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  1. #1
    Gold Member mik's Avatar
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    Mar 2012
  2. Default let's talk tires

    Let's talk about the couple square inches of surface area that keeps us stuck to the road.

    The blast's stock tire sizing is 100/80/16 front (22.30" tall) and 120/80/16 rear (23.56" tall).
    The blast's rim widths are 2.5" front and 2.75" rear.

    The prevailing wisdom is to plus size your tires to 110/70/16 front (22.06" tall) and 140/70/16 rear (23.72" tall), but is that really the best for keeping a good contact patch?

    I just finished reading a book, "total control" by lee parks, about performance riding. It has an entire chapter dedicated to tires. There is a page in it that shows what happens to the profile of a tire when it is put on too narrow or too wide of a rim (or conversely when too narrow or too wide of a tire is put on a given rim width). If the tire is too narrow or too wide on the rim, it reduces the contact patch. The curvature of a given tire is designed for a certain rim width (and of course there is a plus/minus range that is 'acceptable' to run it on, but who wants to be acceptable when you can get the best?).

    When I first got my blast, I went with the prevailing wisdom and got pirelli diablos and had the 110/70/16 and 140/70/16 tires on it. I always had wide chicken strips, no matter how hard I pushed it. Yes, I'm new to riding and only have 30k miles logged so far, but I have learned why I had such chicken strips... my rear tire profile is wrong for my rim. After reading the book I looked at my tire from the rear and I can see that the contact portion of the tire suddenly curves inward and away from the road towards the edge, making it impossible to get that part in contact with the road. I laid my bike over in the garage to see how far I needed to lean it to get it to touch and it wouldn't contact until it hit hard parts, and I didn't even have pegs on the bike.

    After that, I contacted Michelin (since I now use Michelin CityGrip tires for my blast) and inquired as to what is the recommended rim width for various CityGrip tire widths. The below is what I got in response, along with the overall tire height...

    100/80/16: 2.5" (22.30" tall)
    110/80/16: 2.5" (22.93" tall)
    110/70/16: 3.0" (22.06" tall)

    120/80/16: 2.75" (23.56" tall)
    130/70/16: 3.50" (23.17" tall)
    140/70/16: 3.75" (23.73" tall)

    All that being said, I plan to run 110/80/16 front and 120/80/16 rears in the future. It may not be the coolest looking rear tire, but that's not what I'm about. This also isn't about trying to get rid of my chicken strips, it's about getting the biggest contact patch. With inappropriately sized tires, the contact patch can be reduced even tho the tire itself is wider than stock.

    These recommended/designed for rim widths are from Michelin, other manufacturers may have different specs so you'll have to contact your favorite company.

    Discussion? Thoughts?

  3. #2


    More important then contact patch size is grip or friction level which is also a function of tread design and more importantly tire compound.

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  4. #3
    Racer styxnpicks's Avatar
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    Jan 2012
    Cincinnati, OH
  5. Default

    I really like the diablo 130/70-16 on the rear perfect compromise IMO.
    Buell XBlast: NRHS Xb Stage 2 lite, 515 10.5:1, .551 cam, Daytona Twin 1005s-Ex, Vance Hines, Crossroads Fork Brace + Rearsets. Pirelli Rubber
    Buell XB9r: Race ECM/Muffler. K&N

  6. #4
    Mechanic BrandonSmith's Avatar
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    Feb 2015
    Paris, TX
  7. Default

    As long as the 120 tire doesn't run out of tread when the bike is leaned over.

    I liked my $45 Shinko the best out of the CityGrip, Diablo, and Shinko.

    Posted from my Buell using Buell Riders Online mobile app
    2008 Buell Blast - 8000 miles
    Modified Stock Exhaust - 45/175 jetting, No Needle Shim, Idle Mix: 2.75 turns out
    Denso Iridium Racing Spark Plug
    Pirelli Diablo Front - 110/70-16
    Michelin CityGrip Rear - 140/70-16

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  8. #5
    Silver Supporter KennyG's Avatar
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    Jul 2013
    North Texas
  9. Default


    It is good to see you on here this morning.

