ULTIMATE TYRE-SIZE SHOOTOUT!

[blockquote cite=”” type=”center”]”Want to fit bigger tyres but unsure what effect they’ll have on your 4WD? We hit the tracks to test 31s v 33s v 35s in every real-world 4WD scenario imaginable”[/blockquote]

There’d be lots of stuffy-shirt science-type boffins out there who could explain exactly what it is that makes us lust after what the next bloke has. These same boffins with their perfectly trimmed fingernails and their lack of sand and dirt marking the part of their driveway that they park on would probably say it has something to do with human nature. We wouldn’t have a clue – all we know is that it’s in a 4WDer’s nature to want bigger tyres.

Yep, if at some stage you haven’t thought “geez the old bus would look good with a bigger set of boots”, even right down in the back of your mind, then you’re probably already rolling around the tracks four foot above everyone else. Tyres are a big investment though, and they’re something you want to get right because no-one wants to be stuck with a $1500+ tyre bill and a 4WD that doesn’t do what they want it to.

The tyre size you run has a massive effect on your 4WD, both for the better and the worst. It’s easy to see the upside, namely better off-road performance. It’s also equally easy to be scared off by the potential downsides – worst fuel economy, a slower 4WD, the works.

What if you could see into the future, and find out exactly what effect bigger tyres had on your 4WD? That’s exactly what we’re going to do, minus the crystal ball of course (ours just says ‘divorce imminent if sand and dirt not cleaned off driveway’ anyway). Welcome to the biggest back-to-back tyre size shootout this country’s ever seen!

OUR TEST TRUCK

[blockquote cite=”” type=”center”]”It’s old, its rattly, it’s dented and it also happens to be tough as old boot leather. say g’day to project GU”[/blockquote]
So the question has to be asked – what kind of vehicle is suited to testing 31s, 33s and 35s back to back? Ideally we wanted something that would run all three sets of tyres without swapping suspension back and forth, which would massively increase our test time.

Project GU runs a modest 2inch lift, and with its big guards it’ll happily accommodate all three sets of tyres without looking gangly or having clearance issues. It’s also a pretty damned typical truck, representing most wagons out there – big turbo-diesel, coil springs at either end and solid axles for off-road ability. Righto, let’s fuel it up, bolt on the trailer and head bush.

4WD CATEGORIES

For the sake of a clearly understandable cover line, we’re testing 31s v 33s v 35s here. That suits most big wagons and solid-axle utes like Cruisers and Patrols, but what if you drive a dual-cab ute or a medium-size wagon like a Prado or a Pajero?

Think of it like this. We’re testing standard sized tyres (31s) versus 2inch-over standard (33s) versus 4inch-over standard (35s). It’s roughly the same as testing standard tyres versus 31s versus 33s on a medium-sized 4WD – the differences in off-road performance will be the same. The only time the test won’t be entirely relevant is in fuel economy, as modern common-rail four-cylinder turbo-diesels won’t be as affected by bigger tyres as the older engines are.

TEST 1: DUNE HILLCLIMB

[blockquote cite=”” type=”center”]Climbing a big dine is the ultimate test of power, so how much difference do tyres make?[/blockquote]

THE THEORY

Whether it’s a big dune off the back of your favourite beach or a monster out in the desert, dune climbing ability is all about power. The problem is, bigger tyres generally mean slower take-off as more power is used up turning the bigger rubber. On the other hand, the bigger the tyre, the bigger its ‘footprint’ when you air down – the size of the contact patch the tyre has with the ground. The larger the footprint, the more the vehicle’s weight is spread across the contact patch and the less likely it is to sink down into the sand and get bogged. Finally, because we’re testing tyres with different widths, theoretically the bigger and wider the tyre, the more sand it has to push its way through, and hence the harder it has to work.

TEST PROCEDURE

Starting at the very bottom of a big bowl-type sand dune, we set out witches hats to outline a 5m wide test track straight up the hill. Our test starts at the bottom and the vehicle attempts to climb the hill until momentum is lost. The distance travelled is measured and then the test track is moved immediately to the right of the first track. This is to prevent the vehicle following the same wheel tracks up the hill, making it progressively easier. All tests conducted at sand pressures.

