Thoughts on car tire flexing......

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Thoughts on car tire flexing......

Post  Steve-O on Fri Jan 09, 2009 6:12 pm

One of the most common "naysayers" comments is that the sidewall of a car tire will flex when cornering, leading to an unstable ride (read dangerous). Although this has never been documented, it continues to be the thought line of opinionated ones.

Well, I've been thinking about this. I've seen several videos of car tires going through their paces. I've yet to see any sidewall flexing of any kind. Come to think of it the tire maintains it's overall shape all of the time. Which got me thinking if I'd ever seen a care tire flex on a car. I've never seen YouTube videos of car tires on cars, but I have seen a lot of chase scenes in movies where they show the tires from every angle. The tires seem to maintain their shape no matter how fast, turn, skidding, whatever. I've never seen a sidewall buckle on a car tire on a car. Now, considering the car is heavier than a bike - by a lot. But there are 4 tires on a car and two on a bike, so the ratio is about the same (still a bit heavier for the front tires of a car than the back end of a motorcycle), it seems to me that if I've never seen a car tire buckle on a car, the chances of it bucking on a bike are really close to zero.

So if the argument is that a car tire will flex, why have we never seen a car tire flex? I think I'll believe in UFOs before I believe that car tires will flex. At least folks claim to have SEEN UFOs! Very Happy

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Re: Thoughts on car tire flexing......

Post  jedishon on Fri Jan 09, 2009 7:30 pm

Steve here is some flexing for you.......



Jerry

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Re: Thoughts on car tire flexing......

Post  bandito_two on Sat Jan 10, 2009 3:27 am

If the naysayers would really think about it, (That is if you could ever convince them to do so) with motorcycles the force is directed DOWN through the center of the wheel/tire to where the tire touches the road. Even when it is leaned while moving, the force created is pushing down at that angle toward the road. Cars, on the other hand only have that force directly down through the center when they are going straight. Doing any amount of turning with a car puts a lateral (sideways) load on the tires and they do that ALOT (sometimes quite forcefully) and they handle that just fine. About the only times when you could get a lateral load going to the tire on a motorcycle is if you are going into a turn on your bike that is using a sidecar or if you lock up the wheel to make it start sliding out or while doing a burnout/donut so that some force is pushing/pulling on the tread from left to right or right to left across the the tire. But even that is not enough to 'buckle the sidewall' to any appreciable, if at all detectable degree. But I have seen pictures of drag racing cars where the the rear tire can be seen to be distorting a little under the severely hard acceleration delivered by all that horsepower they have.

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Re: Thoughts on car tire flexing......

Post  Smokin'joeVRCCDS#0005 on Sat Jan 10, 2009 6:24 am

I've been ridin' on car tire's for years and never had any " Flex " I've put around 60,000 miles on The DarkSide .The Valkyrie was the first to use The DarkSide in mass numbers. One of my Valkyrie's still has a motorcycle rear but it soon will also be DarkSide . The Cooper Zeon 2XS will out corner , out brake and out shine a motorcycle tire in all conditions but on wet roads is where it really shows its superior.Check the contact patch...MC tire.

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Re: Thoughts on car tire flexing......

Post  Smokin'joeVRCCDS#0005 on Sat Jan 10, 2009 6:26 am

Same bike with a DarkSide tire...Check the contact patch.

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Re: Thoughts on car tire flexing......

Post  Smokin'joeVRCCDS#0005 on Sat Jan 10, 2009 6:30 am

A better shot of the contact patch...No flex whatsoever and this bike is haulin' a full load. I was on my way for a weekend ride across The Blue Ridge Parkway when this picture was taken. Saddlebags and trunk fully loaded.

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Re: Thoughts on car tire flexing......

Post  Steve-O on Sat Jan 10, 2009 7:20 am

bandito_two wrote: ...with motorcycles the force is directed DOWN through the center of the wheel/tire to where the tire touches the road. Even when it is leaned while moving, the force created is pushing down at that angle toward the road. Cars, on the other hand only have that force directly down through the center when they are going straight. Doing any amount of turning with a car puts a lateral (sideways) load on the tires and they do that ALOT (sometimes quite forcefully) and they handle that just fine.

Another great point I had not thought about. Bikes lean, cars don't. If a non leaning car can't get the tire to flex, a leaning bike, that is lighter, definitley won't. Great point.


bandito_two wrote:But I have seen pictures of drag racing cars where the the rear tire can be seen to be distorting a little under the severely hard acceleration delivered by all that horsepower they have.

I've seen this on drag racers too. The tires actually fold up like an accordian upon accelleration....

Good pictures smokey. I like the one with sparks flying. I brought this topic up because it came up several times on the shadow forum. Someone claimed the tire would flex in a turn and the bead would break. As hard as these are to get the bead to set, that's the last thing I'm worrying about.

I can appreciate when someone says they don't like the way it handles. But safety is a non issue in my book.

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Re: Thoughts on car tire flexing......

