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Fender/ tire clearance. How much is enough?

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Fender/ tire clearance. How much is enough?

Old 10-10-20, 10:25 PM
  #1  
XXLHardrock
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Fender/ tire clearance. How much is enough?

Road bike with 32mm smooth Gravelkings. I’ve got 13,maybe 14 mm between the tire and the Paul Racer M brake. But this is under tension. If I release the cable to install an inflated wheel/ tire, it’s down to about 10mm. But in normal operation there’s 14mm clearance.


Is that enough to safely run a fender?

In front there’s 12mm at the front of the fork and a few more at the rear, but it has a disk brake. Is this enough room?

And then, how about with a tire with small knobs like the Gravelking SK?

I’ll likely be using SKS Longboards which are about 3mm thick. That leaves 10 mm actual clearance.

Last edited by XXLHardrock; 10-11-20 at 12:49 PM.
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Old 10-11-20, 06:13 AM
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Sounds like very tight fit. But there is only one for sure way to tell is to (try) install the fenders.

After install your tire/fender clearance will be even less than what you measured. If your taking your gravel kings off road, gravel or mud could easily wedge between the tight clearances.

It sounds like a NO GO to me.
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Old 09-07-21, 06:30 PM
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Stealing this thread, I have new V.O. fenders on a new bike, with lotsa clearance between tire and fender (& mounting nuts under the fender) and between tire and fender stays. Tires spin freely, no wobble no rubbing. Yet when I turn sharply, I get a squeal. If I stand in the pedals, I get a squeal. From the front. I should know how to solve for this, it seems the spinning wheel is reluctant to alter its plane of spin, while the fork & fender are quick to comply. How to get around this? gugie have you seen this before?



And yes, I know... the fender lines are not perfect. I'll get there.
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Old 09-07-21, 07:30 PM
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are you sure it's the fenders making the squeal? could it be the brake pads against the rim? how much clearance do you have between the two? if it's close enough, shifting your weight (like with the turning) can cause the wheel/s to flex enough and rub the pad/s. i have had that happen many times
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Old 09-08-21, 04:48 AM
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i have a frame that does not allow that much fender clearance.

i had to take the fenders off.

there is a section of bike path with small pine needles that must be coated with super glue because if i ride over them, they dam up the wheel so bad that one time the rear wheel actually locked up. now this was on wet pavement with needles, so coef. of traction was down a bit.

cleaning those needles out of the tire/fender area was a pain. i even tried coating the insides of the fenders with teflon tape but those sticky needles did not care one bit.

oh, and these fenders were only about 6 inches long each. i just wanted to protect the brakes and not get stuff up the steering tube.

my average speed went up about 2 mph after i removed the fenders.
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Old 09-08-21, 10:12 AM
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Originally Posted by thook
are you sure it's the fenders making the squeal? could it be the brake pads against the rim? how much clearance do you have between the two? if it's close enough, shifting your weight (like with the turning) can cause the wheel/s to flex enough and rub the pad/s. i have had that happen many times
The sound of brake pads is pretty different than of the tire buzzing the fender. Also, the pads are on the steering axis, and I'm thinking the flex is at the point on the tire furthest from the steering axis, close to where the fender stays attach. Maybe I can simply flare the fender a bit and add clearance. Or, I could attach lightweight "gliders" to the fender stay, which would contact the rim and enforce some separation.

Tire pressure might also be at play, I'm running them at 40psi, well below max. And... that tire is getting pretty good bite on the pavement, adding to its reluctance to change direction.

And spokes! I'll check on tension. It's possible the rim is a bit floppy.
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Old 09-08-21, 10:35 AM
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Originally Posted by BoltBreaker
The sound of brake pads is pretty different than of the tire buzzing the fender. Also, the pads are on the steering axis, and I'm thinking the flex is at the point on the tire furthest from the steering axis, close to where the fender stays attach. Maybe I can simply flare the fender a bit and add clearance. Or, I could attach lightweight "gliders" to the fender stay, which would contact the rim and enforce some separation.

Tire pressure might also be at play, I'm running them at 40psi, well below max. And... that tire is getting pretty good bite on the pavement, adding to its reluctance to change direction.

And spokes! I'll check on tension. It's possible the rim is a bit floppy.
i understand. but, you mentioned a "squeal" which made me think of rim and pads....as that's the sound i would describe that as. anyway, good luck tracking it down. i'm sure it's at least irksome
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Old 09-08-21, 10:42 AM
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Originally Posted by BoltBreaker
Stealing this thread, I have new V.O. fenders on a new bike, with lotsa clearance between tire and fender (& mounting nuts under the fender) and between tire and fender stays. Tires spin freely, no wobble no rubbing. Yet when I turn sharply, I get a squeal. If I stand in the pedals, I get a squeal. From the front. I should know how to solve for this, it seems the spinning wheel is reluctant to alter its plane of spin, while the fork & fender are quick to comply. How to get around this? gugie have you seen this before?

And yes, I know... the fender lines are not perfect. I'll get there.
My 650B conversion has always had this, too. I can make the tire squeak against the front edge of the fender my rocking the bike hard out of the saddle, and chirp against the rear edges of the fender by riding over bumps with only one hand on the bars. I assume it's from cramming 38mm tires and fenders into a frame that was intended for 700x25C at most.

Jan Heine recommends 8-10mm of clearance between fender and tire at minimum, and I think I'm at 8mm in the back, less in the front. Does your front rack have a fender support mount? Those are really helpful for making sure the front edge of the fender doesn't whip down, and cutting down on side-to-side wiggle. My crude fender support brings the amount of squeaks and chirps down to an infrequent/tolerable level:

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Old 09-09-21, 06:36 AM
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If your tires are touching the fenders then you will quickly get marks on the fenders where the tire rubs them.

That's not a dynamo light at the front, is it?
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Old 09-11-21, 01:40 AM
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Originally Posted by BoltBreaker
...I'm thinking the flex is at the point on the tire furthest from the steering axis, close to where the fender stays attach. Maybe I can simply flare the fender a bit and add clearance. Or, I could attach lightweight "gliders" to the fender stay, which would contact the rim and enforce some separation.
This would be my guess.
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