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B gear and cruise control

Discussion in 'Gen 2 Prius Fuel Economy' started by rufaro, Jun 3, 2006.

  1. rufaro

    rufaro WeePoo, Gen II

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    While waiting for the (persistent non-) arrival for my car pool stickers, I am trying to figure out roadtrip driving strategies. (And, keeping in mind I didn't know what gears 1 and 2 and the overdrive were for in 6+ years of driving a '91 Acura Integra GS...) Once I get the stickers, I am planning on a drive from the San Francisco Bay Area (about 40 miles north of SF) to LA. For driving the Grapevine just north of LA, up to about 4100 feet w/ very steep grades (not to mention the Waldo Grade just north of the Golden Gate Bridge), I have always just used cruise control. Does one use B with cruise control, or is that not necessary, since, in theory, the cruise control uses the engine to brake (doesn't it?) so I don't need to ride the brakes anyway...I got the car on May 10, and still have only about 200 miles on it, so I really am still figuring it all out (although, it has occurred to even newbie me that it is obvious that EPA does NOT have ANY stop signs on whatever track it is that is used to calculate city MPG...) Please help! :huh:
     
  2. berylrb

    berylrb Member

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    I cant' help you with strategy, but I do know you will be astounded on the way back from Hungry Valley to Bakersfield is almost all downhill about 45-50 miles. Grapevine to Bakersfield is a pulse and glide dream stretch, enjoy ... and of course the I5 itself is, well, a long straight road LOL

    do an advanced search for "B" lots of posts as I recall,
     
  3. tochatihu

    tochatihu Senior Member

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    <div class='quotetop'>QUOTE(Rufaro @ Jun 2 2006, 09:15 PM) [snapback]265027[/snapback]</div>
    If you have been comfortable with the cruise control before, just keep using it. In your model Prius, shifting into "B" will disable cruise control (don't ask me why, but it does).

    Cruise control will not use the engine to brake (assuming we are both talking about compression braking). If the car desires to accelerate, it will use regeneration to hold back, until the battery gets pretty full. Then the car will accelerate.

    Absent cruise control, you can use "B" to limit downhill speeds whenever you want. It is especially useful when the battery gets full, and you wish to avoid making your brakes hot.

    I have been over the route you describe several times in 2001 Prius and I'm sure you will do just fine. Enjoy.
     
  4. rufaro

    rufaro WeePoo, Gen II

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    <div class='quotetop'>QUOTE(tochatihu @ Jun 2 2006, 09:53 PM) [snapback]265042[/snapback]</div>
    In fact, I am not entirely sure just WHAT I AM talking about, in general, but in this case, what I mean, and what I THINK I understand is:

    In cruise control, the car does not engage the physical brakes to slow the car to the set speed, so I assumed it must somehow use the engine, thus preventing overuse (and therefore overheating) of the brakes themselves. I mean, I can FEEL the accelerator pedal going up and down in cruise control, while I do not feel any action of the brake pedal. Now, from your post, I think I am more confused than before, not to mention worried about damaging the battery, by overcharging it. CAN I just use cruise control as I have in the past, or will I damage the car somehow? (And THIS is indeed where Toyota did, I think, do an oops, as noted elsewhere on the boards, in not having a temp gauge--am I gonna end up stuck somewhere on the grapevine surrounded by mad truckers and overheated...?) On the other hand, given how attentive Toyota has otherwise been to safety issues, I guess I kinda believe that it isn't REALLY likely that regular driving like that--after all, there are more than a few mountains around that Priuses are expected to deal with, and I've not seen any reports of defunct Prii littering the landscape of the Rockies, much less the Grapevine, so I expect this might be a case of TMI for me! ;)

    OTOH, will I get better mileage w/ cruise control or B here? (And, should I REALLY worry about that too much either, since I infinitely prefer to keep an eye on the traffic on the LA route than the speedo--even though the position of the speedo does make it much easier to look at while still watching the road--given the loony truckers...I tend to go about 5 miles over whatever speed limit is posted--all other things being equal--and STILL get passed by trucks blowing my doors off, despite THEIR lower posted speed limits... :eek: )

    Anyway, thank you (and previous poster as well) for the reassurance! It is looking more and more like my trip won't be until the weekend before July 4th, so I will have plenty of time to experiment before that. (But a battle to be fought before--my husband recently replaced his '97 BMW 5series with a 2002 BMW 5whatever, and he wants to take HIS new car--for comfort issues, he claims. I keep trying to tell him that the Arabs have enough money, and we would save enough in gas for the 800+ miles...he says it wouldn't be THAT much $, since his gets close to 30 mpg on the freeway, and nothing much we've seen seems to assure us that I'll do much better than about 45. NOT to mention that I AM more comfortable driving than passenging[!], and, since I have a bum left foot, I can't drive his stick beemer. Anybody got any killer arguments I can use on this one?)
     
  5. tochatihu

    tochatihu Senior Member

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    "In cruise control, the car does not engage the physical brakes to slow the car to the set speed, so I assumed it must somehow use the engine, thus preventing overuse (and therefore overheating) of the brakes themselves..."

    Using the larger electric motor to regenerate electricity decellerates you rapidly.

    "I mean, I can FEEL the accelerator pedal going up and down in cruise control"

    With all due respect, this is an incorrect impression.

    "Now, from your post, I think I am more confused than before, not to mention worried about damaging the battery, by overcharging it. CAN I just use cruise control as I have in the past, or will I damage the car somehow?"

