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Building gravity racer
matty h - 11/2/12 at 10:13 AM

Looking to building a gravity racer want it to a 7 replica.
Seen the MNR childrens replica but not sure they are big enough.
Or could I just down scale the locost dimensions.
Suggestions welcome.
Thanks Matty

mark chandler - 11/2/12 at 11:25 AM

Sounds like you need to cut up a wheely bin

[Edited on 11/2/12 by mark chandler]

Chippy - 11/2/12 at 03:42 PM

The only thing that I know about gravity racers is they need to be as light as possable, (feather weight), and have the thinest tyres you can get, (really thin). Not much help but thats as far as my knowledge goes. HTH Ray

MikeR - 11/2/12 at 05:38 PM

is it to compete or have fun. If its competition, see above. If fun you could probably make it out of plywood.

scotty g - 12/2/12 at 10:18 AM

quote:
Originally posted by Chippy
The only thing that I know about gravity racers is they need to be as light as possable, (feather weight), and have the thinest tyres you can get, (really thin). Not much help but thats as far as my knowledge goes. HTH Ray


In my experience the exact opposite is true, you need it to be as close to the maximum weight allowed, the heavier it is the more mass for gravity to pull on!
A friend of mine built one a few years ago, made it as light as possible and ran it on skinny tyres on mountain bike rims, did quite well for his first year but all the guys that beat him said he was too light.
The next year he went to the maximum weight and changed the wheels to BMX ones and came 1st.

Volvorsport - 12/2/12 at 11:38 AM

couple of dual mass flywheels on axles .......

JoelP - 12/2/12 at 04:43 PM

quote:
Originally posted by scotty g
quote:
Originally posted by Chippy
The only thing that I know about gravity racers is they need to be as light as possable, (feather weight), and have the thinest tyres you can get, (really thin). Not much help but thats as far as my knowledge goes. HTH Ray


In my experience the exact opposite is true, you need it to be as close to the maximum weight allowed, the heavier it is the more mass for gravity to pull on!
A friend of mine built one a few years ago, made it as light as possible and ran it on skinny tyres on mountain bike rims, did quite well for his first year but all the guys that beat him said he was too light.
The next year he went to the maximum weight and changed the wheels to BMX ones and came 1st.


Id agree there, they will accelerate at the same rate whatever they weigh, but the heavy one will have more momentum for the level sections.

Chippy - 12/2/12 at 04:57 PM

I had a friend that did this sport, and contrary to what has been said above he ran a micro light unit, (you could pick it up with one hand), he used bike racing tyres that had a knife edge, pumped up really hard for the least rolling resistance. The wheel bearings were not greased, but oiled with a thin oil at each meeting for the least friction. Now I can't say he won every time he ran, but he did have a fair shelf full of tin ware. Mind you was a long time ago, things may have moved on since then. Cheers Ray

matty h - 9/3/12 at 07:42 PM

My item is to make a seven chassis as per the book but with everything at 60% size.Anyone know anything about what if any suspension it should have.
Matty

MikeR - 9/3/12 at 10:22 PM

Is this a straight line down a hill or a proper race around a twisty course?

I think that may be the difference. IF you look to the scottish gravity racing (cartie?) they have lots of info. They seem to run on racing bike tyres pumped up.

As for suspension i keep thinking that something based around compressing a tennis ball could work quite nicely.