Final drive ratios released for US BRZ

[Panda Grahams]

Since this thread has been revived. Here's a relevant new video:

[ruturaj001]

Originally Posted by tiger1964

For those of us that likely won't at the track... What does that mean for highway rpm in 6th gear at, say, 55mph & 65mph? Considering there are five other gears to choose from, relaxed highway cruising would be nice.

Bigger the final drive, higher rpm would be needed to reach certain speeds.

[ZDan]

Originally Posted by Panda Grahams

Since this thread has been revived. Here's a relevant new video:

1:42 "A little bit closer"? Nope, different diff gearing does NOT give you closer ratios. geez....
1:56 "SO much more power!"?! NO! You have exactly NO more power!

If you want a good illustration of exactly what going from a 4.1 diff to a 4.3 diff will do for you, here's what it did for the '17 BRZ vs. previous 4.1:
https://drive.google.com/file/d/0B78...YU3YzZ0JB/view
https://drive.google.com/file/d/0B78...uaXRfRl9j/view

0-30mph: '13 = 2.3s, '17 = 2.2s
30-40mph: '13 = 1.0s, '17 = 1.0s
40-50mph: '13 = 1.4s, '17 = 1.4s
50-60mph: '13 = 1.6s, '17 = 1.6s
60-70mph: '13 = 1.9s, '17 = 1.9s
70-80mph: '13 = 2.2s, '17 = 2.3s
80-90mph: '13 = 2.8s, '17 = 2.7s
90-100mph: '13 = 3.2s, '17 = 3.2s

30-100mph: '13 = 14.1s, '17 = 14.1s

[ruturaj001]

Originally Posted by ZDan

1:42 "A little bit closer"? Nope, different diff gearing does NOT give you closer ratios. geez....
1:56 "SO much more power!"?! NO! You have exactly NO more power!

If you want a good illustration of exactly what going from a 4.1 diff to a 4.3 diff will do for you, here's what it did for the '17 BRZ vs. previous 4.1:
https://drive.google.com/file/d/0B78...YU3YzZ0JB/view
https://drive.google.com/file/d/0B78...uaXRfRl9j/view

0-30mph: '13 = 2.3s, '17 = 2.2s
30-40mph: '13 = 1.0s, '17 = 1.0s
40-50mph: '13 = 1.4s, '17 = 1.4s
50-60mph: '13 = 1.6s, '17 = 1.6s
60-70mph: '13 = 1.9s, '17 = 1.9s
70-80mph: '13 = 2.2s, '17 = 2.3s
80-90mph: '13 = 2.8s, '17 = 2.7s
90-100mph: '13 = 3.2s, '17 = 3.2s

30-100mph: '13 = 14.1s, '17 = 14.1s

It's kinda feels like it does, with higher final drive you would be shifting more often than usual. It feels more like power due to effective gear. Technically both things didn't change but feel did.

[blackspike]

Originally Posted by ZDan

1:42 "A little bit closer"? Nope, different diff gearing does NOT give you closer ratios. geez....
1:56 "SO much more power!"?! NO! You have exactly NO more power!

If you want a good illustration of exactly what going from a 4.1 diff to a 4.3 diff will do for you, here's what it did for the '17 BRZ vs. previous 4.1:
https://drive.google.com/file/d/0B78...YU3YzZ0JB/view
https://drive.google.com/file/d/0B78...uaXRfRl9j/view

0-30mph: '13 = 2.3s, '17 = 2.2s
30-40mph: '13 = 1.0s, '17 = 1.0s
40-50mph: '13 = 1.4s, '17 = 1.4s
50-60mph: '13 = 1.6s, '17 = 1.6s
60-70mph: '13 = 1.9s, '17 = 1.9s
70-80mph: '13 = 2.2s, '17 = 2.3s
80-90mph: '13 = 2.8s, '17 = 2.7s
90-100mph: '13 = 3.2s, '17 = 3.2s

30-100mph: '13 = 14.1s, '17 = 14.1s

When shifting into the next gear, you end up at a higher engine speed where there may be more torque.
In addition, you get higher wheel torques, which can be very good with a fast revving naturally aspirated engine.

The difference between 4.1 and 4.3 is almost irrelevant, but I will switch from 3.9 to 4.67... it will feel like a completely different car.
Especially with the very long steps between gears in the automatic transmission.

[blackspike]

Automatic speeds with different FD.
As you can see, the automatic transmission has a much too high gear ratio and the gradation of the gears is very bad. I wouldn't change anything with manual transmission, but definitely with automatic transmission:

[tiger1964]

Originally Posted by ruturaj001

Bigger the final drive, higher rpm would be needed to reach certain speeds.

True, but I was looking for an actual value in rpm at those speeds.

[ZDan]

Originally Posted by blackspike

When shifting into the next gear, you end up at a higher engine speed where there may be more torque.

You will end up at exactly the same engine speed when you shift up. The rpm drop when upshifting is strictly due to the difference in the transmission ratios, this does not change with altered diff gearing.

In addition, you get higher wheel torques, which can be very good with a fast revving naturally aspirated engine.

With numerically higher diff gearing, you get slightly higher wheel torques at some speeds, but there will be speeds at which you have to be in the next higher transmission gear, where you'll have *greatly* reduced wheel torque. Net result is usually a wash. Changing diff gearing doesn't magic you any additional power/weight. You benefit at some speeds, but you pay the price at other speeds by having to upshift sooner.

The difference between 4.1 and 4.3 is almost irrelevant, but I will switch from 3.9 to 4.67... it will feel like a completely different car.
Especially with the very long steps between gears in the automatic transmission.

Again, the rpm drop between transmission gears is going to be *exactly the same* with 4.67 gears as 3.9 gears. Strictly a function of the transmission ratios. If your 3rd gear is 1.404 and 4th is 1.00, and you shift from 3rd at 7400rpm, the rpm in 4th is 7400(1.00/1.404) = 5271rpm, no matter what the diff ratio is.

[ruturaj001]

Originally Posted by tiger1964

True, but I was looking for an actual value in rpm at those speeds.

If I understand it correctly, it should be inversely proportional, so rpm should be about 5% more.

[OkieSnuffBox]

Originally Posted by ZDan

You will end up at exactly the same engine speed when you shift up. The rpm drop when upshifting is strictly due to the difference in the transmission ratios, this does not change with altered diff gearing.

With numerically higher diff gearing, you get slightly higher wheel torques at some speeds, but there will be speeds at which you have to be in the next higher transmission gear, where you'll have *greatly* reduced wheel torque. Net result is usually a wash. Changing diff gearing doesn't magic you any additional power/weight. You benefit at some speeds, but you pay the price at other speeds by having to upshift sooner.


Again, the rpm drop between transmission gears is going to be *exactly the same* with 4.67 gears as 3.9 gears. Strictly a function of the transmission ratios. If your 3rd gear is 1.404 and 4th is 1.00, and you shift from 3rd at 7400rpm, the rpm in 4th is 7400(1.00/1.404) = 5271rpm, no matter what the diff ratio is.

It's painful how many don't understand this incredibly simple stuff.