# Tire Rotation Direction



## mikiek (Aug 18, 2014)

I guess I learn something new about my bike every day, but this one has me feeling kinda stupid. :blush2: I'm riding Conti GP4K tires and was looking on the sidewall for the max PSI. Seems like all the lettering on the sidewall that is not painted is really hard to see. I happened to notice an arrow indicating rotational direction. 

Never knew this was important with bike tires. Looked at some of my other tires hanging on the wall and none of those had the same arrow. What has me wondering is 

1. The GP4K tread pattern (what little there is) is symmetrical and most of the tread is just a slick. What difference would it make which way the tires rotated?

2. What happens if your tires are mounted in the opposite direction?


----------



## Jay Strongbow (May 8, 2010)

Ignore it. Doesn't matter at all.


----------



## BelgianHammer (Apr 10, 2012)

mikiek,

As Jay says, for the most part ignore it. Somehow, bicycle tire companies got it in their heads that since automobiles have tire directions (for water displacement), they too could get away with claiming it on their tires. I have tires that are directional (the Vittoria Diamante Pros), and they have microscopic channels in the tread that shuffle water out from the center of the tread to the outside. Supposedly, if you mount them reverse, you'll channel water into your tire and increase hydroplaning. Well, I read some tests (I'll see if I can dig them up) that blew multiple holes in that theory given that the small of contact area these tires have on the tarmac, it is better to maximize that contact and not screw around with supposed channels. They even showed how a channelled tire would slip out on wet pavement equally as easy as a smooth tread tire like the Rubino Pro. So, it's all a marketing thing, it seems. But I am sure some will argue up and down that it is valid. Cycling and components is a heavy degree of perception business


----------



## junior1210 (May 2, 2013)

I just mounted a set of Conti Ultra Sport II and they have the same arrow on the sidewall. The tires I just replaced (Vee Rubber Rounders) also have the directional arrows (but actually have a tread). Considering the speeds and surfaces, I doubt it makes a difference. Then again, since the manufactures went through the trouble of putting the arrow there, why not follow it?


----------



## duriel (Oct 10, 2013)

If they are backwards, when you pedal forward, you go back to where you came from. Sometimes it helps if you forgot where you parked.


----------



## dmanthree (Aug 22, 2014)

*But why...*

Curious: if it really doesn't matter, why is it there?


----------



## Kerry Irons (Feb 25, 2002)

dmanthree said:


> Curious: if it really doesn't matter, why is it there?


If you believe what you read, Continental (and other manufacturers) put those arrows on there to cut down on the annoying correspondence they would otherwise get asking them which direction the tires should be mounted. Really, people do ask this all the time even though it is painfully obvious that for a typical road tire it is completely meaningless.


----------



## cxwrench (Nov 9, 2004)

Kerry Irons said:


> If you believe what you read, Continental (and other manufacturers) put those arrows on there to cut down on the annoying correspondence they would otherwise get asking them which direction the tires should be mounted. Really, people do ask this all the time even though it is painfully obvious that for a typical road tire it is completely meaningless.


^ This ^ is the reason. For reals.


----------



## November Dave (Dec 7, 2011)

On GP4000s specifically, the aerodynamics in the tunnel are significantly affected by tread direction. They are well beyond the margin of error faster in the direction noted by the arrow. There are also multiple GP4000 production molds and one is known to be faster in the tunnel (slightly narrower tires). The kind of stuff that matters in the wind tunnel and maybe not too much in the real world, but I still always mount GP4000s the "right" way.


----------



## Jay Strongbow (May 8, 2010)

November Dave said:


> On GP4000s specifically, the aerodynamics in the tunnel are significantly affected by tread direction. They are well beyond the margin of error faster in the direction noted by the arrow. There are also multiple GP4000 production molds and one is known to be faster in the tunnel (slightly narrower tires). The kind of stuff that matters in the wind tunnel and maybe not too much in the real world, but I still always mount GP4000s the "right" way.


Wow, who'd a thunk that.
I wonder how the aero is compared to no tread at all which is esentially what they are because it doesn't touch the road anyway except maybe in hard learning corners.
Just out of curiosity is that tread designed for aero or is one way being better than the other just a coincidence?
I'm guessing coincidence because with a quick google I found this from Competitive Cyclist: "So we asked. We were told that the little side tread shapes are for show. Slicks grab better and bikes don't hydroplane, but there are people who just refuse to believe that slicks are better. So Continental puts a little side pattern on to make a good show to allay the concerns of the doubters who want tread"
But then again they probably asked some phone rep. at Conti who wouldn't necessarily have all the knowledge of the design department.


----------



## November Dave (Dec 7, 2011)

I think it's just coincidence, but the "correct" direction is the faster one, so who knows?


