Overtaking

[Wossname]

My reason for starting the subject is that I reckon riders have no idea how much time and room they need to complete an OT, and doing the sums might surprise you as to how long - time and distance - you do actually need. That’s without considering matey about to come round the next bend towards you, or a hidden car OTing the approaching tractor and trailer you thought would give you plenty of both.

We all crack on if things are right, and the number of secs/metres used will be less than if doing it ‘by the book’. THAT figure might still be surprising, and I’m pleased to see nobody else has worked it out yet, in spite of me providing the necessary numbers. Makes me feel less inadequate!
PS: another assumption: bike starts the OT after following the target at the same speed, so not a ‘momentum’ OT.

PPS: “Out, out, damn spot”! I can do that too.

[Rockburner]

'ish'

That advice is often taken as meaning 'go as fast as you can't.

But potentially that means that if anything goes wrong you'll have a higher speed differential from the vehicle you're overtaking and travel further before taking any action.

Worst case is that it encourages using smaller gaps with reduced margins.

And worth noting that 'overtaking' is high risk, and one of the three 'gotchas'. RoSPA noted:

" In Clarke et al’s (2004) study, in 16.5% of accidents where the rider was considered partly or fully to blame, the rider was overtaking another vehicle."

Especially on a multi-vehicle overtake. You’re overtaking 4 cars, move out, accelerate, get past 1 and 2, car 3 decides to pull out to OT car 1 and your speed differential seriously narrows your options.

Been there.

The speed differential was the least of the problems when car 3 cuts up car 4 and causes it to spin in front of you. In my case car 4 was a Landy, and IIRC being centre-punched by a BMW did it no favours whatsoever. Approx 20-25mph impact: Bike written off (telelever wishbone is mounted in the engine cases), Landy written off (fuel tank was ruptured), cue me lying in a pool of diesel for 10 minutes.

[Beancounter]

FWIW which is likely very little, when I was going on RoSPA rides I was told any speed differential of 15mph or lower mean the overtake would need to be rushed and therefore not a good idea (in a NSL zone). I know that on 'open rides' this was not put into practice by many of the group.

[Horse]

I know that on 'open rides' this was not put into practice by many of the group.

Years ago, someone explained to me that "IAM is 'safely, go fast', RoSPA is 'go fast, safely '.

That said, another friend stopped going on IAM group rides after there had been crashes during three of them

[Beancounter]

I know that on 'open rides' this was not put into practice by many of the group.

Years ago, someone explained to me that "IAM is 'safely, go fast', RoSPA is 'go fast, safely '.

That said, another friend stopped going on IAM group rides after there had been crashes during three of them

I'm in two minds about IAM/RoSPA. I did 5/6 observed rides with me and feel that my riding improved but there were other concerns - there seemed to be some disparity between observers, commentary didn't match the scoring system and the group rides that I did (only two of them) left a lot to be desired.

[Horse]

To a certain extent, once you have the basics covered, the 'must' and 'need' to know, you get into the 'polishing' - often with [relatively] minor variations of personal opinion or from the instructor's background. A lot of that stuff isn't documented. I learned more from a two lecture from a police instructor than at any other time.

Unfortunately, sometimes those basics can get overlooked. The pursuit of 'progress' brow-beating safety. 'Overtaking being an example of where that happens. 'Chasing the limit point' is another.

Are you actually thinking of doing more?

[Cousin Jack]

I'm in two minds about IAM/RoSPA. I did 5/6 observed rides with me and feel that my riding improved but there were other concerns - there seemed to be some disparity between observers, commentary didn't match the scoring system and the group rides that I did (only two of them) left a lot to be desired.

I had (and passed) the IAM car test. I have a certificate somewhere. I actually learned a lot of useful stuff, although I also 'learned' some stuff I used on the test and then discarded. Observers were a mixed bunch, some excellent, some not. I tried to avoid the ones I thought were too anal

I started a bike course and all went well with the first observer (who reckoned I needed a bit of 'polish' but was near test ready. Then I had a different observer who metaphorically ripped me a new arsehole. Much of what he wanted me to do was alien to me, and contrary to what other Police and Police-trained riders had suggested. That group also held Sunday rideouts which were only for fully trained riders, they had a history of crashing!.

I decided not to bother with the IAM any more. Never tried ROSPA, although I am tempted to give the local group a go, A rider who I consider to be good is an instructor with them, and it might be worthwhile getting any bad habits checked out before they bite me.

[Scootabout]

To overtake or not to overtake, that is the question.

Going back to the original problem. Assume overtake is @ 60mph. Assume no time needed to attain that speed. 10 mph speed differential with target vehicle. 10 mph = c.4.5 metres per second. 60 mph = 27mps.
Therefore, time to complete overtake
= 2 sec lead-in, plus 1.5 sec target vehicle, plus 2 sec finishing off.
= 5.5 seconds.
Therefore distance
@ 27 mps = 5.5*27 = 149m.

Does that sound about right?

