braking distance car vs bike

[pedallingpasty]

which leads to the question of whether a front suspension mountain bike will brake better as the weight will shift forwards and down rather than arching over the front wheel.

Reckon you could be right there. When i first got my hardtail mtb with cantilevers and ali rims, tested brakes ( as you do) on tarmac and was surprised how hard i could use front brakes whilst still under good control due to front suspension compression. Have now fitted hydraulic discs to same mtb, tested them and bottomed out on suspension. Would have looked quite good if the rear wheel didn't lift, swing around and hit garage door
So maybe a disc equiped hardtail could do quite well against a modern car, without denting his door of course.

 

[summerdays]

Nice one coruskate, good explaination there. Didn't think of that one.
Think we only really used F=uR to show the importance of lubrication and how to shift a stationary object, can see the problems of using it to show how to slow something down.
But the formulae is quite good in showing why we cyclists are always going to lock up the back wheel at first when emergency stopping due to the weight shift forward over the front wheel ( have only locked the front wheel when going backwards, don't ask ). So this raises the thought as to wether it best to shift your body slightly over the rear wheel when slamming on your brakes to increase frictional force, so we can increase the braking on the rear wheel slightly to stop in a shorter distance?
Will also have the advantage of moving your face slightly further away from the obstruction.
Think a bike could be ok against Davidc's Ford Anglia, but could really compare against a modern car due to its abs etc.

Err the technicalities of this conversation is going over my head. As regards to braking I was taught that to stop in an emergency you should shift your weight backwards.

 

[pedallingpasty]

Err the technicalities of this conversation is going over my head. As regards to braking I was taught that to stop in an emergency you should shift your weight backwards.

Yes you are right, its all getting a bit nerdy.
You must have had a good tutor.
So all we need now is a person willing to ride a disc equiped hardtail mtb at 30 mph with their ass hanging over the back wheel to prove our theory.

 

[marcw]

Yes you are right, its all getting a bit nerdy.
You must have had a good tutor.
So all we need now is a person willing to ride a disc equiped hardtail mtb at 30 mph with their ass hanging over the back wheel to prove our theory.

Chuck a recumbent in there too to see if the extra weight over the back wheel and lower CofG means they can stop quicker.

 

[Davidc]

I was taught that to stop in an emergency you should shift your weight backwards.

So was I - cycling proficiency circa 1959! Was also told to only use the front one to stop fast.

 

[mr_hippo]

Forget theory, formulae, the coefficient of this, the cosine of that and the price of fish, practical demos are much more fun!
Experiment
Car brakes v bicycle brakes
Equipment:
Long, long stretch of road with a reasonable surface
Average family saloon e.g. Astra, Escort
Average bicycle - road, hybrid or mountain
Measuring device
Cycling helmet - optional
A 'start point'
Driver
Cyclist
Referee
Method:
Drive the car towards the start point at a steady 30mph, At the start point, apply full braking force for an emerbency stop. When the car comes to a complete stop, apply handbrake and exit vehicle.
Cyclist will then ride at 30mph to the start point and then apply full braking force for an emergency stop.
Possible Outcomes:
1) The cyclist stopping distance is shorter, he stays in complete control and upright then puts his feet on the ground,
2) The cyclist stopping distance is longer and the rear of the car is 'customised' by rider and machine; if this happens then the referee will call 999 for assistance.
3) Rider and machine are in an unstable position and part company; again the referee's assistance is needed

.Follow up experiment:
How does a cyclist's BMI affect his coefficient of bounce?

 

[gaz]

If my brakes are tweaked right, i recon i could out brake some cars easily. Just like i can out accelerate some cars (to a certain speed)

 

[marzjennings]

If you get your weight all the way behind your saddle and low to the back wheel, pushing all your weight through your pedals and not the bars, you can pull on both brakes equally, coming to a stop a lot quicker. Bit of a mountain bike technique, but also works on the road.

[media]

]View: http://www.youtube.com/watch?v=-RNAYR3KPIg&feature=player_embedded[/media]


Watch the guy to the right at about 19sec and 61sec. Put's himself right behind his saddle, coming to stop quick enough to avoid the pile up.

 

[smeg]

lol are you going to volunteer yourself for that braking test Mr Hippo? I Don't fancy that myself, 30mph is bloody fast!

 

[mr_hippo]

lol are you going to volunteer yourself for that braking test Mr Hippo? I Don't fancy that myself, 30mph is bloody fast!

Who, me? I know I can be a bit daft at times but not that daft! However, I can volunteer a few few forum members for the job.

 

[DavieB]

So what we are saying in on paper it should be possible. And we have a video of a professional cyclist stopping very fast on a £10000 sports bike lets compare that to a sports car...

I still dont think I or the average cyclist can stop faster than the average car.

As for the ABS being slower to stop you than not having it, that was true 15 years ago modern abs systems are extremely good at what they do.

 

[mark i]

We could now really complicate the matter and add in the wet scenario. I think that one is a no brainer. Modern disc systems "wipe" the discs quite frequently to keep them dry-ish. I need a couple of meters to "wipe" my rims dry enough to brake in the wet. End result is I leave lots of space!

I think that the braking performance is not so disimilar, I think that the variability in reaction time is a bigger issue, along with the ability to press the brake pedal / lever to it's limit of grip!

 

[marcw]

agreed there are many variables. Reaction times alone mean that if you are only a metre away from a vehicle and it brakes unexpectadly you're likely to hit it unless you can get down the sides, the back of buses should be covered in sponge to aid drafting.

 

[HJ]

I have never had a problem with stopping quicker that the vehicle I have been drafting, I am more worried by car try to wheel suck me, I know I can stop faster and I don't have brake lights so they are slower to realise them I am stopping...

 

[Number14]

Highway code figures are not accurate anymore (they also include thinking distance). Your average car now has abs and discs all round and some have massive tyres, compared to no abs and drum brakes back when that was written. I reckon cars can slow faster than me when im on my road bike.

Im no expert but I reckon cars can stop faster.

Mmmm, that's a presumption for some drivers.