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Manual gearbox and saving gas

 
View Poll Results: See the first question in the thread, select one of 4 possibilities
Neutral gear, engine idling (1000RPM) 5 83.33%
Slowly breaking on high (5th) gear on engine (2000-1200RPM) 0 0%
Switching to a higher gear for better breaking (4000-2000RPM) 0 0%
Something else (pls explain below) 1 16.67%
Voters: 6. You may not vote on this poll

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  #1 (permalink)  
Old 29 Oct 2010, 11:50 pm
ProDigit's Avatar
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Location: Travel between Belgium and USA
Posts: 265
Default Manual gearbox and saving gas

Hi,

Suppose I was driving at 45mph in 5th gear, and in the distance there'd be a red light.

I could do one of three things:
1- Switch to Neutral gear, let the engine idle (around 1000rpm), and break the last piece of the road if necessary

2- keep the car in 5th gear, let the engine brake the car (2000rpm), and only in the last hundred feet or so bring the car to neutral, and break (if necessary)

3- Switch to a higher gear to get better breaking on the engine (3-4000 rpm), and in the end continue to drive in a lower gear, accelerating as traffic clears the red (now green) light.


What would you do? (Manual gearboxes only pls.)


Second question connected to this:

Suppose I am choosing choice 2 (slowly breaking on the engine's 5th gear), would this cost me more gasoline than switching to neutral gear (and letting the engine idle)?
I suspect the engine wear will be higher...

Thanks for your opinions!
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Old 30 Oct 2010, 12:33 am
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Join Date: Oct 2010
Location: London, Ontario, Canada
Posts: 66
Default Re: Manual gearbox and saving gas

Quote:
Originally Posted by ProDigit View Post
Hi,

Suppose I was driving at 45mph in 5th gear, and in the distance there'd be a red light........!
Got me wondering if I am doing something wrong. I stay out of fifth gear unless at or above 60mph. I also downshift through all gears letting engine brake gently till at coast in first and need to use neutral to stop. Maybe that is option #2? Was not sure because worded as is, thought it meant 5th gear straight to neutral.
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Old 30 Oct 2010, 12:42 am
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Default Re: Manual gearbox and saving gas

Quote:
Originally Posted by Lakota View Post
Got me wondering if I am doing something wrong. I stay out of fifth gear unless at or above 60mph. I also downshift through all gears letting engine brake gently till at coast in first and need to use neutral to stop. Maybe that is option #2? Was not sure because worded as is, thought it meant 5th gear straight to neutral.
That'd be option 3!

On the PT Cruiser your engine will rotate between 1.200 and 1.500RPM at 35-40mph (rough estimate, I should measure it again later) when being in 5th gear. No harm to the engine, as it idles below 1.000 RPM.

1= straight to neutral
2= remain in 5th gear, no acceleration, until the engine has come close to it's idle RPM's, or until you need to break.
3= shift gears to break
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Old 30 Oct 2010, 12:43 am
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Location: London, Ontario, Canada
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Default Re: Manual gearbox and saving gas

Ahh, I should have read your post a couple more times, now I see you are trying to anticipate green light. I would not be able to choose any of the choices given as I prefer to always be in a gear within the powerband at any given speed. Really helps when someone driving close to you does something really stupid and you need split second reaction to avoid an accident.

Edit- Think I should probably just watch poll results, I like to be closer to 3000rpm. Fifth gear at 45mph on my Cruiser has no get up or go.

Last edited by Lakota; 30 Oct 2010 at 12:47 am.
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Old 30 Oct 2010, 11:40 am
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Location: Tulsa Oklahoma
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Default Re: Manual gearbox and saving gas

I'm in my mid 60's and until recently always had cars with manual transmissions. Until it was totaled we had an 02' standard with close to 60K miles. I always downshift thru the gears when approaching a light or stop sign and let the engine compression assist in braking. At the time of the wreck the car still had the original brakes and they were in very good condition. Also used 5th gear anytime speeds were above 40mph. No lugging and it helped with mileage. We now have an 09' automatic and are having to develop new driving styles. I still like to drop into lower gears and use the engine to assist in braking. Old habits hard to break but I like jammin gears and miss the 5 speed.
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Old 30 Oct 2010, 12:11 pm
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Posts: 27,744
Default Re: Manual gearbox and saving gas

I haven't had a standard shift in a lot of years but always remember what an ole mechanic used to say. What would you rather replace, the clutch and maybe tranny or a set of brake pads? Let the brakes do your stopping, that's what they are there for and they're called disposable items.
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Old 30 Oct 2010, 02:24 pm
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Default Re: Manual gearbox and saving gas

I was a volunteer Fireman in my previous life and we always down shifted the trucks and let the engine help with slowing down, then they went to automatics.
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Old 30 Oct 2010, 06:26 pm
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Default Re: Manual gearbox and saving gas

The clutch and trans in the old 02' were as strong as new after 8 years and 60K miles so it was never a concern using them for braking. The PT isn't a hot rod but some stick drivers seem to think so and abuse them. My hot rodding days were behind me when we bought the PT. I really don't care for the automatic but my wife loves it so by default it has become her car. I do see brake jobs in my future but there isn't anything hard about the work.
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Old 30 Oct 2010, 07:32 pm
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Cool Re: Manual gearbox and saving gas

Quote:
Originally Posted by Lakota View Post
Ahh, I should have read your post a couple more times, now I see you are trying to anticipate green light. I would not be able to choose any of the choices given as I prefer to always be in a gear within the powerband at any given speed. Really helps when someone driving close to you does something really stupid and you need split second reaction to avoid an accident.

Edit- Think I should probably just watch poll results, I like to be closer to 3000rpm. Fifth gear at 45mph on my Cruiser has no get up or go.
I agree with Lakota.
I don't use 5th unless I'm up to speed - cruising on the highway, above 62-65.
If I am "luking" to watch the light change, I will definately want to be around 3500 rpm to get enough power. (that s usually engine breaking)
(Unless I am in the auto stick turbo - then it doesn't matter)
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Old 01 Nov 2010, 08:11 am
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Default Re: Manual gearbox and saving gas

As a driver of several manual vehicles, I totally understand the question the OP has. One technique I use that hasn't been mentioned here is heel-toe double clutch. Approaching a stop light from a distance, I'd probably be in 4th or 5th at 45 mph just like the OP to save fuel. The difference is that I'd pop into Neutral when I thought I was close enough to coast to a stop at the light if I had to. When the light changed (with my foot still on the brake) I'd roll my foot to the gas and "blip" the engine, then down shift to the appropriate gear. This manually synchronizes the input and output shaft to the transmission thus eliminating the wear on the syncros and most of the wear on the clutch plate. This is the technique race cars with no syncros use to save their clutch and transmission during a race. I would contend it is a perfectly useful technique for daily driving as well and helps you get in touch with your gear box. You may have to look at your pedal spacing and the width of your foot as my size 11.5 shoes do make it a tad easier to pull this off. Also I find it easier to do with a naturally aspirated engine versus a turbo as they tend to rev a little faster. The key to this is the idea that coasting up to the light in 5th and coasting to the light at idle are going to use virtually the same amount of fuel. The biggest fuel user is going to be your takeoff when traffic starts moving again. If you develop a feel for what gear is going to give you a good power band to take off in, and get gently to the power, you'll be maximizing the torque multiplication of your gear box and minimizing the fuel it takes to get to speed. Once at speed, hit the highest gear possible to maintain that speed.
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