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brakes and tire clearance question

Old 04-24-21, 02:07 PM
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brakes and tire clearance question

OK, here goes....


New project is a build up of a Serotta Fierte. The challenge was to build it with bits and pieces I had lying around. That included the choice of your everyday Tektros, and a similar set by FSA. I picked the FSA, because, well, because they look different. But when I set it all up with 28mm tires, the rear tire rubbed the brake. Swapped it out for the Tektro with the same result. So I gave up and mounted a 25mm tire.


No sweat, the rear wishbone has some nice bounce to it; it is still a cushy ride, at least from my butt's perspective.


But here's the rub. The crank is set unusually low, a little more than 25.5cm. I discovered this the hard way, pedaling through an easy turn, and earning a molar jarring clank. Lucky I did not shear off the pedal.


So here is the question: can someone recommend a rim brake where the crotch is higher than the ordinary? I am reluctant to go to a narrower pedal, because one knee already tends to brush the top tube.


Thanks in advance for your wisdom and insight.
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Old 04-24-21, 02:46 PM
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I think any small amount of tire profile increase will be at best marginal WRT BB height. Shorter crank arms are likely to produce greater cornering clearance when having to pedal through the apex. And that's the rub (bad pun), technique VS design.

I have read (remember I believe everything I read in print, but not on line) years ago when the crit. scene was where it was at for US racing and many production bike emulated the high BBs that Crit bikes were thought to need. Of course they made for poor road bikes (due to BB height and other reasons too) and were comically head shaked by Euros. The Euro pros would just ride their road bikes in the post tour crits and the good guys would win still. I don't remember reading in Velo News or Winning about many who clipped pedals and went down in their race reviews.

Having said all that a 25.5 (10.03") BB height is pretty low. What frame size is this bike? What crank arm length and pedals are being used? Andy
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Old 04-24-21, 03:28 PM
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Andrew, thanks for the commentary.
yup, the crank is 175mm. The frame was sold to me as a 57cm, but the cockpit feels even shorter. Wheelbase is about 101cm. Compact bars and 110mm stem is too short. shoving the saddle all the back puts knees well behind the spindle. I guess I will learn to adjust my pedaling style, and go to a longer stem and reachier bars.
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Old 04-24-21, 04:14 PM
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If you're a geezer, you may find shorter cranks kinder to your knees.
I've gone to 165mm since 175mm is basically unrideable and 170 gives frequent knee pain.
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Old 04-30-21, 02:23 PM
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Sorry to let this thread get stale...sometimes life intervenes. I considered Bill K's suggestion, but there ain't nothing--nada--zip--zilch--that I could find in the way of shorter square tapered cranksets with a 107mm chain line. There were plenty of 113mm's, but extending the arms would defeat the original purpose. I also looked at shorter pedal axels but the only suitable candidate is the XTR. But it costs $180 to shave off 3mm. Hmmmmmm....



So I looked more closely at the different pedals I am running. (I run SPD's because I run errands and make visits on my bikes) The problem arose using the Bontragers. Although on at glance they look the smallest, they actually have projections that interfere with pavement at less of a lean angle than the ISSI or the Shimano. The Shimano tapers in like the ISSI, but it is also thinner. I also did a little warranty-voiding modification, by filing a little meat from the edges that would be first strike asphalt.
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Old 04-30-21, 03:26 PM
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A question first- " square tapered cranksets with a 107mm chain line. There were plenty of 113mm's" Do you mean a BB axle of 107 or 113? Chain line has nothing to do with pedals although the crank's "Q" factor (distance from the crank arm's face where the pedal seats against it to the same point on the other arm) is very axle length dependent. Am I miss reading?

I do agree that the Shimano pedals shown have a wide body and likely strike the road if pedaling around corners more then the ISIS ones do. It also looks like the center of the cleat clasp on the ISIS is closer to the pedal spindle's crank arm seat then the Shimano's. The angle of the photo's view makes this hard to be sure of. That would be an interesting dimension to have though.

I would only change the crank arm length due to fit reasons, not pedal strike ones. I would change my cornering while still pedaling nature to suit the bike I was riding. My example of this is when on the tandem. The much longer wheelbase makes the pedals more easily strike the ground when riding over things like speed bumps or up sidewalk ramps. I consider this to be a control and technique issue, not an equipment one. Andy
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Old 04-30-21, 04:39 PM
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" Chain line has nothing to do with pedals although the crank's "Q" factor (distance from the crank arm's face where the pedal seats against it to the same point on the other arm) is very axle length dependent. Am I miss reading?"

Andy,

My bad. the BB spindle is 107mm and the crank I installed was what was recommended for that length.


WRT to various pedals--the photos are somewhat misleading. The length of each is almost identical--but with both the Shimano and ISSI, the max. length is in line with the axel. The max. length of the Bontrager is at the two projections, fore and aft of center. On close inspection, the Shimano and ISSI seem similar (in terms of clearance to pavement), but due to its thinner section, the Shimano gains a whisper more clearance. Filing a mm or more off the salient edges gains even more.

It may be worth mentioning that in my admittedly timid riding style, I never ground the pedals. Well, except for the Shimano clipless-platform combos. But I wasn't even riding hard at all, into the turn that caused the grounding. Anyway, I went for a short spin earlier today, with the modified Shimanos, and had no problem.
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Old 04-30-21, 05:20 PM
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Glad to hear that your corner filing on the pedals helps the grinding riding around corners Your bike's BB height (or the frame's BB drop as builders look at this) is rather on the edge of the usual range. That and the 175 arm lengths with the bulky two sided SPD pedals all combine for a perfect storm. Do take care as you ride as it's easy to forget the clearance or do something "in the moment" that exceeds that clearance. Andy
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