Darkside: Using a car tire on the rear wheel of a motorcycle.
Double Darkside: Using a car tire on the rear wheel of a motorcycle and a rear motorcycle tire on the front wheel of the motorcycle.
Among long distance motorcyclists, Darksiding is one topic sure to make riders take sides for and against, with little hope of reconciling in the middle. Yet some riders have run a car tire on a motorcycle successfully for tens, if not hundreds of thousands of miles.
Why do it? because car tires are generally much cheaper than motorcycle tires and the car tires last a LOT longer, especially on the rear wheel of the motorcycle. I go through a rear tire on the ST1300 about every 12,000 miles and a front tire about every 20,000 miles. Texas roads will eat my rear tire in less than 10,000 miles. At $200.00 per rear tire, that gets expensive. I changed out 5 tires in 2019 and 30,000 miles.
It seems counterintuitive that a car tire would work on a motorcycle, but it can. Tire choice is important. Motorcycle rims are generally much narrower than car tire rims, so you end up spooning a wider tire on a narrower rim, which can be difficult. Some car tires have more rounded edges, especially sport tires, which makes them sticky in turns. I’m told it takes a couple hundred miles to get used to the somewhat different feel, and while really aggressive cornering on a mountain road is probably best left to a sport bike tire, a car tire can be pushed quite hard. Mileage is the main advantage. One can get 20 to 30 thousand miles out of a car tire rear tire.
Hancook Ventus V2 car tires are a popular choice for some bikes. My motorcycle rear tire size is a 170/60R17. There are no car tire choices that size. The nearest is a 205/50R17, a much wider tire. But, with the rounded edges and the narrower rim, the tire ends up fairly rounded, especially at the edges when mounted on the motorcycle rim. It’s not easy getting it on the rim with tire irons, but I managed with just a little extra effort, four tire irons, a custom 2×4 frame, and a couple of bungee cords.
I now have the tire mounted and installed on the bike. Unfortunately, it rubs a bit on the right side of the swingarm. There seems to be some casting differences from year to year on the ST1300 and 2007 may have some extra material at the top of the swingarm where the casting seam is.
I have taken about 3mm of material off the right side swingarm with a flap disc on a grinder. Comes off fast, so watch what you are doing. The tire no longer rubs.
Unfortunately, a snowstorm blew in as I was putting the bike back together, so ride update coming…