Why 4×4 ground clearance isn’t the same for all vehicles
Ground clearance is a fundamental measurement for 4x4s, but it’s not always what you think and the message from car makers can be confusing.
Updated March 23 2020
A 4X4 vehicle is designed to traverse rough terrain. Up and down steep hills, across ruts and over obstacles. That’s why you need ground clearance.
The general understanding of ground clearance is simply how big an object you can drive over; say you have 220mm of ground clearance, you’d be able to drive over a small box 220mm high.
Sounds simple? But maybe not. Here are some definitions from the Australian Design Rules (ADRs):
FRONT AXLE CLEARANCE AND REAR AXLE CLEARANCE – the vertical distance from the level surface on which vehicle is standing to the lowest point on the ‘Axle’ differential (when applicable in case of a front ‘Axle’) of the vehicle.
GROUND CLEARANCE – the minimum distance to the ground from the under side of a vehicle excluding its tyres, wheels, wheel hubs, brake backing plates and flexible mudguards or mudflaps.
RUNNING CLEARANCE – the distance from the surface on which an unladen vehicle is standing to the lowest point on the vehicle excluding unsprung mass.
SUSPENSION CLEARANCE – the minimum dimension measured from the front and the rear suspensions to the ground.
So there’s a bunch of different clearances, which is absolutely fine as each one of those measurements is relevant in some way to vehicle engineering standards. But, what the average 4×4 owner cares most about is ‘ground clearance’, as defined in the first paragraph of this article, and above in the ADRs.
Unfortunately, some manufacturers quote running clearance instead of ground clearance. And unless you go and read the definitions, you’d think that the two are the same. It also appears that on occasion the running clearance measurement gets morphed into ground clearance, both by manufacturers and motoring journalists.
The result is that owners read a ‘clearance’ specification and end up thinking that’s actually the height of something they can drive over when it’s not.
Why does this matter? Because ground clearance is a critical part of a 4×4’s capability.
Marketing people would understand if a car rated for 235kW had only 220kW…same deal with 235mm of alleged clearance actually being 220mm. Even worse really, as it would be difficult in daily driving to tell the difference between 220kW and 235kW, whereas the difference between 220mm and 235mm is easy to spot; you’re hung up on a rutted track, wheels spinning, where others have cruised on without a problem.
It’s not just muddy tracks either. Ground clearance is important on rocks too. It’s easy to get hung up on a differential pumpkin and then you’re going nowhere:
We spoke to a few different 4×4 manufacturers to find out how they define clearance.
Toyota told us they: “Only quote the Running Clearance as the ‘Ground Clearance’ requirement was deleted from ADR 34/04 (Clause 6.4.1) in October 2007. As such the only value we publish is the Running Clearance. As per the ADR this is the distance from the surface on which an unladen vehicle is standing to the lowest point on the vehicle excluding unsprung mass.”
In other words, they use running clearance, not ground clearance. As their 4x4s have live rear axles, that’s not good. However, Toyota quotes 220mm clearance for the Prado, and that’s actually what it is under the rear diff. But it also quotes for the Rugged X, Rogue and Rugged Hilux variants running clearances of 251mm, 216mm and 253mm. And these all have the same diameter tyres as the standard Hilux, basically 265/65/17 or close to it. Go stick a tape measure under the rear diff and I think you’ll find it’ll be more like 216mm, not 250+.
So, how about we give the ADR people the measurements they want, and the 4×4 public what it wants which is actual ground clearance?
Ford is doing the same thing. It quoted an amazing 283mm of clearance for the Raptor. Given the Raptor’s tyres are about 33 inches, around 46mm taller than those on the PX2 Wildtrak/XLT, that’s 46 / 2 = 23mm more clearance…yet Ford quote the stock Ranger at 237mm. So, 237+23 = 260mm, not 283mm. And as the photo below shows, a stock Ranger doesn’t have 237mm under the diff, so the Raptor’s actual ground clearance will be more like 240mm, a good 40+mm less than what people think it is based on Ford’s press release.
So we asked, and Ford told us that “[when] we refer to ground clearance we refer to ‘Sprung Clearance’ i.e. anything above the springs like body etc. A differential would be classified as an unsprung clearance. The stated ground clearance for Ranger Raptor is 283mm, and would adhere to this definition.”
In other words, Ford’s clearance measure isn’t the lowest point on the vehicle, it’s some other point. Here’s a screengrab from the current Everest brochure:
It says running and ground clearance is the same, in direct contradiction of the ADRs. Actual owner measurements are lower than 225mm.
