225/50 18 possible

[jorgenson]

hi.
is it possible to install 225 50 18 tires on the mg zt - t? I measured it and I think so. the border seems to be the spring plate in the front.
regards from south germany
jorgen

[T-Cut]

Hello Jorgen, welcome to the forum.
I think the proposed size will cause the speedometer to become too inaccurate/illegal.
The MGR Handbook gives alternative sizes and the recommended tyre for 7.5Jx18 rims is 255-45 18.

There are online calculators that will tell you how these differences affect the running circumference. I think the permitted variance is pretty small.



TC

[jorgenson]

thanks for the answer i know the tire sizes of mg / rover :-)
my question should be understood as follows: what is technically possible


has anyone ever tried if 225/50 18 fit

[Jamiewelch]

Originally Posted by jorgenson

thanks for the answer i know the tire sizes of mg / rover :-)
my question should be understood as follows: what is technically possible


has anyone ever tried if 225/50 18 fit

It is the same width so would fit the rim, but i would reckon you would get the tyres very close to the arch liners, and potentially scrape on them on tight turns.

[Odd Job]

https://www.willtheyfit.com/

Have a look at something like this.

Gives you an idea,

it appears the speedo error is 3.3%

[Avulon]

I've happily fitted 225/50 17 on meteors on the 75 saloon. IIRC I had 225/55 17 on in the past but I cant say that with 100% certainty. What I do know though is different manufacturers tyres when new will measure slightly differently from each other for the same size specification - so it might depend on the brand and specific model of tyre as well.

[jorgenson]

@avulon: that you had installed 225 55 17 is valuable information for me because the diameter of 67.9 cm is almost the same as 225 50 18 with 68.2 cm. were there any problems in the wheel arch?

[Rick-sta]

Yes they'll fit.

The increase tyre profile size will cause the speedometer to under read slightly. At 70mph according to the speedometer, you'll actually be doing 72.4mph. Take into account that the speedometer over reads by about 5mph at 70 anyway, it'll just make your speedometer a little more accurate.

Changing up from 45 profile tyres to 50 profile tyres will increase the sidewall height by 12mm. That'll be fine and won't rub the arches if your ZT is on standard springs. To give an idea, my motobuild lowering springs give a 30mm drop and the wheels don't rub, so a 12mm decrease in the arch gap will be fine.

Only thing to be wary of would be insurance implications of running the incorrect tyre size.

[Avulon]

Originally Posted by Rick-sta

Yes they'll fit.

The increase tyre profile size will cause the speedometer to under read slightly. At 70mph according to the speedometer, you'll actually be doing 72.4mph. Take into account that the speedometer over reads by about 5mph at 70 anyway, it'll just make your speedometer a little more accurate.

Changing up from 45 profile tyres to 50 profile tyres will increase the sidewall height by 12mm. That'll be fine and won't rub the arches if your ZT is on standard springs. To give an idea, my motobuild lowering springs give a 30mm drop and the wheels don't rub, so a 12mm decrease in the arch gap will be fine.

Only thing to be wary of would be insurance implications of running the incorrect tyre size.

No problems with wheel arch clearance with the 225/50 17 tyres. Doing the same with 18" wheels would be very close in size to the 225/55 17, I'm sorry I can't recall clearly if I actually did it, or just considered it.

[jorgenson]

Okay guys. Thanks for your feedback. I will buy some now, assemble them and send you cool pictures.
Best Regards

Jorgen