I have been looking for information on using a ZL1000 wheel on my 06 C10. One question I cant find answer to is will my 06 rear rotor work with the 15" wheel or do I need matching rotor for the smaller wheel?

The ZL uses a 267mm rotor where the C10 is a 280mm, so chances are the C10 rotor won't fit,.... but it might. 
Can I ask why you're going to the 15" rim?

Car tire.  Smallest 16" is a 175R16.  That is basicly a 175/80-16 and it will rub the swing arm.  I run car tire on my 1800 Goldwing and it is fantastic. I also tried one on my 1400 Connie. It was OK but bike little to tall with it on the bike.  I have been doing some resezrch and have wheel on the way.  Ian going to try it.

I run a 175/75-16 on mine.  no rubbing at all.  YMMV

what brand of tire?  I bought a Maxxis and it way to big.

it's a Roadstone Radial A/T.   I bought it used from someone who tried a CT and didn't like it.  you might check the COG forum.  One of the guys that lived up in the pacific NW ran CTs all the time.  he might have sources.

  I sent the guy from Washington a message no reply yet.  He had a post on the COG forum about using the 15" wheel. There are several tire options.  The only thing it says is caliper mount has to be machined.  That what I trying to contact him about.

sounds like you're in good hands then!   

I never heard back.  But I did read the ARTICLE  he posted back in 08 when he did his conversion.  I bought the 15" wheel bolted it on the bike read his aticle again while looking at the bike and wheel. Saw what he was talking about.  Had my caliper bracket machined and now waiting on my 15" tire.  Will have bike together and going this week.  Will post photos and ride report later this week. 

  Well I finally got the 15" tire and wheel on the C10  that is not an easy job for sure.  Thanks for some imput past and present about doing it.  I know lot of people say No way and it is not right.  To me it is great.  I been riding a Goldwing with a car tires for several years.  As soon as I get some pictures loaded I will post them.

 

Easier to just use 175/75R16.
But good on ya for bulldogging it through.
Mine was rubbing at first, but a couple of days in the mountains wore off enough to fix that.
You know, darksiding sometimes requires a bit of adaptation.