I'm going to be mocking up a new front fender for my bike in the next couple days..Was wondering what would be a good Fender to Tire clearence..I'm running a 120/70-21 front tire..I want the close to the tire look..but dont want to run into the tire rubbing at speed..What do you guys think ?? Thanks !!

 

I think it was on OCC that they used a chain over the tire to set the fender.

 

In design engineering terms you need to know what's called the tyre FF (fully flung) condition.......no really. This radius which represents the growth of the centre of the tyre at a given maximum wheel rotation + a clearance for a retained stone (usually around 6mm) will give you an overall clearance figure. HD usually make this clearance more than's necceassry (witness the front fender to tyre clearance on the XL)

 

1/2" rubber hose and duck tape it to the tire. Tire growth in minimal these days. Never had a problem using 1/2" or 5/8" fuel hose. Here are two on my two different bikes:

 

It's still part of the calculation and applied universally within motorcycle design departments....

 

Spot on! 1/2" is minimal.tire expansion can rub the underside of the fender if it is too close.


www.bigmikespinstriping.com

 

Please tell us what the exact measurement would be. I wish to know exactly for my build. Please provide references so I may visit the information....Thanks for your time

 

The equations used by engineers in the UK and China (those I'm aware of) are derived from the tire construction parameters and the manufacturers supplied data. For example a 150/60-ZR17 tire will experience an 6-8mm increase in diameter between 40mph and 150 mph. There's also an additional expansion factor due to temperature rise which can be as much as 8% for a street tire and >twice that for a race tire. As I say, the calculation also includes provision for a trapped object between the tire surface and the underside of the fender (or other parts of the chassis in close proximity to the tire)
Your tubing rule of thumb is probably perfectly ok if you've used and tested it empirically.

 

I've got the same size tire on the front, and maybe 1/4inch of clearance at the closest point with no problems so far. I don't spend much time over about 80mph though.

 

Thanks..looks good..probably go with 1/2" just to be safe..