RUNNING "DARKSIDE"

[burkbuilds]

RUNNING DARKSIDE:
I've been studying this for a while now and I've watched a bunch of You Tube videos where people have done it and I'm thinking of giving it a shot in the near future. Anybody else out there running "Darkside" on their Vulcan 500's? (Darkside is running a car tire on the rear instead of a Motorcycle tire). I just ordered a BF Goodrich T/A radial that I think will fit. Firestone also makes a car tire that should fit. The TA might be just a little wide, I'll have to see when I get it. I put calipers on the narrowest part of the rear fender where the tire needs to clear width wise and got 6.5". The TA is 6.1" at the widest point, which is a little less than a 1/4" clearance on each side but the OD is really close at 24.7" , the OE Bridgestone tire is 25.2" OD and 5.5" wide. I also considered a Firestone Car tire (F560 145 R15) which is 5.6" wide and an overall diameter of 24.3", but it didn't seem to be the same quality of tire that the BFG T/A is. The BFG has a Tread wear rating of 400, Traction rating A and an S speed rating and cost $63 The load rating is about double of the OE Bridgestone and based on what I've read in the rags I should get at least double the 12,000 miles I'm currently getting out of the Bridgestone rear tire and maybe triple or more. Right now I'm having to replace the rear tire every six months, so double that and I'll only have to do it once a year.

[Triangles]

One of my coworkers is planning on doing that with his Suzuki 500cc crotch rocket. You must have a long distance commute to be racking up all those miles. I'm not up to date on my tire tech so my following statements may.. er probably are way off in some fashion or another... I thought radial tires had the steel belts to prevent the center of the tire from flexing out creating a nice flat cross section on the tread with a fairly sharp corner at the "shoulders" to the sidewall. Desirable in a car, but not on a bike. I would think this would make the handling of the bike quite interesting. Let us know how this works.

[burkbuilds]

Hey Triangles,
I'm not sure how the construction of the Radial plays into it, but when I watch the video's where the camera is down there just above the road surface showing the tire in contact with the pavement it seems to work. I'm planning on mounting this tire on a separate rim, that way, if I don't like it, I can just pop the other tire back on without having to remount and balance and all that. I also decided to follow your lead and go with an older style aluminum wheel, which gives me the option of running without a tube. However, I'm not sure I will be able to seat the new tire on the rim without a tube, since I don't have the ability to shoot a high volume of air into the rim like they do at the tire store. If that's the case, then I'll have to use a tube anyway, just to be able to mount the tire. I've got the tire and the rim ordered, maybe they will be here by next weekend, then I'll get to play with the mounting process and go from there. This may take me a few weekends to be ready to give it a trial run.

[Triangles]

I've seen it done by igniting a flammable liquid in the tire, but I wouldn't be brave/stupid enuff to try this. You might be able to seat the bead with a regular tire pump. If you're paying a shop to balance the rim I'd be surprised if they would charge you anything xtra to seat the bead.

[burkbuilds]

So far I have been mounting and balancing my own tires, but I may have to pay someone to do this one for me.

[Triangles]

I've been doing some reading about this here I might give this a try as I have a spare alloy wheel laying around. I couldn't find anything remotely close to our stock tire size. What tire sizes were you considering?

[burkbuilds]

The OE Bridgestone tire on our bikes is 5.5" wide and 25.2" Outside Diameter. Firestone makes a tire, (f560 145 R15) that is 5.6" wide and 24.3" OD. That's slightly smaller in

OD, so your rpms may go up a little. The other possible option is the one I am trying first. BFGoodrich T/A Radial 155/80R15. That tire is wider than our OE by about 0.6"

which might be the kicker since the narrowest part of my rear fender is between two smooth ridges that measure 6.5" apart, leaving a little less than 1/4" on each side of the

tire if I hit a big bump and the tire goes way up in the fender well. The BFG is 24.7" OD, which is about the OD of our tire when it's down to it's wear limits, so it shouldn't be

much different in that respect. The BFG tire has a treadwear rating of 400, Traction rating of A, and a speed rating of S, which in car tires means 112 mph sustained for 10

minutes. I found it new for $63. If it turns out to be too wide, I'll go for the Firestone. There are probably a few others out there that will work but those are the two I'm

looking at. I've found several Darkside riders with the Firestone tire on their bikes but I couldn't find a lot of specification information on it.