TEST RESULTS

  • 31s: 13.9m
  • 33s: 34.8m
  • 35s: 33.6m

The 33s were 150% better on the dune than the 31s, but the 35s were actually 3% worse than the 33s.

OUR TESTER SAYS

“We figured that the 35s would be the best tyres out on the sand dunes, because the largest footprint should equal the most traction, right?” says Brenno. “What happened is the 31s simply dug down into the sand quickly, and the 35s laboured the engine too much to the point where it struggled with power output. The 33s were far and away the best combination of all the tyres – big enough to not cut down into the sand, but not so big as to rob power.”

TEST 2: CHOPPED-UP BEACH DRIVE

[blockquote cite=”” type=”center”]”If you’ve ever bucked around driving s busy beach, you’ve gotta read the results”[/blockquote]

THE THEORY

There you are, minding your own business punting down your favourite local beach on a sunny afternoon. It’s low tide so there’s a lot of beach to drive on, but the problem is there hasn’t been much in the way of high-tides recently and there’s a bucketload of 4WDers sharing your passion for everything salty, so the beach is pretty chopped up. You’re getting rocked and rolled around as you try and keep a steady throttle and prevent your mates from headbutting the roof lining.

Which tyres will perform best in this situation? The theory here has a lot to do with your old BMX as a kid. Remember hitting that pothole and flying over the handlebars, when your mate with his sweet new 26inch 10speed just cruised on over the top of it? The bigger the tyre, the less impact any given hole, rut or rock is going to have. The theory goes then, that the bigger tyres here should smooth out the ride across the ruts considerably.

TEST PROCEDURE

We found a particularly rutted section of soft sand and marked out a 50m stretch. The test started by giving the Patrol a slow-speed run-up, entering the test area at a set speed of 30km/h. The test driver then does his best to hold a constant 30km/h speed with a shock meter running to measure how much the vehicle gets rocked around as it crosses over the ruts. Test conducted at sand pressures.

TEST RESULTS

  • 31s: 0.72 Gs
  • 33s: 0.58 Gs
  • 35s: 0.44 Gs

The 33s smoothed the ride out 19.4% over the 31s, and the 35s were a 28% improvement over the 33s.

OUR TESTER SAYS

“The difference in ride quality was instantly noticeable with the bigger tyres,” says Brenno. “Even without the shock meter, it was easy to tell the vehicle didn’t buck and kick around as much with the bigger tyres. It also didn’t want to change direction as much when the front tyres cut through a sandy wheel track. If you’re into punting down the beach, the long and the short is bigger tyres will be a massive improvement.”

TEST 3: MUDY RUTS

[blockquote cite=”” type=”center”]”Now we’re talking! What counts most when things get sloppy?”[/blockquote]

THE THEORY

Mud, glorious mud. Whether you’re happy as a pig in the proverbial or you do your best to avoid the sloppy stuff, sooner or later you’re going to come across a bit of mud you can’t avoid. It’s pretty obvious that a big, open-blocked tyre like a mud terrain is always going to win out against an all-terrain tyre in the mud, but that’s not what we’re testing here. We want to find out if tyre size makes a difference at all. Theories?

The bigger a tyre we bolt on, the wider they are too, which means there’s more rubber in contact with the ground looking for any available traction. If there’s ruts in the mud, then the taller tyres will hold the vehicle up out of them better as well. On the other hand, there’s the same potential issue with sand – the bigger the tyre, the more power is lost turning them. Test conducted at low-range dirt pressure.

TEST PROCEDURE

We found a 25m long section of track with long deep muddy wheel ruts with a high centre in between them. Along this we marked out a 5m wide section of the track with witches hats. The vehicle starts from a stand-still, with the test driver taking off at a medium pace and holding 2000rpm. The test stops when the vehicle loses momentum, the distance travelled is measured and any notes recorded of why the vehicle stopped.

