Any difference between the Tacx large and small drum rollers?
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  1. #1
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    Any difference between the Tacx large and small drum rollers?

    My faithful Tacx rollers are finally in need of replacement. I estimate that I've put 2500 miles/year on them, each year since 1988. I got them for $60 at a shop that was going out of business, so I think I got my money's worth. The drums/bearings are fine, but the frame is too rusted to survive another rubber band change. My question is this: mine are the larger diameter (110 mm) drum version, now called "rollertrack" model. There is also a smaller drum version (80mm) called "ecotrack". Has anyone used both, and what are the benefits of one over the other? does the smaller give more resistence, as it turns more often? are the bigger ones smoother because they turn less often? I've also got the speedmatic resistence device on the old ones. thanks.

  2. #2
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    Smaller drums will give you more resistance.

    Have you considered fabricating a new frame for your drums? I can't imagine it would be too hard, a quick trip down to Lowes/Home Depot should have everything you need. Might be cool just for the DIY aspect.

  3. #3

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    Rollers

    From www.kreitler.com:

    In general terms, the size of the drum is inversely proportional to the size of the load. Smaller diameter drums have more resistance due to the smaller surface area in contact between the tire and drum. Recreational riders will most likely be content with 4.5” drums, more serious riders/racers will work best on the 3” drums, and the most serious riders may opt for the 2.25” drums.

  4. #4

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    Quote Originally Posted by velochico
    From www.kreitler.com:

    In general terms, the size of the drum is inversely proportional to the size of the load. Smaller diameter drums have more resistance due to the smaller surface area in contact between the tire and drum. Recreational riders will most likely be content with 4.5” drums, more serious riders/racers will work best on the 3” drums, and the most serious riders may opt for the 2.25” drums.
    Sounds like the people at Krietler don't understand the physics behind their products. Surface contact area is controlled by the load on the tire and the inflation pressure, not the size of the rollers. Smaller rollers have more resistance because the tires must flex more as they rotate to conform to the smaller drum diameter.

    The Krietler web site also has this tidbit: "Why does Kreitler use one drum in the front instead of two? So you can develop better control and balance. The trade-off in using two front drums is that you don't have to learn true balance and control because it is doing the work for you (kind'a like hiring someone to do your training). If you were not trying to develop balance, control, a smooth circle spin, etc. you would be on a windtrainer, right?"

    The reason rollers don't have two drums in front is because one drum makes it easier to control, not harder. Bicycle control requires the front wheel be steered easily with little force. The front wheel is steered much more easily with a single point contact (as with a single front drum or on a flat road surface). If two drums were used, it would take far more force turn the front wheel, making the bike more difficult to control (not less difficult as Krietler seems to believe). I defy anybody at Krietler to try to ride a two front drum set of rollers.

  5. #5
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    Kreitler understands their product perfectly. You and Kreitler are saying the exact same thing, only from a different point of view. They state that the reduced diameter decreases the surface area, increasing resistance. This is a true statement, because the decreased area they describe increases the deflection that you describe. It is the lowered surface area that allows the increased deflection, holding weight and inflation constant. A pencil-sized roller would deflect more, the floor less, corresponding to the area in contact. Boyle's law, and a bit of geometry.

    Not long ago, someone posted a pic of a four-roller model. Turns out, they're quite possible to ride. Out of curiousity, I put my bike on the rollers backwards. As you describe, doesn't work out, as it's very hard to steer. On the plus side, that means that it's not as 'squirrely' as some find a regular set. If you get it going straight, it will keep at it until you mess up. Unfortunately, once it's crooked, it's gonna stay that way, too. In fact, your weight tends to jam the wheel between the rollers, so once you get a little crooked, the front goes to right angles quickly.

    The answer is to have the two front rollers closely spaced. That creates the steering stability that some would desire, but reduces the leverage against steering. Feels fairly like riding on a regular road. But like Kreitler says, it defeats the purpose of riding rollers.
    A good habit is as hard to break as a bad one..

  6. #6

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    Quote Originally Posted by danl1
    Kreitler understands their product perfectly. You and Kreitler are saying the exact same thing, only from a different point of view. They state that the reduced diameter decreases the surface area, increasing resistance. This is a true statement, because the decreased area they describe increases the deflection that you describe. It is the lowered surface area that allows the increased deflection, holding weight and inflation constant. A pencil-sized roller would deflect more, the floor less, corresponding to the area in contact. Boyle's law, and a bit of geometry.
    In the range of drum sizes typically used for rollers (3" - 6"), there is very little difference in actual area of contact between tire and drum. What does change is the shape of the contact area. And that shape causes a greater deflection of the tire tread and casing.

    And what does Boyle's Law (which states that under constant temperature, the volume of a gas times its pressure is a constant) have to do with anything? There is almost no change in the volume and pressure in the tire, since the deflected volume is very small compared to the total volume of the tire.

  7. #7
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    My Tacx "rollertrack" frames also rusted.

    Bought them about 1988 as well.

    I recently took them apart and had the frame powercoated flat black.
    The drums and bearing were still in good shape as well.

    Ordered a new band and was off. Almost as good as new.

    You mentioned that yours were rusted beyond repair. What happened to them.

    The powder coat cost almost what you paid for yours but still cheaper than buying a new pair.

    If I were to replace I would go with the Kritler Dya Lite. The alum. drums are sexy.
    Last edited by pigpen; 01-20-2006 at 12:58 PM.

  8. #8
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    Your (correct) statement that the contact area stays the same is true only because of Boyle's law. For simple math, say we have a 200lb rider and a 100lb inflation pressure. We'd end up with a 2sq.in. contact patch no matter what size roller we were on. If it couldn't supply that patch (say, in the case of a pencil-sized roller), we'd bottom out and snakebite. It's simply another application of Boyle's law, by holding a different term as constant. You seem to be thinking of it in a "piston" example, where a force over a fixed area effects the gas' volume and pressure inversely. But we can as easily hold the pressure and volume and effect the area, which is what we are doing here.

    So, a load deflects more on a small roller than a big one, but the area stays the same. That's what you have effectively said, and of course it's correct.

    But we have to be careful, because it's a loaded sentence. If we rearrange it in a mathematical sense, it's equivalently saying that for a given deflection, the smaller drum has less surface area available. Which is what Kreitler said. Okay, so they left out a term or two. They're writing marketing materials, not junior-high science papers. Fault them on their writing style if you like. but the physics is just fine.
    A good habit is as hard to break as a bad one..

  9. #9
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    JFC - talk about people w/ too much time on their hands here....

    Um, Kreitler makes the best rollers period. I'd venture a guess that they understand what's going on w/ rollers as well as anyone. Gosh!

    My sis has a pr of Kreitlers that are 15 yrs old and she's only replaced the rubber band.

    I have a set of the 3" rollers and love them (4 yrs old). I'd not consider any other brands

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