To draft or slow down? - Page 14 - Fuelly Forums

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Old 05-08-2008, 12:08 PM   #131
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Yeah, my 1st gear is pretty decent, but then everything else is too close. I'm in 5th by 30mph with reasonable acceleration, I can ride 5th down to 20 and re-accelerate, and it won't stall in 5th down to 12mph.....then I'm at 3000 rpm on the highway. Sure, it's lively on the highway without having to downshift, but really there's no reason the gears need to be so close.

In fact, not only would economy benefit, but acceleration would too; if 2nd was just a little taller, it could get up to 60 in 2nd and lose 1 second worth of shifting, instead 2nd goes to like 54 or so. Marketing and engineering departments both failed on the gear ratios...
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Old 05-08-2008, 12:29 PM   #132
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interesting... I hadn't thought of that issue.

Your pain is the start, in first gear. My pain is at speeds above 50-55 in 5th. Anything between those, we should have equivalent options. Maybe it's a different gear, but the speed/rpm combination is similar.
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Old 05-08-2008, 04:37 PM   #133
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1993: "First gear is so tall"

First gear in my '95 VX feels a bit tall, but I figured that's because my tires (175/70) are larger than stock. This gives me a speedometer error of more than 2%. Sometimes I think having the stock size would be nice.

I wonder what your tire size is.
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Old 05-08-2008, 05:45 PM   #134
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Quote:
Originally Posted by usxpop View Post
[snip]

If you want to draft, do so at least several vehicle lenghts back.

[snip]
I did some calculations:
3 car lengths is about 50 feet.
Driving 68mph, you travel the distance of 3 car lengths in precisely one half second. I'm not sure how many "several", but I usually think of it meaning about 4 which is about 67 feet and precisely 2/3 of a second time lapse between you and the trailer.

Quote:
Originally Posted by RoadWarrior
The aerodynamics of the sitch are usually that there's a "draft" out to 3 lengths of the vehicle making it, so a nice big semi with 20ft of rig followed by 55ft of trailer has draft out to 225ft at 65mph. However a typical van will only have draft out to about 50ft. So obviously the bigger the vehicle you follow, the further back from it you can be, and the safer it is.
Thanks for pointing this out RoadWarrior, I was never aware of it.

225 feet is 2.25 seconds time lapse at 68mph between you and the trailer and is 13.5 car lengths back.

So it looks like I can resume drafting at a safe distance without endangering myself or truckers--a win win. Good news! I wish I had a spacial sense for how far back 200 feet is from the back of a tractor trailer.
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Old 05-08-2008, 05:47 PM   #135
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Quote:
Originally Posted by monroe74 View Post
1993: "First gear is so tall"

First gear in my '95 VX feels a bit tall, but I figured that's because my tires (175/70) are larger than stock. This gives me a speedometer error of more than 2%. Sometimes I think having the stock size would be nice.

I wonder what your tire size is.
My tire size is the same as you my friend, and oft is the time I have felt the same way that it would be nice to have stock tires for these reasons.
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Old 05-08-2008, 07:10 PM   #136
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"My tire size is the same as you"

Thanks for responding. That's what I figured. Out of all the VXs on this forum, I've noticed just one who is using the stock tire size (and it's because it's a low-mileage car with the original tires). You probably know who I mean.

I think the bigger tires most of us use are a mixed blessing. One drawback is they make 1st gear a little too tall, as you noticed.
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Old 05-08-2008, 07:41 PM   #137
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Best way I found to guage the distance is counting the stripes between yourself and the truck. The stripe and the space between is about 43 feet.

If I am following a big rig I like to see at least 3 stripes between us or about 125 feet, which is close to stopping distance and enough time to avoid a chunk of truck tire on the road or other debris.

If I get closer than that I will go to neutral or even back to fifth with no gas pedal to shut off the fuel if I need to decelerate.

Here is the ebay auction number if you want to see my VX before it was fixed. Should get some paint on it in the next couple of weeks. Almost time for second oil change.

Auction #230220896589

regards
gary
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Old 05-08-2008, 09:04 PM   #138
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Hi Gary, you probably noticed I was just talking about you.

"Here is the ebay auction number"

This is a direct link for that page (folks, take a look now, because after a while eBay will take the page down).

That's a super find. Like you said, it's a time capsule. It's great that you were able to get it back on the road and save it from various ignominious fates.
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Old 05-09-2008, 02:08 PM   #139
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Quote:
Originally Posted by racertim
To draft or slow down?
To draft. I did three stripes back from the tractor trailer and he never got buggered and I was amazed by the difference--*and* it was raining, so hydroplaning wasn't helping, although he was plowing two tracks for me to follow in the rain. Understand I drive this stretch of the Mass Pike (I-90) on a regular basis. Coasting down any of the slight hills westbound in neutral has me gradually dropping speed and leveling out at about 50-55mph, 60mph for a short portion near the exit, but the following didn't happen there. So I'm drafting behind this truck at 3 stripes back--throw it in neutral--70mph... waiting.. waiting.. waiting... 70mnph.. waiting.. waiting.. 70mph.. waiting.. finally it starts to drop to 69 and then slowly to 65 at which point I put it back in gear to close the sight gap that's grown. I didn't time it, but this in neutral draft lasted about 30 seconds. I found it pretty remarkable and it confirmed my other experience I've mentioned a couple times on this forum drafting with the Prius. So it is my belief I'm using roughly the same amount of fuel at 70mph drafting three stripes back (roughly 125 feet) as compared to not drafting at 60mph. I wouldn't be surprised if I'm using less fuel drafting at 70mph. If I was in neutral at 60mph and not drafting that truck I would be steadily losing speed--at 70mph, it took about 20 seconds before I started to lose speed, and I didn't pulse right before putting it in neutral to create momentum--I was driving along at a steady rate and felt that I was being pulled so I put it in neutral expecting, at 70mph, the draft wouldn't be strong enough to hold me in place and I would slowly drop back. It sometimes felt like there was a sweet spot, as in this just mentioned example. I wonder if there is and how many feet variance it has. (say 110-140 feet)
All this is confirmed by the post Holycow referred to:

"notes from this mornings commute...

on a 2-3 mile stretch on a constant downward grade at ~68mph (via gps)
I noticed the MDF stated I was getting ~57mpg's in an open lane.
Behind a box truck with a 1.5 count I dropped to ~50 mpg's.
Behind the same truck with a 3 count I jumped up to 75-80mpg's and sustained that until I pulled out from behind it.

The grade was very constant and I was moving within the draft and keeping a specific distance and the exerted effort of the car was noticable.. but I tested this a few times, followed that truck for ~18 miles and noticed the 3 count was critical to making the drafting work; too close and it actually hurt performance slightly, too far back and it hurt alot.. that 3 count rule..

JUST RIGHT...

thanks guys..."

So, too close meant less effective draft for him.
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So there you have it. 3 stripes the charm.
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Old 05-09-2008, 03:05 PM   #140
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Quote:
Originally Posted by 1993CivicVX View Post
All this is confirmed by Holycow's post:

"notes from this mornings commute...
JUST RIGHT...

thanks guys..."
So, too close meant less effective draft for him.
To re-clarify, that was not my post, but a post I brought in from another forum.
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