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Nicht Uber Max: Tires and brakes (again!)

Tuesday, May 9, 2017   (0 Comments)
Posted by: George Mangicaro (#136221)

Q:

Why does my 2005 K 1200 LT eat up rear tires? -Matthew M. via email

 

A:

Even though it looks and acts like a luxury touring machine, your ’05 LT shares a number of characteristics with the K 1200 RS, including its torque rating of 85 foot-pounds. Torque is what gets you up to speed from a dead stop. If you jump on that throttle, you’re going to wear out more rear tires than front ones.

It also depends on what you’re doing with your LT. If you’re pulling a trailer and all three cases are packed to the max with gold bars while your partner hangs out on the rear seat and has their pockets full of depleted uranium rods, you could be overloading the rear tire and causing it to wear out prematurely. As a side note, overloading your bike like this could also damage your final drive; in other words, it’s important to pay attention to BMW’s max load specification. Your bike’s “wet weight” (all fluids on board) is about 860 pounds and BMW says the GVW is 1,323 pounds, leaving you a load capacity—which includes you and your passenger—of 463 pounds. Exceeding that amount significantly can damage components, including the tires, which have their own load ratings.

Without getting into a discussion about tire preferences, you should endeavor to purchase a tire that is rated for your motorcycle and application. This seems like an obvious thing to say, but there’s a difference between “I heard these tires are great” and “This tire is rated for an 800-pound load.” Purchasing off-brand tires isn’t a great way to save money, largely because you end up replacing them more often than high quality (and more expensive) tires. In the long run, you’re likely to come out even in rubber costs, but you’re likely to install (or paying to have installed) more of the cheap tires, which eliminates any perceived savings on parts costs. The tire that’s appropriate for a sport bike isn’t appropriate for a touring bike even if the wheel sizes are the same. It’s the application that is the determining factor, not the size.

Tire Sidewall
Look at your tire’s sidewall to get important information, such as max load ratings. On this Metzeler ME880, which many LT riders use, you can see it is rated for 963 pounds at 50 PSI. Most riders don’t inflate their tires to 50 PSI, but how PSI affects load rating is a conversation for another time.

Q:

George, I'm surprised at your response to Doug's question. Doug mentioned that the bike had ABS and that they had "blown out the ABS module," but you made no mention of the ABS module in your response. I know nothing of motorcycle ABS; however, ABS modules in automobiles include a pump that returns brake fluid released to control braking pressure into the pressurized system. That keeps the brake pedal from dropping out from under the driver's foot as a result of ABS activation.

Could it not be that something in the ABS module has gone awry and that fluid is being pumped back to the master cylinder, creating the leakage that Doug comments upon? If that is not possible, would it not then be appropriate for your response to rule it out?? --Brant M.

A:

Brant, The R 1100 RT used an ABS pump that, when in ABS mode, shunts the flow from the master cylinder. This prevents the lever from "going to the floor." If you stay in ABS mode long enough, eventually you will "go to the floor." Every time the pump cycles you lose a tiny bit of pressure until it reads wheel slip and reactivates. It has no way of pushing fluid back to the master.

Doug's complaint was during normal operation, not in ABS mode. During normal operation, his ABS pump is passive. If the pump were running when not needed, he would have heard it and lost pressure. I had an R 1100 RS that would go into ABS mode when not needed. The only way to stop the bike was to release the brakes, turn off the key and reapply the brakes.

If Doug had a modern, linked system (post IABSI), what you are describing is possible. In those models, a stepper motor is used to activate the caliper of the non-applied circuit. This causes a slight push back at the non-applied lever. If the lever was not adjusted correctly and the reservoir was over-filled, it would be possible to build pressure in the reservoir. Hope that answers your question.

Have questions for Nicht Uber Max? Send them to TechQuestions@bmwmoa.org.


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