i just got a 21" wheel for my street glide and i need tires. Hd dealer told me i need to get both tires new because different treads would ruin the ride, is this true?

 

My thought is, it might be a little on the tough side to find matching tread patterns of tires as different in size as that. I'm not saying they don't exist, I have not looked. Limited selection to say the least. But any difference in handling while possibly noticeable, shouldn't pose any great threat. I've noticed my riding style change just from tread wear. Rear is getting thin, so don't count on it doing what it used to do for me. Front and rear are getting there this go round, so I'm much easier on both tires. Just have to get used to it as you go.
If a tire choice doesn't pan out for you, sell the tire/s, or just ride and wear it out.

 

I don't think you'll notice a difference unles you start mixing radial tires with non-radials. Then you could run into some issues. I've never had an issue using a new tire with a worn tire, but Dunlop's lawyers tend to disagree.

This is from Dunlop's website:

Mixing radials, or mixing radials with bias or belted bias tires may adversely affect handling and stability. It should be noted that many factors other than tire incompatibility can affect the handling of a motorcycle, including the weight and height of the rider, mixing worn with unworn tires, and the fitment of luggage or fairings. Consult the motorcycle manufacturer before making modifications from stock.

You can read more here: http://www.dunlopmotorcycle.com/default.asp

 

I wouldn't worry about it, unless you ride it like a crotch rocket.

 

Been doing it for years with no ill effects.

 

cool thanks for the info!