Sram Red front brake clearance

Discuss light weight issues concerning road bikes & parts.
Delorre
Posts: 966
Joined: Sat May 24, 2014 12:09 pm

by Delorre

I just upgrade my dad's bike to Red Etap. He's running 25mm gp4000s on new wide Paradgm rims. There is normal clearance inside the fork (a least 3 or 4mm in every direction), but the front caliper ends up less than 1mm above the tyre. The caliper seems angled a little forward. Is there a 'hack' to improve the clearance a little? On the rear, no problem at all. Frame is an older Madone 5.2 with regular single brake mounts.

pdlpsher1
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by pdlpsher1

I don’t think there’s much you could do except to get a different fork. Front rim brake clearance is determined by the fork’s crown to axle distance. I have the same Red brake on a tandem carbon fork with a ridiculous long crown to axle, and the brake can clear a 32mm tire and still have 3mm gap all around. Take a look at the position of your brake pad holder. Is it in the middle of the adjustment slot? If so getting a different brake won’t solve the clearance problem. If you mount the same brake on a fork with a long crown to axle, the brake pad holder will be at the bottom of the slot.


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by Weenie


bilwit
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Location: Seattle, WA

by bilwit

the hack is to use 23mm tire

Delorre
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by Delorre

pdlpsher1 wrote:
Thu Jun 07, 2018 2:22 pm
I don’t think there’s much you could do except to get a different fork. Front rim brake clearance is determined by the fork’s crown to axle distance. I have the same Red brake on a tandem carbon fork with a ridiculous long crown to axle, and the brake can clear a 32mm tire and still have 3mm gap all around. Take a look at the position of your brake pad holder. Is it in the middle of the adjustment slot? If so getting a different brake won’t solve the clearance problem. If you mount the same brake on a fork with a long crown to axle, the brake pad holder will be at the bottom of the slot.


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Clearance on the fork is OK. It's about the same front and rear. At the rear, the lowest point of the caliper is on the same height as the brake bridge. At front, the caliper sits a lot lower than the inside top of the fork. Now I think about it, there is something I can try and that I already saw over here : put a 1mm spacer something inside the fork dropouts. That should give me 1mm more clearance... Other sigestions are welcome ;-) Have to say, with the previous Campa calipers, the clearance was not that great either...

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Calnago
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by Calnago

Does a Campy caliper fit any better? I know you were switching the components over so if you still have the caliper handy it would be easy to check. The fork clearance itself seems plenty adequate, it’s just the placement of the mounting hole and/or angle of that hole (and the design of the SRAM caliper) that’s creating the issue. Do you have one or two of the serated washers between the fork and the caliper? In the event you have two, you might try removing one which will give you a very small amount of extra clearance in your case. But you don’t need a lot more anyway. Other than that, you’re using a tire/rim combo that’s going to sit very high relative to just about every other tire of the same nominal size. How big a tire do you need? For a road bike? Like Bilwit says... a 23mm Conti of the same type (for aesthetic consistency) may be your best and simplest option here. On a wide rim they plump out every bit as wide as a 25mm Tubular would be.

Just saw your reply above... don’t really like the dropout spacer route, but yes, that’s an option. Till one of the spacers gets lost. And yes, the campy calipers aren’t so great either, especially on a wider rim, due to the fact that as the brake pads have to be farther apart the arms over the tires come down. A set of new Shimano 9100 brake calipers are really nice and would have the most clearance you could get. And the clearance above and around the tire is independent of the adjusted width necessary between the brake blocks. Just not sure how well they’d play with SRAM levers. While they play ok with Campy levers on narrow (20.5mm external width) rims, they did not play well when paired up with a 24.2mm external width rim and Campy levers.
Oh, and clearance is really independent of axle to crown distance, although obviously the longer that is the more room there is for placement of the mounting hole. But if there’s a lot of fork material below the mounting hole, then that is what’s going to limit your clearance, regardless of how long the axle to crown distance is.
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pdlpsher1
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by pdlpsher1

Delorre wrote:
pdlpsher1 wrote:
Thu Jun 07, 2018 2:22 pm
I don’t think there’s much you could do except to get a different fork. Front rim brake clearance is determined by the fork’s crown to axle distance. I have the same Red brake on a tandem carbon fork with a ridiculous long crown to axle, and the brake can clear a 32mm tire and still have 3mm gap all around. Take a look at the position of your brake pad holder. Is it in the middle of the adjustment slot? If so getting a different brake won’t solve the clearance problem. If you mount the same brake on a fork with a long crown to axle, the brake pad holder will be at the bottom of the slot.


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Clearance on the fork is OK. It's about the same front and rear. At the rear, the lowest point of the caliper is on the same height as the brake bridge. At front, the caliper sits a lot lower than the inside top of the fork. Now I think about it, there is something I can try and that I already saw over here : put a 1mm spacer something inside the fork dropouts. That should give me 1mm more clearance... Other sigestions are welcome Image Have to say, with the previous Campa calipers, the clearance was not that great either...
As I’ve stated earlier the fork is the problem, not the brake. Axle to crown length describes the length of the fork legs. A longer fork will ‘pull’ the tire further away from the brake. On my tandem fork the Red caliper lines up perfectly with the fork. If your brake sits below the fork then you have a short fork. Most older forks are designed for smaller tires. Newer forks (except Enve rim forks) have longer fork blades to clear a 28mm tire. The newer Treks are known to use long blade forks. I have one (not the same as the tandem fork) and it clears a tire that’s 30.5mm wide (measured) with 3mm clearance to the brake caliper. Your idea of adding a 1mm spacer is the same as adding 1mm to the fork’s crown to axle length.