TEST RESULTS

  • 31s: Made it 10m into the mud before coming to an unceremonious halt. The vehicle came to a rest firmly on its diff centres, with the tyres unable to reach the bottom of the ruts.
  • 33s: Made it a further 5m through the mud, finally bringing the Patrol to a rest at the 15m mark. The reason was exactly the same – the vehicle was resting firmly on its diff centres with the tyres unable to reach the bottom of the ruts.
  • 35s: Now we’re talking! With no more effort on the part of the driver, the 35s let the Patrol claw its way through the mud. While the diffs dragged on the high-centre between the ruts, there was enough tyre size to find the firm bottom of the ruts without much fuss.

The 33s were 33% better than the 31s in the mud, and the 35s were a whopping 333% better!

OUR TESTER SAYS

“A bit of a no brainer this one, height makes all the difference in mud and heavy ruts,” says Jeff. “On the 31s the vehicle has more lateral movement, chasing traction from the sidebiters of the tyre until we got hung up on the diff centre. The 33s did not move as much but again that under diff clearance is what stopped us. The 35s, with height and width on their side made it look easy but the engine certainly had to work harder for the result.”

TEST 4: ROCK STEPS

[blockquote cite=”” type=”center”]”If it’s tough low-range crawling you’re into, here’s the test for you”[/blockquote]

THE THEORY

Rock and roll! Rocky tracks are technical and require a lot of thought and skill to properly negotiate. Vehicles come to grief on rock steps not generally because of traction, but because of clearance – clearance to door sills, to barwork and most often to the underside of diff housings and suspension arms.

Suspension and body lifts raise up the body and the barwork, but there’s only one way to gain under-diff and suspension component clearance, and that’s with bigger tyres. Because the diffs are mounted on the same plane as the centre of the wheel, for every 2inches of increased tyre diameter, you’ll generally gain a bit under an inch of clearance downstairs for any given tyre pressure. It’s not necessarily a big-tyre home-run here though – the taller the tyre, the faster the vehicle will want to go for any given RPM, meaning some ability to slowly crawl a hill without stalling will be lost.

TEST PROCEDURE

We located a track with large rock steps that will potentially either diff the vehicle out or lift wheels. On this hill we marked a section of test track 5m wide up the rock steps. The 4WD starts from a stationary position and takes off in 2nd gear, keeping engine RPMs at 1500rpm. To take any wheel lift out to the equation and allow us to evaluate tyres, we locked the rear diff. The idea here is to keep vehicle speed as low as possible without stalling or stopping, and let the vehicle walk slowly. The test ends when the vehicle stops moving forwards at any time or drives out of the test area. Distance travelled is measured, and reason for stopping is noted.

TEST RESULTS

  • 31s: Made it 15m up the hill before getting hung up on a large rock step. On closer inspection, the rear diff had dragged on a large rock to the point where forward progress was no longer possible.
  • 33s: On these tyres the Patrol managed another 5m to take it to a total of 20m of progression. Interestingly though, what stopped it was not the rear diff but in fact the rock slider that dragged until the vehicle stopped.
  • 35s: Running the largest tyres, the Patrol simply walked its way to the top of the hill with the old scrape here or there, but nothing to halt progression. Strike up another win for 35s if tough 4WDing really is your thing!

In this test, the 33s were 33% better than the 31s, with the 35s being a whopping 250% better than the 33s.

OUR TESTER SAYS

“Stating the obvious, before we started we thought the 31s would get stuck on the steps,” says Al. “The 33s and 35s shouldn’t have an issue. Much to our surprise, the 33s actually got hooked up worse than what the 31s did, as they drove over where the 31s got caught but fell in the next hole which allowed them to get hooked up even worse on the sliders. The diameter and width of the 35s allowed them to grab the side of the  hole that the 33s fell in and walk up over the steps.”

TEST 5: WHEEL LIFTS

[blockquote cite=”” type=”center”]Could tyres really makemuch difference to how much your 4WD lifts a wheel?[/blockquote]

THE THEORY

When you’re pushing through a rough bit of track and come across a big old rut that needs crossing, the obvious danger is that the vehicle cross-axles and lifts a wheel in the process. At best this can  simply halt progression as all the power is sent to the wheel(s) in the air – at worst it can result in your pride and joy rolling over onto its side.

