Recently watched "Can I get More GRIP from a Wider Motorcycle Tyre?"

[TacomaJD]

You're welcome to go let air out of a tire and watch this miraculous phenomenon for yourself. (-;

What I have described (in both posts in this thread) is well known and well demonstrated in tires, both on-road and off-.

I'm still trying to wrap my head around the physics of all this. I am pro-science, so don't think otherwise. I'm still trying to understand the coefficient of friction thing and how it applies in other areas.

Like take rock crawling for example. I was big into crawling for about 6 years. #1 cheapest/easiest thing to do to improve offroad performance is to air down. This increases contact patch, but I guess moreso allows tire to conform to the object it treading on. The tire doesn't spin and rotates very slowly, so how does the whole object of managing heat work there? There is very little heat created unless you cant make it up the obstacle, then you roast the tires for a minute, they heat up, become more sticky, then walk right up the obstacle with no problem. Same with drag tires, heat them up by burnouts to achieve optimal stickiness for the best launch. This is all very interesting to me, as I like to figure out how things work.

Old rock crawling vid below from a few yrs back for entertainment purposes, and also example of what I am talking about. The tires I ran were BFGoodrich red label Krawlers (stickies). Wasn't so much that they were soft compound, because there are several other softer tires for crawling that simply cannot keep up with the BFG red label. Something in the rubber mix, things are stupid grippy on anything, dry or wet.

YouTube



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[MZ5]

My post you quoted was a reply to junkie’s claim that the air in pneumatic tires (they’re properly named) isn’t what holds the vehicle off the ground.

You’re absolutely right that letting air out of tires helps you get around off-road. It’s the best and often _only_ way to get your roadgoing vehicle un-stuck from sand, because deflation causes the contact patch to grow in size and decrease in pressure, which is the only way to float back up on top of the sand.

One must remember to stay in context when considering this stuff. Moving out of context (eg. throwing disparate items into a comparison) will cause many people to mistakenly lose sight of what is being illustrated.

In your rock crawling example, you don’t experience excessive heat build-up because you’re going too slow. Where you’ll see heat build-up is (staying within a single context for clarity in this example) if you take that deflated-tire rock crawler and drive it down the freeway at 80. That’ll heat those tires enough that you’ll see it easily.

 

[Doc True]

I'm still trying to wrap my head around the physics of all this. I am pro-science, so don't think otherwise. I'm still trying to understand the coefficient of friction thing and how it applies in other areas.

Like take rock crawling for example. I was big into crawling for about 6 years. #1 cheapest/easiest thing to do to improve offroad performance is to air down. This increases contact patch, but I guess moreso allows tire to conform to the object it treading on. The tire doesn't spin and rotates very slowly, so how does the whole object of managing heat work there? There is very little heat created unless you cant make it up the obstacle, then you roast the tires for a minute, they heat up, become more sticky, then walk right up the obstacle with no problem. Same with drag tires, heat them up by burnouts to achieve optimal stickiness for the best launch. This is all very interesting to me, as I like to figure out how things work.

Old rock crawling vid below from a few yrs back for entertainment purposes, and also example of what I am talking about. The tires I ran were BFGoodrich red label Krawlers (stickies). Wasn't so much that they were soft compound, because there are several other softer tires for crawling that simply cannot keep up with the BFG red label. Something in the rubber mix, things are stupid grippy on anything, dry or wet.

YouTube



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On the road, it's almost entirely the friction equation. Off-road, different forces come into play. The friction equation still applies to off road, but it's effect is reduced an enormous amount due to the extremely low coefficient of friction between the tire and dirt. On the dirt, or rock crawling, the tread shape becomes much more important. This is why dirt bikes have knobbies. Here, you gain traction by the flat vertical surface (knobbie) of the tread digging in to and acting against the dirt. The limiting factor is the shear strength of the weaker of the two things (dirt on the trail/rubber on the rick crawler). In this case area does apply as the shear modulus equation has area as a component. For the dirt tire, by increasing the area the of the vertical tread in contact with the dirt, you distribute the force to a larger area of dirt. The goal is to increase the area so that the dispersed force is less than the shear strength of the dirt. Conversely, if you increase the area the force is dispersed, the more force you are able to apply before dirt shears and causes the tire to spin.

So even here, it's the increased vertical surface area not the increased horizontal surface area that makes a difference. The size of the horizontal contact patch is incidental.

Does this make more sense?

