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2Addicts | BMW 2-Series forum Technical Topics Wheels and Tires -- Sponsored by The Tire Rack 235/40 R18 on M240i OEM front wheels?

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      11-26-2019, 07:10 PM   #1
pkabra
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235/40 R18 on M240i OEM front wheels?

Just got a new set of Falken Azenis RT615K+ tires. Took them to local shop and just got them installed.

I'm running the stock staggered wheels on my M240i, which I believe are 18x7.5 on the front, and 18x8 on the rears.

I threw on 235/40R18 on the front (up from the 225 stock Michelin's), and 255/40R18s on the rear.

I was testing the fronts by turning the wheel lock to lock, to check for rubbing (I've got 12mm spacers on the fronts so no issues there). But I noticed that the sidewalls for the tires were flexing a lot where the tire made contact with the ground, as I turned the car full lock in either direction.

Was wondering if thats normal?

The fronts are at 37 psi so I didn't think it was a tire pressure issue, but now its got me worried that the rubber may tear off from the rim at speed. I also plan on tracking the car, so not sure if its safe to do so anymore with the flexing.

Any folks out there running 235s on the front OEM staggered rims?
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      11-26-2019, 07:25 PM   #2
dradernh
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Quote:
Originally Posted by pkabra View Post
I also plan on tracking the car
The rim width range for that tire is 8-9Ĺ", so your setup is not ideal.

My guess is that in terms of safety you'd be okay on the track. However, absolute performance will suffer as your tire's tread profile will be rounded as a result of the narrow wheel. If you had, say, a 9" wheel instead, the tread would then be much flatter, and you'd have noticeably more grip and stopping power.
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      11-26-2019, 07:59 PM   #3
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Quote:
Originally Posted by dradernh View Post
Quote:
Originally Posted by pkabra View Post
I also plan on tracking the car
The rim width range for that tire is 8-9½", so your setup is not ideal.

My guess is that in terms of safety you'd be okay on the track. However, absolute performance will suffer as your tire's tread profile will be rounded as a result of the narrow wheel. If you had, say, a 9" wheel instead, the tread would then be much flatter, and you'd have noticeably more grip and stopping power.
Michelin and Tire Rack both to,d me the max width on a 7.5" wheel is 225. I had to replace 245/35/18s from my stock OEMs because of the safety concerns. I drove them on the street for a month without issue but absolutely would not run at speed on the track. The bead could break loose.
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      11-27-2019, 03:01 AM   #4
pkabra
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Quote:
Originally Posted by dradernh View Post
My guess is that in terms of safety you'd be okay on the track. However, absolute performance will suffer as your tire's tread profile will be rounded as a result of the narrow wheel.
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Originally Posted by ralawren View Post
...but absolutely would not run at speed on the track. The bead could break loose.
Getting mixed feelings about it now. I guess if I'm really concerned, I should just step back down to 225s (already spent the money on these tires though! )

I am definitely more concerned about the safety aspect, then about the performance loss at the moment. I've spent the money on the tires, so kinda want to use them, but if its clearly going to be unsafe, and I risk a blowout, or worse, ripping the tire from the rim, then I should figure out downsizing.

Anyone else with experience tracking or autoxing with a 235 on the stock 7.5" rim?

Appreciate the responses so far!
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      12-04-2019, 11:24 AM   #5
jnu
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I know someone who autoxs a 245 on a 7.5Ē rim. Crazy IMO but he does it without issue. I run a 225 and am faster than him. I suspect 215 would be faster still due to the flatter tread profile.
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      12-07-2019, 12:34 PM   #6
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This concern is absolutely correct:
".... but now its got me worried that the rubber may tear off from the rim at speed. I also plan on tracking the car, so not sure if its safe to do so anymore with the flexing. "

You need to either go down to 225 or spring for new wheels (can't use the stock rear 8"ers in front, those have the wrong offset). It will roll about just fine, but with either a pothole or a hard turn you can unseat the bead and blow it out suddenly - if it is in a turn you dig in the rim and the car usually flips. Both of those sizes are off of factory spec, so if the tire place that sold them to you told you they'd fit it would be worth seeking a return for the proper sizes. And jnu (above) is correct - even narrower tire:wheel ratio will give sharper handling and less heat buildup if you actually track it (225 on 8", 245 on 8.5" is working very well for me).
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      12-08-2019, 12:57 PM   #7
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Bigger isn't always better, it seems. When I replaced the wheels / tires on mine I read up on wheel sizes. Seems that EVERYONE wants to put at least 19s maybe even 20s so there has to be some performance benefit, right? I was hesitant to go with 19s purely because there is a lot of road works going on and will be going on where I live and I'd already banged up the front wheels / tires on some knarly potholes. After doing some research and watching some videos, turns out that, at least from the tests I saw being done in videos, you actually LOOSE performance past 18s and other than brake clearance the only reason to go higher than 18 is purely aesthetic.

