Tyre Size

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Wed 18 Feb 2004 19:02
Tyre Size - Tim J

I want to change the size of tyre on the car.

I currently have 155/70 13
If I wanted to put 165/70 13 on the car, would I have to change the rims (I have steel rims, alloys would be worth more than the car!)
or would what i have at the mintue be ok?
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Thu 19 Feb 2004 15:54
Tyre Size - billy25
hi tim,

you wouldn't have to change rims, 165 is the width of the tyre tread, 70 is hight of sidewall, 13 is size of rim. therefore a 165/70/13 tyre will fit on a 155/70/13 wheel. just don't get carried away and go too wide, or you may foul other bits of chassis on full lock.

billy.
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Thu 19 Feb 2004 17:10
Tyre Size - Stargazer {P}
Billy25, Tim J
The 70 is the height of the side wall expressed as a percentage of the width, for example the original tyres are 70% of 155mm or 108.5mm high, the replacement tyres are 70% of 165mm or 115.5mm high.

This has the effect of increasing the diameter of the wheel and hence the circumference of the wheel. in this case a 13 inch wheel
has a diameter of approx 330mm (13*25.4) and the original wheel plus tyre will have a diameter of 330+108.5+108.5 or 547mm
whereas the new wheel will have a diameter of 330+115.5+115.5mm
or 561mm. The difference is about 2.5% which will mean that on the larger wheels the speedo will be running about 2.5% slow (ie the car is travelling faster than expected.)

Somewhere somebody posted a link for calculating tyre and wheel sizes vs speed and working out allowable combinations. try a search.

regards

Ian L.

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Thu 19 Feb 2004 17:33
Tyre Size Calculator - Stargazer {P}
Here try this:

www.tyresave.co.uk/tyresize.html

Putting in the numbers suggested in Tim's original post agrees with my calculation of 2.5% error and it gives guidance that the maximum difference recommended is 2.5%. So OK but I would chage the tyre size to 165/65R13 if they are available and the difference is almost unmeasurable (<0.4%).
cheers

Ian L.
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Thu 19 Feb 2004 17:35
Tyre Size - autumnboy
This is the website you should use. You put in your standard tyre size, then you can experiment with tyre sizes and tells you what your speedo error will be.


www.chris-longhurst.com/carbibles/index.html?menu....l
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