rear tire, 190/55 or 190/50 whats the difference?

[DaveO]

Not mine, Newtonian physics: F = P/A. The Force (in pounds) on the tire which is both the overall weight as well as any cornering / braking / accelerating forces on the tire will equal the Pressure (in PSI) divided by the Area (in square inches) of tire in contact with the ground. The contact patch area will be the same given the same force and pressure no matter what the tire's size (within reason of course- let's not use model car tires as an example). Certainly between a 190 / 50- 17 and a 190 / 55 - 17 mounted on the same wheel.

 

I sorta agree here but you have use tire of same carcass construction for that statement to be true..
190/50  as opposed to 190/55  would be different construction  no??

 It has a different shape...
I think a tire with different profile could put more rubber on the road at certain lean angles even using same psi

[Jeremy Mitchell]

I will add my 2 cents here, take it or leave it.

I ride very aggressively and with the 190/50 I had ZERO chicken strips, which told me I was possibly getting to the point of not having much rubber in contact with the road when running at my max lean angle.  With the 190/55. I have somewhere between 1/16 and 1/8 of an inch left on the side, that tells me that the tire has more rubber left in reserve when I am at the same max lean angle. 

The amount of rubber in contact with the road is debateable like BDF stated but for me I can see an improvement.  My best advice is just to try a 55 and see for yourself.  If you don't like it just sell it to me and go back to a 50. 
 

[B.D.F.]

Yes, there are other factors such as the tire carcass stiffness and the tread. But the overriding factor is still the internal pressure, especially so when considering two tires that are identical other than the aspect ratio. Again, a common belief is that changing a tire to a higher aspect ratio changes the amount of rubber in contact with the road is just not correct.

A toy balloon would act more like a perfect vessel than a vehicle tire regarding the pressure / area function. For example, all the stiffness in a balloon comes from internal pressure only- bring that pressure to zero and the balloon really will lay flat. The same is not true for a tire of course, even without pressure there is enough stiffness in a tire to hold it upright and hold its shape. So yes, there are other factors and they must all be considered; it is certainly not universally simple and true that contact patch area is a function of internal pressure alone but it is the predominant factor.

As far as tire shape goes, again that will be overridden by the pressure / area relationship. If the shape of the tire is brought more toward a triangle in an effort to increase patch area, and the same internal pressure is used, the actual result will be that the patch is wider but shorter (in the direction the motorcycle travels). Even a clever designer cannot outsmart or outrun physics.

One obvious example of other forces would be the way wrinkle- wall tires act when used in drag racing. The contact area is a function of the internal pressure (which is extremely low to use a lot of contact patch area) at first but then centripetal force must be factored in. With the vehicle sitting there the tires appear almost flat but once the tire is spun up to high speed, it becomes much more round and much larger in diameter as well as narrower. The back end of the vehicle is raised up quite a bit- it is not a subtle effect. I do not know but suspect that the contact patch area changes with this great increase in centripetal force. Of course such things are hard to duplicate on street vehicles, not to mention that fantastic acceleration is never used when a motorcycle is leaned well over in a curve so it is irrelevant.

The short version is this example: if you replace a Michelin PR3 190/50- 17 with a Michelin PR3 190/55- 17 and like the taller tire better, I betcha' it ain't 'cause of the idea that the contact area changed (assuming the same tire pressure is used!).

Brian

I sorta agree here but you have use tire of same carcass construction for that statement to be true..
190/50  as opposed to 190/55  would be different construction  no??

 It has a different shape...
I think a tire with different profile could put more rubber on the road at certain lean angles even using same psi

[B.D.F.]

Yep, the taller tire may well work better. Again, my only point was that any change noted is not because the contact patch area changed as long as the same internal pressure was used.

I never meant to imply in any way that a different aspect ratio tire would not perform differently. In fact, I am quite sure they do although I have not tried a 55 on a C-14 yet. I would really like to try a 180/55 as they are lighter and less expensive.

So many choices, so few tire donations.... 

Brian

I will add my 2 cents here, take it or leave it.

I ride very aggressively and with the 190/50 I had ZERO chicken strips, which told me I was possibly getting to the point of not having much rubber in contact with the road when running at my max lean angle.  With the 190/55. I have somewhere between 1/16 and 1/8 of an inch left on the side, that tells me that the tire has more rubber left in reserve when I am at the same max lean angle. 

The amount of rubber in contact with the road is debateable like BDF stated but for me I can see an improvement.  My best advice is just to try a 55 and see for yourself.  If you don't like it just sell it to me and go back to a 50. 
 

[Son of Pappy]

I have a set of lightly used 021's (10,000 miles) that I'll send ya for the cost of postage

[ZG]

I have a set of lightly used 021's (10,000 miles) that I'll send ya for the cost of postage

 

[jjsC6]

I will add my 2 cents here, take it or leave it.

I ride very aggressively and with the 190/50 I had ZERO chicken strips, which told me I was possibly getting to the point of not having much rubber in contact with the road when running at my max lean angle.  With the 190/55. I have somewhere between 1/16 and 1/8 of an inch left on the side, that tells me that the tire has more rubber left in reserve when I am at the same max lean angle. 

