Well there you have it. I guess there is a situation where you will find Jan say 20mm. Again it is useful to remember context. Jan says right here 20mm of headroom when you are specifying the clearance on a custom frame. Most people posting on these lists are not specifying a custom frame, though. They are assessing the bike they already have. My memory of Jan's recommendation for headroom was based on this quote from Jan's blog:
"You can get away with smaller clearances and still have fenders that work fine. You need at least 12 mm between tire and fender, plus about 1 mm for the fender, and another 2-3 mm for the leather washer that cushions the fender against the frame. This adds up to about 15 mm between tire and bridges/fork crown. (Better would be about 20 mm.)" Most people "get away with smaller clearances", in part because people tend to always want to try the widest tire that will fit. On Sunday, December 13, 2015 at 11:07:24 PM UTC-8, Jan Heine wrote: > > Interesting discussion. Just to clarify, I really do like to see 20 mm of > "air" between the top of the tire and the fender. Here is a photo: > > https://janheine.files.wordpress.com/2014/02/compass_babyshoe.jpg > > Anything less risks trouble when your tires pick up small rocks and drag > them through the fender. Even on gravel roads, you shouldn't get the > "scrtchh" of a rock rolling between tire and fender more than once every > 500 miles... You can ride a bike with less clearance, but it's a little > risky for my taste. I know too many people who've fallen on their faces > when fenders collapsed and jammed the front wheel. > > There really is no reason to have less clearance on a custom bike. The > fender lines on the bike shown in the photo above look great, see > > https://janheine.files.wordpress.com/2012/06/jhherse_full.jpg > > There really is no reason to mount the fenders closer to the tires, except > that when you remove the fenders, the clearances may look excessively > large. (Just like my car, my bike always carries fenders, so that isn't an > issue for me.) > > Of course, you don't need (and won't get) 20 mm all around the tire, > because your fender doesn't need (and cannot) to be 40 mm wider than your > tire! You won't drag debris along the sides of the tire, so less clearance > there is fine. You just need enough so that if your fender's position moves > a bit after you lean your bike against a wall or something like that, the > tire doesn't rub on the fender. 10 mm probably is fine there. > > The chainstays and fork blades will encroach a little further into your > clearance. It's fine to indent the fenders there - the fenders are firmly > supported, so they won't budge. In those places, you just need enough that > frame flex, wheel flex or a slightly out-of-true wheel won't cause the tire > to rub on the fender. I'd say 5 mm is OK, 8 is better. > > Of course, you can ride bikes with much less clearance. I have done so for > many years. The fenders may rub a bit when you rise out of the saddle, and > you have to hope for the best when riding over gravel, but most of the > time, it's fine. > > Jan Heine > Editor > Bicycle Quarterly > www.bikequarterly.com > > > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