    The computers actually drive the car; you make 'suggestions' with the pedals on the floor. It will not overcharge the battery. No aspect of cruise control will damage the car.

    No, let me take that back at the risk of confusing the issue yet again. If you drive with cruise control on a slick road or while tailgating, this could damage the car. Cases of 'uncontrolled acceleration' have been reported for Prius, but other than getting the accelerator pedal stuck by a misplaced floor mat I do not regard those reports as credible.

    "(And THIS is indeed where Toyota did, I think, do an oops, as noted elsewhere on the boards, in not having a temp gauge--am I gonna end up stuck somewhere on the grapevine surrounded by mad truckers and overheated...?)"

    You will not overheat on the Grapevine. If you did it would be Prius History. Instant fame. Ways to display temp and other parameters are availble in the aftermarket, but this temperature is *pretty boring*.

    "Anybody got any killer arguments I can use on this one?"

    You will save 5 to 7 gallons of gas each way, which could allow you to upgrade your dining on the trip.
     
  6. Maytrix

    Maytrix Member

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    I'm on the east cost, so I don't know what the ride is like, but if it's a lot of up and down hill driving, I would think you'd get better mileage manually rather than cruise control.

    When driving in hills, I'll speed up on the down hill and bleed off that extra speed on the up hill. It's a lot less wasted energy, especially when just gliding will increase your speed many times on downhills. Your speed will fluctuate quite a bit, which is something the cruise control won't do.

    I will add that when I do this, I usually exceed the speed limit a bit (never more than 10mph) on the down hills.
     
  7. rufaro

    rufaro WeePoo, Gen II

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    <div class='quotetop'>QUOTE(Maytrix @ Jun 4 2006, 06:50 AM) [snapback]265546[/snapback]</div>
    Now here is maybe something that might be yet another incorrect assumption of mine. It has always seemed to me that I get better mileage w/ cruise control, which I have always attributed to the maintaining of a steady speed, combined with the more constant acceleration/deceleration used by cruise control (and with all the other acronyms/abbreviations, can't we just agree on CC?). Is this yet another fantasy of mine gone forever? :(

    <div class='quotetop'>QUOTE(tochatihu @ Jun 4 2006, 06:44 AM) [snapback]265543[/snapback]</div>
    Ok, I don't know about the accelerator movement or lack thereof with the Prius--it DID definitely move perceptibly in my Acura, and in a rental LeSabre I drove recently. And I would never use CC in any conditions other than wide open dry roads!

    As to making history in this fashion--I reckon I'll pass and look for my 15 minutes of fame elsewhere :lol:

    And I don't think the dinner upgrade'll do it--my younger sister in LALALAND is at a culinary school, and my older sister is married to an Italian who learned how to cook from his mama, who was born in the Old Country, so we do better eating with my family!
     
  8. berylrb

    berylrb Member

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    <div class='quotetop'>QUOTE(Rufaro @ Jun 4 2006, 02:47 AM) [snapback]265505[/snapback]</div>
    Well I don't know if I have a killer argument but I've taken the trip you want to do but kept going to San Diego. I did cruise control almost the entire way and now that I've become a regular reader of Priuschat.com I would probably forego the cruise control on upside of the hills decreasing speed by +-2mph and on the downside back to CC or add 2mph, also I have begun to increase tire pressure 42 front 40 rear. Ooh yeah, no problems on the Grapevine as I recall the battery did get full but not for long, LOL, it really is a long rolling hill with the exception of the major slope to Bakersfield coming back.

    But I digress, here are my real world numbers from my August 2004 trip which ended with 12,219 miles on the Prius, SF to San Diego with minimum stops and mostly parked in San Diego I5 going and 99 coming back to SF. (three passengers and luggage, but able to see out the rear window, LOL, standard tire pressure)
    1. first leg- AC, at least 90 F out of the bay area, heavy CC tried real hard to maintain 67-70 mph, 341.3 miles, 50.07 mpg
    2. en route fill up- same conditions as above, 289 miles, 50.00 mpg
    3. return first leg- includes some San Diego city driving AC, at least 90 F, heavy CC and I cranked it up to 73-77 mph, 279 miles, 39.02 mpg
    4. en route fill up- same conditions as above, 306.5 miles, 39.97 mpg (much heavier traffic on the 99)

    So if I were to argue you'll do much better than 30 mpg and if you can stomach driving the speed limit and staying on the I5 you should be able to do 50 mpg easily, especially if you increase your air pressure, eh? I have early signs of arthritis in my driving knee and I found the leg room very comfortable. Knowing what I'm starting to understand now I don't see why this trip couldn't be in the high 50's or low 60's!

    bb
     
  9. rufaro

    rufaro WeePoo, Gen II

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    <div class='quotetop'>QUOTE(berylrb @ Jun 5 2006, 08:03 AM) [snapback]265959[/snapback]</div>
    'Nother question here...I keep seeing references all over the board for these tire pressure settings. The sticker inside my doorframe says 35/33. Does everyone else have different tires than I do? (OOOhhh, now you're gonna ask me what the tires are, aren't you--well--the garage is upstairs, and I ain't goin' there just now...the tires are whatever standard tires came with the car, bought in NoCal May 10 & manuf in, I think, Apr or Mar...Yup, I could also get THAT info by going up to the garage...I'M LAZY :rolleyes: )