RE: "Dark Side" Article by Tom Austin

HBarlow

Premier Member
#1
I enjoyed reading the outstanding article. I've read a lot of mostly unsupported opinions pro and con but mostly in favor of the use of car tires on a motorcycle. I've also talked with several good friends who run car tires on their Goldwings.

Ordinary old common sense told me that car tires were designed and tested on car rims used on cars and motorcycle tires are for motorcycles. I never wanted to try one.

I've been mildly concerned about the temperature of my rear tire at interstate highway speeds in 100°+ temps also.

Tom Austin's article is the first objective and thoughtful article on the subject supported by facts that I've come across and it was valuable to me. I'll stay with Dunlop Elite IIIs.
 

Rollin'

Premier Member
#2
I have been darksidin' for the past four years with no issues.
Love the wet weather traction, also works well on gravel and mud. Dunlop Winter Sport run flat snow tire.





Death Valley - 115 degrees

 

rodneyw71

KLR'er
Premier Member
#3
I have been darksidin' for the past four years with no issues.
Love the wet weather traction, also works well on gravel and mud. Dunlop Winter Sport run flat snow tire.





Death Valley - 115 degrees

How many miles are you getting out of your tires and how well do they work on roads like the Dragon?
 

Rollin'

Premier Member
#4
Never had a problem with the curves. Did a two up trip to Nova Scotia and the Cabot Trail.



Independence Pass -



Alaska Highway -



Completed 15 IBA rides on the Vision, 13 on the darkside.

.
 
#5
Count me in as a Darksider. I'm on my second CT after getting about 30k out of the first one. I've ridden plenty of twisties (Hwy 191 from Clifton, AZ to Alpine, AZ for one) without any concern about having a CT on the rear. When I first decided to try the darkside, I bought a spare rim to mount the CT. I figured if the CT wasn't my cup of tea, I could switch back to the Pilot Road I already had on the bike. It's been a couple of years now and the Pilot Road has not been back on the bike since I went to the darkside.

I can understand why it's not for everyone. If running a CT gives a rider the least bit of doubt, they shouldn't do it. I know plenty of riders who won't turn a wrench on their bikes because they think the engine will explode if they change the oil themselves.

I wouldn't have had the guts to try the darkside if it wasn't for the many riders who tried different CTs and posted their findings to the forums.

As with anything else motorcycle related, don't push yourself outside of what you feel is safe for you and the riders around you.

John
 

John Cooper

Premier Member
IBR Finisher
#6
I like the CT on the rear of the Wing for both longevity and the run flat. In May of 2014 in the MERA 5 & Dime, I was many miles down a gravel road with no mobile service and the run-flat saved me from a long wait for a flatbed, so I never consider any tire except a run-flat. I too have ridden through Clifton and Alpine AZ (2015 Bit Nippy) and - yes a lot of curves but I finished the ride ahead of every other finisher, so the CT was not too much of a distraction on the miles of curves. The indy guy who mounts mine cusses a lot but always gets it mounted and I use Centramatic balancers. I run a BT-45 rear on the front and that I might not do in the future (I am a double darkie) because I get some shake at about 82mph - it disappears at 85, but there is a sweet spot between 79-82 where the Wing does not feel happy. This does not happen with the E3 on the front. Regarding heat, my TPMS does not report temperature, so I have no idea if it is hot or not. In the 2015 IBR, I was running 80+ in the heat-bowl (NM AZ UT) and nothing bad happened.
 

rodneyw71

KLR'er
Premier Member
#7
I read the article in the New Ironbutt magazine and I'm mixed on this subject, I run Michelin commander II's on my voyager and right now have 11k miles on them and they still have tons of tread left, I may have to change them out in June though because I'm going to the grand canyon, Vegas, Utah, just piece of mind knowing I'll have new tires under my butt.
 

kwthom

Rider
Premier Member
IBA Member
#8
Another point of reference...

Some of the guys that I ride with are more 'sporty' with a GL1800 than many that enjoy our type of motorcycling. I like both kinds. :D Nearly all of them are on the extremes of use; all have transitioned to CT's; zero reported issues that I'm aware of with tens of thousands of miles annually.