What we’ve seen multiple times, but never had any facts to back it up with, is that vehicles with bigger tyres seem to lift wheels less. The theory makes sense – a wheel lift occurs when the diagonally-opposite tyre drops down into a hole. The bigger the tyres, the less they’re going to feel that effect of dropping into the hole, so does that mean the less the vehicle will lift a wheel? We devised a straightforward test to find out.

TEST PROCEDURE

We ran this test on a hill with a seriously big cross-axle rut – the kind that would be guaranteed to lift a wheel. First we determined the safest comfortable line that the vehicle would take in order to lift a front wheel, and directly next to where it lifts the wheel we hammered a large timber garden stake into the ground with height measurements marked every 10cm.

We then set up a video camera to record a close-up of the wheel lift with the timber stake and measurements in clear view. The test driver crosses through the rut on each set of tyres, lifting wheels as the vehicle drives forwards and the camera captures the wheel lift. Finally, we reviewed the camera footage to determine the height of wheel lift.

TEST RESULTS

  • 31s: On the smallest of our three sets of tyres, the Patrol cocked a wheel exactly one metre in height. That’s enough to get the adrenaline pumping!
  • 33s: Second time around on the 33s, the wheel lift measured in at 72cm. Getting better.
  • 35s: Third time’s a charm – for our final run on the biggest rubber, the wheel lift measured in at 61cm. That’s a big difference!

The 31s lifted a wheel 28% higher than the 33s, and the 33s cocked the wheel 15% higher than the 35s.

OUR TESTER SAYS

“This one was fun!” said Jeff. “The feeling of weightlessness in the front corner is something that many people take a bit to get used to. The 31s certainly made the left hand front of the Patrol shoot to the sky. With the rear dropping into the hole physics took over and it was spectacular.

When the 33s were bolted on we found this same obstacle more controllable, less nervousness from both vehicle and driver. Again the 35s won with less lift however the extra engine strain climbing with the larger diameter made me feel the 33s were a good all round choice.”

 

TEST 6: SWERVE TEST

[blockquote cite=”” type=”center”]we find out how our three sets of tyres react to in an emergency situation[/blockquote]

THE THEORY

Okay, so with off-road abilities tested, let’s move onto the gritty stuff. It’s time to find out the effects on handling that changing tyres has. This is going to be very interesting, because there’s logic that says bigger tyres can make handling either better or worse. It makes sense that the bigger and weightier the vehicle, the less sharp its handling will be. On the other hand, bigger wider tyres have a much firmer footprint on the ground, and any increase in tyre width means more tread in contact with the dirt at any one time. Finally, with all tyre pressures being equal there’s the potential for slightly more movement in the sidewall of the bigger tyres. Enough theories – let’s put it to the test.

TEST PROCEDURE

On a long straight stretch of empty dirt road, we set out a single line of six witches hats 10metres apart in the middle of the track. Using a large broom, we brushed the test area of track clear of debris so tyre marks in the dirt could be easily determined. Our test truck enters the test area at 30km/h, and the test driver attempts to maintain that speed while swerving back and forth through the witches hats. The aim is to stick as close as possible to the witches hats. On completion we measured the distance of the outer tyre marks away from the cones at each turn. The test was replicated at both road pressures, and dirt road touring pressures.

TEST RESULTS

  • 31s road pressure 390mm
  • 31s dirt pressure 315mm
  • 33s road pressure 620mm
  • 33s dirt pressure 510mm
  • 35s road pressure 850mm

The 31s at road pressures were on average 400mm from the centre cones and the 35s at the same pressure were over double the distance from the cones.

OUR TESTER SAYS

“We were surprised with the results of the swerve test,” says Al. “The fact that we had more control on dirt pressures was no real surprise as the tyre was able to flex and grip the dirt more than at road pressures. The fact that as we stepped up tyre sizes, the rear began to slide more and more was an outcome we didn’t predict. This was due to the bigger tyres having a taller sidewall, which allowed the tyre to move about a bit more and shift the weight off the rear, causing a small loss of traction.”

