Clearance Pt. II – Road Frames

By blackmountaincycles,

Filed under: Black Mountain Cycles frames

While I do get questions about just how big a tire can be stuffed into the monster cross frame, I don’t get the same question about the road frames.  Last week, however, I asked that question.  I designed the road frame to fit a Jack Brown 33mm tire.  At the time, 10 years ago or so, the 33mm Jack Brown was the largest, decent riding tire, that wasn’t a touring tire available.  Today, there are plenty of 32mm (close enough) nice, supple tires.  And with rims becoming wider, actual sizes of tires can be bigger than what’s printed on the sidewall.  Combine a certain 28 tire with a wide rim and it may become an actual 30mm or more.

But, that 28 on a wide rim is still a 28 tire and because it’s bead is set into a wider rim, that pulls the outer tread down making the actual diameter slightly smaller.  Not a lot, but smaller.

I’ve been running and trying to wear out an old set of Challenge Eroicas (they have since changed the name to Strada Bianca) that are labeled as a 30, but measure 32mm.  They fit in my frame with plenty of clearance.  And they feel good.  And then I started thinking.  “Will a 35 fit?”  And I can say, “yes, provisionally.”

First, it depends on the 35 tire.  A thick treaded touring tire might not fit.  But a Compass Bon Jon Pass 700c x 35 fits.  Provisionally.

There’s no issue with the fit at the chainstay or between the fork blades.  The issue is with the brake caliper.  Not all long-reach brake calipers are created equally.  Some testing was in order.  Here’s what I did to test the fit:

  • Fit a Compass Bon Jon Pass 700c x 35 tires to wheels built with Velocity A23 rims
  • Fit wheels into frame front and rear
  • Check clearance with popular (read only) long-reach, 47-57, brakes available

The photos do a better job of showing how the tires fit.  All the photos are of the front, but the rear is virtually the same.

Compass Bon Jon Pass 700 x 35 | Tektro R539 brake calipers | This combination is not recommended. The clearance is just too minimal. At speed a tire will increase very slightly in diameter (think dragster at the complete opposite end of the spectrum). There’s just not enough clearance present that I would not personally use this combo.

Compass Bon Jon Pass 700 x 35 | Tektro R539 brake calipers | This combination is not recommended. The clearance is just too minimal. At speed a tire will increase very slightly in diameter (think dragster at the complete opposite end of the spectrum). There’s just not enough clearance present that I would not personally use this combo.

 

Compass Bon Jon Pass 700 x 35 | Velo Orange Grand Cru Brake | Sufficient clearance.

Compass Bon Jon Pass 700 x 35 | Velo Orange Grand Cru Brake | Sufficient clearance.

 

Compass Bon Jon Pass 70c x 35 | TRP RG957 brake calipers | Better clearance. Actually, really good clearance. More than the Velo Orange.

Compass Bon Jon Pass 70c x 35 | TRP RG957 brake calipers | Better clearance. Actually, really good clearance. More than the Velo Orange.

 

Compass Bon Jon Pass 700c x 35 | Shimano BR-R600 | Beaucoup clearance!  These are the brakes that I run on my personal bike and are probably 12 years old (they are from the era of Ultegra 9-speed).  If you can find these brakes on the interwebs, they are worth snatching up for your long-reach brake needs.  Visibly has way more clearance than any of the other brakes.

Compass Bon Jon Pass 700c x 35 | Shimano BR-R600 | Beaucoup clearance!  These are the brakes that I run on my personal bike and are probably 12 years old (they are from the era of Ultegra 9-speed).  If you can find these brakes on the interwebs, they are worth snatching up for your long-reach brake needs.  Visibly has way more clearance than any of the other brakes.

 

Clement Strada LGG 700c x 28 | Tektro R539 Brake | For reference. Really shows how big the 35mm Bon Jon Pass tires are.  Huge.

Clement Strada LGG 700c x 28 | Tektro R539 Brake | For reference. Really shows how big the 35mm Bon Jon Pass tires are.  Huge.

Note that all parts listed above are for sale at Black Mountain Cycles.  I don’t do a great job of pushing that issue, but, yes, I sell stuff and usually sell stuff I write about.

(What’s playing:  Patty Smith Boy In The Bubble)


16 responses to “Clearance Pt. II – Road Frames”

  1. Jimmy says:

    Hi Mike, great pics and investigation! I was just talking to a friend about this very issue on an obscure fixie forum.

    The way the front tire rises up to meet the brake arm can be a significant issue for tire and fender clearance. The pinch point is at the foreward-most arm of the caliper. This is especially noticeable on high-offset forks.

