Highway tyres size/diameter fuel usage comparison for automa

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Highway tyres size/diameter fuel usage comparison for automa

Postby Stiff1 on Fri, 09 Aug 2019 3:40 +0000

Hey fellas, what tyre/fuel comparisons have you blokes have done. It may be old news but I was surprised to find that my Mickey Thompson AT P3’s (265/70/17) seem to add around 3L/100 to my fuel usage on the highway! Thought I’d start a thread to see which tyres and sizes perform the best on the highway. Still not sure whether it’s the weight of the tyres or the diameter increase from 65 to 70 profile, but with the larger tyres, the trans searches up and down between 5th and 6th a lot more. My rig is a 2018 SR dual cab auto, (accessories in pics) show us what you’ve found with yours [emoji1360]Image


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Highway tyres size/diameter fuel usage comparison for automa

Postby Stiff1 on Fri, 09 Aug 2019 3:49 +0000

Brand: Mickey Thompson AT P3’s
Size: 265/70/17
Type: Aggressive All Terrain
Fuel Economy: 12.5 to 13.5L/100
Speeds: 100-110km/h
Carrying weight: 200kg constant

Brand: Yokahama Geolandars
Size: 265/65/17
Type: Highway Terrain
Fuel Economy: 8.5 to 10.5L/100
Speeds: 100-110km/h
Carrying weight: 200kg constant


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Last edited by Stiff1 on Sat, 10 Aug 2019 4:20 +0000, edited 1 time in total.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby HK1837 on Fri, 09 Aug 2019 4:49 +0000

Where are you getting your km travelled from? It will change with the bigger tyres. The 265/70’s are about 3.5% larger in diameter so your km covered decreases by the same.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby hiluxxury on Fri, 09 Aug 2019 7:19 +0000

It's a good idea for a thread. I agree with HK1837 though. My 285s (33in) are make speedo 12% out.

I'm often testing the calibration on this using Google maps distance estimates or gps. 12% seems to be about right.

So equates to say 12l/100kms using my odo distance to about 10.7l/100kms actual consumption.

Might be worth measuring the diameter as well as sizes vary between manufacturers.
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Highway tyres size/diameter fuel usage comparison for automa

Postby Stiff1 on Sat, 10 Aug 2019 4:49 +0000

Sorry fellas just edited couple of grammar errors in my original post.

Yep both good points, my speedo reads slightly under my actual speed with the factory issued Geolandars (65 profile) on (checked against GPS, Dash Cam and Speedometer App)

Interestingly, the higher profile Mickey Thompson’s (70 profile) make the speedo read spot on accurate.

Obviously the higher profile 265/70/17’s increase the overall diameter significantly and from what I’ve found so far, my luxxy does not like it at all...

Ive also noticed an average 10-20 degree increase in trans and converter temps when running the Mickey Thompson’s, largely due (I imagine) to the trans constantly unlocking the converter and changing back to 5th to maintain speed with the bigger tyres.

The width (265) should have no bearing on the diameter or wheel speed. That said, wider tyres, such as 285’s might add more weight and so may increase fuel usage somewhat, but not wheel speed or distance travelled.

I travel a 505km journey once a week, same route, so it’s a good time and way to do comparisons.

For the sake of comparison, the fuel usage figures I’ve quoted (eg 10.5l/100) are the averages directly from the dash average, not what I have manually calculated.

Ive noticed in other threads and forums that some people are comparing dash read outs to manually calculating actual litres used over distance, which obviously will give varying results, given the issues with DTE and the fact that there is over 100km left in the tank after the dash says “refuel.”!!!

I’m simply doing the 505km drive, maintaining the same speed range (100-110km/h) and logging the differences in fuel usage over those trips.

There are variations each trip such as road works, headwinds, bloody caravanners :D etc but on the whole, I’ve noticed quite a difference between the two tyre types, just wondering if anyone else is doing similar tests seeing as fuel usage is a hot topic with N80 owners.

I’m interested to see if anyone knows whether it’s the weight of the 10 ply Mickeys or the larger diameter that is making it use the extra fuel and heating up the trans/conv? I measure the trans temp using pids on the OBD Fusion app for IOS. ImageImageImage




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Re: Highway tyres size/diameter fuel usage comparison for au

Postby TOYZX on Sat, 10 Aug 2019 7:27 +0000

It's simple the diameter and the fact that it requires more force to rotate them hence more fuel. I think you need to read up on how to read tyre sizes, 285 may on be the width but the profile represents a percentage of that width meaning a larger diameter.