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Fiery
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Joined: Sat Mar 16, 2013 9:21 am

by Fiery

There is so much more to it than just axle to crown length. As Calnago said, different callipers have different clearances and different fork crowns have different clearances as well. I have a 368 mm axle-to-crown fork that can fit 30 mm tyres with a Sram Force calliper, but a Red calliper would cause problems unless the rim was quite narrow.

pdlpsher1
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by pdlpsher1

Fiery wrote:There is so much more to it than just axle to crown length. As Calnago said, different callipers have different clearances and different fork crowns have different clearances as well. I have a 368 mm axle-to-crown fork that can fit 30 mm tyres with a Sram Force calliper, but a Red calliper would cause problems unless the rim was quite narrow.
A 368mm CTA fork and a 30mm wide tire? How much clearance around the tire do you have? Have a pic to share? It’s possible that your fork has a longer CTA than you think. One other thing. Being able to fit a tire vs actually being able to ride it is another thing. You need a minimum of 3-5mm clearance so that your brake won’t get all scratched up by little pieces of gravel that get caught up between the tire and fork/brake. I highly doubt that your 368mm fork and Force brake can function without getting damaged.


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Last edited by pdlpsher1 on Fri Jun 08, 2018 12:08 am, edited 1 time in total.

pdlpsher1
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by pdlpsher1

Here’s a pic of a long fork and a Conti 23mm tire (25mm actual width). This gives you an idea of the clearance a long fork gives. This fork (Trek Domane) has a crown to axle of 380mm.

Image



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Last edited by pdlpsher1 on Fri Jun 08, 2018 12:11 am, edited 1 time in total.

alcatraz
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by alcatraz

You should really use 23c in the front. Like the previous poster said it's really closer to 25mm. Considering the front wheel has less weight on it you don't need the same width as the rear to maintain same comfort/rr. Better aero is a bonus.

There is also the trick of using an extra spacer(s) on the caliper bolt, and tightening the recessed nut while pulling the brake upward. That could give you the extra millimeter you need.

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Calnago
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by Calnago

alcatraz wrote: There is also the trick of using an extra spacer(s) on the caliper bolt, and tightening the recessed nut while pulling the brake upward. That could give you the extra millimeter you need.
In this case, being the front wheel and considering the angle of the mounting hole, he needs to remove a spacer, not add, but only in the event he already has two knurled washers between the fork and caliper. His brake is angled downward. He needs to pull it back not push it forward into the tire. The curvature of the tire will also help his clearance a bit in the process as well if the caliper can come rearward a millimeter or two.
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Delorre
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Joined: Sat May 24, 2014 12:09 pm

by Delorre

Thx for the comments!! I only use 1 knurled washer, so nothing that can be removed. Bolting the brake more upwards is not possible, the rear bolt is a very tight fit in the frame, no play at all. First option is using a 23mm gp4000s tyre or a little spacer (I read about 2 pieces of a spoke glued in the dropout). I still have some space between QR and lawyer tab, all good.

Fiery
Posts: 420
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

pdlpsher1 wrote:
Fri Jun 08, 2018 12:08 am
A 368mm CTA fork and a 30mm wide tire? How much clearance around the tire do you have? Have a pic to share? It’s possible that your fork has a longer CTA than you think. One other things. Being able to fit a tire vs actually being able to ride it is another thing. You need a minimum of 3-5mm clearance so that your brake won’t get all scratched up by little pieces of gravel that get caught up between the tire and fork/brake. I highly doubt that your 368mm fork and Force brake can function without getting damaged.
Here it is:

Image

Current tyre is 27 mm (actual width). A 30 mm should be perfectly usable with at least 3 mm clearance all around, and even a 32 mm would possibly fit and spin freely on a workstand at least.

Notice how short the fork crown is. This is what gives it clearance even though the total axle-to-crown length truly is 368 mm.
Last edited by Fiery on Fri Jun 08, 2018 11:15 am, edited 1 time in total.

pdlpsher1
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by pdlpsher1

Your fork does look unique. I can also see that the brake pad is positioned very near the end of the adjustment. This would suggest that the brake mounting hole is positioned very high. Most short forks have the mounting hole positioned quite low, thus causing the brake to be the limiting part for clearance. Your pics also shows the brake to be even with the fork, which is the best case scenario for maximum tire clearance.


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pdlpsher1
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by pdlpsher1

alcatraz wrote:You should really use 23c in the front. Like the previous poster said it's really closer to 25mm. Considering the front wheel has less weight on it you don't need the same width as the rear to maintain same comfort/rr. Better aero is a bonus.

There is also the trick of using an extra spacer(s) on the caliper bolt, and tightening the recessed nut while pulling the brake upward. That could give you the extra millimeter you need.
+1. A smaller front tire gives the best and sharpest handing IMHO. I’m running 23mm front (25mm measured) and 25mm rear (27mm measured).


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by Weenie


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