Why would anyone in their right mind put a car tire on a motor bike? My opinion on Darkside

When I first found this darkside thing I thought they were crazy! But the more information I read convinced me they cant all be crazy surely. So I investigated all the pros and cons for about 12 months before making the change in 2017. I put that 300+kg cruiser bike through some SERIOUS testing dry and in the wet before I took my wife for a ride.

The following are some common questions and observations.

Q: What are the advantages to running a car tire on a heavy cruiser or touring type motorcycle?
Safety is improved with better braking traction, better wet weather traction and higher weight bearing capability.
Also expect a smoother ride with better straight line traction and up to three times the life of that expensive motorcycle tire that still had plenty of side tread when the center was worn out!
There’s also the Run Flat option if you’re worried about punctures but trade off may be a firmer ride.

Q: So how much contact patch does a car tire have compared to a mc tire?
A motorcycle tire only uses 10% of it's available surface at any given time. A car tire uses 100% of it's available surface at least 50% of the time (assuming you’re going straight half the time and turning the other half).
When leaning on a car tire you will never be on less than the 10% patch that you would have with the motorcycle tire. If your leaned to the max you'll have about 10% of the available surface being used. Any lean less than max will increase that percentage all the way back to 100% as you straighten the bike back up (see the diagram at the end of this video).

Q: Does the bike handle differently and will it handle the curves?
YES of course it handles differently. Requires a bit more effort to "turn in" more noticeable at low speed but thousands of people have been riding twisty roads on car tires at speed for many years without problems.

Q: Will the car tire ride on the sidewall? That sounds dangerous!
UPDATE 2021: This will depend on the type, brand and/or model of tire and pressure. If the sidewall is too flexible, it MAY ride on the sidewall AND THIS IS BAD. I found this out with a Dunlop SP Sport 9000 which has done 14000kms on my C109RT and is starting to get twitchy even though it still has heaps of tread left. Keep an eye on pressure and wear markers etc.

Q: Are there negative aspects of switching to a car tire?
YES. Due to the tire's flat profile it will want to follow road grooves and imperfections. At slow speeds it will want to stay perpendicular to the road surface. If the road is sloped to the right, the bike will want to lean to the right. Motorcycle tires do this too but the car tire exaggerates it. When you stop on that sloped surface, you need to put your foot out quickly and the bike may feel heavier to hold. If you have a bad knee or your boot slips out, this will potentially suck.
Small air pressure changes will affect the handling of the bike as well. Your relying on a certain amount of tire flex to maintain a consistent contact patch. Check your pressures at least monthly.

Q: How hard is it to get used to the handling?
Your bike will handle differently as explained above. Once you work out the optimum pressure for your tires, it won’t take long to get the hang of it. And just because you have better traction now, doesn’t mean you should push harder. Remember the Darkside is for big heavy bikes, not sport bikes. Relearn the bikes capabilities and stay within them.
UPDATE 2021: Because of the extra rear grip confidence, there is a tendancy to push that land tractor faster in corners especially in the wet. The front will let go before the back ever does and this is BAD! My current front tire has started slipping in the wet and its only half worn. Finding a really good front tire is my new mission and I'm willing to pay top dollar for that.

Q: Are motorcycle rims and car tire beads designed to work together?
NO, they are NOT but they WILL work together. The bead profile is different, making some tires difficult to seat the bead especially on 15” mc rims. However, there are tips that make this job easier. To date, no car tire has fallen off a motorcycle rim.

Q: Which car tire is best and where is the proof?
A good quality car tire is often cheaper than the mc tire - don’t skimp on quality. Spend a bit more on a good car tire with a symmetrical tread pattern (the pattern on each side of the centre is the same) and a rounded shoulder.
It's not my intention to convince anyone to change. But if you've read this far you must be curious like I was.
There are many online forums. Search for and join these groups to get accurate and proven information from experienced riders who are out there doing it on a bike like yours.
Darkside is not for everyone and there’s no shortage of “experts” with compelling arguments against so do your own research and make an informed decision.
Search for facebook group rollindarkside   / rollindarkside   for more information.