TEST 7: ACCELERATION

[blockquote cite=”” type=”center”]”How much difference to tyres really make to acceleration”[/blockquote]

THE THEORY
It’s one of the most common complaints out there – that fitting bigger tyres makes a vehicle slower. But it’s not simply a case of bigger tyres being heavier than smaller ones – sure, they are to a degree, but that’s not the root cause of the issue. It comes down to maths, something we’ve never quite understood properly since we skipped that one class and never learned how to do long division.

It’s all about final drive ratios – which are a combination of everything from the gear ratios in your transmission, to those in your diffs, and finally the overall rolling diameter of your tyres. A significant change in tyre size up or down will change your final drive ratio, either making the vehicle slower to accelerate but with a higher overall top speed, or faster off the mark but quicker to reach its top speed. It can be fixed by changing your diff’s crown wheel and pinion gearing ratios, but before we go to that extent let’s first test just how much of a difference taller tyres do make.

TEST PROCEDURE
Anyone with a manual diesel 4WD will attest to just how quick first gear is. You’re barely off the clutch taking off from a standstill when it’s time to clutch back in and grab second. All that time spent off the power would throw our acceleration test results out the window, so instead of a standing start we’re going to measure rolling acceleration.

On same stretch of high-range dirt as the swerve test, we marked out a 50m stretch of track. Our test vehicle enters the area at 30km/h in second-gear high-range and immediately accelerates. We would then measure the top speed of the vehicle at the end of the 50m stretch. Gear changes required at 3000rpm if needed – no revving it to redline, it’s all about replicating a normal driving experience. Finally, the test was repeated at both highway and high-range dirt pressure, using a GPS to ensure the exact same speed was reached for each test.

TEST RESULTS

  • 31s Road pressure 58km/h
  • 33s Road pressure 56km/h
  • 35s Road pressure 54km/h
  • 31s Dirt pressure 64km/h
  • 33s Dirt pressure 61km/h
  • 35s Dirt pressure 59km/h

On average, the 31s were 3km/h faster across the test course than the 33s, and the 33s were also 3km/h faster than the 35s.

OUR TESTER SAYS

“Conducting this test of a gravel surface showed us a few things, one being how important pressure is to traction,” says Jeff. “A 6km/h difference between road and off-road pressures is huge. The other part is overall diameter, the taller the tyre the more stress on the drivetrain. This is also why it does make sense that when increasing tyre size you should also consider a driveline ratio change.”

 

TEST 8: BRAKEING

[blockquote cite=”” type=”center”]”There’s go, then there’s whoa. here’s how your 4WD’s breaks react to bigger tryres”[/blockquote]

THE THEORY

On the opposite side to acceleration is braking – how well your 4WD pulls up to a stop. If your 4WD was originally designed to stop while wearing one particular set of tyres, how does changing tyres effect that braking performance? On one hand the physics involved in slowing down bigger, meatier tyres could potentially have a negative effect on braking. On the flipside, that bigger contact patch that the larger tyres have with the ground has the potential to actually bring a 4WD to a halt much quicker. Let’s put it to the test and find out once and for all.

TEST PROCEDURE

This is a pretty straightforward test, and it should clearly highlight the differences the tyres make. On same stretch of dirt track, we marked out a 50m length of test area with witches hats. The test vehicle enters test area at 40km/h and immediately brakes. We then measure the distance required to bring the 4WD to a complete stop, including any sections of wheel lock-up. The test is then repeated for both highway and high-range dirt tyre pressures.

TEST RESULTS

  • 31s Road pressure 13.1m
  • 33s Road pressure 13.3m
  • 35s Road pressure 13.8m
  • 31s Dirt pressure 9.7m
  • 33s Dirt pressure 10.4m
  • 35s Dirt pressure 10.9m

On average, the 33s took 0.2m longer to stop than the 31s, and the 35s took 0.45m longer to pull up than the 33s.

Tony T

OUR TESTER SAYS

“We figured there would be some difference going into this test, but the end results blew us all away,” says Al. “We all know that on the dirt a tyre grips better when it has a lower pressure, but three metres better braking distance from each tyre size was pretty impressive. It’s proof that the right tyre pressures could save you from a serious crash. The vehicle only marginally took longer to stop on bigger tyres than on smaller ones – about a metre difference between the 31s and the 35s.

