2021 Mirage - changes to manual gear ratios?

[dspace9]

Heavy traffic is the worst for fuel economy. Another one is extremely high speeds, when you're running super high RPM's, and you have the most wind resistance to push through.

My Mirage gets the best fuel economy when going down the freeway at a steady speed, but going faster than 60 miles an hour ,or 120 km's an hour, and my fuel economy starts to go down again..

I don't have cruise control, but that probably gets anyone a few bonus mpg's.

My thinking is that a 6 speed manual would save on fuel at high speeds, and be annoying in city traffic. The Mirage is "geared" to the urban dweller.

I don't get the RPM and fuel economy connection, I think it goes all sorts of ways. Sometimes running my Mirage in 4th and not 5th and I seem to consume the exact same amount of gas. Other times, like when accelerating, the lower gear is clearly being thirstier.

[Pimp_Daddy_Patty]

Another concern for the gearing is just how sluggish it would be in a hilly environment. Also the fact that people would likely be lugging the piss out of it in 6th gear at low rpm. I can imagine there are warranty concerns there too.

[01-7700]

I may be misunderstanding your statement, but why have most manufacturers moved to 6 speed automatics or infinite ratio CVT's to increase fuel economy If higher gear ratios don't matter? Also if I'm going 65 mph in 5th but turning fewer RPM'S than going 65mph in 4th, then less fuel should be used as engine is turning slower. I'm no engineer, but I'm pretty sure my engine uses less fuel at idle than at 4000 rpm

i can't tell you why car manufacturers do what they do - all i know is that at 65 mph, the power needed to propel the car forward is the same regardless of how fast the engine is spinning - how could it be different? how does the wind know to resist less or more if i have an 8 speed manual transmission or a 3 speed ?

[Pimp_Daddy_Patty]

All the moving parts inside an engine create windage and there is resistance as parts move through air (and oil) inside the crankcase. The resistance increases as rpm goes up. That being said, our little 3 cylinder is a lot easier to spin than a 4, 6, or 8 cylinder engine because it has many less moving parts. Running our little engine at too low an rpm will cause it to work at much higher loads. Any gains from dropped rpm would be lost by making the engine work harder to move the vehicle. Even if there were gains from more gears, the added cost would also cancel out any savings from increased in fuel mileage.

[Mark]

All the moving parts inside an engine create windage and there is resistance as parts move through air (and oil) inside the crankcase. The resistance increases as rpm goes up. That being said, our little 3 cylinder is a lot easier to spin than a 4, 6, or 8 cylinder engine because it has many less moving parts. Running our little engine at too low an rpm will cause it to work at much higher loads. Any gains from dropped rpm would be lost by making the engine work harder to move the vehicle. Even if there were gains from more gears, the added cost would also cancel out any savings from increased in fuel mileage.

I don't think a slightly taller 5th gear would add anything to the cost of building a Mirage, & the engine could easily handle higher speeds @ a lower rpm. You may have to downshift sooner when climbing a steep hill, but I would be ok with that.

The Mirage is not bad as is. If I wanted to improve it, I would use a slightly higher 5th gear.

[Pimp_Daddy_Patty]

I find the road noise and wind noise is much worse in my car than engine noise.

[Mark]

I find the road noise and wind noise is much worse in my car than engine noise.

I agree, & I like the sound of the engine. I still think the Mirage would be a bit more efficient (highway) with a slightly taller 5th gear.

Presently, 5th gear handles 35-40 mph fairly well. Some of that may be lost. Thus, there are trade offs.

[Cobrajet]

i can't tell you why car manufacturers do what they do - all i know is that at 65 mph, the power needed to propel the car forward is the same regardless of how fast the engine is spinning - how could it be different? how does the wind know to resist less or more if i have an 8 speed manual transmission or a 3 speed ?

Manufacturers have started using transmissions with more and more gears because doing so keeps the engine in the narrow rpm range where it is most efficient. This helps with fuel economy and emissions.

Let's say a particular engine is most efficient at 3000 rpm...this is where it makes the most horsepower and torque while using the least amount of fuel. Instead of the engine revving from 2800 rpm to 3600 rpm before shifting from second to third gear in a 5-speed transmission, it now only has to rev from 2800 rpm to 3100 rpm before shifting from third to fourth in an 8-speed transmission.

The 8-speed probably doesn't have a higher top gear or higher final drive. It just shifts more often to keep the engine in the 'sweet spot'.

[ProDigit]

I wonder if the Mirage can reasonably handle a taller 5th gear within the power capabilities of the motor. If you had to downshift at every slight hill on the interstate that wouldn't seem like an improvement to me.

I belong to a low-power motorcycle forum and folks are always talking about stretching out the shift points by using a smaller sprocket in the rear. It works great in lower speeds but actually reduces the top end speed because the motor can't push the bike as well as with the stock configuration.

Depends. Honda usually does well with a +1T in front and a -3T in rear. Never had any less top speed.
In most cases, identical top speed.
Sure, the engine gets taxed more, due to a higher gear, but in another way, the engine doesn't have to rev as high, meaning less friction. You'd be running that engine closer to the torque peak, rather than HP peak.

One way to change gears in any car, is get a slightly taller profile tires.
Swapping out the stock tires, for 0,5 to 1 inch larger diameter ones, should net you 6-10% higher MPG, but the readout will differ by the same amount (showing lower MPH and MPG numbers, or, at an actual GPS rated speed the RPMs will lower by that amount).

