riding this weekend, I was wishing for closer spaced gearing. I ran the numbers for switching to a compact crank with an 11-21 and was surprised to see that it was almost as low as my 39x25 (close enough that I likely couldn’t tell the difference), and actually taller than my 53x12. All that with the added advantage of more closely spaced gears.
ISIS bb
as a campy guy, I would have to switch to an ISIS bb. I don’t know what the good brands are. I was looking at the FSA’s since I was looking at the FSA compact crank. Chris King mentions that he’s working on one, but no mention of when it would be out. others?
Q-factor
one of the advantages I’ve seen listed for the compact crank is the reduced Q-factor. but looking at the width of the FSA Platinum Pro Ti, it shows the narrowest it comes is 108mm. My campy bb is 102mm. how is that going to give me a more narrow Q?
I am not sure about all this hoopla with compact cranks, I think it is a ploy to get us all to change components when the old stuff still works great. In the 1950s in the US car industry, they called it ‘planned obsolesence’. No doubt a smaller small front chainring will give you a lower gear, but so could a cassette with a bigger big cog–and this is a LOT cheaper fix than having to buy a new cassette, a new crank, AND a new BB. Also, many cassettes already come with an 11 tooth cog, so you don’t really get an equivalent big gear (to a 53 x 11). Also the compact drive folks forget to tell you that switching to all smaller gears means one thing: a lot faster drivetrain wear.
I am not sure about who makes the most and best ISIS spline BBs. However, about Q-factor, the BB width is just one element in the Q-factor width. True, it is likely that a narrower BB would give you a smaller Q-factor, but Q-factor is still highly dependent on the length of the BB spline, how the cranks seat on the spline, the thickness of the cranks and spider, and the angle of the cranks (how they splay outward to give the rider ankle clearance). So Q-factor can only be evaluated as a package of BB and installed cranks.
ISIS bb – look at both FSA and truvativ. if you’re buying an FSA crank, tho, seems the FSA bb is also a logical choice.
Q-factor – bb axle width has nothing to do with Q-factor. dura ace (back in the square hole days) went from a 112mm bb axle to a 103mm when updating to a new model crank, and it was just a factor of how far the bb axle stuck into the bb hole into the crank. both cranks had the same Q.
Q-factor is taken from the outside of the crank, at the pedal eye, to the centerline of the frame. most cranks have about the same Q these days. more of an issue is what the taper of the crankarm looks like on the outside, the lateral side. does it taper in much before it attaches to the bb axle? shimano hollowcranks don’t, campy does. this is important ONLY if you need that clearance on the medial side (inside) of your shoe. if dura ace stops saying dura ace on the outside of your crankarm after 50 miles, your shoe’s heel is rubbing on the crank and you need more medial heel clearance.
otherwise, all the cranks are within 1mm or 2mm of having the same Q. c’dales cranks have slightly less Q. others have slightly more. but they’re all pretty close. obvious exception is walser.
The advantage of the compact set-up over standard is that you get smaller jumps between cogs while you maintain essentially the same top and low end. A Division 1 pro cyclist may need a 53-11 but there are very few triathletes who do.
I also don’t think accelerated drive train wear is an issue on a road bike. Especially not with the 3-5 tooth differences we are talking about.
You are exactly right in pointing out that spindle width is only one small part of the Q-factor.
I dont get it…on MTN bikes the “Compact” deal IMO makes a perfect justification - GROUND CLEARANCE. On a Tri bike…change your damn cogset. Have we all thought about the fact that F-Der’s for road use are designed with a 52-54 chainring in mind? How about them nasty braze on hangers that might just not be low enough for your fancy new “compact” chainrings?
Once again I think that the smoke will be billowing out of our ass’s as the marketing folks walk to the bank singing Bio-Pace carols of glee.
And as for Q Factor…not really an issue as has been stated. The #1 thing that will alter your “Q” factor is your cleat alignment and show/pedal options. (and if you have “Kang-Kels” as George Castansa would put it)
Compact chainrings, spiders and cassettes typically weigh less, which is the main benefit in my opinion. However, I don’t see it justifying a switch unless you’re looking to help the economy.
And actually, removing a couple teeth on the front chainring makes a negligible difference in a mountain bike’s ground clearance.
I think the goal is to keep the “jumps” between gears small.
Campy and Shimano don’t make “straight block” cassettes with a 13t first position cog.
I used to run a 13-23 in the 9 spd days with a 54/42
no I’ve got a Campagnolo 52/42 with a 12/23 and I just love the 16/17/18/19 middle range. great with the 42 for going easy and even better for the 52 where the 14/15/16/17 range make very small changes to my pedalling rhythm. Some folks can ride at 90 rpm, then shift and drop to say 74 or upshift to 99 and not care or notice, others are more sensitive.
FSA makes a 105 or 106 mm spindle for in an ISIS spline, but you need to use their BB shell in your frame.
Ritchey’s new ISIS BB has the largest bearing diameter of any ISIS BB on the market AND their steel spindled unit is only 170 grams. It should last much longer than current designs. However their Compact road cranks is Shimano splined, design to be a bolt on for all the Octalink cranks users mashing on their 53t.
