Autobahn Shelby

SVT PP vs non-PP: gear ratio misnomer

Hello everyone. A quick check around the forums as well as the rest of the internet, and you’ll find it to be a common misnomer that the SVT Performance Pack equipped 2011 and 2012 Shelby GT500’s have an advantage in acceleration due to the shorter 3.73:1 rear gear ratio versus the non-SVTPP’s rear gear ratio of 3.55:1.

I say there's effectively no difference.

The difference between the two ratios is about 5%. What what is frequently overlooked, is the fact that the SVTPP’s tire size (285/35-20) is exactly one inch (or 3.9%) taller than the non-SVTPP’s 285/35-19’s. The taller tire effectively cancels out most of the benefits of the shorter 3.73:1 gears. In the end, the torque multiplication benefit (combining tire diameter and gear ratio) of the SVTPP is a miniscule 1% „better“ than the regular Shelby. That’s effectively like going from 3.55:1 to 3.59:1 (if there were such a ratio). Which is peanuts.


Sorry if I’ve just pointed out the obvious to some of you, but take a look around, and it’s interesting to see just how many people are under this (wrong) impression.


(Discounting the fact that acceleration on stock tires would probably be worse with 3.73:1 vs 3.55:1 gears, due to traction issues, all else being equal. But that’s a different topic altogether.)

2cokeman

How about the stock tire size on the 08 with the 3.31 gears compare to the 3.55 on the 2010+?

Autobahn Shelby

The 2008's 285/40-18 tire is actually about 0.5% taller than the 285/35-19 on the 2010's. Multiply that with the 7.3% taller gearing, and you end up with a combination that is 7.8% taller on the 2008 vs the 2010. Effectively the 2008 is like running a 3.29:1 gear vs. the 2010's 3.55:1.

That's all else being equal. Because I've been completely ignoring transmission gear ratios. I'm assuming they'Re the same 2007-2012.

cheftjpeck

Awesome info.. On your last point... In fact I have read that the gearing ratio is different in the 11 and 12's I believe... I know they did something with 1, 2 and 3 if I'm not mistaken ... Something about doing it so shifting was smoother or something like that.. I will try and find the exact details and post

Autobahn Shelby

Hey, cool. I know the 2013's gear ratios have been redone.


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Autobahn Shelby

Looks like 1st through 4th gear ratios stayed the same from 2007-2012. But they changed 5th and 6th for the 2010-2012 models.

http://media.ford.com/images/10031/2011_GT500_Specs.pdf

http://www.muscularmustangs.com/2006...helbygt500.php

2cokeman

Thanks.

IA Shelby

I have a 2011 non svtpp with 3.55. Changed to 3.73 gears. Personally wished I would have kept the 3.55.

Autobahn Shelby

If you're running the stock 19 inch tire size, then your overall gearing will be about 4% shorter than the SVTPP setup with 20 inch wheels and 3.73's. That's a whole lot of torque multiplication! Time for some drag radials

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