Why do people use different tire sizes than stock...? ? ?

[Tusayan]

Contact patch area does not enter into the equation if the road surface is perfectly smooth.  If it isn't perfectly smooth, and if the force per unit area is high enough to allow mechanical interlocking of the tread to the road, with soft enough rubber to allow it, you typically get more traction with a bigger tire patch.  That's why drag racers use large, ultra soft tires.  Their quarter miles times require much more than Amonton friction, which is the model for more-or-less smooth surfaces where contact patch size is irrelevant (Google it to see where oldbike54 is coming from).

That said, increasing the tires sizes on most bikes, definitely including many Guzzis, is a way to make them handle poorly and there isn't a huge amount of interlocking with street rubber... although there must be more with soft 'race' compounds used by some the street. Otherwise on a motorcycle wider rear tires promote weave instability, and wider front tires require handlebar forces to counteract the weird self-steering that results from the contact match moving around more relative to the steering axis when the bikes leans.  Most people on most bikes ride better with narrow tires, stock size or sometimes less... and a lot of sport bikes have been embarrassed by people on narrow tire dual sport bikes.

[oldbike54]

 Tusayan , you are correct about the ultra soft tires , that was my point . Simply increasing contact patch does nothing for traction . Those monster slicks that Fuel cars run use really low inflation pressures and grow very rapidly under acceleration , losing more than 50 percent of their width . Those cars rely on increasing down force to increase traction as they increase speed . Aren't modern fuel cars capable of like 5000 lbs of down force at 200 MPH , something a motorcycle is incapable of .

 Dusty

[Aaron D.]

Think about what you just said Aaron ? The only way to increase shear is to increase the load , or make the tire softer . Making the contact patch larger simply spreads the load out , thus negating the effect of a larger contact patch .

 Dusty

Well, yes. In pure friction it would have the same grip..
Maybe I missed the question. Happens to me all the time!

[Arizona Wayne]

Tusayan , you are correct about the ultra soft tires , that was my point . Simply increasing contact patch does nothing for traction . Those monster slicks that Fuel cars run use really low inflation pressures and grow very rapidly under acceleration , losing more than 50 percent of their width . Those cars rely on increasing down force to increase traction as they increase speed . Aren't modern fuel cars capable of like 5000 lbs of down force at 200 MPH , something a motorcycle is incapable of .

 Dusty

Sorry, Dusty, once again I can't agree with you, no matter what you have been taught.  When I put car tires on the back of my Piaggio MP3 scooters (DARKSIDE) I got a softer ride (lower psi) and more traction because I had more rubber on the road surface.  Got more stopping power too.    Believe what you want.  My experience beliefs are from real results.

[oldbike54]

 It's OK Wayne , lots of people don't believe in the laws of physics , like that motorcycle counter steer .

 Dusty

[Arizona Wayne]

It's OK Wayne , lots of people don't believe in the laws of physics , like that motorcycle counter steer .

 Dusty

Your MC countersteer is for bike riders who rarely ride on roads with many curves.  Sure, it exists, but only for riders like that.  Riders who have never learned how to ride regularly indifferent turning radius curves, so their backup is sudden/quick direction changing manuevers.  Done it myself when needed.    First time I saw Frank Wedge (Kansas) do it when I didn't see it necessary it freaked me out.  It's a last resort manuever.

[oldbike54]

Your MC countersteer is for bike riders who rarely ride on roads with many curves.  Sure, it exists, but only for riders like that.  Riders who have never learned how to ride regularly indifferent turning radius curves, so their backup is sudden/quick direction changing manuevers.  Done it myself when needed.    First time I saw Frank Wedge (Kansas) do it when I didn't see it necessary it freaked me out.  It's a last resort manueaver.

 I have a headache , but you really need to do some research .

 Dusty

[Arizona Wayne]

I have a headache , but you really need to do some research .

 Dusty

I have personal research......succe ssful years of amateur road racing + 55 years of street riding in most of USA.  What are your credentials on this?

[oldbike54]

I have personal research......succe ssful years of amateur road racing + 55 years of street riding in most of USA.  What are your credentials on this?

