PaulTrikeBoy

Why at most trike manufacturers, the front wheels are 20" ? Is it a question of minimum size in relation to price or for security or whatever reason ?

newbert

I'm guessing here, but among the reasons may be:

1. It allows the frame to be shorter, which lowers cost of materials
2, It makes the trike more "nimble" (ie - smaller steering radius).
3. It probably allows the distance between the front wheels to be shorter too (so turning does not interfere with the pedals and/or the frame). Smaller distance between front wheels means easier to fold, store and transport as well.

I'm sure there are other reasons.

VegasTriker

The lower the center of gravity on a trike, the more stable it will be going into a turn at higher speeds. Some owners have switched from 20 to 24" tires but I'll bet it changed the handling characteristics of the trike. Catrike used to make a models with 16" wheels as did Greenspeed. However, there were a very limited selection of 16" tires. 20" wheels are used on a lot of BMX bikes so the selection of tires is much greater. I use BMX tires (Tioga Powerblock S-Spec) since buying my 2013 Catrike 700. It is available in a couple of different widths and has proven to be a tough tire at a reasonable price.

BlazingPedals

Mostly I think it's because small front wheels impinge on the cockpit less during turns. It's also true about the wheelbase, because larger wheels would have to be moved forward to prevent them hitting the seat in turns. Of course, if they're not hitting the seat, they'd still hit the rider's legs!

williaty

Have you tried a trike with larger front wheels? I've ridden both 3x24" and 3x26" wheels. Compared to a 20" front/something rear, they feel TERRIBLE. They feel tippy, awkward, and clumsy compared to trikes having smaller front wheels. The only time it makes sense is on something like the ICE Full Fat where the whole intent of the trike is something entirely different and then it feels suited for that use.

linberl

Smaller wheels are stronger, too.

PaulTrikeBoy

Thank you for your information. I think the only advantage of 24" front wheels is to increase speed and distance with the same effort when compared to 20" wheels. The larger the diameter of a wheel, the longer the distance, as everyone well knows.

williaty

Your understanding is wrong, but it's a thing that is really commonly misunderstood in the bike community.

Larger wheels do not automatically increase speed or distance and certainly not with the same effort! In terms of what you can feel as a human, all larger wheels do is to give you higher gearing. You still have to be able to support the same power output to go the same speed regardless of whether you're on 20" or 29" wheels. Putting a larger wheel on is functionally equivalent to putting on a larger chainring. Any other effects require either good lab equipment or quite a lot of marketing BS to perceive.

There's a SMALL difference in rolling resistance due to the larger wheels having a lower rotational velocity at the bearings, but I really do mean SMALL.
There is also a SMALL increase in the a larger wheels ability to roll up and over a bump due to the change in the tangent angle when the wheel meets the bump. Again, over the range of wheel sizes we're talking about, that's a SMALL effect.
There's also a SMALL difference in rotational inertia that makes the wheel harder to accelerate, harder to decelerate, and harder to change direction when you make it larger.

Again, never underestimate how many people will fool themselves into believing there's a difference just because they spent some money on something the magazine said would make them faster!

PaulTrikeBoy

It's comments like yours that I like to read. I am not an expert and I could be wrong. A 26" wheel travels a slightly longer distance (to make a single turn) than a 24" wheel and a 24" wheel travels a slightly longer distance (to make a single turn) than a 20" wheel. This a little more can make a difference on a 100 km course.

BlazingPedals

A larger wheel will travel further per revolution; but what you're really trying to impugn is that a wheel/tire takes a certain amount of effort per revolution based on its diameter. That's not really true. Rolling resistances of tires varies wildly. It's true that even high-quality 20" tires have higher rolling resistances than even middle-of-the-line 700c tires; but the same is true of 24" and 26" tires. So I don't think you can make a hard-and-fast rule about wheel size being directly related to efficiency. Also, since front tires aren't driven, they don't affect drive ratios. (You didn't really say that but I'm not sure you WEREN'T saying it.)

Trikes in general take more energy go run down the road for a given distance, as compared to a 2-wheeled road bike. That's because they have 3 wheels instead of 2, and also because in spite of their low profile, they're wide and still have a fair amount of frontal area.

williaty

The poster after you covered a lot of it, but I'll take a swing at it too.

Two things are true simultaneously:

1) Bigger diameter wheels have a larger circumference (they roll farther per revolution)
2) How far you roll per revolution has no meaningful impact on how much work you have to do to go a given distance.

Your effort is per unit distance not per revolution. So you're going to work the same amount to go a mile regardless of the size of your wheel (within reason. We're ignoring, say, roller skate wheels or wheels so big you need a ladder to climb on). The dominant factor in how much work you have to do is (for normal people speeds) whether you're going uphill or down. The second biggest factor at normal people speeds is going to be your overall efficiency which is composed of things like your chain path (tubes, idlers, etc), if your drivetrain is in good condition and lubed properly, losses in the tire/tube, wheel alignment, and other mechanical factors. The smallest effect at normal people speed is going to be aerodynamics (again, assuming we're ignoring things like carrying a 4' diameter pinwheel off the back of the trike). Wheel diameter doesn't play into any of that other than a very small impact on your mechanical losses due to slight changes in rotational speeds of the bearings in the hubs.

To say it a different way: You have to do the same amount of work to go the same distance on the same course in the same weather because the amount of work you do is based almost exclusively on things that don't change with wheel diameter. How far your travel each time your wheel turns over doesn't matter because the *distance* matters, not the wheel turning over. If you turn your wheel over 1.3 or 0.8 times per meter doesn't change the fact that you still had to ride a meter and *that's* what actually matters.


The meter maters. The revolutions don't.

PaulTrikeBoy

I appreciate your comment "williaty" . Really relevant.

mobilemail

Added to that, the front wheels (topic of this question) don't really contribute to how far you roll. The rear wheel is driving the bike, and that energy cause the front wheels to move. So if the front wheel is 12" or 26", it will go as far as the rear wheel takes you!

79pmooney

An interesting aside - somewhere near the beginning of last century a fellow measured rolling resistance to different sized but otherwise similar wheels on various surfaces. His conclusion: On hard, smooth surfaces smaller wheels were OK, down to IIRC ~26". But on rougher surfaces, bigger was better. His finding were either not recognized or lost. Independently, the French and English both went to ~27" diameter for the then less than perfect pavement. That researcher would have approved. Mountain bikes came along on smaller wheels, being rolled over gnarly terrain. 26". (Horrors!) 29ers came along. (About time!)

And 20 or so years ago, a fellow was routinely racing criteriums on 24" wheels and paying no penalty at all. Yes, a tiny bit under the best RR diameter but better on centripetal inertia so he was benefiting every turn.

So, to tricycles - you are paying for smaller diameter all the time. Inertia is probably a toss between 20" and less but two wheels vs a regular bike with 700c.

I've wondered if it would be possible and feasible to have wheels that lean in turns to get the outboard tire patch further out for stability. My further investigation however will wait until I need such bikes/trikes and it matters more than "armchair".

rydabent

Well if you have a 27 inch back tire and and 20 inch fronts, you are always riding down hill, That makes riding easier!!!!