I remember hearing something about gear ratios and such....
I have my own ideas but I will let the experts deal with it...
I have my own ideas but I will let the experts deal with it...
Why is a 5speed considered to be better than a 6spd again?
- Thread starter Goosemaster
- Start date
I remember hearign that using standar ratios a 6spd can't stretch as far as a 5speed can in terms of full speed.
I would think that more gears, if configured correctly, would constitue higher speeds but whatever
Eh, a 5 speed isn't better than a 6 speed. It all depends on the gearing. Neither is just plain "better", as it depends on the application.
A good example of this is a regular Miata and a Special Edition Miata. Regular Miatas have 5 speeds, and SE Miatas usually are equipped with 6 speeds. I can hit a little over 60mph in 2nd gear at the rev limiter in my 5speed Miata. A 6 speed Miata's revlimiter in 2nd might is around 55mph. Lets say we are in an autocross competition, If we get on a straight where we will hit 60 mph at the end, he'll either have to upshift (lose a tad bit of speed) and then downshift after the turn, or he can keep tapping on the rev limiter. Not ideal at all! In a 5 speed car, you can stay in 2nd throughout the whole thing, not lose any speed or have to shift.
A 6 speed might be ideal in different situation (gas milage, maybe a drag race). It is all very dependent on how the gear ratios are, not really how many gears there are.
A good example of this is a regular Miata and a Special Edition Miata. Regular Miatas have 5 speeds, and SE Miatas usually are equipped with 6 speeds. I can hit a little over 60mph in 2nd gear at the rev limiter in my 5speed Miata. A 6 speed Miata's revlimiter in 2nd might is around 55mph. Lets say we are in an autocross competition, If we get on a straight where we will hit 60 mph at the end, he'll either have to upshift (lose a tad bit of speed) and then downshift after the turn, or he can keep tapping on the rev limiter. Not ideal at all! In a 5 speed car, you can stay in 2nd throughout the whole thing, not lose any speed or have to shift.
A 6 speed might be ideal in different situation (gas milage, maybe a drag race). It is all very dependent on how the gear ratios are, not really how many gears there are.
There's no 'better' transmission. It has a lot to do with application and gearing. With a 6 you can have shorter low gears, and taller hi gears for top end speed and down low acceleration. But most car manufactuerers don't work that way.
yup. neither is intrinsically better. if the tallest gear in a 5sp and a 6sp is the same, the 6sp will have better resolution, but you can say its also heavier and mechanically more complex. as far as real world applicability is concerned, 5sp is generally good.. personally, though, i wouldnt mind if my tranny was the same, with an extra 6th gear added for freeway cruising. but again.. neither is 'better' per se
TheLonelyPhoenix
Diamond Member
- Feb 15, 2004
- 5,594
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Generally, the peakier the power curve, the more a 6-speed helps. Also a slight boost for fuel efficiency, although there's a ton of variables that go into that.
In other words, it depends on the car.
In other words, it depends on the car.
for example, if a motor produces most of its power in a small range... say 5000rpm-7000rpm.. the better resolution allows you to stay in that power range... upshifts from 7000rpm will drop you down to 5000rpm in the power range.. whereas a tranny with lesser gear will drop to 4000rpm --outside of the power range.
huge trucks (peterbilts and stuff) typically have turbo diesel motors with a very very limited powerband and thus they require something like 15 speeds in the transmission. some of the older muscle cars have a pretty generous powerband and can get away with 4speeds
huge trucks (peterbilts and stuff) typically have turbo diesel motors with a very very limited powerband and thus they require something like 15 speeds in the transmission. some of the older muscle cars have a pretty generous powerband and can get away with 4speeds
As Actaeon mentioned, the gearing is more important - not necessarily how many gears there are. The 6th in a Vette is so tall/overdriven that it allows for pretty decent highway/cruising mileage. But 6th gear in cars with small displacement is usually geared fairly short because there's not much torque down low in the powerband. Gearing can end up helping or hurting depending on the situation.
In the case of the STi, it forces a shift into 3rd gear to hit 60mph and 5th gear to complete the quarter mile (or bouncing off the rev-limiter in 4th as you cross the line). If the gearing had been slightly extended those performance figures would've improved - but the gearing of the STi is more suited for a track, less so for making good magazine racing numbers. (0-60, 0-100, 1/4mi ET)
As Nutbucket alluded to, the 6spd in the STi is actually shorter than the 5spd in the WRX. That is, in their respective top gears the STi engine is spinning faster than the WRX at any given speed. Along with that it has an additional gear over the WRX - so this extremely short gearing allows for easily finding the right gear to pull yourself out of a corner on a track with great haste.
