Each step from 33s to 35s to 37s on the 70 Series is a trade, not an upgrade. Go too small and you leave capability on the table. Go too big and you build a vehicle that drinks more, wears faster and needs more supporting modifications than you budgeted for. The right size depends on what you actually do with your 70 Series, and the tyre debate is the most argued topic in any forum thread, campfire circle or work car park.
The 70 Series arrives from the factory with more wheel arch room than most platforms. Boxy guards, long-travel suspension and the sheer height of the body mean you can grow a fair bit before you reach for a cutting wheel. That room isn't unlimited. Plenty of builds end up with modifications that cost three times more than the tyres did.
At a Glance
- 33s bolt on with little or no modification on most 70 Series variants and suit the majority of touring use.
- 35s are the sweet spot for serious off-road work, but gearing, braking and fuel consumption all need attention.
- 37s transform the stance and the capability, but the supporting modifications list is long, expensive and unforgiving, and sizes past the factory allowance need state engineering approval before they're road legal.
- Every tyre size increase rotates the speedo reading further from reality and reduces effective braking force unless the rest of the drivetrain is addressed.
- The build that photographs best at camp isn't always the one that gets you home.
33s, the honest choice nobody regrets
On a stock or mildly lifted 70 Series, a 285/75R16 or 285/70R17 sits close to the 33-inch mark and clears the guards with minimal drama. No guard rolling, no body lift, no differential drop, no immediate need to re-gear. Your speedo error stays manageable and fuel consumption doesn't fall off a cliff. For the Great Central Road, the Gibb River Road or a serious Victorian high country run, 33s are plenty of tyre.
The honest case for stopping here: a well-chosen 33 in the right compound, a quality mud terrain or aggressive all-terrain, will outperform a cheap 35 in nearly every real-world scenario. Tread compound, construction and sidewall strength matter more than diameter at this end of the range. A 33 also stays more civil on the highway, which counts if your 79 does weekly driver duty or tows a trailer.
The look is noticeable but not dramatic. The guard gap closes and it reads purposeful rather than stock. It hasn't got the planted stance that turns heads at the servo, so if that's part of your brief, 33s might leave you wanting more inside twelve months.
35s, where serious touring begins
A 315/75R16 puts you firmly in 35-inch territory. This is where the 70 Series looks the part in photographs and where off-road capability takes a real step forward. More sidewall volume absorbs corrugations better, spreads a bigger contact patch at low pressures in soft sand, and improves approach and departure angles once you add the ride height from a moderate lift.
The checklist grows with it. Most guards need careful attention at minimum, particularly at full lock and full compression on the front. A quality suspension lift in the 50mm range is strongly advisable, for clearance and to keep the geometry honest. Then the gearing argument becomes real. Factory differential ratios were engineered around a stock tyre diameter, so a 35 makes those ratios effectively taller, which blunts low-speed torque, increases turbo lag under load and puts more heat into the drivetrain when you're crawling. Re-gearing fixes that directly and is the most worthwhile supporting modification at this size.
Braking is the other conversation. A larger diameter increases the lever arm against your brakes, and the factory stoppers are sized for the factory tyre. That doesn't make 35s dangerous to stop. It does mean the braking you rely on is quietly degraded unless brake upgrades are in the plan. Fuel use on a 70 Series diesel goes up, and on a long highway run you'll notice it at the bowser rather than on the gauge.
The stance at 35 inches on a modest lift is genuinely impressive. Guards filled, sidewall showing confidence, approach angles that look serious sitting still. That's why 35s dominate the builds that actually get used: real capability without the complete drivetrain rebuild the next step demands.
37s, the build commitment
A 37 on a 70 Series is a statement and the photograph proves it every time. It looks like it means business before it has left the driveway. The arch fills completely, the ride height is commanding, and on genuine rock crawling terrain or in deep sand the extra diameter and sidewall volume deliver what 35s can't match.
What that costs you is comprehensive. Guards need trimming or flares to avoid contact through the full suspension travel. A significant lift, body modifications and likely a differential drop or re-positioned steering geometry all go on the list. Re-gearing moves from advisable to mandatory: without it, the effective ratio change from a 37 makes motorway cruising laboured and fuel consumption punishing. Diff, gearbox and transfer case all work harder, and if they weren't in perfect condition before the tyres went on, they'll tell you about it.
Wheel and tyre weight climbs a long way at this diameter. You feel it in steering effort, in steering return, and in the wear rate on wheel bearings, steering components and CV joints. The spare becomes a project of its own: a full-size 37-inch spare changes the weight equation for any rear-mounted carrier, and potentially your towball mass calculation if there's a camper trailer behind you.
The right owner for 37s is doing a dedicated off-road build where highway kilometres are minimal and the supporting modifications budget is already allocated. The wrong owner bolts on the tyres first and sorts the rest later. Later always costs more, and in the meantime the vehicle is genuinely compromised.
The verdict, take a position
If you tour seriously but also cover real highway distance, 35s are the right answer. You get a genuine capability step, you get the look in every campsite photograph, and the supporting work, while real, is finite and well understood. Re-gear, lift properly, check the brakes, and your 79 becomes a better version of itself instead of a compromise in two directions.
33s aren't a consolation prize. They're the correct choice if you value low running costs, highway comfort and a vehicle that needs nothing changed to work well. For long-distance touring with occasional technical terrain rather than dedicated rock crawling, a quality 33 will serve you better than a budget 35 with no supporting work done.
37s are for a specific build and a specific owner. Respect them as a full commitment rather than the next rung on a ladder.
If the tyre change has you looking at the cabin while the 70 Series is off the road anyway, the PVS Automotive 70 Series headunit range is worth a look. A larger screen makes maps legible in dusty conditions, and Newtracs or Wiki Camps alongside a dedicated offline maps app becomes far more usable on a quality display.
