Improve BB flex with alternate BB and crank?

[TronnyJenkins]

I've got new toy that's really a joy to ride aside from one thing. Chain rubs the FD when I really lay into it. No, it's not an adjustment thing because I've tried moving it both directions. Fix one way, it rubs the other!

The frame is a 1997 Bianchi EL-OS, and I realize that the 'weight limit' is around 160. I'm only ten pounds over that, so I'm not overly concerned. Group is Dura Ace. 7410 crankset and BB, 9000 derailleurs, Giant SLR 1 wheelset.

I'm wondering if a 9000 series crankset and BB would help at all with the wider bearing placement. Would it look as cool? Heck no. But if it would help, I might consider trying it.

Honestly if it boils down to it, I'll get over it. It's not my race day bike or anything.

I need to take a photo. Here is one with some Zipps that I've since sold.

[Black Dog]

You are flexing the frame not the cranks and BB. Changing them will not make a difference.

[montag]

You are flexing the frame not the cranks and BB. Changing them will not make a difference.

Assuming that the spacing between 11 speed chainrings is less than 8 speed, then I would think the 9000 FD cage is similarly narrower than the FD meant for his crankset and thus more likely to rub with flex.

I agree he’s not going to fix the flex but he might improve the rubbing.

[Kontact]

Assuming that the spacing between 11 speed chainrings is less than 8 speed, then I would think the 9000 FD cage is similarly narrower than the FD meant for his crankset and thus more likely to rub with flex.

I agree he’s not going to fix the flex but he might improve the rubbing.

9000 chainring spacing is very slightly wider, not narrower.


EL is flexy tubing.

[jumphigher]

You could install a Hollowtech II set-up. The Ultegra HTII I run on my 2000 Koga considerably stiffened up the bike on climbs. Would of course change the look of the bike considerably..

Re-reading your post I see that's what you were asking in the first place, OP. So yes, I think the 9000 would stiffen up the frame due to the HTII BB.

[Peter P.]

You are flexing the frame not the cranks and BB. Changing them will not make a difference.

We don't know what's flexing and how much. There's no reason the crank and chainrings can't flex from the O.P.'s prodigious output. :)

From the photo, it appears to me the O.P. has a very quad-dominated pedal stroke; the zero-offset seatpost indicates forward positioning. I would advocate they either consider sliding the saddle rearward/using a setback post, and retraining for a rounder pedal stroke. In the absence of that, I like the idea of an outboard bearing crank. If it doesn't work, sell it; so it seems to make sense to buy a used setup on eBay first.

[oldpotatoe]

I've got new toy that's really a joy to ride aside from one thing. Chain rubs the FD when I really lay into it. No, it's not an adjustment thing because I've tried moving it both directions. Fix one way, it rubs the other!

The frame is a 1997 Bianchi EL-OS, and I realize that the 'weight limit' is around 160. I'm only ten pounds over that, so I'm not overly concerned. Group is Dura Ace. 7410 crankset and BB, 9000 derailleurs, Giant SLR 1 wheelset.

I'm wondering if a 9000 series crankset and BB would help at all with the wider bearing placement. Would it look as cool? Heck no. But if it would help, I might consider trying it.

Honestly if it boils down to it, I'll get over it. It's not my race day bike or anything.

I need to take a photo. Here is one with some Zipps that I've since sold.

A outboard bearing crank 'may' help but it's mostly frame, particularly with the very short BB(103mm) and pretty dern stiff cranks(7410).

[berserk87]

Frame flex. There's no way that you are flexing a 103mm piece of steel that's secured at either end.

[Lewis Moon]

I have to mind the FDer on my Denny Masi 3V every time I get up and hammer bigly. I don't get any overt chain rub but the shifter clicks down a notch quite often. Just waiting to get the 'cross bike back up and running to dig into the shifter and tighten things up. You may want to take a good look at the angle of the derailleur cage...if it's slightly twisted it may effectively have a narrower opening. Also: is it a braze on with an adapter? always use the adapter from the same company as the derailleur. Different adapters can put the FDer in different fore/aft configurations.

