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renfield90 · 03-05-2015, 06:53 PM

http://www.advanced-ev.com/Calculators/TireSize/

For the purposes of 2nd gear in a Twin, use 9.307 for the differential ratio. You can verify this by entering redline (7500 RPM), top speed in 2nd (59), and OEM tire diameter (24.6").

At 30mph, the 245/40 is at 3798 RPM and the 235/40 is at 3845 RPM. That is a difference of just 47 RPM. Ever had your tach jump a couple hundred RPM just cause you go over a bump or expansion joint? 47 RPM is a rounding error.

We are not talking tenths here, and maybe not even talking hundredths. An extra 1-2mph apex speed from putting more meat to the ground is a much bigger difference than this, assuming you can deal with the compromised sidewalls.

03-05-2015, 06:53 PM	#2317
renfield90 The Stig's German cousin Join Date: Mar 2013 Drives: 2013 FR-S Location: Tempe, AZ Posts: 1,071 Thanks: 140 Thanked 519 Times in 345 Posts Mentioned: 8 Post(s) Tagged: 2 Thread(s)	http://www.advanced-ev.com/Calculators/TireSize/ For the purposes of 2nd gear in a Twin, use 9.307 for the differential ratio. You can verify this by entering redline (7500 RPM), top speed in 2nd (59), and OEM tire diameter (24.6"). At 30mph, the 245/40 is at 3798 RPM and the 235/40 is at 3845 RPM. That is a difference of just 47 RPM. Ever had your tach jump a couple hundred RPM just cause you go over a bump or expansion joint? 47 RPM is a rounding error. We are not talking tenths here, and maybe not even talking hundredths. An extra 1-2mph apex speed from putting more meat to the ground is a much bigger difference than this, assuming you can deal with the compromised sidewalls.