3.31 with autox

[ScottyP3821]

Hopefully someone will chime in. If i have a 3.31 in my ecoboost and I have base 235/55/17 wheels buy upgrading to a 285/35/18 should bring my gear ratio up to 3.44? Basically what I am after is to be able to have a slightly shorter gear without it being 3.55 short. The goal is to be able to stay spooled up but in the midrange at the autox course. The turbo makes good power between 3k-5k. So if I could keep it in 2nd gear through out the whole course and be in the powerband that would be great. the 3.31 is great but I just want to bump up the rpm slightly more but not 3.55 more. If I put a 3.55 in I would have to run taller wheels/tires to bring it down. IDK someone please chime in that know this stuff.

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[Grimace427]

235/55/17 = 27.2" diameter
285/35/18 = 25.9" diameter 4.8% shorter
http://www.rimsntires.com/specspro.jsp


3.31 + 4.8% is about 3.46 but my math could be off. Basically going to the shorter tire will definitely increase the effective gear ratio.

 

[ScottyP3821]

Thanks Grimace

 

[Grintch]

I think the 3.31 gear is close to optimum for autocross. I wish they could be had with the PP. But 27"-ish tires are hard to find with under a 20" wheel.

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