I knew this would come up! While several people believe what is posted above, it is not quite accurate!
A dealer can refuse a warranty claim and they do not have to prove the failure was due to an aftermarket part. Aftermarket replacement parts do not have to be covered by OEM warranty.
Adding items as previous mentioned can Void your warranty and it's up to you to prove those items didn't cause failures.
The MM act does not cover non-OEM add on or add "in" parts/modifications made to any warranted vehicle.
Please read the MM act in it's entirety and you shall learn.
To the extreme-what you say would mean one could highly modify the motor/add NO2 and then when you blow it up expect Honda to pay for a new motor. NOT!
Actually...
(c) No warrantor may condition the continued validity of a warranty on the use of only authorized repair service and/or authorized replacement parts for non-warranty service and maintenance. For example, provisions such as, ``This warranty is void if service is performed by anyone other than an authorized `ABC' dealer and all replacement parts must be genuine `ABC' parts,'' and the like, are prohibited where the service or parts are not covered by the warranty. These provisions violate the Act in two ways. First, they [[Page 631]] violate the section 102 (c) ban against tying arrangements. Second, such provisions are deceptive under section 110 of the Act, because a warrantor cannot, as a matter of law, avoid liability under a written warranty where a defect is unrelated to the use by a consumer of ``unauthorized'' articles or service. This does not preclude a warrantor from expressly excluding liability for defects or damage caused by such ``unauthorized'' articles or service; nor does it preclude the warrantor from denying liability where the warrantor can demonstrate that the defect or damage was so caused.
While I understand your reasoning behind the NOS argument, it seems to me that if we take your argument in it's entirety, then a paint job would violate the warranty.
Basically, anything not done by the dealer would violate the warranty, and for that matter anything done by the dealer not involving OEM parts would violate the warranty.
Now, I'm not a lawyer, but it seems to me that there are three things in effect here.
1. For the NOS argument to work on a CT, you would have to prove that the CT would damage the bike. Not might damage it, but would without a doubt. NOS by it's nature causes damage to engines. I'm not a mechanic, but I've been told this is due to increased compression, increased revs, and increased heat. Anyone of which should be easy to verify and prove causes damage to the engine. A car tire is a bit more vauge at best. People assume that it is more dangerous, but is it more damaging to the bike? I've never seen anything that states so, and my problems started before I put the car tire on.
2. If we accept that a car tire violates the warranty, then we are looking at a situation where any tire, excepthe OEM tire violates the warranty. So you couldn't switch from a Dunlop to a Metzler. And that specifically violates the law.
3. If the tire failed, then the damage to it and from it would not be covered by the warranty. That's obvious. But if your tire does not fail, they do not have an out.
Their only real hope is to outwait you, and hope you don't make a stink.
But since I'm an *******, my first stop after being denied would be to the trunk where I have the relevant laws in hard copy, and if they continue to deny, I will make a stink like an unserviced portapot on the forth of july!