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Re: Highway tyres size/diameter fuel usage comparison for au

Postby HK1837 on Sat, 10 Aug 2019 8:23 +0000

It is pretty simple once you stand back and think about it. If you want to fit larger tyres and want it to perform similarly to how it does as delivered you need to change the axle ratios and fit larger rotors for the same reason. As TOYZX says the radius of the tyre affects the force required to turn them as you are basically changing the gearing of the vehicle. Almost identically the force required to stop the vehicle also needs to increase. You overcome the engine versus tyre diameter by changing the gearing. You don't have this gearing option with braking so you change the rotor diameter.
You've already cottoned onto the transmission temperature, this is essentially all generated by the torque converter being unlocked. You will probably find that what you think is 6th to 5th transition is actually the converter unlocking. You can only fix this by changing gearing, but by fitting another inline air to oil cooler you'll alleviate it. Wholesale Autos sell a decent cooler that is a bolt in, but they also sell a good lockup kit for the converter if you want to go down that path. I have a full manual kit, but I don't use it that much. I find knocking it back to 4th (from 5th as I have an A750F 5spd auto) when towing drops the trans temperature quickly. I have a Wholesale Autos cooler too.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Blocklayer on Sat, 10 Aug 2019 1:03 +0000

HK1837 wrote:Where are you getting your km travelled from? It will change with the bigger tyres. The 265/70’s are about 3.5% larger in diameter so your km covered decreases by the same.


You can calculate the differences in tyre sizes for Speedometer and Odometer pretty easily here:
https://www.blocklayer.com/tire-size-calculator.aspx

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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Stiff1 on Sat, 10 Aug 2019 1:53 +0000

TOYZX wrote:It's simple the diameter and the fact that it requires more force to rotate them hence more fuel. I think you need to read up on how to read tyre sizes, 285 may on be the width but the profile represents a percentage of that width meaning a larger diameter.

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Thanks mate, I didn’t know it was a percentage of the width, i guess it’s true we do learn something every day! :D
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Stiff1 on Sat, 10 Aug 2019 1:54 +0000

Blocklayer wrote:
HK1837 wrote:Where are you getting your km travelled from? It will change with the bigger tyres. The 265/70’s are about 3.5% larger in diameter so your km covered decreases by the same.


You can calculate the differences in tyre sizes for Speedometer and Odometer pretty easily here:
https://www.blocklayer.com/tire-size-calculator.aspx

.


Handy little tool, cheers mate!
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Stiff1 on Sat, 10 Aug 2019 1:59 +0000

HK1837 wrote:It is pretty simple once you stand back and think about it. If you want to fit larger tyres and want it to perform similarly to how it does as delivered you need to change the axle ratios and fit larger rotors for the same reason. As TOYZX says the radius of the tyre affects the force required to turn them as you are basically changing the gearing of the vehicle. Almost identically the force required to stop the vehicle also needs to increase. You overcome the engine versus tyre diameter by changing the gearing. You don't have this gearing option with braking so you change the rotor diameter.
You've already cottoned onto the transmission temperature, this is essentially all generated by the torque converter being unlocked. You will probably find that what you think is 6th to 5th transition is actually the converter unlocking. You can only fix this by changing gearing, but by fitting another inline air to oil cooler you'll alleviate it. Wholesale Autos sell a decent cooler that is a bolt in, but they also sell a good lockup kit for the converter if you want to go down that path. I have a full manual kit, but I don't use it that much. I find knocking it back to 4th (from 5th as I have an A750F 5spd auto) when towing drops the trans temperature quickly. I have a Wholesale Autos cooler too.



Yep thanks mate! I do realise the affect of increasing the diameter of the tyres, I guess I just underestimated the affect it would have on fuel economy without changing gearing. Thanks for the info fellas, good stuff!
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Gipsy on Sun, 11 Aug 2019 6:36 +0000

After reading most of what is posted here it seems that the 6speed auto is way overdriven and even worse if you play with tyre sizes. It appears that the 6th is only good for over 110kph and definately no good for towing!
Don't be afraid to use 5th and even 4th when towing and your fuel economy may even improve! 6th is way overdriven!
Your engine might last longer too because any diesel doesn't like slugging at low revs... Find the sweet spot and use it. Check your engine torque curve and drive the car in whatever gear puts you in that rev range... That's the sweet spot! (Probably around 2.5-3.5k rpm.) Edit: After reviewing the stats below 2-3k seems about right. I would also argue that transmission lockup devices are not good for towing! Use your gearstick... That's what it's for! Imagine a V8 supercar locked in top gear :shock: I bet it wouldn't be very fast around mount panorama!
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Torque
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Power to Weight Ratio
63.7 W/kg
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby HK1837 on Sun, 11 Aug 2019 8:10 +0000

Yes, you only use the converter lockup them when you are cruising at light throttle. The latest Wholesale kit will unlock automatically too once certain criteria are met.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby gaspergartner on Mon, 12 Aug 2019 2:20 +0000

Stiff1 wrote:Sorry fellas just edited couple of grammar errors in my original post.