Post  Otis56 on Sat Jan 10, 2009 7:29 am

great write up you guys, Smokin'joe you've posted some outstanding shots of your bikes, I've had to print em and put on the cubicle at work. thanks both of you .

mark f

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Re: Thoughts on car tire flexing......

Post  DS-Wing-Nut on Sat Jan 10, 2009 2:28 pm

jedishon wrote:Steve here is some flexing for you.......



Jerry

hey! i've posted that picture before!! it's a good one huh!

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Re: Thoughts on car tire flexing......

Post  Poppawolf on Sat Jan 10, 2009 2:37 pm

I believe you can get a sidewall to flex. But this would require running the air pressure below safe limits. Or in our case, running air pressure that may be considered for the tire. As an example most of us have run upwards of 40psi or more in their tire. This may be to give the impression of a more rounded profile or fix a percieved flex. This has the side affect of causing the tire to wear in the middle more than the sides like a M/C tire. If you lower the pressure you will get some sidewall flex. This reduction in air pressure will flatten the profile out with weight on the tire and give you an even wear across the tread. This is all the same as you do on your car and tire pressure. Now, I don't think that you will ever flex it enough to get it to come off the rim, again don't think. But with a the reduced pressure and a softer profile there will have to be some flex. With the inertia of the rotating wheel/tire it may be hard to see it in pictures, but an experienced rider may be able to feel it. On the other hand, I am not so sure the squishy/flex feeling that I have felt on my rides in low speed turns isn't from the actual tread itself. We have all seen the durometer readings posted by Twin which showed car tires softer than M/C tires. Give that and the fact there is more rubber on the road, whose to say that the tread isn't moving or flexing when on edge? This would be more noticeable at slower speeds where the centrifical force of the tire isn't as great, but could be a factor at least in my case during a turn from a stop and gassing it.

Now, none of this is scientific. It is all my opinion. The great thing about this site is there are a lot more smarter people on here than me and I can tell my wife I come here to get educated.

DB

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Re: Thoughts on car tire flexing......

Post  horseman8m on Sun Jan 11, 2009 2:57 pm

the only flexing i ever had was when i didn't keep an eye on the tire pressure, OK so i have a 215 wide tire on a stock 1300C rim so the pressure is a must to keep it right on the 36-40 PSI range . but it was my fault that i hadn't checked it before a ride and sure as i am sitting here it flexed on a tight turn in AUG. at about 100 F. and the tire pressure was low, 31psi .
For my tire and my bike and the way i drive , i must keep 36-40 psi in it all the time. I hope this helps.
your friend , Horseman8m

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Re: Thoughts on car tire flexing......

Post  Steve-O on Sun Jan 11, 2009 9:02 pm

My definition of flexing is either:
1) teh contact patch shifts from directly below the rim
2) Inner sidewall contracts and outer sidewall stretches - thought to happen in turns

What is your definition of flexing and why do you think it happened to you?

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Re: Thoughts on car tire flexing......

Post  twin1300 on Mon Jan 12, 2009 9:22 am

Here's some flexing of a car tire....WOW! We can't possibly do any damage to a car tire if they can't tear one up!

http://www.youtube.com/watch?v=QQMoJaRgfrs

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TIRE FORCE TEST

Post  DS-Wing-Nut on Mon Jan 12, 2009 12:50 pm

THIS MIGHT HAVE BEEN POSTED HERE BEFORE BUT IT'S AMAZING WHAT THEY DO TO THIS TIRE AND IT NEVER BREAKS A BEAD OR POPS....

THIS IS DONE WITH TIRE PRESSURE... NOT A FLAT TIRE... JUST A LOT OF FORCE!!

AMAZING....

http://www.youtube.com/watch?v=nmo_dkNZIHM

I'm pretty sure I'll never put my tires to that much pressure... and I can only hope that my current tires would hold up to that test...

Very cool.


ENJOY.


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Re: Thoughts on car tire flexing......

Post  wrongway on Mon Jan 12, 2009 3:46 pm

dragsters only run 6-8 psi , heavy drag cars run around 12-15 psi with a large slick. Lightweight tire , low pressure , high horsepower will distort a tire ...


I have seen sidewalls flex on an Indy car , but they pull 3 - 4 g's and run a pretty low pressure as well. Most cars will never see 1 G , and that is why you may never see any flexing with recommended tire pressure. As stated in a previous reply , the bikes are usually no where close to the max weight rating , making this a non-issue with any tire pressure over 20 lbs. except maybe for a Boss Hoss with a bigblock :-)

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Re: Thoughts on car tire flexing......

Post  horseman8m on Sun Jan 18, 2009 11:48 am

Steve-O wrote:My definition of flexing is either:
1) teh contact patch shifts from directly below the rim
2) Inner sidewall contracts and outer sidewall stretches - thought to happen in turns

What is your definition of flexing and why do you think it happened to you?


i thought that flexing was when the center line of the tire moved off of the center line of the rim

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