I accept pitch over is the limiting factor – I just think its not as limiting as you think. your .67G is presumably a calculation from cosines and stuff. I think you can move the CoM ( if you must) further back and down than you think and its not a static thing its dynamic. From a simple calculation you such as I think you have used you shouldn't be able to slow a unicycle at all as the CoM is above the contact patch

had a bmw driver run a red light this morning on me and about 4 other cyclists all taking off from the same cycle box at the traffic lights

the fat f*ck laughed at us then proceeded to run the red on the pedestrian crossing 5 metres along, nearly taking out a woman

I think braking is slightly more complex than size of contact patch. I can quite easily lock my front wheel on my MTB on the road without pitching over, ESPECIALLY if I put my weight back.

Now I ride motorbikes and have had many close encounters of the cage driver kind.

Yesterday infact I was nearly killed by a lambo racing me off the lights and then cutting infront of me and 4 others on a roundabout infront of a police camera van. which caught it on tape bu because nothing happened.. wasnt bothered. If I hadnt gambled the amber to beat the Lambo and my friends not thought me the fool and done the same instead of sitting on the line they'd of been splattered by the kid in the lambo.

On other occasions I've both collided and avoided cars.

Upon colliding i suffer pain, insurance excess, eventual compensation and a disrupted life possibly even the threat of a court case for speeding etc as the perceived speed of a motorcycle is greater when the cage driver glances last minute at the small, often loud object.

Upon avoiding I have to fix my own bike (if i binned it) suffer the pain and the financial short term loss (no ongoing raised insurance expense)

So from that point of view they're about equal so I'd just go for whichever you think will hurt less.

In your case I'd probably just check whatever's down that side road on a regular basis for the car. Report the car driver driving off to the police and hope to get their reg at some future date.

remeber dodgeball rules prevail
Dive Duck Dodge!
Simple

25mph on corstorpine seems reasonable to me on a quiet day, cars or motorbikes would have been doing more, yer speed was fine IMHO.

You did well to stop and you did well to avoid the red mist club of chasng them down and mouthing off.

There are more tales of BMW drivers being responsible for near death experiences or bad driving, I never see the same about say Ford Focus of Golf drivers and it makes me ponder … I think we all have impressions of what a BMW represents, to the owners it seems to mean, look at us, havent we done well. To non owners it seems to say, theres a to55er who thinks hes better than us. I am sure there are exceptions to this but as a generalisation it seems to hold some water.

.. wish I'd done psychology for my degree. lol.

think braking is slightly more complex than size of contact patch. I can quite easily lock my front wheel on my MTB on the road without pitching over, ESPECIALLY if I put my weight back.

with motorcycles you're taught to brake 50/50 in the wet and 75/25 in the dry. front and rear respectively there.

I'd of grabbed the back and swung the back of the bike into the car. I'm a bit naughty like that though.

Well we are at least discussing the interesting bit then, TJ, rather than trying to argue about something that is accepted.

From a simple calculation you such as I think you have used you shouldn't be able to slow a unicycle at all as the CoM is above the contact patch

Not at all – I accept the unicyclist moves their CoM (that is after all how you balance at all on one of those). I also accept it is possible to move the CoM on a bicycle, and that the calculation must be done when the CoM is moved as fear rearwards and down as possible. I just don't accept it's possible to move it that far back and down from a normal riding position.

I'm basing that on the assumption of the normal position being a roadie in the drops – if your normal position is more upright then you can move the CoM more, but you still won't do any better than the roadie does (it's just that your initial position is worse). The only possibly dodgy assumption is the use of a full height saddle, but then that's presumably what you use on the road?

It doesn't actually involve any complicated trig calcs at all. Simply consider where the CoM is relative to the front tyre contact patch in both horizontal and vertical directions. The limiting g is the horizontal distance divided by the vertical one – ie for 0.67g, your CoM height is 50% more than the CoM distance behind the front axle.

I can quite easily lock my front wheel on my MTB on the road without pitching over, ESPECIALLY if I put my weight back.

Yeah, I mentioned that possibility in the post I linked to above. It's because knobbly tyres have less grip on tarmac than narrow slicks, due to squirm, and very small actual contact patch. I should be very surprised if you couldn't skid a proper spiky mud tyre on road (when I used Panaracer Spikes you could feel them walking sideways when cornering on tarmac – was very disconcerting!)

All that means though is that you stop even more slowly.

ti_pin_man – Member
25mph on corstorpine seems reasonable to me on a quiet day, cars or motorbikes would have been doing more, yer speed was fine IMHO.

You did well to stop and you did well to avoid the red mist club of chasng them down and mouthing off.

