Along the theme of "stuff I want to get done this winter" is this idea of modding a CycleOps Fluid Trainer.
One of the biggest shortcomings of a normal trainer is that it doesn't rock side to side. Way back when there was a mild attempt to make such a trainer, manufactured and sold by Technogym. A friend had one and I tried it briefly. To use it you took the front wheel off and clamped the fork into a spring-mounted "fork mount". Two springs, about the size of a coil spring you might find inside an old suspension fork, allowed the "fork mount" tilt from side to side.
I don't remember much of the device except that the springs forced the bike back to vertical with too much power - I felt like I was on a coil spring playground ride rather than on a bike on a pretend road.
Kurt Kinetics has a better design. Theirs rocks from side to side at a natural height, about halfway between the hub and bottom of the tire. Ideally I think a bike would rock around about the bottom bracket - if you watch a rider coming directly at you while rocking the bike you'll see the bottom bracket follows essentially a straight line, the tires carving small arcs under it, the rest of the bike waggling above the bottom bracket.
Having said that I decided that modding my CycleOps to resemble a Kurt would make sense. I'm sure they tried putting the pivot a bit higher and found whatever they found and therefore decided to put the pivot a touch lower.
Having tried one as well as watching numerous other try one, I think they got it right.
In addition the CycleOps and Kurt basically share the same "frame", meaning the trainer frame. There's a connection between the two companies that, although I don't know the details, results in the fact that both companies use what I consider to be the best (aka most rigid) trainer frames around.
A final vote in favor of using the CycleOps frame - I have an extra one. Yes, an extra frame. I had a Fluid trainer and a Power trainer, both by CycleOps. The power trainer, which used a proprietary head unit matched with some electric motor/generator resistance unit, literally started smoking one night, the smell of burning electrical stuff filling the room. CycleOps, to their credit, sent out a Fluid unit as a replacement. Although I asked for just the resistance unit they sent a whole trainer, including the frame. This left me with an extra frame with no resistance unit.
In the meantime I'd switched resistance units to the former-power frame (and for the life of me I don't remember why I thought this was a good thing). This left me with a gray Fluid frame for modding purposes.
A scrap piece of metal gave me the raw materials needed to mod the frame. The thick metal plate would have felt at home as a side skirt on a WW2 tank. It weighed a good 60 or 70 pounds and it was only about 15"x15". Let's put it this way - I had a hard time carrying it on my own.
I recruited the same guy that painted my red frame. He can do some very basic welding and in fact I'd been thinking about having him fix some of the white van's rusty areas. He, in turn, recruited a local metal artisan to cut the metal into smaller pieces with a plasma cutter. That artisan, incidentally, covered his whole house in metal, and who made a local bike sculpture. With the raw plates in hand (the rest of the plate was essentially payment to the artisan) the painter guy could start his work.
First, though, I had to tell him what I wanted from the project. The painter is not a bike guy, and in fact he lights up a cigarette if he doesn't have one already in his mouth. He understands mechanical stuff but really doesn't understand the bike riding part of bike riding.
I tried to get some angles and fit type things in place. I planned on using a 2x6 as a wide base for the trainer, with wooden extensions reaching forward. The regular folding legs won't work because they'd lock the trainer and prevent it from rocking. I know that if I had a 2x4 under the front wheel it's about the right height off the floor, so I figured that if I "fitted" everything with the bike flat on the floor then I could raise/lower it in "2x4" increments.
Thoughts on height, plate angle.
Regular folding legs are the lower tubes, with the black caps on them. They'll go away.
You'll see that the bike's rear tire is sitting on the floor. I don't have the rest of the bike in the frame, just the rear wheel. I wanted to get an idea of where the trainer would sit, what angle the arms would hit, what sort of angle I needed on my "rocking plates".
Gusset shape, if needed.
