RE: "Dark Side" Article by Tom Austin

#21
"I use the same argument when the BMW crowd gets their panties in a wad about the type of oil..."

Now that you mention it, I prefer Shell Rotella 5W-40 because... ;) LOL!
 

kwthom

Rider
Premier Member
IBA Member
#23
Excellent response, sir! An excerpt, and a reply...

<...>When this experiment started way back in 2008, it was with the motivation for making ownership of this FJR platform a bit more affordable. Fortunately for all of us the variables were complementary and gave favorable results. That is not always guaranteed, hence Engineer Tom Austin's suspicions and unease with the concept. I believe if he looks deeper into the data that these various user forums offer - the empirical evidence gained with experience, he would tend to feel a bit more at ease with the concept - at least where it has been proven successful.

In my humble opinion, as far as the fitment of these tires on the 5 1/2 width rim found on the back of our current Yamaha FJR platform, they work exceptionally well. In my own personal experience of ownership, the altered handling characteristics are well within the safe operational range for the typical rider. <...>
Several years' earlier when this became prevalent enough on a popular GL1800 forum, one thread in particular attempted to quantify the mileage of DS operation - only on the GL1800 platform.

With just the members of that specific forum, I believe the mileage with no reported adverse reaction was well in excess of nine million miles. Anecdotal evidence, perhaps, but still should not be completely discounted. Tell me what other means of real world evaluation would acquire that kind of reported mileage in 15 years?
 

Rusjel

Premier Member
#24
I really enjoyed Tom's article and am intrigued by the uses these tires have been put to, especially the Victory.

Have there been any instances of people suffering reduced edge grip because of the car profile. I imagine the car tire would be a harder compound as well, how does that effect grip?
 
#25
Have there been any instances of people suffering reduced edge grip because of the car profile. I imagine the car tire would be a harder compound as well, how does that effect grip?
"Grip" is an interesting concept. Most of the bikes we ride have more grip, or traction, available than we need under most circumstances. That is, riding a motorcycle on regular roads rarely gets anywhere near the limits of the performance envelope of the tires. If you watch video of bikes on track days, shod with regular m/c tires, you will see what I mean. Generally we sacrifice a lot of wear for traction we don't use or need.

Under some riding conditions it is possible for a tire to lose traction, and slide, but usually hard bits of the bike will ground well before the tire gives up. This is true even of motorcycles with car tires on the rear. If that sounds difficult to believe, look up the video of the Gold Wings at Laguna Seca, and see it for yourself.

Where motorcycle tires are poor is when the surface is wet. That is one condition when a car tire will usually perform better. In that instance, the ability to clear water is more important than grip, and the car tire is simply better at it. Equally, the car tire is better at braking in the wet, something Darksiders have been aware of for a long time.

There are a couple of areas where the m/c tire has an advantage. The first is handling. They steer much more quickly, and with less effort. That is something you either get used to, or you don't. They also weigh less, so they accelerate faster and are easier on the rear suspension.

There are all sorts of reasons given for sticking (sic) with a motorcycle tire. Much of that has to do with the approval of manufacturers and internet experts, neither of whom have done any real testing. Indeed, most manufacturers only really approve of the tires the bike is shipped from the factory wearing, a laughable position but one they stick to.

Virtually all the testing of car tires on a motorcycle is anecdotal. That is it has all been done by tens of thousands of riders who have adopted the practise with no known issues. The beads do not come off the rims. The tires do not come unstuck from the road any more than any other tire, and you do not crash in flames and die (well not, it would seem, from your choice of tire).

Some like it, some don't but there are no known safety issues, just "tut-tutting" from those who have decided it shouldn't be done. Darksiding offers motorcyclists a choice. You give up some things for advantages in other areas. It's a free choice and no one is saying you should do it :D
 

Rusjel

Premier Member
#26
Thanks for the considered response Steve. As an former motorcycle racer I have some idea of the reserves of grip afforded by modern tires. Given that we are one track vehicles can have fairly serious consequences for getting it wrong the whole reserve of grip thing appeals to me.

I imagine the transition from the flat to the shoulder of the tire would be a critical point.

As you state, doesn't say it can't or shouldn't be done, you take responsibility for your own decisions.

I'm asking the questions of,you experienced darksiders to help me make my decision.
 

kwthom

Rider
Premier Member
IBA Member
#27
<...>I imagine the transition from the flat to the shoulder of the tire would be a critical point.

As you state, doesn't say it can't or shouldn't be done, you take responsibility for your own decisions.

I'm asking the questions of,you experienced darksiders to help me make my decision.
Generally speaking, each bike has a slight variation from moto tire to CT; it may not be an apples-to-apples comparison, but it should be reasonably approximate.

I needed about 300 miles when I switched to actually get comfortable with the transition.

A bit more input to maintain a turn is one of the big differences (on a Goldwing...); and it can be a bit unwieldy in areas adjacent to intersections when a uneven road surface can take you for an unexpected shift; particularly at slightly faster than walking speeds.
 