At the ~28,000 mile mark on my motorcycle, MT #3 (ME880) decided to delaminate on me. I was able to nurse it home, put on my first CT and have not looked back.

Right now on my bike, CT#5 is nearing it's end of life. It presently has ~16k and the last identical tire was replaced with slightly less than 20k of use. My bike has ~104k on the odometer, and I'm not what you'd call a high mileage rider in keeping with the forum's membership, with an average of only 1k/month on my bike. I have a rim with a used tire that will be replaced in the next few weeks with CT#6.

It would seem that there is a significant percentage of LD riders - as well as some pretty sporty riders of GL1800's at least - that have yet to report any detrimental effects of using this non-standard combination of tire and OEM wheel. Who knows, this may be the optimum non-standard combination, solely based on rim diameters matching so well; who knows.

That being stated, I'd defer any comments in regards to this non-standard tire/rim combination on other motorcycle models to those that have significantly more experience on that platform and knowledge than I do.
 
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rodneyw71

KLR'er
Premier Member
#9
I put around 20k miles a yr on my bikes, so tire cost is a big one, I'd like to try the car tire, but doesn't sound like it would last any longer than my Michelin's.
 

tdragger

Premier Member
#12
I've been darkside on my Triumph Rocket III for 70+k miles. The first lasted 29k and the second 31k. The current one still looks brand new.

My only issue with the IBR requirements is in regards to the "run-flat" specification. The assumption that run-flats are appropriate artificially imposes a m/c tire mentality onto the use of a car tire. On a car tire, you don't want the sidewalls to be overly stiff. That's why we run them under-inflated around 28-30 psi. The sidewall flex allows for the tread to remain in contact with the road at increased lean angles. The stiff wall of the run-flat forces the tread to lift.

Please pardon the somewhat crude illustration:
 

Patrick Ford

Premier Member
IBR Finisher
#13
The IBR requirements regarding run flat car tires require a working TPMS. The reason for this requirement is that a two up couple were running a runflat Kumho and had a puncture. They didn't know the air was missing and continued until bad things started happening. On the back of a GL the Kumho can go flat without any indication to the rider.
 

tdragger

Premier Member
#14
The IBR requirements regarding run flat car tires require a working TPMS. The reason for this requirement is that a two up couple were running a runflat Kumho and had a puncture. They didn't know the air was missing and continued until bad things started happening. On the back of a GL the Kumho can go flat without any indication to the rider.
I've gone back and read the article and rule and now humbly admit that I mis-read it. If you have a run-flat tire, you must have a TPMS. If it is a regular car tire like I have on my Rocket III, I could still qualify for the IBR. No TPMS required. Thanks for setting me straight.

Come to the Darkside. We have cookies.
 
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#16
It's a good article written by an Engineer and targeted to a large diverse crowd with an overabundance of variables in the hardware, both in rides, rims, and tire choices. However it's interesting to note in the referenced article that the illustration given of the motorcycle tire bead profile vs. the automotive tire bead profile fitted in the motorcycle rim, does not take into consideration the soft flexible nature of rubber, and the angle of the bead due to the range of rim widths for that given tire.

The illustration below is from that article.




Note that the black filled in profile is the tire. The upper picture shows a motorcycle bead having an exact fit into the rim as designed. The lower picture shows an automotive tire riding on the bead hump of the rim keeping it from nesting properly in the seat area. This cookie cutter illustration fails to show the deflection that takes place at that corner due to rubber's soft nature. It also fails to show, at least in the case of our application, the angle of the sidewall to rim caused by the width of the tire. The 205/50 size tires we run on the FJR is rated for a 5 1/2 to 7 1/2 inch rim. Our rims are at the minimum width for these tires which causes the tire to squeeze narrower to fit within the rim. This helps force the outer corner of the tire bead to nestle into the corner radius of the rim, and the side profile of the bead to ride further up the side of the bead seat area.

I have run 4 automotive tires now on my 3 FJRs, and I mounted and balanced all of them myself. My method is to use a sheet of plywood on the garage floor, and use tire spoons with rim protectors. I cannot use my NoMar tire machine, because of the large rim clamps which do not accommodate the extra wide tire profile of the automotive tire; remember, we have to modify the brake strut to gain the necessary clearance to run this set up.

