Originally Posted by GBarnes
Actually, I think they are just trying to cover their ass.
I've mixed radial front and bias rear, worked great.
I've mixed bias front & radial rear; worked OK, but I did notice some "handling irregularities". Nothing too serious.
Anecdotes and case histories are not data, they are more like opinions and we all have them. There was a time I told people that mixing was no problem too. Not any more. "Nothing too serious" maybe, but serious can happen fast and unexpectedly when the conditions are right for things to go wrong. Sure lots of folks ride on all kinds of tires. If you're going to ride fast, and around corners, do you want to take unnecessary chances? I don't.
I rode a bias/radial mix (new tires, well balanced) from Vermont to Fla down Skyline drive and the Blueridge Parkway in November. In fog, wet roads, and leaves, they handled great; this was spirited riding in the twisties.
Got to Fla on the interstate, doing 70-80 in a straight line. The road surface changed. No problem it seemed. Then all of a sudden the bike started to squirm, pretty severely. Not a tank slapper, but a whole bike fishtail kind of motion; a relatively high frequency oscillation. The sensation was like going over a steel grate deck bridge with the old Conti-Twin tires, the kind with the straight tread pattern; some will know what I am talking about. But this squirming was at about 80 mph and was severe enough that Spiros, riding behind me noticed and radioed to ask if everything was okay. Things were not okay, I had just had the ... scared outta me. I pulled over and checked the final drive, tire pressures, etc. Nothing wrong. After I experimented with riding and noted that this unsual behavior could be repeated by going 80 mph and starting a gentle turn as in initiating a lane change. If I had had to make a sudden change in direction to avoid something before I discovered the problem I'm sure I could have lost it, the bike was very unstable. BTW Spiros was running a matched set of tires (Metzs I think) and had no problems, matching speed with me. What caused this unusual problem? I think (opinion) it was a combination of road surface, tire temp and pressure, and the bias/radial mix I was running.
This discussion comes around time and again. And the same opinions come up. In my opinion the tire companies are "covering their asses" because they know there is a risk associated with mixing tires. The question is: do you want to cover your own ass or not, since it's your ass that is literally gonna hit the pavement if the tire companies are right and opinions to the contrary are wrong.
BTW, we rode back to the northeast from Fla and I never had a recurrence of the problem. High speeds trying to outrun a northeaster snow storm on the Garden State Parkway. Then finishing the ride in a few inches of snow as I got back to VT. The instability never recurred (the snow was a different story). I changed to a matched set of tires and have never had a similar experience since. IMO the instability the tire companies are warning about isn't something you are going to notice unless you find just the right conditions or you are an experienced professional rider, on a track, testing various combinations under varying conditions.