[213e90n51]

I have stock Oem Bmw rims that are 8.5 and 8. Right now I have 225 40 r18 and the other is 255 35 r18. I use to have 19s with 265 rear and 235 fronts but i forgot the sidewall number. Can I get 235 tires front and up the sidewall by 5 front and rear so 235 45 r18 and 255 40 r18? Will it mess up the handling characteristics or balance?

[b1aze]

Your tire diameter will be almost 5% larger which may affect your speedometer/mileage accuracy but more importantly, there’s essentially no benefit to using a larger-than-factory diameter tire. What’s driving you to do this?

[213e90n51]

I want a more thick tire look and squared sidewalls. I envy wheel fitment on some of the e90s here and even tho my rims are 18 and my michelins have big sidewalls i want to know why some e90s have a more meatier tire setup with the same sidewall size!

[b1aze]

Sidewall is a ratio, not an absolute measurement. A 225/40 is a different sidewall height than a 255/40.

It’s your car and your money. Do what makes you happy.

[Efthreeoh]

Lemme help here.

So there is actually math to this, not just absolute numbers on the sidewall of the tire. The tire size 225/40-18 means the inside diameter of the tire (the hole) fits an 18-in wheel rim. The tire tread width is 225 millimeters and the tire sidewall number of "40" is the height of the sidewall in ratio to the tread width. So "40" means the sidewall is 40% of the tread width. So in this case .4 x 225MM = 90MM. Divide 90MM by 25.4MM/inch and the sidewall height is approximately 3.5 inches. So if you were to go to a 235/45-18 tire for the front the sidewall height would grow to approximately 4.2 inches, a difference of .7 inches, or a bit less than 3/4ths of an inch. Go look at a ruler and see how small 3/4th is (its 12 marks on the ruler).

MM = millimeters.
.4 = 40%
1 inch = 25.4 millimeters

I'll let you do the math for the rear tire.

[b1aze]

Originally Posted by Efthreeoh

Lemme help here.

So there is actually math to this, not just absolute numbers on the sidewall of the tire. The tire size 225/40-18 means the inside diameter of the tire (the hole) fits an 18-in wheel rim. The tire tread width is 225 millimeters and the tire sidewall number of "40" is the height of the sidewall in ratio to the tread width. So "40" means the sidewall is 40% of the tread width. So in this case .4 x 225MM = 90MM. Divide 90MM by 25.4MM/inch and the sidewall height is approximately 3.5 inches. So if you were to go to a 235/45-18 tire for the front the sidewall height would grow to approximately 4.2 inches, a difference of .7 inches, or a bit less than 3/4ths of an inch. Go look at a ruler and see how small 3/4th is (its 12 marks on the ruler).

MM = millimeters.
.4 = 40%
1 inch = 25.4 millimeters

I'll let you do the math for the rear tire.

While you’re 100% correct, don’t forget that adding 0.7” to the sidewall (radius) of the wheel equals a 1.4” diameter increase. This does 2 things. Raises the level of the car by approximately the 0.7” as well as reduced the amount of revolutions per mile (pi*d) resulting in inaccuracy of Speedo and mileage.

[lookalikehuuh]

Originally Posted by b1aze

While you’re 100% correct, don’t forget that adding 0.7” to the sidewall (radius) of the wheel equals a 1.4” diameter increase. This does 2 things. Raises the level of the car by approximately the 0.7” as well as reduced the amount of revolutions per mile (pi*d) resulting in inaccuracy of Speedo and mileage.

This increase may actually help to negate of of BMW's "optimistic" speedometer offset they instituted on E90s. Not like its accurate at this point anyway.

[213e90n51]

Originally Posted by Efthreeoh

Lemme help here.

So there is actually math to this, not just absolute numbers on the sidewall of the tire. The tire size 225/40-18 means the inside diameter of the tire (the hole) fits an 18-in wheel rim. The tire tread width is 225 millimeters and the tire sidewall number of "40" is the height of the sidewall in ratio to the tread width. So "40" means the sidewall is 40% of the tread width. So in this case .4 x 225MM = 90MM. Divide 90MM by 25.4MM/inch and the sidewall height is approximately 3.5 inches. So if you were to go to a 235/45-18 tire for the front the sidewall height would grow to approximately 4.2 inches, a difference of .7 inches, or a bit less than 3/4ths of an inch. Go look at a ruler and see how small 3/4th is (its 12 marks on the ruler).

MM = millimeters.
.4 = 40%
1 inch = 25.4 millimeters

I'll let you do the math for the rear tire.

I see so in the end the oem BMW specs are best for the suspension of the car right? I mean their the ones that have the engineers that designed this wheel and size. I always wondered why the rear had to be 35 sidewall instead of 40 like the front? What tire sizes you run on your 400k miles e90 325i?

[freakystyly]

OEM sizes 225/40/18 and 255/35/18 is 0.1" difference in diameter.

Google tire size calculator and play with the numbers to educate yourself on what you're after.

And as stated, the second number is a ratio not an absolute number of thickness. Be careful of going too thick as the wheels likely will not fit in your wheel well when turning or on rough roads as many have experienced rubbing.

[213e90n51]

Yeahh got it thanks!

[nsjames]

Originally Posted by lookalikehuuh

This increase may actually help to negate of of BMW's "optimistic" speedometer offset they instituted on E90s. Not like its accurate at this point anyway.

but will affect every other thing like mile per gallon calculations.

the kombi displays the corrected speed, but the DME knows the real speed for all the other stuff.

