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      02-17-2020, 05:37 AM   #1
Goc187
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Tyre dimension confusion - F20 help

First of all I want to say hello to all members here. I am new one here.

Bought my f20 116d few months ago.

I am little bit confused about tyres size on my F20. I am running now winter setup 225/40 R18 7,5Jx18 ET45 OEM 385 double spoke rims. Soon i will have to move on summer setup, and i was like okay, I`ll put same dimension tyres on my rims. But then i got confused a lot.

I saw that dimensions are different for rear summer setup, but rear rims are also different 8Jx18 ET52.
In My CoC said that i can put 225/40 R18 7,5Jx18 ET45 for M+S tyres and 225/40 R18 7,5Jx18 ET45 front,245/35 R18 7,5Jx18 ET52 rear for summer tyres.
Can anyone explain me reason why? I know the better traction is with wider tyre, but here i am talking about normal daily car driving.

Can I put 225/40 R18 7,5Jx18 ET45 summer tyres on all four wheels?

You can see in attach my CoC tyre report.

My apologize if i post this thread on wrong place

btw. I try to get answer from my dealer here in my country but he just send me copy of CoC with no explanation
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Last edited by Goc187; 02-18-2020 at 03:46 AM..
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      02-17-2020, 05:58 AM   #2
ovekvam
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The rules are different from country to country, but using only front wheels in all corners is not only okay, it is most like better than the wider rear tyres. Some of the wheel/tyre sets from BMW are like this from the factory.
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      02-17-2020, 10:40 AM   #3
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Tyres must fit the rims. This simple. Say, my M-Sport car has wider (summer) rear wheels it came with from the factory and I have an OEM winter wheels set with all four of the same size.

The tyre sizes suggested from your VIN (I suppose) presume the car's factory tyres and the OEM winter wheels' tyres BMW offers for your car, apparently. If you have optional accessory rims you should choose the tyres based on the fact.
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      02-17-2020, 01:01 PM   #4
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Quote:
Originally Posted by No one View Post
Tyres must fit the rims. This simple. Say, my M-Sport car has wider (summer) rear wheels it came with from the factory and I have an OEM winter wheels set with all four of the same size.

The tyre sizes suggested from your VIN (I suppose) presume the car's factory tyres and the OEM winter wheels' tyres BMW offers for your car, apparently. If you have optional accessory rims you should choose the tyres based on the fact.
Thank you all for answer. Of course tire have to fit the rims. Unfortunately i have only this rims. All 4 ET45.
As i said that summer/winter tyres dimenision got me confused. If they fit as winter, why shouldn't they fit as summer.

If i had ET 52 rims for rear, i would put 245/35 so they can fit.
I just want make myself sure that summer 225/40R18 et45 is okay to put on all four wheels.
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      02-17-2020, 01:29 PM   #5
ovekvam
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Just for the record, the ET number is not about size, it is about offset. The higher offset, the less they stick out. For 225 tyres, you would usually run 7.5 inch wheels. For 245 tyres, you would use 8". It is however not very critical, so 225 on 8" or 245 on 7.5" is possible.
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      02-17-2020, 11:11 PM   #6
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Quote:
Originally Posted by Goc187 View Post
Of course tire have to fit the rims. Unfortunately i have only this rims. All 4 ET45.
As i said that summer/winter tyres dimenision got me confused. If they fit as winter, why shouldn't they fit as summer.

If i had ET 52 rims for rear, i would put 245/35 so they can fit.
I just want make myself sure that summer 225/40R18 et45 is okay to put on all four wheels.
So you have two sets of front rims and no rear ones: https://www.realoem.com/bmw/enUS/sho...diagId=36_1642. This is the recommended winter rim setup. But the recommended/factory summer setup with those rims includes wider rear rims and tyres. Your CoC quote presumes/includes that explicitly.

Yes, 225/40R18 is the recommended size for the 7,5JX18 ET45 rims you have. Your current 225/45 winter tyres have excessive sidewall height. You can check it in the wheel configurator (there's a winter wheel set with the Double-Spoke 385 rims, click "Details" for tyres). Also you might want to consider BMW specific, star-marked tyres (for ultimate pleasure ): https://www.realoem.com/bmw/enUS/sho...diagId=85_0103.
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      02-18-2020, 03:56 AM   #7
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Quote:
Originally Posted by No one View Post
So you have two sets of front rims and no rear ones: https://www.realoem.com/bmw/enUS/sho...diagId=36_1642. This is the recommended winter rim setup. But the recommended/factory summer setup with those rims includes wider rear rims and tyres. Your CoC quote presumes/includes that explicitly.

Yes, 225/40R18 is the recommended size for the 7,5JX18 ET45 rims you have. Your current 225/45 winter tyres have excessive sidewall height. You can check it in the wheel configurator (there's a winter wheel set with the Double-Spoke 385 rims, click "Details" for tyres). Also you might want to consider BMW specific, star-marked tyres (for ultimate pleasure ): https://www.realoem.com/bmw/enUS/sho...diagId=85_0103.
Sorry guys I made mistake in first post. Now i have change my first post.
I am now on 225/40R18 7,5JX18 ET45 winter setup on all 4. That is recommended setup for winter, but why they didn`t wrote that this setup is recommended also for summer setup, that is my confusion

Sorry once again for mistake in first post
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      02-18-2020, 06:17 AM   #8
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Most summer sets are with wider tyres in the rear to provide more traction and better looks. For the smaller engines, the traction is hardly an issue anyway, so I prefer the better cornering balance you get from having same width tyres all around. BMW have such sets too, but the rules for documentation can be different between countries.
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      02-18-2020, 04:25 PM   #9
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Quote:
Originally Posted by Goc187 View Post
That is recommended setup for winter, but why they didn`t wrote that this setup is recommended also for summer setup, that is my confusion
Because they don't recommend it for summer!

The winter setup is (obviously?) the summer one adjusted for the winter when narrower tyres are considered mostly an advantage (to dig through the snow/ice for traction), with DTC (see the manual, page 99) in mind, obviously.

In summer they probably mind oversteering (see those stupid RWD turn exit crashes videos) but those who are confident appear to favour some agility instead, going for the "square" setup. ovekvam has shared plenty on that around here (besides the answer just above).

Just by the way, if the nature of your concern is not really curiosity but safety , it's all right to have the "square" winter size setup in summer. As it has been noticed already, BMW did not always offer wider rears from the factory for this car. I have those only due to the M-Sport package I chose, it would've been same size wheels all around otherwise.

Last edited by No one; 02-18-2020 at 06:02 PM.. Reason: Another consideration added.
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      02-21-2020, 04:31 AM   #10
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Thank you so much for detailed explanation. I just want to make my self sure that i am not doing anything wrong
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