4X4 makers continue to get ground clearance measurements wrong…
Why do ‘ground clearance’ measurements differ so much from vehicle to vehicle, and why do other media organisations gulp down the nonsense? We explain the truth about 4X4 ground clearances and manufacturer claims.
Words and Photographs by Robert Pepper: The term ‘clearance’ essentially means a distance between two things, but that’s not quite “clear” enough. So, 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 are actually 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 4X4 owner cares most about is ‘ground clearance’, as defined in the ADRs. That’s because 4X4s are designed to traverse rough terrain, up and down steep hills, across ruts and over obstacles. 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 box 219mm high.
Unfortunately, quite a few 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 4×4 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.
This article was prompted by Unsealed 4X4’s latest test vehicle, the Nissan Navara N-Trek Warrior, or more specifically, its claimed 268mm ground clearance, which is impressive indeed, its 32-inch tyres and a rear live axle. Wow. Only it’s not, wow.
See, according to the tape measure, it’s more like 240mm. We reached out to Nissan for clarification and were told, “Ground clearance is calculated by design from a ground plane to the lowest point of the vehicle frame at simulated GVM”. Note the expression, ‘vehicle frame’. That doesn’t include the diff pumpkin. So, according to ADRs, Nissan is wrong and by some significant margin. But that hasn’t stopped other media outlets swallowing the measurement being peddled…one well-known brand even referenced it in its recent 4X4 of the Year. Hmmm. Maybe no-one had a tape measure.
We spoke to a few more 4X4 manufacturers to find out how they define clearance. Toyota told us it: “only quotes 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 its 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 clearance 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+. They made a similar error with the Fortuner, claiming it was 279mm when in fact it was 225mm. When I got a Fortuner on test after the launch, measured it and pointed out the error, Toyota did at least admit its mistake and issue a press release changing the figure…which was mostly ignored by all the journos who had simply written it down without thinking or checking…same as with the N-Trek Warrior. Hmmm.
Ford is the same. 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, and both have live axles, that’s 46 / 2 = 23mm more clearance…yet Ford quote the stock Ranger at 237mm. So, 237+23 = 260mm, not 283mm. And a stock Ranger doesn’t have 237mm under the diff, more like 220mm, 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 marketing information. Want to see me underneath a Raptor measuring the thing in a really shaky video? See it HERE. So, I 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. They’re correct in their measurement, but their measurement is useless to off-roaders, and misleading. Here’s a screengrab from the current Everest brochure:
This says running and ground clearance are the same…in direct contradiction of the ADRs. Actual measurements are lower than 225mm.
Mitsubishi claims 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, but apart from an acknowledgement, we never got a reply we can publish. It does appear it also uses ground clearance in the proper sense of the word, and we measured a stock MY17 Jeep Wrangler to check which was 240mm, exactly what Jeeps specs say it should be. Wranglers have taller tyres than the average 4X4.
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”. Well, why don’t we keep that in mind…read on.
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 4X4 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.
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, but I wouldn’t recommend it – the Great Wall Steed I 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 4X4 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 4X4 owners and those who tow do with them on a day-to-day basis.
I don’t think there’s any malicious in this, just people simply not understanding the difference between the clearances, because every time I’ve gone over it with a carmaker representative they have been surprised, and none have ever been able to explain how my tape measure manages to confound their spec sheets. But now you know.