Since I started my initial vehicle research two odd years ago, I’ve changed the rim and tyre selection many times. I had a basic understanding of the pro’s and con’s to changing wheel size from OEM, but I never thought it would take me down the rabbit hole it has.
Early Hot Tip – Unless you’ve tried and failed with the OEM tyre, don’t change it.
There are more negatives to changing rim size, offset and tyre size than there are positives. I have tried getting where I want to go with OEM tyres, unfortunately the OEM tyres failed me in the wet and stopped me getting to places I want to go due to lack of clearance (tyre and suspension). I’ve sat my car on its belly many times, having to turn around and back out of tracks.
If you haven’t tried getting to the places you want to go, then you’re doing it wrong. Modify your vehicle based on your needs, not popularity, the aftermarket industry, YouTubers, your work mates or other influence.
Try first, you will truly be surprised how capable a stock 4WD out of the showroom is. If your vehicle comes standard with highway terrain tyres, you probably want to upgrade them to all terrain, but keep them the same size. Let me put it this way, 31″ (265 size) all terrain tyres will get you around the majority of Australia and the Victorian high country tracks.
Lets look at the outside diameter (OD) of tyres and the common upgrades to how much additional force you’re transferring onto your driveline.
- 31″ = 787mm diameter
- 33″ = 838mm diameter (6.48% larger)
- 35″ = 889mm diameter (6.08% larger than 33″ – 12.96% larger than 31″)
Most utes today are released with a 265 wide tyre, typically around the 30.5″ average diameter. Australia typically fits metric size tyres, not imperial. 4WD owners have this imperial fascination, trying to meet 33″ or 35″ when talking how big their tyres are. This usually means illegal changes.
Using Maxxis Razr AT811 for example, dealers typically use 17″ and 18″ rims with 265/65/17 (777mm) and 265/60/18 (782mm). Every tyre will have a unique OD.
When you change your vehicles tyre lift by more than 25mm, which is the legal amount in most states, you will notice all the negatives mentioned in this post. The best thing you can do is make minor changes, for example, 265/65/17 (777mm) to 275/65/17 (790mm/1.67% increase) or 265/70/17 (808mm/3.98% increase), which are legal changes and you won’t have scrubbing issues. Similar for 18″. No need to widen your rim or change your offset. You will experience less issues with these changes than going larger or chasing imperial dimensions.
If you change your tyres within legal limits, minor changes, your fuel economy will only change 1-1.5lts/100km. If you change them chasing imperial sizing and maximum tyre lift, 2-3 lts/100km change is realistic. These are not highway tyres, AT and MT are much heavier. Now add the loss of economy from accessories weight. When added together, suddenly your fuel economy has changed significantly from when you drove it home from the dealer, admiring how economical your new 4WD is, now confused why you’re using 4-5 lts/100km more than that time in your life.
This goes with fuel economy below, but changing your tyre diameter in an automatic vehicle will change how any overdrive gearing functions. Most new four wheel drives today have an overdrive gear that works above 95kph. When you change your tyre diameter and subsequently your speed is then different, your overdrive may no longer function at 100kph, and only work in 110kph zones. Or neither!
So you’re thinking you can just change to manual gearing to get overdrive? Sure, but now any cruise control stops working. Yep, active cruise control works on automatic only. Most vehicles have a passive cruise system, old school type, but a sacrifice, along with remembering to now change gears manually as your vehicle slows / put it back into automatic.
A larger diameter tyre takes more force to move the tyre from standing start and rolling resistance, including using a wider tyre which takes additional force to rotate the tyre. More force equals more torque from your engine, which equals more fuel. Larger rim and/or tyre equals more weight. More weight equals more force required to move the weight, more fuel.
Using Ronny Dahls below video, he discusses his fuel economy from stock 30.5″ to 31.5″ to 33″ tyre changes he had made on his 2020 SR5 Hilux.
- 30.5″ HT – 9.5lts/100km combined driving – 730km from a tank of diesel.
- 31.5″ AT – 11lts/100km combined driving – 630km from a tank of diesel.
- 33″ MT – 13.5lts/100km combined driving – 500km from a tank of diesel.
A significant change in how far your vehicle gets you from a tank of fuel changing tyre size. If you leave the tyre size at, or near, OEM size, you’ll have better economy when you add weight to the vehicle and suffer its consequences.
My fuel economy for the 2021 Dmax X-Terrain on stock tyres (265/60/18 – 781mm OD) has been:
- 7.4lts/100km highway at 110kph
- 9.2lts/100km city driving in Melbourne
- 13lts/100km off-road driving Mt Disappointment
Power & Performance
Your vehicle is engineered with a specific gearset through the entire driveline, engine to wheels. When you change any part of that driveline gearset, wheel size in this case, you change how that gearing responds through the entire driveline. With larger wheels your vehicle now moves faster in low range first gear than it did at OEM. At highway speed it now moves faster, which means instead of being in high gear at optimal RPM for cruise, now the automatic box may hunt (higher RPM), the manual may shudder / be sluggish due to power loss.
Increasing engine power is what people do, but is not the solution to this problem, because there are speed limits and regardless how much power your vehicle has, the same issues occur at each speed limit. Instead you have to change your front and rear diff ratios to transfer that power more efficiently to the wheels once again. Reduction gears in the transfer case only fixes low range, not high range driving.
You have to bring back the engines capacity to turn the wheels at the engineered optimal speed.
A common problem with 4WD’s sporting larger wheels than OEM is that they often break driveline parts. Axles, bearings, universal joints, the list goes on. When you make the engine turn the wheels at a lower RPM than engineered, you place more force on all the parts. More force means you break things faster, in some instances, much faster.
Typically this affects vehicles under more stress, off-road, GVM upgraded with tools and heavy towing, compared to those just driving on the bitumen unladen with such modifications (driving the kids around or such).
All of my research says curb my attitude, put the “looks cool” factor out of my mind and make smart decisions based upon the long list of negatives in changing rim and tyre size. My conclusion is that small changes are best. If you need large tyres to get where you’re going, then you need them, but accept you need to change your diff gears as part of the process.
I’ve tried with OEM tyres, failed. I’m going to stay legal with my choice, 22mm of lift. If that fails me, then the next set of tyres I will shift to the next size which is 850mm OD (34mm lift from OEM), change the diff gears and get it engineered. Honestly, I believe legal tyre changes will get me where I’m going combined with maxtrax and a winch.