Also keep in mind 5mm is 3/16"

 

That's why I need to find out if they'll provide enough clearance before purchasing them.. I know that you mentioned earlier that it doesn't matter if the size is 17, 18, 19 or 20.. As it's the offset that matters, however what I don't quite understand is why Ford would recommend +45 offset for their SVT 18x9.5 wheel but recommend the +40 offset for the 20x9.5 Shelby Venice wheel, unless the difference in backspace is also the reason

 

The +45 offset will move the wheel / tire 5 mm inward in the wheel well, compared to the +40 offset. 5 mm is about 1/5 of an inch or 3/16 like he said above.

That could create a clearance issue on the strut and/or strut mounting bolt and/or swaybar end link bolt on the front, if you are going with the extreme widest tire which is about 275 or 285 on a 9.5" wheel. I tried my GT500 wheels with the original 285 tires on the front once just for grins, and there was less than a finger width clearance. So it will be pretty close.

The difference between the 19 and 20" wheel could be because the strut slopes inward as it goes up, so you can move a larger wheel inward a little. But usually you use lower profile tires on a 20" wheel so the overall tire diameter comes out the same . . . . so I am not sure.

Since Steeda designed those wheels for a Mustaing, I think they will be OK . . . but I would talk to Steeda about it before I bought them.

 

I spoke with Rodney over at Steeda and he assured me the Spyders will fit despite the +45 offset.. And as you said Bert, they should be OK as Steeda designed those wheels exclusively for the Mustang..

In addition, I also spoke with Mike from Roush Performance about their 20x9.5 wheel package for the 2005-14 Mustang and found out they have the same +45 offset as the Steeda Spyder wheels, however he did mention that Roush also recommends purchasing their Mustang steering rack stop and clamp kit when using Roush 20" wheels.. But for just $12.00, it's a very small price to pay for preventing clearance issues lol.

I was also able to find out from BMC customs, that Saleen also has a 20x9.5 wheel for the 2011-14 S302 models that has an offset of +35 which would provide the ideal spacing for front wheel clearance, but for $437.50 per wheel, is a bit too rich for my blood lol.

I agree when you tried your GT500 wheels with the original 285 tires in the front, that you'd be cutting it really close as far as clearance is concerned..

IMO I wouldn't recommend using anything wider than a 275-35-20 tire on a 20x9.5 wheel in the front or a 275-40-18 tire on a 18x9.5 wheel..

Anyhow I don't think I'll have any issues with the Steeda Spyders along with the Mustang steering rack stop kit from Roush..

In the meantime, here's the link for the Roush steering rack stop & clamp kit if your interested

http://www.roushperformance.com/part...005-2010.html#




-Rocky