Did you talk to a sales rep at the dealer or a mechanic? In any case there is a big difference.
Physical evidence is proof. These are the measurable changes in clearance under the fender to tire, causing in some cases bottoming out of the tire and hitting the rub indicators.
Not allowing the shock to bottom out as the stock size tire would.
Also the width is wide enough for the tire to rub the lower belt guard in some cases.
Then you have the visual proof, it's noticeably larger by sight. Then you have feel, it is noticeable when you set on the bike your feet don't reach the ground the same, and the ride is much different too, much more stable and like some one said you don't ever get all the way to the edge of the tire in lean like you do with the stock.:wink:
The diameter of the tire is a percentage of the width, so increasing the width from a 210 to a 240 also increases the over all diameter even though the 2nd # 40 remains the same. This equates to 1/2" to 1" increase in height of the bike depending on what brand you use as they very slightly.
I'm am on my 3rd 240. I can tell you there is even a noticeable difference between brands and a night and day difference from the 210 to the 240.
So I would question the intentions of the guy you spoke to at the dealership or at least his level of knowledge.
I can't speak for the Avon but the bands I have used are Bridgestone being the stock, and I have had 2 , one I wore completely bald side to side, then the 240s starting with Metzler ME Marathon 880 front and rear, then a Dunlop E3 rear, and now Michelin Commander II front and rear. I put only 2,000 miles on the Dunlop because I was waiting on the C II to come in and needed a rear tire badly. I can say that the Metz is a far better tire than the E3 and the Michelin even better than the ME 880.
I haven't tried the Avon because they are said to be a low mileage tire in this area, but I'm finding out that all tires are low mileage in this area. Bridgestones 2,500 miles. The E3 had 2,000 miles on it and was half way to the wear bars, would have been lucky to get another 1,700 off it. Metzler was way past the wear bars at 4,850 miles. I can only hope that the C II gets the claimed double the miles as their competitors.