Hi
I am intending purchasing some alloy wheels with fitted tyres for my Mk4
Fiesta (1997 R). Currently the tyres on the car are 165/75 R13 but these new
alloys are 185/60 R14.
I am sure they will fit... but any confimation would be cool.
TIA
Moby
PS
I know that the first number is the width of the tread in milimetres and the
last number is the diameter of the wheel in inches (why not metric??!). I
have a vague idea of what the second number means... some sort of percentage
or ratio?
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I have a vague idea of what the second number means... some sort of percentage or ratio?
Actually its the side wall width (profile of the tyre)
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Hi
Those alloys tyres will definitly fit as i just upgraded my wheels to that same size as you specified to my mk3 fiesta
one thing i do reccomend having done after fitting them is to go to your ford dealer have them check the tracking if it needs adjustments its a flat £14.99 i was weary of that fee at first but its worth it,
Regards
J Stephenson
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>> I have a vague idea of what the second number means... some >> sort of percentage or ratio? Actually its the side wall width (profile of the tyre)
It is the aspect ratio of the tyre. This means the depth of the sidewall as a % of the width of the tyre, so your 185/60 has a sidewall depth of 185*60% = 111 mm.
As regards whether the wheels will fit or not... it depends whether the offset, stud-hole spacing and the profile of where the studs or nuts fit against the wheels are correct or not. If you don't know you should ask for the data from whoever you're buying the wheels from.
Andy
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Whenever you change wheel/tyre sizes, you need to consider the overall diameter of the "wheel plus tyre" and the effect this will have on your speedometer. It just so happens that the overall wheel diameters of the two tyres you've listed are exactly the same, so you're OK.
Overall wheel diameter = two sidewalls plus diameter of the metal bit.
Original wheels = (165*75%) *2 /25.4 + 13 inches = 22.74 inches.
New wheels = (185*60%) *2 /25.4 + 14 inches = 22.74 inches.
Coincidence or good planning?
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165/75R13? - that's an unusual size - typical aspect ratio of european tyres is '70', '65', '60 series' etc. What make are they?
Sure, if they are 165/75/R13 then they will be have a very similar rolling circumference or 'revs per mile' so your gearing and speedo accuracy will be preserved.
Ideal rim width for 185/60R14 is 5.5"x14 or 6"x14.
As you say , it's a little strange but rim sizes have stayed imperial although tyre widths went metric with the advent of the radial tyre.
Also, most rims are accurately fitted to a spigot on the hub so that wheel centrality doesn't rely on the studs/bolts - as Andy says, best check all these points with your supplier.
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IanT:
Thanks for the advice - I realised I needed to take into account the rolling circumference of the tyres to see how badly affected the speedo may be. Thanks for clarifying what the second number meant on the tyre specification.
howy686:
You're right, the tyres are actually "70" so there would be a slight reduction in original wheel diameter from 22.74 inches to 22.09 inches. Converting to metric (I'm too young for imperial!) and calculating the original and new wheel circumference (pi*diameter):
Original tyres circumference = pi*0.561m = 1.763m (3dp)
New tyres circumference = pi*0.578m = 1.815m (3dp)
Since the new circumference is longer than the original the speedo would underread. To work out the percentage error introduced we need to work out how many times the tyres rotate at a constant speed of, for example 100km/h (again metric, sorry guys!). At this speed the original tyres would need to rotate 15.755 times per second to cover 100km in one hour. However, the new wheels have a larger circumference and so to cover the same distance would need to rotate less, nearer 15.308 times per second.
Consequently my speedo will end up underreading by nearly 3.0km/h at said speed, or overread by 3%. So thats nearer 62mph when the speedo read 60mph.
Is this error significant? If so, how do you go about rectifying the situation?
With regards fitting - I believe the wheels also came off a Mk4 Fiesta, and so presumably there wont be a problem with fitment onto my Mk4 Fiesta - but I will check!
Thanks again,
Moby.
Moby
------
Life it too short to stuff a mushroom
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