Here are some random thoughts, or as I prefer to think, bits of random wisdom, that have been going through my mind recently.
Suspension: When I was much younger, I concluded that adjusting the preload on the rear strut (shock) on my motorcycle was essentially just setting the ride height of the back of the motorcycle. After all, once the bike was off the centerstand, the combined bike’s and rider’s weight was all resting on the coil spring that was compressed short of full extension. But then a while back I was riding a recently purchased used motorcycle ahead of a friend of mine. I hit a modest bump in the pavement and felt a somewhat jarring thump. The next time we stopped, my friend told me the rear tire had hopped off the pavement at least two inches when the rear shock fully compressed. All I could think was “wow.” It wasn’t that much of a bump.
Then Jim explained it in terms even I could understand. He said, “You need more preload on your rear shock. It has a progressively wound spring and you used up all of the travel on the soft end of the shock spring.” So in addition to setting ride height, adjusting the preload, particularly of a progressively wound spring, controls both the distance and rate of travel as the suspension is subjected to jarring forces.
This brings up the confusing terms of “high speed” and “low speed” damping. It also brings up the less confusing but still misunderstood terms “rebound” damping and “compression” damping. Simple struts, or what we call shocks, are composed of a coil spring around a hydraulic damper. The spring compresses when the tire hits a bump in the road, and the hydraulic damper slows the extension of the spring back to its normal ride length. That slowing of the extension of the spring is rebound damping. More sophisticated struts also use the oil, valves and piston movement inside the hydraulic damper to slow the compression of the spring when the tire encounters an increased load. This is called compression damping.
The terms high-speed damping and low-speed damping don’t have anything to do with how fast you are riding your motorcycle. They refer to the quickness at which the piston in the hydraulic damper is moving. Rolling into and then out of a corner increases and then decreases the load on the rear tire. The spring compresses slightly and then extends in response to this change in loading. That is slow speed piston movement moderated by slow speed damping. When you hit a sharp bump, the spring compresses quickly and then seeks to extend just as quickly. The oil, valves, and piston in the hydraulic damper slow these quick movements. That is high-speed damping.
This means that if the strut on my recently purchased motorcycle had better high speed compression damping, the soft progressive spring might not have allowed the suspension to reach the limit of its travel when I hit that little bump.
BMW now makes so many models, fitted with such an array of different rear struts and for Telelever models, front struts, I can no longer keep track of them. The aftermarket adds variety, and the variety adds complexity. Some struts have adjustable high-speed damping and adjustable low-speed damping. Some have a single adjustment, and some are not adjustable at all.
My advice is don’t guess. Carefully read and follow any instructions that come with your suspension components and when in doubt, talk to the vendor or somebody who really knows that suspension.
Lighting and Wiring: I have read recently on the BMW MOA Forum of several cases where owners had headlight connectors or headlight wires melt after installing higher wattage headlight bulbs. The legalities of using headlight bulbs marketed for “off road use only” aside, using a 100-watt bulb in a circuit designed for a 55- or 60-watt bulb is a recipe for a roadside problem. The wires and switch simply are not sized to carry the increased current. With or without higher wattage bulbs, I recommend the use of relays for the headlight circuits.
Relays confuse a lot of people. They shouldn’t. A relay is nothing more than an electrically activated switch. Instead of physically moving the switch with your hand, you do it with electricity. A properly installed relay will draw electrical current directly from the battery (through a fuse, of course) through the relay to the light. The original OEM circuit will carry very low current used only to magnetize the relay coil and close the “switch.”
A few vendors sell pre-wired relay circuits that are almost plug and play. As an alternative you can use wire, connectors, fuse holders, and relays to build and install your own. Even with a stock headlight bulb, you will find reduced resistance in the circuit and higher voltage at the bulb than with the stock wiring. This translates into a brighter headlight even with a stock size bulb.
Tire Life: I read a question the other day from a rider wondering how many miles he might expect using a certain brand of tire on a certain model BMW motorcycle. The range of answers was all over the place. In total the answers were almost, but not quite, meaningless. There are many variables, and unless you fully understand those variables, you can’t draw much of a conclusion.
For example, in the first 200,000 miles on her R1100RS, Voni used Bridgestone BT54 tires, which were the OEM tires when she bought that motorcycle new. She averaged 8,400 miles per rear tire over those 200,000 or so miles, but that average included one tire that lasted 14,200 miles and another that lasted 6,100 miles. This is the same rider on the same bike with the same brand and model tire. A forum answer to the question could range from “I just got 14,200 miles on a BT54” to “I only got 6,100 miles on my BT54.” Sample size matters. So “Over 24 tires I averaged 8,400 miles” might be meaningful, where the other two possible answers would not be.
A careful look at the data regarding those 24 tires reveals the difference in tire life to be caused by where and when she rode on them. In the low mileage case, it was mostly on abrasive chip-sealed roads in Colorado and New Mexico in the middle of the summer. In the highest mileage case, it was mostly on smooth machine-laid asphalt roads commuting to and from work in Kansas in the fall and spring.
Riders vary, loads vary and riding environments vary. Unless you understand all of the important variables, information can be meaningless at best, and misleading at worst. Be careful.