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Topic: Rear Tyres for economy. (Read 914 times) |
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ro284
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Posts: 508
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Rear Tyres for economy.
« on: Jan 28th, 2013, 11:12am » |
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I've been checking my tyres, At the moment i have 225/50/16, All round, the rears are badly worn, the fronts have around 6 mill tread on both, i checked the rolling distance between front and rear, The result is that the worn rears do 1-inch less distance per revolution, so in theory i would get better mpg if i fitted new tyres! Even If i kept to the same size i would get an extra inch Per revolution! That is a lot of inches over say 10 miles! So if i were to go to 225-60-16 in theory i might improve on the 29 mpg, i am getting now! And /or travel further for the same cost! Any thoughts on this, Where do you stop? Bob
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Bob Dorset
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Matt
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Manual'd and a 4.0 in the making
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Re: Rear Tyres for economy.
« Reply #1 on: Jan 28th, 2013, 12:29pm » |
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a quick test would be to swap the wheels round, front to back and vise versa
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FDS2000 Scans - Birmingham
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bernard_slade
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Re: Rear Tyres for economy.
« Reply #2 on: Jan 28th, 2013, 7:29pm » |
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i noticed that on fords own figures a scorp with 195 tyres acheived about 2mpg better than with 225 tyres as the 195 has less drag but of course less adhesion at the limit--- low profile tyres spoil the ride and need bigger rims to keep the same overall diameter . i think you will find thar if you put a 185 x 70 x 14 , a 195 x 65 x 15 and a 225 x 50 x 16 side by side they are all about the same height so increasing the profile for a given rim size will give higher gearing in all ratios it will give wrong speedo readings and you are limited by wheelarch size and distance of suspension travel-(suspension needs to hit the bump stop before the tyre bottoms in the wheelarch you get a better result by fitting a higher ratio diff unit but again an auto would would be totally confused by sensor readings that did not match reality. finally economy will ony improve if the throttle settings for a given speed remain the same --if the higher gearing causes the engine to marginally labour the increased throttle needed to offset this will result in more petrol air mixture being admitted to the engine and give worse economy.-in the corporate quest for economy ford spen millions optimising gear ratios fuel injection and electronics to give the best all round settings leaving us virtually no margins to improve---in the early days of fuel injection ford cheated the boy racers saying fuel injection gave more power and more economy --yes it tended to give better economy but to give the impression of more power they lowered the rear axle ratio effectively givin them lower gears to zoom away from traffic lights but the reality of the illusion was the more frugal fuel of injection needed a lower axle ratio to even acheive the status quo with carburettor jobs performancewise. you could actually improve economy on early sierras by fitting a 2 litre carburettor job axle to a 2 litre efi but all the lively zoom was gone;;; to sum up on a scorp the economy is best achieved with a bog standard set of 195x65x15 wheels -less drag less unsprung weight but probably not a good idea on cosworths
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another OAP past sell by date
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Mike H
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Renault Clio
Posts: 2594
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Re: Rear Tyres for economy.
« Reply #3 on: Feb 2nd, 2013, 1:24pm » |
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Just FYI I try to keep pressures 2 - 3 psi over, helps enormously, as also evidenced by "goes faster more easier", so implies the friction must be less
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Mike H
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