There are more tales of BMW drivers being responsible for near death experiences or bad driving, I never see the same about say Ford Focus of Golf drivers and it makes me ponder … I think we all have impressions of what a BMW represents, to the owners it seems to mean, look at us, havent we done well. To non owners it seems to say, theres a to55er who thinks hes better than us. I am sure there are exceptions to this but as a generalisation it seems to hold some water.

.. wish I'd done psychology for my degree. lol.

The only two cars I have actually been hit by were a Focus (who knocked me off) and a Golf (who I went into the side of, but stayed upright).

ti_pin_man – Member
25mph on corstorpine seems reasonable to me on a quiet day, cars or motorbikes would have been doing more, yer speed was fine IMHO.

You did well to stop and you did well to avoid the red mist club of chasng them down and mouthing off.

There are more tales of BMW drivers being responsible for near death experiences or bad driving, I never see the same about say Ford Focus of Golf drivers and it makes me ponder … I think we all have impressions of what a BMW represents, to the owners it seems to mean, look at us, havent we done well. To non owners it seems to say, theres a to55er who thinks hes better than us. I am sure there are exceptions to this but as a generalisation it seems to hold some water.

.. wish I'd done psychology for my degree. lol.

The only two cars I have actually been hit by were a Focus (who knocked me off) and a Golf (who I went into the side of, but stayed upright).

I had a book in the 90s which recommended trying to lay the bike down on its side by skidding the back wheel rather than t-boning a car that pulled out in front of you like that. I'm not sure I much like that idea either, but the author reckoned you would then slow rapidly due to bike and body friction on the road and would have less chance of breaking yourself – although you'd get badly scuffed.

If you have enough time/space to do this, I reckon you've got enough distance to stop/swerve.

Better – skid the back wheel around, bringing you parallel with the car, and fall into the side of it. Crumple zones are great. 🙂

Got a static CoM test procedure for you, TJ – not sure if you'll like it! What you need is an inclined ramp with variable incline that you can fit your bike on – I guess a plank and some bricks might work. Just raise it to a fixed incline (I'd suggest starting with the distance up being 0.67 of the distane along 😉 ), sit on your bike on it, and see if you can get your weight far enough back and low enough that you don't tip over. You'll probably need one or two assistants for this!

I'd suggest that's a tad more scientific and repeatable than a stopping distance test, which will almost certainly result in a longer distance than is theoretically possible if you were skilled enough to do a rolling stoppy with your back wheel just touching the ground.

Are we talking about the same Corstorphine High Street? It's only about 200 yards long as it starts just before the primary school and finishes at the right turn where it becomes Saughton Road North. There is no bus lane either.

St. Johns Road is pretty dodgy though, especially West to East as it goes from single to dual lanes several times and the number of lanes is pretty ambiguous in places too.

Fiddlesticks. I just lost a post.

Right been out to test. You accept that whether the limiting factor is skidding or front wheel lift is about position of CoM? I am talking about an MTB with high bars, short TT, rearward weight bias and discs with 2.1 sticky tyres – cos that is what I ride.

Very unscientific and inaccurate measurements but I have done my best to be fair.

Test 1 – flat braking surface ( but hill to build speed) 30 mph at least approach, greasy wet road. 48 feet including a front wheel lockup about 8 ft.

Test 2 – in an old railway tunnel to find some dry tarmac. 1;30 downhill slope
Test 2 – 44 feet but loads more to come
Test 3 24 ft
test 4 26 feet small lockup front
test 5 22 feet – almost at max. Front tyre squirming for grip in that 5% slip zone where braking is greatest but rear wheel still on the floor
Test 6 – mahoosive front lockup. Kacked me pants. Time to go home.

2 – 6 where all around 30 mph – possible a bit less but well over 25 mph. measurement done with feet. Accuracy low to say the least but the ballpark is right and that is rather better than you thought.

Of course I was ready in position as I passed the line to start breaking – arse over the rear wheel and set up for it. On dry shellgrip I am sure I could do better.

So the answer – on an MTB when you can get the CoM back and down and you have wide tyres I remain convinced that the braking distance can be less than a car from 30 mph.

Aracers static test easy peasy mate. Just went and measured it up. Wheelbase 45 inch, make a 45 long ramp with a 30inch rise. Very straightforward to balance a bike on that stationary

edit – is there a mistake in your challenge- thats only a 30% slope – I think you meant a 60% slope where the height is 1.5x length. That would be tricky but perfectly possible

Your mistake was belting down an urban street and not backing off when you saw a car at a junction. Was the driver looking your way? Was he on the foot/hand brake or on the clutch? Had he just let go of the footbrake in readiness for pulling out? Was a small gap in traffic (other than you) opening up requiring him to accelerate hard to get out?

You need to know the answers to all these things to avoid accidents!

the other thing to do is watch the top of the front wheel – thats where you see movement first.