[BLD 25]

while not knowing much about the frame, it seems that most think it is pretty flexy. However, from what I have read about different BB standards, I seem to think that the proposal of the OP would help. As I understand, the square taper BBs were more flexy. It may not be the actual steel that is flexing, but rather the bearing placement inboard makes for a less stable platform. I think that was one of the bigger advantages of moving the bearings outboard, and also, that DA crank will be super stiff. May be worth a try if you already have the parts. If you don't, I wouldn't invest $400 on that proposal.

[tv_vt]

Contrary to some of the other posts, I think you might find less flex with a 9000 bb and crank. And the 9000 crank would look OK to me on that bike, with the bit of silver still in that model crank.

I noticed less flex when switching from a DA7700 octalink crank and bb to a 9000 setup.

[Black Dog]

You could install a Hollowtech II set-up. The Ultegra HTII I run on my 2000 Koga considerably stiffened up the bike on climbs. Would of course change the look of the bike considerably..

Re-reading your post I see that's what you were asking in the first place, OP. So yes, I think the 9000 would stiffen up the frame due to the HTII BB.

This is simply not true. No BB can stiffen up a bike. In fact, a stiffer crank/BB will increase frame flex not decrease it. The only way that a stiffer crank/BB will decrease flex is if the existing crank/BB has more flex than the frame. That will not be the case with the frame in question. There is a lot of guessing and assumptions made here in some posts that are not, in any way, backed up by imperical data. As for the various claims that people can feel how much stiffer one crank/BB setup is compaired to another; I am skeptical. This is likely a placebo effect unless your old cranks were made of bamboo. Let's not forget that the flexy crank vs a stiff crank will have flex measured in a few mm. There is more slop in your shoes and cleat pedal interface. BTW, if this were all true why do all the track sprinters (who put out more power than anyone) all compete with campy square taper or shimano octalink BB's?

[12snap]

This is simply not true. No BB can stiffen up a bike. In fact, a stiffer crank/BB will increase frame flex not decrease it. The only way that a stiffer crank/BB will decrease flex is if the existing crank/BB has more flex than the frame. That will not be the case with the frame in question. There is a lot of guessing and assumptions made here in some posts that are not, in any way, backed up by imperical data. As for the various claims that people can feel how much stiffer one crank/BB setup is compaired to another; I am skeptical. This is likely a placebo effect unless your old cranks were made of bamboo. Let's not forget that the flexy crank vs a stiff crank will have flex measured in a few mm. There is more slop in your shoes and cleat pedal interface. BTW, if this were all true why do all the track sprinters (who put out more power than anyone) all compete with campy square taper or shimano octalink BB's?

Fairwheel bikes did a crank test a few years ago which does include imperical data. It's an interesting read. http://blog.fairwheelbikes.com/reviews-and-testing/road-bike-crank-testing/

As far as the OP's question, we really don't know if it's the frame or the crank/chainrings that are flexing to cause the rubbing. Most likely it's a combination of both. My suggestion would be to try a different crankset and see if it makes a difference. Maybe see if you can borrow one from a friend to try out before spending any money on something that may not help at all.

[Black Dog]

Fairwheel bikes did a crank test a few years ago which does include imperical data. It's an interesting read. http://blog.fairwheelbikes.com/reviews-and-testing/road-bike-crank-testing/

As far as the OP's question, we really don't know if it's the frame or the crank/chainrings that are flexing to cause the rubbing. Most likely it's a combination of both. My suggestion would be to try a different crankset and see if it makes a difference. Maybe see if you can borrow one from a friend to try out before spending any money on something that may not help at all.

I have seen this data and it shows that the difference in flex between the most flexible (solid Al crank with squat taper BB) and most stiff cranks/BB is about 2.0mm. And that is at a power equivalent of 880 watts!! So in the real world where we all ride; the data shows us clearly that your crank BB is not a significant source of flex and certainly no one would be able to detect crank flex in a blind test, the differences are likely well below the sensitivity threshold for humans. Believing that we feel a difference does not make it true. The numbers show is this.

http://blog.fairwheelbikes.com/wp-content/uploads/2016/09/deflection2016.jpg

[Mark McM]

I have seen this data and it shows that the difference in flex between the most flexible (solid Al crank with squat taper BB) and most stiff cranks/BB is about 2.0mm. And that is at a power equivalent of 880 watts!! So in the real world where we all ride; the data shows us clearly that your crank BB is not a significant source of flex and certainly no one would be able to detect crank flex in a blind test, the differences are likely well below the sensitivity threshold for humans. Believing that we feel a difference does not take it true. The numbers show is this.

http://blog.fairwheelbikes.com/wp-content/uploads/2016/09/deflection2016.jpg

This data doesn't really apply. Fairwheel Bikes measured vertical deflection, whereas derailleur rub is caused by lateral deflection.

