how big of a TIRE can i put on front of 2012 road glide

 

width, or diameter? Why would you need a wider front tire? The diameter is another story, some go all the way to 30 inch diameter , but you can't do that without other modifications, as I'm sure you already know.

 

Choice of non-stock tyres is governed by what industry makes for us, available clearance on your bike, plus the diameter and width of your rims. If your RG is an Ultra your front wheel is 17" x 3" wide rim, if you have a Custom your wheel is 18" x 3.5". Which do you have? When asking questions like this please give us full details, which you can do by adding them to your signature.

 

Here is a chart for you.
http://www.hdwheels.com/Product.htm

 

Presuming you want to fit this tire under the stock front fender, you might want to consider road debris and such.

As the tire gets closer to the rim, the more easily damaged the rim becomes, from a rock or such lodged between the tire and the rim. If you're lucky, it just dents or creases the rim. Sometimes though, it locks the front wheel. I've watched riders go down from locking a front tire this way.

So think carefully about your riding and getting the front tire close to the rim.

Still want to go as large as possible? OK. Measure it. Easiest way is some playdo or clay on the tire and roll the tire under the fender, all the way. Use a ribbon of playdo or clay all the way across the tire, and pack it into the tire so it sticks well. Roll the wheel under the fender and now measure cut down height of the playdo or clay. That's the room you have. Use an online calculator for tires and figure out how far up you can go on size. It's not going to be a lot. Probably on the order of a 140/70, maybe a 150/70.

 

Note that the current trend is for wide tyres to also be low profile and to get lower in profile as rim diameter is increased. As examples, the various front wheels Harley has used on the Touring models include:

• 130/90 x 16,
• 130/80 x 17,
• 130/70 x 18,
• 130/60 x 19.

Also check your preferred manufacturer's website for recommended rim width. As examples, Avon make 17" tyres in 140 and 150 width, but minimum recommended rim width is 3.5". Their 18" 150 will fit a 3.5" rim.