MrInitialMan

I've seen in tadpole trikes where the front wheels are only attached on one side. Are these special wheels, is it a specific spindle, or what?

FBinNY 

Single side mount wheels have been around for a while. Cannondale dabbled with them some time back.

As you suspect, they often require a special hub and axle which is more like a pedal spindle than typical hub. However, some have standard shells and axles that are simply moved across for single side mount.

You might find one if you search for wheelchair or sulky hubs, as these are typically of this design.

Before jumping in, keep in mind that they need a special fork designed to handle the twisting force that the system creates.

Jeff Wills

Not quite. Many recumbent trikes used “through-axle” mountain bike hubs with 15mm or 20mm diameter axles when they first appeared. Now they are specifically manufactured for trike wheels with disk brake mounts or drum brakes.

There are a few recumbent bike part suppliers out there but they tend to offer complete wheels instead of bare hubs. Look at Hostel Shoppe or Utah Trikes.

FWIW: I was manufacturing recumbent trikes 40 years ago. I have tales to tell about hubs.

Dan Burkhart 

One option is the Sturmey Archer SD series. I think I would seriously consider these if I was doing a build as the brake is entirely self contained and no caliper mounts required.
https://www.sturmey-archer.com/en/products/sd-hubs

grumpus

The disc brake type are often just regular 15 mm through-axle front hubs, sometimes with bushes to use smaller steel axles. Sturmey Archer makes drum brake trike hubs.

dedhed

Some trailers use stub axle setups as well

RB1-luvr

...and joggers. My kid's Thule had sweet button release hubs.

wheelreason

Racing chairs use those hubs as well, cause they are like F1 bent trykes.

grumpus

Commonly used on wheelchairs. They come with 12 mm or 1/2" axles, and various lengths.

Duragrouch

In addition to the single-blade hub issue, also be aware that on a trike, if cornered hard, the tire and wheel experience lateral loads that it would never see on a bike banked into a turn. There's a good illustration of this in a book I read decades ago, showing a Speedy(?) early 'bent trike in a hard turn and the lateral distortion of the tire at the pavement was noticeable. I don't have specific info, but would guess this would require stronger wheel builds, and perhaps also, especially well-fitting clincher tires. Tubulars are an absolute no, they would roll right off.

jgwilliams

Cannondale do a bit more than dabble in them. Every bike with a 'Lefty' fork has them.

Dan Burkhart 

The fact that most trike wheels are smallish and can be built symmetrically rather than dished helps to alleviate those concerns.
One thing the OP does need to take into account if designing and building the trike is to work out the Akerman angles to avoid tire scrubbing.

grumpus

I'm not sure that zero dish is the way to go: most cornering force is going to be on the outside wheel, so doesn't it make sense to have a greater bracing angle on the outside of the wheel?The usual approximation is to point the steering arms at the middle of the rear wheel, which doesn't really need calculation - just use a piece of string. I'd anticipate more trouble getting the caster and camber set up.

Dan Burkhart 

Agree with that. Ideally, the caster and camber should be tuneable, but that takes some engineering.

Jeff Wills

The usual way around this (with conventional spoked wheels) is to build the outside with radial spokes and the inside with tangential spokes to resist braking torque.

Most commercial trike builders use tangential lacing, probably to reduce the number of different length spokes they need to stock. A 32- or 36-spoke 20” wheel can absorb a surprising amount of lateral force.

Besides, most recumbent trike riders don’t corner that hard- it tends to wear out tires lots faster than it loosens spokes.

FBinNY 

Wheels can tolerate a decent amount od side force. In any case, side force is limited by traction and the tip/slide ratio of the loaded trike.

BITD upright racing trikes with tangent spoked wheels were routinely lifted onto the inside wheel for high speed cornering. Otherwise, cornering speed had to be limited to avoid tipping.

