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Old 10-26-06, 07:22 PM   #1
Wheelchairman
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My attempt at building a lowracer

Hiya!

Ive been pretty busy last couple of days trying to build a lowracer. I started this project months ago, and I got as far as building a jig. I gave up then so I could concerntrate on training for a 24hr race. Anyways, after a bit of inspiration from lowracer1, Im back into it and am progressing without a problem.

The Jig
The jig cost me $15 to build. I got some scrap square from 2nd hand place and put it together. The base of the jig represents the ground surface, so there's no guessing how high or low it will sit when on wheels. The angle of the headset jig is 63*. I made life very easy for myself by tacking in a "dummy front fork". The fork is permanently set at 63*, and all I do is place my headset case onto the fork and Im ready to go. I worked out my ride height with a simple brick placed on the jig surface. The bottom bracket case is just a hole drilled through the angle steel. A machined "BB jig thingy" is place inside the BB and keeps it true. A bolt then goes through the "BB jig thingy" and sits snugly in the holes in the angle steel.


My progress so far; Mainframe


1st thing I done was grab the forks off a MTB frame. These will house my rear wheels. I've kept the original dropouts in place, as I believe I can manipulate and add to these to make sure the wheel will never fall out under heavy load. I've then tacked the spine into place, making it as level as possible with the jig surface with the help of my trusty brick


Next the tube leading up to the headset from the spine was tacked in place. Im using 1 1/2" mild steel tube for the entire mainframe. The wheel you see in the picture simply bolts on to the jig and allows me t size up how much room I have left before the tube touches the wheel. Pretty agricultural, yet very effective and easy


Finally the boom was tacked on yesterday and then I pulled it out of the jig. I couldn't work out how at 1st, but with a slight flex of the "dummy forks", the whole frame popped out without any trouble. After that I welded it together carefully, and here's what I've ended up with at this stage;

So I guess Im progressing OK. I will add metal plate in some areas, to help in strengthening the mainframe, but that will come later. So far the frame cost me $15, and most of that was in purchasing the tubeing.

So do any Lowraceing riders have any tips for futhur progress? Your opinions and thoughts on my progress are appreaciated.

Next time: Working out my drivetrain path
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Old 10-26-06, 10:47 PM   #2
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Looks pretty cool, I'm thinking about building a lowracer as well. Mostly because my college student self can't even imagine the possibility of spending 5k on the fujin SL II. I want to build one though, or something like it.
I'd love to see more of what you've done. Keep working on it!
Mike
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Old 10-28-06, 07:02 AM   #3
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looks pretty good so far. keep in mind that you are going to have to find a pretty good sized chain ring for a 20" wheel. I run a 58 tooth big ring with a 11/32 cassette on a 700 c rear wheel. Thats how I can pedal down those hills at over 40 + mph.
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Old 10-29-06, 09:07 PM   #4
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Quote:
Originally Posted by lowracer1
looks pretty good so far. keep in mind that you are going to have to find a pretty good sized chain ring for a 20" wheel. I run a 58 tooth big ring with a 11/32 cassette on a 700 c rear wheel. Thats how I can pedal down those hills at over 40 + mph.
I'm aware of that, and luckily for me a 24hr race is coming up in the next 3weeks that usually has a greenspeed stand on site for 4 days. I know that a 61tooth ring coupled with a 20" on a faired trike will get you to 43mph easily(and 53mph if you wanna spin at 130rpm ). I was thinking of going up to 65tooth for downhills.... but I think I'll compromise between what I know and what I'll need. Expect to see a 62-63 on there when it finished
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Old 10-30-06, 07:00 AM   #5
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Quote:
Originally Posted by Wheelchairman
...I know that a 61tooth ring coupled with a 20" on a faired trike will get you to 43mph easily(and 53mph if you wanna spin at 130rpm ).
Really? What do you think the actual diameter of a 20" wheel is? I recommend a SRAM dual-drive rear wheel, which will allow you to use 'normal' chainrings. Nice-looking bike so far, BTW.
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Old 10-30-06, 08:32 AM   #6
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Quote:
Originally Posted by BlazingPedals
Really? What do you think the actual diameter of a 20" wheel is? I recommend a SRAM dual-drive rear wheel, which will allow you to use 'normal' chainrings. Nice-looking bike so far, BTW.
I would not have a clue about diameters- Ive always assumed BMX sized rim=20" but I know from building jigs that it usually aint as simple as that. I understand I could easily find out, but I personally don't really have a need to. I just simplfy things by matching a rim with the tyre i'd assume to use and base jig measurements on that.
I'm simply basing those speeds of my last post on one vehicle, Bendigo Youth Racing's BY-06. I know youse are all probably bored with me posting this up, and nor do the majority of you even care for faired trikes, but youse should know that this is the finest example of a faired trike in this current day and for many days to come. On a packed racetrack this will do up to 43mph through the speed-trap. Most trikes couldn't run a 61tooth and be doing 80rpm up a hill in the highest gear, but this one will do it everytime. This is not a speed trike (how boring ), but with a larger chainring (65?), tailwind and open, smooth road, I'd assume 60+mph would be possible. Bascially what I'm getting at Blazing Pedals, is that it is possible to reach those speeds with a 61tooth running a 20"rear, but only in the most sorted, efficent and most slippery of faired trikes. I'd assume they're small speeds to what those lowracer streamliners will do though


