Stock size tire RPM through the traps
03-25-2007, 03:54 PM
#4
Senior Member
Join Date: Sep 2005
Posts: 213
Hi Pronto. According to Maxima.org, a 6th Gen’s (5spd auto) 3rd gear ratio is 1.982 to one and the final drive ratio is 2.440 to one. If your tire is 26.8 inches tall, it is therefore 2.233 feet tall. This establishes your diameter. We know that circumference equals diameter times pie, therefore the tire’s circumference is 2.233 feet time 3.1415, which equals 6.98 feet.
With this information we can calculate the rpms at 60 mph. To do this, divide 5280 feet by 6.98 feet, which equals 756.44. Now multiply 756.44 by 1.982 (3rd gear ratio) and by 2.440 (final gear ratio). This equals 3,658. This tells us the 5sp auto Maxima should crank 3,658 rpms at 60 mph.
If a stock auto 6th Gen travels 94 mph at the end of the quarter mile in 3rd gear, it will translate to 5,730 rpms (94 times 3,658 divided by 60 equals 5,730). 5,730 is your mathematical answer. That may not be the actual rpm, but it should be very close. (This is math. There is usually a fudge factor with real life numbers. Tire circumferences expand at higher speed and may throw off the actual number.) I own a 6-speed and cannot confirm anything. Perhaps an auto owner can confirm the math.
Pronto, if you want to test reality, put your car in 3rd, travel exactly 60 mph and check your rpm. Take that rpm and multiply it by 1.567 (94 mph divided by 60 mph). That will tell you the car’s rpm at 94 mph in third. If you think you’ll cross the traps at 95 mph, multiply your 3rd gear rpm by 1.583 (95 mph divided by 60). Good luck.
With this information we can calculate the rpms at 60 mph. To do this, divide 5280 feet by 6.98 feet, which equals 756.44. Now multiply 756.44 by 1.982 (3rd gear ratio) and by 2.440 (final gear ratio). This equals 3,658. This tells us the 5sp auto Maxima should crank 3,658 rpms at 60 mph.
If a stock auto 6th Gen travels 94 mph at the end of the quarter mile in 3rd gear, it will translate to 5,730 rpms (94 times 3,658 divided by 60 equals 5,730). 5,730 is your mathematical answer. That may not be the actual rpm, but it should be very close. (This is math. There is usually a fudge factor with real life numbers. Tire circumferences expand at higher speed and may throw off the actual number.) I own a 6-speed and cannot confirm anything. Perhaps an auto owner can confirm the math.
Pronto, if you want to test reality, put your car in 3rd, travel exactly 60 mph and check your rpm. Take that rpm and multiply it by 1.567 (94 mph divided by 60 mph). That will tell you the car’s rpm at 94 mph in third. If you think you’ll cross the traps at 95 mph, multiply your 3rd gear rpm by 1.583 (95 mph divided by 60). Good luck.
03-25-2007, 06:21 PM
#8
Senior Member
Thread Starter
Join Date: Nov 2004
Location: Nashua, NH
Posts: 344
Excellent. I've been looking at the BFG gForce 245/40/18s and they are 25.6 diameter so with those calculations the trap rpms should be about 6034. which is right over the stock peak hp at 5800. I wanted to figure out if I could stay in 3rd with that size tire and still be near 5800 or just past it.
03-26-2007, 02:10 AM
#12
Senior Member
Thread Starter
Join Date: Nov 2004
Location: Nashua, NH
Posts: 344
Originally Posted by NismoMax80
I recall hitting 4th gear just at the end of the 1/4 mile 
not quite dead... but yeah i'm trying to stop around more 
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