2 – 6 where all around 30 mph – possible a bit less but well over 25 mph. measurement done with feet. Accuracy low to say the least but the ballpark is right and that is rather better than you thought.

Innocent Railway?

I like the testing. I don't like the accuracy. It does look like you're getting more deceleration than I was expecting (short TT and presumably short stem are the crucial factors I hadn't allowed for). Still not that convinced you're doing better than a car, given if I assume 25mph (no speedo, so speeds are a guess, hence I'll take the lowside), and assume 10% measurement error, then that "22ft" stop could be no better than 0.85g

Wheelbase 45 inch, make a 45 long ramp with a 30inch rise. Very straightforward to balance a bike on that stationary

Yes, but how high can you lift the back and still balance (that's only proving you can do 0.67g, which I was expecting you could)? Seriously very interested if you can do this. Though having thought about it, is your front wheel touching the ground in front of the ramp (your assertion that you could do 60% implies that!) – that changes things somewhat – you need to be balancing on a tyre contact point on the ramp.

TJ – I look for the suspension moving as the brakes come off and torque goes into the front wheels.

I remain convinced that the braking distance can be less than a car from 30 mph.

No chance. You can stop in no time in a car from 30mph with decent tyres, ABS etc.

Molgrips – I can stop in about 20-25 ft from 30 mph from the ( very unscientific) testing I did above. I remain convinced that this is true. I suprised myself how quickly I could stop. Most people I have seen ride can't use the brakes properly.

Highway code say 45 ft from 30 mph. Modern cars can easily beat this but get below 30 ft? Perhaps but so can I on a bike

Aracer – innocent railway indeed. I accept accuracy is low. Speed guestimated by spinning like a loon in 36 / 11 which from using a speedo equates to around 28 – 34 mph. using 25 mph as the figure for caluculations seems fair. Measuring the distance and where I started braking from is also hugely approximate. Say under 30 ft from over 25 mph and I think that would be very conservative.

I was suprised just how much I could brake and that I could lock the front wheel on tarmac. Hanging right over the rear wheel tho with nads on the tyre just about and chin halfway along the TT.

I think you simply did not allow for the fact it is a dynamic system with the CoM moving around hugely

Edit – of course stomping on the brakes in an ABS car requires no skill. I pride myself on being very skilled at braking have practised reaching the limit and exceeding them many times until it is in muscle memory and I still locked the front twice giving longer stopping distances. so hypothetically 4 times out of six I missed the car, 2 times in 6 I hit it

I think you simply did not allow for the fact it is a dynamic system with the CoM moving around hugely

I just didn't think you could move it that much – I think you're moving it more than I expected due to how far back your handlebars are relative to the front axle (which is the crucial measurement), but still not that convinced you can move it enough.

The trouble is, 30ft from 25mph is only 0.7g, so right down where I was suggesting in the first place (and worse than the cars!) I accept you do probably do a bit better than that, but then the car decelerations are based on stopping from 60, and I'm also convinced they will do better on the 30-0 bit than the 60-30 bit, so their figures are pretty conservative. I'll have a go at a test in my car to see what I come up with for that.

Ok – Just make sure I am behind you not infront when you test.

Highway code says 45 ft from 30 mph – but modern cars can beat that. 30 ft would be reasonable for a car from 30 mph I think – or about what I can do from the above figures. Without proper measuring kit we ain't gonna get much better figures.

Taking the best of my figures I stopped in 22 ft from 30 mph. 🙂 Much quicker than a car. ahalf the highway code distance. plenty of inaccuracy there tho. Taking a large allowance for error(30 ft from 25 mph) I still beat the figure you stated originally and I am sure I did better than that.

Want to meet up to try for more accuracy?

Release the brakes at the last moment and make sure you hit the car ( gently)twist the bars so one end of the bars hits the car. He wouldn't have been blase with a nice handlebar end dent in his car or a nice scrape down the side.

That generally annoying militant cycling advocate Richard Ballantine used to suggest something similar about throwing yourself over the bonnet of a car and I remember even then that I'd never read anything so stupid (although some posts on here run it very close…)
If you can plan and execute such a manouvre, in the fractions of a second that you're trying to control a bike to avoid an accident, then you're capable of avoiding even a near miss in the first place.

absolutly agree crazy legs. I have done this twice – once I could have easily avoided the accident ( but it still would have been a very near miss)but was so annoyed I basically threw the bike at the car at 2 mph. I fully intended to get the driver to pay for a posh new wheel. she was so shocked and apologetic and I felt so guilty that I let her off as it were.

The other time was a glancing blow. I couldn't avoid the hit totally but I made sure the car got a good scratch from the handlebar end rather than me hitting the ground or the car.