Yep both good points, my speedo reads slightly under my actual speed with the factory issued Geolandars (65 profile) on (checked against GPS, Dash Cam and Speedometer App)

Interestingly, the higher profile Mickey Thompson’s (70 profile) make the speedo read spot on accurate.


Note that ODO and speedo are not synchronised, speedo shows you higher speed, but distance on ODO is accurate with stock tyres.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Stiff1 on Mon, 12 Aug 2019 3:30 +0000

gaspergartner wrote:
Stiff1 wrote:Sorry fellas just edited couple of grammar errors in my original post.

Yep both good points, my speedo reads slightly under my actual speed with the factory issued Geolandars (65 profile) on (checked against GPS, Dash Cam and Speedometer App)

Interestingly, the higher profile Mickey Thompson’s (70 profile) make the speedo read spot on accurate.


Note that ODO and speedo are not synchronised, speedo shows you higher speed, but distance on ODO is accurate with stock tyres.


Yep that’s right mate. So the averages from the dash are always comparable because the distance travelled is still the same regardless of what the speedo reads, calculated against what remains in the tank. The speed range in my stats is not from the speedo but rather the GPS, Dash cam and Speedometer App. This makes the comparisons more reliable as speed is a big factor in fuel usage as we all know

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Re: Highway tyres size/diameter fuel usage comparison for au

Postby Gipsy on Mon, 12 Aug 2019 3:40 +0000

I'm not certain but I think the average fuel consumption calculated isn't taken from what's in the tank but calculated by the ecu as fuel is injected into the engine and distance travelled by the odo. I could be mistaken but this is what I understand. My basis for this is that my fuel consumption is inaccurate according to the dash average fuel consumption because my chip fools the ecu with the amount of fuel being injected. This is a function of the chip giving extra fuel over what the ecu is demanding. :?
The results using any OBD2 readout are also fooled because the OBD2 uses the same data from the ecu.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby HK1837 on Mon, 12 Aug 2019 4:56 +0000

gaspergartner wrote:
Stiff1 wrote:Sorry fellas just edited couple of grammar errors in my original post.

Yep both good points, my speedo reads slightly under my actual speed with the factory issued Geolandars (65 profile) on (checked against GPS, Dash Cam and Speedometer App)

Interestingly, the higher profile Mickey Thompson’s (70 profile) make the speedo read spot on accurate.


Note that ODO and speedo are not synchronised, speedo shows you higher speed, but distance on ODO is accurate with stock tyres.


Really? Where do the two different signals come from? I can tell you that on my 2011 the odometer changed between standard 255/70/15 tyres and 265/65/17 tyres. As Measured against the 5 x 1km signs along the M1 motorway it ended up close to correct with the bigger tyres but was way off with the smaller tyres. It had an Eclipse AVN726EA fitted when it was new and the speedo was almost corrected against the satnav with the bigger tyres.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby hiluxxury on Thu, 15 Aug 2019 6:19 +0000

HK1837 wrote:
gaspergartner wrote:
Stiff1 wrote:Sorry fellas just edited couple of grammar errors in my original post.

Yep both good points, my speedo reads slightly under my actual speed with the factory issued Geolandars (65 profile) on (checked against GPS, Dash Cam and Speedometer App)

Interestingly, the higher profile Mickey Thompson’s (70 profile) make the speedo read spot on accurate.


Note that ODO and speedo are not synchronised, speedo shows you higher speed, but distance on ODO is accurate with stock tyres.


Really? Where do the two different signals come from? I can tell you that on my 2011 the odometer changed between standard 255/70/15 tyres and 265/65/17 tyres. As Measured against the 5 x 1km signs along the M1 motorway it ended up close to correct with the bigger tyres but was way off with the smaller tyres. It had an Eclipse AVN726EA fitted when it was new and the speedo was almost corrected against the satnav with the bigger tyres.


Yes, I've observed the same. Both my speed and odo are out by the same % when I change my tyres to 33in. I was of the understanding that the odo and speedo read the same signal off the gearbox.
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Re: Highway tyres size/diameter fuel usage comparison for au

Postby gaspergartner on Mon, 19 Aug 2019 2:59 +0000

The signal is obviously the same, it's just a matter of displaying speed, typically off 5-10% in any car, it may also be fixed value for slower speeds + percent value for higher speeds. This is trivial math, as speedometer is probably not mechanically connected, but is just displaying data that ECU sends.

When you change for bigger tyres some would assume that with correct speed also ODO is more correct, but actually ODO is measuring shorter distance, so when you read that you travelled 700 km with a tank, actually with 265/70/17 you travelled 723 km.

As far as I know there is no GPS correcting this on the car, you could only do it with reprogramming, but I wouldn't bother for this small changes (3-4%) in diameter.
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