A towering 4×2 cabover tractor unit, towing a semi-trailer with three axles and six super singles. Travel anywhere in Europe and you’ll notice that this is the most common big rig configuration on the continent. And in the UK and Ireland, for that matter. Usually the tractor has a 450 to 550 hp engine and is built by DAF, Scania, Volvo, Iveco, Mercedes-Benz, MAN or Renault.
Pictured above is a 2017 DAF XF with a Super Space Cab and a 450 hp DAF-Paccar MX-11 engine (as in 10.8 liter displacement). The semi-trailer is a so called curtainsider, the usable bed length of this widely used type of semi-trailer is around 13.60 m (44’7”).
During the seventies, super singles started to replace the dual wheels more and more. Instead of a semi-trailer with a widespread tandem and dual wheels, the norm became a chassis with a tridem and super singles. The main advantages of these wide, single tires are less wear and tear and a better fuel economy for the tractor. The closer a tire is to the center of the axle, the more it will wear and tear when cornering. On a dual wheels setup, the inner tire will always wear faster than the outer tire.
Regarding the tractor’s fuel economy, a wide super single has less rolling and air resistance than a set of standard dual tires.
A very similar rig to the one in the first picture, yet this superbly 2015 DAF XF tractor has more grunt, as it’s equipped with a 460 hp MX-13 engine (12.9 liter displacement).
In multiple EU-countries, these 12-wheelers are rated at a maximum GVM of 44 metric tons (97,000 lbs). The gross weight is limited to 40 metric tons (88,185 lbs) though when the rig is crossing borders, so when transporting goods internationally.
A close-up of a tridem I shot last year, BPW axles with Fulda super singles.
Many types of transport follow the 12-wheeler concept, like this Scania R-series V8 with a LAG dry bulk tipping tanker. LAG (Lambert & Arnold Geusens) is a renowned Belgian manufacturer, specialized in tankers. The company used to build buses and coaches too, but in 1991 that division was taken over by Van Hool, also from Belgium.
An Italian O.ME.P.S. dry bulk tanker, towed by a 2017 Scania S450 tractor (450 hp – 12.7 liter). The drive axle of a 4×2 tractor in this segment is rated at a legal maximum axle load of 11.5 metric tons (25,350 lbs).
A 2018 Volvo FH (460 hp – 12.8 liter) with a dry bulk tipping tanker, actually tipping. Modern trucks and tractors have a big mouth. Especially when said mouth -aka the grille- is completely blacked out and stands out even more, like on this Volvo. Currently, engines compliant with the latest emission standards need a lot of cooling capacity, so there’s the answer.
Since we just walked by some tankers, another important advantage of the super single tires worth mentioning, is the fabrication of a wider (semi-) trailer frame so that the tank can be mounted lower, which means more stability while on the road. Of course the same applies to the self-supporting type of tankers. Dual wheels on tanker trailers and semi-trailers have become extinct almost entirely.
The last one, a reefer, towed by a splendid and brand new DAF XF with a 480 hp MX-13 engine. These days many top segment tractors are fully air suspended: front axle, drive axle, cab and seats.
Dual wheels on big drawbar trailers and semi-trailers are still prevalent in logging and heavy- and special haulage. In the earth moving and brick hauling business they also hold their own quite well. For the rest the duallies are long gone and won’t come back.
I’d say 6×2 tractor units are more common in the UK.
You will see British plated 4x2s in the Netherlands because companies involved in continental haulage buy those. UK is 44,000kg so UK-only hauliers go for 6x2s.
I don’t know why, if 4x2s can be rated at 44 ton. Local laws? Backward thinking…?
I know in the US the weight limits are tied to the number of axles, ie XX ton per axle, and their spacing. So if there are lower axle limits that would explain why they run 6×2’s.
Personally I’m not understanding 3 axles on the trailer and only one on the business end of the tractor. 2 and 2 just makes more sense from a balance perspective.
Never thought about axle limits. The UK is full of ancient little stone bridges which might not enjoy heavy trucks.
I’m studying for my US Class A CDL and it’s bringing home how little I knew about the law and theory side of trucking despite being an ex trucker in the UK. It was 4 days driving, pass the test, here’s the keys.
Seeing 3 axle tractors with tandem trailers here is jarring to my eyes. Virtually all big “artics” in the UK will have a tri-axle trailer. (usually but not always 6×2)
The max loading on axles and total vehicle weight are calculated using the “Bridge Formula” in the US and the name says it all as the biggest concern is bridge loading.
