Do 285 tyres reduce or increase fuel constumtion?

Drew,

I assume from the talk of fitting flares that yours is a DX. The normally aspirated donk might struggle a bit with the increased tyre diameter. Can't say for sure. I have 285/75/16s on mine, but it is a 4.5 petrol so handles it pretty well power wise.

Fuel consumption a bit difficult to determine. It will certainly appear that your consumption is worse because the larger diameter tyres will give you about a 4% lower speedo reading. I haven't tried to calculate the exact impact on fuel consumption because it is often difficult to isolate one factor over another. My gut feel is that it has made no (or negligible) difference, but the diesel might be a different kettle of fish. Spare still fits under the body OK if you have retained that set up.

Cheers,

Matt.

I had worn 275 AT's on my 105 Cruiser and went to 285 MTZ's. I lost 2lts/100km. (10/100 to 12/100 first tank with the new rubber)

Not only did the fuel ecconomy suffer but I also lost a significant amount of off the line grunt. It was noticable the minute I drove out of the shop.

On the highway I could hold 5th up hill and down dale on all but the real steep stuff. These days I'm back in 4th much quicker.

Interestingly, my speedo and odometer are now more acurate when compared to my GPS.

I don't think it will help you at all in your quest for better ecconomy but it does give a little more diff clearance plus it looks tougher LOL.

Seriously, If I had my time again I would probably looked at 275's or even 265's

Larger (wider) tyres will increase your fuel consumption because the rolling resistance is greater for tyres of the same type (e.g. Bfg AT).
If you go to mud type pattern fuel consumption will increase again, because of the energy required to bend the blocks.

If on the bigger tyres (of the same type) you increase air pressure such that the contact patch now matches that of the 265's then fuel consumption will drop and approximately be the same or slightly better because of the secondary effect of less revs.

For my car I also have the 265 and use sets of 255/85/16 to get more ground clearance, less revs and less contact patch, and
they stay compatiable with lighter 7 inch rims.

This allows a win win situation in that with tyre pressures up (40) I get lower consumption and with tyre pressures down (18) I get extra traction to match what a 285 has normally due to longer contact patch.

One of the biggest differences would be the tread pattern - the smoother it is, the quieter, and the less rolling friction. But also less friction/traction on dirt/mud/etc. When I put road tyres on my mountain bike (for the commute to work), I realised the significance of this like never before!

Putting a larger dia. tyre on will make your gearing slightly 'taller' and reduce your engine revs for the same vehicle speed, but not the same wheel speed. The wheels still go around the same number of times per minute for your speedo to record 80km/h, but because the rolling dia. of the tyres is bigger, you cover more distance each time the wheel goes around. I calculate the difference to be around 7.5% - you'll need to be careful around speed cameras because (assuming your speed is accurate now) with the bigger tyres, your speedo will UNDER-READ by 7.5%, so if it says 80km/h, you are actually going closer to 86km/h.

You'll also need to factor this in for your fuel economy calcs. If you are using the odometer/trip meter to record distance, these will also be affected. Instead of recording L/100km, you'll now be recording L/107.5km! It might seem like the figure goes up, but you could still be better off as your are actually covering more distance per km recorded on the odo/tripmeter.

Putting bigger tyres on will increase the vagueness of the steering/handling as the sidewalls of the tyres are bigger which generally means more flex as your corner - this is why racing/sports cars have low-profile tyres. Using a M/T tyre in place of an A/T tyre will further increase tyre flex because the tread flexes more (which helps significantly with grip on rough/slippery surfaces) therefore resulting in even further vagueness.

I would expect the biggest change in fuel consumption to come from the more aggressive tread pattern rather than the bigger tyre size.

Drew

I think people may be getting things around the wrong way a bit.

This is from the San Jose Classic Chevys Club

The first number is the width of the tire in millimeters, measured from sidewall to sidewall. . . .
The second number is the aspect ratio. This is a ratio of sidewall height to width. . . .
The last number is the diameter of the wheel in inches.

To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.

Example...185/60R14 85H or 185/60HR14

185mm x .60=111mm x 2=222mm + 355.6mm(14")= 577.6mm or 22.74"
"

Overall you will get more rubber on the road which produces more friction etc etc as others have said.

Can't help with the offset question.

But I wonder if you change the alignment of the center of the wheel with respect to the center of the wheel bearing/s would that cause damage. I was told it would years ago. I know technology has changed but is this issue still relevant. I am interested also.

Anyone???

Phil

Drew


Check what the ADRs are. I am not aware for your vehicle but for some you are only supposed to fit what is on the tyre placard in the vehicle.



Tjilpi

More ofter than not, vagueness is caused by,
square shoulders on the tyre,
incorectly adjusted wheel bearings,
slap in king pin bearings,
different tyre pressures on the same axle,
worn steering damper,
play in tie rods, worn bushes (especially control arms)
incorrect caster / camber due to alignment or susp. lift,

I usually run 285's and the larger width/ height can make it feel worse if everything else isn't spot on.