 

[TacomaJD]

On the road, it's almost entirely the friction equation. Off-road, different forces come into play. The friction equation still applies to off road, but it's effect is reduced an enormous amount due to the extremely low coefficient of friction between the tire and dirt. On the dirt, or rock crawling, the tread shape becomes much more important. This is why dirt bikes have knobbies. Here, you gain traction by the flat vertical surface (knobbie) of the tread digging in to and acting against the dirt. The limiting factor is the shear strength of the weaker of the two things (dirt on the trail/rubber on the rick crawler). In this case area does apply as the shear modulus equation has area as a component. For the dirt tire, by increasing the area the of the vertical tread in contact with the dirt, you distribute the force to a larger area of dirt. The goal is to increase the area so that the dispersed force is less than the shear strength of the dirt. Conversely, if you increase the area the force is dispersed, the more force you are able to apply before dirt shears and causes the tire to spin.

So even here, it's the increased vertical surface area not the increased horizontal surface area that makes a difference. The size of the horizontal contact patch is incidental.

Does this make more sense?

Yes it does, thanks for your time. I have a curious mind and always willing to learn more, even when I thought I had it figured out.

Here is another thing I think of. Say I cut up a bike tire and lay the tread flat on the ground in two different lengths and put 50 lbs of weight distributed evenly over the entire top surface area of both sizes, tie a string to the other end, and do pull tests. You are saying, theoretically speaking, that it would take the same force to pull that tread across asphalt by tugging on the string for either a 5" long piece of rubber under the weight of 50 lbs, and a 24" long piece of rubber under the weight of 50 lbs? Initially, I would think the increased "contact patch" in the longer piece would require more force to be drug across the asphalt, but there is less psi regarding weight distribution on the larger piece, so maybe it would be about the same for each? Or could the 5" piece actually be harder to pull since there is more lbs of weight per sq inch than the longer piece?

I realize that is not a rotational example like a tire rolling down the road and around a curve, but it's an example I've been fixated on in how it would relate to the friction of a rotating tire. Knew I should have majored in Engineering instead of Business. LOL

 

[Doc True]

Initially, I would think the increased "contact patch" in the longer piece would require more force to be drug across the asphalt, but there is less psi regarding weight distribution on the larger piece, so maybe it would be about the same for each?

You may be on the right track with this. It's my understanding that this is why area doesn't matter. I may be completely wrong about it though. Learning the equation was all I needed to get the correct answer. I don't remember discussing how the equation was derived.

You're right though, as long as the two surfaces (rubber and asphalt) on each object are the same, it will take the same amount of force to move them. As long as the extra weight of the longer piece of tire is subtracted from the 50lb weight

 

[TacomaJD]

The other thing I am stuck on too is when I used to do trackdays, I began on Michelin Pilot Power 2CT's (aggressive street tire). It didn't take long before I was outriding that tire, it would overheat in just a few laps and get what they refer to as "greasy" and would spin up exiting corners hard. So I switched to DOT race tires of the same exact size (Dunlop D209GP and Michelin Power Race) as I began to move up into Intermediate class and onto Advanced class, the newfound grip was AAAAA-MAZING. Wish I had swapped to them early on. Unfortunately that grip would be the demise of my sportbike days as in between trackdays, I would swap out my race fairings and put the street fairings back on to go ride on the street with my friends. Sometimes, I was too lazy to put the Pilot Powers back on, and just rode on the street with the dot race tires. They are approved for the road, just not recommended under street conditions. I somehow went into a freak tank slap on the interstate while playing around with my friends, the extreme grip of the dot race tires amplified the tank slap to where it was super violent, no fixing it, ran up against the guardrail and kicked off into the woods breaking both legs with one having to be amputated below the knee. I 100% believe if I had been running my street tires, the tank slap would not have been near as violent and I could have corrected it and went about my day.

Anyways, I think about grip of tires quite often, and I never really thought about "why" a race tire and street tire differ in grip physically, it's not so much grip as it is managing heat I guess? But wouldn't that only come into play when you are melting tires from riding so hard? Even running super sticky DOT tires, they look like they are melted all to pieces when you get done with a hard 20 minute track session, rubber balled up all over the tire, but they still grip extremely good whereas an aggressive street tire can melt and look the same but end up being "greasy" and not holding up as well entering and exiting corners. I know nobody here is melting tires on an NC, therefore if all the tires we are talking about are operating within their heat handling capabilities, does the same coefficient of friction equation apply in increased or decreased grip between narrower and wider tires? Or does that mean that say under normal riding, under the point of melting the tire, a 150mm rear tire is capable of gripping the same as the same tire in a 190mm? Heat management shouldn't matter if that is the case until the tire is pushed beyond it's limits right? Also going by that, we all know tires operate better with heat in them, which is why racers utilize tire warmers before hitting the track, so does that mean the narrower tire may heat up to operating temperature faster than the wider tire and since we aren't outriding that tire on NC's a narrower tire ends up being more advantageous than a wider tire in this specific application?

