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Hi Guys ... I have a 2019 BMW 5 Series G30 , I have installed 20" Rims and installed 245/35/20 in the front and 275/20/30 in the rear . I have kept the factory shock absorbers and springs and have not made any amendments to the suspension . Now , the rear tires have a slightly bigger gap with the fender that I would like to reduce , and the front tires I feel some vibration ( oscillations ) in the suspension on slightly uneven roads ( as if there is a problem in the shock absorber ) ... what should I do ? should I change the Springs or the Shock Absorbers ? Which types should I get ?

Thanks every one for your help .
 

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What was on it before, and which suspension do you have? It would also help to know what the tires and wheels are. Are they BMW wheels, standard offset etc?
 

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silberma1
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You need to understand that the car is designed as a system. Changing a few parameters will affect the system and require a computer dynamic analysis to restore proper operation. This is a job for automotive engineers and beyond the scope of the reader of this forum. The motto should be don't fix it unless broken.
 

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You need to understand that the car is designed as a system. Changing a few parameters will affect the system and require a computer dynamic analysis to restore proper operation. This is a job for automotive engineers and beyond the scope of the reader of this forum. The motto should be don't fix it unless broken.
What?

You do not need "a computer dynamic analysis" when changing wheels & tyres. You need to ensure you get the correct offset & width of wheel (which will vary depending on the result desired) and correct tyre sizes to keep the rolling radius identical. i.e. You simply need to know what you are doing.

It is nothing that is beyond the scope of the average enthusiast, when making changes within reason.
 

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silberma1
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What?

You do not need "a computer dynamic analysis" when changing wheels & tyres. You need to ensure you get the correct offset & width of wheel (which will vary depending on the result desired) and correct tyre sizes to keep the rolling radius identical. i.e. You simply need to know what you are doing.

It is nothing that is beyond the scope of the average enthusiast, when making changes within reason.
The 20" tires have shorter stiffer side walls which will cause a stiffer more bouncy ride compared with the original wheels. I would think that the springs and shocks are matched to the wheel/tire size. If the OP does not mind the worse ride they will work.
 

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The 20" tires have shorter stiffer side walls which will cause a stiffer more bouncy ride compared with the original wheels. I would think that the springs and shocks are matched to the wheel/tire size. If the OP does not mind the worse ride they will work.
Springs/shocks are not mated to the alloys chosen - M Sport suspension/standard suspension/adaptive dampers - those are the choices. For example, an M Sport suspension car could have 18's, 19's or 20's from the factory, there is no difference in the suspension.

There is no computer coding that can be/needs to be done to the suspension when changing wheels.

However, you are right that a bigger alloy with lower profile tyres will change the feel (stiffer yes, more bouncy no - the opposite). OP needs to accept that fact. But there are numerous factors to take into account.
 

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Hi Guys ... I have a 2019 BMW 5 Series G30 , I have installed 20" Rims and installed 245/35/20 in the front and 275/20/30 in the rear . I have kept the factory shock absorbers and springs and have not made any amendments to the suspension . Now , the rear tires have a slightly bigger gap with the fender that I would like to reduce , and the front tires I feel some vibration ( oscillations ) in the suspension on slightly uneven roads ( as if there is a problem in the shock absorber ) ... what should I do ? should I change the Springs or the Shock Absorbers ? Which types should I get ?

Thanks every one for your help .
Have the wheels/tires balanced again, that is my guess on the issues. Changing wheels and tires will affect the overall spring rate so the car could feel softer or harsher depending on the tires chosen. The wheel gap is a function of the overall diameter and not much you can do without changing out to different tires (sidewall heights) or actual suspension parts.

How many miles on the shocks?
 

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Hi Guys ... I have a 2019 BMW 5 Series G30 , I have installed 20" Rims and installed 245/35/20 in the front and 275/20/30 in the rear . I have kept the factory shock absorbers and springs and have not made any amendments to the suspension . Now , the rear tires have a slightly bigger gap with the fender that I would like to reduce , and the front tires I feel some vibration ( oscillations ) in the suspension on slightly uneven roads ( as if there is a problem in the shock absorber ) ... what should I do ? should I change the Springs or the Shock Absorbers ? Which types should I get ?

Thanks every one for your help .
A bigger fender gap implies a smaller total wheel diameter than with the original tires. I'm no expert but I would want replacement tires with the exact same outside diameter. A smaller tire means more rotations per mile and speedometer/odometer readings on the high side.
 

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Hi Guys ... I have a 2019 BMW 5 Series G30 , I have installed 20" Rims and installed 245/35/20 in the front and 275/20/30 in the rear . I have kept the factory shock absorbers and springs and have not made any amendments to the suspension . Now , the rear tires have a slightly bigger gap with the fender that I would like to reduce , and the front tires I feel some vibration ( oscillations ) in the suspension on slightly uneven roads ( as if there is a problem in the shock absorber ) ... what should I do ? should I change the Springs or the Shock Absorbers ? Which types should I get ?

Thanks every one for your help .

The wheels you've fitted, assuming the same offset are within 0.2mm (front) and 6.3mm (rear) of a similar diameter so the rolling circumference of the wheel is nigh on identical to the 17" wheels you removed. I suppose the 6.3mm rear gap increase may be obvious.

As for you now having a bigger gap and based on the above 0.2mm/6.3mm difference you could lower the suspension as I'm sure many have done but the gap should be no different from your car had it been specified with 20" rims and tyres from the factory. As others have said, there is one suspension setup with different wheel combinations available.

Remember there is now a much narrower sidewall 123.75mm previously 85.75mm now (on the front wheel) so the drive is going to feel very different as the previous higher sidewall is going to be adding to the rebound capability of the suspension and this has been dramatically reduced with the new tyres.

If you are feeling vibrations now I would be going back to the tyre fitter to get them re-balanced as the larger rim/narrower sidewall of the 20" wheels is often quite challenging to get perfectly balanced.

I'd live with the car for a while to get used to the different driving experience as it will never be what it was with the 17" rims and tyres. But the car will look very good.

Here are the different rim and tyre sizes available as standard/optional factory fits:

G30 17***8221; Tyre: 225/55R17 Rim: 7.5J x 17 ET:27
G30 18***8221; Tyre: 245/45R18 Rim: 8j x 18 ET:30
G30 19***8221; Tyre: 245/40R19 + 275/35R19 Rim: 8j x 19 ET:30 + 9j x 19 ET:44
G39 20***8221; Tyre: 245/35R20 + 275/30R20 Rim: 8j x 20 ET:30 + 9j x 20 ET:44
 

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Just re-reading your post are the rears 275/30/20? You may have a typo there. In any event, obviously its very important to comply with the specific options specified by BMW. Vibration can be caused by out of balance tires, a defective or bent rim (and that is very difficult to remedy with just a wheel balance), an out of round tire, or defective tire which on a run flat can happen if you hit a pot hole, or a suspension problem.

From experience, most of the time, a proper wheel balancing does it. If you have run flats, they can be a little more complicated because the sidewalls are very stiff to assist you when driving if you have a deflated tire. But I found the sidewalls can be slightly deformed after a constant pounding depending on road conditions, and the rim size.

From experience, I hate vibration in wheels and you have to be insistent to get it right and watch out for a bent rim. As to ride quality, I believe you will find that the bigger the rim, the less rubber on the road, hence you will feel a lot more road imperfections. Not much you're gonna be able to do about that.
 
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