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Discussion Starter #1
Im a certified master technician and notice alot of these z125 including mine. The front tire rotation is going the wrong direction from the factory. Check your tire direction of rotation. There should be an arrow pointing the direction of rotation. Its even funny that most pictures of these bike shows the front tire are in the wrong direction too.... LOL.
 

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There should be 2 arrows. One for front and the other direction for rear. It was like that with my stock IRC tires anyway.
 

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LOL! Read the fine print before the arrow. One side says front rotation and the other says rear rotation. A lot of people seem to get tricked by this.
 

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Discussion Starter #5
My front tire rotation is backward. Its going counter clockwise. Just by looking at the tread pattern it doesnt look right. I only notice my tire rotation at 300miles after my first rain ride. As the picture I posted. What I know as a certified master technician. The rotation should be arrow going foward, not backwards.
 

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I don't ride in the rain, so I never car about tread direction. My only concern is that some tires don't react well to being run backwards.

Internal plies favor rotation in one direction and can tend to delaminate when rotating backwards. Delamination was a big problem with Dunlops at the race track for many years. That said, I don't know if it's a problem on a bike with this little horsepower.
 

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Crimson, do you have a picture of your tire mounted backwards?

Zaph, these tires are okay to run in either direction outside of the rain. The front is mounted opposite the rear, so they are basically designed to be run either way.
 

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Discussion Starter #10
My bad guys. I dont know anything about motorcycle engineering. But you guys are right. The front tire has 2 direction arrow. Why do they do that????
 

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My bad guys. I dont know anything about motorcycle engineering. But you guys are right. The front tire has 2 direction arrow. Why do they do that????
I'm not a certified master technician, but my guess is they found the tread pattern provides better braking traction in one direction and better acceleration traction in the other.
 

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Discussion Starter #12
You would think the front tire moving the water away is better then inward. Still doesnt make sense to have it backward. Any engineer know the reason why??
 

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I'm not a certified master technician, but my guess is they found the tread pattern provides better braking traction in one direction and better acceleration traction in the other.
This is correct. Under braking the tire is technically accelerating backwards, therefore the tread looks backwards compared the rear, which is designed to channel the water away like we are used to on directional car tires.

This is how motorcycle tires are designed and mounted, note Michelin example front/rear:
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjU9Kie6cXWAhXEWhoKHRYPC2AQjRwIBw&url=http://moto.michelin.com/DC/en/tyres/products/pilot-road-2.html&psig=AFQjCNG7NpMP2096rK2u95GlzuvVA3Pxcw&ust=1506617366293873

If I remember correctly, the 'front' tire on the Z is actually a narrow-sized rear tire mounted backwards. And as far as the concern about tire construction, I don't think the speeds and loads this little bike sees will affect the tire adversely.

Disclaimer: I am not an engineer, but I work with them everyday at a tire company.
 

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Back from the dead.

I was recently looking for the answer to this same question except no one could tell me why.. Then I found someone..who I should've asked in the first place.

"There is a Life and Death Reason! The Tires are made from 1 strip of Rubber wrapped around a Mould. At the Joining section, they GLUE the ends together at a 45 Degree angle.

Think about getting on the Gas with the rear tire and that seam edge AGAINST the direction of Rotation. Eventually you can Split the Seam and tear the tire apart.

The Front tire does Braking which applies force 180 degrees Different from the rear. And under Braking you can force the Seam to come apart and destroy the tire and maybe your Behind. Understand now?"

Thought this might be of interest to someone else as well.
 

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Back from the dead.

I was recently looking for the answer to this same question except no one could tell me why.. Then I found someone..who I should've asked in the first place.

"There is a Life and Death Reason! The Tires are made from 1 strip of Rubber wrapped around a Mould. At the Joining section, they GLUE the ends together at a 45 Degree angle.

Think about getting on the Gas with the rear tire and that seam edge AGAINST the direction of Rotation. Eventually you can Split the Seam and tear the tire apart.

