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  #1  
Old 4 Aug 2010
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Rim size vs tyre size question

Hey guys,
I took my tire off and my rim was rusted quite badly on the inside, too badly to clean in my opinion. Anyway I bought the only rim I could find which was a 1.85, slightly thinner than my old one, which I would assume was a 2.15 (don't have it here with me).

Anyone know if I'll have problems riding with a 120/90-18" knobby tire on a 1.85" rim?
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Old 6 Aug 2010
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Up here in the UK - if you deviate from a standard wheel size - it invalidates your insurance

Keep searching - there must be one somewhere
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  #3  
Old 6 Aug 2010
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I'm thinking a 120 section tire will be fine, but not sure I'd go any larger.
I believe several dirt bikes use a 185 rim and run either 100, 110 or 120 tires.

Do some searches to find stock sizes to be sure as I'm "guesstimating" here.

I think you are OK but I'd get a stock size rim when one pops up cheap.
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Old 6 Aug 2010
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Just looked at a 21" tube and that goes up to 100, a 120 may "balloon" the only way to be sure is to try it, but it could be an expensive test. I've tried bigger tyres on standard rims and it got vague at speed.
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Old 18 Aug 2010
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Works ok for me.
What happens is only that the side of the tire have a different look. I have -not- tested highspeed (less you consider 140-160km/h as fast) driving with it.

Pigfords warning is important!
In Sweden our insurances are not affected by tire choices. Here they only look at the condition of the tires, not the size, not the make, nor the model.

You do need to check with your Australian insurance what their fine-print says/reads.
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Old 18 Aug 2010
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Thanks everyone for the help! It's on now and seems to be okay, the only problem which I had was that it took quite a lot of pressure for the tyre to seat on the bead which I hope doesn't cause me problems should I get a puncture in the middle of nowhere

Also insurance isn't a problem because I'm in Bolivia and don't have motorcycle cover.

Cheers again!
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Old 18 Aug 2010
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Pleased you're up and running, be interesting to know what, if any, difference it makes to the ride, handling. Take it steady
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Old 18 Aug 2010
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I used to "overtyre" bikes as a matter of course in the dim and distant past, wanting to make them look more butch and manly! I'd fit the widest tyre I could get my hands on as long as it would physically fit - and I did quite a few long trips like that.

Nothing actually happened (other than me wasting some money). The bike still ran ok and I don't remember the handling being any worse, although tbh the handling on most 60's / 70's Jap bikes was so bad you'd be hard put to notice it get worse.

If you look at a bike wheel that's been over-tyred or under- rimmed, the tyre seems to have a more rounded profile so you'd think the effect would be for the bike to fall into corners more easily. The fact that I never noticed probably says more about me than any inherent problems with getting the tyre / rim match wrong.
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Old 19 Aug 2010
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Quote:
Originally Posted by backofbeyond View Post
If you look at a bike wheel that's been over-tyred or under- rimmed, the tyre seems to have a more rounded profile so you'd think the effect would be for the bike to fall into corners more easily.
Yes, that would certainly be the theory but in my experience, the reverse is the result. I deliberately ''undertyre'' all my big bikes - I find going down one size makes tip-in to the corner much quicker, and gives the bike a generally much more agile feel to it.

I'll take handling over macho any day.
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Old 19 Aug 2010
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My experience also, smaller tyres= quicker, more precise steering, more responsive, more confidence inspiring. Bigger tyres= slower, more vague handling.
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Old 19 Aug 2010
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Rim to Tyre Application Chart

rim to tyre list
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  #12  
Old 19 Aug 2010
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Quote:
Originally Posted by Pigford View Post
Up here in the UK - if you deviate from a standard wheel size - it invalidates your insurance

Keep searching - there must be one somewhere
Are you sure? Millions of people fit different sized wheels to their cars - I being one of them - and still have valid insurance. You're meant to tell them of course, but I bet most don't.
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Old 19 Aug 2010
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I think these days if insurance companies can avoid paying out, they will do.
Buyer beware.
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