[photosbymark]

Well I am in the final phases of my mental design for a trike of my own design. This is something I hope to do some touring in so reliability is important, as well as simplicity.

Most of the recumbent trikes I have seen have brakes on both front wheels and none on the back. Not only does that add some complexity of construction, it means you have to grab both brakes evenly to get a straight stop. Though I did it for years with my feet in another machine, its something I'd rather avoid if I could.

Yet this bike will be heavy enough that without some kind of modification of the standard road bike rim brakes, if there is only one brake on the rear wheel, it might not be enough stopping power, though it would be safer in many ways.

Now I have an idea. If I cut a piece of steel in the shape of the rim and put holes in it so I could mount more than one brake pad per side, I should be able significantly increase the stopping power of the rear brake and not have to deal with front brakes at all. Even better would be a disk brake system on the back, but that would probably break the budget on brakes.

Anyone ever seen a system like this? Any ideas of whether it should work or not work? Any input is appreciated.

[fleeter]

from what I remember of my physics classes, the amount of surface area doesn't improve the amount of grip (or stopping force in this instance). All that matters theoretically is the type of material, and the force being applied.
But it might be worth the try.

[Industry_Hack]

If you don't want to go with hydraulic discs, I would suggest that you try one of these:



A single rear brake is a bad idea. Even two rear brakes sounds sketchy.

[photosbymark]

I can understand what you say about size of the discs to a point. At some point you would reach a point of diminishing return. Yet if size of the braking surface didn't matter, why do sports cars have calipers that are so much bigger than that of a typical passenger car.

In a perfect world hydo disk brakes on all three wheels activated through a single lever would be the very best in stopping power. Trouble is getting them and keeping them adjusted becomes a key component. Yet cars can have the same types of pull too so it should be controllable. It would also be more expensive than the rest of of the bike combined.

The goal is to build this out of junkers. Yet the single brake handle activating two cables should work well for the both the front brakes. Keeping all the controls and brakes on a single handle would be desirable if possible.

Yet still I have some ways to test it without a big risk. Relatively flat land with relatively low traffic, I should be able to at least see what happens in a safe manner

[BlazingPedals]

Tadpoles have two brakes in front because a rear brake just skids. Tads deliberately put the center of gravity at about the trailing edge of the front wheels, for high-G turning capability; which makes them front-end heavy from the start. Weight transfer makes it even worse for using a back brake. Most of the commercial tadpoles I've seen use disc brakes in front. That simplifies mounting because the bracket can be part of the knuckle (or whatever it's called.)

[photosbymark]

That makes perfect sense. The weight transfer I hadn't considered under braking because with a regular bike I use rear brake most of the time. Yet when the braking starts the weight is going to shift forward, and doesn't matter how big the brakes are if their isn't as much force to hold the tire to the road.

New plan

[fleeter]

Originally Posted by photosbymark

I can understand what you say about size of the discs to a point. At some point you would reach a point of diminishing return. Yet if size of the braking surface didn't matter, why do sports cars have calipers that are so much bigger than that of a typical passenger car.

I had to rummage through my old books -- to find the amount of friction (or stopping force), all you need to know is the materials that are in contact with each other, and the force being applied. Surface area has nothing to do with it. The only reason cars have larger disks and calipers is for 1) heat dissipation, and 2)larger calipers are able to exert more force, increasing the stopping power.

So, if you're limited in the amount of pressure you can apply with your braking system, increasing the surface area isn't going to help you stop faster.

[photosbymark]

Well wouldn't the bigger brake surfaces have the same ability to apply more force, just as the 4 discs in a sports car apply more stopping power than the 2 discs in a passenger car. All I would be doing is the same thing, weight transfer issues aside

[BlazingPedals]

I'm not sure what you're arguing, but brakes work by converting kinetic energy to heat. Larger pads can convert more heat than smaller pads. If brakes get too hot, they fade. Larger brakes are the solution, because being larger means they are bigger heat sinks and have more radiator surface. Not just the rotors, the calipers too (they both get hot.)

[lowracer1]

The important thing I've found with front brakes on a trike is the improved cornering ability at high downhill speeds. If you are making a left hand corner at high speeds you grab more of the left hand brake and it actually pulls you around the corner. A rear brake would actually be dangerous in this case and cause you to slide out in a fast corner.