Mitsubishi says that “MMAL uses the ADR definition for Ground Clearance and the lowest point varies by specific model whether that is a 4WD or not.” That’s as it should be. Their ground clearance definition appears to be actual ground clearance.
We also asked Jeep and it does appear it also uses ground clearance in the proper sense of the word. Below is a 2017 Wrangler:
Now for Mercedes-Benz. I was contacted by a reader in Switzerland who owns a G-Wagen and was not happy the quoted ground clearance measurement of 245mm seemed to him to be overstated, as his measurement was more like 230mm. He was told by his local Mercedes-Benz customer care that:
“In addition, the ground clearance is measured by drawing a circular arc through the deepest point (differential) and the track gauge. The angular point of the arc defines the ground clearance. Consequently, the ground clearance does not correspond to the deepest point of the vehicle”
Which to my mind is bizarre, it’s like saying our definition of the length of the vehicle doesn’t include the bumpers.
A quick look at the Mercedes-Benz Australia website shows the G300CDI, a twin-live-axle vehicle with a claimed ground clearance of 230mm; impressive, considering it runs 265/70/16 tyres, same diameter as most other 4X4s. And even more impressive is that the ute version, the Cab Chassis, has 252mm, albeit with slightly taller 265/75/16 tyres. So that’s another 22mm of clearance, and given it’s a live axle, that means another 44mm of tyre diameter. Yet the tyres aren’t anywhere near that much larger, and you wouldn’t think the diff pumpkin has been made any smaller, particularly for a ute.
I checked with Mercedes-Benz about the 252mm figure and was told: “It is correct and not a typo. Keep in mind that this figure is with no weight/tray on the back.”
So it’s clear that ‘clearance’ is a term that is not properly and consistently used by the 4×4 manufacturing industry.
One big misconception is that I’ve got this wrong because I’m not allowing for suspension compression under load. And this is from people talking about 4x4s with at least one live or solid axle. So, to explain why that’s not the case:
Adding weight to a live-axled 4×4 does not change the ground clearance as the live axle is unsprung weight – the chassis and body compress onto the axle, but the distance between the differential and ground remains the same. The worst that will happen is that the tyres will compress a little, but you’d add air pressure to compensate.
If the vehicle was equipped with fully independent suspension then, yes, adding weight would make a difference to ground clearance. But even that argument isn’t relevant, as we’re talking here of unloaded vehicles.
Here’s my Ranger showing its independent suspension up front, and its live axle at the rear:
A suspension setup such as the Ranger above is known as IFS, or Independent Front Suspension. In these cases, there is typically a bit more clearance at the independently sprung front axle than the rear live axle. As weight is added to the vehicle the two clearances tend to equalise. But again, the whole weight-on-vehicle argument is moot, as we’re measuring ground clearance unladen.
Okay, enough background. Here’s the advice.
What you need for a touring 4×4 is ground clearance of 220mm or above. You can work with less – the Great Wall Steed we drove over the Simpson had 170mm and while it scraped, we never got stuck or needed a second run. More is good too, as 4x4s like with independent suspension front and rear such as the Nissan Patrol Y62 and Land Rover Discovery offer up to about 280mm, the latter depending on its air suspension mode.
In order to check the ground clearance just get your tape measure out and check for yourself, as it’s hard to tell from the specifications, and you’re liable to be told whatever you want to hear by someone who might even believe they understand the question.
A suspension lift will only increase ground clearance if the vehicle has independent suspension front and rear, such as the Pajero, R51 Pathfinder and Y62 Patrol. It will not change the ground clearance on any vehicle with one or more live axles – all it does there is lift the chassis and body a bit higher, which has definite benefits but ground clearance is not one of them. And yes, live-axle fanatics, that is static clearance not dynamic, but we’re talking here of static measurements so save the whole live-vs-indie suspension date for another time, just like film camera purists haven’t yet fully given up the fight against change.
Running taller tyres will increase the ground clearance on any 4×4, which is one reason why it’s done. The road regulations for doing so are shamefully inconsistent between states and within the industry misunderstood, but it may be legal to run taller tyres in which case going up another 25mm to 50mm or so on the average 4×4 is fine, and you’ll get half that extra diameter as ground clearance. Even another 10mm is worth it.
It’s now time for all 4×4 manufacturers to measure ground clearance properly, as per the ADR definition, and quote only it in their press releases and spec sheets. Oh, and maybe also stop misleading people about tow ratings too. All we want is a bit of real-world thinking in the specifications to reflect what 4×4 owners and those who tow do with them on a day-to-day basis.