My GI Multi-hubs Arrived

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gravity
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Too Long

Post by gravity » Sat Apr 13, 2013 2:51 pm

GG and all,

I did make a gravity kart with several wheel choices and have not posted because I am lame and usually need help getting pictures on the forum. If anyone is interested I will get some up. But I thought I should finally let you know the results. First tire choice were 4 Duro 200x50 inflated to the maximum 60 psi. I have used these tires on offroad rollerskis with good results except for the high weight. They were slow, but only because my local hills are not steep or long. I think in the Black Hills or the eastern or western mountains on a mile long twisting downhill they would be a blast. Because I wanted better speed on my local hills we tried some 100mm inline skate racing wheels (duromter was hard I think 83 or 85). These were very fast. On a straight downhill speed run these would be my choice. The problem with a simple friction brake on the back tires is they flatspot with any significant braking effort, so we ruined some tires. So my third choice for our local conditions was Abec11 Flyweels 81A durometer and 97mm. I had to try them figuring they had the speed and were also wide enough not to flat spot on braking and also give grip on corners. They work well. Me my wife my son and his friend drove through the Black Hills of South Dakota last year on vacation and and would have brought the gravity kart except for lack of room in or on the car. It turned out lucky because some of the good downhill runs I remembered were interupted by cattle crossing grates which would have sucked up 100mm tires, the Duros would have been OK though. Slicks would be better yet.

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Post by BgSurfer » Thu Apr 18, 2013 5:35 pm

Just now saw this thread gravity. Mostly just show up once or twice a week to lurk in The Shed subforum these days.

Would love to see photos of your gravity cart. If you can give me some URLs of photos you have posted on the internet (Flickr, Photobucket, etc.) I'll post them for you over in The Shed. Or upload some here at SD by creating your own photo album:

http://www.surfingdirt.com/forum/album.php?do=addalbum
~~~~~

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http://www.bgsurf.blogspot.com/2009/10/street-carver-keeping-stoke-riding.html
The older I get, the better I was...
Ride what you like. :cool:[color="Green"][/color]

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gravity
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Post by gravity » Mon May 06, 2013 6:07 pm

Bg

Sorry I did not check back sooner, looked after a couple days and thought their was no interest and old threads are hard to get started, I should have started a new one anyway. The kart is very and probably too simple, but I like that for a starting point. I will get help getting pictures up but it may be a few days. As long as I am sending pictures I will try to send some of my offroad inline skate/rollerski development. Somebody in the forum will get a kick out of these.

Jim

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gravity
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Gravity kart and all terrain skate pictures

Post by gravity » Mon Jun 17, 2013 9:20 pm

Bg

I am posting pictures here because I am lame on the computer and it was possible. Thank you and feel free to move them on the forum. I forgot the Airline tire picture and 5 pics is all I get so let me know I can repost if their is interest ( the chassis is the same). The kart needs to be extended by a good 6" for adults. Sorry it took so long to get this out.
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markbrosnan78
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Post by markbrosnan78 » Tue Jun 18, 2013 12:59 am

What's the idea of the gravity cart? Do you lie on it street luge style or do you sit up in it?
[align=center]Trampa[/align]

[align=center]Allowing even fat blokes to ride since 2000...[/align]

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gravity
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Sit up

Post by gravity » Tue Jun 18, 2013 11:12 am

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[ATTACH]1360[/ATTACH]But luge style with kart steering is tempting. This kart needs to be longer. Luge style would be longer yet and the steering linkage would be more complicated as well as the brakes (unless foot braking was used). The picture with airline tires cannot be found, but it is the same frame with the brake rub bar mounted at the top of the pivoting uprights. The 8" Airlines were mounted through a 3/8" hole 2" behind the 5/16" hole for the 4" Flywheels. On the front when I took the Airlines off I bushed the 3/8" axle hole with 3/8 x 5/16 aluminum tubing to accept the 5/16" Flywheel axle. My intent with this project was to make something simple, cheap, light and compact enough to throw 3 or 4 in the back of a car to head for the top of a hill. This is a good start. We have gone 33 mph according to GPS, It was stable. It would be slower with Airlines. Those off road inline skates with the orange wheels in my last post were Airlines. Thank you Bg for putting up with this takeover.
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markbrosnan78
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Post by markbrosnan78 » Wed Jun 19, 2013 2:27 pm

I was interested in the luge aspect. I know someone over here who is a board builder but also makes luges. Some are on traditional trucks some on axels but all are steered using leverage and braked in the traditional manner al la foot.

I was wondering if the kart style offered any advantages? I guess less speed wobbles and more stability?
[align=center]Trampa[/align]

[align=center]Allowing even fat blokes to ride since 2000...[/align]

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gravity
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I think you are correct

Post by gravity » Wed Jun 19, 2013 6:37 pm

I do not think Kart/ auto steering is allowed in sanctioned street luge racing. Their is no getting around the problem of bump steer with the existing system. When one wheel hits a bump or depression it steers the luge/skateboard/mountain board. I am surprised we stay on these things. The advantage of the system is simplicity and perfect wheel alignment (good speed). A Kart/auto style steering needs to be designed and adjusted and will never be perfect, but no bump steer, should be more stable and predictable at high speed. Thanks again Bg kick me off here anytime.

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Post by BgSurfer » Sat Jun 22, 2013 1:12 pm

No hijack here gravity. The thread was dead. Post away. Takes me awhile to notice threads not posted in The Shed.

Cool stuff!

Mark, I still think my 3-wheel design has good luge/skeleton potential. Someday, I'll finish that project ...

Image
~~~~~

Keeping the Stoke
http://www.bgsurf.blogspot.com/2009/10/street-carver-keeping-stoke-riding.html
The older I get, the better I was...
Ride what you like. :cool:[color="Green"][/color]

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markbrosnan78
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Post by markbrosnan78 » Sun Jun 23, 2013 1:33 pm

Dirt Luge? Could be an idea. Have you seen the steering system on a kite buggy? Essentially two bars off the front wheel with a strap over the top. Stock that on the front wheel and that would sort the front end out. Not sure if the deck would be big enough to lie down on. You'd need a wider axle on the back wheels as well otherwise you'll burn your ears.

On of the local skate groms had a truck that has the usual hanger system but the axle then screws into the hanger from the outside of the wheels. Get longer axels made and that would work or a kite buggy rear axel might work.

I've tried a kite buggy down a grass hill. A bit of a bugger to control but it would work. They're pretty close to a dirt luge already just need to be lowered and the rider laid out a bit more.
[align=center]Trampa[/align]

[align=center]Allowing even fat blokes to ride since 2000...[/align]

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gravity
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Post by gravity » Wed Jun 26, 2013 2:52 pm

On asphalt Bg I think your design would be a nice luge ride; probably slower than urethane wheels but on rough/typical roads a better ride. Luge off road would be good on the right course; maybe Pikes Peak downhill. I think a gravity kart would be fun on the right off road downhill. Stretching the front maybe 6" for more legroom and using mountain board tires and maybe contact cement some quality foam to the seat for some minimal comfort. Mountain biking at Steamboat in Colorado years ago we did an up and down on a great hard packed trail; wide enough and few rocks, great corners, through a canopy of trees; it would be fun on a gravity kart. All the other trails we biked that summer in Colorado were far too rocky or narrow or just radical for a gravity kart to work, I think a luge would be tougher yet. The road hill we got an honest 33 mph on with the kart is quite steep and long; wind resistance killed the speed. A lay down luge conversion would add 10 mph or more but I am not flush enough to buy racing leathers for my 16 year old yet.

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