Duragrouch

Funny you should mention. It depends on how much lateral load transfer. A more highly loaded tire experiences more "slip angle" (difference between wheel intended direction and actual tire tread direction at the ground) in a turn versus lower loading; So a vehicle with a lot of load transfer (higher speeds, higher CG) and tires with flexible sidewalls, will automatically have some Ackermann steering, which is why road cars typically have a lot less Ackermann in the steering linkage than one might think, because with 100% Ackermann in the steering linkage, in reality it will have too much Ackerman. As performance cars have gone to increasingly lower profile tires, barely "rim protectors", with less slip angle, that matters, the car is designed around particular tires. However on a golf cart, low speeds, operating on turf, they tend to have 100% Ackermann in the steering.

Know what else has Ackermann? Boats with two widely space rudders, like on a catamaran or monohull offshore "maxi" sailboat; The tiller arms will not be parallel, but converging to far forward on the hull or futher forward, the turn center for the boat. Twin tail airplanes (or (wing)tip-sails like on a Long-Ez or a Beech Starship), it depends on the lateral spacing between the rudders, and tightness of turns relative to speed.

Dan Burkhart 

Interesting. That may be related to a phenomenon in heavy semi trucks that experience negative off track on curves taken at speed. I have about 4 million miles worth of practical experience with that one.

Duragrouch

What do you mean by negative off track? Wanting to go more straight than intended, or tighter turn than intended?

I don't know the Ackermanns on heavy trucks, but do know they have tall and skinny tire sections, so may have larger actual Ackermann angles in practice, or at least more when cornering hard versus low speed or slow lane changes. Also, some high-speed race cars actually may incorporate a bit of negative Ackerman in geometry or total combined practice (steering linkage + tire effects), because it improves stability at high speeds, IIRC.

FBinNY 

In discussing Akermans, it pays to consider a very fundamental difference between bikes or trikes and autos or trucks.

Trike tires are far more rigid against cornering forces owing to the combination of high pressure, small, circular section, and much lower loads.

Duragrouch

Maybe. The illustration I saw many decades ago showed considerable lateral flex, but that was then, trike tires now may be much better. However compared to auto tires, I could easily understand more lateral flex, as modern car tires in even moderate aspect ratio, have much wider tread section to section depth. I really have no idea of the lateral gap of bike tires when held vertical, versus banked in bicycle use.

IIRC, Formula 1 just in the past year or two, went to larger wheels and lower section tires. The old ones were much smaller rims and taller section height, and lower pressure I think, and when catching air in a tight turn running over the inner curb, in slow motion, that rear tire would actually oscillate laterally with respect to the wheel.

FBinNY 

Lateral flex is desirable in auto tires. Those of us driving long enough may remember how our bias ply tires handled terribly climbing over parallel height changes, like the slabs on concrete roads.

Lower profiles and radial tires minimize the problem with their greater ability to flex.

Duragrouch

I think all of the above is true with radial tires for most of their existence. But the very low profile tires that are common now, definitely have less sidewall flex, especially so if run-flats. (And I hate them, for me. On a later 'Vette or 911 etc, crisp steering, handling, and space for bigger brake discs. On passenger cars, it's mostly about styling, and man does it hurt ride, and I'm not a ride fanatic, I don't like float, but it's harsh, and it bashes the heck out of the rims and car structure. Heck, I have 14" 60-series on my car (tall section by today's norms), put a set of Michelins on it (all costco had in 14"), nice performing tire, but sidewalls were so much stiffer I had to lower the air pressure 3 lbs from spec at both ends.)

FBinNY 

Flex is hard to define. Low profile tires are actually more flexible rradially, but obviously through a smaller range. Side to side, they're extremely flexible, compared to rounder profiles. Those properties are why they ride so nice. It also make them more forgiving of uneven pavements.

I drove a Miata for 20 years. Using 60 ratio tires moat of the time. (never 50 ratio or less on lousy east coast roads). But used narrower, more upright tires for winter. You could feel the difference through the steering wheel.

Duragrouch

I'll take your word for it.

I had an NA package B.