Double Darkside? - Page 33 - BMW K1600 Forum : BMW K1600 GT and GTL Forums
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post #321 of 371 Old 06-18-2019, 12:29 AM
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Double Dark Update: 2014 K1600GTL with a 205/50ZR-17 BFGoodrich g-Force COMP-2 A/S XL on the back with the .25 spacer, and an Avon Roadrider AM-26 130/70R17 back tire mounted backwards on the front, both set at 40psi.

Just returned from the running the Tail of the Dragon et. al, some 700 miles away, and the verdict is in. You can have my car tire when you pry it from my cold dead hands! We stayed in Robbinsville on Hwy 129 a couple miles South of the Dragon at an AirBnB called the "Dragon's Nest" 2 Bedrooms was all we needed, but the place had a Pantry big enough for a blow-up mattress for 2, and room enough in the living room for two more if need be. Spectacular location, for under $100 a night.

We took at least 7 passes on the Dragon, and found that it is far better after 6pm, as the traffic dies out to the point you can sometimes run the 11 mile stretch with minimum impedance... which means FAST! While there, we also ran the Cherohala Skyway on the Ocoee Loop, Six Gap in GA, Ruby Run, the Moonshiner, the Great Smoky Mountains National Park Loop, Devil's Triangle, and a bit of the Blue Ridge Parkway. I found Six Gap as challenging as the Dragon, and Devil's Triangle even more so! (Corners down to 10mph, that had to be respected, as opposed to the Dragon's 15mph corners, that can be negotiated between 30 and 50 with some practice.)

The tires performed impeccably (even when wet), and I don't even understand how. Anybody who says the contact patch is the same or bigger than motorcycle tires is just flat out wrong; but somehow the grip is near absolute anyway, even while scraping my boots and pegs (which isn't something I'd done before on the K16, but had to become comfortable with, fast!) My buddy was on a Katana 600, which should have outperformed my big tour bike, but didn't stand a chance: He couldn't corner any faster, and was hopelessly over-matched in the relatively straight sections.

As for running Double Dark on the super-slab; no contest. The car tire is a dream on the highway, so effortless to maintain a straight line, I'd run one forever even if the performance wasn't outstanding in the twisties, which it is.

Attached find a couple pictures of my first pass on the Dragon, caught by the guys at 129photos.com. This was on our way into town, so was by far my slowest pass, but you can see in the second picture how little of my rear tire was actually in contact with the road, even going slow. If you look closely at the my fairing on the first picture, you'll see a reflection of the Sheriff who issued me a warning for riding sans helmet. Cool cop, who gave us the obligatory suggestion to pick up a whistle and tourniquet in case we left the road when no one was looking. Judging by his demeanor, and the large stack of blank warning citations on his seat, I think it's safe to say they know why we go there, and are NOT in a hurry to punish us for testing/developing our skills. As I was chatting with the Sheriff he got this weird look on his face, as if he didn't understand what he was seeing, then asked point blank: "Is that a car tire?" He rattled off some nonsense about the Dragon requiring Manufacturers' recommended tires (specifically citing slicks, which is real), but didn't pursue it further, beyond the apprehensive look covering his face.

At the end of the day, I now have 3,500 miles on the Double Dark setup and the chances of me ever going back are firmly set at ZERO. They still look fresh, and I absolutely love the way they perform!

P.s. Thanks again to all ya'll who provided guidance on the tire change, and I'm sorry I missed ya'll at the BMW MOA. Second AirBnB was about an hour North of there in Kentucky, but I couldn't see paying $85 dollars each for admission to what would have been a beer tent with live music, where I couldn't drink much beer on account of being an hour from home-base. Frankly, I wish I'd have spent another couple nights in Robbinsville.
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post #322 of 371 Old 06-18-2019, 01:04 AM
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Originally Posted by Bill Ward View Post
Anybody who says the contact patch is the same or bigger than motorcycle tires is just flat out wrong


you can see in the second picture how little of my rear tire was actually in contact with the road, even going slow

It is an illusion. You are looking at how much of the tire is out of contact with the road, and that makes it "seem" like you have less contact patch.

I had a friend riding behind me while I was on the Rune (I have a darkside rear on the Rune), who told me there was "almost nothing" in contact with the road when I went around a corner. He said almost all of the tire is off the ground and it is just running on a small sliver of tread near the edge.

I told him consider this: that is what a motorcycle tire does ALL the time, even when you are going straight--there is only ever a small contact patch with the road. That is why if you ride a lot on the highway, the flat strip wears into the middle of the tire. The car tire only looks goofy, because it appears there is so much contact patch when going straight, that your eye sees a relatively small percentage of what is "possible" for contact patch when you go around a corner, and your mind translates that into how much potential contact patch is off the road. Look above at the bike in the forum header/banner. How much of that rear tire is actually in contact with the pavement? Not much. But since the tire is crowned, you are not looking at it mentally as the rest of the width of the tire "should be" on the ground. What is in the air is not relevant. What is on the ground is relevant.