The structural members between the pedal and the front derailleur (crank, BB, frame) are in series, so their deflections are additive. Flex in any of the components will increase the total deflection.

However, I agree with the general sentiment that the majority of the deflection in this case is probably in the frame. While increasing the stiffness of the cranks or BB will result in a small decrease in the total deflection, it may not be enough to make up for the flex in the frame.

[Kontact]

Everything flexes, but switching cranks on a frame made of EL with a very low 160 weight limit sounds like putting a bandaid on an ax wound. And that's only if you actually believe the 7410 set up flexy in the relative scheme of things, which I have not found to be the case.

[Black Dog]

This data doesn't really apply. Fairwheel Bikes measured vertical deflection, whereas derailleur rub is caused by lateral deflection.

The structural members between the pedal and the front derailleur (crank, BB, frame) are in series, so their deflections are additive. Flex in any of the components will increase the total deflection.

However, I agree with the general sentiment that the majority of the deflection in this case is probably in the frame. While increasing the stiffness of the cranks or BB will result in a small decrease in the total deflection, it may not be enough to make up for the flex in the frame.

Yes, mostly vertical deflection, but not entirely. The measurement is then at the midpoint of the spindle. Thus the measurement is a combination of vertical deflection and torsion (twisting) of the crank arms. I would be surprised if the lateral deflection at the chainrings amounted to more than a fraction of the deflection at the spindle. And again their measurements were based off of an input energy of 880 watts, this certainly puts a scale to the data.

Mark, I would love to set you free on their test rig and let you make any modifications and measurements you wished. The results would no doubt be informative and comprehensive.

[jumphigher]

Well OP, I cant back my opinion up with charts and 'how comes' but I do believe if you change out your BB and crankset as you mentioned, you will see less flex. JMO of course. :)

Oh and aesthetically I think the HTII crankset would look great with that frame.

[TronnyJenkins]

Thanks all for the input.
I don't think it's the 7410 flexing, I have it on two other bikes and don't get this rub... well at all.
My thought was widen the BB itself and potentially see some decrease, but it sounds unlikely. I figured!

[audiojan]

I've got new toy that's really a joy to ride aside from one thing. Chain rubs the FD when I really lay into it. No, it's not an adjustment thing because I've tried moving it both directions. Fix one way, it rubs the other!

The frame is a 1997 Bianchi EL-OS, and I realize that the 'weight limit' is around 160. I'm only ten pounds over that, so I'm not overly concerned. Group is Dura Ace. 7410 crankset and BB, 9000 derailleurs, Giant SLR 1 wheelset.

I'm wondering if a 9000 series crankset and BB would help at all with the wider bearing placement. Would it look as cool? Heck no. But if it would help, I might consider trying it.

Honestly if it boils down to it, I'll get over it. It's not my race day bike or anything.

I need to take a photo. Here is one with some Zipps that I've since sold.

Won't make a difference... it's not the crank flexing, but the actual frame. Getting an even stiffer crank will only increase the flex (greater energy transmission)

[El Chaba]

...and somehow Eddy Merckx made do with flexible old SL tubing, square taper BB's and Campag Record cranks....

[cachagua]

Two pages and nobody said bend the derailleur cage? Bend the derailleur cage.

This isn't a frame flex problem. Your chain just needs a little more room, is all. Pull the whole lower edge of the outer plate outboard a little, except for the front tip -- bring that in a little narrower. And arch the region behind the bridge that connects the two plates outboard a little too. Also it may help to bring the whole derailleur down to just a hair's breadth above the big chainring. Expect to adjust the limit screws as part of the process.

Go at it judiciously, don't savage the thing, but you can reshape it enough that the chain will quit hitting, and will shift reliably and never get thrown off. A chainring-straightening tool is usually a good thing to start with, and a little baby pair of slip-jaw pliers may be helpful too.