This makes my head hurt. And I'm sure quickly typing all that may contain some incoherency or grammatical errors. So overlook it if any exists. Lol.

 

[dduelin]

In the practical, stock tire sizes provide more grip than a rider can generally exceed. Anyone riding a track day can attest to this. Going to larger tire sizes adds little incremental grip and if the tire exceeds the recommended rim width it may even have less grip than stock or cause undesirable changes to steering geometry. Riders overwhelmingly crash from mistakes in cornering and braking technique not from lack of grip.

Riding on the street should not be an exercise in ultimate grip and riders should stay well within a safety margin to account for other road users, pedestrians, critters, and loss of traction from street markings, debris on the surface, drains/manhole covers, etc..

I enjoy the theoretical discussion as well as the next guy but just wanted to inject a little reality.

 

[TacomaJD]

That is true. I used to wear my leathers and drag knee on the street in the canyon/mountain roads around where I live quite often, and I never did outride Pilot Power 2CT's (aggressive street tire) on the street. I plan to push the limits of the NC occasionally, but not as extremely obviously. I hope the Pilot Road 5's on it now will provide plenty grip for what I want to do without having to sacrifice wear-mileage by swapping to a more aggressive street tire. I know that isn't the case with most NC riders, I ride an NC due to limited options for my disability, but also am happy with it thus far given the primary reason why I chose it. Haven't had a chance to take it to the local canyon or any other really curvy roads yet. Hopefully will hit some sweet twisties this weekend though!

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[TacomaJD]

Pray tell, where is the local canyon / really curvy road in NE AL?

Little River Canyon rim road on lookout mountain is darn close to some Deal's Gap material, beautiful lookoffs. I always start the road by the bridge there at Little River Falls, ride the curves, and exit out the back toward Dogtown, back into Fort Payne, and then on back home. It's about 30 min from my house. It's a favorite of most anyone that rides any type of sporty bike around here, even cruisers frequent it sometimes. Generally park law enforcement is scarce, I've never really had a problem out there. Although I have been hauling *** on a few separate occasions and meet a park ranger and never check up, I'm sure he knew it wasn't worth his effort to turn around. Lol. If you live anywhere remotely close to Fort Payne, AL and have not been to Little River Falls and rode the rim road, plan a trip, you won't regret it.

There's also a stretch of road between Stevenson and Sewanee that we will likely take in route to Lynchburg, then on to Nashvile --> Clarksville where we will be attending a Black Label Society concert and staying the night. It's in a really remote area, never seen any law enforcement up there. Me and a buddy used to wear our leathers up there and ride up and down that road through the curvy section multiple times.

There are several good roads on different parts of lookout mountain and the opposite mountain on the other side of me around the Skyline area. Also around the area of Desoto State Park on lookout mtn has some good curvy mountain roads, although some aren't perfect pavement. Some good roads in and around Guntersville State Park, but that's generally a high traffic area unless you ride through during a weekday.

 

[TacomaJD]

Here is Little River Canyon rim road 176. The red blip is where the road starts near the falls.

And here, road 56 is a remote back country road with very little traffic, gets super curvy and very fun above where it says Sherwood.

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[Doc True]

The other thing I am stuck on too is when I used to do trackdays, I began on Michelin Pilot Power 2CT's (aggressive street tire). It didn't take long before I was outriding that tire, it would overheat in just a few laps and get what they refer to as "greasy" and would spin up exiting corners hard. So I switched to DOT race tires of the same exact size (Dunlop D209GP and Michelin Power Race) as I began to move up into Intermediate class and onto Advanced class, the newfound grip was AAAAA-MAZING. Wish I had swapped to them early on. Unfortunately that grip would be the demise of my sportbike days as in between trackdays, I would swap out my race fairings and put the street fairings back on to go ride on the street with my friends. Sometimes, I was too lazy to put the Pilot Powers back on, and just rode on the street with the dot race tires. They are approved for the road, just not recommended under street conditions. I somehow went into a freak tank slap on the interstate while playing around with my friends, the extreme grip of the dot race tires amplified the tank slap to where it was super violent, no fixing it, ran up against the guardrail and kicked off into the woods breaking both legs with one having to be amputated below the knee. I 100% believe if I had been running my street tires, the tank slap would not have been near as violent and I could have corrected it and went about my day.