That kind of difference is nothing to worry about – it’s the difference between various brands of brake pads, for instance. The biggest shock was the imprint that the tyres left in the ground when the GU came to a complete stop. You could see where the tyre had spread and dug in. The different feel while under brake was impressive – at dirt pressures, we had more control when coming to a stop.”

TEST 9: DAILY DRIVER FUEL ECONOMY

[blockquote cite=”” type=”center”]”What you’ll spend on fuel around town and on the way to work and back”[/blockquote]

THE THEORY
Whether you have a fuel-sipping common-rail ute or drive a big old thirsty petrol bus, none of us want to spend more at the petrol pump than we need to. In the same vein as the idea that bigger tyres take away power, it’s a generally accepted concept that big rubber uses more fuel. But is this true, or is it simply because a larger diameter tyre travels further for every rotation, therefore tricking your odo into thinking you’ve done less kays than you actually have?

Our first fuel test simulates a ‘daily driver’ mode – the 4WD’s mostly empty, and it’s all blacktop driving, a mixture of city and highway runs. This will be interesting, as the taller tyres actually drop the engine’s RPMs at any given road speed. 110km/h on 35s will put the vehicle at a much lower RPM than 110km/h on 31s, so will this actually improve fuel economy?

TEST PROCEDURE
First things first – the 4WD is to be emptied of all camping gear but anything that someone would typically leave in the vehicle, remains. That means a(n empty) fridge, tools and spares in the drawers, etc. Next, we mapped out an approximately 150km test route that takes in a 50/50 split of highway driving at the speed limit, and around-town/backroads driving. The real trick here is to measure exact distance travelled and exact fuel used as accurately as possible. This means using a GPS to log distance, and filling up via a jerry can to a specific point in the fuel filler neck just under the tank breather, not just ‘first or second click of the fuel pump’. Finally, fuel economy was worked out per 100km/h. All of these tests were conducted at road pressures.

TEST RESULTS

  • 31s: 12.03L/100km
  • 33s: 13.58L/100km
  • 35s: 15.01L/100km

Running 35s used 3L/100km more fuel than 31s.

TEST 10: LOADED OFF-ROAD FUEL ECONOMY

THE THEORY

Righto, we’ve got our around-town fuel figures, but what about the really juicy ones? What effect do bigger tyres have on your 4WD’s fuel economy when you’re loaded on a trip? There’s actually a bit more in this than you might first think. Fuel economy is a funny thing. The effect that tyres have around town at road pressures is likely to be markedly different from the same effect that they have when you’re out on your next dirt-road adventure. To figure it out properly, we filled the jerry cans and headed back out on a test loop.

TEST PROCEDURE

This test is all about replicating fuel usage on a typical big trip – say, Fraser or the Cape. You’re loaded up, there’s a lot of weight going on and you’re spending a lot of time aired down on the dirt. We mapped out another approximately 150km route that takes in at least 30% dirt. We then loaded the big Patrol like we were heading away – full fridge, swags on the roofrack, plenty of weight inside the vehicle to replicate a family, the works. We then followed the same test procedure as the on-road fuel test, filling via a jerry can. At the start of the dirt we aired down to dirt-road driving pressures, and once we were back on the tarmac we aired back up to road pressures.

TEST RESULTS

  • 31s: 16.46L/100km
  • 33s: 17.90L/100km
  • 35s: 19.75L/100km

OUR TESTER SAYS

“This test clearly showed the effect that bigger tyres have on older engines like the Patrol’s TD42,” says Brenno “In the bush it’s not like the Patrol ever really lacked power, but you do find yourself squeezing the throttle just that bit more. Not the end of the world – if tougher off-road driving is your thing then you’d happily pay that bit of extra fuel for the traction benefits. However, once again the 33s were the real winners, only effecting fuel economy by a small amount.”