I'm not paying any attention to the HC official figures – they're based on the same car capabilities the 70mph limit was set for 😉 Gave my source earlier http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Kinematics/BrakingDistData.html – which suggests a BMW M3 can manage a 1g stop (which is what 30mph in 30ft is). There's some other car (they don't mention what) which can do ~5% better than that. Though as I've mentioned several times, a 1g average from 60mph implies >1g from 30mph.

Have to admit, from what you've said I'm no longer completely convinced you can't manage it though, at least compared to something more ordinary than an M3.

My god – a debate on here that someone changes their mind 😯 I have seen sports motorcycles with high CoM and no abs tested at over 1G and I know that from the seatofthepantsometer I can stop a bike as quickly as I could my motorbike

Normal car without ABS and with eco ( licorice) tyres and skilled biker ready for the stop – biker wins.

Sporty car with ABS and sticky fat tyres, inattentive biker – car wins

Real world – it hurts to hit something hard. Don't do it.

I'm willing to perform the "normal car" 25-0 test tonight if required?

, ABS etc.

does nothing but make stopping distances longer IME.

I wondered what the smell of burning rubber was in the burgh today.

Tj earlier

Coffeeking – do it – it will be interesting. 30 mph would be better as I am sure I was over 25 ( but quite possibly under 30). Try to have my superhuman accuracy as well 🙂

a debate on here that someone changes their mind

Careful – I was just admitting that my assumptions might be wrong 😉

It also struck me that you'd admitted you're assumptions were wrong (you weren't expecting to be able to skid the front tyre?)

I'm willing to perform the "normal car" 25-0 test tonight if required?

How were you planning on measuring speed and distance – something that struck me I needed to get right having criticised TJ's methods? Speed via GPS, but distance? Won't be doing any testing here tonight – roads are damp enough I'd be lucky to manage HC distances.

I'm a bit naughty like that though.

Why didn't you told us that BEFORE the BBB 😉

I think that taking in consideration a change in the CoM of the bike is not representative of what happen in the situation described by the OP.

I think that taking in consideration a change in the CoM of the bike is not representative of what happen in the situation described by the OP.

What's the OP's situation got to do with anything?

well tj argues that he can stop his bike better than a top gear car because he can put his CoM on the back bla bla bla bla.
Probably very well true during a brake test I give you that. However when a car pull in front of you I have very much doubt that you can stand up move your body on the back wheel and then brake… You are more likely to start braking first praying the JFC that you'll be able to stop…

aracer I wasn't really thinking I would lock the front wheel on dry tarmac ( but wasn't surprised to do so). I think the reason I did is I got the weight back before hitting the brake and snatched at it rather than squeezing so got to maximum braking force before the weight transfer to stick the front wheel down.

The other thing I was surprised about was how inconsistent I was

Criticise my methods? How dare you! I had my seatofthepantsometer calibrated just last year.

Edit: Juan – I still think even in real roads conditions I could beat a normal run of the mill car in stopping distance. I fully accept that what I was doing today was not the same thing at all tho. However when hitting the brakes I stand up and move back automatically. Don't you? . A motorcyclist like you should be better at braking than most cyclists who seem to me to neglect that as a skill to practice. faster / more skilled riders than me cannot brake hard as I can from what I have seen

erm, do you take any offence if I said that after having ridden with you I would not categorise you as skilled rider 😉

Plus I usually dont touch the brake on angela I grind the footpegs instead too 😉

Just to go back to the original subject for a moment…

Most modern cars, in particular German ones, have very wide A and C pillars. The wide A pillar blocks a pretty good chunk of the road when looking left/right at a junction – very easy to lose a bike in the blind spot created. Granted the driver should compensate for this…

As for hitting the car or going over – I tend to agree that in this situation you react, you don't think, and every fibre of your being will be pulling brake levers!!!

The wee wave was probably a very embarassed and shocked reaction by the driver who just looked up and saw a bike; from apparently no where. They just didn't know what else to do – it was probably an appology wave more than anything.

All said and done though – you controlled the bike and stopped: no injuries, no damage. So you live to ride another day. I'd say that was a good thing?!

Juan – unskilled I would take offence. slow and scared I wouldn't. Less skilled than most of the folk I ride with would be quite fair however 🙂 How do you define pedantry?

anyhow you hardly saw me ride as you dissapeared off into the distance.

Well I did a bit of testing on the way in this morning with dry roads. I reckon my speed accuracy was a lot better than TJ's (have a speedo, and I know roughly how much it overreads – was within 5%), though my distance accuracy was about the same. Anyway I stopped from 30 in well under 2 car lengths, say 8m or 27ft. Was actually surprised I could stop that fast, and on that basis I've changed my mind back again and reckon TJ would have run into the back of me 😉

Better that than you run into the back of me 🙂 Sounds like you measuring is as accurate as mine as well