If you are concerned try to borrow a set and go for a drive on an uneven road.

If you are worried about fuel consumption and $ per km buy a petrol on gas or a corolla. We don't drive large 'trucks' for the economy.
Personally I drive petrols now as I find that overall the performance is far superior and sevicing is cheaper. Even without being on gas I find the fact that when I need power to overtake or tow it is there right away, no waiting for the turbo to spool up (if fitted) or for a 4km overtaking lane (1HZ) and the economy of 14 litres per 100km out of the 105 auto is fine. The last 80 I had with a 1HZ used to get the same economy with about 1/4 of the driveability.

Just my 2c worth.

Cheers
Dave

More ofter than not, vagueness is caused by,
square shoulders on the tyre,
incorectly adjusted wheel bearings,
slap in king pin bearings,
different tyre pressures on the same axle,
worn steering damper,
play in tie rods, worn bushes (especially control arms)
incorrect caster / camber due to alignment or susp. lift,

I usually run 285's and the larger width/ height can make it feel worse if everything else isn't spot on.

If you are concerned try to borrow a set and go for a drive on an uneven road.

If you are worried about fuel consumption and $ per km buy a petrol on gas or a corolla. We don't drive large 'trucks' for the economy.
Personally I drive petrols now as I find that overall the performance is far superior and sevicing is cheaper. Even without being on gas I find the fact that when I need power to overtake or tow it is there right away, no waiting for the turbo to spool up (if fitted) or for a 4km overtaking lane (1HZ) and the economy of 14 litres per 100km out of the 105 auto is fine. The last 80 I had with a 1HZ used to get the same economy with about 1/4 of the driveability.

Just my 2c worth.

Cheers
Dave

If you are trying to reduce fuel consumption and also revs at cruising speed just slow down to 100 kph and that will do it all. The 80 series are not aerodynamic (which 4wd is?) so trying to push a house brick faster can only cost fuel.

Just a quick one, we had a lot of trouble getting 285/75/16 BFG's in Broken Hill, Mt Isa and a couple of other places. We were told that they are not as popular as 275's & 265's so they didn't stock them. So I will be going back to 275's when my BFG's finally wear out, could be waiting a while though.

Might pay you to weigh it as well cos if you reckon it weighs 3200kg It will be of doubtful max legal weight even before you get in it.
A 100 series 1 Hz is legally to be only 3180 ATM.

Something to think about also lighter means a better fuel figure.

Hi Drew,

I also have an 80 series with 1HZ engine. A couple of years ago I made the move from 275/75/R16's fitted to 16x7 rims.
I replaced them with 18x8 rims and 285/75/R16 mud tyres and my consumption increased on average about 2Litres/100km.

Yes I have lost power and really notice the difference even with an empty trailer on the back.

Would I do it again. Absolutely. I have a rather large property with some pretty tough tracks and the difference off-road is amazing.

At the end of the day, generally everything you do to a 4x4 to change it from standard will increase fuel consumption. It is all about compromise and what type of driving you will be using your 80 series for most of the time.

When I purchased my 80 it was completely standard and could get 10L/100km. fit bullbars, spotties, roof rack and it hits 12, fit 33"mud tyres and it goes up to 14L/100km, fit winch, and 2nd spare wheel and rear drawers full of recovery gear and rarely get under 15L/100km now. Stick a big trailer on the back that weighs a couple of tonne and I have had up to 18L/100km.

Good luck with your decision and I hope this info is helpful to you.

BW

Drew

I done this on my old 3.0L Patrol and am looking at doing it with my 100 series TD Cruiser. I found on the Patrol that the bigger tyres did not increase fuel consumption. What did increase fuel consumption was going from a A/T tread to a M/T tread both in 285's, about 0.5-1 L/100km. Acceleration did suffer slightly. My Patrol was automatic, where as my Landcruiser is manual and has a sweet-zone on the torque curve that starts to drop off at 2600 rpm, which will be at around 110km/h with 285 tyres. May help if you could find a torque/power curve for your vehicle, look at where the revs will be sitting with the bigger tyres at highway cruising speed, if it sits in the sweet spot with 265's then don't change, if it is with 285's then upgrade.


Cheers

Snowy

Thanks for the replies everyone - I think I will stick with the 265's at the moment as they still have a fair bit of tread left and I dont really want to risk less power and economy... When these wear out I will look at it again!!

Drew

All I read was bla bla bla.
It will not make any noticable difference in fuel economy, your speedo at 116kph will be actual road speed of 120kph, your 80- will feel more torquey (if that is a word) and the gas will improve your performance that much it would not matter how much bigger you go. I know this as I have the 1hz and did the tyre change the only difference is mine is the gxl and is standard wide wheels and flares. In my opinion the factory flares (avail on ebay) look great and can be easily fitted but the black strip flare is adequate.