(In some ways, this is a follow up to Espada's thread, but since I am asking a slightly different question, I thought I'd start a new thread.)
I've been looking at the tyre size calculator on the Wheel & Tyre Bible: www.carbibles.com/tyre_bible_pg4.html
I have noted that on the old shape (2002-08) Berlingo, one can get, depending on the engine size (not trim level, oddly enough), either 14" or 15" wheels, which take, respectively, 175/70 R14 and 185/65 R15 tyres.
When I use the W&TB tyre size calculator, it tells me that the difference between them is 65.66 mm, or 3.36%.
However, it tells me that if Citroen had used 175/65 R15 tyres instead of 185/65 R15 the difference in circumference would be 24.82mm or 1.3%.
If the W&TB tyre size calculator is correct - and I assume that it is - this raises certain questions in my mind.
1. The obvious practical question is whether it would be appropriate to change wheels and tyres from one to the other, since 3.36% sounds to me like quite a big difference. Even 1.3% is a reasonable difference.
2. How close is OK? W&TB says that a difference of 1.69% is more than close enough. Is he correct?
3. Why might Citroen choose to offer 185/65 R15s as an alternative to the original 175/70 R14s, instead of the more similarly sized 175/65 R15s?
4. Does this mean that Berlingos with different engines (and therefore wheel sizes) will have differently calibrated speedometers (and odometers)?
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...the difference in circumference would be 24.82mm or 1.3%...
Or just under one inch.
Given the circumference of car tyres is in the region of six feet*, I don't think there's much to worry about.
An inch difference could easily be caused by tread depth or maybe even compression of the sidewalls under different loads.
* The diameter of the tyres on the CC3 is 24", which times pi gives a circumference of 75" - 6ft 3" - give or take the odd grain of road salt.
Last edited by: Iffy on Mon 3 Jan 11 at 12:57
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FWIW the calculator looks to be giving the right answer.
One I made earlier when trying to find some tyres for the Land Rover - you'll have to work your own %age out as it was for comparing metric and imperial -
goo.gl/JrQn7 (E&OE)
and another internet one here that more or less agrees
www.miata.net/garage/tirecalc.html
It's entirely possible, even likely in my uninformed opinion, that different engined vehicles will have a different speedo rate.
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wheel and tyre sizes - yet again. - Iffy