    How is the wife's progress?

    Kenny G
    *** 2009 Blast *** V&H Exhaust *** Dan's Intake System Along With Recommended Jetting By Dan *** Yellow Skins Purchased, New Old Stock, From Dealers Who Used Yellow Blasts For Riders Edge ***
    *** Pirelli Diablo Tire Front *** Pirelli ST 66 140 70S 16 Tire Rear***

    *** Hope To Work On Suspension Next ***

  10. #6


    I remain very interested in this topic....especially with regard to the City Grips....

  11. #7
    Gold Member mik's Avatar
    Join Date
    Mar 2012
  12. Default

    Crackhead- total traction is a function of contact patch (size of patch, also tread pattern as racing slicks have more contact than lots of grooves and sipes), and compound, and down force, and temperature (which affects how sticky a particular compound is at any given time), and the road's surface.

    I loaned my book to a friend, but here's a graphic I think I can use to help describe what I'm getting at:

    When the bike is vertical (left most) it's not going to matter if you run a 120/80/16 or a 140/70/16.
    When the bike is moderately leaned (middle) it probably won't matter much
    But when you're at full lean and you have one tire that's meant for a wider rim (140/70/16) squished onto a narrower rim (visually that means bringing the two parallel lines of the bead together from the optimal width, which curls the edges of the tread inward, pulling it away from the road), you are going to lose that big contact patch. Does that make sense?

  13. #8
    Gold Member mik's Avatar
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    Mar 2012
  14. Default

    Ok, I took some pictures of the tires on my bikes and used a straight edge (angle steel) to give a good visual of what I'm talking about. This is with 130/70/16 tires, not even the extreme 140/70/16 tires. The furthest edge of the tire tread should be straight, not curved.

    Click image for larger version. 

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    First off, we have a perspective view so you can see what I'm doing. The angle steel is just in contact with the end of the axle to show hard parts contact in a lean, and I ran it tangentially to the tire.

    Click image for larger version. 

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    This is a closeup shot of the angle steel at tire contact. I had a rough time getting a good picture, but there is a gap between the widest part of the tire tread and the steel. This means the entire tread is not being used. The gap is small on the left side, maybe 1/16", but it's not just about using the entire tire. This is just a graphic demonstration to show you that the tire is not sized properly, this also means that the profile is distorted. The edge of the tire is supposed to be straight so you have the greatest contact patch at full lean, but instead it's bent/curved so it's a very tiny contact patch.

    Click image for larger version. 

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    The gap is much more pronounced on the right side with our gigantic pulley.

    Click image for larger version. 

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    I set the straight edge on the tire and rotated it until it came just to the edge of the tread. This shows where that line intersects with the axle.

    Click image for larger version. 

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    On the right side I had to use a stubby piece of steel, but same thing, I rotated it until it just barely got to the edge of the tread. Look where it intersects on this side to be able to use the entire tread!

    Click image for larger version. 

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    This is a comparison picture of my xb12 with its stock sized tires. With the bar just touching the edge of the tread the bar intersects the axle line way away from the edge of the axle and has no interference points anywhere. This is what a properly sized tire should look like to maximize your contact patch.

    I hope these pics help.

  15. #9
    The Boss
    Jet-Lee's Avatar
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    Mar 2012
    Antioch, CA
  16. Default

    All good info.
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

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  17. #10
    Gold Member mik's Avatar
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    Mar 2012
  18. Default

    Quote Originally Posted by Jet-Lee View Post
    All good info.
    Glad you think so. That being said, I'm not saying everybody should cut off their 140/70/16 tires, they're still good sticky tires and they definitely look cooler than the factory 120/80/16 tires. I am simply convinced that for maximum traction with the michelins and using the entire tire if you're a rider that wants to push it, sticking with the factory size is the way to go. I have a set of 130/70/16 on right now that have maybe a couple hundred miles, plus a brand new 140/70/16 sitting on my shelf. I plan on using them and *then* going to the 120s. However, if someone wants to take the brand new 140 off my hands I'd sell it at a killer price...

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