Can a change in offset cause rubbing (tire question)

Discussion in 'After Hours Lounge (Off Topic)' started by Jay H, May 5, 2003.

  1. Jay H

    Jay H Producer

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    Here's the story..

    '97 BMW 328i w/ Sports package which at the time meant 16" wheels.. OEM Bridgstone Turanzas (225/50 16")

    A few years ago I replaced the rims with a set of Borbet Type T because I mounted snow tires on the original alloy rims. So I had Borbets with the Bridgestones. The borbet seems to have a higher offset I believe when I was looking at the tire. But as I bought them from the Tirerack.com, it was supposedly compatible.

    Fast Forward a few years. The bridgestones were almost bald, replaced the set with a set of Dunlop SP8000s SAME size, 225/50 16". Now I am getting alot of rubbing in the back. I'm wondering if this could be a combination of the different tire, perhaps the Dunlop has a wider tread even though they're both 225s or could it have something to do with the offset??????

    The Dunlops seem to be soft, or softer than the Bridgestones and I've tried to inflate the tire a bit higher than the recommended doorjam pressure (while still under the max PSI of the tire of course)... Helps a bit but still lots of rubbing in the back if I have a moderate sized person in the back seat. I am OK when by myself and only rubs when the car goes through dips.

    If it's not the offset or the tire tread, I'm wondering if my springs should be replaced... it's at 47k miles.

    Jay
     
  2. Cam S

    Cam S Screenwriter

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    Rims with the incorrect offset will rub with either the fender lip or the inside of the fender well. This usually only occurs when the suspension is pushed to it's limits, such as corner, or hitting a bump. It's very important to get a rim with the same offset as the original rim, or at least keep it within a few mm's.
     
  3. Sean Conklin

    Sean Conklin Screenwriter

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    Right Cam, you are now noticing it probably because the sidewall is giving a little more that your old tires, or just the fact that there is more rubber on the new tires.

    I would measure the offset and see how close you are.
     
  4. Jay H

    Jay H Producer

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    I can probably dig it up in from Borbet and from BMW, but I don't recall how much other than I do remember it being a little more positive when I got the wheels.

    I guess I'll have to look at new rims somewhere down the line. I'm quite positive that the rims come up as compatible when I bought them from tirerack a few years ago. [​IMG] [​IMG]

    Jay:
     
  5. Andrej Dolenc

    Andrej Dolenc Stunt Coordinator

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    OK, different tires, non stock rims, and they rub. Could be a couple of things.

    First off, not all 225/50/16 tires are the same. The width of the tire will be different from manufacturer to manfacturer. That could certainly be part of it.

    Different offset could be the culprit as well. There is some flexibility there for different offset tires, but not a whole lot. On my 97 M3, the stock rear offset is 41mm, the current rims I have have an offset of 37.5mm and they fit fine without rubbing. But it's awfully close. With a tire that's known to be really wide (Bridgestone Potenza S-03's are known to be wide), I'd likely get some rubbing.

    Last possibility I can think of would be that the plastic wheel well liners are breaking. There's a few screws that hold those to the body, and if the plastic there starts breaking, the liner will pull away from the body and you'll get some rubbing. I had that with one of my front tires. Should be pretty easy to identify if they are breaking on you (and they're not that expensive to replace).

    Of the 3, I'd look at the offset 1st, then at the tire width itself.

    At 47k, no worries about your springs wearing out. Shocks maybe, but springs should last a really long time.


    Andrej
     
  6. Jay H

    Jay H Producer

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    Thanks folks, I am now 90% it's the offset, the plastic inserts are still OK, but between my snow tires which are on the original rims that I bought the car with, the tires are slightly closer to the car. The snow tires I have are basically the same width but the profile is a 55 not a 50 so it has a slightly greater diameter. I have noticed that the Dunlops do sit out a little further from the car causing the back tires to rub the wheel well at the top. If I buy rims with slightly more offset, that brings the tire away from the rim, correct? I've seen the description at Tirerack.com and a few other websites.

    Jay
     
  7. Seth_L

    Seth_L Screenwriter

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    Jay,

    Negative. Offset does not relate to how far the tire is from the rim. Offset is how far the mounting surface of the center hub is from the centerline of the rim.

    So, say you have a 16x6 rim. The rim is 6" wide. If it had 0 offset the back of the mounting surface would be 3" from the back of the rim, or dead on the centerline. A 16x6 rim with 25.4mm (1") of offset would have a mounting surface that is 4" from the back of the rim. Positive offset moves the mounting surface further away from the car. Negative moves it closer.

    Seth
     
  8. Andrej Dolenc

    Andrej Dolenc Stunt Coordinator

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    Yay, I have a computer at work again. With that, I can now get to HTF and post again.

    If you're getting just a little bit of rubbing on the outside of the rear tire, you can 'fix' this. If you feel where it's rubbing, the lip of the fender liner angles towards the tire a little. You can do what's called rolling your fenders. Basically bend that inner lip to give you more clearance for the rim. Tire rack has a machine that will do that fairly easily, here's a site that has some pix that explains what I'm talking about: http://www.bmw-m.net/Gallery/haweka.htm
    Others have accomplished this by wedging a baseball bat between the tire and the fender liner, then roll the bat. The one thing you gotta be careful of is to heat the area up with a heat gun or hair dryer so the paint won't crack on you.

    That'll get you a little more clearance, possibly that little bit extra that will prevent rubbing and obviate the need for new rims.

    Andrej
     
  9. Jay H

    Jay H Producer

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    Yeah, I've thought of that, but I don't think I trust myself not to mess that up... Shoot, I manage to make simple stuff into projects... I did tell you about the whole weekend spent drilling out the fixing bolt on my driver side front brake rotor. [​IMG] !!

    I was going to ask some bodyshops but wondering how much it would be... any idea? I would only do the back tires, the front ones are fine.

    Jay
     
  10. Andrej Dolenc

    Andrej Dolenc Stunt Coordinator

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    Shouldn't be much. You may want to get a hold of the local BMW car club chapter up there, see what shops they recommend that deal with racers. Likely they will have done it before.

    Andrej
     

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