    Do you have any side-view pics of those calipers? The shorter a caliper is front-to-back also helps with clearance. I’ve found old single-pivot calipers to have more room than almost any dual-pivot. I haven’t done much investigation into centerpulls, no idea on them.

    Anyhows, with the idea in mind that front-to-back “thickness” of the caliper matters, it seems that if you can remove some washers from behind the caliper a person could also increase their clearance marginally. In addition, note that the more you squeeze the brakes, that foreward arm actually moves up a bit, giving more clearance. I speculate that thinner brake pads (or remove the washer between the pads and arms) would allow you to set the brake caliper up with a tiny bit more tire room too.

    These are all small gains, and I’m not sure that going to a single-pivot caliper is worth it, but I’d like to know your thoughts on all this and if you have experienced the same thing.

    • blackmountaincycles says:

      Jimmy, Sorry, no sideviews. I don’t think there is enough adjustability in the Tektro R539 caliper that fitting thinner pads or varying the washers at the mounting point would give them sufficient clearance. At that point, it’s best to fit up a VO or TRP caliper. The gains are much better than marginal. I will say that the wider the rim, the more clearance is decreased. A rim like an old Open Pro will improve caliper to tire clearance. A super wide rim like a HED Belgium Plus will decrease clearance – probably to the point this tire won’t physically fit under the Tektro caliper.

  2. Mark says:

    Thanks for the useful post! I’ve got a unrelated question, I’ve been wondering if your blog is set up for rss. I use a blog reader but since you switched to the new website I can’t follow your new posts, which i want to!

  3. Chris VanZyl says:

    I’m running a set of the new 32C Gravel Kings, after using the Gravel Kings SK’s in the summer. Great to be able to use such a variety of tyres.
    I also teased myself with a set en Demo ENVE SES 3.4 wheels for a few days. Amazing just how it brings the frame to life ( compared to the 32H TB 14 DT Champion set)
    Question: If I’m considering an upgrade of my Tektros, which of the TRP or the VO would you recommend first ?

    • blackmountaincycles says:

      Chris, As the photos show, the TRP has the most clearance. The VO is a stiffer brake. The TRP has a more organic shape vs. the VO’s more blocky, CNC look. You can’t go wrong with either one. My personal aesthetic leans to the TRP shape.

  4. christian says:

    If you are willing to spend more on your brakes, The Paul Racer Medium works really nicely on BMC road frames (mine is a 62 with the old style fork crown) and essentially makes the frame the limiting factor rather than the brake caliper. 32mm tires with fenders look like they’ll fine (still wearing out some 28mm Gravel Kings), and I even tried a wheel with a 35mm Pasela and fenders. It seemed to fit, but I didn’t actually test ride.

  5. Jason says:

    I have the first version road frame, almost always had Jack Browns mounted to Velocity A23 rims (measured 35mm). I’ve since changed forks so I could mount a nitto mini rack to lowrider mounts, the fork is flat crown like the new BMC road frames and I have Tektro 539 brakes and feel comfortable running WTB’s 37c riddler on my bike as well as the Clement MSO 36c tubeless. The tires do need to be deflated to squeeze past the brakes and from what I’ve read tektro 539’s open up wider than any other brake of its kind. Aside from that I have enough clearance for dry conditions.

    • Jason says:

      Also been running WTB exposure 30 tubeless (measures 32-33 on Velocity A23) with PDW 45mm fenders. This is a very tight fit with the fenders and though it works its too tight for me to recommend it. The tires are awesome and highly recommended but the fender is a little to wide for the frame. I do not have them yet but I feel the WTB exposure 34c is the tire that was designed for the BMC road frame, it is tubeless ready, should fit fine, has a fast rolling center for pavement, with light side knobs for dirt/gravel exploration.

  6. Scott Lodzieski says:

    Does anyone know how the Shimano BR-650 compares? Does it have as much tire clearance as the Shimano BR-600? Thanks.

    • blackmountaincycles says:

      Scott, not sure on that one. I didn’t have a 650 caliper to check. I do believe, however, that the shape of the 650 is the same as the 600. The main difference between the two, I believe, is only the level of hardware.

  7. Vlad M. says:

    I don’t suppose anyone tested Velo Orange Grand Cru Brake next to TRP RG957 when it comes to performance? Based of my research, most people compare performance with stock pads. If I were to do this, brake pads would have to be the same on both brake sets. Either SwissStop or Kool-Stop.
    Thanks!

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