Measuring accurately was proving challenging with the wheels on the car so for the complete avoidance of doubt I pulled the wheels off.

Yep - the 18x9s were on the right hand side, the 18x8s were on the left, with 245/45R18s all round... and pressures wrong on every corner.

That explains the pull to the right even after an alignment! Much nicer now. Testament to how smooth/nice these cars ride that I barely felt that before.

Well, I have it booked in at a tire place in a couple days for rotation and balance; seeing as the existing tires are really new/clean (2016 DOT code, but there's no cracking/weathering and only done about 2k on them) I will probably get some matching continental 255/45/r18s for the back instead of the rotation and keep the leftover tires as spares for the front, or whack one on a full size 18x8 of some description and use as a full size spare. Just need to find out the offset on the double 5s.

Very glad to find this thread and love this forum!

 

Well done. I wonder how many of these vehicles with staggered wheels are running around with the wheels out of order. Combine clueless owners with clueless tire shop employees and my guess would be quite a few....

 

To the OP. You should be able to put the same size tires all around.

I have a '97 XK8 with the 10 spoke 18" XKR wheels - wider wheels at back. Tires are 245 all around because 255 wasn't available in the brand I wanted. I did it because - well I'm cheap. And also have never driven the car over 90 and then only once to 90.

The car looks better, in my opinion with the wider tires at back. Probably handles better too. But you can put the narrower tires on the wider wheels. That's what the tire store told me and it seems so.

 

When I replaced the lousy factory Atlas chrome staggered 19-inch wheels on my wife's 2006 XK8 Victory Edition convertible back in early June, I went with a set of four Vertini RFS1.2 Silver with Brushed Face wheels with all four being identical at 19-inch by 8.5-inch. I kept my staggered tires (245/40/19 front and 255/40/19 rear) because they were installed new in January of this year, but I now have the option of going with non-staggered tires in the future. Very glad to now have that choice....

 

It was even more surprising that the wheel nuts had been torqued correctly to spec, I removed them with a torque wrench and it only took a smidge more than 85ft lbs to remove each nut. Entirely plausible that the previous tires were wrong too and the tire shop just copied what was there already but at least torqued the bolts to spec instead of just giving it lots of ugga dugga.

Of course, once I was under the car I found an oil leak from the rear diff, a little trans fluid leak around one of the bolts on the sump on the gearbox, some from around one of the bolts on the engine sump... lol. Hopefully the diff is just the breather. Ordered a dipstick for the Merc trans and ill just monitor that. Diff oil worries me more. Wonder if I can hook up an expedient diff temp sensor. I'll probably end up dropping the whole rear suspension unit at some point, but we'll see. I'm starting to gather that the diffs on these are known to leak profusely.

I'm going to have fun with this car lol. Not selling the mx-5/miata anytime soon. I'll need something to go to the auto parts store/pick'n'pull in.