18inch or 19inch in sdrive23?

[Ermis]

Got my new Z4 sdrive 23i and i would like to replace the stock 17 inch wheels with 18inch or 19 inch. I am just wondering if 19 inch wheels will affect in a bad way the performance of the car.

[teagueAMX]

Some may say that 19's look better, but depending on your roads, 18's may be a better setup to prevent flats and wheel damage. 18"'s will ride nicer, too.

[alan64]

Originally Posted by teagueAMX

Some may say that 19"'s look better, but depending on your roads, 18"'s may be a better setup to prevent flats and wheel damage. 18"'s will ride nicer, too.

yes, absolutely.

[bill123]

I have 326 19" fitted and the ride is better than my e85 with 18" wheels

[cdeslandes]

As a rule of thumb, bigger wheels will make a car's ride harsher (due to lower profile tires) and will degrade handling (due to higher unsprung weight and higher moment of inertia.)

That's why F1 cars use tiny 13" rims!

If you want larger wheels and compansate for the handling degradation, you'll have to spend more money to get really lightweight rims.

[Memphis1]

Originally Posted by ermis27

Got my new Z4 sdrive 23i and i would like to replace the stock 17 inch wheels with 18inch or 19 inch. I am just wondering if 19 inch wheels will affect in a bad way the performance of the car.

put it this way... the stock 17" wheels weigh in at 26.5 lbs... if you get, as an example, miro 942s 19" rims, they weigh less at 24 and 25lbs. so you wont' get unsprung weight but just be aware that they will bend easier if you go thru a pothole big enough and your ride will be a bit stiffer, but not in a bad way, since you're not driving an F1 car, i assume greece has speed limits on the streets and highways. having said that, as far as looks they will definitely look worlds better.

[Z4Andy]

I test drove a car on 17's.

Then I was told the only car available at the time was coming in on 19's. I was getting a really good deal so I went for it and to be honest the car drives great on 19" runflats.

I was concerned at first but the car really drives fine even on our crumbly N.Ireland roads.

[Ermis]

Thank you all, for your opinions

[zEdP]

Originally Posted by cdeslandes

As a rule of thumb, bigger wheels will make a car's ride harsher (due to lower profile tires) and will degrade handling (due to higher unsprung weight and higher moment of inertia.)

For 'normal' tires, none RFT’s this is the case. But for RFT's I'm not quite sure. These tires are already very stiff. I assume the difference won’t be that noticeable. And about the weight, I assume that 17" need more steel within the tires than 19" will have. This will be compensated because the 19" rims will be heavier than the 17" ones.

EdP

[teagueAMX]

Originally Posted by ermis27

Thank you all, for your opinions

What are your roads like? I've been watching some tube vids and it appears that in various parts of Europe and the Mediterranean the roads are pretty good. In other parts it's been noted the roads are not good. A Greek friend of mine has family in a very rural area. He visited his parents and I had to cal his village to send somebody out to his family's farm so he could come into town and call me. Anyway, he indicates some of their roads are not very good.

If you drive in areas with good roads, then low profile tires won't be much of a problem for you. On the other hand, poor roads can quickly damage low profile tires and wheels. I see it all the time in Southern California, a place that you'd think has pretty good roads. Keep in mind that an average sized pot hole can be equal to or actually deeper than the cross sectional height of the tire. What this translate to in normal use is a low profile tire sidewall can pinch down to within a few millimeters at speed. That force can damage your wheel, resulting in tire decompression.

FWIW

[solidgold]

Any recommendations for those going for 19"?

Option 1 :
225/30/R19 (front) 255/35/R19 (rear)

Option 2 :
235/30/R19 (front) 265/35/R19 (rear)

For option 2, will tyre rub arches when it is too wide at the rear?

[Ermis]

I live in Athens.There are not actually good or bad roads. You can drive your car let's say in a 'good' road and suddenly see a large pot hole. My previous car was a Saab 93 Aero with (225/45/17) and i've never had a problem before with damaged wheels.

[teagueAMX]

Normally with a 45 (225/45/17) profile height you wouldn't have trouble unless you hit some really, really bad potholes. However, with 19" low profile tire I think you would see a problem. With a 19" wheel your profile is getting down to 35 in the front and 30 in the rear.

If you roads are not so bad most of the time, I'd suggest that you go no larger than 18". They have a profile height of 40 in the front, which is where your greatest impact occurs and 35 height in the rear.

If they run good and bad about 50-50 you might consider using the 17" wheel. The 17" wheels are 225/45 front and 255/40 rear, which is very close to the profile height of your previous car.

It's really up to you. Smaller wheels don't look as sporty to some people. I like them personally, and they can be less expensive in the long run for you if you have bad roads. Plus they will help cushion the ride when you go over rough pavement.

[T89]

Is it possible to run 255/35 19" at the rear?


T

[teagueAMX]

If you don't have staggered wheel widths front/rear - same wheel width front and back. Nowadays they like to have the same tire height front/rear.

The middle number of the tire size (e.g., 225/45/17) is the tire sidewall profile ratio. It is multiplied by the tire width, so if you have wider wheel in back than the front, to keep the overall tire height the same front/rear, they change the profile height for the rear.

[T89]

Originally Posted by teagueAMX

If you don't have staggered wheel widths front/rear - same wheel width front and back. Nowadays they like to have the same tire height front/rear.

The middle number of the tire size (e.g., 225/45/17) is the tire sidewall profile ratio. It is multiplied by the tire width, so if you have wider wheel in back than the front, to keep the overall tire height the same front/rear, they change the profile height for the rear.

I guess it's a no then, since I'm running a staggered set up.

But the e92 m3 runs a staggered set up but still runs 245/35/19 and 265/35/19...?


