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AZBMW Forums › Model Specific Discussion › Other BMW Models › How much tire rub is acceptable?
How much tire rub is acceptable?
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wkohler
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PostPosted: Wed Aug 03, 2011 7:00 pm
Post subject: Re: How much tire rub is acceptable?

azroadie wrote:
wkohler wrote:
Wheel diameter has nothing to do with it. You increased the width and lowered the offset. That's your problem. No wheels/tires are worth modifying the car for, in my opinion.

I just noticed that too as the 18s are almost exactly the same size (but less sidewall on the tire). But here's the thing...the 18s are a standard option (same width as the 19s). So maybe the rubbing is a sign of some other suspension issue?

You don't seem to be understanding this. The diagrams you posted contain the answer, but I'll explain further.

Your wheels were 17x8 ET47 front and rear with 225/40/17s. Let's talk about the front first.

What you did here was go to a 19x8.5 ET35 wheel. So, before we even get into the tires, you now have a wider wheel that has a lower offset than the wheel it replaced. Offset is measured from the center of the wheel. Positive offsets (such as yours) place the mounting pad towards the outside of the wheel relative to the center and negative offsets towards the inside of the wheel. ET0 is a mounting pad in the dead center of the wheel. So, if you had gone with a 19x8 ET35 wheel, your wheel will sit 12mm further outboard than the wheel it replaced. Once you add width, the calculation changes. With no tire mounted on your wheel, the 19x8.5 will sit 18mm further outboard than the 17" wheel it replaced.

For the rear, you went from a 17x8 ET47 to a 19x9.5 ET43. This puts the wheel (no tire) 23mm further outboard compared to the previous setup.

That's all well and good and I don't know the specifics surrounding your car, but where I can definitely figure you went wrong is the tires. They're way too big. Going from a 225/40/17 to a 255/30/19 in the rear results in an overall diameter increase of 1" (25.4mm). You also increased the width of the tire at least 1.5" depending upon the brand of tires you went from and what you went to (some run narrower and some run wider). Your speedo will also be very optimistic.

In the front, you're at a nearly 1.5" increase in diameter going from a 225/40/17 to a 235/35/19. You have also increased the width (all while moving the wheel closer to the fender).

The general rule of thumb when it comes to maintaining the overall diameter is that for every inch of diameter increase, you subtract 5% from your sidewall height. Had you stayed with a 225 going to the 19s, you would run a 225/30/19 to keep roughly the same diameter as the 17s (it will never be 100% perfect, but a percentage point here and there never killed someone. Since the sidewall height is a percentage of the width, when you increase the width of the tire, the sidewall height increases as it's height is say 30% of the section width.

All the info is in the graphics you posted. You just need to know what it means. It sounds as though your rubbing isn't too bad, so if you went with tires that both fit the wheels and the car, you should be fine. All of my calculations are theoretical, so I don't know if the correct size tire actually exists.

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wkohler
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PostPosted: Wed Aug 03, 2011 7:02 pm
Post subject: Re: How much tire rub is acceptable?

Stevohill wrote:


Fender rolling simple "rolls" the fender edge flush or smooth with the body and gives you more clearance.

And gives a nice trap for debris and other shit so your fenders rust out. That's all cool and shit, though, bro, yo. Rolling Eyes

Sounds to me like the OP wants to know WHY his new tire/wheel setup has interference with the body. I explained it, so instead of going "who gives a fuck, roll your fenders," why not let him look at the reason he's got the problem and determine how he wants to fix it. It's not your car. I don't care if he rolls the fenders or not. Not my car. I simply stated my opinion and if you don't like it, tough shit.

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azroadie
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PostPosted: Wed Aug 03, 2011 7:54 pm
Post subject: Re: How much tire rub is acceptable?

wkohler...Thanks for the explanation. It makes complete sense. But I was hoping to avoid thinking too much about this as I had expected to simply buy the proper fitment and not worry about it.

So that's what's confusing me...no matter where I look, this setup should work with no rub. I'm 60k miles right now with the original sport suspension. I'm hoping this rubbing isn't going to make me start a new thread entitled "best suspension options." Sad
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tron
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PostPosted: Wed Aug 03, 2011 8:04 pm
Post subject: Re: How much tire rub is acceptable?

