Gravity racer - Calling all daredevils!

[breakurnees]

With the tires that come in fractions, they don't fit because the diameter is wrong. They are meant for taller rims than bmx 20".

[Philphine]

ok, i see. probaly like the rims on a schwinn fastback.

ok, i'm not sure when i'll get this actually on the bike, but this kneeler footrest deal should end up sort of like this





i'm thinking if i had my feet on the suspended back axel and maybe hit a bump, the swing arm would swing down from the shock expanding and then pop up again. that could be painful. plus it would affect how the rear suspension would work anyway. it'll probaly need all the help it can get to work well. so the idea is to put this as close to the suspended chainstays as possible without interference. things have been kinda hectic at work (sometimes they get this crazy notion that you should actually do some work there) so i may not get much further than some trimming and fitting 'til i can actually start putting it on. but this is the plan anyway.

[Philphine]

i got pretty decent cooperation from my home welder today, at least enough for some good tack welds. so short of a few more braces and maybe a gusset around the footpeg area this is the bike in about it's final form











the kneeler part seems like it's gonna work. i got it a little crooked so the right side is a tighter fit, but i think i can improve it some.

the foot pegs, i have to hang my feet over them with my knees on the kneeler, but i think with a few extra bracing points and a couple gussets, i could stand on them. don't ask me why this is important to me. it just seems like you should be able to.

the goal is a test ride next weekend. that'll give me a week to hopefully get it back to work with time to finish up the welding, look around to see what i have for better wheels and tires, fix the brakes and see if i want to do anything about adjusting the seat a little more.

we'll see what happens. if there's no post next weekend check the local hospitals for the admission of a phil t.

[Philphine]

i meant to add that as best as i can balance it on my bathroom scale, it weighs about 35lbs. it might end up closer to 38-40lbs before it's done.

i don't plan to add weights. at the beginning i said it was kind of a style exercise, plus the bike is pretty heavy on it's own. also because i added suspension, since it's from kids bikes (the rear is using a adult bike spring though) adding more weight would probaly take it even further past it's intended capabilities. if i catch some wild hair and decide gravity bikes will be my life, i'd probaly try to upgrade at least the front fork before i added more weight.

[S.I.N. CYCLES]

more questions for the experienced.

i notice on the s1 vid it looks like theres as much weight on the knee pads as the seat during the ride. on other bikes that dosen't look possible, at least not without some sacrifice to the knees. being able to support yourself on your knees is a good thing? ....



alright, minds out of the gutter



and the rear foot rest. some have their feet wrapped over them, some have them under their feet. does it matter, or is it just how the frame happens to fit a particular rider so they set their feet however they will reach? seems like being able to stand on them would be better, but since i've never made one of these i don't know.

since i need to make both i figure i'll try to make them in whatever way works best. thanks.

As for the kneelers having weight on your knees is a good thing in our opinion. If you have adequate padding of course. The seat on S1 gets used very rarely thank goodness... recessed manholes at 45+ can abuse the junk something fierce.
Putting your metatarsals on the foot rest compared to the ball of your foot is more of and aerodynamic choice just happens to help nail our preferred tuck switching footing around often through out a course is common. If you are riding technical roads with lots of body language having the ball of your foot on the peg will allow you to take weight off of your knees and put it to the back wheel. We have had riders from 5'9" to over 6" on S1 and all have the ability to put feet where they feel comfortable. It's just a matter of maybe having your more of your shin on the kneelers.
Some riders don't even require kneelers they just rock it all on the rear pegs. We like options and the added protection of kneelers acting as sliders.

Lots of theories none proven Possibly the best thing about the sport of Gravity Bikes is the diversity of rides. Keep it up!

[Philphine]

well, i've been down my test hill already. no idea how fast i might have gone (creeping probaly), but the bike felt pretty good.

can't say it was the brightest way to do it. two nights ago i had it at work doing some finishing and tried it out on the bit of slope of my work parking lot. really slow but it felt ok. so when i got off around 12:30 i tried it again on a slightly bigger drop just outside my work entrance. again, nothing real big but a little faster. still felt pretty good.

so i get back to the area i live in and go over the overpass i'm meaning to try it out on, and pretty much just decide to try it... at about 1 in the morning.

still felt good. it's only about a 1/4 mile ride though.

i've picked up a cheap bike speedo and still plan to go back to the over pass this weekend. i should add also that i'm disqualifying my self since i can't do a vid, but i'll post whatever the speed is, and any others if i find a bigger hill.

also started another bike. had to try the occ idea so i switched back to freakbike (where i usually do my builds) and have started on it.

[breakurnees]

Congrats on getting it rolling! I bet with some high pressure tires and some weight you'd really be cooking.