Anyway....an update then?

Well today I attached a drivetrain. I welded a derailiur hanger on, mounted a long cage, and a BB. A crankset then went on, followed by a 57tooth chainring. Thats the best I have at this stage, but according to my estimations a move to a 62 would only add 9mm to the chainring's radius, which I've taken onboard.
A chain has been mounted and suddenly Ive hit a problem . The front fork is dead-center in the chains path. I could only assume that running like this will result in instant derailment and loss of efficentcy. Does anyone have an answer? I understand you can buy BB spacers. Can anyone confirm that or even give me a link or product description?
The idea Im thinking of right now is pretty extreme, but involves building what can bascially be called a idle pully cage minus the idle pullys. This cage will be part of the fork, and will bascially split the fork in two pieces, then rewelded with the cage.
My other idea is to experiment with a single blade design. I have the components and know-how to make it work very easily.......but will a run of the mill BMX fork withstand the forces? Just many questions that need answers.....or actions to find answers.

Ive got another question for all you lowracer owners out there. How much do you have to change your riding habits over a DF bike? I layed a board on the spine and had a seat, clipped into pedals, and found my heels touch the tyres when they're turned at an extreme angle. Its as simple as pedeling forward to avoid this. Im sure this is a normal evil for some lowracers, but is there any other compromises I'll just have to live with?

Anyway, Cheers
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Old 10-30-06, 10:28 AM   #7
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Quote:
Originally Posted by Wheelchairman
Well today I attached a drivetrain. I welded a derailiur hanger on, mounted a long cage, and a BB. A crankset then went on, followed by a 57tooth chainring. Thats the best I have at this stage, but according to my estimations a move to a 62 would only add 9mm to the chainring's radius, which I've taken onboard.
Is that for purposes of determining how long the derailleur tube will be? You should allow a bit extra, you can always use a tubing cutter to get rid of what you won't need.

Quote:
Originally Posted by Wheelchairman
A chain has been mounted and suddenly Ive hit a problem . The front fork is dead-center in the chains path. I could only assume that running like this will result in instant derailment and loss of efficentcy. Does anyone have an answer? I understand you can buy BB spacers. Can anyone confirm that or even give me a link or product description?
A spacer is only good for a couple of mm. Get a bb with a longer spindle, to move the crank outboard further? Narrower forks help too. BMX forks normally don't worry about being narrow. If you can get to the point where the chain is only rubbing a little bit, you can use a chain tube to protect the fork from being damaged. Chain tubes can be fabricated from 1/2" pvc sprinkler tubing. Or, depending on how bad the rub is, it might be advisable to run a second power idler to route the chain over the fork. Power loss can be minimized if you use a large diameter pulley.

Quote:
Originally Posted by Wheelchairman
My other idea is to experiment with a single blade design. I have the components and know-how to make it work very easily.......but will a run of the mill BMX fork withstand the forces? Just many questions that need answers.....or actions to find answers.
Most BMX stuff I've seen is just 1010 steel, and the remaining dropout might bend too easily. You'd also need a different wheel, one with a one-sided hub. If you're willing to make a monofork, are you able to cut the existing fork to make it narrower at the crown?

