From Honda's site for 08 6spd:
Gear Ratios: 1st: 3.933, 2nd: 2.478, 3rd: 1.700, 4th: 1.250, 5th: 0.976, 6th: 0.771, Reverse: 4.008, Final Drive Ratio: 3.55


From autotrader:
Final Drive Ratio
The reduction ratio of the transmission gear set furthest from the engine. In other words, the ratio of the number of rotations of the drive shaft for one rotation of a wheel. In general, a low final drive ratio results in better fuel efficiency, and higher final drive ratio results in better performance.


I'm a little confused .. is the final drive ratio the same for all gears? What factors go into designing for a specific FDR?

I'm not sure what you're asking. Final drive ratio is the gear ratio of the differential. It never changes.

To calculate the overall ratio you have to factor in the tranny gear ratios.

the number you get will tell you the number of drive wheel rotaions, compared to the number of engine revolutions.

If you had a car with a driveshaft, the final drive ratio could be visually verified by counting the number of drive wheel rotations compared to the number of driveshaft rotations. Not so easy to do since the tranny and final drive (differential) is all in one case (no driveshaft).

A higher numberice final drive will yield better off the line performance, but will also yield higher engine rpms for a given speed and thus, lower fuel economy. Our cars have quite high final drive ratios which yield relatively high cruise rpms compared to other makes.

If you think 3.55 is bad, the V6 5AT's are even worse at 4.31

So to get the total ratio of engine rotations to tire revolutions, you multiply the drive ratio by the ratio of the gear the car is in?

So to get the total ratio of engine rotations to tire revolutions, you multiply the drive ratio by the ratio of the gear the car is in?

Ya. for instance suppose we use your numbers.

3.55 final drive, cruising in top gear 0.771

3.55x.771=2.74

The engine turns 2.74 turns for every tire rotation. Not a very meaningful number since there's other considerations that should be calculated, like actual tire rotations per mile, etc.

Lowest cruise engine rpms are would be your target for great fuel economy. Only care about performance? forget cruise rpm, go for a higher final drive.

When it comes to getting a 3500# car moving briskly, and still maintaining reasonable fuel mileage numbers requires some trade-offs however....Like the 4.31 final drive in the V6 5AT's, and adding VCM to compensate.

gotcha .. thanks

Nice write-up turbodave.

I agree tho, one of the first things I noticed with my 6 spd is that I felt I was crusing at too high of an rpm on the highway. I almost wish 6th really kept the engine a lot lower when crusing at 65-80... I can't remember off the top of my head, but at 75-80 I believe I'm over 3k. 65 probably around 2.5-2.7k

Nice write-up turbodave.

I agree tho, one of the first things I noticed with my 6 spd is that I felt I was crusing at too high of an rpm on the highway. I almost wish 6th really kept the engine a lot lower when crusing at 65-80... I can't remember off the top of my head, but at 75-80 I believe I'm over 3k. 65 probably around 2.5-2.7k

Ya it's pretty bazarre all the different combinations available. Yours unfortunately is almost the worst.
Your differential (final drive) is 3.55, but your 6th spd is only a .771 OD which yields an overall of 2.74 .That number alone doesn't mean anything without comparing it to something, so I'll use mine.
final drive of 4.31, and 5th of .612, which yields and overall of 2.64, meaning a little bit fewer revs per mile.

The worst of the bunch is the 5mt in the 4I's. final drive of 4.39 and 5th at .647, yielding 2.84
MORE revs for mile for them. :thumbsdow Which might explain "some" of the less than steller mileage for the 5speed 4I's.

The 5AT 4I's have the most favorable overall drive train at 2.51

The 5AT 4I's have the most favorable overall drive train at 2.51

You are assuming that higher (numerically lower) ratios are always better.

I have a 5AT I4 and I wish mine had a lower (numerically higher) final drive ratio. I would gladly take higher rpms at highway speeds, and the resulting fuel economy penalty, in exchange for faster 0-60 times. :yes:

You are assuming that higher (numerically lower) ratios are always better.

I have a 5AT I4 and I wish mine had a lower (numerically higher) final drive ratio. I would gladly take higher rpms at highway speeds, and the resulting fuel economy penalty, in exchange for faster 0-60 times. :yes:

You're correct. I was basing my statements around fuel economy. Performance numbers are diametrically apposed. Numerically higher numbers will be beneficial to 0-60 times. But then again, so would more cylinders. :naughty:

You're correct. I was basing my statements around fuel economy. Performance numbers are diametrically apposed. Numerically higher numbers will be beneficial to 0-60 times. But then again, so would more cylinders. :naughty:

That's why Honda puts the numerically higher ratios on the V6, because it's buyers are the ones who want more performance, and the numerically lower ratios on the 4 cylinder cars because they're targeted at customers who want more fuel economy. Makes perfect sense :wave:

You are assuming that higher (numerically lower) ratios are always better.

I have a 5AT I4 and I wish mine had a lower (numerically higher) final drive ratio. I would gladly take higher rpms at highway speeds, and the resulting fuel economy penalty, in exchange for faster 0-60 times. :yes:

60 mph is right about 2100 rpm in my 5AT I-4. I don't need fast 0-60 times, I have an M3 for that...........:thmsup:

60 mph is right about 2100 rpm in my 5AT I-4. I don't need fast 0-60 times, I have an M3 for that...........:thmsup:

Same here. When I need an adrenalin rush, I just fire up one of my Grand Nationals and take it out for some "frisky" driving. :thmsup:

Although I must add, this V6 Honda is NO slouch.

Yes, even us 60 somthin's can have fun now and then. :thumbsup:

damn the 4-cyl A/T has a 4.44 Final drive ratio that's pretty high!