Big tyres & fuel consumption

It does to me. It also means when you go to sell the car, it has 5-10% less kilometres on the clock depending on how big the tyres are. There would be a slight increase in rolling resistance but not as much as most seem to think.

Im hopeless with math but I know when I went up to 33s on the patrol it used a fair bit more juice.

After going up 40mm on the colorado the speedo is identical to the gps which is great, not sure if it uses more juice though, would have to though, odometer, not sure?

Power didn't suffer to much on either of them though, the collie still flies!

Yes was warned/advised of the same some tears ago when I fitted 31" ham kooks to my LN65 Hilux but I also found that I had absolutely no negative impact on fuel consumption. I did find that it was a little slower off the mark and that braking was a tad less responsive. I later fitted a turbo which helped with other areas.

Generally a vehicle fitted with bigger tyres will use a bit more fuel.
It all depends on how the manufacture set the gearing for the torque and also the way the injection happens at that speed to get the torque.
At some speeds it may be worse and at others a bit better because the use of the fuel energy relative to distance travelled is the critical factor. This combined with various loads also has an effect.
Manufacturers settings & sizes are a compromise for all round normal use, once outside that it could go either way.

It is a very interesting subject.
I put larger diameter tyres on my car, which made the speedo exactly correct and the odometer 6% slow i.e when I do 100klm I actually have done 106klm.
I found a good way to check the odometer was by checking it against measured distances, between small targets, like the klm posts on the roadside.
Travelling from Perth to the North or the East, gives heaps of opportunity to check the speedo, also kills a bit of time.lol

Another aspect is that often with the bigger tyre comes a more aggressive tread pattern with consumes more fuel another issue is lifting of the vehicle which effects its aerodynamics

Too many variables to be certain Keith but the extra weight of four larger tyres, and changes to the factory set parameters in your engine mgt system (primarily gearing I guess) will often result in increased fuel consumption according to my mechanic bil. The difference is probably greater for smaller vehicles with less power/torque and mass (a few extra kilos makes a bigger difference). Of course increased fuel consumption is just one possible side effect of bigger tyres. If you go to extremes as some do the additional stress on your suspension and steering is significant, hence the need to beef some components up goes hand in hand, or should.

Keithb
I did correct my odo in my calculations and yes there is a 1to 2 l/100km difference based on real distance travelled.
This has been confirmed by several people on Lcool. But is must also be said that the 200's consumption is susceptible to change. This includes bullbar roofrack etc.
It may depend on the car you drive as to how much difference, but it will be more: more power needed to accelerate, bigger rolling resistance, heavier as well,
CJ

I have been using a GPS for my speedo and for calculating fuel economy for a few yrs and ignoring the cars speedo because of larger tyres. I had a 4.2ltr petrol GQ and found that 32" A/T tyres gave me the best fuel consumption any bigger it uses more fuel and my current 4.2 ltr turbo diesel GQ gets it's best fuel economy running 285/75 A/T tyres. I don't use the cars speedo because it's 6kph out and even a vehicle like my neighbours 2006 stock standard Mazda BT50 is reading 4kph out gps reads 100kph cars speedo reads 96kph. My wife's elantra is 1kph out so even the cars computer gives incorrect fuel economy reading when I checked it against the GPS so how many people out there are getting incorrect figures on the same note I hope that my GPS isn't lying to me and I've been getting it right.

The OP does well to bring up the odometer error introduced in the calculations, that I am sure many do not consider.

As others have said there are so many factors.

Size, weight, type of motor and how well the vehicle was optomised in the first place.

Then there is terain.
A steeper gear ratio due to larger tyres would advantage a vehicle running on flat terain and or a lighter loaded one and or one that is lighter with a smaller motor.

I expect to see less difference in a diesel than a petrol motor.

If the terain was hilly, particularly consistently uphill, I'd expect larger tyres to be more of a disadvantege, particularly in a heavier vehicle or heavier loaded.

Out on the highway, where acceleration and enertia are less of a cost there will be less difference, but in the city with lots of acceleration and deceleration, the overgeraing may cost some vehicles considerably.

Then there is the question of how much increases in size....modest size increases are more likley to make bugger all difference...where as substantial tyre and wheel size increases are likley to make far more difference.

cheers

Hi all,
When I purchased my 80 series it was fitted with 10R 15 tyres. These are undersized at about 30.5". Truck went very well but revved too high and I could not keep up with my mate with the same vehicle on 33"s when cruising on the open road. Fuel consumption was very good however.
I then changed to 285 or 33" tyres for a slight loss of performance and a slight increase in consumption when not towing. It was better in the rough stuff however. A big bonus however came when towing the caravan and where 5th gear was a no no. 4th gear then became the perfect towing gear when pulling the camper trailer and later the caravan. It enabled a higher cruise speed for the same revs.Fuel consumption was little changed when towing.
regards
Guy

Likewise, personal experience, Years ago I went up 2 sizes on my Jackaroo and noted little difference in fuel consumption or take off acceleration.
Did the same with a 1.3lt Jimny and found the only difference was I could cruise at 95 without feeling the pistons were going to pop out of the cylinders. Will be looking for new tyres for the Cruiser shortly and will look at going larger. The only thing is of course is insurance coverage and speedo error

Diameter of tyre equates to distanced travelled per revolution, your 804 diameter tyres carry you 2526mm per revolution where your 841 diameter tyres will carry you 2642mm per revolution. The larger diameter tyres are fine on nice on long straight roads as it gives a higher ratio drive the same higher ratio drive also applies going uphill which means the engine has to work that little bit harder. Conversely if you put smaller tyres on you lower the drive ratio which is fine going uphill but on the level you need more revolutions to maintain the same speed. Basically larger tyres gives you slightly better ground clearance and worse fuel economy in hilly country, so no major gains only more expensive tyres.

About 2 litres extra on mine going from the same size HT to AT BFG.
Would be a lot worse if I increased the tyre size as my car is an auto and would not lock up the torque converter till a higher speed was reached.
New car has 18 inch rims so will have to buy some new 17 inch rims when I put off road tyres on.

Myles