this post was submitted on 27 Aug 2024
333 points (96.6% liked)

Today I Learned

17785 readers
377 users here now

What did you learn today? Share it with us!

We learn something new every day. This is a community dedicated to informing each other and helping to spread knowledge.

The rules for posting and commenting, besides the rules defined here for lemmy.world, are as follows:

Rules (interactive)


Rule 1- All posts must begin with TIL. Linking to a source of info is optional, but highly recommended as it helps to spark discussion.

** Posts must be about an actual fact that you have learned, but it doesn't matter if you learned it today. See Rule 6 for all exceptions.**



Rule 2- Your post subject cannot be illegal or NSFW material.

Your post subject cannot be illegal or NSFW material. You will be warned first, banned second.



Rule 3- Do not seek mental, medical and professional help here.

Do not seek mental, medical and professional help here. Breaking this rule will not get you or your post removed, but it will put you at risk, and possibly in danger.



Rule 4- No self promotion or upvote-farming of any kind.

That's it.



Rule 5- No baiting or sealioning or promoting an agenda.

Posts and comments which, instead of being of an innocuous nature, are specifically intended (based on reports and in the opinion of our crack moderation team) to bait users into ideological wars on charged political topics will be removed and the authors warned - or banned - depending on severity.



Rule 6- Regarding non-TIL posts.

Provided it is about the community itself, you may post non-TIL posts using the [META] tag on your post title.



Rule 7- You can't harass or disturb other members.

If you vocally harass or discriminate against any individual member, you will be removed.

Likewise, if you are a member, sympathiser or a resemblant of a movement that is known to largely hate, mock, discriminate against, and/or want to take lives of a group of people, and you were provably vocal about your hate, then you will be banned on sight.

For further explanation, clarification and feedback about this rule, you may follow this link.



Rule 8- All comments should try to stay relevant to their parent content.



Rule 9- Reposts from other platforms are not allowed.

Let everyone have their own content.



Rule 10- Majority of bots aren't allowed to participate here.

Unless included in our Whitelist for Bots, your bot will not be allowed to participate in this community. To have your bot whitelisted, please contact the moderators for a short review.



Partnered Communities

You can view our partnered communities list by following this link. To partner with our community and be included, you are free to message the moderators or comment on a pinned post.

Community Moderation

For inquiry on becoming a moderator of this community, you may comment on the pinned post of the time, or simply shoot a message to the current moderators.

founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
[–] [email protected] 26 points 2 months ago* (last edited 2 months ago) (3 children)

The company car I get to use has an automatic transmission that drives me mad.
Its shift points are always right above the speeds I usually drive at.
It shifts into third at 40 km/h which is too fast for a speed limit of 30.
It shifts into fourth at 60 which is too fast for a speed limit of 50.
And it shifts into fifth at 80 which is too fast for a speed limit of 70.

So you're constantly driving with too high rpm's, burning more fuel and making more noise than you'd have to.
It has a "manual mode" where you can shift by moving the stick up or down. But it doesn't actually do anything. If you shift at a different point than the automatic would, you just get a "shift denied" message on the dash, even though the rpm's wouldn't even get close to being too low.
And when you push the gas pedal just a bit more than half, it shifts down and the engine roars, but it doesn't actually achieve much cause the car doesn't have much power.

Internal combustion engines are most fuel-efficient at low rpm's (<1500) and full throttle, and that's impossible to do with this transmission. So it only gets 34mpg (7l/100km), and it's a Diesel hatchback. My old manual car also had a 34mpg rating, but the way I drive I could get 47 (5l/100km), and it had a gasoline engine.

[–] [email protected] 8 points 2 months ago* (last edited 2 months ago)

My current car with a stick is able to squeeze 34 MPG highway, 3 over the rated 31. However, the CVT version is rated for 38 highway in the same conditions.

[–] [email protected] 3 points 2 months ago

It's been a while since I regularly used a car, but I remember the automatics my father had having some sort of logic that shifted up when driving at a constant speed, than back down when wanting to accelerate.

Now those where fancy pants Systems (I think they called them 7G-Tronic), but this was also over 10 years ago, and such logic doesn't strike me as overly complicated, so I'm surprised there's current cars with static shift speeds.

[–] [email protected] 3 points 2 months ago (1 children)

What's the torque band? Driving a diesel, it's really high compression and torque is applied low in the rpm range. Gasoline is a lot lower compression and might be twice the rpm to get the most torque. Outside of that torque band and your using more fuel for less movement.

[–] [email protected] 12 points 2 months ago* (last edited 2 months ago)

Every engine is the most efficient at max torque, which for a typical car's gasoline engine would be around 4500 rpm.
But that "efficiency" means fuel burnt per unit of power. At max torque, the engine makes much more power than you need for normal driving, burning more fuel than necessary.
As a rule of thumb, you get the best real-world fuel economy at full throttle just above the low rpm limit where the engine would run "jerky".
That's at 1000-1500rpm for a passenger car's gasoline engine.
At that rev range, you may only get 40 horsepower out of an engine rated for 100 at max torque, but that's enough. You only need around 10 to maintain your speed against wind resistance, and you don't actually lose any time accelerating slowly cause you're gonna be at the next red light soon, anyway.

For reference, when I'm accelerating from a stop to highway speeds, I'll shift to 2nd gear as soon as I've moved one car length, 3rd at 30km/h, 4th at 40, 5th at 50, flooring the throttle the entire time I'm not shifting. Then I'll stay in 5th unless I'm forced to brake below ~45 again. Up or down a hill I'll go one gear lower.
In my Diesel van, I regularly drive 40 in 5th gear.

I can't make you take my word for it, but this is what I learned in a work-sponsored course for fuel efficient driving, and it got me much better fuel economy than the manufacturer's claim for any car I drove in the past 20 years.