Rear end gearing calculations

[DRM500RUBYZR-1]

Did somebody say 4.10?

Bolt in and GO!

http://www.zr1.net/forum/showthread.php?t=30195

Marty

[JSad]

Paul, fantastic input and I would agree that it depends on what someone wants that determines the upgrade. I am in the Tulsa area and do some Oklahoma back roads, Arkansas "twisties" and in town driving...and I really enjoy rowing the gears.

Right now the syncro is grinding on a hard shift between 1st and 2nd so that gets fixed first. Then after enjoying the 3:45s for a bit, with the way I drive, the 4:10s are next. I am attempting to keep the budget at $2000+/- every 6 months or so.

From what little I could find, I would agree the 4:30s would be more than I want.

Marty - when I am ready I will check and see if you still have the "bolt and go" 4.10s

[Mystic ZR-1]

From Marc’s chart, with 3:45s, we’d be going
338 mph in 6th at 7500 rpm!!! 🤪
Probably be a little slower when the rev limiter kicks in?
What? Your ZR-1 won’t pull 7500 in 6th?

[JSad]

Well, I hit 300 mph the other day and it scared me almost to death. I am actually getting the 410s to keep the top end under 300...😀

[BigJohn]

Well, here I am complaining about my hood pushing up above 190!

[kluketic]

Doing the Math: Tire Size (mm) /25.4 (mm)/in X (aspect ratio x2) + Rim Dia = Tire height

So: 315/25.4 X (.35X2) + 17 = 25.68 in for tire height for a 315x35x17 tire.

Tire Air pressure could factor when measuring as you did as well as being installed with the car sitting on the tires.

Just sayin'

[JSad]

Good point on using better numbers, but using the 25.68 in place of the 25.25 in my calcs doesn't get to the 3:45 ratio we came up with jacking the car up marking and spinning the tire/drive shaft per Hib's suggestion.
So good news and bad news I guess...bad news is I need to buy 4:10s, good news is I get to buy 4:10s and improve the car even more.

[Paul Workman]

Originally Posted by kluketic

Doing the Math: Tire Size (mm) /25.4 (mm)/in X (aspect ratio x2) + Rim Dia = Tire height

So: 315/25.4 X (.35X2) + 17 = 25.68 in for tire height for a 315x35x17 tire.

Tire Air pressure could factor when measuring as you did as well as being installed with the car sitting on the tires.

Just sayin'

Because air pressure affects the actual radius of the tire, a more accurate way to calculate speed is measure the actual distance traveled for one tire revolution (rear tire inflated with the proper pressure) and use that actual distance in the calculation.

[kluketic]

Certainly circumference (one tire revolution) is the key here [(Pi) X Diameter] => 3.14.16X25.68 in. = 80.68 in., this is probably relatively insensitve to inflation (within limits).

[Paul Workman]

Originally Posted by kluketic

Certainly circumference (one tire revolution) is the key here [(Pi) X Diameter] => 3.14.16X25.68 in. = 80.68 in., this is probably relatively insensitve to inflation (within limits).

Yeah, you would think....