Since 75HP gets a motorcycle up to 120MPH, and the mirage up to 100MPH, changing gear ratios could affect top speed, but nowhere near were you'd suffer when driving at legal speeds.
The change in gear ratio, can easily be compensated for, by making sure the larger tires are pumped up to 40PSI or higher.

Imagine how much more your Mirage would lug in the wrong gear. I say they should make an optional 6 speed manual, to satisfy the true fuel sippers out there!

It wouldn't lug. You can lug your mirage, by trying to depart from 3rd or 5th gear, but no one does that.
You go by the sound and feel of the engine.
Most cars, anywhere over 2k RPM won't lug.
But if by some miraculous reason, it does lug, give it a squirt of graphite in the engine oil!
That stuff does miracles to low RPM torque, and, in my case, allowed me to run my oil for about ~2-3k miles longer!

thing is - for a given speed, if you are in one gear doing x rpms or another higher gear doing x-y rpms - the fuel use would be the same - the same amount of work is being done

Not true. Each engine rotation consists of 1 power, 1 compression, 1 exhaust stroke.
Compression and exhaust stroke are losses, and they're pretty identical at 2k RPM vs at 4k RPM, save at 4k RPM you'll get twice as many of them.
The lower the RPM, the less losses you'll get; which is why your MPG is always better in final gear than in a gear above it (save for when your engine is lugging, usually when cruising that would be below 1-1,5k RPM).

My thinking is that a 6 speed manual would save on fuel at high speeds, and be annoying in city traffic. The Mirage is "geared" to the urban dweller.

No one said you'd have to use the 6th gear! You can still use 5 out of 6 gears when going 40MPH or below.
That 6th gear is made for highways and interstates.
But, as long as you keep the throttle steady, and cruise at a constant speed, there's no reason your engine won't be able to push you to 35MPH in 6th gear, and get even better gas mileage than in 5th!
As long as you don't floor it at those RPMs (lugging).

Another concern for the gearing is just how sluggish it would be in a hilly environment. Also the fact that people would likely be lugging the piss out of it in 6th gear at low rpm. I can imagine there are warranty concerns there too.

Shouldn't be.
The engine has knock sensors, and is electronically controlled. It would just slow down, until the driver decides to downshift. That's what downshifting is for, for acceleration.
If I would have to choose between running 5th gear at 3000RPM to go uphill, or downshift from 6th to 4th to hit 3k RPM, I'd choose the latter. In either case, the engine load is identical. Only now the driver has options to choose an extra gear.



I don't care so much about more gears as I care about a taller final gear.
Even if it means they'll have to space out the last gear, or all the gears.
I never got those narrow spaced gears. I often run my car from 1st, to 2nd, to 4th and 6th, because the gearing is too short!
4th is just to push it a bit further to the right speed, and 6th is when I reach cruising speed.

[ProDigit]

All the moving parts inside an engine create windage and there is resistance as parts move through air (and oil) inside the crankcase. The resistance increases as rpm goes up. That being said, our little 3 cylinder is a lot easier to spin than a 4, 6, or 8 cylinder engine because it has many less moving parts. Running our little engine at too low an rpm will cause it to work at much higher loads. Any gains from dropped rpm would be lost by making the engine work harder to move the vehicle. Even if there were gains from more gears, the added cost would also cancel out any savings from increased in fuel mileage.

Not if they just space out the gears more.
It would cost next to nothing.
One could run larger diameter tires, to kind of achieve the same.
And you'll only drop MPG when you lug the engine. That's usually below 1250-1500RPM while cruising, and 2k rpm when accelerating (different for every car and engine combination).
Your best MPG is where the torque curve peaks.

If this is your Mirage torque/HP curve:
Attachment 5045
You'll get best MPG per gear at ~3k RPM from this engine.
But you should get better MPG in 5th than in 4th.
Then it just depends on how fast you want to go.
If you're ok with doing 3k RPM at 60MPH to get good mileage to bring you home, or
Get much better MPG at the same speed at 2,5k RPM, or get similar MPG at ~2,75k RPM at 75MPH, I think many will prefer to get the taller gear that provides you with the option of either faster home, or better MPG.
But if you never take it out this 'fast' (above 40MPH), a gearing change won't matter to you.

This engine should be able to get peak MPG, by increasing the final gear ratio by between 16% and 25%; that's doing 70-75MPH at 3k RPM (where you do stock 60MPH).
At this gear ratio, you'll still have a good 5-10HP spare at 60MPH; which is not a lot of surpassing power, but it is sufficient for cruising, and the 10HP headroom continues all the way to about 85-90MPH, where the car would need a downshift to surpass that speed.

Manufacturers have started using transmissions with more and more gears because doing so keeps the engine in the narrow rpm range where it is most efficient. This helps with fuel economy and emissions.

I think that's a bunch of balloney.
It's much better to just stretch the gear and rev lower, which is what a CVT does, and if you want to accelerate, learn to downshift.
Even if the engine is revving a bit below the torque peak of 3k RPM, it'll still net a higher MPG with a taller gear.
Short gears are only good if your cruising speed is exactly the most common roads (35-60MPH).
Most people drive anywhere to 80, sometimes even exceed 90 in some areas.

One thing I hated about my Honda Rebel 250, was that it was so nice to cruise in final (5th) gear, at 35MPH! Means all my travel was above this.
I immediately upgeared it by the maximum value (+30%), where now that sweet spot was 45MPH.
It truly was one of my most loved bikes.