hello in need of some advice if anyone could please help.

I have a standard 1.2 GP (cheap skate spec) with 15 inch steel wheels running 185/65/15. anyway I happen to have a set of vaxull combo van 16 inch wheels that have the same pdc and cb so fit on but what tire size would then need to keep the overall tire the same size for speedo calibration
many thanks

Hi,

185 x 0.65 = 120.25 = tire high in mm
15" x 25.4 = 381 = rim dia. in mm
381 + (2 x 120.25) = 621.5 = wheel dia. in mm
621.5 x 3.14 = 1,951.51 = wheel development in mm

16" x 25.4 = 406.4
(621.5 - 406.4) / 2 = 107.55 = ideal tire high for 16" rim
195 x 0.55 = 107.25 = pretty good matching and still reasonnable in width and price ;-)

Regards, Bernie

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Hi,

would anybody replace a (relatively) cheap 185-65-R15 by an expensive 215-35-R16 as suggested by the alloywheel link ? The (little) calculation I gave was to help readers to understand the meaning of tire numbers. To make the story short: the bigger the rim (in ") the smaller the width/high ratio (in %) FOR THE SAME WIDTH and the same circumference. As not all size/ratio exist one need to chose what's available and fits one's wallet thickness. I don't see any point to install 215's on a 1.2 petrol GP, unless it's only for the show (which I could understand).

Get the 195-55 on your 16" rims and you'll be happy with the look and the cost...

Regards, Bernie

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these shod for 16inch got the tire shop to dig me a 195 55 16 out the bin and I'll put it on and check clearance before going ahead with new rubber. the rims fit the hub spot on with no wobbles bolts no rigs no spacers

Good decision ! You should have a lot of clearance, that's excatly the size I have on my GP 1.3 Multijet 90hp...

Regards, Bernie

thanks all for the advice I'll upload pics when complete