I'm currently running 225/50/17 winter tires.

uncorrected speed is low by 2mph.
corrected kombi speed is spot on mostly. slightly high.

this is a useful website.
https://tiresize.com/calculator/

[Efthreeoh]

Originally Posted by b1aze

While you’re 100% correct, don’t forget that adding 0.7” to the sidewall (radius) of the wheel equals a 1.4” diameter increase. This does 2 things. Raises the level of the car by approximately the 0.7” as well as reduced the amount of revolutions per mile (pi*d) resulting in inaccuracy of Speedo and mileage.

Of course I am correct. I was going with introductory course material to address the OP's initial concern, which was trying to improve the visual esthetics of the tires. It seems he was looking for a "meatier" sidewall appearance, which he was equating to a taller sidewall height. I was trying to address his concern of ethestics.

Delving into total tire circumference changes by doubling sidewall height and how it would affect the speedometer reading due to an increase in linear tread length is a higher level course curriculum, which I charge for. My PayPal account is currently suspended because of the COVID-19 pandemic .

[213e90n51]

Originally Posted by Efthreeoh

Of course I am correct. I was going with introductory course material to address the OP's initial concern, which was trying to improve the visual esthetics of the tires. It seems he was looking for a "meatier" sidewall appearance, which he was equating to a taller sidewall height. I was trying to address his concern of ethestics.

Delving into total tire circumference changes by doubling sidewall height and how it would affect the speedometer reading due to an increase in linear tread length is a higher level course curriculum, which I charge for. My PayPal account is currently suspended because of the COVID-19 pandemic .

Ahh why yes Mr F3OH! Did you ever try to have a meatier tire fitment?

[Efthreeoh]

Originally Posted by 213e90n51

Ahh why yes Mr F3OH! Did you ever try to have a meatier tire fitment?

No. I've always gone with a lower profile.

[John 070]

Imagine in HS we or at least I couldn't envision how calculus and integration could possibly be of any use

[Efthreeoh]

Originally Posted by 213e90n51

I see so in the end the oem BMW specs are best for the suspension of the car right? I mean their the ones that have the engineers that designed this wheel and size. I always wondered why the rear had to be 35 sidewall instead of 40 like the front? What tire sizes you run on your 400k miles e90 325i?

I now run the stock tire size on my E90. I have the sport package, which comes with a staggered 17" wheel package. Those sizes are F: 225/40-17 and R: 255/35-17. That equates to a total tire nominal diameter of 24.06. From 23,000 miles to around 336,000 (going from memory) I ran a square setup (i.e. not staggered) with 18" wheels. The closest tire to stay near 24.06 inches in diameter is a 235/35-18 tire, which is what I ran on the car.

No one can really answer your question because there are many different tires that you can fit on the car (excluding winter tires), all from summer high performance to All-Season, High performance All-Season, to Touring tires. So outside of changing the intended engineering design of the suspension/tire system by switching the sidewalk height, tire design also effects handling performance and ride feel.

[213e90n51]

Thanks what tires did you use in those times? And how did the e90 drive on a square setup?

[Efthreeoh]

Originally Posted by 213e90n51

Thanks what tires did you use in those times? And how did the e90 drive on a square setup?

I've posted about this question before. So I've had 14 sets of tires on the E90. Seven (7) of those sets were different brands or models of tires from the same manufacturers. All of the tire sets have been high-performance All-Season. None (9) of the 14 sets were on the square setup. The factory tires were Bridgestone REA 50 RFT on the 17" staggered wheels. The E90 with performance summer tires is a great handling car. It was quite an experience driving when new with the Bridgestones.

But the Bridges' were spent at 24,000 and I started my super long commute about the same time so I switched to the 18" square setup and high-perf. all-seasons. I was looking for a balance of tread life vs. handling.

In summary, high-perf. All-Seasons are an excellent choice to get a balance of handling vs. tread life. They are a bit less grippy than summer tires, but one sacrifices tread life with them (nothing new there...). But High-perf. all-seasons provide more performance than you can use on the street and stay out of jail. Between all the different sets I've had, all are extremely close in performance and wear. IMO it really doesn't matter much what tire you pick because there is no marked difference between them.

[213e90n51]

Originally Posted by Efthreeoh

I've posted about this question before. So I've had 14 sets of tires on the E90. Seven (7) of those sets were different brands or models of tires from the same manufacturers. All of the tire sets have been high-performance All-Season. None (9) of the 14 sets were on the square setup. The factory tires were Bridgestone REA 50 RFT on the 17" staggered wheels. The E90 with performance summer tires is a great handling car. It was quite an experience driving when new with the Bridgestones.

But the Bridges' were spent at 24,000 and I started my super long commute about the same time so I switched to the 18" square setup and high-perf. all-seasons. I was looking for a balance of tread life vs. handling.

In summary, high-perf. All-Seasons are an excellent choice to get a balance of handling vs. tread life. They are a bit less grippy than summer tires, but one sacrifices tread life with them (nothing new there...). But High-perf. all-seasons provide more performance than you can use on the street and stay out of jail. Between all the different sets I've had, all are extremely close in performance and wear. IMO it really doesn't matter much what tire you pick because there is no marked difference between them.

Ahh why yes! I have performance all seasons and the 500 treadwear really helps but more importantly it grips similar and gives me better feedback than my 320 treardwear summer tires.