So I went with 225 front / 255 rear on 18" rims. I did get the 8.5" for the front so I could go with 235 if I wanted to, but it's RWD so as far as I know / read there is zero reason to need larger than 225 up front.

Doesn't make any sense to me to put 235s on a 7.5 rim when it's going to give you less contact / make the tire unsafe. I would think twice about tracking that setup.
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      12-12-2019, 11:58 AM   #8
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Quote:
Originally Posted by MarkDemma View Post
So I went with 225 front / 255 rear on 18" rims. I did get the 8.5" for the front so I could go with 235 if I wanted to, but it's RWD so as far as I know / read there is zero reason to need larger than 225 up front.
Front end grip?
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      12-12-2019, 12:25 PM   #9
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Quote:
Originally Posted by MassNerd View Post
Front end grip?
It's my understanding that you use a staggered setup in RWD cars because the rear tires actually need to be wider to put the power down and that you want a narrower tire up front to favor understeer. So guess it may be a bit of a tradeoff / down to individual preference.

Would love to see the Engineering Explained guy do some tests with different sizes and square / staggered.
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      12-20-2019, 11:44 AM   #10
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Quote:
Originally Posted by MarkDemma View Post
It's my understanding that you use a staggered setup in RWD cars because the rear tires actually need to be wider to put the power down and that you want a narrower tire up front to favor understeer. So guess it may be a bit of a tradeoff / down to individual preference.

Would love to see the Engineering Explained guy do some tests with different sizes and square / staggered.
Most of us are trying to dial *out* the understeer - thatís why we go with square setups and wider fronts.

If you donít track or autox then favoring understeer with narrow front tires is fine since I hope youíre not exploring the limits of your car on public roads.
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      12-20-2019, 05:51 PM   #11
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Quote:
Originally Posted by jnu View Post
Most of us are trying to dial *out* the understeer - thatís why we go with square setups and wider fronts.

If you donít track or autox then favoring understeer with narrow front tires is fine since I hope youíre not exploring the limits of your car on public roads.
Oh no, certainly not doing that.
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      01-23-2020, 06:11 AM   #12
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Bought my m235 CPO and they put 235 up front at the dealership, worked for me
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      01-13-2021, 04:13 PM   #13
pkabra
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Just a general update to close this thread out, I did end up tracking the car with 235s in the front, on pretty soft Falken Azenis tires.
It wasn't great. The frontend grip was all over the place, I'm pretty sure because the tires were rolling in higher speed corners. So I'd get grip, and then tons of understeer depending on how much I was pushing things.

Learning experience, I ended up buying some 8inch front rims and putting the tires on to those instead, and the grip is much more consistent.

Car is still pretty understeer-y on exit, but corner entry, and mid corner traction is much much better. However, I'd imagine it wouldn't be that bad either with 225s, just with the slicker tires I was running.

Lesson: 10mm here or there on size isn't going to matter for an amateur like me. You'll notice the "type" of tire a lot more, if you're running higher performance, softer rubber, than if you're running a slightly wider tire.

My recommendation: DO NOT run oversized tires in performance use cases. It's not going to extract the best out of the tires, or the car, and at worst, could lead to some damage.
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      01-13-2021, 05:05 PM   #14
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Quote:
Originally Posted by pkabra View Post
Lesson: 10mm here or there on size isn't going to matter for an amateur like me. You'll notice the "type" of tire a lot more, if you're running higher performance, softer rubber, than if you're running a slightly wider tire.

My recommendation: DO NOT run oversized tires in performance use cases. It's not going to extract the best out of the tires, or the car, and at worst, could lead to some damage.
Good to hear that you got it figured out.

Hoosier recommends tire tread widths within +/-1" of the wheel width. Placing a narrower tire on a wider wheel will generally work better on the track.

Fortunately for us, Tire Rack uses a procedure of their own creation to measure tread widths for most of the tires they sell: https://www.tirerack.com/tires/tiret...jsp?techid=201. As buyers, this gives us a chance to compare actual tread widths across brands and models before choosing a tire.
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