Darkside contact patch vs Motorcycle tire contact patch.... videos

[tallannie]

Ok...for all you who wonder about this...here are two videos side by side of a MC and CT tire...on two big bikes...going thru the same corners at the same speeds ( watch at 58 seconds into the CT video....and about 1.24 in the MC tire video when we are going thru the same corner at the same speed......). To my eye each one puts down about the same size contact patch.

[Motorcycle Forum]

[JmalB]

Not exactly a confidence inspiring video for me. Looked like the end of the tire's traction area would come sooner on the car tire. Sure it works fine for those on the dark side though.

[Quazievil]

I have to agree with JmalB. One would have to change up their driving style on the CT, well at least I would. I can easily see me low siding with a CT tire on. By the time my peg drags I'd be eating pavement.

But if it works for you and your riding style then this video does show the contact patch, as you say annie, look to be the same size.

[tallannie]

Thanks but not sure I understand the concern. I have scraped my pegs with this tire already... It felt the same as with my former tire. The width of this car tire is almost exactly the same as the width of the MC tire I had...so when you are down at a low angle the geometry of the bike to the road is not much different...? ... and I HAVE lowsided on a MC tire...this has no additional risk for that imho.

I have to agree with JmalB. One would have to change up their driving style on the CT, well at least I would. I can easily see me low siding with a CT tire on. By the time my peg drags I'd be eating pavement.

But if it works for you and your riding style then this video does show the contact patch, as you say annie, look to be the same size.

[JmalB]

The more I watch the less convinced I am that the traction area is the same in the turns.


Could just be me still not jiving with the idea.

[tallannie]

that is why I gave two specific times... in these videos the sun and shadow effects often do strange things to the views.
The times I mention had sun angles about the same... and showed each tire at the same speed, etc... at that point the images each show about half the tread of the CT and the sidewall of the MC on the road... mebbe still photos would have been a better comparison just at those points...lol

I can also see this now when the bike is sitting in the garage leaned on its stand. When my weight is on the bike, the tire has more than half the tread on the garage floor solidly..... mebbe if I get motivated again I will take a picture of that too....

The more I watch the less convinced I am that the traction area is the same in the turns.


Could just be me still not jiving with the idea.

[Y2K]

The more I watch the less convinced I am that the traction area is the same in the turns.


Could just be me still not jiving with the idea.

Even if the contact patch is the same size the car tire is obviously on edge,the transition point could be a problem IMHO.
Then there is the fact that the pressure applied to the pavement is probably uneven across the contact patch with the car tire.
For easy cruisers it's probably not a problem but for people like me that like to rail the corners I would be very uncomfortable with a car tire after seeing that video.
If I rode in a straight line all the time it would be fine but that's most definitely not the case.
There are reasons motorcycle tires are made differently and the videos here clearly show that from my vantage point.

[tallannie]

interesting how different people can see such different things in the same video.
now we have general agreement that the contact patch is large and probably equally so....
but no video can show if a contact patch is 'uneven'...or if there is something funny about a 'transition point'.... whatever those things mean...

I give up.

[Easy Rider]

I give up.

Thank you.

[inspiron]

Annie, in my opinion, it's not a question of the size of the contact patch. Obviously, when riding straight ahead, a car tire is going to have a much larger contact patch than the motorcycle tire.

The big question in my mind is how long a car tire's sidewall can handle the stresses of a motorcycle-style turns. The sidewalls of a car tire are designed to keep the contact patch on the ground, but not designed to be part of the contact patch themselves. The rubber on the sidewall is much thinner, as anyone who's ever hit a curb knows. A motorcycle tire, on the other hand, has virtually no sidewall - much more of the tire is designed to touch the road.

Look here:

Versus here:

Personally, I wouldn't trust the sidewall of a car's tire, which I'm using for something it wasn't designed for, with my life. The tires of my motorcycle are truly life or death decisions - if I have a blowout at the wrong time, I may not survive the accident. The risk is, in my opinion, too high.

[tallannie]

I think car tire sidewalls can take the modest flex you see in the video I made just fine....and the sidewalls are never part of the contact patch themselves as you say.

[JmalB]

The 2nd video makes it look like the tire is under inflated. And you can see sidewall touching the "road" surface.

And as some one who autocrosses and pushes street tires to their limit (some times beyond) I can tell you that the sidewalls are indeed sometimes apart of the contact patch. Not ideal but it happens.