TEST 11: HIGHWAY RANGE CLIMB

[blockquote cite=”” type=”center”]Proof that bigger tyres don’t always mean being passes by B-doubles[/blockquote]

THE THEORY

There you are, punting away happily up the blacktop on the way to Aunty Agatha’s annual Christmas get-together. Your 4WD’s running beautifully, you’re sitting on the speed limit and even over-taking a couple of P-platers here and there. And then it strikes – that massive range climb that seems to go on forever and threatens to end with you being over-taken by grannies in old VWs and fully loaded B-Doubles. Or does it? Like the sand, big highway ranges need power. That power can potentially be robbed by bigger tyres, but on the other hand bigger tyres may just move the highway rev-range to a point that’s spot-on. Only one way to find out.

TEST PROCEDURE

To test this theory out, we punted up the highway and up three big range climbs. The first is a two kay climb straight up a hill, the second a shorter but steeper run up a mountain range and the final a monster four kilometre, two-stage climb that picks up again just as you think it starts to taper off. We started each climb in fourth gear at 100km/h, and held no more than half throttle to see how each set of tyres made the vehicle react. The lowest speed seen on the GPS at any stage on the hill was recorded.

TEST RESULTS

    • 31s 76km/h 86km/h 72km/h
    • 33s 87km/h 93km/h 72km/h
    • 35s 84km/h 87km/h 82km/h

OUR TESTER SAYS

“This one was another massive win for the mid-sized tyres,” says Brenno. “Interestingly, the 31s made the vehicle rev too hard in 4th gear at 100km/h, meaning it was outside of its peak torque range. The 35s as expected sapped a bit of power but still out-paced the 31s, and on all three hills, the 33s shone through superbly. It sat beautifully on boost and in its peak power range right up all the range climbs.”

TEST RESULTS

[blockquote cite=”” type=”center”] Two weeks of full-blown testing comes down to this moment. So which tyre size takes out the gong?[/blockquote]

In this test we put three of the most common tyre sizes back to back against each other. In reality there are bucketloads more sizes available, but the general idea is this. You’ve got three choices – factory sized rubber, tyres around 2inch bigger in diameter and tyres about 4inch bigger in diameter.

Our 31s shone through in a variety of tests. Understandably they were the best when it came to fuel economy, acceleration, handling and braking – makes sense, since the vehicle was originally designed for a tyre size very similar to this. If any of these factors weigh heavily for you, then the best tyre upgrade you can make is to stick with a standard size and simply fit a good aftermarket tyre.

It’s not hard to figure that 35s will be the best when the going gets tough. 4WDers have bolted bigger tyres on their vehicles since the dawn of low-range transfer cases. We’ve now got hard facts and figures that show just how much improvement 35s make if punting up a low-range track is your thing – and it’s a bucketload!

And then there’s the 33s. These really were the quiet achievers of the test. They never truly shone above the other tyre sizes in many terrains save for sand. What they did offer though, was the very best compromise across every single test and terrain. For most of us, our 4WDs are all-rounders – they’re daily drivers, they’re weekend warriors and we escape bush whenever we can. If that sounds like you, then there’s no question about it – 33inch tyres, or 2inches over standard diameter, is the very best option. 33inch tyres take out the test!

BONUS INFO! TYRE SIZES

31s, 33s and 35s are an easy way to refer to the tyres we’re testing, but that’s technically incorrect. The majority of the time you hear tyre size measured in inches, it’s for a 15inch rim (but not always). The official measurement would be 31(inches diameter or height)x10.5(inches wide) by 15 (diameter of wheel in inches). These size tyres almost always measure in at 31×10.5R15, 33×12.5R15 and 35×12.5R15.

On the other hand, our GU runs 16inch wheels. That means we’re ditching the imperial measurement for a metric one – 265(millimetres in width) x 75 (tyre profile – the height of the sidewall from the tyre bead to the shoulder, measured as a percentage of the tyre width) x 16 (diameter of the wheel). Confused yet? Don’t sweat it. This table should help you out a little.

While these two measurements are generally accepted as being fairly close to one another (ie a 265/75R16 is a 31, a 285/75R16 is a 33 and a 315/75R16 is a 35), there are small differences. But that’s just nit-picking, so let’s keep moving.


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