Quote:
Originally Posted by Wheelchairman
I ... found my heels touch the tyres when they're turned at an extreme angle.
Most short wheelbase recumbents exhibit this feature. It is not a problem at normal riding speeds, only at very slow speeds (mostly while parking.)
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Old 10-31-06, 09:30 PM   #8
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Quote:
Originally Posted by Wheelchairman
but with a larger chainring (65?), tailwind and open, smooth road, I'd assume 60+mph would be possible.
Unless you're going to build a full fairing, don't expect a lowracer to give you those kinds of speeds. And if you fair it, you're going to want bigger gears. 60 mph using a 65/11 gear and a 20x1.5 wheel will require 180 rpm. a 65T big ring and an 11T top gear will be just about right for street riding, though.
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Old 11-01-06, 01:53 AM   #9
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UPDATE: Basic drivetrain worked out

UPDATE: Basic drivetrain worked out

After much thinking, I decided it would be easier on my wallet to just turn my problems into something much more managable. Hence my rear wheel driven project is now a front wheel drive



Its worked out really good! Nothing in the picture is secure, but it works.....a little inefficently at that. An idle pully cage will be added soon, and I will attach the chainring on the other side of the spiderarms to straighten the chain out. Im experimenting between a short and long cage to see what works better. Next couple of days will be spent making it all work for real.

Quote:
Originally Posted by BlazingPedals
Most BMX stuff I've seen is just 1010 steel, and the remaining dropout might bend too easily. You'd also need a different wheel, one with a one-sided hub. If you're willing to make a monofork, are you able to cut the existing fork to make it narrower at the crown?
I found that out the other day. Not very strong at all. I had a couple of sturmey-archer front drum brake hubs lying around that I was planning to use. They're esspecially built for trikes or single blade jobs. I guess it doesn't matter now though.

Quote:
Originally Posted by BlazingPedals
Most short wheelbase recumbents exhibit this feature. It is not a problem at normal riding speeds, only at very slow speeds (mostly while parking.)
That is a relief. I get the feeling that most of a lowracer's movements involve leaning, rather then huge lock to lock steering inputs.....?

Quote:
Originally Posted by BlazingPedals
Unless you're going to build a full fairing, don't expect a lowracer to give you those kinds of speeds. And if you fair it, you're going to want bigger gears. 60 mph using a 65/11 gear and a 20x1.5 wheel will require 180 rpm. a 65T big ring and an 11T top gear will be just about right for street riding, though.
Cool. I guess a 65t is the go then . So where do you get those figures from? All estimates based on mathematical equations right? They'd be helpful
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Old 11-01-06, 06:34 AM   #10
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Originally Posted by Wheelchairman
Cool. I guess a 65t is the go then . So where do you get those figures from? All estimates based on mathematical equations right? They'd be helpful
Yup, I have a speed/gear program. Calculations are simple but tedious to do for all the gears that a typical bike has, which makes it something that computers can do really easily. I could produce a chart, but it there's not a good way to make it readable on this forum.

The FWD looks good, as long as the chain doesn't hit the fork in low gear. You might be limited in how big a cassette cog you can put on it. Do you ultimately plan on having two idler pulleys since the chain will be going in opposite directions at the same time? (Can't tell from the pic if you are ganging pulleys on the same shaft.)
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Old 11-01-06, 05:48 PM   #11
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Quote:
Originally Posted by BlazingPedals
The FWD looks good, as long as the chain doesn't hit the fork in low gear. You might be limited in how big a cassette cog you can put on it.
I positioned the pullys so the chain will reach low gear without any scrapage. Wether or not I can put a larger low gear on in the future is another matter.....I really haven't thought about it TBH . The only trouble I was having at the time was actually in the highest gear. The chain would rub on a spot weld on the fork's dropout. I simply made some space for the cluster and fixed that.

Quote:
Do you ultimately plan on having two idler pulleys since the chain will be going in opposite directions at the same time? (Can't tell from the pic if you are ganging pulleys on the same shaft.)
Sorry, that picture is a bit misleading . There are two pullys on there. Here's a better pic;



Remember, none of its attached properly yet .
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Old 11-01-06, 06:17 PM   #12
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Quote:
Originally Posted by Wheelchairman
I positioned the pullys so the chain will reach low gear without any scrapage. Wether or not I can put a larger low gear on in the future is another matter.....I really haven't thought about it TBH . The only trouble I was having at the time was actually in the highest gear. The chain would rub on a spot weld on the fork's dropout. I simply made some space for the cluster and fixed that.
Cool! In this case, having a wide fork is a Good Thing(tm).
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Old 11-02-06, 09:40 AM   #13
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Idler location

Hi,
In looking at your pics, I have one observation: you may need to relocate one of the two idlers to a different location to avoid your inner knee from banging up against it.
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Old 11-02-06, 06:43 PM   #14
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Hi,
In looking at your pics, I have one observation: you may need to relocate one of the two idlers to a different location to avoid your inner knee from banging up against it.
Hmmmmmm.......good point that. I havent really tested the theroy but I was getting the feeling that maybe it would be a close call . Where to relocate though? It works so well! Im just gonna sit on it for awhile and see what happens. If it doesn't work on a practical level, then I can easily change it.....then you can say "i told you so"