But as you say Annie, for your situation, a CT is a workable solution. You're just not going to get many converts to the Dark Side (dun dun dun duuuuunnnnn).

If I were drag racing a motorcycle seriously I'd definitely go with a car tire.

[Quazievil]

Interesting information, This is one of those personal choices where regardless of which side your on you're not likely to sway the opposition to your side. Like any modifications there can be upsides and downsides so the risk, real or perceived, is a choice one makes. I've found all your videos interesting, but I think the first video showing sidewall flex would be better suited for a motorcycle application if the entire tire rotated putting max load and pressure on the edge of the tire tread and sidewall.

Again I don't think there is a right or wrong here, just choice. I know a lot of riders love the darkside

[fear_cartaidh]

Can of worms opened Annie.

I love the lab video posted @2:55 pm. That's just cool. My understanding is that the risk is not in the sidewall touching but rather over heating from flex (my fear as I've seen it on hundreds of car tires) causing a scaling break down effect only truely visible from inside. And having a different tapper and bead seat heigth causing risk of catostraphic deflation.. Areas identified as # 13 & 11 in your diagram.

As for the contact patch I have a theory and an idea. It seems to me that at mild lean angles the contact patch should be an accute trangle with the short side being the edge of the contact patch but I hypothosize that at extream lean angles the traingle should sorten and leangthen to a wide obtuse triangle. This may not cause the contact patch to change as much as we fear. I have a way to prove it if you are interested. Take some large sheets of paper (like the floor mats used at auto service centers) and with the help of a freind roll the bike on a sheet at both mild and peg grinding angles. This is an easy trick for finding contact patch on non stock tires for autos and lifted vehicles.

I also hypothosize that because the profile is more square that the distance to the pavement at angle is increaded giving slightly more lean angle before parts gring than on mc tires. Two points come to mind. CTs may be fine for cruisers but my be much more dangerouse on low profile equiped sport bikes that are prone to lean angles that embarrase cruisers. In any case I HIGHLY advise against running low profile car tires on bikes as the shorter sidewall effectivly centrallizes the flex point causeing them to heat faster and self consume faster. The thing I keep coming back to when I hear about the dark side is that damnage can be had with out being seen caused by sidewall flex. To date however no one has seemed to have a problem with this leading me to think my fears are unfounded.

Perhaps there simply isn't enough weight on a bike to cause the damage I have seen countless times on cars and trucks. You probably have too if you've ever had a flat on the highway. It starts as a "fresh" darker ring around the side wall. It is a sign of over heating caused by over flexing. The inside detieriorates to the point air starts to escape faster untill a blow out occures. At this point you may notice coffee grind like rubber grinds are everywhere. (and really make a mess of tire machines) Again my fears appear unfounded as no one has complaned about this. Low profile tires are especially prone to this because A: the flex is centralized and B: the sidewalls are so stiff that the clueless driver does not see that the tire is low untill it is flat and the steal caseing is broken down. Having stiffer shorter flex also means that as they go flat it is harder to feel.

Taper and bead seat heighth differences. The engineers that compile numbers for the TIA (Tire Industry Association) tell me that the tire holding difference between a 9mm (car) rim lip and an 11mm (light truck, racing & runflat) rim lip is a few thousand pounds. What's more the bead seat angle differs which is what causes the (real or unfounded) fear of catostrophic and instantanious deflation. My experince however is that almost nothing yealds when a few thousand pounds is applied to hold it inplace ei the pressure inside the tire vs the external forces moving against it. Off roader types know that they can run tires down below 15psi and goose on it with out unseating a bead. In the effort to cause severe sidwall flex (at very low speed / heat levels) I was able to run as low as 6psi in my Tracker equiped with 30" Lt tires. It is however a risk. They do carry a spare and they are not likely to to be severly injured as we are in the event of instantanious deflation.

Your bike your decision.

NMc

[fear_cartaidh]

I have another idea! Dark side is ilegal in many states because of the bead seat differences NOT because of contact patch err go if one should equip a bike with off road (and NASCAR) style bead locks there should be no concern right?

Staun Inner Beadlocks. Lowest Prices on Staun Inner Beadlocks.

Currently Staun is the only manufacturer of street legal beadlocks. If contact patch is not the fear but rather instantanious deflation and unseating then this is the answer.

NMc