offset calculation brain ache

[ArtfulHussy]

Evening all,

Spied a set of wheels that I rather fancy but they are 8J and ET30. They are still 15" and I currently have 12.5mm spacers. Can anyone tell me what width of tyre I would need (assuming this would affect the height percentage value (the middle number!?) as well cause the tyre would be wider?

Can anyone help me figure out what offset I would end up with using the 12.5m spacer and if these would rub on the inside? My brain hurts. I tried doing some research but i couldn't get my head around it.

 

[Catweasel]

http://www.willtheyfit.com/" onclick="window.open(this.href);return false;

 

[ArtfulHussy]

I did use that but didn't really know what the meaning of their answer was

 

[YOG]

http://www.1010tires.com/Tools/Wheel-Offset-Calculator" onclick="window.open(this.href);return false;

Offset Information (1)

• YOG
• Dec 3, 2014

Offset Information (2)

• YOG
• Dec 3, 2014

 

[ArtfulHussy]

That one was a bit easier to understand thank you. I'm thinking 8J is just too wide.

 

[trublustu]

Its quite easy to work out which tyre/wheel combo matches you original rolling diameter..

you start with the three tyre size numbers
so for us its 195. 50. 15
As a rule of thumb if you go up one size in one, you need to go down one in another.

Eg 195-50-15 = 205-45-15 = 215-40-15 etc
It works for wheels too
Eg 195-50-15 = 195-45-16 = 195-40-17 etc

And both
Eg 195-50-15 = 215-30-17

Whether tyres are available in your preferred size is another matter..

 

[TGPlayer1]

By my calculations (based on the original setup being standard Puma) the closest match for a 15x8J is 215/45/15 with an offset of 10, effectively requiring 20mm spacers to achieve the same back spacing to stop rubbing on lock. Also the outer edge of the rim will stick out nearly 2 inches further, which may just be doable, but I can't quite picture it properly in my head right now. As a further point, in all my years of fitting tyres I've never come across a 215/45/15. Mainly because run of the mill cars would never have wheels that wide on a 15, maybe back in the day some serious machinery would but on modern cars 8J is generally only found on German sports and 4x4s, which would have bigger wheels or higher profile tyres respectively.

So in short, you need 215/45/15 and with 12.5mm spacers you would get rubbing on steering lock.

 

[ArtfulHussy]

I couldn't explain any if what you just said but I kinda figured it wasn't doable. :lol: I think the would stick out past the arches. Shame, they are bonnie wheels.

 

[ArtfulHussy]

I read another post somewhere (I believe it was Errol's?) that I think suggested that 8in wheels could potentially upset the handling because the contact patch would be affected.

Obviously my standard puma is lighter than the duratec beast. Would I struggle on 8in wheels?

Would they be okay if I mostly wanted them for posing? :lol:

 

[TGPlayer1]

People have fitted 8J wheels and it's been ok. The thing with the contact patch is about how much weight is applied per square inch; the more weight per sq inch effectively means more grip, in a nutshell. So a light car on big wide tyres will have the weight spread across a large area, reducing the gripping potential. Obviously for posing purposes practicality can be thrown out of the window, but you'd have to watch your self on twisty country roads if you're pressing on a bit because the drive will be a bit more skittish an you may be getting very familiar with the wildlife.