| Q. Isn't the Jump Stop just
treating a symptom rather than fixing a problem? Isn't
inward derailment really caused by poor shifting technique and/or
improper derailleur adjustment? A. We tend to be suspicious of fixes that are cheap and easy, and often for good reason. A patch that temporarily hides a worsening problem is not a real fix, and it can make things worse later on. But the Jump Stop merely bridges a small gap in bicycle transmission design--hardly different in principle from the many ramps routinely used to guide machine parts in industrial applications. It doesn't hide any underlying problem, it doesn't cause damage, it can actually prevent damage, and the performance benefits are permanent. Front derailleurs are for initiating shifts--which they accomplish by derailing the chain from whatever ring it is running on. Preventing overshifts is not really part of their design. In an ideal downshift, the chain will land squarely on the next smaller ring--preferably with the rollers lined up with the inter-tooth spaces. The limited side flex in the chain usually helps it to land close to the ideal position, but there are a large number of factors which can affect how the chain lands, such as component configurations, chain lines, pedal pressure, rotation speeds, bike bounce, bike sway, equipment wear, and so on. Even so, it will usually land correctly, but every time you downshift, there is a chance it will overshoot.. For shifts that would overshoot the smallest ring, the front derailleur has only one backup--the upshift plate. But the upshift plate is designed and optimized for upshifting. It is sometimes accidentally in the right place to help prevent a derailment, but the shape and position that make it a good upshift plate also make it a lousy chain guide. It has to work at a distance from the inner ring, or else upshift performance suffers and it might not clear the middle chainring. But that distance leaves a sizeable gap for the chain to dive through. And the further back you go, the bigger the problem with chainline sweep, so the upshift plate would need to have a different horizontal position for each rear gear for it to operate as a guide. But its position during a downshift is dictated, not by where it needs to be in order to prevent a derailment, but by where the downshift plate needs to be in order to initiate the downshift. The Jump Stop, on the other hand, is an anti-derailment specialist. It doesn't have to perform any other function, so its shape and position could be optimized for its one job.. But that also lets the front derailleur specialize in its job. With a Jump Stop in place, there is no need to settle for some mediocre compromise between safe and fast downshifts. The "proper" inner limit setting simply becomes the one that delivers the highest-performance downshifts. Q. Will the Jump Stop prevent chain suck? A. I try to sort out the issues relating to chain suck here. Q. Is the Jump Stop the best chain guide out there? A. Depends on what you need. See my chain guides overview page for a comparison of the properties of the various designs. Q. I'm running a single front chainring and my chain keeps coming off. Will the Jump Stop work even though there isn't a front derailleur? A. I have many single-ring customers who use the Jump Stop in conjunction with an outer ring guide. Even though I did not foresee that application when I was designing the Jump Stop, it seems to work quite well. (Too bad Dave Millar did not have guides on his single ring bike in the 2003 Tour de France prologue time trial--finishing less than a tenth of a second away from victory after dropping his chain. Ouch.) Q. How much side-to-side adjustment range does the Jump Stop have? A. Measuring the distance between the seat tube and the chain when it's on the smallest (or only) ring, the Jump Stop can cover a gap from 15mm to 35mm (9/16" to 1-3/8"). Q. I have a rear suspension linkage (or pivot) that is right where the Jump Stop would need to go. Is there some way the Jump Stop can work on my bike? A. Probably not. However, an inner ring guide will sometimes work on full suspension bikes. Q. I have a carbon-fiber frame which has oversized tubing and a high joint between the seat tube and the down tube. Will the Jump Stop work on my bike? A. Such bikes generally need a high clamp and a low guide. A standard Jump Stop will not work, but see my drop-down adapter kit (link pending). Q. Do you have a list that shows what tube size the different bike brands have? A. Makers often use different tube sizes for different models, and that can change from year to year, or even within a year, or sometimes according to frame size. The best way to determine size is to read the size off the derailleur clamp or measure the tube directly (see the paper measuring technique on the specs and order info. page). Q. I need to lower the Jump Stop a small amount, but the downtube weld is in the way. Would it hurt the clamp to shave off some plastic in front where it meets the weld? A. The clamp experiences the highest stresses in back. Up to 1/3 of the clamp width can be removed in front without seriously reducing overall clamp strength. A bench grinder, Dremel, or a belt sander are among the quickest ways to get a reasonably smooth cut. If the Jump Stop needs to be lowered more than 5mm, the drop-down mount adapter kit may be a better solution. Q. I need to lower the Jump Stop, but a pulley weld / suspension weld in back is in the way. Can material in back be removed so it can be mounted lower? A. That would mean removing structural metal from the mounting arm, and making the clamp weaker at its highest stress point. The Jump Stop probably will not work in this application. Q. Can I turn the Jump Stop over and use it upside-down? A. In that position, it would be likely to catch an edge and jam into the crank. I recommend not doing this. Q. I can't mount the Jump Stop on the seat tube. Will it work if I mount it on the down tube? A. No. Derailments can start well before the down tube. Once a derailment has begun, it is uncorrectable. Q. My front derailleur cable rubs on the Jump Stop. Will that hurt anything? A. No. Q. My front derailleur cage touches the upper rear corner of the guide, but I can't lower the clamp. Is there a way to move the guide forward a little bit? A. Yes. There is a 90 degree bend between the guide plate and the mounting arm of the guide bracket. If you open that bend up to a larger angle, and then rotate the clamp to bring the guide plate back into roughly parallel with the chainrings, that will move the guide plate forward. Q. My tubing seems a little bit oversized and the Jump Stop won't quite fit.. What do I do? A. There are several ways to deal with that, including a deep socket modification, heat-resetting, and going to a larger clamp and shimming back. Let me know what the tube circumference is and I'll try to figure the best solution. Q. Have you considered making the Jump Stop in different colors? A. I plan to stay with basic black. It has the best UV resistance, doesn't fade or change color over time, and offering a single color cuts production costs, so it helps in my efforts to hold the price down. Q. Couldn't I make a chain guide myself out of an old front derailleur? A. Very possibly yes, if you are running a standard high-clamp (bottom swing) front derailleur. A low-clamp dummy derailleur stands a much better chance of not interfering with a high-clamp working derailleur, but in a few cases you can mount a high-clamp dummy without interfering. All you'd need to do is remove the downshift plate, the top bridge, the tail bridge, and maybe the rear portion of the upshift plate, and it would be ready to mount. If you don't mind doing a little work, and if the dummy doesn't interfere with your working derailleur, and if the working derailleur doesn't block access to the set screws in the dummy derailleur, and if you don't mind a little extra weight, and you don't care about the usual derailleur clamp damage to your frame finish, and if handling reverse derailments is a low priority, then a scrap front derailleur may very well serve as an inexpensive and stout guide--one that likely works better and holds up longer than some commercially available guides. Q. What sort of racing sponsorship program do you have? A. Nothing at this time. For now, I have my hands full just keeping the business going. Q. Do you accept orders from outside the U.S.? A. I can ship outside the U.S., but I can't process payments in foreign currencies. Most of my international customers either mail back cash or use PayPal. International shipping costs two bucks. |
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