If you ask me though, extremely short gearing and 6 gears is pretty annoying in normal driving. I tend to get lazy and skip shift 1-2-4-6 or 2-4-6 if I'm particularly lazy. If anything the peakier WRX powerband would benefit more from a close-ratio 6 speed, while the more torquey STi could probably make do with a 5 speed.
In the case of the STi, it forces a shift into 3rd gear to hit 60mph and 5th gear to complete the quarter mile (or bouncing off the rev-limiter in 4th as you cross the line). If the gearing had been slightly extended those performance figures would've improved - but the gearing of the STi is more suited for a track, less so for making good magazine racing numbers. (0-60, 0-100, 1/4mi ET)
As Nutbucket alluded to, the 6spd in the STi is actually shorter than the 5spd in the WRX. That is, in their respective top gears the STi engine is spinning faster than the WRX at any given speed. Along with that it has an additional gear over the WRX - so this extremely short gearing allows for easily finding the right gear to pull yourself out of a corner on a track with great haste.
If you ask me though, extremely short gearing and 6 gears is pretty annoying in normal driving. I tend to get lazy and skip shift 1-2-4-6 or 2-4-6 if I'm particularly lazy. If anything the peakier WRX powerband would benefit more from a close-ratio 6 speed, while the more torquey STi could probably make do with a 5 speed.
No, big diesel engines have a lower "usable" rpm band. If you take your usual car engine (on gas), it can pull enough from 1200 rpm up to 6000 rpm. A turbo diesel engine (as in my brother's Renault Clio) will pull enough from 800rpm to some 5000 rpm.
However, a train engine diesel engine might have idle at 300 rpm and top rpm at 900-1000. This reduced ratio of idle/top rpm is what force lots of gears.
Also, the fact that trucks are greatly underpowered compared to cars don't help in reducing gears (to start moving or move on a 10% uphill, a truck might need a gear in which max speed is at 10 miles per hour. My car could ride up such a hill at 40-50mph)
So, many gears are needed to have enough force to pull the truck with max load on steep hills, and to have enough range to move the truck at max speed on straights, preferably in a rpm that is at the econo range and not at top range.
However, going back to the original topic, my 5sp manual VW Passat is not so good for city traffic: in 2nd gear its rpm is a bit on the high side at 30mph, and in third gear its rpm is a bit on the low side at 30 rpm, so city traffic (accelerate and brake at max 50 km/h) needs gear changes.
It would have been good to have a 6sp with a gear good for 30-70 km/h, so 50 km/h would be at a lower rpm
It would have been good to have a 6sp with a gear good for 30-70 km/h, so 50 km/h would be at a lower rpm
uh, that is what i said. it matters NOT whether the powerband is lower or higher on the rpm scale, the point is that the powerband on those vehicles are NARROWER, requiring more gears to keep the motor IN the powerband at all times.
Doesn't help unless it's geared that way. My RSX-S ('05) turns about 3900 RPM at 80 MPH in 6th gear. Redline is at 8100 RPM, but still, that's kinda high just for highway cruisin'.
I still get ~27.5 MPG overall though, which isn't too shabby.
Demon-Xanth
Lifer
- Feb 15, 2000
- 20,551
- 2
- 81
Here's a comparison of the NV4500 and NV5600 that were used in Dodge Ram pickups:
NV4500:
5.61, 3.04, 1.67, 1.00, 0.74
NV5600:
5.63, 3.38, 2.04, 1.39, 1.00, 0.73
They both have similar first, and top two gears. The difference is that the range taken by the 2-3 with the 4500 is taken bu 2-4 in the 5600. The advantage that the application has, in that they're usually attached to diesels, is that the latter has an easier time keeping in the diesel's reletively narrow RPM range.
Note: in normal driving 1st is rarely used.
NV4500:
5.61, 3.04, 1.67, 1.00, 0.74
NV5600:
5.63, 3.38, 2.04, 1.39, 1.00, 0.73
They both have similar first, and top two gears. The difference is that the range taken by the 2-3 with the 4500 is taken bu 2-4 in the 5600. The advantage that the application has, in that they're usually attached to diesels, is that the latter has an easier time keeping in the diesel's reletively narrow RPM range.
Note: in normal driving 1st is rarely used.
Generally, the 6th gear is taller than 5th gear in cars which offer an option.
What RPM is it turning at in 5th in a non-S at 80 MPH?
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