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sleek lemur · Oct 22nd, 2019, 22:38

I've spent an embarrassing amount of time researching this. Here are my conclusions. Spoiler alert! There's a happy ending ( unless anyone knows better). Here goes.

Standard wheel is 15in X 5.5J and tyre 165/80 or 185/70. Bolt configuration or PCD is 5x108 (5x 4.25inch) (different from the 1800S, which is 5x4.5 inch and the same as a Mustang. The other important measurement is Offset or ET, which is the measurement between the mounting surface of the wheel and the geometric centre of the wheel. ET comes from the German 'Einpresstiefe' , which means "insertion depth". There are vids on You Tube as to how to measure this and it's v v simple. The ET of a Volvo 1800E wheel is 40mm, meaning the mounting face is 40mm towards the outer face of the wheel from the centre, ie there is more wheel behind the mounting face than in front (An ET of zero would have 50% of the wheel inside and outside of the mounting face).

Next, with the axle on axle stands to have the wheels in the position they would be under the weight of the car, measure from the mounting face of the hub and brake disc assembly to the inside of the outer wheel arch and in the other direction to the outside of the road spring. This is 80mm and 170mm respectively. In other words, you have much more space behind the wheel to play with. There is much more wheelarch at the front, so that's ok.

I chose a 17inch 7J rim with 205/55 tyre. The diameter is very similar to the 15inch 165/80.

Thinking about the width of the 165 tyre, you have 80mm minus (165/2) minus your 40mm ET spare space for a wider tyre. This = 37.5mm. The free space behind is much greater and therefore unimportant. I don't know what the effect of widening the track of the vehicle would be, so I'm not going to use up all that space. The 205 tyre is 40mm wider and the 7inch wheel 38mm wider. So, if we choose a wheel with the same 40mm offset, the wheel will "poke" out 20mm further, leaving 17mm room. Also 20mm on each side doesn't seem a hell of a difference in track. If I want to maintain standard track for my 7J wheel, I will need a wheel with an ET of 60mm.

Of course I haven't considered whether the inside of the front tyre will rub on full lock, hence choosing a 40mm ET means I'm widening inner and outer by the same 20mm or so.

After gathering all this knowledge, I found the following website !

https://www.willtheyfit.com/

And now the good news. There are tons of 17inch wheels out there with 40-50mm ET. If you want an 18inch, then use the above site to find your fit. Trouble is which one to choose! Oh - always check delivery time.

A note of caution, I was given conflicting advice from many sites as to fit. Member powen1 above recommended R&R Alloys and I found them the most helpful and knowledgeable of all. But they don't stock a wheel for the 1800E !

Oct 22nd, 2019, 22:38	#16
sleek lemur Senior Member Last Online: Dec 29th, 2022 11:47 Join Date: Jun 2019 Location: Thorndon, near Eye, Suffolk, England	I've spent an embarrassing amount of time researching this. Here are my conclusions. Spoiler alert! There's a happy ending ( unless anyone knows better). Here goes. Standard wheel is 15in X 5.5J and tyre 165/80 or 185/70. Bolt configuration or PCD is 5x108 (5x 4.25inch) (different from the 1800S, which is 5x4.5 inch and the same as a Mustang. The other important measurement is Offset or ET, which is the measurement between the mounting surface of the wheel and the geometric centre of the wheel. ET comes from the German 'Einpresstiefe' , which means "insertion depth". There are vids on You Tube as to how to measure this and it's v v simple. The ET of a Volvo 1800E wheel is 40mm, meaning the mounting face is 40mm towards the outer face of the wheel from the centre, ie there is more wheel behind the mounting face than in front (An ET of zero would have 50% of the wheel inside and outside of the mounting face). Next, with the axle on axle stands to have the wheels in the position they would be under the weight of the car, measure from the mounting face of the hub and brake disc assembly to the inside of the outer wheel arch and in the other direction to the outside of the road spring. This is 80mm and 170mm respectively. In other words, you have much more space behind the wheel to play with. There is much more wheelarch at the front, so that's ok. I chose a 17inch 7J rim with 205/55 tyre. The diameter is very similar to the 15inch 165/80. Thinking about the width of the 165 tyre, you have 80mm minus (165/2) minus your 40mm ET spare space for a wider tyre. This = 37.5mm. The free space behind is much greater and therefore unimportant. I don't know what the effect of widening the track of the vehicle would be, so I'm not going to use up all that space. The 205 tyre is 40mm wider and the 7inch wheel 38mm wider. So, if we choose a wheel with the same 40mm offset, the wheel will "poke" out 20mm further, leaving 17mm room. Also 20mm on each side doesn't seem a hell of a difference in track. If I want to maintain standard track for my 7J wheel, I will need a wheel with an ET of 60mm. Of course I haven't considered whether the inside of the front tyre will rub on full lock, hence choosing a 40mm ET means I'm widening inner and outer by the same 20mm or so. After gathering all this knowledge, I found the following website ! https://www.willtheyfit.com/ And now the good news. There are tons of 17inch wheels out there with 40-50mm ET. If you want an 18inch, then use the above site to find your fit. Trouble is which one to choose! Oh - always check delivery time. A note of caution, I was given conflicting advice from many sites as to fit. Member powen1 above recommended R&R Alloys and I found them the most helpful and knowledgeable of all. But they don't stock a wheel for the 1800E !