Correct Clearance Used When Installing Fenders
 

Is there a rhyme or reason to fender clearance beyond simply clearing the wheel, or is it just up to personal preference?

When I installed fenders on my Trek 7100 many, many years ago, I installed them as closely to the wheel as possible, with barely a few millimeters of clearance. The only downside I ever saw to this was hearing minuscule rocks that would get tossed up between the wheel and the fender and the sounds that go with it until the rock was shot out the other side.

Well, I got a new bike that will take the same fenders. Since the new bike costs far more than my old one, I don't simply want to throw the fenders on in the same manner if there is actually a better way of doing so.

So, should I install them as closely to the wheel as I can, or should I actually leave quite a bit of clearance this time around?

I looked at bikes with fenders pre-installed by the manufacture, and there seemed to be a very large clearance between the wheels and the fenders, but I am not sure if this actually means anything.

I do realize that I simply prefer the look of almost-no clearance between the wheel and the fender, but I don't want to ruin anything prematurely, either.

Thanks in advance!

You want to leave enough clearance so if the fender flexes it won't touch the tire. Other tha that, yeah, it's a preference. The tires will pick up debris and throw it up there though, so you don't want it too close.

The rule of thumb I've read is that you should have 10mm of clearance from the tire to the fender. The big concern is that a stick wedged between your front tire and the fender will introduce you to the pavement in a hurry. SKS and newer Planet Bike fenders have breakaway clips that are designed to prevent this, but I wouldn't want to bet my teeth on it.

Get them close enough that you can't see any light between the tire and fender, but not any closer.

The distance is critical on the front. You will notice (on most fenders) that the actual fenders are attached to the stays via a bracket that is riveted to the fender. If that bracket gets too close to the tire, there is the risk that the tire will wear down the rivet(s). If that happens, and the bracket comes loose, there is the risk that the tire will pull the bracket forward. The further forward the stays are pulled, the closer the bracket gets to the tire, until the bracket and stays actually stop the tire like a very effective mechanical brake. This will cause the bike to come to a VERY sudden stop.

Trust me on this one, it's happened to me. The force of the stop was enough to bend the steel downtube (which probably helped reduce the force of the impact when I landed with enough force on head and shoulders to destroy the helmet).

So now I keep a very healthy gap between the front tire and the race blades I now use.

It's not as critical on the back, but you can still lose control when the rear wheel comes to a complete stop!

Luis

Fashion or Function?

In Minnesota , the issue of having Snow and Mud, pack into the space above the tires,
and inside the mudguard is never a consideration?

or it there another winter beater, and this is a bike just for summer showers?

The rule is, there is no rule. Personally I like them close regardless of the season. I like the way they look, they stay out of the wind better, clearance for mud or snow has never been an issue for me.

You might not them close, Then you shouldn't run them close.

as mentioned above 10mm is a good rule of thumb. It's close enough that you generally don't see a space between the tire and fender, but far enough away that you don't hear every rock. I don't think it will really help with sticks

As a machinist, and a mechanical designer, all I've got to say is ... :twitchy:

Seriously, if your tires are wearing down the aluminum (generally) rivets, then perhaps your using studded tires or your from some other plane of existence.

Rivets tend to get lose for many reasons, from bad installation generally being the start of the problem, to vibrational loading on it, to dynamic stresses, and a few other factors, all of which are in play on a bike on anything but a smooth indoor track.

Rivets fail, but they will not fail due to the tire wearing them out. The tire will wear out first if they are making contact.

Jim

I've experienced the 'stick in the fender makes rider go over the bars' thing...not very much fun and it cost me a new fork.

I use the SKS fenders with the little pull away tabs exclusively now. And I also like the 10mm rule. I actually go slightly over, and run the excellent 45mm SKS Long Boards with the 28s on my Smoothie.

Hey I'm one of those too...

and tires will definitely wear down rivets. I've seen steel frames destroyed by prolonged tire contact.

That is like saying your rubber brake pads will destroy your wheels due to the rubber on metal contact.

Maybe after several hundred brake pad changes, and even then, it will happen cause of the pressure applied during braking causing the rim surface to flex repeatedly and it will fail due to fatigue stresses not rubber on metal contact.

That is like saying you are going to finish cut a diamond using a block of aluminum. Good luck with that, if it works I'd love to hear about it.

Jim

I'm with JimCanuck. And furthermore, your tires should not be rubbing on your fender rivets or your frame or anything else...EVER. C'mon people.

I wonder if it's less wear and more prolonged friction causes something to work loose.

But yeah, tires shouldn't be rubbing on anything.

I will try 10mm and see how that looks.

I, honestly, have no idea what any of y'all are talking about. Why would I let my tires rub on anything in the first place? Seems like common sense; even my three year old would notice something was not right...? I must be missing something glaringly obvious here, like usual. :D

Well, some rims do have warning strips that tell you when the walls are wearing too thin. It's not the rubber so much as the crap that gets embedded into the pads. Sand is a very effective abrasive, for example. Tires also pick up all kinds of abrasive particles from the road.

I agree with other posters that say you shouldn't have the tires rubbing against anything. However, I can't discount the possibility that they could wear down alumninum, or even steel, if one did let them rub.

I use the general rule of 10mm minimum difference between tire size and fender width; which allows for a 5mm (approx 1/4") clearance all around.