[Philphine]

thanks. i did change tires from the previous pics, but they're not much, if any, better. i pulled them wheels and all from another bike more for the straiter rims, and didn't swap tires around off them. their max pressure is only 40lbs, but i figure if i have enough fun with it i have at least one thing i can improve right off the bat.

[Philphine]

no need to make room in the records book yet, i went a blazing... err,,, 22.7mph




here is my test hill




two pics 'cause it has a slight curve in it. can't get it all in one pic. an overpass near my house, about 1/4ml top to bottom. if you go down westward it eventually parallels the railroad tracks it goes over, so there's nowhere to make a right turn and/or be cut off. seemed like a good place for initial tests.

i'd liked to have had better first numbers, but i'm not too discouraged yet for a couple reasons.

all of the vids i've found show much longer rides. mine lasted about 30 seconds, so i'm hoping a longer hill will give better results

it was a compleatly drama free ride. no shakes or wobbles. so it's not like, "i barely made it down but i'm trying the side of a mountain tomorrow". whatever the bike's limit is, i don't think i was anywhere near it.

some little tunings things could still happen, straiter rims, a bit of brake rub, higher pressure tires. i'm hoping to let those improvements come with finding good deals.

latest version of the bike



lowered my "clip- ons", added a bit more bracing back to the foot pegs, wheels/tires off another bike i had around, slight seat tilt adjustment, and a cheap bike computer (about $12. the most expensive thing i got particular to this build. i had spent about $4 up 'til then).

still a fun experiment though. i mean to go by a couple of skate shops and see if they know of any street luging that gets done locally to find a better hill. also playing with the second bike (i call it "the poseur" 'cause it looks like it would be faster than my first, but most likely wont be) and will probally try it on whater hill i try the first on to see what difference there might be.

no need to make room in the record books i guess, but hopefully i can do better eventually.

[breakurnees]

I'm impressed that you are running hills already. I don't have welding gear, so I am waiting on heim joints to come in the mail. Then tires and I can start fitting the brakes and cables.

[snydur]

i got the bars on right on mine today, going to find a different seat. i was sitting on it earlier and just realized how small it is. ill be honest, im kinda scared bout this. shooting for a finish next week. its been sitting outside adding some "character" for a while now.

[Philphine]

i just wish the finding good hills part were easier. i have a line on a couple but i don't think either will show a faster result. one is part of an exercise loop in a big local park, so even if i could go faster there would probaly be complaints if i did. it's kind of curvy though, so i could test that.

the other is a local road fairly recently built that doesn't get a lot of traffic yet. there's about a 1/2ml section that's downhill but it's pretty gradual.

if nothing else, i'm still digging through parts to see if i can improve wheels/tires etc and maybe go back to the same hill and see what, if any. difference it makes. the second bike may be done soon too so i can play comparision games bettween them on that same hill.

[Philphine]

another question for the experienced, including bmx-ers.

going through the parts stash i picked up a rear wheel i got a few years back. it should be perfect (48 spokes, nice and strait, flip flop hub for maybe spin on disc in the future), except it has a huge axel in it, like maybe 1/2", and the loose bearings in it are really small. no idea what it would be for. i picked it up at a flea market.

i'm meaning to change it out for a regular 3/8"axel, but i had to leave for work before i found one. will that work or should i just put it back together before i loose the bearings (a few fell out already. i hope i found them all).


edit: nevermind. i tried it. didn't work.

[Philphine]

i got the bars on right on mine today, going to find a different seat. i was sitting on it earlier and just realized how small it is. ill be honest, im kinda scared bout this. shooting for a finish next week. its been sitting outside adding some "character" for a while now.

do like i did and find some little slopes first. at this point, i actually have a little more confidence in the bike being capable of going faster than i have in myself wanting to go much faster. truthfully i'd just like to make it to the 30-35mph range goal of this thread, unless the bike still feels good and stable at that point. i can stick my motorcycle helmet on, but i don't have all those other racy leathers and stuff.

[MiniMe]

i got the bars on right on mine today, going to find a different seat. i was sitting on it earlier and just realized how small it is. ill be honest, im kinda scared bout this. shooting for a finish next week. its been sitting outside adding some "character" for a while now.

do like i did and find some little slopes first. at this point, i actually have a little more confidence in the bike being capable of going faster than i have in myself wanting to go much faster. truthfully i'd just like to make it to the 30-35mph range goal of this thread, unless the bike still feels good and stable at that point. i can stick my motorcycle helmet on, but i don't have all those other racy leathers and stuff.

you need to come to my house to ride the hill behind me house...... u'll get the confidence u need (at 50mph)