Larger tires fuel economy

[Nick Montrose]

Just wondering, I have a curremt model Ranger Raptor I’m considering upsizing from the current stock 285/70/17 KO 2 s to a 305/70/17 MT Baja boss but the fellas at the tire store told me I’ll use a heap more fuel! Has anyone whose upsized tires had much difference in fuel mileage? I obviously understand there’s going to be a bit of a change and I’m comfortable with losing a litre per 100km(I’m Australian so work in L/100km) but if it’s going to be more than that I’ll have think twice as I drive around 1000km (650m) a week . Which turns out to be around $1,000 more a yr.

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[stuartmunto]

But you're not upsizing tyre? You're just going wider? 285/70/17 to a 305/70/17 is only 20mm wider, which means gearing isn't effected at all

There will be a little more resistance in initial rotation due to there being more rubber on the ground, but I would say any extra fuel usage would be negligible?

It's most likely that you're going from an All Terrain tyre to a Mud Terrain tyre that will increase fuel consumption. If you're doing so many kms of on road driving you shouldn't really consider a MT tyre unless you really go offroading every weekend. MT are great for offroad but terrible on road - louder, less grip and don't last as long

Stick with an AT tyre if you're primarily doing on road kms with occasional offroading

 

[Nick Montrose]

I thought the same thing but they are adamant that it increases, they say roughly every 10mm in width even staying with a 70 it increases around nearly half an inch so a 305 will be roughly 20 to 25mm taller than a 285/70/17

 

[stuartmunto]

I thought the same thing but they are adamant that it increases, they say roughly every 10mm in width even staying with a 70 it increases around nearly half an inch so a 305 will be roughly 20 to 25mm taller than a 285/70/17

I've never heard this - but don't know enough about tyres to say otherwise

I think it's more common knowledge that wider tyres will use more fuel than narrow tyres due to increased rolling resistance, and that MT are not as good for fuel efficiency as AT tyres

 

[maus92]

The larger tire is heavier, greater in diameter, and has more friction which will result in lower fuel efficiency.

 

[CodyMac]

inb4 the people coming in here with "i DiDnT bUy It FoR tHe FuEl EcOnOmY"

 

[Satex]

The larger tire is heavier, greater in diameter, and has more friction which will result in lower fuel efficiency.

That's all true. But as I read the question, he's not asking IF but by how much.

It seems to me that the only way to assess the degree of impact is to get feedback from others who have made similar changes. Then you're going from a wild ass guess to a minimally educated guess.

 

[Reddog99]

But you're not upsizing tyre? You're just going wider? 285/70/17 to a 305/70/17 is only 20mm wider, which means gearing isn't effected at all

Going to a wider tire also increases the tire height because the "70" in the size callout stands for the height of one sidewall being 70% of the width of the tire. So, 70% of 305 is greater than 70% of 285 (times two for two sidewalls) which increases tire overall height. There are calculators on tire dealer web sites that will calculate this for you if you don't want to do the math.
How it may affect gas mileage is a different story.

 

[maus92]

That's all true. But as I read the question, he's not asking IF but by how much.

It seems to me that the only way to assess the degree of impact is to get feedback from others who have made similar changes. Then you're going from a wild ass guess to a minimally educated guess.

I suppose that reading the entire thread would explain my reply. One responder implied that only the tire width was changing which would be incorrect.

 

[superj]

you need to check the weight of hte tire versus what you have. that makes a heck of a difference in gas mileage. i went up a size on my older truck but didn't realize i got tires that were 18 pounds heavier. i had to take those suckers off after the first tank of gas because i went from 19 to 15mpg

 

[Nick Montrose]

you need to check the weight of hte tire versus what you have. that makes a heck of a difference in gas mileage. i went up a size on my older truck but didn't realize i got tires that were 18 pounds heavier. i had to take those suckers off after the first tank of gas because i went from 19 to 15mpg

72lb to 59lb per tire so 52 lbs over all. All over weight not really a factor as my RR has 850nm of torque but I wonder what that extra weight that each wheel has to turn each revolution is a concern, most likely with take off too. Before I put all accessories on it I was getting 0-60 in under 5 seconds

 

[Asmith]

I am running 315/70/17 Maxis MT. Have done about 35,000km on them
If I cruise around very gently, think grandma speeds, on B roads, stay under 80km/h, then I can get fuel consumption as low as 12.5L/100.
If I drive normally then I get around 17.5 L/100.
The car has a steel bullbar, winch and long range tank, no lift and I have been running 28 to 30psi tyre pressures because I am offroad every day (live on a farm).
This is using 4A which likely increases fuel consumption over 2H.
Using 91 unleaded, 98 would likely be better.
I am trialling 36PSI as of yesterday and will see what happens.

Its been over a year since I put these tyres on so I am a bit vague as to what the original 285/70/17 were getting but I think between 12 and 15L/100 depending on how i drove it.

I think it's worth running the larger tyres, the stance is far better (I am also running a +35 offset rim so the tyres sit slightly outside the guards), you get a lift from the larger diameter(better ground clearance) and much better protection of rims and the car overall offroad.

I will continue the trial of higher tyre pressures and then move to 98 fuel and 2H to see what that does. Ask me again in 3 months...

Keep in mind the tyre is around 5% larger rolling circumference, this means my speedo went from reading 5km high stock to being spot on with the larger tyres.
That 5% speedo change needs to be taken into account in your fuel consumption figures if your using the instrument cluster fuel consumption figures.

Without a lift, you will be trimming the front mudflap area for extra clearance with those tyres.

 

[Nick Montrose]

I am running 315/70/17 Maxis MT. Have done about 35,000km on them
If I cruise around very gently, think grandma speeds, on B roads, stay under 80km/h, then I can get fuel consumption as low as 12.5L/100.
If I drive normally then I get around 17.5 L/100.
The car has a steel bullbar, winch and long range tank, no lift and I have been running 28 to 30psi tyre pressures because I am offroad every day (live on a farm).
This is using 4A which likely increases fuel consumption over 2H.
Using 91 unleaded, 98 would likely be better.
I am trialling 36PSI as of yesterday and will see what happens.

Its been over a year since I put these tyres on so I am a bit vague as to what the original 285/70/17 were getting but I think between 12 and 15L/100 depending on how i drove it.

I think it's worth running the larger tyres, the stance is far better (I am also running a +35 offset rim so the tyres sit slightly outside the guards), you get a lift from the larger diameter(better ground clearance) and much better protection of rims and the car overall offroad.

I will continue the trial of higher tyre pressures and then move to 98 fuel and 2H to see what that does. Ask me again in 3 months...

Keep in mind the tyre is around 5% larger rolling circumference, this means my speedo went from reading 5km high stock to being spot on with the larger tyres.
That 5% speedo change needs to be taken into account in your fuel consumption figures if your using the instrument cluster fuel consumption figures.

Without a lift, you will be trimming the front mudflap area for extra clearance with those tyres.

Awesome feedback, I’ve got aftermarket rims that are 25+ . Sit just outside the guards, too scared to go any more as the highway patrol where I am are nabbing vehicles with poke. Will be interesting to see how it differs with an inflation change. I’m currently getting around 16l/100km on 4A with the KO2s l. Interesting I was getting better fuel economy until I hit around 40k kms, they also got noisier. I was actually going to get the KO3s but they can’t get anything above 285s until May and I need them for Easter. Thanks for your feedback

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