This works well for riding in the lowland PNW where we don't get a lot of solid precipitation. Rain, no matter how heavy it's falling, doesn't pack up inside a fender like snow and slush so a tight clearance is optimal. You want a wider fender with a deep profile so it actually wraps around to the side a bit. This gives maximum spray containment, and when coupled with a mudflap up front, you can eliminate >90% of the road spray. That's not to say you won't still get wet from the rain, but at least rain doesn't contain all the oily grimy bits that the road spray does.
I've got my brevet/commuter/distance bikes set up this way with 32mm tires and 47mm stainless fender on one, and 45mm plastic fenders on another.

On my CX bike, which I ride on muddy trails, I have a crud-catcher on my downtube, and a seatpost mounted splashguard on the rear. All either one does is keep some of the trail **** off of me; at least the stuff that would go right up the middle. Good for mud/snow clearance. Crap for actually staying clean.

Brakes will wear out the side of rims. Both from the rubber and the embedded grit.

http://pardo.net/bike/pic/fail-026/000.html

http://www.google.com/imgres?imgurl=...9QEwCw&dur=499

Haha was that meant to be a joke or are you just being unintentionally ironic?

I promise you your rims will wear out if you use rim brakes. I go through at least one pair every two years or so.

Do you use a grinder at your work? Does the diamond dresser last forever?

There are (some) good answers in this thread already. I like the above as a simple eyeball approach.

Other considerations: will you be changing out tires for different uses or seasons? The stays are adjustable but don't trim them down for a narrower tire and then realize you will run out of adjustment room once you put your studded tires on (for example).

One good recommendation I've seen is to keep the back edge of the fender tighter to the tire, to help keep objects out, and the front edge somewhat more open to help release the crud that does end up in there.

My studded tired bike has barely 3mm tire to fender clearance because that's the most I could get. No touch, no problem. As for the stick jamming in and locking up the tire issue, a bigger gap allows for a bigger stick! I doubt it's possible for a stick thick enough to lock up the wheel to even fit in such a small gap.

Compared to the life time of the wheels your redressing yes it does. Single point diamond dressers will last nearly forever unless you bang them up, the diamond grit coated ones for bench/pedestal grinders tend to wear out quicker. But then again that is a bonding issue, as the bonding of the diamond grit to the steel components can very in quality.

Similar to Silicon Carbide wheels, they can do things Aluminum Oxide wheels cannot do easily, but their bonding materials tend to be weaker (intentionally to prevent loading), so they appear to last less time then the Aluminum Oxide wheels which tend to have bonding compounds that are not designed to break away the grit as easily.

Similar with brake pads, or tires, you will go through many more sets of of the rubber composites before you wear out the aluminum parts, even if the rubber is embedded with dirt/sand particles.

So no I am sorry my point still stands, your tire will wear out a lot quicker then your aluminum rivets, as will your brake pads will wear quicker then your aluminum rims. You will replace a lot more tires and brake pads then you'll ever have to replace the rivets or the rims.

In addition to that, due to the manufacturing of the tires and the fenders, your more then likely rubbing on more then just the rivet no matter how good of a installation you did.

Therefor, question becomes, if the tire is rubbing on a rivet, and large sections of the fender, the installer should either be fired, or not allowed to ride a bike again, as they clearly lack any ability to properly adjust and maintain a bicycle if they cannot check (or for that matter feel) a fender for rubbing after installation.

A rivet on a fender is much more likely to fail due to dynamic loadings on the bike itself (such as vibration) then it is due to a totally clueless installer/cyclist and the tire rubbing on it. No instead, since the introduction of riveting, things like mechanical fasteners, welding and adhesives have been slowly chipping away at the market for rivets, which are more prone to dynamic loading failures. Rivets tend to however, have the upper hand in thermodynamic loading resistance which is why they are preferred for ship building and planes (although with the latest generation of planes such as the Boeing 787 and Airbus 380, they are moving towards adhesives over rivets as well).

Jim

Ouch! I didn't realize that 30 years of experience riding & working on bikes could be so thoroughly trashed by so much engineering theory!

But, I assure you, the tire did wear down the rivets. Yes, I knew there was light contact, but it was unavoidable due to the tight clearances of the bike and the length of the stays, and I was of the opinion, as you so insist, that tires cannot wear down rivets. But they did. In Vancouver, in the winter, the streets are sanded due to the snow. The tire picks up the sand (in the rainwater), and the sand rubs against the aluminum rivet. The fenders were mounted a little too close, there was just enough rubbing, and it just took a good bump for everything to come together.

As far as brake pads wearing down rims, you should try commuting daily in Vancouver for about three years. That's how long it takes (for sure) to wear down a rim to the point that it cracks. Once again, sand gets on the rubber pads and wears down the rim.

With all due respect, I think it's kind of arrogant to make suppositions based on ivory-tower theory. I'm merely telling you what happens in real life! But you could be right about my being clueless, although I have been able to properly adjust and maintain bikes for a few years, enough to win races on, anyway!

Luis

But wait, now your talking about my previous point, assuming I'm reading this sentence properly. That you going through a "good bump" caused the rivet to fail. In which case due to your lack of clearance, more then likely it was shear loading and dynamic loading issue that caused the rivet to fail anyways, not the rubbing of the tire and rivet wearing each other down, but the lack of clearance allowed your tire to make contact and apply a load onto the rivet itself, which was fixed to the frame, so the energy had nowhere else to go but the weakest link (the rivet).

In in those three years of commuting how many brake pads did you go through due to the wear of the rubber between the sand and the rims? Stating that the rubber wears out the rim without a point of reference is meaningless. Which is my entire point.

Its like someone saying they can bike 40km/h all day long, without mentioning that they can only do that while biking on a decline.

Jim

There's also the issue of how many tires used

OTOH if it's rubbing, you'd probably hear it, and/or notice the additional drag.