Wheel and Tire Data Base.

[Bad Wolf racing]

Definitely the slight lowering, I ran 225's for years before. I'll check out tiresize.com; wasn't aware of that site. A friend of mine is running 315/30R18s on his Camaro that is heavily modified. I may run that size through the calculator. I'll be running some massive HP so I need as much stick as I can get. Rear I'm not too worried about, our Monte's almost have a mini tub back there from the factory LOL.

[Bad Wolf racing]

Thanks for the help. tiresize.com was great! It does look like by going to a 315/30R18 I will shorten the tire enough to run it without issue once I measure my inside radius and figure out exactly what offset I need. 

 

BTW, Keeping the stock rally wheels for show / cruising.

[Darrell 2 Rs and 2 Ls]

I am also looking to remove the stock 215/70/R15 and go to 4 identical rally wheel combos on all 4 corners.  Everything is stock.  It appears running a 255/60/R15 on 15X7 with a 4.5" BS will work for front and rear with no mods. Does that sound correct? 

[MCfan]

Darrell, 

Yes, that combo will work both front and rear.  That is the exact combo I run on the front of my '70, although I did insert a 1" spacer in my front coils to eliminate minor tire rubbing on tight, compressed turns (i.e. backing out of a driveway with a dip at the street).

A 15x7 with 4.5" backspace has a +12 mm offset which is only slightly more than the stock Monte rally rim at +8 mm. However, the 255/60 is a full 1.5" wider (same height) than your 215/70 so you will lose .75" of clearance both inboard and outboard.

No worries on the rear. You should have just over an inch of outboard clearance with your wheel well lip and about the same clearance with the frame inboard. Your Monte will have about the same stance but with a lot more rubber on the ground!  Good luck.

[Darrell 2 Rs and 2 Ls]

Hey Dennis;

Thank you so much for the advice/help.

I see on another post to Brendan W you stated-

Brendan,

If your rims are actually 15x7 with a measured 4.25" backspace, they should work beautifully with 255/60s both front and rear.  Having a measured 4.25" backspace on a 7" wide rim gives and offset of +6 mm (versus a -6 mm offset with the same backspace on an 8" wide rim).  That means your wheel/tire combo will be moved .5" further inboard (compared to an 8" rim) which increases your rear wheel well lip clearance.  

 

Would the 4.25" BS be better than the 4.5" and eliminate the need for the 1" coil spacer?

[MCfan]

3 hours ago, Darrell 2 Rs and 2 Ls said:

Would the 4.25" BS be better than the 4.5" and eliminate the need for the 1" coil spacer?

Yes, Darrell, if I were to do my current wheel/tire selections again, I would choose the 15x7 with 4.25 backspace (instead of 4.5" backspace) for mounting my 255/60 tires on the front.  That would move the wheel/tire combo .25" further outboard and probably eliminate any tire contact with the frame, even on tight, compressed turns. 

At the time I did my original wheel/tire selections in 2010, I wasn't aware of any online tools like the Wheel Offset Calculator (if it even existed then).  After using that tool many times since, I now believe that offsets of +6mm for the front and +12mm for the rear are the very best specifications for centering any wheel/tire combo within the available wheel/tire space on a first gen Monte. My primary objective was to avoid risky clearances with the wheel well lips on the rear quarter panels and front fenders.

Note that it makes sense to specify different offsets for front and rear on new/custom wheels if you are using different width rims and tires on front and rear.  If you want to use the same size tire and rims on all four, you have to make a compromise which is exactly what the factory did when they offered 15x7 rally wheels with 4.30" backspace (+8mm offset) for use both in front and rear interchangeably.