After going through three rear tires this year in 20K miles (two of which came to end-of-life while travelling away from home), I decided it was time to take a different approach and put a car tire (a.k.a. “CT”) on my rear motorcycle wheel. Known as “darksiding” or “going to the dark side”, this practice has been going on for many years, especially in the long distance riding community. The primary reason is simple: car tires will generally last many more miles than most motorcycle tires due to the tougher compounds and higher weight loads they are build to withstand.

For some reason, some riders get offended when the subject of darksiding comes up, possibly because some converts tend to proselytize. There are plenty of logical theoretical reasons why installing a CT may not be the best idea including:

• Motorcycle wheel rims are shaped differently, made to fit the bead of a motorcycle-specific tire very snugly. A CT bead fits on pretty well, but the bead shape is slightly different, creating a possible point of failure.
• Motorcycles are made to lean and the cross-section of MC tires is rounded to allow this to occur very easily. In contrast, car tires have a squarish cross-section, with the tread pattern not extended much past the “corners” of the tire. A pro rider would not be able to lean a darkside bike safely as much as they could that same bike with a MC tire.
• Again, due to the square cross-section, handling is affected as the bike now has a much larger tire patch on the road when going straight, as compared to a smaller one when leaned up on the edge.
• Many motorcycle dealers will not mount a CT on your bike due to concerns about safety (read: liability) since no motorcycle manufacturer recommends car tires on their bikes.

Despite these well-reasoned points, I have yet to hear any first-hand accounts of a tire failure or crash that has been attributed to someone riding darkside. Quite the opposite, it seems to me the riders that use CTs tend to put a lot more safe miles on their bikes than the casual motorcyclist. I personally know several people who ride as aggressively as I’ll ever hope to do in the twisties with a CT mounted.

So: is it a risk? Yes, definitely, but motorcycling is inherently risky and we all draw our own lines of acceptable risk.

Not all bikes are good candidates for a CT (apparently?), but the ST1300 has a reputation of eating tires due to it’s weight, horsepower, and handling ability, and there is is a lot of information online on various tires that will work on this bike. The two most popular seem to be the Hankook V12 and the Goodyear Triple Tread, with riders reporting getting mileage of 25K and 35K from those tires respectively. The Goodyear apparently requires some sanding down of the swing-arm metal on the bike to avoid rubbing, so I decided to start off with the Hankook to see if I even liked the feel of darksiding.

I ordered a Hankook V2 tire off the Internet and decided that if I was going to try this, I would go whole hog and go double-darkside. This means mounting a rear MC tire on your front rim, in addition to the CT on your rear rim. It is supposed to even out and improve the handling with the CT on the back. So I ordered a Bridgestone Battlax rear MC tire as well.

Once they arrived, I just needed to find a place to mount them. With low expectations, I put in a call to my local Honda dealer where I usually get my tires mounted. Told them I wanted to mount a car tire and (to my surprise) they said it would be no problem. So when the weekend finally rolled around I brought both wheels and the new tires down…only to be turned away by who I think was the head mechanic. He wanted to lecture me on safety and tire physics, but I just told him I didn’t want to argue and would respect his choice not to provide service to me.

They had no moral issues mounting the rear tire on the front rim, so I left that in their hands and called up Jim at Break’r Bikes in Exeter NH. Jim has a small tire change business he runs out of his garage, and I’d heard he would mount car tires. That was indeed the case and we agreed to meet later, as it would take me over an hour to drive up.

This was the normal MC tire before I removed the wheel.

After pulling in to their driveway, I was greeted by Jim’s wife Keely (whom I later found out drag races bikes) who immediately took my wheel and began the process of dismounting the off-brand racing tire I’d had mounted on my way through Missouri a couple weeks previous.

Jim joined us and we chatted while they finished removal of the tire and prepped to mount the CT. They have a nice big pneumatic tire changing machine, but I still lent a hand (and some weight) to seat the bead of the Hankook onto the rim.

They gave the new tire a quick wash down and then balanced the wheel.

“That’ll be $20, plus $2 if you leave the old tire.” I gave them $30 and thanked them profusely for taking care of me. The tire looked pretty badass and I couldn’t wait to get back home to mount it on the bike. I was rolling out of there less than an hour after I arrived – super efficient and friendly service…can’t recommend Break’r Bikes enough!

I got home and set about mounting the wheels. No problem with the front but that wide car tire just would NOT fit through the gap. Figuring I was missing something I sent out a quick message to my buddy who’d been through this process. I needed to DEFLATE the tire to get it mounted…*facepalm*. I mounted the wheel in short order, inflated to 29 psi (per a comment from a fellow ST rider) and verified that there seemed to be sufficient clearance for the tire to spin without touching any part of the bike.

Went for a quick spin around town taking it very easy and all seemed well, if a little “squishy” feeling in the corners.

Something had started nagging at me during this whole process and when I looked at some of the photos of other Hankook tire users I could see that the tread looked different from my tire. I must have gotten in a bit of a hurry and had misread the tire recommendation. I’d purchased and mounted a V2 model rather than the recommended V12. I did some more focused online searching and found at least one other ST rider that had used the V2 successfully. It’s an all-weather tire compared to the summer V12 model so the tread is deeper and the tire compound is probably a bit less “sticky”. Both are performance tires however and so far so good, I decided to just roll with it.

I’ve got maybe 1000 miles on the tire now, after having immediately increased the psi to around 39 which greatly improved the feel in the corners. I can definitely feel the difference from the Pilot Road 4 tires I’d been running…the bike doesn’t lean quite as quickly and there are other things that I can’t quite describe. But I’m getting comfortable with it and have run some curvy roads, though nothing crazy yet (more from lack of riding time in the past few weeks than any lack of confidence in the tire). I can pull a U-ey on a two-lane road just as easily as before I think.

So far so good on the experiment, and I’m looking forward to seeing how many miles I can get from the CT, and to increasing my comfort factor in the twisties in the coming season. It would be nice not to worry about tires on the next long trip, but we’ll see how it goes. I fell in love with the ST for it’s hippo-in-ballerina-shoes qualities and want to make sure I haven’t compromised too much fun in the corners.