We’ve always done the speed limit where possible. Before we had the boat or camper trailer that meant 110km/h, and once we were towing we’d sit at 100km/h. Occasionally we would sit at 90km/h to stick with our folks, or just to tick along and I always noticed there was a stark contrast in the way the vehicle drove, and the fuel economy.
On our latest trip up north, I decided we’d give the 90km/h a real go over 3 weeks, to see what actually happened over a longer distance. Leaving Perth we sat on the speed limit, and did 100km/h for the first few hours just to make some extra progress, and get out of the big smoke.
The next day though, and from then on, I set it on cruise control at 90km/h (our speedo is accurate according to GPS with the larger tyres), and we just ticked along.
So, why the change from 100km/h (maximum towing speed limit in WA) to 90?
Its far easier on the vehicle
If you’ve never compared the difference between 90 and 100kmh in your own vehicle, you should do it. Our Dmax and camper trailer is about 5300kg, and that’s a fair bit of weight to keep moving down the road. It will sit at 100km/h except for large hills, but it has to work pretty hard to do so.
It would frequently bounce between 4th gear and 5th gear, and the engine load would often be 75 – 100%. Every hill that wasn’t a minor incline it would be pushing hard to maintain the speed limit, because we all know cruise control cares about nothing else than speed!
At 90km/h, the coolant temperature is about 10 degrees cooler. The transmission is generally around the same, although sometimes even up to about 15 or 20 degrees cooler. The Dmax sits in 4th most of the time and just putts along up gentle inclines without much of a fuss. When we first started doing it I actually looked down at the dash thinking that there’d be a fault light on as it was just ticking along to maintain the speed and I continuously thought something was wrong.
All of this means your vehicle leads a kinder life, which should directly translate to a longer life, all things being equal.
You save a heap of fuel
When you are paying a minimum of $2.20 per litre of diesel, it becomes pretty expensive to travel long distances in a hurry. We are glad that our setup is pretty frugal anyway (generally around 13 – 14.5L/100km towing at 100km/h), but if you can save a few bucks easily, why not?
Now, I will admit the first trial wasn’t done very accurately, and we had to stop more times for kids to pee than I care to consider, but I’m positive the fuel difference is around 1 – 2L/100km. That’s 4 bucks for every 100km, and on a lap of Australia you can be talking around $1600 saved!
Its more relaxing to drive
I’ve never really had an issue driving at 100 or 110km/h, but I must say there’s something awfully relaxing about ticking along at 10km/h less. Its probably almost all mental, but you feel less rushed, less stressed and you certainly have more time to react and make a better decision.
One of the surprising things that we noticed too was that you no longer have to worry about the big trucks. Most of them are happy doing 90km/h, and if they aren’t, its easy to back off once they are ready and let them around.
When you are doing 100km/h you are constantly catching them, and trying to overtake a triple road train is going to use a lot of extra fuel, and you need to pick a safe time to do so. Its so much easier not having to worry about overtaking them at all!
What’s the downside of doing 90km/h?
Of course, there’s no free lunch and doing 90km/h when you are towing instead of 100km/h does have its downsides. For starters, every 10 hours driving you essentially lose an hour; you have to do 11 in order to travel the same distance.
We noticed the time really dragged driving from Perth to Newman, but that might just be because its incredibly boring, and we had two young kids in the back that would fight, whinge and complain at least a couple of times an hour!
It also means you can become a road block to others, and we are very cautious to never inconvenience anyone. We are always on channel 40 talking to those in front or behind us, and as long as you do this, there’s no real issue.