BK544E34 wrote:
bastarde38 wrote:
where can one buy a fender roller?
A lot of places!

Or you can do it like a man

www.youtube.com/watch?...re=related

Only did my front fenders (witch look horrendous for anyone that has seen my car in person). like this with a jack handle cause I didn't have a fender roller available when I did my front suspension. =\

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Petrucci
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PostPosted: Wed Aug 03, 2011 8:32 pm
Post subject: Re: How much tire rub is acceptable?

Rubbing lol what's that?

Herrafrush checking in. Come at me.

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azroadie
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PostPosted: Wed Aug 03, 2011 9:16 pm
Post subject: Re: How much tire rub is acceptable?

Guess everyone will want to see how it looks before determining if it's worth it...Before and after pics...
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azroadie
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PostPosted: Wed Aug 03, 2011 9:38 pm
Post subject: Re: How much tire rub is acceptable?

[quote="wkohler"][quote="azroadie"]
wkohler wrote:
...In the front, you're at a nearly 1.5" increase in diameter going from a 225/40/17 to a 235/35/19. You have also increased the width (all while moving the wheel closer to the fender).

The general rule of thumb when it comes to maintaining the overall diameter is that for every inch of diameter increase, you subtract 5% from your sidewall height. Had you stayed with a 225 going to the 19s, you would run a 225/30/19 to keep roughly the same diameter ...

I think you're my savior in this section!! For some reason they thought I wanted 235/35-19s. They never checked to see better options. So I'm getting 225/35-19s tomorrow for the front. That should be a much better fitment! If that saves me, I owe you a beer tomorrow night!
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bullfrog
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PostPosted: Wed Aug 03, 2011 10:02 pm
Post subject: Re: How much tire rub is acceptable?

Please don't roll it yourself!!!! Take it in to a good body shop and have them do it. You have a nice Z, don't chance it by screwing up your fenders.

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MATTY_T
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PostPosted: Wed Aug 03, 2011 10:27 pm
Post subject: Re: How much tire rub is acceptable?

Nice choice on the wheels man

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Stevohill
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PostPosted: Wed Aug 03, 2011 10:50 pm
Post subject: Re: How much tire rub is acceptable?

Petrucci wrote:
Rubbing lol what's that?

Herrafrush checking in. Come at me Bro...

Chris...



I know your stance(no pun intended) on any sort of stance related issue/modification. To each his own, I just like giving you shit and I know you love giving it back.

Cool

Btw...wheels look sick. Good choice.

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wkohler
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PostPosted: Thu Aug 04, 2011 12:05 am
Post subject: Re: How much tire rub is acceptable?

[quote="azroadie"][quote="wkohler"]
azroadie wrote:
wkohler wrote:
...In the front, you're at a nearly 1.5" increase in diameter going from a 225/40/17 to a 235/35/19. You have also increased the width (all while moving the wheel closer to the fender).

The general rule of thumb when it comes to maintaining the overall diameter is that for every inch of diameter increase, you subtract 5% from your sidewall height. Had you stayed with a 225 going to the 19s, you would run a 225/30/19 to keep roughly the same diameter ...

I think you're my savior in this section!! For some reason they thought I wanted 235/35-19s. They never checked to see better options. So I'm getting 225/35-19s tomorrow for the front. That should be a much better fitment! If that saves me, I owe you a beer tomorrow night!

You need to have tires installed that have the same overall diameter as the ones originally on the car. Front and rear. Before you sign on the dotted line, make sure the tires are as close as possible to that number. No use throwing money away at a guess. Wink

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7/75 E12 530i | 7/80 E12 M535i | 2/85 E28 Alpina B7 Turbo | 3/85 E28 528i | 2/87 E28 M535i | 8/94 E34 525iT
10/80 E12 M535i | 12/82 E28 533i | 4/83 E28 533i | 3/85 E23 745i | 6/85 E28 M535i | 7/86 E28 535is | 5/94 E34 525iT
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