[burkbuilds]

I meant to say thanks for the link to the "darkside" . I've read this guys stuff and it's pretty good, he certainly puts a lot of miles on his bike too. I also found the video's on Youtube to be very revealing. Nothing like actually watching the tire at ground level while it's being ridden to give you an idea of what it does.

[Triangles]

I may try the F560 155 R15 it's 6.1 wide and 25.1 outer diameter. Where did you find the dimensions for the OE tires? I found the dimension for the Dunlop 140/90 15 here and it was 24.72 OD I realize tires vary by manufacture by I didn't think there would be that much difference.

[burkbuilds]

Those sizes are all basically the same except for the tire width. 24.7 -25.2 is only a half inch total difference in diameter, not really all that significant if you think about it. Since Circumferance = 2 Pi r a tire with a 24.7 OD would travel 77.6" per revolution and a tire with an OD of 25.2 would travel 79.16" per revolution, I guess it would add up, but that's only a 2% difference. So, if you normally got 50mpg, with the largest tire, you'd now get 49mpg with the smallest one.
Right off hand I don't remember where I found that OD on the OEM tire, but theoretically you can calculate any tire from it's listed size and convert it to inches if that's what works for you, as it does for me. So, a 140/90 15 tire means, 140mm wide at the widest point under full inflation which converts to 5.5118" wide and the next number is a % of that width, so in this case 90 means 90% of 140 which is 126mm (the height of the tire above the rim) converted to inches that's 4.96" or basically 5 inches and then the number 15 is in inches so you can just add the numbers 15" + 5" +5" to get 25" OD of the tire. There are other ways to do it and as you say, each mfg. will have a slightly different final product but that should get you pretty close. (I often wonder what insane genius decided to mix mm, %, and Inches to determine a tire size?)

Using that same formula a 155/80 R15 will be 6.10" wide and 24.76" OD Theoretically.

You can simply divide the mm measurement by 25.4 to get inches.

Man, I just reread my post before I submitted it and I can't believe how much I sound like an egghead!

[Triangles]

some interesting videos of how the darkside looks.

[burkbuilds]

I did it. Switched over to the car tire today. I had a lot of trouble getting the tire to seat completely on the wheel. It would seat about 300 degrees but that last little bit just didn't want to pop out all the way. I tried several times in my shop and then took it down the road to a mechanic friend that does mainly front end alignment and tire replacement work. He got the same results and wasn't willing to put more than about 80 lbs of pressure on the tire. Next I went to a Suzuki dealer that's right behind my friends shop, they spent about 45 minutes on it and got the same results. Surprisingly, they never even mentioned that I was putting a car tire on a bike, I kinda expected to get some flak from them, but they seemed to think it was fairly common, and had no objections to trying, but they wouldn't put more than 55lbs of pressure on it. So I went back to my shop and tried a few more times, but no success. Next I called a commercial tire installation company and explained my situation, the owner told me to bring it on down and he'd get it on. I took it in and his first words after seeing the tire were, "well, there's your problem, your trying to put a car tire on a motorcycle rim." Yes, I replied, I'm tired of replacing the rear tire every six months. He told me that he rode a bike too, and he took my tire back to the shop area. I looked through the shop window and watched as he hooked it up to an air hose with a clip on it and then got about 6 feet away and put the air to it. In a few seconds I heard a loud "pop" then a few seconds later I heard another "pop". He then instructed one of his guys to let some air out of the tire and then brought it back to me fully seated. I asked him what he did to get it to seat and he said, "I put 110 lbs of pressure on it". Wow!

I was pleased when I got home to find that the 155 width tire, mounted on my rim, was exactly the same width as the 145 motorcycle tire mounted on the rim. I put calipers on both tires and they were exactly the same width, about 5 5/8".

Here is a shot of the calipers on the new BFGoodrich 155/80 R15 tire.