----------



## looigi (Nov 24, 2010)

It's likely not relevant to bicycle tires but back in the day it was said motorcycle tires had directional arrows due to the direction of the tapered overlap the tread rubber made during tire construction. From the current Continental website: "Where a tyre has directional arrows moulded upon it, the tyre must be fitted so that the relevant front or rear arrow follows the direction of rotation. Road handling and tyre wear may worsen, or damage to the tyre can occur in extreme circumstances if these instructions are not followed." And from Avon: " The arrow tells you which way to mount a tire for maximum water dispersal. Another, less apparent reason for directional arrows is the tread splice...To further ensure the strength of this bond along the tread splice the directional arrow will show you which way to mount the tire so that when the rider is “on the gas”; the acceleration force on the rear tire is pressing the splice together, rather than peeling it back. As for braking, 80 % of the braking should take place in the front on most bikes. Therefore, the front tread splice is run in the opposite direction than that of the rear, so when the rider is on the brakes, he’s not peeling the tread splice back.."


----------



## cxwrench (Nov 9, 2004)

November Dave said:


> On GP4000s specifically, the aerodynamics in the tunnel are significantly affected by tread direction. They are well beyond the margin of error faster in the direction noted by the arrow. There are also multiple GP4000 production molds and one is known to be faster in the tunnel (slightly narrower tires). The kind of stuff that matters in the wind tunnel and maybe not too much in the real world, but I still always mount GP4000s the "right" way.


Please tell me you're kidding. 


Right?


----------



## November Dave (Dec 7, 2011)

Nope, not at all. It's less than a watt but more than the minimum you can afford to not worry about it I mean if you test two wheels and don't switch THE tire you're using in order to use it in both wheels, it's not even close to being a valid test. 

On the direction thing, whether there's a reason for it or no, there's an established right and wrong, so I do it right. In my life, I have to REALLY pay attention to all of the wheel stuff.


----------



## cxwrench (Nov 9, 2004)

November Dave said:


> Nope, not at all. It's less than a watt but more than the minimum you can afford to not worry about it I mean if you test two wheels and don't switch THE tire you're using in order to use it in both wheels, it's not even close to being a valid test.
> 
> On the direction thing, whether there's a reason for it or no, there's an established right and wrong, so I do it right. In my life, I have to REALLY pay attention to all of the wheel stuff.


Like I said...less than a watt.


----------



## November Dave (Dec 7, 2011)

The market is such that you can't afford to ignore such things. Differences overall between good wheels and bad is actually pretty big - it can be 20 watts, which is instantly noticeable in the right conditions. Differences among better wheels are smaller and no one would willingly throw that away. It would get sold against you. 

We compared one of our wheels against an established competitor and gave them an advantage of 6mm more valve stem sticking out of our wheel (their wheel is 58mm vs 52 for us, same tube used in both wheels). They would NEVER have given us that advantage - no way. 

A lot of people are "weenies" about grams of mass, a lot are "weenies" about grams of drag. 

It's just how it is.


----------



## cxwrench (Nov 9, 2004)

I think it's pretty humorous because:

1) If you're an average guy, it doesn't matter.
2) If you're a pro, it doesn't matter. 
2) If you're faster than average, not a pro, and you worry about grams of drag, it doesn't matter AND you need to get a life.


----------



## SwiftSolo (Jun 7, 2008)

I've wondered why I'm so dammed slow climbing. 



cxwrench said:


> Please tell me you're kidding.
> 
> 
> Right?


----------



## 4slomo (Feb 11, 2008)

I can envision that there may be some directionality to how they lay up the layers when building up the tire carcass, such that it rides faster in one direction than the other. I'm not a tire design engineer, so I can't present it as a fact. My perspective is that if a manufacturer puts a directional arrow on a tire, they are indicating the tire works better in one direction than the other, and you may as well take advantage of that characteristic, if you're concerned about such things.



mikiek said:


> I guess I learn something new about my bike every day, but this one has me feeling kinda stupid. :blush2: I'm riding Conti GP4K tires and was looking on the sidewall for the max PSI. Seems like all the lettering on the sidewall that is not painted is really hard to see. I happened to notice an arrow indicating rotational direction.
> 
> Never knew this was important with bike tires. Looked at some of my other tires hanging on the wall and none of those had the same arrow. What has me wondering is
> 
> ...


----------



## November Dave (Dec 7, 2011)

cxwrench said:


> I think it's pretty humorous because:
> 
> 1) If you're an average guy, it doesn't matter.
> 2) If you're a pro, it doesn't matter.
> 2) If you're faster than average, not a pro, and you worry about grams of drag, it doesn't matter AND you need to get a life.


It's not for me to judge, certainly, but the awareness does help drive better wheels. 50mm rims can now be faster than old 90mm rims, as well as lighter and way easier to handle. 

Some might think it's silly or even counterproductive to prioritize a 20g weight saving over other aspects in a wheel set, but there's no question to me that a wheel set that's 400g heavier has a notable downside. A wheel that's got 15w more drag has a notable downside. 

The thing that does irk me is when companies respond to the competitive nature of the market with silly games - 'most people will never weigh them' stated weights and 'impressive graphs are impressive even if they're badly misleading' aero info. One company would have you believe their 30mm rim is faster than a 404, and people really believe that this rim is that much faster than other, quite similar 28 to 30mm rims.

One man's 'meaningless' is another man's 'game changer' which is why I prefer to communicate these things in purely objective terms


----------



## tvad (Aug 31, 2003)

November Dave said:


> One man's 'meaningless' is another man's 'game changer'.


Oh boy, is that ever true. Spend some time in high end audio discussion forums.


----------

