I have to agree with AvGeek, in that some of the posts are getting too personal. Keep it civil. The passion in this thread is exactly why I split this from the other thread.
Every time this debate comes up, RC is right in that there are a few actual data points for the positive/pro side, and a lot of opinions and passion on the anti side. Most of the anti sentiment begins like one of our original ones did, with loud people not understanding half of what they tried to use to make their case, further muddying the water.
What got my interest has been to see what the objective facts would be. Why are people successfully running car tires and not killing themselves left and right? After some research this week, I both think I have some answers and can see the design issue giving the tire companies an objective reason to recommend against using car tires on motorcycles. (Dunlop is a great example that the mfgs can also sound like Chicken Little and diminish their own credibility by stating that motorcycles must never pull trailers, owners should not change their own tires, etc.)
My goal in all of this has been for all of to better understand what we are discussing. Any time risk is discussed objectively, there is an acceptance of some frequency of expected failures which is then weighed against the potential results if a failure occurs. We would rather have little things fail sometimes which aren't catastrophic, rather than expecting that something really bad WILL happen.
So from that basis:
On the pro-CT side, I see lots of owners with usage (frequency) data, they have lots of miles (more frequency data), the CT has a heavier load rating which is nearly a 20% safety margin, and cooler running which is important to tire reliability. The fact is that Goldwing owners are experiencing less failures with car tires, and the above are probably part of that. Handling changes of CT are increased straight-line stability which is a positive for highway touring bikes. While the handling change would be an undesirable increase in force/response effort for sport and ADV style m/c, but the additional effort to maneuver is not unpredictable. Tire structural integrity hasn't been an issue since radials became popular. (You ought to see the lateral forces tires endure when a jet has a cross-wind landing!) Note that none of these benefits have to do with better mileage, reduced cost, or being cheap.
Coming out as neither a pro or a con, some math indicates that Yellow_Wolf running his Goldwing as hard as he was really wasn't even close to the loads the tire was capable of. Even though he was not running at gross weight, the CT has an 18% increase in potential gross weight capability (1,201 lbs vs 992 lbs), there is typically a 2X factor or more in tire design, and the 'Wing is limited to 42 degrees in lean. That lean is only about 1.6G total and his lateral doesn't even reach the 1G lateral of a 45 degree bank. None of this lessens his comments about the car tire taking more effort.
However, what people have missed as the biggest anti-CT aspect is that the potential risk in the failure mode can be instantly catastrophic. I write potential, because the known factual basis so far is based in the difference of rim designs and a limited amount of NHTSA testing which was done for a change in FMVSS tire standards.
In his GoldwingFacts post, 82gl1100iwingman pointed to the CT tire's bead toe potentially being 5mm wider than that of the MC rim. Wheel rims have a "safety hump" (he labeled it as a bead hump) intended to keep the bead toe against the rim when pressure is lost. His upper right illustration shown below has a CT on the left flange of a MC rim in the upper right and you can see how the extra 5mm could place the bead slightly beyond pocket created by the hump:
There is a CT bead unseating test required for NHTSA FMVSS 119 and 120 (none required for MC) and I've been looking for actual test results. One tire was been a 16" and not too much bigger than a Goldwing would use; it was pretty typical of the rest of the CT in the bead unseating. While tires inflated to 36 psi passed the test, at 28 psi some did not. At first glance, anybody running a CT on a MC would just say "OK, I'll keep my pressure up." The problem with that logic is that this was for a CT on a matching CT rim and I can't find any records of anybody performing a bead unseating test for a CT on a MC rim, where the tire toe is already not fully seated. In addition to the legal argument I pointed out once before for the tire companies, here's a technical objection for them to cite.
So the bottom line is that there are some good reasons and experience for the use of CT, but the risk is that if your tire starts to lose air, you really do have something to be concerned about. The difference means that the designs indicate that a hard cornering maneuver at gross weight with low pressure could lead to instant loss of the tire, as could a slow leak while riding straight up.
[font=verdana, arial, helvetica, sans-serif]Again and agreeing with Groundhog, this isn't offered to change anybody's opinion about whether or not to use a CT. It's been a curiosity exercise on my part, adds to the collective knowledge, and in the end reinforces the need to constantly check tire pressures, no matter what kind of tire you use.[/font]