The next picture is the calipers on my Michelin 145/90 15 motorcycle tire and I didn't move the calipers at all after measuring the BFG tire, and you can see that they are both touching at the widest point.




Here is a shot looking down on the two tires side by side. You can see a big difference in the profile of the tread, and the motorcycle tire appears to be larger in diameter, but for all practical purposes, they are close enough.




Once I got the new tire balanced, which was a lot easier than balancing the motorcycle tire, and took a lot less weight to make it balance, I installed it on the bike and took it for a spin. I am using 35lbs of air in the tire. I don't really know how to determine the proper amount of pressure, so I'll just have to play with it a little and see how the tire is wearing.

I started out running some neighborhood roads and then took it up on state highway 27. Got it up to about 70 mph for about 3 miles and then turned around and came back the other way. Next I ran a local twisty road to see how it handled in the curves and then I took it up on Missionary Ridge and ran some more curves. Dropped down to East Ridge, Tn and headed out to I-24, took it back up to about 70-75 then headed south on I-75 for a few miles. Got off the highway, took some more twisties and came home.

Here's my impression. It does feel different than the motorcycle tire. Not worse, just different. I found it to run smoother and with less vibration than the motorcycle tire. It is easier to maintain your direction when going straight ahead, and you can almost balance out and not put your feet down at a stop, which is kinda cool. I also found that it corners great, just as well as the MC tire, maybe even better, but definitely not any less. It does take more "effort" to lean into the turns, but it's also easier to pop back up when you come out and switchbacks are not a problem at all. I never scraped the pegs but I was fairly aggressive in running the s-turns I hit tonight. I also took a few minutes and drove around in a gravel parking lot to see how it would do. Not a lot of difference there, but the back end never felt like it was sliding out at all, so maybe a little improvement over the mc tire.

Well, I'm not saying anybody else should do this, and I'm not saying it is a good idea or recommending it, but I will say that I'm glad I tried it, and I think I will probably stay with it. I like the way it feels, and I'm hoping it will last 2-3 times as many miles as my MC tires were. My friend who owns the alignment shop also rides and he said he had three people he knew who rode CT on the back tire of their Motorcycles.

[burkbuilds]

I failed to mention that I also changed from a spoked wheel to an aluminum rim so I wouldn't have to deal with all the labor of cleaning and shining the spokes and I also don't have to run an inner tube in the tire now. The only kinda weird thing is that the BFGoodrich tire is blackwall on one side and raised white letters on the other.

[Triangles]

I envy you! nothing but snow and ice here today Keep us updated on how it works out. It will be interesting to see how if at all it affects your fuel economy. If you get a chance take a pic or two of it on the bike. I think I now know what tire I'm getting next summer

[burkbuilds]

I've put about 1,000 miles on the car tire now. Fuel economy about the same, can't really tell any difference there. The "feel" is different. A lot of the people I've read posts from that switched to a car tire said that they got used to it and didn't notice it after a short time. I can't say that. I can still feel a difference. Kinda hard to put it into words, but I will try. The car tire reacts to some things that the motorcycle tire ignored, but it also dismisses things that the motorcycle tire was affected by. Examples, grooves in the road and long gouges left in the highway by car wheel rims when their tires blew out are less noticeable with the car tire on my bike. Uneven pavement is more noticeable though. When you are in a curve one direction and pop back up over the top and lean the other direction, the feel is seamless on a motorcycle tire, but on the car tire you feel like you hit a flat spot at the top. I've also noticed that in cold wet weather, you need to get a few miles on the car tire before it "sticks" as good as the motorcycle tire. The only time I've felt it "slide" a little was leaving work on a cold rainy day and pulling out in a fairly sharp left turn while aggressively accelerating onto the street. Now it's possible that I would have had the same "feel" with the motorcycle tire, not sure if I've ever had that exact set of circumstances when I had the bike tire on or not, but I've done it twice with the car tire. Never lost control or anything, just felt like it slid a little bit. Having said that, I'm happy with the change if it gets me double the mileage I was getting from much more expensive motorcycle tires. I plan to ride it out and see how well it wears. If this was a motorcycle tire it would be out of tread by June at the latest, so it shouldn't take long to answer this question.