dream super bike

[Licramite]

I,m looking to build a bike , something that will do 40-50mph.
looking for a conventional bike shape (not a recliner - thats a bed on wheels)
the largest normal racing chainring is 56teeth that gives a max diistance for one complete revolution of 9.97m
an 85tooth chain ring is nearly the same radius as the pedal crank - these are commercially available
that would give you a revolution distance of 15.12m
thier is a system that uses 2 chainrings working together but I don,t undestand it.

I have a 54tooth chainring and have experimented in not changing the chainring just the rear gears to maintain speed on hills and that works - to a great extent, some hills defeats me.

the world record was set by a recliner at 82mph, don,t know what the fastest speed acheived on a conventional bike is.
seen recliners encased in body shells but these arn,t normal on road bikes.

have considered having two sets of chaindrives , on left side a conventional 2 ring 42-54 chainring and on the right an 85 chainring with a switching mechanism so you can engage one or the other.

I reckon on a 85t chainring you could acheive 30-40mph , young and fit 40-50+mph.

just wondering if anyone knows of deveopments of this being already done or acheived?

 

[black'n'yellow]

I,m looking to build a bike , something that will do 40-50mph.

A conventional bike will do that in the right circumstances. You don't need mental gearing either - I've ridden in road race bunches on the flat at 40mph on 50/12.

 

[Peter Armstrong]

I can hit 40-44 mph down hill on my 22 year old, 12 gear steel road bike, I carnt get any faster due to the gears. I have no idea what gear ratios are or chain rings etc are. I dont get it

 

[fossyant]

Hang on, are you trying to do this on the flat at a sustained speed unassisted ?

Then having a 85t chain ring won't help. A bike is powered by an engine, that is you - you've got to power it.

Even Mr Cavendish uses conventional gears in a sprint.

 

[Licramite]

Hi
this is all good to hear, I have practicly no experience of speed cycling. but I suspected 30-40mph as a top speed for the flat & prolonged . -

and yes the engine is you, but can you get the max power out of your limited leg power.
starting on an 85t ring would be flamin hard so you need a smaller set to get going and for going up hills
but once you have momentum and its realitivly flat or even in your favour downhill an 85t ring would give emense power,
the question is would the resistance of the 85T be greater than the power you gret from the smaller ring considering the resistance. or is it more efficient for a smaller ring but turned more often as the resistance is less.

I admit on this bike much of the cycling would be done on the 56/42 rings as the ideal situation for the lager ring would be limited.

does any of you recumbant guys have experience of this.

tanks for the replies this is useful stuff.

 

[fossyant]

You are barking up the wrong tree, I am afraid.

If you are riding a conventional bike, wind resistance is an issue - a very big issue. Unless you are called Bradley Wiggins, you will not sustain 30 mph over a set distance.

A very good amateur cyclist can time trial at around 25 mph for a sustained hour. They all use 50-53 tooth chain rings.

Chain rings don't give you power, and mechanical resistance is small on a bike compaired to aerodynamic resistance. Even Chris Hoy (he of very large legs) will only use a chainring in the 50's, and the speed he does on the track.

What is your goal - is it to make a HPV (human powered vehicle) ?

 

[fossyant]

I can hit 40-44 mph down hill on my 22 year old, 12 gear steel road bike, I carnt get any faster due to the gears. I have no idea what gear ratios are or chain rings etc are. I dont get it

Aero tuck, and with the right hill you will do 50-60mph, but you'd not be able to pedal even if you had the gears, the buffeting and shifting on the saddle from pedalling would scare you.

 

[Rickshaw Phil]

I'll start by admitting I am no expert, but I believe the biggest problem you are going to face is wind resistance.

If you double your speed the wind resistance is four times greater, so if you intend to try and ride at 50mph you face four times more drag than you would at 25mph. Effectively this means that even if you can gear the bike as high as you are suggesting, you are likely to be unable to generate the horsepower to overcome the drag.

In a pack this becomes easier as riders are able to go faster when within a slipstream and by regularly changing over the rider(s) at the front it is possible for a peloton to go faster than a single rider.