The amount of rubber in contact with the road is debateable like BDF stated but for me I can see an improvement.  My best advice is just to try a 55 and see for yourself.  If you don't like it just sell it to me and go back to a 50. 
 

I agree - my results are the same.

Brian - we're still good.  No need to open a new debate on oil just to put the tire issue behind us, but if you DO want to discuss oil.....

[Jaxter]

one more thing puzzles me...changing tire size does what to the accuracy of the speedometer

[lt1]

Well, I didn't get very far, but the first article I read agrees with Jim.  http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

Since we are not dealing with perfectly elastic substances, it appears that contact patch area, not just shape, depends on much more that merely vehicle weight and tire pressure.

And I did appreciate the humor in the thread: "As always, I am more than willing to listen to any other thoughts on this, or any other subject."

[lt1]

one more thing puzzles me...changing tire size does what to the accuracy of the speedometer

Increasing rear tire diameter will increase actual speed in relation to indicated speed.  Most C14 speedo's read fast, so switching to a 190/55-17 will reduce the speedo error in most cases.

[GaryW]

one more thing puzzles me...changing tire size does what to the accuracy of the speedometer

With the 50 the speed was off 3-4 mph at 70, with 55 is within 0.5 mph versus GPS.

[wally_games]

With the 50 the speed was off 3-4 mph at 70, with 55 is within 0.5 mph versus GPS.

But once you get that Texas highway flat spot down the center ... ...

New, my stock tires yielded about 4-5% error lower than actual (indicated 84 at GPS 80).

[wally_games]

If the contact patch is the same area, but is wider in the bead-to-bead direction while in a lean with the taller tire, does the longer length of the contact patch yield less "slip" in the lean?

[B.D.F.]

Clyde you charming devil you.... glad to see you back. Can I safely assume you have finished downloading that manual and now have more time for the forum?

 

Brian

<snip>

And I did appreciate the humor in the thread: "As always, I am more than willing to listen to any other thoughts on this, or any other subject."

[B.D.F.]

I do not know but it is an interesting question.

Smooth surfaces create friction without regard to the area in contact. For example, smooth steel against steel will have a certain coefficient of friction that does not change with area. Rubber tires on asphalt or concrete is different; the tire is soft and will deform to dip into the little pores of the road surface, so increasing area increases friction. I don't know if changing the shape of a given area changes friction but cutting slices into tread blocks so that they might move independently does. As that is odd behavior, perhaps there are better and worse contact shapes for better or lesser traction?

Brian

If the contact patch is the same area, but is wider in the bead-to-bead direction while in a lean with the taller tire, does the longer length of the contact patch yield less "slip" in the lean?

[lather]

So far no one has mentioned the fact that a 55 aspect tire raises the rear, affecting steering geometry. I suggest that this has more to do with any handling improvement than contact patch size and/or shape.

[martin_14]

So far no one has mentioned the fact that a 55 aspect tire raises the rear, affecting steering geometry. I suggest that this has more to do with any handling improvement than contact patch size and/or shape.

I think you nailed it. (although it is a very interesting discussion so far)
I usually change front and rear at the same time. With the first two sets (the original BS) the front was more wasted than the rear, and the last two sets (Angels) it was the other way around (as it is more usual) but they were still similarly worned out.
But last week, seeing that the front still had lots of thread and is round (no cupping) I decided to change only the rear. When the tire was out of the wheel, I compared it with the new one before being mounted and could appreciate the huge change in profile and what astonished me more was the difference in weight between the two. I wish I weighed them, but I bet is next to a pound.
Anyway, I immediately thought that the tail (and only the tail) of the bike would be higher now, and indeed the first thing I noticed when I drove off if how the steering got a tad more responsive (less rake angle). A quick calculation, assuming 59,8 inches wheelbase and 0,2 inches more radius on the new tire, shields a 0,19° less rake angle. And that is noticeable.

[Jeremy Mitchell]

So far no one has mentioned the fact that a 55 aspect tire raises the rear, affecting steering geometry. I suggest that this has more to do with any handling improvement than contact patch size and/or shape.

It will only raise the rear about 1/4 inch, I think the taller profile combined with raising the rear is the reason it works so well.  A symbiosis of sorts. 

[stevewfl]

gotta' love a tire thread. who mentioned on this forum that the 190/55 is a better performer way back when Michelin 1st introduced it heh  millions have tried it and verified the difference since 

old news, if you don't understand why the 55 performs better pay the 10 bux extra and try one. that simple.  but the physics class and debates have been interesting.

tire threads rule! next we need afresh  flying luggage thread, with directions for pinning and available aftermarket parts to prevent this phenomenom 

the 190/55 will turn in quicker.

[Conrad]

gotta' love a tire thread. who mentioned on this forum that the 190/55 is a better performer way back when Michelin 1st introduced it heh  millions have tried it and verified the difference since 

old news, if you don't understand why the 55 performs better pay the 10 bux extra and try one. that simple.  but the physics class and debates have been interesting.

tire threads rule! next we need afresh  flying luggage thread, with directions for pinning and available aftermarket parts to prevent this phenomenom 

the 190/55 will turn in quicker.

Dang Steve! You're slipping man, a post without how many trouble free miles you currently have on your bike?

Maybe it's not really you and someone hacked in to your account, perhaps a pod Steve?