I had never thought about the number of axles on tractor units, but during my 2 1/4 hour drive to work through the middle of Wales this morning I made it a 60/40 ratio of 2×6 to 2×4
Lee, the 4x2s would likely be for lighter loads, ie plated to run at 38 ton or whatever. The trucks running to the continent will be plated at 40 ton.
I am hearing Ford, through their JV with Otosan in Turkey, is planning to get back into the over-the-road market in Western Europe with a new large cabover. I wonder what their chances of success are.
In the very near term? Not too good. Turkey has just been slapped with double the tariff on steel and aluminum that the other NATO allies are required to pay. Of course, that is probably going to go away when Ford points out to the POTUS that it will impact their business case for this JV.
On a smaller scale, pun intended, one of the vehicles that I am considering for my next new “car” is a Transit Connect. These are built in….Turkey? Or is it Spain now?
The POTUS will just tell Ford that they should build the trucks 100% in the US and ship them over there. Anything else wouldn’t be fair. This JV seems DOA.
Jim, to clarify things, it’s this cabover. To be unveiled at the upcoming IAA in Hannover. So it does exist, further technical specs are not available yet. At least, I didn’t find them…
Regarding its cab design: half Volvo – half Scania. Even a blind man can tell.
The issue at hand: no dealership network whatsoever in Western Europe, Ford sold its Euro-truck division to Iveco in the mid-eighties. Since then we only got the Transit (you also drove one), that’s all, nothing bigger.
Wow. The styling is an embarassingly obvious ripoff, just as you say – and dated with it, before it even launches.
I guess it won’t matter on a truck which will presumably sell on price only.
From 1975 to 1984 Ford built/sold around 8,000 units of the top segment Transcontinental. Prior to and after that period they never offered anything in Western Europe in what’s called Class 8 in the US.
Back then they already found out, the hard way, that the market for high-end long distance trucks and tractors is not the same as building, selling and servicing light and medium-duty short distance machinery.
Chances are utterly slim, IMO. They will have to start from scratch in Western Europe. An extremely hard task in today’s (global) heavy truck market, dominated by Daimler, Volvo, Iveco, Volkswagen (through MAN and Scania) and Paccar.
I don’t know why Super Singles have not gained more traction in the US. According to the MFGs the increase in MPG is significant enough to pay for the new wheels and then it would all be gravy. Specing it with Super Singles from the get go in theory should be cheaper than duals.
The only market where Super Singles are the norm is on “pup” trailers and sometimes the dump which is towing them. Tri-axle dry vans with Super Singles are getting to be a little more common but I have to wonder if that is cost effective vs tandem duals. However a tractor wearing Super Singles is still quite rare in my area.
Yes, super singles on drive axles are basically non-existent here too. There have been plenty of practice tests, going on for years now, but apparently they’re not quite there yet.
Super singles on steering, tag and pusher axles are very common though. Both on trucks and tractors. And both on- and off-road.
I’m confused about super singles on steering axles, since the tires at that end are always singles. Other than for flotation, where wide front tires have been used on mixers or off highway trucks for decades in the US, do they allow higher front axle loads to compensate for having only a atwo axle tractor? I would expect a short wheelbase COE tractor would tend to put more load on the front so maybe that makes sense.
Extra-heavy front axles (with an increased axle load, legally rated at 9 or even 10 metric tons) simply need super singles. Too much weight for standard tires. Hence, many 4×2 tractors roll on super singles on the front-/steering axle. The total axle load for such a tractor is then 9 + 11.5 = 20.5 metric tons.
Note that pusher and tag axles are often also steering axles.
On an American double-axle trailer, you have 8 tires. If you have a blowout, you lose 12.5% of your load-carrying capacity.
On a European triple-axle trailer, you have 6 tires. If you have a blowout, you lose 18% of your load-carrying capacity.
BUT… if you put super singles on a double-axle American trailer, you only have FOUR tires. If you have a blowout, you lose 25% of your load-carrying capacity.
That’s a lot of risk.
May I suggest four super singles….on each side 😉
On the rare occasions a tyre blows here you stop, phone whichever tyre service is contracted to you and they come and sort it spares are not carried on board.
In Maine I see trailers hauling wood chips using super singles. Everything else is duals.
Those 10 wheel rigs arent seen here tractors tend to be 6×4 or 8×4 single drive is very rare, wheels are either single tyred or twin tyred a dual wheel is just a wheel for counting purposes, or just count axles.
Saw for the first time a semi with super singles on my back to New Jersey on U.S.81 in Virginia .I have seen sing!e tires on moving vans but not on a trailer
Now I know it’s a Euro thing