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Old 07-26-2012, 07:47 AM   #1
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Rim Job ... What size should I use?

This might be a loaded question ... but I am doing a 'StevenB' rear hub treatment to a '85 R80 (The Dobber) to make it a spoked wheel. This really means that I have a load o' options where the rear rim is concerned. The bike is now a 1000cc, dual plugged, larger carbed, extended swingarm, massive forked monster.

The question would be which rim should I lace up?

These are the factors I'd like to take into account.
1. Final Drive choices. I have a good line on a 32/10, currently there is a 37/11 on it, and I could get a 33/11. I'd like for the bike to do 80mph on the highway and have the rpm's be reasonable < 5K.
2. Cheap tires and availability. Which dual purpose tire size is most common? 17" rim, 18" ... 19"?

If I got a 33/11 final drive, I would probably keep the 17" rim that's on it. If I got the 32/10, I'd probably look into an 18" rim ... depending on what the outcome of this thread ...

What have I forgotten? Are there more factors in play? Any advice out there?

As always, Thanks in advance. Fred
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'85 R80RT G/Sified <|> '91 R100GS Bumblebee (103K miles and climbing) <|> '73 R75/5 LWB
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Old 07-26-2012, 08:04 AM   #2
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Well. I'd go for the 33:11 if you're thinking of mostly highway. GSPDs have a 3.09:1 final drive, so 3:1 wouldn't be far off. You're current 3.36:1 is even on the low side for 800cc IMO, 3.2:1 could be a little low for 1000cc also. As for what size rim, the 130-17 is probably the easiest tire size to find anywhere and has the most options available. If you want to dish your wheel to the left a little more to fit a 140, you could move up to the 2.5"x18" rim as there are plenty of good tires made in 140-18 for KTMs. 120-18 is a little slimmer pickins though, especially outside the US, unless you're looking for full-on knobbies. Don't even consider 19". It's really only for MX bikes and you'll only find knobbies for it. Overall 130-17 is the most widely available and has the most options for dual sport tires.
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Airhead Wrangler screwed with this post 07-26-2012 at 08:09 AM
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Old 07-26-2012, 08:35 AM   #3
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Exactly the information I wanted to have. Thanks Spencer.


Quote:
Originally Posted by Airhead Wrangler View Post
Well. I'd go for the 33:11 if you're thinking of mostly highway. GSPDs have a 3.09:1 final drive, so 3:1 wouldn't be far off. You're current 3.36:1 is even on the low side for 800cc IMO, 3.2:1 could be a little low for 1000cc also. As for what size rim, the 130-17 is probably the easiest tire size to find anywhere and has the most options available. If you want to dish your wheel to the left a little more to fit a 140, you could move up to the 2.5"x18" rim as there are plenty of good tires made in 140-18 for KTMs. 120-18 is a little slimmer pickins though, especially outside the US, unless you're looking for full-on knobbies. Don't even consider 19". It's really only for MX bikes and you'll only find knobbies for it. Overall 130-17 is the most widely available and has the most options for dual sport tires.
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Old 07-26-2012, 08:48 AM   #4
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I just remembered Anton's gearing comparison page. It looks like 33:11 would get you 84mph at 5000 rpm. Go check it out.

http://largiader.com/articles/gearing/
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Old 07-26-2012, 09:59 AM   #5
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Quote:
Originally Posted by Airhead Wrangler View Post
I just remembered Anton's gearing comparison page. It looks like 33:11 would get you 84mph at 5000 rpm. Go check it out.

http://largiader.com/articles/gearing/
Those are great ... but what wheel were they using?

You see it's a bit of a wash with a 17" wheel and a 33/11, vs an 18" wheel and a 32/10. The 33/11 is ~6% taller than the 32/10, but the 18" wheel is 5.3% taller than the 17". The 17" rimm would give the swingarm more travel ... but the 18" rim would give a smoother ride.

Loads to debate. I'm leaning toward the smoother ride, and loss of 1/2 of travel.

But, I'm still on the fence.
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