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Discussion Starter · #1 ·
I've got an 18" rear invader that looks 3.50" from inner to outer beadseat

Everyone I talk to has been saying it will be OK to run 18" Avon SM Mark II on it. On the Avon sheet it says "RIM MIN-MAX 2.15-3"

Could bad stuff happen running it on a 0.5" oversize bead seat? Would the rim favor a larger tire (4.50)?

1646801 is the Avon part # for the 18" SM Mark II
http://www.avon-tyres.co.uk/sites/default/files/18388_Avon%20MC%20Databook_Web%20PDF_v1%2012_0.pdf

the rim to tire guide says no go as well
http://www.dropbears.com/u/utilities/tyrerim.htm
 

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The Avon you are thinking of running is a bit narrow-4.00x18........the sidewall will be nice and straight-ish, but possibly a little bulged-the tire might look like the Cali style lowrider cars with the rim edge showing when looking at the tire from front or rear (tire isn't wide enough.) I would try to go to a bit wider tire, possibly an older Dunlop style that came on early Sportsters-like a K70. The original Grasshopper tires are great too-don't remember all they're sizes. Coker's diamond tread tires play the part, and have a 4.50 x 18" tire too-they just get a little pricey.

Tires are the last thing between us and the road-I don't like to fuck around with what ifs myself!!! Hope this helps.
 

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You say the wheel "looks" 3.50" Are you actually measuring it, or "sorta" measuring by looking at the wheel with the tire mounted? Since whatever you decide, you'll need to dismount the tire (if there is one) anyway, do that an get an accurate measurement.

If it is too wide, consider a different tire. Twowheeledhell has some good suggestions. Also, there are a couple of K181 Dunlops in the 130/90-18 size on eBay now. It's a non computer designed universal tread, but it's a pretty tall tire. The Conti Supertwin isn't too bad looking either. Some guys run Dual Sport tires, the ones designed for 80-90% road use.

You can also call around to shops and dealers in your area, anybody that sells motorcycle tires. Almost all of them have one or two (or more) oddballs laying around that aren't really in the mainstream of what they sell, but were special ordered for a customer who never picked them up, or misordered, or something. I saw a 19" whitewall the other day in one of the shops I'd visited. It had likely been there for some time.
 

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Discussion Starter · #5 ·
I should chose my words, the rim actually measures 3.5" from inner to outer bead seat. The actual width from lip to lip is larger, obviously. My concern was that Avon product sheet and the tire/rim guide say to NOT use a 4.00x18 on a 3.5" bead seat (if I am reading the chart correctly)

As a point of discussion the dropbear's rim to tire guide says a tire less than 120mm or 4.72" tire should NOT be used on a 3.5" bead seat rim.
But then again the difference in measurement of a 120mm(4.72") tire to a 4.50(114.3mm) tire is .2 inches or 5.08 millimeters..a relatively small amount?

There are some modern tires I have been seeing that wouldn't look so awful in hard tail -- Bridgestone Spitfire, the continental supertwins are great but I cant find them anywhere, there was a Metlzer tire that didn't look so bad. Modern dual sport rear might be a good option permitted its not so knobby. There may be something even better out there that doesnt look like it belongs on a ocean city shopper. The Dunlop K70's are cool but stop at 4x18 and I would ideally prefer to stay away from NOS tires in the case of the 181's (that's an old tire right?)

I hope to log a lot of miles on this bike, starting with good tires cuts out a lot of "what if" brain trains when Im cookin down a state highway pushing 70mph
 

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Discussion Starter · #6 ·
Rim Width Range
Because tires have flexible sidewalls, a single tire size will fit on a variety of rim widths. A tire's rim width range identifies the narrowest to the widest rim widths that the tire is designed to fit. The width of the rim will influence the width of the tire. A tire mounted on a narrow rim would be "narrower" than if the same size tire was mounted on a wide rim. NOTE: Because the overall diameter of a steel belted radial is determined by the steel belts, there is little, if any, change to the overall diameter of the tire due to differences in rim width.

The industry rule of thumb is that for every 1/2" change in rim width, the tire's section width will correspondingly change by approximately 2/10".
Interesting bit I found just now
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=198
 
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