Better factor that into the budget as well.

Oh, and don’t forget—these beefier tires will wreak havoc on stock steering components. Tie rod ends, ball joints, and everything in between is going to need an overhaul, too. Overlooking this aspect is what can leave you up Schitt’s Creek without a paddle when you’re out wheelin’.

Aaand, speaking of bigger tires, Guyer reminded us of yet another side effect. “You’re taking a vehicle like a JK that has 32-inch tires—they’re probably 60 pounds each mounted and balanced—up to a 37-inch tire and wheel combination that weigh 120 pounds and you have the stock brakes. So while you’re at it, bigger brake kit.”

This is something you truly can’t afford to skip. Bigger brakes with stock wheels will help increase stopping power. But with a setup like this, they’re working more to restore it. You’ll need upgraded brakes both for safety when traveling on road ways and for ensuring you have proper control while off-roading. And if you wheel with friends and family? This is non-negotiable when the safety of loved ones is on the line.

Do you have the guts?

Oh no, no—we’re not done yet, pal. We told you, pain is gain, and now we’ve got to talk axle assembly. Guyer describes how many off-roaders obliterate their factory axles when they hit the trail with 37s. He recommends that when you take the leap from 35s to 37s, you should set yourself up with chromoly axle shafts to handle the upgrade, and that you can’t ignore those ring gears either.

The Jeep or truck at hand has gears meant to turn stock wheels. And even if you upgraded them to handle 35s, you can still find your vehicle struggling to turn 37s. Yes, it is expensive—“when you get into your axles, you can spend $4000,” says Guyer. Your wallet will be screaming at this point, but you really don’t want to wind up with a sluggish vehicle or, worse, out on the trail with a snapped axle. And Guyer gives us this pro tip for Jeepers: Sleeve the front axles on JKs when looking to run 37s.

When the wheels and potential ring gear upgrade are installed, it’s time to look at recalibrating the speedometer. Oh, and while you’re there, it’s worth looking at the engine, too. If you haven’t done the work to turn 35s, you definitely need to now. Tuners from Hypertech, among others, can double as calibrators, so you can start there. Complementary upgrades include looking for some additional performance from a cold air intake and a proper exhaust. However, if you’re really looking to get the snap back, you’ll want to consider some more serious mods on the engine, such as boost.

Is this the right investment for you?

It’s true, upgrading from 35s to 37s requires a lot of work. A lot more than you probably thought. It may just be one size up in tires, but while 35s keep a vehicle well-balanced between street capabilities and off-road performance, 37s majorly tip the scale toward the off-road segment. Guyer reiterates that this is a mod that should be taken seriously. “It’s not for everybody. I highly recommend anyone considering straight to 37s to drive something with those bigger tires for more than a trip around the block before they decide to do it.”

If you decide to take the step, however, you will undoubtedly be elated with the improved off-road performance. We warn you though, once you’ve been bitten by bigger tires, that desire for “more” doesn’t go away. But maybe just settle for some harder obstacles and trails while you pay off this mod…