T

[teagueAMX]

Originally Posted by T89

I guess it's a no then, since I'm running a staggered set up.

But the e92 m3 runs a staggered set up but still runs 245/35/19 and 265/35/19...?


T

Sorry, don't get me wrong, I'm not saying you can't run the same profile ratio for different width tires. I'm sure it's done all the time. As mentioned before the profile is a ratio, or multiplier, based on the tire width. This is say that the sidewall height is taller for 265 width tire vs a 245. Given in our discussion the wheel diameter the same, then the overall diameter of the tire increases. Not necessarily a bad thing, but as mentioned the trend today is to use tires with equal height front and back. Some super performance cars today have different diameter wheels to compensate.

Look at the 1st chart below that I screen captured from tirerack.com. This is for staggered wheel/tires that have the same diameter, which is the OEM configuration. The consideration in the days of old when using different height tires is the speedometer needed adjustment. However, I'm sure that today there is a different compensation mechanism (likely software or automatic calibration).

Frankly, it's been a long time since I read all those books on setting up your suspension for optimum performance so I don't recall the impact of having a taller tire in the back except to say it likely would shift your weight distribution and alter braking slightly. Wider tires in the rear of the car does give you a bit more grip back there, but people will tell you that also contributes to additional understeer, which is a condition the Z4 is subject too.

Hope that helps. FWIW

.

[Memphis1]

Originally Posted by solidgold

Any recommendations for those going for 19"?

Option 1 :
225/30/R19 (front) 255/35/R19 (rear)

Option 2 :
235/30/R19 (front) 265/35/R19 (rear)

For option 2, will tyre rub arches when it is too wide at the rear?

hi solidgold, option 2 is fine, they wont rub, BUT the correct set up is 235/35/19front and 265/30/19rear

Originally Posted by ermis27

I live in Athens.There are not actually good or bad roads. You can drive your car let's say in a 'good' road and suddenly see a large pot hole. My previous car was a Saab 93 Aero with (225/45/17) and i've never had a problem before with damaged wheels.

hi Ermis, 17" will only bend on a huge pothole doing maybe 80mph(i've done it before). 19" wheels will bend pretty easily, (i've done it at like 30mph in NYC, notorious for huge potholes) i would suggest 18" wheels for you; 19" at your own risk

Originally Posted by T89

Is it possible to run 255/35 19" at the rear?
T

Originally Posted by T89

I guess it's a no then, since I'm running a staggered set up.But the e92 m3 runs a staggered set up but still runs 245/35/19 and 265/35/19...?T

hi T89, the M3 has the suspension set up differently than the Z4, that's why OEM it's the same ratio, which clearly gives a diff height front to rear, but the suspension compensates for that. for the Z4 you need to take that into account, so you can run 225/35/19front and 255/30/19rear or even what I suggested to solidgold, 235/35/19front 265/30/19rear

the basic math is 25.4 mm = 1 inch (using the first suggestion):

front
225 is the width in millimeters = 8.86" inches
35 is the percentage of the width = 3.10" inches (from rim to road)
19 = obvious (the wheel size in inches)

rear
255 is the width in millimeters = 10.04" inches
30 is the percentage of the width = 3.01" inches (from rim to road)

[solidgold]

hi solidgold, option 2 is fine, they wont rub, BUT the correct set up is 235/35/19front and 265/30/19rear

Thks alot. My mistakes in the middle number. Should be lower number 30 at the rear and 35 in front to balance.

[Ermis]

I will go for 18''. Thanks

[T89]

Originally Posted by teagueAMX

Sorry, don't get me wrong, I'm not saying you can't run the same profile ratio for different width tires. I'm sure it's done all the time. As mentioned before the profile is a ratio, or multiplier, based on the tire width. This is say that the sidewall height is taller for 265 width tire vs a 245. Given in our discussion the wheel diameter the same, then the overall diameter of the tire increases. Not necessarily a bad thing, but as mentioned the trend today is to use tires with equal height front and back. Some super performance cars today have different diameter wheels to compensate.

Look at the 1st chart below that I screen captured from tirerack.com. This is for staggered wheel/tires that have the same diameter, which is the OEM configuration. The consideration in the days of old when using different height tires is the speedometer needed adjustment. However, I'm sure that today there is a different compensation mechanism (likely software or automatic calibration).

Frankly, it's been a long time since I read all those books on setting up your suspension for optimum performance so I don't recall the impact of having a taller tire in the back except to say it likely would shift your weight distribution and alter braking slightly. Wider tires in the rear of the car does give you a bit more grip back there, but people will tell you that also contributes to additional understeer, which is a condition the Z4 is subject too.

Hope that helps. FWIW

.

Originally Posted by memphis2012

hi T89, the M3 has the suspension set up differently than the Z4, that's why OEM it's the same ratio, which clearly gives a diff height front to rear, but the suspension compensates for that. for the Z4 you need to take that into account, so you can run 225/35/19front and 255/30/19rear or even what I suggested to solidgold, 235/35/19front 265/30/19rear

the basic math is 25.4 mm = 1 inch (using the first suggestion):

front
225 is the width in millimeters = 8.86" inches
35 is the percentage of the width = 3.10" inches (from rim to road)
19 = obvious (the wheel size in inches)

rear
255 is the width in millimeters = 10.04" inches
30 is the percentage of the width = 3.01" inches (from rim to road)

Thanks for clearing it out guys.

I'm looking to upsize to 235/35/19 and 265/30/19 to accommodate the wider wheels I just got (8.5"/ 9.5"). But due to swiss homologation laws, we need to stick within Bmws OEM specs which are 225/35/19 and 255/30/19.


T

[teagueAMX]

^"But due to swiss homologation laws. . ."

They really tie your hands.