The only way the bike does not sink into the ground, is physics. There is x amount of force (weight) on the rear tire. That means there is x amount of force on the ground, whether that is through a 1 inch contact patch at a higher contact PSI or 20 square inches at a lower contact PSI. If a tire were a flexible balloon, 600 lbs of weight on the rear tire would result in 30 contact PSI across 20 sqin, or 40 contact PSI across 15 sqin. A tire is semi-rigid, so it is not quite that simple, but it is similar. It takes so much force to hold the bike up, and that force is applied to the ground, whether it is through a motorcycle tire or a car tire. The size of the contact patch will be similar. The lower the pressure, the bigger the contact patch will be. The higher the pressure, the smaller the contact patch will be. Since the tire is semi-rigid, it will not be linear.
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post #323 of 371 Old 06-18-2019, 01:27 AM
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I guess that makes sense. Looking at the Front (back) tire, there does appear to be a similar amount of contact, just not nearly as much not being used. Thanks for the explanation!
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post #324 of 371 Old 06-18-2019, 12:42 PM
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The tires performed impeccably (even when wet)...the grip is near absolute anyway, even while scraping my boots and pegs
Yeah, we know.

Like phat6 says, your contact patch is fine. When you're upright, it's way larger than on a bike tire, and when leaned over, it's still equal to what a bike tire does all the time.

You can see this by running through a large puddle of water, then running onto the dry and turning. Stop and look at the wet tire pattern left behind, and you'll see the rear car tire has as much or more contact patch as the front, even when leaned into a turn.

And yeah, I love chasing "faster" bikes on the Big-K...
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Ken IBA# 366
'13 K16GTL & '09 K13GT-LD
Some people see the gas tank as half empty. Some see it as half full.
All I care is that I know where the next tankful is coming from...

Last edited by Meese; 06-18-2019 at 12:51 PM.
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post #325 of 371 Old 06-24-2019, 06:13 PM
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Not going double darkside. Ordered a standard front. So this will be the setup when I change over:

  • Front: Avon Spirit ST -- 120/70ZR17
  • Rear: Pirelli Snowcontrol 3 -- 195/55R17

Fingers crossed that there are no fit issues and that the setup works well and lasts long.

Pirelli Snowcontrol 3 -- 195/55R17 - fits, without a spacer!


It is a TIGHT fit. It rubs on both sides while squeezing it into position. Did not remove the exhaust--put it in through the back. Once mounted and torqued, no rubbing while on the center stand. Took it out ran it up to ~70, did some gentle turns, and brought it back to inpsect for any rubbing or issues. I forgot to check the tire pressure. Turns out the shop that mounted it on the rim aired it up to 51 psi--way too much pressure. Let it down to 42 psi and will be doing some more testing, but so far looks like this one works!
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post #326 of 371 Old 06-24-2019, 06:23 PM
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post #327 of 371 Old 06-24-2019, 07:03 PM
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Quote:
Originally Posted by phat6 View Post
Quote:
Originally Posted by phat6 View Post
Not going double darkside. Ordered a standard front. So this will be the setup when I change over:

  • Front: Avon Spirit ST -- 120/70ZR17
  • Rear: Pirelli Snowcontrol 3 -- 195/55R17

Fingers crossed that there are no fit issues and that the setup works well and lasts long.

Pirelli Snowcontrol 3 -- 195/55R17 - fits, without a spacer!


It is a TIGHT fit. It rubs on both sides while squeezing it into position. Did not remove the exhaust--put it in through the back. Once mounted and torqued, no rubbing while on the center stand. Took it out ran it up to ~70, did some gentle turns, and brought it back to inpsect for any rubbing or issues. I forgot to check the tire pressure. Turns out the shop that mounted it on the rim aired it up to 51 psi--way too much pressure. Let it down to 42 psi and will be doing some more testing, but so far looks like this one works!
Snow tires in Vegas. Must be all this global warming....

Had 2014 gtl premium spring 17 - winter 2019 (rode 25k miles). Bought used Wing to try out (10k miles), Nah-too boring and slow. Like GTL better, bought another GTL. Ha.
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post #328 of 371 Old 06-26-2019, 11:31 PM
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Few more miles on the Pirelli Snowcontrol 3. My observations so far:

  • A car tire on a sport bike is definitely more noticeable than a car tire on a cruiser
  • This particular tire seems especially sensitive to acceleration in a corner
    • It bites hard (great traction) with all that siping when you are on the throttle enough
    • It is a little squirmy, more so than other tires, when you are not on the throttle enough in a corner
  • The "tipping point" can be felt on this tire on this bike. I cannot even feel the tipping point with the BFG g-force TA on the Rune

That is it so far. Need more miles to get better feel of it.
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post #329 of 371 Old 06-27-2019, 05:32 AM
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Thanks for the update.

You might want to experiment with different tire pressures to address the squirminess.

Ken IBA# 366
'13 K16GTL & '09 K13GT-LD
Some people see the gas tank as half empty. Some see it as half full.
All I care is that I know where the next tankful is coming from...
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post #330 of 371 Old 06-27-2019, 05:54 AM
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Quote:
Originally Posted by phat6 View Post
Few more miles on the Pirelli Snowcontrol 3...
  • The "tipping point" can be felt on this tire on this bike. I cannot even feel the tipping point with the BFG g-force TA on the Rune
  • Could it just be the tire? I don't feel the "tipping point" with a BFGoodrich g-Force COMP-2 A/S XL.

    Sketchiest it ever felt to me was today, for about 20 miles en-route to the Mississippi River, where they had ground grooves into the road in preparation for a new layer. Initially felt like I was off road, with ruts moving me where they pleased. I played with it a little, and just stopped caring. Even swerving side to side or going no handed; that little bit of play wasn't hurting anything. Approaching 4,500 miles since the change; and I remain in love with it!
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