During the times my automotive tires were mounted, I've occasionally needed to remove them to replace my TPMS sensor mounted inside the tire and /or swapping the tire over to the new bike's rim. As always, I scrub the rim seat area clean of all residue with a kitchen scouring pad and soap before mounting/remounting the tire. I see first hand the contact pattern the tire has with the rim. The tight radius in the outer rim bead seat area does have evidence of a very slight gap, as the tire bead radius is indeed larger, and the wire within the bead isn't tight enough to force all of the rubber to fill this area. However, it is tight enough to force the bead to sit in the floor of the bead seat proper. There is also a very slight gap at the base of the hump where the rubber is forced to bridge this tight radius. The inner corner of the tire bead is forced up the center of this hump, which in my mind, causes a better chance of an air tight fit. My tires show no more air loss than any of the motorcycle tires I ran previous to this 'Car Tire Experiment' we are taking part of.

Please note that the motorcycle tires I have run on my first FJR AE (pictured in my avatar above) were the Avon Storm, the Michelin PR2, The Dunlop RoadSmart, and the OEM Metzler; I might have even run a Pirelli, off hand I don't remember that far back. Note that these are all premium tires, which command a premium price. All told these tires took me to about 75,000 miles on that bike. The automotive tires I have run since are the Bridgestone 019 Grid, 2 Michelin Pilot Exaltos, and the General G-Max AS-03. All 3 of the automotive tires are the 205/50 specification and are Steel Belted All Season Radials of the Sport Tire variety - not RunFlat tires. I have since clocked over 120,000 miles on these automotive tires. When I was running the motorcycle tires I was consistently getting 4 - 5,000 miles on them before they were worn out in the center - I must have a heavy throttle hand. Every 7 weeks I was looking to replace a tire, something had to change. These automotive tires are giving me approx. 36,000 miles each, and I am well pleased!

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. Granted, the bike is capable of sustained elevated speeds in the 130 - 140 mph range, but who does that on a regular basis - without getting multiple performance awards? Also note that these tires are known to affect the handling adversely at these speeds - it gets a bit squirrelly, which seems to put a cap on the speeds run. If you want to run these speeds, by all means mount a properly speed rated motorcycle tire to this bike and enjoy!



As always, Your Mileage May Vary






Brodie

 
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#17
I might also add that for the FJR platform, it only takes one modification to the brake strut arm in order to run this tire. No other modification is needed. If the desired results do not meet with satisfaction, it is completely reversible - just remount another motorcycle tire.

Brodie
:)
 

tdragger

Premier Member
#18
Nice post, Brodie. Quite a large number of Rocket III owners run darkside as well. Particularly on pre-ABS models the rear brake would easily overpower the stock m/c tire and lock up. Reports of low-sides, high-sides :eek: and other offs related to locking up the rear tire are far too commonly reported on the R3Owner sites. Various injuries have been reported and sadly we lost one founding member to a highside accident.

In all that time, there has not been a single report of a darkside tire contributing to an off among Rocket owners.

When someone inquires about running darkside, I always respond first with "What kind of rider are you?" Darkside is not for everyone. We have owners that are intent on flogging an 800lb gorilla in the mountains like it was a Gixxer. Those guys should stick to m/c tires. Those of us that are commuters or LD riders are good candidates for darkside. If the peg feelers touch down, I get such a tight pucker that I slow down immediately. You get my point. Darkside is fine for me. Others not so much.
 
#19
The argument about bead shapes has raged for years. One particular guy went to a lot of trouble a few years ago to tell us, in excruciating detail, how we were all irresponsible asses who would crash in flames, and die.

My question, because I simply refuse to enter that debate, is a simple one.

Does anyone, spanning the thousands of bikes and millions of miles, have a link to an example of a tire used this way breaking free of the rim?

I'll confess ... I've looked, and I can't find one.
 

Paul Knight

Premier Member
#20
Steve Bracken, I use the same argument when the BMW crowd gets their panties in a wad about the type of oil...

I have scoured the internet for any examples that the actual make of oil when changed every 5K miles or so has ever been documented to cause an engine failure or even cause for a warranty to be denied.

just my .02 cents