This is the reason why a recumbent cycle holds the current world speed record - they are much more aerodynamic as standard and if fitted with a fairing can reach the kind of speeds suggested fairly reliably.

Edit: Cross posted.

 

[Licramite]

yea that was my next issue, wind resistance and stability.
the idea is produce a bike that will norm at 30mph. - and burst upto 50-60mph

up gearing will give the power , but increase in resistance is the killer. methinks one will cancil out the other.
will have to look at changing the geometry , maybe recunbants of CV2 is the answer or more a motorbike position. , but thats certainly not what I was looking at.
mayhap a motocycle windscreen would work. or a front fairing.
I will look up wind tunnel tests on bikes.

cheers ,
many brains make like works.
and
a dog is for lunch not just for breakfast
(two misread bumper stickers)

 

[Rob3rt]

yea that was my next issue, wind resistance and stability.
the idea is produce a bike that will norm at 30mph. - and burst upto 50-60mph

up gearing will give the power , but increase in resistance is the killer. methinks one will cancil out the other.
will have to look at changing the geometry , maybe recunbants of CV2 is the answer or more a motorbike position. , but thats certainly not what I was looking at.
mayhap a motocycle windscreen would work. or a front fairing.
I will look up wind tunnel tests on bikes.

cheers ,
many brains make like works.
and
a dog is for lunch not just for breakfast
(two misread bumper stickers)

Go and have a think about that!

 

[black'n'yellow]

This is the reason why a recumbent cycle holds the current world speed record - they are much more aerodynamic as standard and if fitted with a fairing can reach the kind of speeds suggested fairly reliably.

it's also the reason why - in over 100 years of bicycle design - that nobody else has ever succeeded in achieving what the OP is suggesting..

 

[black'n'yellow]

the idea is produce a bike that will norm at 30mph. - and burst upto 50-60mph

not sure if you are grasping this or not....

 

[Andrew_Culture]

I know that extreme examples are the death of good forum discussions (see Godwin's law) but I'd like to give you an example of how irrelevant the size of rings can be (and this is anecdotal, I'm a total cycling numpty):

Until a few weeks ago I rode a touring bike that was built nearly forty years ago, the biggest front ring was 50t, the smallest rear ring was 12t (I think), it had chubby touring tyres and was built for Enid Blyton style tra la la cycling around country lanes in search of ginger beer and mysteries, but on a decent downhill I could get it over 40mph with some pretty hardcore leg work.

I switched the venerable tourer for a single speed bike that was built by discarded parts donated by friends sympathetic to my chronic fiscal embarrassment. The single speed has a very worn down front ring of 52t and a rear ring of 18t (I think), approaching a moderately steep hill I decided there was no point in pushing so I tucked in my arms and legs and squished my considerable frame into an aerodynamic position that I thought made me look like Wiggins (but in reality probably made me look like an ape in a fat suit attempting coitus with an unwieldy and unwilling ancient bit of mathematics apparatus). I thought nothing of it, but when I got home I was astonished to find out I'd cracked down the hill at nearly 37mph, for zero effort barring making a noise of child-like glee.

The point of this post? Well if you see what looks like romantically inappropriate simian whizzing down a hill making a noise like escaping gas you'll know it's me.

Now what were we talking about?

 

[Rickshaw Phil]

it's also the reason why - in over 100 years of bicycle design - that nobody else has ever succeeded in achieving what the OP is suggesting..

Indeed.

up gearing will give the power , but increase in resistance is the killer. methinks one will cancil out the other.
I will look up wind tunnel tests on bikes.

Upping the gearing will not give you more power, it will just give you higher gearing, which will require more power to turn. Added to the extra wind resistance you will find that you will run out of power before getting anywhere near your target speeds on the flat.

You mention looking at motorcycles - if you do you will find that motorbikes are actually not very aerodynamic. (I seem to recall reading that a motorcycle has a worse Cd than a bus).

 

[Licramite]

does anyone know what the top recorded speed for an upright bike is- not traveling behind a vehicle (thats about 132kmph) - ?

I,m not after records, but the latest landspeed record was 1989 so new design is coming up all the time,