Rat Bikes! Pub Bikes Beaters! Frankenbikes!

correct

WDF
I would have done the reverse :
The small wheel in front and wide handlebars

Back to rat !

Horrible bikes ^

One might even describe them as 'frankenbikes', just a thought

Second one is a gravity bike

On that one, are the cranks fixed in position, or do they have a function at all? (such as a brake)

You are not supposed to pedal on one of those bikes.
You go as fast as you can and as you dare.
Maybe is just to rest the riders feet on pedals screwed on cranks instead of puting them straigth on the BB
Bike looks incomplete, as it doesn't have grips too

Yeah not really sure why they've done it that way. I guess as the TT is slanted down, when one goes up hill, the TT is closer to horizontal than a regular frame hence less uphill gravity force.

Diagram is missing the uphill gravity force and the tire buoyancy force.

In my mind, surely wouldn't you want a smaller front wheel so get a 'flat' surface?

Would love more on the gravity bike.

Does that even happen in the UK ? actual gravity racing, i am aware of the concept and have seen similar set-ups but out side of random one off races around the world it's something you never hear much about.

The crank arm appears to have the pedal insert filled, could be camera angle, could just be the pedal spindle/axle threaded in place.
The bike is ace, would love a go, with full face helmet and lots of armour for when you slide out on a corner at high speed :)

Does that even happen in the UK ?

I don't think we have hills long enough for it.

Funny how you think of Scotland being quite mountainous until you go somewhere like the Alps then it just seems like little bumps.

Yeah, I just meant did the cranks purely serve as a footrest or were they rigged up as a foot operated brake. Which the more I think about it seems like a silly thing to do.

Ah, quick you tube search turns up some 2011/12 stuff from Dalby & Cairngorm.
Seems to be attached to soap box/go kart gravity racing.

https://www.youtube.com/watch?v=DgWXPTAhdFo

https://www.youtube.com/watch?v=Jl2g4hIru5Y

https://www.youtube.com/watch?v=hNO6r-aT1yY

Don't forget dh skateboarding/longboarding ;) All part of the international gravity sports association: http://www.igsaworldcup.com/

I used to live near belchford. when I was little my dad would always turn off the engine in the truck and we would roll down that hill to see how far we would get on the flat. pretty much the only big hill in lincolnshire

This is that gravity bike btw:
http://www.cycleexif.com/mls-gravity-bike

Been looking into this.

Seems fairly underground but found some info.

Appears the bikes are based on a 127cm axle to axle wheelbase and 20" wheels, based around stock BMX bikes.
Rules are fairly simple with 4 classes, Stock unfaired, Stock faired, Custom unfaired, Custom Faired. So stock is based on an OTP BMX, custom is home build frame, Faired is with a fairing for aeros added.
Max bike weight of 34kg
No pedals, must have fixed pegs of a certain min diameter.
Full leathers to be worn and full face helmet.

Haven't found yet if there is an active sanctioned race ciruit scene in the UK, it might just be an add on to other gravity classes, luge, skateboard, go karts etc etc.

But that explains why they all have little wheels, not sure if i fancy 50mph on bmx wheels :) and a twitchy short wheel base :)

Would the lower centre of gravity go some way to making a short wheel base more stable? Not really sure of the specific physics involved there.

I can't answer that for sure AlexD.

Still looking into it, there are several variations on rules. The BMX size seems to come from an old X games, where BMX racing and freestyle would be normal, so convert the bike used already into something more dangerous. Thats just a guess.

If you look carefully at photo's you will see bikes sporting a steering damper. Low center of gravity is always good, but a short wheelbase and tiny wheels and high speeds and potholes and cats eyes make for some scary tankslapping moments.
I have some old frames knocking about but 26" and 700c. If i find an old BMX.......... missed one chucked in a hedge months ago....... thought about, should have rescued it :(
I think more silly project bike as it involves a whole new wheelsize and frame size than i have and very limited chances to race.

Physics probably all wrong but surly the vast amount of stability would come from the gyroscopic affects of the wheels, less so the centre of mass. The steering damper seems to suggest that thats the case. That said, smaller wheels wouldn't help in that regard.

If you look carefully at photo's you will see bikes sporting a steering damper

Moar bieks

Franken

That's really cool

HOLY! SHIT!

would ride

Gravity bike thing needs its own fetish thread.