 I know you think I live in flat country where the roads are straight , I don't . Edge of the
Ozarks , and 80 miles from the Ouchita Mtns . I won't brag , but many here have ridden with me on some very curvy roads , ask them . But rather than go by anecdotal evidence , I will steer you towards the bike that Keith Code built that had fixed a fixed handlebar , it proves a motorcycle can't be leaned W/O counter steering , otherwise , believe what you want .

 Oh , a fair amount of time on flat track bikes also .

 Dusty

[Rough Edge racing]

The force of friction is equal to the product of normal force and the coefficient of friction .

 Basic physics , contact area never shows up in the equation .

 The force per unit area is all that matters .

 Dusty

 You do know that in the 1950's, physicists said a dragster could not exceed about 160 MPH because of their formulas ...They did not know that a tire can exceed 1.0 coefficient of friction....You can look that up    No doubt about it, I have experienced it along with 1000's of others, a A wider tire of the same rubber compound offers better traction...

[Perazzimx14]

I think it safe to say when there is a lack of "contact patch" touching the underlying surface life starts to get interesting.

[oldbike54]

You do know that in the 1950's, physicists said a dragster could not exceed about 160 MPH because of their formulas ...They did not know that a tire can exceed 1.0 coefficient of friction....You can look that up    No doubt about it, I have experienced it along with 1000's of others, a A wider tire of the same rubber compound offers better traction...

 Not on concrete , that happens because the COE of rubber to rubber is already something like 1.15 to 1 . Those incredibly soft tires are literally glued to the rubber laid down during the burnout .

 Oh , and once again , simply increasing contact patch does not increase traction . Softer compounds , heat , increased loading yes , not contact area . A dragster under initial acceleration transfers 90 percent of its weight onto the rear tires , thus increasing traction , and as it increases speed the down force goes up keeping traction as more or less a constant despite the tire losing over half of its width .

 Dusty

[rocker59]

increasing the tires sizes on most bikes, definitely including many Guzzis, is a way to make them handle poorly and there isn't a huge amount of interlocking with street rubber... although there must be more with soft 'race' compounds used by some the street. Otherwise on a motorcycle wider rear tires promote weave instability, and wider front tires require handlebar forces to counteract the weird self-steering that results from the contact match moving around more relative to the steering axis when the bikes leans.  Most people on most bikes ride better with narrow tires, stock size or sometimes less... and a lot of sport bikes have been embarrassed by people on narrow tire dual sport bikes.

Yep.  Dropping to a 170/60-17 from a 180/55-17 on the 5.5-inch rear of my V11 LeMans dramatically improved the bike's turn-in and cornering.

I've also known Ducati guys with 6.0 rear wheels who dropped from the stock 190/50-17 to the 180/55-17 and improved the bikes' feel on curvy pavement.

[Xlratr]

I'm with Dusty on this. Try hitting a patch of water at speed with wide tyres and see how much traction you have. :-)

Oh, and counter steering? Everybody does it, even if they don't know they do. It's something you learn subconsciously as a kid with your first bicycle.


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[HDGoose]

Counter-steering is a myth. Just like the theory of electrons is also a myth.

[oldbike54]

Counter-steering is a myth. Just like the theory of electrons is also a myth.

  Where have you been son ?

 Dusty

[Orange Guzzi]

More rotating mass, less h.p. to the ground.  And everyone seems to want more h.p. to the ground.  Going as far as making spoked rims tubeless for weight reduction. 

[Perazzimx14]

More rotating mass, less h.p. to the ground.  And everyone seems to want more h.p. to the ground.  Going as far as making spoked rims tubeless for weight reduction.

Where else would you want the HP to go?

[Arizona Wayne]

The force of friction is equal to the product of normal force and the coefficient of friction .

 Basic physics , contact area never shows up in the equation .

 The force per unit area is all that matters .

What I've been talking about here all along is tire contact area, not friction.  This is why road racing bikes now have lower profile tires so that they have more contact area with the pavement when upright or leaned over than during earlier years.  More contact area to handle the more hp the MC has to deliver now.   Otherwise the bike would not be controllable when pushed in corners. 

