This may be just rambling, but has anyone used something like Tremec's gear ratio calculator (https://www.tremec.com/calculadora.php)? There's others online, but essentially you provide your diff/trans gear ratios, tire size, and RPM and it spits out the cars speed in each gear at that specific RPM. At the bottom is a separate calculator you can use to calculate your "Tire Height" based on rim/tire info. There's several of these calculators out there as I'm sure the math is simple, but it doesn't add up for my G35 unless it's user error. Reason I'm rambling about this is that I'm trying to select the final drive for a project car of mine.
My inputs are for my 05 G35 coupe manual/LSD/stock 19's/stock tire size as shown in the image.
Real world results: In 6th gear at 3k RPM I'm at 77-78mph (tires are properly inflated). That's around 7% different from these calculators that are saying I should be going 85mph. Am I missing something? Is everyone else driving a manual at 3k rpm at 77-78 mph?

 

3.538 afaik.

https://cdn.z1motorsports.com/upload...GearRatios.pdf

 

Keep in mind your tire height is a little different for real world application, since the weight of the vehicle does shorten up that distance as it flattens the tire onto the road.

3k sounds about right though for roughly 80mph though.

 

Maybe that's the missing variable, I guess it could be measured/averaged out. But it was throwing me for a loop

 

I verified yesterday in my coupe that 80mph is almost an exact 3k rpm. Stock size 19" rubber.

 

I'm at 2500 rpm at 70 mph in 6th. The 235/50/17 tires are the same height as the OEM 215/55/17 tires. And GPS (Garmin, Google and Waze) says my speedometer is dead on. Have to check where it is exactly at 3000 rpm.

 

Moderator EDIT: Banned for... honestly I don't even know what that was, TrustedBroker botting? But the link went to a bunch of different flag shapes?!?!?! I think their Evil Bot™ program is broken.