Tire wear/reverse front wheel

Discussion in 'Dakar champion (950/990)' started by Greg Minor, May 27, 2004.

  1. Greg Minor

    Greg Minor The Trespasser

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    I was just putting my forks back on after having Precision Concepts install stiffer springs and revalving them. I noticed I could mount my front wheel backwards by just reversing the spacers I don't see what it would hurt and it would even out the wear on my front tire (Conti TKC) these tires like any Knobby get that weird wear and it seems I could increase the life of the tire by "rotating the direction I guess the wheel is independantly balanced and it should not make any difference does anybody know why this may not work???
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  2. Jinx

    Jinx Call me Renzo

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    Most tires, or more accurately the treaded rubber bits, are not initially formed "round" The tread is manufactured in long strips because this is the most efficient way to do this.

    These strips are then cut to length to match the final diameter, but here is the kicker, both ends get an angled "scarf" cut where they meet, which increases the contact area of the bond, and partially loads the joint in shear, which we want (Try and remove duct tape by pulling it sideways sometime), and not wholly in tension, which is nasty (and is what you overcome, easily, when you pick up the edge of the duct tape and "lift"). The final construction is in a nice round mold of the appropriate diameter. So far so good.

    The problem is that the scarf cut splice is much stronger in one direction than the other. So the scarf angle points one way on the rear tire, to deal with acceleration, and the opposite angle on the front tire, where the highest load is under braking.

    Reverse the direction of tire rotation and you are putting the scarf cut in an orientation that is weaker.

    Normally, on most street tires this is not an option, as these tires tend to have tread patterns that are uni-directional, and nobody would want to reverse them in any event. But with knobbies or semi-knobbies you have a tread pattern that appears to be the same in either direction of rotation. But the underlying construction is not.

    And to add to the fun, a lot of manufacturers do not use the same "arrow" designation on their front tires (all of them have the arrow on the rear pointing in the actual direction of rotation). Some arrows indicate direction of rotation, but some indicate the direction of greatest force (what drunken bastard came up with that), so you do have to check with the manufacturer to get it right. Because some front arrows point in the opposite direction of rotation.

    Can you get away with it? Maybe. I wouldn't do it. JMHO, YMMV. Cheers.
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  3. kirkmoon

    kirkmoon Making up for lost youth

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    I'm no expert on tires, but if you have a bias ply tire or perhaps even a radial with angled plies, the rotation direction probably matters. Also, the tread pattern is designed to work better (for acceleration and braking) when oriented in the proper direction. There must be a pretty good reason why the tire manufacturers indicate a direction of rotation on each tire.
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  4. Frank Warner

    Frank Warner Traveller

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    If the manufacture thought it mattered they would put an arrow on the tyre.




    There is no arrow on the TKC front tyre I have. So you can run them any wich way.

    The only problem I see with reversing the rim/hub is that you are alos reversing the disk rotors. Any ware on the rotors will also ware teh pads to the same shape, by changing th erotor you may have reduce the braking untill th epads ware to the 'new' rotor..
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  5. Greg Minor

    Greg Minor The Trespasser

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    This is true I looked and could not find an arrow either the break situation is interesting maybe I'll try it and see since I'm not doing a lot of road racing it may not be noticable
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  6. Jinx

    Jinx Call me Renzo

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    :dunno :confused :dunno

    [​IMG]

    [​IMG]

    PS - Borrowed your picture, Mr Cob. Sorry. Just in the interest of science. :hide
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  7. Frank Warner

    Frank Warner Traveller

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    I'll have a look tonight Jinx.. but two of us found no arrow when it was mounted. And you look hard when fitting new stuff. :freaky
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  8. Greg Minor

    Greg Minor The Trespasser

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    Was that a 19 or 21 I have heard the the 19" was built especially for the GS now I know exactly where to look
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  9. Jinx

    Jinx Call me Renzo

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    Dunno, Frank, might be something new in response to:

    1) These tires are winding up on some very fast bikes, which leads to.....

    2) Septic Trial Lawyers. :evil :deal :evil


    It was from Mr Cob's GS, but I believe he did a 21" conversion and so is running a 90/90-21, which this was a picture of.
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  10. Greg Minor

    Greg Minor The Trespasser

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  11. MAXVERT

    MAXVERT O.G. on da O.C.

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    It looks to me like the front brake discs are directional, and the parts
    manual shows a left and a right side disc, which would also indicate that they are in fact directional. I personally would hesitate to run them in the
    opposite direction they were engineered to be turned. The 21 in. front TKC 80
    on my LC8 does have a directional arrow as does the 19 in. TKC80 on my
    Triumph Tiger.

    MAX
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  12. Greg Minor

    Greg Minor The Trespasser

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    Yup there is an arrow it was hard to find in a half lite garage so for me this solves the problem
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  13. Mack

    Mack Gone, but never forgotten. RIP, Mack...

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    Sidenote: The rear Michelin Endurostar for my 640 actually has depressions molded into the knobs so you can tell when it is time to flip the tire around for better grip. (Not sure if the 950 uses a magnet or caliper bolt for the IMO, but if it is a magnet you would have had IMO issues flipping the front as well.)
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  14. Frank Warner

    Frank Warner Traveller

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    Yep .. found the arrow .. and it is mounted wrong way around! Murphy at work again. :1drink It is a small arrow ...

    Mine is a 21 front.
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  15. Jinx

    Jinx Call me Renzo

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    And now you get to flip it around and get the extra mileage....which was probably your plan all along, you clever bast....... :evil

    Well, that would be my story anyways. :nod

    Probably not the end of the world as while the scarf cut at the front was being loaded the wrong way under braking, a properly mounted rear tire always has the scarf cut loaded the "wrong" way under braking.

    My main concern would be a fast road bike being run at high speed with lot's of heavy braking. But like we discussed, there are some very fast bikes now running TKC-80's.

    Of greater concern to me is the combination of high speed and low tire pressures. Are people inflating to the max on these 100+ MPH runs? This is, imho, the real safety issue. Speed rated tires are only speed rated at certain pressures and loads. Go outside the envelope and you are asking for trouble. Are people taking this seriously? I have seen the pics posted here of some of these tires after a speed run. They would scare the stink off a monkey.

    What pressures do people run their TKC-80's at for high speed? :ear :ear :ear

    PS - Everything you wanted to know about TKC-80's

    From Conti's website - Info on sizes, applications, speed ratings, loads, inflation. The stuff you want is between pages 88 and 122.

    It's a PDF file, so give it a little time to load. Cheers.
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  16. Greg Minor

    Greg Minor The Trespasser

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    I have run as low as 15 but I'm now running 32 as I'm afraid of denting the rim or getting a flat I just had my fork revalved and stiffer springs put in and it made a word of difference in the front end stay put I think with my weight the soft springs would make the rake much steeper as they would dive too much in the corner which caused a lot of tuck in I seldom run my bike more than 90 as I also have a 16 tooth countershaft sprocket
    #16