[Wossname]

Thanks for trying… but I’m not sure that’s right. 5.5 sec at a 10 mph speed differential seems a very short OT time to me.
The 2 sec (“safety bubble”) following distance is a distance, IYKWIM, (not the time needed to close it), which would be covered at the speed differential, not the road speed.

Struggling with logic here…

[Scootabout]

Yes, you're right. I realised after I'd posted it that it was wrong. I couldn't get to sleep for a while last night because I was recalculating it in my head!

I think it's necessary to work out the 'length' of what needs to be passed, including the 2 secs either side. Then calculate the time needed to cover that at the speed difference, ie 10 mph. Then apply that time to the overtaking speed.

If I'm right, the answer's more like 550 metres, I think.

[Horse]

Yes, you're right. I realised after I'd posted it that it was wrong. I couldn't get to sleep for a while last night because I was recalculating it in my head!

I think it's necessary to work out the 'length' of what needs to be passed, including the 2 secs either side. Then calculate the time needed to cover that at the speed difference, ie 10 mph. Then apply that time to the overtaking speed.

If I'm right, the answer's more like 550 metres, I think.

IIRC the OP / other thread mentioned travelling ... swiftly ... and 300m. No wonder it was squeaky bum time!

[Wossname]

2 sec before and after at 60 (27m/sec) =54m each x2=108, +6m for the car =113m total.
This is covered at (10mph) 4.5m/sec differential and takes 113//4.5=~25sec.
27m/sec for 25sec =675m

So…the OT takes 25 sec and needs 675m.

But that seems too long/slow. Doesn’t it? Where’s the deliberate error?

[Horse]

Ta-Dah!!!!

https://www.vcalc.com/wiki/time-to-overtake
https://www.vcalc.com/wiki/vCalc/Distance-to-Overtake

Not what I'd seen before, but may fit the bill.

[Scootabout]

2 sec before and after at 60 (27m/sec) =54m each x2=108, +6m for the car =113m total.
This is covered at (10mph) 4.5m/sec differential and takes 113//4.5=~25sec.
27m/sec for 25sec =675m

So…the OT takes 25 sec and needs 675m.

But that seems too long/slow. Doesn’t it? Where’s the deliberate error?

I think the 2 secs each side should be @50 mph, not 60. That reduces your passing time to about 21 secs.

I'll look at horse's calculator now.

[Scootabout]

Seems similar

[Cousin Jack]

Who leaves a 54m gap to the vehicle you are looking to overtake? I might well leave that distance on some roads where the chance of an overtake is small, and I am planning to follow for a mile or two, but if I am looking for an overtake I will be much closer, and looking over/around the vehicle to keep myself safe(r). 5m might be a more reasonable assumption if I can stay a little way to the offside..

Similarly getting in again, if I need to I can resume my place ahead of the vehicle within 15-20m without causing anyone any anxiety, much less than that if I have screwed up and need to get onside fast.

[Horse]

if I am looking for an overtake I will be much closer, and looking over/around the vehicle to keep myself safe(r). 5m might be a more reasonable assumption if I can stay a little way to the offside..

At what speed?

As a f'rinstance, 50mph is 22 metres per second.

That 'little way offside' hopefully is far enough to continue on past the vehicle ahead into a gap without leaving a knee embedded in its rear bumper.

[Scootabout]

Alternative scenarios need to be accompanied by calculations

[Wossname]

Who leaves a 54m gap to the vehicle you are looking to overtake? I might well leave that distance on some roads where the chance of an overtake is small, and I am planning to follow for a mile or two, but if I am looking for an overtake I will be much closer, and looking over/around the vehicle to keep myself safe(r). 5m might be a more reasonable assumption if I can stay a little way to the offside..

Similarly getting in again, if I need to I can resume my place ahead of the vehicle within 15-20m without causing anyone any anxiety, much less than that if I have screwed up and need to get onside fast.

I used 2 secs as that’s the recommended “minimum” following distance, and when you finish an OT I think it’s reasonable to leave the overtaken car his 2 sec bubble as well. I’ll accept that when you’re completing the OT you’ll be accelerating AWAY from the target so could cut the gap a bit, but only a bit. And 2 secs at 60 mph is 54 m - hence my 54m. 5 m? That’s tailgating. Crazy. I detest people who cut in as soon as they’ve passed, making me back off to give myself a bit of space again. Fairy nuff, at very low speeds you may not need the full 2 secs but concertina crashes on main roads/DCs etc are almost always the result of people driving too close.

[Wossname]

Ta-Dah!!!!

https://www.vcalc.com/wiki/time-to-overtake
https://www.vcalc.com/wiki/vCalc/Distance-to-Overtake

Not what I'd seen before, but may fit the bill.

Those calculators don’t define when your OT is finished - it doesn’t seem to allow time/space to return to your own lane. They just ask for “distance between vehicles”.

But if you put in the distance and speed parameters I’ve used above, you still get huge answers.

Are the sums all wrong?