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Robgosty

Wheel change help

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Hi all, wanting a softer ride on 2009 530D GT (F07), has 245.45.19 on front & 275 40 19 on back all run flats, will fitting  245.45.18 on front & 275 40 18 normal tyres make any difference ?  think it will drop ride height 10mm or so but will it make any change to ride quality

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In my opinion it is the profile (40/45) that has the biggest affect on ride quality. I doubt simply reducing the wheel diameter will have any positive effect. I would recommend dropping the wheel diameter and at the same time increasing the profile to say 55. Reducing the wheel diameter without upping the profile will drop the ride height (as you have noted) but will also affect things such as speedo accuracy.

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They are the wrong tyre sizes if you drop down to 18” rims. You would need to double check but you would need to add 5 to the profile size to maintain the correct rolling radius. 
 

245/50 front and 275/45 rear if you want to run an F07 on 18” rims. 
 

Also worth a check but I’m not sure you get a staggered set up on 18” rims for the F07.

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Andrew is right. The correct tyres for the F07 on 18" rims are 245/50. If you used the 245/45 tyres, which are correct for the F10, you will indeed lower the ride height marginally, but more importantly the rolling circumference of the tyre will be less, resulting in the wrong gearing and a misreading speedo etc.

 

I agree completely about the harsh ride on thinner sidewalls. The ride on my 20" rims with runflats is horrible (275/35 rear and 245/40 front). My winter runflats on 18" rims are so much more compliant and I don't have to worry so much about hitting the odd pothole or kerb.

 

The sidewall depth is calculated as follows:-

275 x 35% = 96.25mm

245 x 50% = 122.5mm

Giving an overall diameter

For 20" rims:- 20 x 25.4 = 508mm plus 2 x sidewall depth = 700.5mm

For 18" rims:- 18 x 25.4 = 457.2mm  plus 2 x sidewall depth = 702.2mm

If you used 245/45 tyres on 18" rims, the overall diameter would be 457.2mm plus 2 x 110.25 = 677.7mm

 

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18 hours ago, Robgosty said:

Hi all, wanting a softer ride on 2009 530D GT (F07), has 245.45.19 on front & 275 40 19 on back all run flats, will fitting  245.45.18 on front & 275 40 18 normal tyres make any difference ?  think it will drop ride height 10mm or so but will it make any change to ride quality

 

As others have said; make sure that you get the sizes of your tyres right

 

Use a tyre calculator and suss out what you can fit; needs to be within 2.5% +/-

 

https://www.tyresave.co.uk/tyre-size-calculator/

 

Moving over to non-RFT will help a lot, just make sure you inform your insurance that you've done this; as long as they meet the same specs (ie. sizes and profiles etc) you'll be fine

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