#28
... and it can be a bit unwieldy in areas adjacent to intersections when a uneven road surface can take you for an unexpected shift; particularly at slightly faster than walking speeds.
This is the bit I like the least. I try to mitigate it by not making the angle too shallow, but I still don't like it :) The worst is getting back on the road after pulling over for a bonus, etc. I try to park the bike to give myself as close to a 90 degree transition as I can get.
 

TripperMike

Premier Member
IBR Finisher
#29
Under some riding conditions it is possible for a tire to lose traction, and slide, but usually hard bits of the bike will ground well before the tire gives up. This is true even of motorcycles with car tires on the rear. If that sounds difficult to believe, look up the video of the Gold Wings at Laguna Seca, and see it for yourself.

Where motorcycle tires are poor is when the surface is wet. That is one condition when a car tire will usually perform better. In that instance, the ability to clear water is more important than grip, and the car tire is simply better at it. Equally, the car tire is better at braking in the wet, something Darksiders have been aware of for a long time.




I agree and disagree with these comments Steve. I also believe the CT is better in the rain as well as on gravel. But only when the bike is vertical. I've learned through experience to slow down considerable in the twisties if the roads are wet or if gravel has been kicked up off the shoulders by cars. Sure you can watch videos of bikes leaning it hard into turns at a race track, but the track crews tend to do a good job of keeeping them debris free. Heck even I have taken my Feejer on a track while running a CT, and yes it's kinda surprising how you can still drag hard parts. But the thing is, once you start leaning the bike over, you truly are not single tracking it anymore. The rear tire will be tracking further to the inside of the turn than the front will be. There is an imbalance. So depending on the road conditions, it is my opinion that the BT and CT are not equals. The rear tire will hold, but I believe it is because of this "imbalance" that will cause the front to wash out first.

Before one chooses to run a CT, they should even hear from some of us naysayers. But truth be told, I am a naysayer who just mounted his 4th CT in preperation of BL8. I just ride more cautiously depending on conditions.
 

igneouss

Premier Member
#30
Compliments to Tom Austin for bringing us rational article on a subject that often leads to irrational discussions. I'd like to add an element to his analysis that I believe significant.

Austin's analysis focuses on the risk of a tire separating from the rim due to incorrect fit. Car rims and tires have a different profile than motorcycle tires and rims.

The addition I'd like to make is a consideration of the forces that act on tire/wheel combinations. In straight line use, car and motorcycle tires are subject to similar forces.

This is not the case when one examines cornering forces. In short, cars do not lean. Car tires are subject to enormous shear forces that are carried by the tire sidewall. Imagine skidding sideways... Motorcycles obviously lean when cornering. This keeps the forces roughly normal to the tire/wheel center line. The shear forces on motorcycle tire sidewalls are far less than the forces acting on car tire sidewalls.

In turn, car tire sidewalls are designed to withstand far more shear than motorcycle tires. I would posit that if you tried the ridiculous experiment of putting motorcycle tires on a car that you would run a serious risk of peeling the tire off the rim when cornering.

Although simple conjecture, it may be the case that, due to differences in sidewall design, car tires might actually be less likely to separate from the rim than motorcycle tires.
 
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John Cooper

Premier Member
IBR Finisher
#31
I enjoyed reading the facts about tires that Mr. Austin presented but I am curious if any of y'all have experience with a CT just separating from the rim in a corner or anywhere else? Know anyone who has had this happen using a CT?

I run run-flat (or ZP) 195/55-R16 on the rear of my GL1800 and I have used one of many brands. In July 2014 while riding in the MERA 5 & Dime, 20+ miles from Concordia, KS, on a gravel road with no cell reception my rear was punctured by something about the size of a pencil and lost all its air. My plug kit was old and long since dried up. I rode the motorcycle with no air to town, rode it around town the next day looking for help and a new tire (Concordia is a tiny town). Even after more than 35 miles (including 10 on gravel) at zero-pressure, Andy who changed the tire commented: "that tire was a bitch to get separated from the rim". Without being able to run a CT I would have been down another day and not finished the rally at all.

I believe the science that indicates CT's are not suited for motorcycles but I think it is possible the studies are not complete. There is a mountain of anecdotal evidence that suggests CT is not dangerous so long as you understand its limitation (low-speed issues and corners).
 

Patrick Ford

Premier Member
IBR Finisher
#32
I'm not the greatest rider by any means but I have not found any limitations with my C/Ts. The rear end grabs a little at low speed on uneven roadways. The GL takes a bit more to pull over in a turn but takes about 10-15 minutes to get used to.
I have leaned over to the point of scraping hard parts with a KU-31, not on purpose but it did so with no problem.
I like the run flat Kumho best for John's reason. The best deal is an Atlas, found on Amazon for $48. It was recommended by Greg Rice and was an excellent tire. I have s brand new one in the garage along side a new KU-31 for use next June.
YRMV.
 

Patrick Ford

Premier Member
IBR Finisher
#33
I said Atlas and ment to say Achilles tires. I need a caretaker to help me with e mail.
Sorry about that. But I did get that from Greg. :(