Was looking at a used 4 x 4 3.2 lt diesel. It's running big fat nobbly tall kumho tyres. Sorry not sure exact specs and has a full size roof rack. Seller says he uses 14lt per 100km open rd fully loaded sitting on 110. Seems way too high for me but then I am used to guinea pig powered tiny diesels. Just wondering if I lost the roof rack and ran standard skinny tyres ( go more places imho, and less punctures ) how much improvement on economy I might get ?
How much economy do you loose by running big tyres, roof rack ?
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I reckon around 1.4L/100km, and nearly as much again if you slowed to 100kmph.
My jeep went from 10.7 to 12.4L/100km with large tyres, full roof rack, snorkel and bull bar (at 100kmph).
My jeep went from 10.7 to 12.4L/100km with large tyres, full roof rack, snorkel and bull bar (at 100kmph).
I'd agree with Bigwave, my oid Pathfinder jumped about a 1.5 litres per 100ks when up upped a tyre size and ran the roof racks, so up to 14 to 14.5 litres per 100kms, 3l petrol auto.
I can't tell on the Challenger as I just leave the roof racks on all the time and I'm running stock tyres at the moment, last trip away towing the camper trailer, sitting on 100 was 13.4 litres per 100kms, 2.5l diesel, auto
I can't tell on the Challenger as I just leave the roof racks on all the time and I'm running stock tyres at the moment, last trip away towing the camper trailer, sitting on 100 was 13.4 litres per 100kms, 2.5l diesel, auto
I minus 100ks per major item. Eg, bigger mud terrain tyres large roof racks etc.. Maybe a little less on bigger powered motors. My Colorado was 7.5 p/100ks. After a bull bar, winch side rails tyres Steel tray (full of tools) etc.. Sits on 12.4 p/100ks. Every car I have owned was similar from 2.8duesel to 4.2 Diesel. Automatics in my opinion guzzle more when loaded.
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I remember an article donks ago in the NRMA open road magazine on the wind resistance of the old pipe type roof racks. They where saying up to 10%, or equal to 40kgs in extra weight.
Why people buy nobby tyres and drive 1% in mud is beyond me.
Loud, vibrate and have a very poor road grip on wet sealed roads.
Tyre overall height can make a vast difference. More so than a wider tyre.
This can also affect the ratio of gearing and speedo a lot!
The tyre place card gives the info of what series tyre it was meant for.
Less height/ less speed, but more grunt = more fuel
Higher profile will give better top speed, but you loose a bit of grunt down lower.= Less fuel
Same as playing with diff ratios.
Speedo calibration is needed after changing things around, if you want to keep it accurate.
Mud tyres/wide tyres can be advantageous in some circumstances, yet they have their down sides as well.
Why people buy nobby tyres and drive 1% in mud is beyond me.
Loud, vibrate and have a very poor road grip on wet sealed roads.
Tyre overall height can make a vast difference. More so than a wider tyre.
This can also affect the ratio of gearing and speedo a lot!
The tyre place card gives the info of what series tyre it was meant for.
Less height/ less speed, but more grunt = more fuel
Higher profile will give better top speed, but you loose a bit of grunt down lower.= Less fuel
Same as playing with diff ratios.
Speedo calibration is needed after changing things around, if you want to keep it accurate.
Mud tyres/wide tyres can be advantageous in some circumstances, yet they have their down sides as well.
I have an on screen display with gps digital speed readout-hardly ever look at the speedo.
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Just in the mirrors for blue flashing lights! :lol:Jaros said:
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Keeping the same tyre series the same, but going from a 15" wheel to a 16" wheel effects the ratio turn ratio of about 8%
16" to 17" wheels is about 6.5% difference.
Yet even getting a tyre that is higher in the wall (profile) can be like upsizing the wheel itself.
16" to 17" wheels is about 6.5% difference.
Yet even getting a tyre that is higher in the wall (profile) can be like upsizing the wheel itself.
mudgee hunter said:
Hey MH,
It would be easier in laymans terms to just say if you had a tyre with a larger overall diameter than the original, economy will be less and speedo would read lower that what you actually are going.
Cheers
Doug
shakergt
Moderating Team
If it's a 3.2 Ford ranger you aware looking at then that file useage is about right.
How much ?
Not as much as getting stuck or not being able to take the long things you need to put on the roof.
Not as much as getting stuck or not being able to take the long things you need to put on the roof.
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I've lost one litre per 100 Ks just by changing from stock tyres to ones with a larger rolling diameter - so they are taller, although still in an AT style tread (not muddies). Same rims.
The speedo over-read like crazy with stock tyres - now it's spot on. You can always take a roof-rack off and hang it under the carport etc., until you actually need it. Less weight, less noise and less fuel.
The speedo over-read like crazy with stock tyres - now it's spot on. You can always take a roof-rack off and hang it under the carport etc., until you actually need it. Less weight, less noise and less fuel.