EDIT: Spent the last 20minutes checking; I believe there is no issue with it. Unless I was a Time Trial rider, my knees will not hit- Im sure

Last edited by Wheelchairman; 11-02-06 at 09:32 PM.
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Old 12-02-06, 07:05 PM   #15
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Cool looking bent so far, in either RWD or FWD. I was going to suggest the same thing about the idler pulley sticking out too far in FWD mode and causing knee clearance issues, but if you've got no problem with it, the dual pulley certainly simplifies things. Sometimes with a pulley up around there, it can be a good idea to put some kind of simple guard on it to prevent greasing up the inside of your leg, hitting your leg or pulling out leg hairs if they get too close to the pulley-chain combination. We had minor issues with that on our Nitro clone, and our pulley was only about 3/4" thick and close enough to the frame to just allow the chain past the head tube.
http://fleettrikes.com/nitro%20clone%20pulley.jpg

As for gear ranges, we had the same concerns with 20" drive wheels. My Speed came with a 52T top gear and I ran out of gears on a very slight decline on the first ride on it. I switched out the original triple and replaced it with a 60/40 double and I'm pretty happy with the gear range with a 9 speed 34/11 cassette. I've had it up to just a little over 85 kph and haven't spun out yet with 110 gear inches in high gear, but I have 130mm cranks on it too. It gives a low gear of 25 gear inches which has been fine so far for some fairly steep climbs and some long climbs around here, but I don't have grade numbers to quantify it unfortunately. Vuelta makes some nice, and inexpensive over sized chainrings but they only seem to come in 110 BCD. I made a simple adapter to fit it to a 130BCD spider though. With a long cage RD, it manages to soak up the extra chain when I go down onto the 40T ring, and the only gear I lose is the 11T, so I still manage to use 17 of 18 gears. I was also concerned with how well it would shift between the 60 and 40T rings, but it's as smooth as the original triple.
http://fleettrikes.com/cs618%2060%2040%20chainrings.jpg

Another option that allows you to use more conventional road triples is to use a Shimano Capreo hub. It comes as a 9 speed, with a 26T - 9T range. I've seen a couple of these in use and the guys drilled their cassettes and replaced a couple of the larger gears so they could use a 30 and 32T for some better hill gearing. You have to buy the cassette with the hub, and I've seen them come in 32 and 36 spoke drillings. Sheldon Brown has a lot of information about them and also sells them.
http://sheldonbrown.com/capreo/index.html

Lastly, in experimenting with different 20" (406) tires that are smooth, narrow and high pressure, I've found that some of them can reduce the tire diameter to 18", which further reduces the top speed a little. I like the Stelvios because they're the best ones that I have access to for their cost, and they are pretty close to 18" final diameter. The high pressure Kenda Kwests would be my #2 choice, again for the price/availability criteria.

I'm looking forward to seeing the progression.
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Old 12-02-06, 07:50 PM   #16
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I know for a fact that you can get 130BCD in 60T, and I suspect they come even bigger.

I've tried 'a few' of the skinnier, high pressure tires. The fastest ones seem to be Conti GP and Schwalbe Stelvio. Unfortunately, they are also the most fragile. I've never worn out a Stelvio - they alway suffer some sort of failure first. For 20" Stelvios, the most common failure seems to be cord delamination, which can happen without warning and without any abuse. Suddenly you get an 'S' in your contact patch which gets progressively worse until you stop riding just to make the wobble quit.



I've also had crashes because the rubber on the shoulder literally peeled off in strips, causing a crash in a turn when I forgot how little rubber was left for traction.

Contis aren't much better. They have extremely fragile sidewalls, to the point of breaking cords if you hit the slightest gravel in the road (like the stuff that always accumulates at intersections.

I've found that the 3rd fastest tire is the lowly Primo Comet. At 1 3/8" it's not terribly skinny; but it's light, it'll take 100 psi, it wears fairly well, and it costs $16-20. Compare that to $30 for a Stelvio and $48 for a Conti (USD). From there, there's several 1 1/8 -1 3/8 tires that are really more for touring at the expense of speed: Kenda, Vredstein, more Contis, etc. If you really want skinny tires, then the best choice is to use 451 wheels; you can get tires for that size down to at least 22mm. But it might be too late for that already; the forks may not be able to take them.
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