I am about to get a B15 trans for my turbo classic. However I am a little worried about the 4.437:1 final drive ratio. You guys who are using this transmission.....are you screaming at highway speeds with this tranny. Is it possible to compensate a little with a larger rim/tire combination?

I've got one in mine. at about 65 i'm at about 3k. so it is kinda hard to cruise for miles at like 80.

i have the trans but no turbo.. its at about 4 k when your doing 80... its not that much of a difference as the b14 ser trans only a couple hundred rpm no big difference

doesnt the p11 trans have a taller final drive?

you guys have to realize these motors rev to about 8k... so cruising at 3-4k is not big deal

yes it does so it will be a little lower than... it will go liek this b13/b14---p11---b15 in terms of how high the rpm is at cruising at 80mph from lowest to highest

Damn. I have to drive 50 miles to and from work on the NJ Garden State Parkway,
where the average daily commute pace is like 80-90 MPH. I think it might be worth it for me to hold out for the P11 trans with the better final drive ratio.

i have a p11 it doesnt matter which one you get

Check the mph vs rpm in 5th on the b15 tranny. IIRC the 4th and 5th on the b15 tranny are longer then the b13/b14 4th,5th but the shorter final drive does come into play. IMO go with the b15 tranny, when I did the numbers out awhile back 8000rpms with 205/50/15 tires was like 187mph in 5th. Its like 167mph in 5th with the b15 tranny. So its kinda like giving up the high rpm power band in the upper gears.

ill check tomorrow what exact rpm it is at 70 and at 80mph in my p11 with stock 205/50/16.. i dont have my b14 anymore so i cant tell you exactly

B15 tranny has a longer 5th gear vs. P11.

@ 63-64 mph....my P11 tranny is around 3K RPMs. This was with 18" rims with 35s profile.

B15 tranny has a longer 5th gear vs. P11.
@ 63-64 mph....my P11 tranny is around 3K RPMs. This was with 18" rims with 35s profile.
What width tire though? You can't calculate tire circumference without the wheel size, profile and the width.

B15 tranny has a longer 5th gear vs. P11.
@ 63-64 mph....my P11 tranny is around 3K RPMs. This was with 18" rims with 35s profile.

Your P11 with 18's is only at 3K because those tires are huge. Was your 63-64 MPH statement corrected for that tire size? You speedomoter is probably way off with that larger tire diameter. The B15 may have a longer 5th gear than the P11 but it doesn't mean that much because the final drive of the B15 is so much lower. A 4.176 to a 4.437 is a pretty large jump for final gearing, so large that I feel it will affect driveability in most situations. Nissan went with the 4.437 final gearing to compensate for the larger tire size on the B15 with performance package. I have a strong feeling that my B13 with 15" tires and the B15 tranny will feel overgeared, shifting too much, tire liquidation in the lower gears, screaming on the highway....etc. Drivability suffers greatly on a car with the wrong gearing. If this was not true why would nissan spend so much money and time in R&D developing a new SR tranny for the heavier and larger wheeled B15. The shorter lower gears are to get the heavier B15 rolling from a stop and for better low MPH acceleration. The lower final drive is for the larger wheel and tire combo. A P11 doesn't have the lower final drive because it still uses the same smaller tires that it always used in previous models. I will still think of the B15 trans as an option for me only if I can fit some larger tires to make up for the difference in gearing. A car that is geared too low is no fun, at least on the street. Some V8 musclecar guys do it all the time, they drop the gearing in the rear for fast 1/4 mile times. So at the end of the quarter mile they are close to top speed, redline in the last gear. Then they have to drive in the slow lane on the highway because their ride is screaming at 70 MPH.

What width tire though? You can't calculate tire circumference without the wheel size, profile and the width.
You don't need width to calculate the circumference of a wheel.
Circumference = pi * d

I provided the wheel size and profile which is sufficient to make the calculation.

I have a B15....and i hate my tranny at high speed. I do a lot of mileage, and i rev to much...around 4500 rph at 120 k/ph.

Like some people said, the besty thing beside a tranny swap...bigger tire. I have some 215/55/16 and the rev drop of +-200 rpm...and now, it much better !

Mart

You don't need width to calculate the circumference of a wheel.
Circumference = pi * d
I provided the wheel size and profile which is sufficient to make the calculation.

You did NOT I repeat did NOT give d!

We need width to calculate d! (I.E. 18 inches + sidewall height = d)

The profile mean nothing without the width. The sidewall height is a percentage(profile) if the width. I.E. 35 equals 35% of the width is the sidewall height.

You did NOT I repeat did NOT give d!
We need width to calculate d! (I.E. 18 inches + sidewall height = d)
The profile mean nothing without the width. The sidewall height is a percentage(profile) if the width. I.E. 35 equals 35% of the width is the sidewall height.

He's right. You need the width to determine the diameter. A profile aspect ratio of 35 could mean a sidewall dimension of 7" if the width was 20".

He's right. You need the width to determine the diameter. A profile aspect ratio of 35 could mean a sidewall dimension of 7" if the width was 20".
I understand...however, I guess not everybody knows that 18s are basically limited to a width between 215mm - 245mm. Can you fit 245mm wide tires on our chasis? I highly doubt it.

35s profile on 215mm - 245mm width varies in sidewall length by a minute .4"
215mm = 3" sidewall
245mm = 3.4" sidewall

You are talking about a difference of approximately 2.5" in circumference length. However, you can bring that difference a little closer together since we can't fit 245mm tires on our chasis. ;)

The B15 tranny has basically the same feel as a B13 tranny. I really couldn't tell the difference on the highway, because with either tranny you're really winding it up at 65+mph.


Now a P11 tranny could be a different story.

I understand...however, I guess not everybody knows that 18s are basically limited to a width between 215mm - 245mm. Can you fit 245mm wide tires on our chasis? I highly doubt it.
35s profile on 215mm - 245mm width varies in sidewall length by a minute .4"
215mm = 3" sidewall
245mm = 3.4" sidewall
You are talking about a difference of approximately 2.5" in circumference length. However, you can bring that difference a little closer together since we can't fit 245mm tires on our chasis. ;)

You are right... but when somebody asks for width... you could just answer them rather than telling them how to calculate circumference. Just makes it easier on people.