Back in the late 90’s when we did our landmark TV series “Beyond The Bitumen” (the world’s first dedicated 4WD TV show – seen on TEN and Foxtel) we ran Isuzu 4WDs (with Holden Badges) in the form of a Rodeo ute and a Jackaroo wagon. Both vehicles featured 16” wheels and the stock standard tyres choices were typically 245/70R16. Not too tall and not too wide, really an average size to do both the on and off-road tasks some justice.
Well we swapped the steel rims for alloys (from our good friends at CSA/Mullins Wheels) and went wider, running 16 x 7” instead of 16 x 6”. That extra inch of width opened up a bit more scope for tyre selection and based on our past experience in the 4WD world we opted for what I still believe to be one of the best size/profiles for many 4WDs, even today… the LT235/85R16.
Now the “235” as we still refer to them offers some really desirable benefits on and off-road:
- An increased amount of ground clearance thanks to the tall sidewall height (810mm diameter) and
- With each 1% increase in diameter comes a 1% decrease in rolling resistance = less fuel used
- A narrow profile for less wind resistance (again enhancing fuel efficiency) and less puncture susceptibility (less rubber on the road reduces the likelihood of copping a penetration)
- A narrow profile works off-road too with the same lesser rolling resistance benefit this time in sand and mud, thus preserving momentum
- With reduced pressures the contact patch is longer meaning better flotation on those same imperfect surfaces and greater flexibility in the tyre sidewall means a more comfortable ride as the tyre becomes a de-facto suspension component
- “235”s also come with a 120 load index = 1,400kgs carrying capacity and on average around a 25% stronger tyre carcase (less punctures/better durability and longevity) when compared to standard issue 4WD tyres
Now unfortunately this wheel/tyre combination won’t suit all 4WDs today because in the quest for greater safety, brake diameter has been steadily increasing. The combined rotor/caliper dimensions of late have been dictating bigger wheels and that’s why we’re seeing 17”, 18”, 19” and even 20” wheels on some vehicles. Fashion based on the racetrack has in turn dictated that tyre widths go wider, so now we’re stuck with large luxury 4WD wagons having utterly useless wheel/tyre combos for the bush. In fact they’re not even much good around town because with a lower profile or sidewall (the tyre height measured from bead to tread) comes a stiff and inflexible tyre carcase that transmits a lot more road imperfections straight into the cabin and through the steering wheel which isn’t too pleasant!
Add to that the inevitable over-inflation (people you really need to be more vigilant with your pressures because 80% of the vehicles we see here at Adventure 4WD are over-inflated and some more than double the prescribed amount seen on the tyre placard) and the resultant ride can be also very dangerous with a vehicle reacting to potholes and bitumen ripples by weaving all over the road requiring constant steering attention and contributing to driver fatigue.
There’s a priceless piece of video we’ve posted a couple of times now on our Facebook page of a 1920s era Dodge car negotiating the oil fields of central USA and it appears unstoppable in all weathers because of its skinny tyres on massively tall wheels (that’s that long footprint effect I mentioned earlier). Have a look here: http://www.youtube.com/embed/nq2jY1trxqg?rel=0
The modern spin on tyre evolution in the quest for greater efficiencies is skinnies once more and this article seen in Drive.com.au shows the development of the modern tyre might mean we’ll be getting used to a tyre shape that looks nothing like what is the accepted norm today. Have a read here: http://goo.gl/iov0sw
I’ve got an open mind on it, because I remember fondly the excellent results we got with “Roger” the Rodeo and the “Jack”, two vehicles that regularly used to surprise the traditionalists. They wagered that our pretender vehicles would go nowhere off-road How wrong they were! A combination of good clearance, clever use of the gearbox and range selection by the driver meant anywhere you can go I can go better!
Picture: Here’s a tall skinny 235 that works a treat, Toyo’s M55, a good multi-use tread pattern that lasts!