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Old 04-01-14, 10:53 AM   #1
lectraplayer
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why do delta trikes seem to "push" with only one rear wheel?

I am finding that many delta trikes seem to just use one wheel to drive with. While I can see reducing tire wear and improving agility on flat ground, it is really awkward riding mine as it makes mine feel like it "digs," tends to want to lift a tire, and in general loses traction easily. Has anyone tried a delta that "pushes" with both rear wheels? Most I find online speaks of using just one wheel.
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Old 04-01-14, 11:02 AM   #2
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Same issue with cars. In a nutshell, you can't drive both wheels equally with a solid axle because when you turn, the inner wheel will be rotating less than the outer wheel even in a very slight turn. Cars have differentials, too expensive for generic trikes.

Handling and performance suffers for everyday use when you have a solid axle with no differential action allowed. If you have a welded rear axle, you will feel like you are plowing. The bike will seem to skip and stutter as you make harder turns. Not very pleasant.

For racing though, it is desired to have a solid drive axle. Most trike racers will lean the trikes so to be only on 2 wheels when they turn which mitigates the negative impacts of a solid rear axle.
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Old 04-01-14, 11:05 AM   #3
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When building a delta, rear wheel drive trike you have two inexpensive options:
1) single wheel drive
2) "live" axle = both wheels fixed and dual wheel drive

and then there's the expensive option: a differential, allowing both wheels to drive but also to rotate at different speeds.

Basically a live axle drive will handle equally poor in both directions of turn, and due to the difference in circumference between the inner and outer wheel, one wheel will have to "scrub", slip & slide a little, fighting the turn and causing tire wear.
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Old 04-01-14, 11:15 AM   #4
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Having 2 driving wheels on a common axle calls for a differential so that one can go faster (or slower) when going around curves. These are pricy and heavy so cheap trikes opt out and have single wheel drive.

Years ago there was a trike (don't ask, I don't remember) that had both wheels share a common axle, but each wheel was on a freewheel and so the outer wheel on a curve could overrun the inner. This is a nice simple and efficient design, except that it can' be used with any kind of hub brake, which is why you don't see it often.
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Old 04-01-14, 12:06 PM   #5
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Years ago there was a trike (don't ask, I don't remember) that had both wheels share a common axle, but each wheel was on a freewheel and so the outer wheel on a curve could overrun the inner. This is a nice simple and efficient design, except that it can' be used with any kind of hub brake, which is why you don't see it often.
Although they still turn funny, as the driving inner wheel will fight the turn a bit.
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Old 04-01-14, 12:13 PM   #6
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Although they still turn funny, as the driving inner wheel will fight the turn a bit.
Yes, but it wasn't that bad, and it made for a very light design. Also, back in the day, it was necessary to lift the outer wheel on racing trikes to maximize cornering speed without tipping. (ask a 5 year old) That argued for inside wheel drive, so it worked out.

Like all design, it's about trade offs. I suspect that the OP's problem and that many (most?) adult trikes are designed for seniors or utility purposes, and a hub brake greatly simplifies the design. Since performance isn't a real issue (to the designers) they opt for the cheap simple solution of single wheel drive.

I suspect that the differential question is one reason that so many recumbent trikes are opting for single rear wheel drive.
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Old 04-01-14, 12:17 PM   #7
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Because there is only 1 wheel driving, and it is off center ...


there are German deltas with a differential but those Germans don't work for cheap.

they would be Recumbent rather than Upright types ..

Tadpole types are simplet to drive via 1 center rear wheel ..

there are front wheel drive delta designs too ..
A hand driven crank friendly design for Para cyclists W/O leg function.

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Old 04-05-14, 11:31 AM   #8
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For racing though, it is desired to have a solid drive axle. Most trike racers will lean the trikes so to be only on 2 wheels when they turn which mitigates the negative impacts of a solid rear axle.
Ok, I have not looked closely at trike racing so apparently my assumptions were wrong, please tell more.

had assumed it was a sport for people with handicaps preventing balance on 2 wheels.
but they actually balance on just 2 when turning? this blows away my assumption of lack of ability; why not race bikes then?
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Old 04-05-14, 02:13 PM   #9
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Here's a quick link to observe some trike racers negotiating corners at speed:https://www.youtube.com/watch?v=1k-o2-1IA4A

They appear to lean into the corner while accounting for road camber and given slope, maintaining their COG inside the turn to avoid an upset.
The differential design was originally patented by a fellow named Starley in the mid 1880's, and incorporated into their trikes. There are quite a few contemporary differential systems being used in delta configuration.
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Old 04-05-14, 02:33 PM   #10
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What you need is a Posi Trac differential, might be a little heavy though.
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Old 04-05-14, 02:42 PM   #11
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What you need is a Posi Trac differential, might be a little heavy though.
I'm more of a Torsen fan myself.
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Old 04-05-14, 03:25 PM   #12
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I'm more of a Torsen fan myself.
You sent me to the Wikipedia on that one. Looks like a good choice too, but I think a Ford 9-inch may still be the torque monster choice.
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Old 04-06-14, 07:31 AM   #13
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In cars I am a great fan of torsen diffs. Does anyone even make one for a trike?
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Old 04-06-14, 09:43 AM   #14
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Now that we're in race car terminology, a "push" (running straight in the corners) is what's going to happen to a delta trike that drives both rear wheels via a solid axle.
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Old 04-06-14, 11:22 AM   #15
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fb

In cars I am a great fan of torsen diffs. Does anyone even make one for a trike?
No, not only because of the massive weight penalty involved, but because they're simply not needed since trikes generally aren't used climbing hills in ice and snow. If wheel slippage is so bad that you can't move, lift the trike into a new rut and continue.

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Now that we're in race car terminology, a "push" (running straight in the corners) is what's going to happen to a delta trike that drives both rear wheels via a solid axle.
There'a a bit of fighting on low speed turns, but at anything higher the weight shift (tipping) causes the inside wheel to slip, and the outside wheel drives it around the turn. I don't know what would happen on a recumbent trike where the tipping forces are much lower, though I suspect it would be similar.
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