What are the pros and cons of mounting a rear caliper stay arm to the swingarm vs to the frame?
Wade
if its on the frame it will pivot when the suspension moves. dont do it. (unless its a pivoting mount ON the swing-arm bolt, not likely what you had in mind)
Right, does the pivoting of the caliper adversely affect the suspension? In my little pin head it seems like it could cause the rear end to squat under braking.
Wade
well, the caliper bracket is typically mounted, fixed, to the axle. if it pivots on that it cant be tight or it needs to be mounted on a bearing of some sort.
does the whole assembly moving on the swing-arm under 'normal' mounting affect suspension negatively? no. there is zero benefit from my point of view of mounting the stay on the frame though, why are you trying to go this way? IMHO, its a bad idea because it adds complexity to do correctly (add pivots, etc) and offers zero benefit aside from just being weird. I'm trying to understand the 'why' is all. I mean, ANYTHING can be done.
I'm just exploring options at this point. I've seen it done both ways and there must be a reason for each. A fixed, non-pivoting caliper does seem to be the norm.
Wade
id like to see an example of it done the other way. i've never seen that done except on a rigid framed bike.
:thumbs: Challenge accepted! I'll do some looking and get back to you.
Wade
(https://external-preview.redd.it/77G3bn05I9oXR4pQ9_d2m2LmFTLAKRZC1baSZK_gynk.jpg?auto=webp&s=9391670d214f7363f7cc77b11263eac5c68e8292)
Draw a line from the center line of the swing arm pivot to the center line of the axle. The center of the brake pad should be EXACTLY 90 degrees from that line, otherwise it loads the wheel weird.
(https://imgwebikenet-8744.kxcdn.com/catalogue/10822/wq194001.jpg)
ok. not seeing any benefit but on a bearing as i figured. to me, that would just add another few wear points and complexity for no real reason? unless i'm missing something here.
i disagree about the pad being 90 degrees from the pivot, it doesn't matter in a conventional setup, you can actually put it anywhere on the perimeter of the disc, the load will transfer the same. on that setup, should be the same as it just will act as a bell crank.. But yup, you found one.
I don't know what the advantage, if any, of this system is; I was hoping someone would chime in with an explanation! As a last resort, I will open a book. I have a couple out in the barn that I think might address this. Maybe it's just another way of doing things. Regardless of where it's anchored, I find I like the look of the caliper under the swingarm.
Wade
thinking about this, it may have been an attempt at planting the rear tire to reduce potential wheel hop?. look at this very crude load diagram. the force on the brake stay will be in tension, but put compression on the swingarm. the ISSUE i see here is the affect on the arm will change depending upon the angle the arm is sitting. In the pic above, if the force is loaded it will actually unload the rear shock pushing the rear tire down under harder rear braking, but push the front end down. IF THE swingarm and brake stay were made to follow the same radial arc and move in unison, it will not load the arm in a weird way. note the arms are adjustable. again, fail to see any real benefit.
Sort of hard to see in this pic but you can always do it this was as well. There is no stag arm, it's just a slot in the caliper bracket and a pin on the inside of the swing arm that holds it in place. Unless you like the look of a brake stay for some reason. I'll try to get some better pics later.
Quote from: Jspooner on December 13, 2019, 01:39:56 PM
Sort of hard to see in this pic but you can always do it this was as well. There is no stag arm, it's just a slot in the caliper bracket and a pin on the inside of the swing arm that holds it in place. Unless you like the look of a brake stay for some reason. I'll try to get some better pics later.
It's true. Modern bikes do not have brake stays at all. The swingarm usually keys into the caliper bracket, and in some cases (like my TDR which isn't very "modern") the caliper bracket is bolted directly to the swingarm.
(https://i.ibb.co/VTRmGDj/D6412882-AF2-D-49-DD-AB6-D-68-AF51018-AC5.jpg)
same on a few of my bikes, way better way to do it. IMHO, nice and clean.
This kind of setup is called a "floating rear brake" and was pretty common on MXers years ago. The idea was to isolate braking forces from the rear suspension, and let the suspension work the same way whether you were braking or not. The ideal setup would be a paralellogram shape. So the potential advantage is a slight improvement in rear suspension when braking.
Disadvantages would be possible conflict with exhaust system, added weight and complexity, joints and bushings that need to be lubed and maintained. It would also be very difficult to use a brake stay for a rear drum brake, instead a brake cable would be used.
If I was to build this kind of setup, I would use ball joints at both ends of the static brake stay, and some kind of bushing where it pivots on the wheel axle spacer. A ball or roller bearing is neither suitable nor neccessary. A needle bearing may be, though.
Quote from: Dvsrd on December 13, 2019, 07:14:18 PM
The ideal setup would be a paralellogram shape.
yup, and neither of those seem to be at first glance. :twocents: