9 replies to this topic

[NMAv]

From what I've read on this forum and others, it seems that optimally, an 18" wheel is better suited for the GT 500 if you are doing either road racing or DR (DR could even go smaller subject to brake clearance).  So why does Ford SVT put 20"'s on the rear?   In researching all this and trying to get the best hook for my ride it seems that a smaller wheel running a tire with the same overall height will work better - ie, low profile, while neat, inhibits traction.  Is this an accurate statement?

[TrakRat]

Smaller sidewall sharpens response.  18's would be a great choice for an extra set of track rims.  On the street rarely are you cornering at 10/10ths.

I personally want to install a set of rear 20's in the front.  I think 285 width trumps the short sidewall factor.

[Madlock]

It's not quite so simple as an optimal wheel size - or even tire diameter, as everything from the rear springs to the relative front end height, which is based upon both the springs and the wheels and tires being used there, is interdependent.

I suspect Ford found raising the rear stance by 1/2" made a big difference in handling  - provided the springs didn't have to account for all the height.  Note that Ford accomplished this through the wheel, not the tire, as the performance 19" wheels use 285/35's too.  The 3.73 then became a combination of giving back what the taller tire took away and marketing hype for those who never bothered to do the math.

[ilmor]

20's are for show (if you like the big wheels); 18'sare for go.  Take a look at the road race Mustangs, for example, in the Continental Tire Series...small wheels and very low profile tires.  The Mustang Challenge cars ran on 18's.  Shelby also put the KR on 18's for this reason.

[Madlock]

ilmor, on 21 July 2011 - 01:46 AM, said:

20's are for show (if you like the big wheels); 18'sare for go.  Take a look at the road race Mustangs, for example, in the Continental Tire Series...small wheels and very low profile tires.  The Mustang Challenge cars ran on 18's.  Shelby also put the KR on 18's for this reason.

Well, yes... and no.

The older FR500 series has 18" wheels, as does the BOSS 302R.  However, the big bad ass of them all, the 302R, which specifically favors road course rather than cross-discipline or circuit racing, uses 19" wheels and lower profile tires.  Of course, all bets are off with the various Cobra Jets.  The 20" rears may indeed be "for show", but not entirely.  Why would Ford go through the hassle - only to further impose it upon customers?  20" rear wheels with equivalent tire profiles allow for increased rake without resorting to taller and/or softer springs - which most definitely improves launches for the supercharged 5.4L's massive amounts of torque, particularly with the accompanying 3.73 gearing.  Note, they kept 19's up-front.

18's may be better suited for both smaller and quicker diameters - and more manageable for long sets of laps.  But when it comes to changing direction,  filling the circle with more metal rather than rubber is invariably going to improve handling - even if only on the rear.

[SteelTownStang]

Looks...  

[Madlock]

TrakRat, on 10 June 2011 - 01:30 PM, said:

I personally want to install a set of rear 20's in the front.  I think 285 width trumps the short sidewall factor.

Unfortunately, the OE 20's won't clear the calipers without either spacers or some fancy milling.

Edited by Madlock, 21 July 2011 - 06:09 PM.

[TrakRat]

Madlock, on 21 July 2011 - 06:09 PM, said:

Unfortunately, the OE 20's won't clear the calipers without either spacers or some fancy milling.

Way ahead of ya. Already test fit them and know that I need spacers and longer studs, which I'm fine with.

[Don Breech]

Use 18" wheels for performance.  Put 20's all around for daily use and looks.  The KR looks really fine with 20" rims all around (like the SuperSnakes), but if you want to blow and go--for example, road course racing--them put the 18's on and get a good road course tire.

[SGT/SC#0471]

19's work for me.