The Front tire does Braking which applies force 180 degrees Different from the rear. And under Braking you can force the Seam to come apart and destroy the tire and maybe your Behind. Understand now?"

Thought this might be of interest to someone else as well.
This is half true. The part that's not true is where "the rubber is wrapped around a mold." It's not done that way at all, the rubber is fully 100% injection molded.

The internal plies (in many tires) however are wrapped inside the first injection molded inner rubber portion. The way they are wrapped, they overlap in one direction. Because these plies overlap, serious acceleration in one direction makes the plies tighter, while running it backwards makes the plies loose, which can start the outer rubber delaminating from tension stresses.

I know this because I talked to a Dunlop engineer and asked why everyone's race tires are delaminating. It's because racers are flipping their tires after a couple races. One side wears out depending on track direction and the tire is flipped to get more life out of it. Many tires can't handle this, especially high hp supersports. You end up with something like this:



If it gets bad enough, chunks start coming out and then you have catastrophic deflation at high speed. This is only a problem with some tires, mostly Dunlop Q3's and older Ntec race tires. Pirellis are designed with interlocking plies that don't come apart if run backwards. New Dunlop GPA Pro race tires are bi-directional with a new internal ply design. It's a design change Dunlop had to make because racers need to flip their tires. People were running more expensive Pirellis because they could be flipped and therefore lasted longer. At one point my race tire budget was $3K a year, and if I can't flip a tire to save money, well F that tire.

Now on a bike like the Z125, this type of delamination will never happen. There's not even close to enough power. The tire rotation direction is determined by tread siping for water ejection. And it differs depending on the primary force a tire sees - on the front it's braking and on the rear it's acceleration.

Racing rain tires - run those backwards on a wet track and you are going down HARD the moment you try to brake for turn 1. The siping HAS to go a specific direction, and the front is opposite from the rear because of the primary forces each tire sees. (unless it's a bi-directional thread, there are some of those - but normally fronts only.)


You better run these the right direction in the rain....

Sorry, I have some race history behind me and a lot of what I talk about comes from that perspective. :D
 

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I got this info from my dad who raced many years in the AMA from the 60s-80s. I'm sure somethings have changed since back then.

I'm also glad to hear this updated info as well!
 

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It appears that they sell this tire for use as both a front fitment and a rear fitment - so I am assuming that the tread direction has to do with how they want to "squeeze" the water out when running as a front.

Arrow issues aside, the DOT date stamp on my front tire is on the right side of the bike and my rear tire has this date on the left side.
 

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@Zaph: Thanks for dropping that knowledge bomb on us.

I trust your experience and the collective knowledge of every tire engineer in the world, but it still doesn't fit right in my head.

Yes, the front tire's job is to take the negative rotational acceleration provided by the brakes and push on the pavement to slow down the bike. This makes perfect sense, all acceleration forces are backwards from the rear wheel. But from the perspective of the water (not the road) the tire is still moving forward so any water caught under the tire is going to follow the sipes directly towards the center of the wheel. Also does the "reverse tread for braking forces" argument mean that wet tires hydroplane slightly at steady state and forward acceleration?

Why doesn't it make sense to mount directional car tires backwards on a RWD car? I'm guessing this is key here, I'm thinking about this too much from a car tire perspective. Motorcycle tires have a completely different contact patch.

I need to draw a force diagram of this or something, or take a nap.
 

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Well I can't say I know a single **** thing about car tires, hahah.

I also don't know the technicalities of why tread has to go a certain direction in the rain. I only know the result of mounting a rain tire backwards... pain in turn 1. Lol.

But yeah pretty sure it has something to do with acceleration and trail braking forces vs hydroplaning. That's why rain tires mostly go from very directional in the middle to almost horizontal on the side, you aren't on the gas or brakes at full lean angle.

 

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Aww shucks. Well, this is a good late-night-youtube subject. I'll let you know if I find a good explainer. I'm having better luck imagining the recovery process of a tire that is already hydroplaning. I was thinking too idealized previously.

It makes logical sense, but my mental image of the physics isn't quite there yet.
 
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