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tire size issues


reegs01

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i have a 71 240z lowered about a inch and i have on it now 245/60/14 all around the front tires rub . i need to put a different set of tires on the front that wont rub and give me maximum height because i have clearence issues with my exhaust .will 205/75/14 or 195/75/14 work

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The 245/60-14 size you now have is already two sizes taller than stock, and much wider. The normal 60 series equivalent to the stock 175SR14 is/was 225/60-14 on a 7" wheel.

What tire size you should now consider depends on where and when the tire rubs. If it rubs when turning, you might get away with a narrower tire. In this case try a 215/70-14 which should be close to the same height as you have now.

If it rubs when you hit a bump while driving straight, then the tire is already too tall. In that case, you're hosed. Either raise the car back up, or change the exhaust.

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Be careful of major shifts in tire sizes though.

If you get them too wide, you may find that the front end rolls around ok....until you go for a hard curve while going downhill, and then the tire contacts the lower front valance. This occurs from the flexing of the tire. More often than not, however, the problem is when you are backing up OUT of your slightly inclined driveway and the tire now grabs the valance and folds it.

This is a common problem due to the curve of the valance AND it's proximity to the tire. I've seen guys with as little as 1/4" of clearance while stopped...you do the math. There are things you can do to reduce this, all of them involve playing with the alignment of the fenders to the hood, sugarscoops, bumper etc, but that would take hours to explain out properly.

In the meantime, I found this formula for determining actual tire dimensions at www.tirerack.com (don't know whom to credit) :

Width x Aspect Ratio = Section Height

Section Height x 2 = Combined Section Height

Combined Section Height + Wheel Diameter = Tire Diameter

The example they give: 185/60R 14 85H or 185/60HR14

185mm x .60 = 111mm

111mm x 2.0 = 222mm

222mm + 355.6mm(14") = 577.6mm or 22.74"

Now, with a little bit of playing you can sit in your driveway and find out what your max tire size is, or at least get a good idea.

I went to the tirerack and punched in a 71 with the example rating, and here are their 30 picks for tires.

http://www.tirerack.com/tires/Compare1.jsp?width=185%2F&ratio=60&diameter=14&vehicleSearch=true&startIndex=0&search=true&pagelen=20&pagenum=1&pagemark=1&speed_rating=SR&speed_rating=TR&speed_rating=UR&speed_rating=HR&speed_rating=VR&speed_rating=ZR&speed_rating=WR&speed_rating=YR&RunFlat=All&x=75&y=7

FWIW

E

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  • 1 month later...
here is a link to a good tire calculator

http://gs.tolan-hoechst.com/tirecalc.htm

We are trying to determine what size tires to install on our stock 71 240 with 14" wheels.

Toni, since I have seen your car (and it's wheels) in person, and also because I have almost 25 years of tire selling experience behind me (prior career), I can probably help. What is it that you want in new tires? Stock height? How wide?
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