I’m going to move to the compact cranks for a couple reasons. When I train, I like to have a 26 in the rear so I stay in zone, but sometimes spin out the 13 - especially on long, shallow hills. With the compact crankset, I figure I can keep my 11/23 on full time and climb pretty much anything, put the 13/26 on for training in the Sierras, and maybe pick up an 11/21 for some of the local sprint races that are hill-free (Not sure I would really need that, though).
On the plus side, it’s lighter and more versitile for me, on the minus side, I have to spend some green, but I can sell my old kit to cover part of the cost, and I no longer need the 13/29, so that’s for sale, too.
Let me say that I’m probably gonna go to compact cranks, when I can scrounge up the money (2 big ticket items need to be bought by next may, cranks and wheels)
If you actually do the math, the jumps are more or less the same given 52/39 with a 12-27 and a 50/34 and a 11-23. If I remember right the gaps are, smaller at the small end of the cassette, and larger at the large end of the cassette. The smaller front rings makes the rear end have more difference in gear ratios, its simple division.
The only good reason for getting a compact crank is if you need a lower granny gear or wanna save some weight.
Me, I need a lower granny gear, I don’t like having a 40 something cadence pushing my pig of a bike up some of the hills around here.
before I get started, thanks Dan and SuperDave, exactly what I was looking for re: brands to look at. as for the Q discussion, I realize the Q calc’d from foot to foot and not just the spindle length but I wouldn’t have thought there would be that much variability in space between the end of the spindle and the outside edge of the crank. Given other comments, I’m even more at a loss why some argue reduced Q as an advantage to the compact cranks
Now, the math may be the similar but that assumes that you’re really going to shift the front der to get to all those middle gears. I was in the “why bother” camp until this last weekend when I ran the numbers myself. I don’t get Record9’s marketing related argument. If I can cover the same usable range with smaller jumps and less crossing over then how is that not a real feature?
this probably won’t format well, but I’ll give it a shot anyway (data pulled from http://www.panix.com/~jbarrm/cycal/cycal.30f.html), using 50/34 & 11/21 10 speed. The gear inches aren’t exact, I used 701mm for the wheel diameter which doesn’t take the tire into account. using the same wheel diameter with a 53/39 & 12/25 gives a low of 43.06 and a high of 121.90. So this actually gives me slightly more on the high end and slightly less on the low end, the only thing keeping it from being a straight block is the lack of a 20 tooth.
Now, here’s the kicker, if I remove the 4 worst crossover gears (50x19 & 21, and 34 x 11 & 12, which I have grayed out, or at least attempted to gray out) then there is absolutely no overlap between the 50 and the 34. For better or worse, that’s how I actually shift in the real world, so this setup matches my real world needs, with no apparent loss, better than the generally accepted standard.
“Ritchey’s new ISIS BB has the largest bearing diameter of any ISIS BB on the market AND their steel spindled unit is only 170 grams. It should last much longer than current designs.”
Do you know the diameter of each individual bearing? The knock I’ve heard on regular ISIS is that the bearings are exceptionally small and more prone to wear than an Octalink system.
I would say that I am skeptical about frame manufacturers changing their frames to accomodate a proprietary bottom bracket system, but I said the same thing before about 1.125" integrated headsets.
I don’t know the bearing diameter off hand, you can contact Ritchey through www.ritcheylogic.com and they’ll unload reams of info on their product on you.
Enjoy.
I agree, the MEGA size BB or whatever FSA is marketing is pretty exclusive, I do thing they make a BSC adaptor so that you can run a regular BB also, it also allows for an ALUMINUM spindle instead of Ti or Steel, like Cannondale’s SI system. With some FSA Compact cranks, you’d have a sub 650 gram crankset.
jamesframe.com can weld you up a bike with the fancy GT Superbike tubing using the FSA BB for under $2000.
Dear Lennard;
A comment about the article on the FSA chain ring sizes (50/34). I live in Sonoma County CA where many roads are steep - 12 percent or greater. I have been riding a Ritchey ‘Swiss cross’ crank 48/34 with a 28/12 cassette for six years. It is great. I don’t have to carry an extra ring or worry about an extra shift. It is prefect except when you have a huge tail wind.
I will look into this other crank as well. I know I am nobody to quote, but if you do any kind of steep climbing this double ring setup is the way to go.
Paul
Dear Lennard;
Just saw your Q&A regarding small chainrings on cranks. I am a 50-year retired mechanical engineer, career spent racing motor vehicles, 800 mile a month road cyclist. I’ve been testing the FSA crank for a couple months over hill-and-dale in California’s wine country, and used for the Mt. Diablo Challenge race. I have 34, 36, & 38 inner rings, FSA 50, with TA 52, and 54.
I have used every conceivable ring combination with excellent results, no problems, using Cycle Dynamics cogs from 11 to 28 in various combinations and a Campy 26/29 pair for the toughest training climb in the county, a hill I never made the summit of with 39/29, never made it past mile marker 3.2 of 5.0!
Tom