[oldbike54]

 OK lets try this one more time . A wider tire will have a wider contact patch , but the contact patch will actually be shorter in length , so there is no net gain . The main reason why modern roadracing motorcycles run those really wide low profile tires are for two reasons . The low profile prevents the sidewall from flexing , thus keeping localized heat under control , and giving more predictable handling . They are really wide , for a couple of reasons , the first being that to maintain structural integrity a tire must hold a sufficient volume of air . Second , and this relates to the low profile thing . a wider tire is more capable of maintaining the proper heat range after warming up . while not overheating
and cooking the compound . Third , a wider tire allows for more lean angle , simply because there is more area to spread the actual contact surface over .

 Dusty

[Huzo]

Was common in early v11 sports to go a size smaller than stock on the rear for improved handling. I did when I swapped and it did handle noticeable better.  I love my v7 but there are days I miss this.




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Holy mother of **** that is absolutely stunning !!!

[Huzo]

The force of friction is equal to the product of normal force and the coefficient of friction .

 Basic physics , contact area never shows up in the equation .

 The force per unit area is all that matters .

 Dusty

Basic physics bears you out Dusty, Newton says you are correct. I'm thinking of the dragster argument though also. The larger contact patch will dissipate the heat over a larger area in more extreme cases like dragsters and Moto GP et al. However back to the top, I think a large amount could be fashion. I guess the more tyre area that is AVAILABLE for use, the more km the tyre should last, allowing softer compounds and the opportunity to employ the "mechanical grip" aspect you mentioned where the tyre actually conforms to the shape of the road surface. You think also?

[Rough Edge racing]

Not on concrete , that happens because the COE of rubber to rubber is already something like 1.15 to 1 . Those incredibly soft tires are literally glued to the rubber laid down during the burnout .

 Oh , and once again , simply increasing contact patch does not increase traction . Softer compounds , heat , increased loading yes , not contact area . A dragster under initial acceleration transfers 90 percent of its weight onto the rear tires , thus increasing traction , and as it increases speed the down force goes up keeping traction as more or less a constant despite the tire losing over half of its width .

 Dusty

  You may find this interesting , drag slicks..

    http://www.onallcylinders.com/2016/07/14/drag-slicks-traction/

[Huzo]

Counter-steering is a myth. Just like the theory of electrons is also a myth.
[/quote If you were to get a push bike for example and push it up to a high speed say 50 mph. The bike will continue in a straight line counter steering for itself. There is no external force available to stop yours or my bike falling on it's side unsupported other than the constant re positioning of the point of support under the centre of mass. Why do do hold the opinion that countersteering is a myth and what argument do you gave to support it? And please, no  analogies.

[oldbike54]

 Easy Peter , HD goose was being sarcastic to make a point .

 Let's not let our emotions run away , keep this civil please .

 Dusty

[oldbike54]

  You may find this interesting , drag slicks..

    http://www.onallcylinders.com/2016/07/14/drag-slicks-traction/

 Good article , the doubters all need to read it . Thanks .

 Dusty

[elvisboy77]

Honestly, I would never presume to know more than the engineer who designed my vehicle.

[Huzo]

Honestly, I would never presume to know more than the engineer who designed my vehicle.

If the designs were not re thought we would all still be riding bikes un altered from the start of last century. Also, you can build the best bike in the world but you still have to be able to sell it to someone. Fashion has a masssive bearing on how our bikes are styled.

[elvisboy77]

If the designs were not re thought we would all still be riding bikes un altered from the start of last century. Also, you can build the best bike in the world but you still have to be able to sell it to someone. Fashion has a masssive bearing on how our bikes are styled.

I understand the allure of "upgrading" your vehicle to some people, however I must disagree about the cause and effect of owners modifying their vehicles driving manufacturers' evolution.

Sure, it happens every now and then, but I doubt it would be a primary motive in evolution of design.

Me, I am happy with a stock bike, stock tires and engine/fueling/ignition, shocks etc.  Other than windscreens and luggage etc I have never been so unhappy with a motorcycle as to change it from basically stock.

[Guzzistajohn]

If not for counter steering iron butt riders would ride right off the edge of the earth wouldn't they?