Anyways, I think about grip of tires quite often, and I never really thought about "why" a race tire and street tire differ in grip physically, it's not so much grip as it is managing heat I guess? But wouldn't that only come into play when you are melting tires from riding so hard? Even running super sticky DOT tires, they look like they are melted all to pieces when you get done with a hard 20 minute track session, rubber balled up all over the tire, but they still grip extremely good whereas an aggressive street tire can melt and look the same but end up being "greasy" and not holding up as well entering and exiting corners. I know nobody here is melting tires on an NC, therefore if all the tires we are talking about are operating within their heat handling capabilities, does the same coefficient of friction equation apply in increased or decreased grip between narrower and wider tires? Or does that mean that say under normal riding, under the point of melting the tire, a 150mm rear tire is capable of gripping the same as the same tire in a 190mm? Heat management shouldn't matter if that is the case until the tire is pushed beyond it's limits right? Also going by that, we all know tires operate better with heat in them, which is why racers utilize tire warmers before hitting the track, so does that mean the narrower tire may heat up to operating temperature faster than the wider tire and since we aren't outriding that tire on NC's a narrower tire ends up being more advantageous than a wider tire in this specific application?

This makes my head hurt. And I'm sure quickly typing all that may contain some incoherency or grammatical errors. So overlook it if any exists. Lol.

We're getting into speculation on my part when it comes to why the front tire is skinnier than the rear. I would guess that it has to do with energy transfer. The engine force has to be transmitted through the carcass of the tire and no energy transfer is 100% efficient. My guess is that the excess energy is lost in heat and that the larger sized tire is needed to dissipate the heat. If we were just dealing with cornering forces, I see no reason for the offset tire sizes.

 

[TacomaJD]

We're getting into speculation on my part when it comes to why the front tire is skinnier than the rear. I would guess that it has to do with energy transfer. The engine force has to be transmitted through the carcass of the tire and no energy transfer is 100% efficient. My guess is that the excess energy is lost in heat and that the larger sized tire is needed to dissipate the heat. If we were just dealing with cornering forces, I see no reason for the offset tire sizes.

Haven't even thought about that, I was solely comparing rear tire size examples only. I think I will drop the topic now, although this has definitely sparked my interest enough that I won't stop thinking about it now. Lol good discussion!

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[Doc True]

Haven't even thought about that, I was solely comparing rear tire size examples only. I think I will drop the topic now, although this has definitely sparked my interest enough that I won't stop thinking about it now. Lol good discussion!

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You also have the added complication of is the front and rear tire the same compound of rubber

Also, I know from watching MotoGP that they'll often put a different compounds on the left/right sides of the tire based on the number of left/right turns

I bet it's fun to be a race tire engineer

 

[TacomaJD]

You also have the added complication of is the front and rear tire the same compound of rubber

Also, I know from watching MotoGP that they'll often put a different compounds on the left/right sides of the tire based on the number of left/right turns

I bet it's fun to be a race tire engineer

My guess would be:

Front tire is skinny to help turn in faster. I've ridden various bikes with 120mm, 130mm, and 150mm front tires. Giant difference between them all with 120mm turning in the quickest, which is probably why 120mm front width seems to be the standard across more sporty type bikes, while rear tire width fluctuates in relation to the power each bike puts to the ground. Which makes for great evidence supporting the theory that a wider rear tire does improve grip when used with the correct width wheel and compared to the same model tire in a narrower size.

Regarding compound, Michelin uses different compounds for the front and rear in their dual-compound technology tires. Rear tire gets harder compounds, I'm sure because it will heat up faster under engine load, and front tire gets softer compounds, because it is narrower and also under neutral load. This is interesting too because front tires usually outlast rears by a significant bit, even while having softer compounds. At this point, one could also infer that since narrower tires have less grip than wider tires, softer compounds are needed on the front tire to make it perform in parallel with the rear. LOL but who knows.


Think this was a Pilot Road 4 chart.

This one labels each tire.

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[Junkie]

In the practical, stock tire sizes provide more grip than a rider can generally exceed. Anyone riding a track day can attest to this. Going to larger tire sizes adds little incremental grip and if the tire exceeds the recommended rim width it may even have less grip than stock or cause undesirable changes to steering geometry. Riders overwhelmingly crash from mistakes in cornering and braking technique not from lack of grip.

Riding on the street should not be an exercise in ultimate grip and riders should stay well within a safety margin to account for other road users, pedestrians, critters, and loss of traction from street markings, debris on the surface, drains/manhole covers, etc..

I enjoy the theoretical discussion as well as the next guy but just wanted to inject a little reality.

even on a fairly low power bike, get ham fisted with the throttle and you can spin up the rear on corner exit no problem (or at least I can consistently do it on my WR450 supermoto, which puts mid 40s to the tire).

 

[TacomaJD]

even on a fairly low power bike, get ham fisted with the throttle and you can spin up the rear on corner exit no problem (or at least I can consistently do it on my WR450 supermoto, which puts mid 40s to the tire).

Gearing on that bike probably helps put a little more powah to the wheels creating more tire spin-up torque. Lol

Any idea what top speed in top gear is on it? Just curious.