I had no idea how strong the welds would be so I figured we'd need a gusset plate. I knew that I had given the painter an extremely heavy piece of steel, significantly thicker than the plates used in the Kurt. Plus if the thing broke I'd just topple over, it's not like I'd be going 60 mph in a tuck.
Probable placement of plate.
After a lot of debate I decided that putting the plate under the U-tube would work best. It gave a lot of surface area to the weld area, it would clear the controls of the resistance unit (the spring loaded lever thing), and it gave me enough height off the ground to give me room for the additional plates necessary to create the non-rocking part of the frame.
The guy welding didn't do the gussets immediately and I told him, after checking things out, that they didn't seem necessary. The welder guy did paint everything so it looks semi-pro. He also shaved the original leg mounts, for the folding legs. Although I wasn't keen on that it does clean things up. It also commits me to trying this out.
Bolting things together, the various plates in the right order.
Wood works really well although it looks pretty ghetto.
I didn't get a 2x6 piece of wood but I had 2x4s left over from my garage organizing binge; I decided to use them instead of going out and buying another piece of wood. This seems to be totally fine, very rigid and secure. I used galvanized carriage bolts, galvanized washers, and stainless steel nuts, all in interest of their anticorrosion properties.
(2x4s are 1-1/2" thick so I bought 3-1/2" carriage bolts to give me 1/2" for threads and washers.)
The carriage bolts come up from underneath - I use a gym mat type thing under the trainer so the rounded head underneath won't hurt anything, and on a rug it won't hurt either. This allows me to periodically check the nuts on top without having to tilt the whole trainer on its side.
Now one error the welder made, not realizing how things were going to work, is that he welded the wide plate to the trainer stand. I meant to have the wide plates sandwiching the narrow plate, so there's more room for the rocking motion. He also assembled them in the wrong order, which to me illustrated that he had not fully realized the idea of the whole thing. This is my bad.
My first trial ride ended unsuccessfully inside of two minutes. I used OEM spec rubber spring tower bushings from the now-gone 1993 Honda Civic. It's a light car, 2000 lbs or so, and the bushings are pretty soft. I bought polyurethane bushings for the car but I actually installed them in the car. I thought I had extra bushings and went looking for them. See, back then I bought the shock install kit as well as a "full suspension" kit, but apparently the full suspension kit didn't include shock bushings.
Note the downward tilt (the rest of the trainer is to the left).
Rubber bushings, not polyurethane.
At any rate the rubber bushings allowed too much tilt to the front. This exacerbated something that already happens to the Rock N Roll. The tilt allows the angle to change between the trainer support arm and the bike, forcing something to flex a bit. It appears the skewer moves within the locking arm but the skewer could easily rotate on the frame. The latter would prematurely wear out the dropouts on the frame, not a good thing.
The solution, at least temporarily, is to insert a nylon washer to act as a (bearing) bushing. A better solution would be to use a thrust bearing, typically used in a clutch assembly to allow the clutch to slide back and forth while allowing the shaft to spin. Thrust bearings allow the shaft to rotate (or something to rotate around the shaft) while supporting mainly a side load. Modding the skewer holder to accept two thrust bearings is a bit much right now but at least I have something to think about.
My plans for step two include a couple different things.
First, I need to get much stiffer bushings, probably polyurethane, hopefully a bit taller. A friend who is revamping his car's suspension my have some used poly bushings for me but if they don't work out then I'll just go and buy some poly bushings. I may get larger ones if I buy them, like bushings that fit between a chassis and body (typically in trucks).
Second, I'd like to tackle that pivoting issue with the skewer and skewer holder. There's a great site McMaster Carr and they sell all sorts of hardware. I've bought things like sway bar clamps, stainless steel license plate screws, and even suspension nuts (metric fine thread), and they have an assortment of thrust bearings. I think just having a thrust bearing between the skewer and the skewer holder will work out fine.
For for now that's where I stand. Everything has worked out well so far except for the too-soft bushings. After I fix that I'll see how the trainer actually works when I do out of saddle efforts.