Would you?

Topics relating to Advanced Driving in cars
User avatar
StressedDave
Posts: 428
Joined: Mon Sep 28, 2015 8:27 am

Re: Would you?

Postby StressedDave » Tue Feb 16, 2016 2:17 pm

Horse wrote:
StressedDave wrote:
Horse wrote:So, SD, you've had a few answers - what do we win? :)

My undying affection and a framed certificate saying 'I joined in a thread posted by SD'. They're going to become very rare...


Wot, no chocolate? :(

Or indeed spooning...
All posts are licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Do what you like with it, just don't make money off it.

Playtent
Posts: 202
Joined: Mon Sep 28, 2015 3:00 pm

Re: Would you?

Postby Playtent » Tue Feb 16, 2016 4:39 pm

Gareth wrote:
trashbat wrote:The overtake is off in large part because the driver has made it off - a laid back follow that inherently precludes the opportunity.

What do you think you would be doing differently, and how much time do you think it would gain you?


I'd be closing the gap from 6s onwards, watching the solid for a break and be just moving to the contact point as the vehicle in front hits 12s. I'd be out by 14s and done and dusted by between 19 - 20. I'd probably hold out through the dip looking for contact marks on the road where any vehicles have grounded so closer to 20s unless I could get back in before the dip. I wouldn't want to be out any later than 20s. The dip would be my main concern due to the speed required.

These times are based on the car in front, not the position of the following car. The over take start position is crucial and is on for around 1s, any longer and its off.

Obviously also depends on the car.
Last edited by Playtent on Tue Feb 16, 2016 11:12 pm, edited 1 time in total.

Pyrolol
Posts: 68
Joined: Sun Oct 04, 2015 1:52 am
Location: San Francisco

Re: Would you?

Postby Pyrolol » Tue Feb 16, 2016 8:07 pm

waremark wrote:I would want to gain more than 2 seconds, and to reach a peak speed of less than 90. If your maths is right, my judgement that I would have taken the overtake may have been wrong. Are you sure it is? Empirical experience suggests that if I have 16 seconds to where the view disappears I would have enough space for an overtake with a differential of not more than about 20 mph.

I will repeat an exercise I have tried in the past of using an overtake of an LGV on a multilane road to simulate a single carriageway overtake and trying to note time and distance.


Couple of things
- Peak theoretically required speed won't need to be reached in 99% of actual overtakes. Every second you continue into the overtake without a fastest-reasonable oncoming car appearing gives you more time to complete the overtake than you had at the start, so in practice you'd be slower almost all the time to avoid looking like too much of a hooligan (the +20mph you suggest sounds reasonable). This might partly be why it sounds high.
- The main issue with assessing this overtake based on the video timeline is that the video car starts out fast (mid 50s) and ends up slow (falling to ~40 thanks to the hill). An oncoming vehicle could reasonably cover ground much faster down the hill. The timeline if you went for the overtake (what matters) would look quite different. The bend after the overtake could be exited quite fast.

None of the above allows for a plan B of 'hit the brakes and tuck back in behind if something appears in the first second'. To what extent to people find themselves doing this / think it's acceptable to rely on?

I agree with playtent that starting as early as possible makes a huge difference; and is the only way to complete that safely.

Personally I would never do it in those conditions, and I doubt I would in the dry either. Having said that I do miss a lot of overtakes.

----
Painful details of my original calculation follow. Probably nobody cares, but I did it so hey.

Average Dave speed = 48mph (I guessed) gives the distance of 386m (~48mph * 18s). Target vehicle speed during the part where you'd actually pass ~=54mph = 24m/s (this appears alot later).
To avoid needing to consider complex acceleration profiles; I've simply took the overtake as jumping a certain amount forward from the target's perspective (2s is probably about as tight as this reasonably gets).
The overtake time (6s) could be estimated by matching a lorry from 2s back, accelerating to alongside and changing lane. It needs to be padded to include all reaction times and moving back in time. You can approximate an acceleration from this if you like: gaining 2s in 5s (leave 1s lane change time) means you need to gain 48m (2s * 54mph). 48m = 0.5At^2 = 12.5A, so A = 2.84ms^-2 (and therefore top speed of 5*2.84+24 -> 85mph - note that this depends on many factors not modelled here).
This means distance used until you're back in is 8 seconds of the target's speed. 24*8 = 192m.
That leaves 194m for the oncoming car. It it can cover that in 5 seconds, you crash (or abort), if not you're clear. 194m/6s = 72mph. This seems borderline for declaring 'safe' to me.

54-85 in ~5 seconds is pretty fast - my RX-8 won't do that anyway. As such I don't believe it could complete that overtake safely in any conditions. A quicker car would be able to, subject to the above (you might have to get quite close before and after).

(Am I just being annoying here? I'm genuinely unsure.)

User avatar
Horse
Posts: 1788
Joined: Mon Sep 28, 2015 9:20 am

Re: Would you?

Postby Horse » Tue Feb 16, 2016 8:49 pm

Was there a particular reason for closing up the following distance towards the end of the clip?
My own views. For better or worse :)

TheInsanity1234
Posts: 450
Joined: Fri Oct 02, 2015 8:03 pm

Re: Would you?

Postby TheInsanity1234 » Tue Feb 16, 2016 9:44 pm

Uh.

No.

But then I'm quite a chilled out driver (mostly) and often miss overtake opportunities simply because I wasn't close enough to the car in front to make it viable.

I may have gone for it if I was gaining on the car with a decent speed differential, and proceeded to do a sweeping overtake, but even then I'd be moving to the offside at the moment the double white lines ended.

Gareth
Posts: 518
Joined: Mon Sep 28, 2015 2:44 pm
Location: Berkshire
Contact:

Re: Would you?

Postby Gareth » Tue Feb 16, 2016 9:52 pm

Pyrolol wrote:None of the above allows for a plan B of 'hit the brakes and tuck back in behind if something appears in the first second'. To what extent to people find themselves doing this / think it's acceptable to rely on?

I think it's not acceptable; I even think flinching when nothing untoward could happen is not acceptable, as I was reminded (and reminded myself), recently.
there is only the road, nothing but the road ...

User avatar
StressedDave
Posts: 428
Joined: Mon Sep 28, 2015 8:27 am

Re: Would you?

Postby StressedDave » Tue Feb 16, 2016 10:10 pm

Horse wrote:Was there a particular reason for closing up the following distance towards the end of the clip?

not me driving...
All posts are licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Do what you like with it, just don't make money off it.

User avatar
Horse
Posts: 1788
Joined: Mon Sep 28, 2015 9:20 am

Re: Would you?

Postby Horse » Tue Feb 16, 2016 10:55 pm

StressedDave wrote:
Horse wrote:Was there a particular reason for closing up the following distance towards the end of the clip?

not me driving...


I'm presuming you were there at the time?
My own views. For better or worse :)

TripleS
Posts: 227
Joined: Tue Sep 29, 2015 5:39 pm
Location: Briggswath

Re: Would you?

Postby TripleS » Sun Feb 21, 2016 2:51 pm

I'd like to have had a look at this, but it tells me I need a plugin (which I don't seem to have) in order to view it so I guess that's that.

chriskay
Posts: 112
Joined: Mon Sep 28, 2015 2:08 pm
Location: Shrewsbury

Re: Would you?

Postby chriskay » Sun Feb 21, 2016 4:46 pm

TripleS wrote:I'd like to have had a look at this, but it tells me I need a plugin (which I don't seem to have) in order to view it so I guess that's that.

Doesn't it give you a link to download the plug-in?
Carpe diem


Return to “Advanced Driving - Cars”

Who is online

Users browsing this forum: No registered users and 2 guests