Technical FAQ with Lennard Zinn: The right shoe
Q. Dear Lennard,
I have been riding for more than 12 years and have always rubbed the inside of my crank and chainstays as well as worn out the inner part of my shoes because my foot tends to collapse inward with each pedal stroke.
I will even rub my top tube with my knees because of this and have to get bikes with narrow top tubes, something I am told Indurain was infamous for. I believe this is called a valgus strain; I have been told I am an “overpronator” when I buy running shoes and need to get shoes with “stability” to help correct this. I have tried the Specialized shoes, which have a built in valgus wedge of 1.5mm that they say 90 percent of the population needs according the famous Dr Pruitt at Specialized.
However, I have this ever-annoying feeling that something is in my shoe; and cannot get used to the feeling. My setup now is good supportive specialized insoles in Shimano shoes with about 4 mm of spacers on both of the pedal axle to space my foot away from the crankset, effectively increasing the “Q” factor. Do you have any more recommendations; or is this as good as I am going as it gets?
A. From D2 Shoe:
It sounds like he has a “Hyper Mobile” foot. It’s more than just pronation. The entire foot is very flexible. While the generic insoles do have more support; they are not specific to his problem. He also needs more support in the middle of the foot to help tension the plantar fascia. Forefoot varus (not valgus) alone won’t solve the problem by itself with this type of foot. So he needs to have a proper orthotic along with forefoot varus. The Specialized shoes do have a certain amount of varus built in but it may not be enough for him, and he still needs the real orthotics. Some foot exercises along with the orthotics can also help to realign his feet and actually make them stronger and less likely to collapse.
— Don Lamson
A. From ReTul:
He needs to get a good foot evaluation to see if he has a neutral, varus, or valgus forefoot. His foot may overpronate because it is extremely flexible, not necessarily because he has forefoot varus. I have seen this a lot as a fitter. And this is probably why he did not like the built in varus cant on the Specialized shoes. According to his success with trial and error here, the forefoot may actually be angled in valgus, in which case I would recommend a first-ray drop (cutout under the first metatarsal head). That combined with his well-supported longitudinal arch (courtesy of the BG footbeds) should do the trick. But once again, he should get his foot mechanics checked.
— Todd Carver, MS
Q. Dear Lennard,
I have read much about the potential for BB30 cranksets to be lighter and potentially stiffer than standard cranksets that require external bottom bracket cups. I am interested in a BB30 crankset for this reason but I have a 2009 Cervelo S2 frame that is not BB30 compatible. However, I’ve noticed that Rotor makes a special bottom bracket called BSA 30, and it appears to have oversized external BB cups that allows for their BB30 Rotor 3D+ crankset to be compatible with a standard threaded bottom bracket. First, I am wondering whether such a setup can still take advantage of the extra stiffness provided by a BB30 crank seeing as now external BB cups are being used in this instance rather than having the bearings internal within the frame? Also, is a BB30 crank primarily lighter because it does away with external BB cups or is there something inherent about the BB30 crank arm, spider, or spindle design that allows for a lower total crankset weight? Finally, could this Rotor BSA 30 bottom bracket be used to install any BB30 crank on the market for use on English-threaded frames?
A. Dear Arthur,
Rotor’s BSA30 would not reduce the stiffness of the BB30 Rotor crank, because its stiffness is achieved mainly by virtue of its 30mm-diameter spindle. Any possible slight movement of the external cups that might reduce stiffness relative to an internal-bearing system would be offset by the wider stance of the bearings adding back some stiffness.
BB30 is primarily lighter by virtue of dispensing with cups and replacing them with press-in bearings and a single, lightweight snapring on either side. The 30mm-diameter aluminum BB30 spindle is not significantly lighter than a steel 24mm-diameter spindle on an external-bearing integrated-spindle crank. And there is nothing in the geometry of the cranks or spiders that saves significant weight in the one system versus the other.
Finally, I’m sure you could not use Rotor’s BSA30 cups on other BB30 cranks because there would not be enough space between the frame and the crankarms for the external cups. A BB30 road bottom bracket shell is 68mm wide – the same as a BSA (English-threaded) road bottom bracket shell (both systems are 73mm wide for mountain bikes). And one of the much-hyped features of most BB30 cranks is the fact that ankle clearance is improved. In other words, most BB30 crank manufacturers have taken advantage of the fact that there is not an external bottom bracket cup taking up space and have moved the head of the crankarm inward on both sides. So you couldn’t fit the BSA30 cups in between the frame and the cranks with any crank other than Rotor. And that doesn’t even address the fact that, even if you could fit them in, the raised and ground bearing-contact surfaces on either end of most BB30 spindles would not line up with the external bearings, since they are placed to contact the inner races of bearings that are internal to a 68mm (or 73mm mountain) bottom bracket shell.