Machine Politics vs Beaver Boys, May 2011. Photo by Bruce Carver
I have been doing some more thinking about frame design and I have been toying with concept of experimenting with a wider bottom bracket to allow a slightly wider stance for increased balance.
So do I stick with what i know and keep the square taper based 68mm shell? Do i experiment with the potential of a single speed 73mm shell?
My internal battles on this subject are mostly mechanical, partially political.
I found thats parts availability are minimal for 73mm square taper bottom bracket. Shimano is the only manufacturer that I have found that produce a varying square tapper spindle widths with a 73mm cartridge bearing. I bring up the importance of square tapper because of the popularity of 110 bcd sugino cranks as well as the availability of older used cranks that could be salvaged for polo usage.
I question the longevity of square tapper bottom bracket because of the amount of abuse and torque that is exerted on the spindle. I wonder if a splined spindle might be more practical. I think of other single speed systems like Profile Racing cranks, shimano splined spindles and the isis spindle as maybe being more applicable to our sport in the long term.
My argument for staying with 68mm square tapper is the availability of 165mm crank arm and used crank arms that are salvaged from old mtn and road bikes.
My argument for 73mm shell is to push for a diverse selection of beefier crank arms and bb bearing systems, as well as my own theory of increased center of gravity at the bottom bracket.
Note: the 73mm would still allow for usage of square taper cranks, but would yield a smaller selection of cartridge bearing bottom brackets.
These are some tech dork issues that I am struggling with, tell me what you think.
fire away.
This is aside from the joust. The Joust is done as far as design, my self along with strong input from brian have tweaked the finalized design of the Joust.
This conversation is one of theory not of last minute changes to the joust design.
My mind is always on design, and I have to ask these questions to the polo community as a checks and balances system so to avoid impractical design.(ie 650c wheels, i like em, but i like my 26" more).
I've had all sorts of problems with ISIS bottom brackets, both on MTB and cyclocross (raceface and truvativ). Their design is kinda flimsy, they are really just held on by the crank bolt. When I looked online I found I was not alone in this regard. Ive been way more into the new shimano design where the drivetrain side crank is connected to the "bottom bracket" and the bearings are exterior. The other crank arm then bolts on in a pretty solid way...OK thats a crap description but you probably know what Im talking about.
He's right, ISIS is crap. Works OK for some applications, but in polo, especially fixed, the arms will be prone to walking off. There's nothing wrong with square taper for what we're doing, and parts availability more than trumps any weight or flex drawbacks. The real issue is chainline: assuming 120mm (track/SS) rear spacing, at 73mm, you'll have a shit chainline even with a 107mm spindle, and most Octalink or outboard BB setups will put you even wider than that. The only fix would be to widen the rear dropout spacing to 135, requiring everybody to use MTB hubs. You'll be swallowing the spider to catch the fly. Leave well enough alone. And call me about that exhibit thing.
As a mechanic, I'll tell you this. you could just as easily get shorter old MTB cranks for a wider stance and stay with a 68mm BB shell. the only practical reason to switch to a 73mm shell is so you can widen your chain and seat stays to run wider tires, such as in the case of my surly 1*1 which by the way has an raceface Isis BB 73mm wide BB shell and 165mm gravity free ride cranks with a bashgaurd. I built this bike for polo, the thing is light and nimble with the durability of a panzer tank! Montana's comment that isis is crap is not unfounded, a lot of isis bottom brackets are crap and as well so are there counterpart cranks, what happened was this Shimano put out octalink and everyone else said "Oh snap!" what are we gonna do? we gotta come up with something to! and hastilly put into production Isis. anyhoo point being, if you want to go with Isis that's worth a shit you gotta spend money. Also if you want a polo bike that preforms you gotta spend money, whether initially or on constant upkeep of wear parts. lastly I believe there is something to your theory of wider stance.
call it!
first off thanks for being apart of this conversation. I'm stoked to get some mechanic input outside of my own.
I agree with the downfalls of ISIS, and there is a lot that is sacrificed for 5mm extra spacing.
Rear drop out spacing, hubs, and chainline then factors.
I'm considering the 73mm argument dormant, after talking to ya'll and my number cruncher.
Thanks for the input.
I think i might try to experiment with crank designs that angle arm outwards for widening weight distribution.
Is this a conversation anyone would like to have?
I'm pretty sure that designing a crank arm at any angle other than 90 degrees to the bottom bracket axle will build flex into the system, as the forces at work will always be trying to straighten out the arms. This would mean that you would need to build extra strength (read "heavier") into the crank arms to get the same stiffness as a crank arm at 90 degrees to the bottom bracket axle.
Also, it seems to me that the best way to make a crank stiffer is to increase the distance between the bearings without increasing the distance between the pedals. Think of the axle extending beyond the bearings as a second-class lever and the bearings as a fulcrum. The weight of the rider is on the end of the lever and the force in the center of the lever is the axle resisting being bent. The longer the lever is, the easier it is to bend. So by this theory, using a wider bottom bracket shell probably has very little effect on stiffness. What really effects bottom bracket stiffness is moving the bearings out in relation to the pedals: outboard bearings. A crank like the Shimano 105 uses outboard bearings and a splined left crank arm that also uses two pinch bolts. The pinch bolts in combination with the spline make for a very solid connection, and the outboard bearings mean less axle is hangin' out in the wind and flexing.
I'm an engineer and an aspiring frame builder, but I'll be the first to admit that my theories don't always pan out. Can anybody blow any holes in this?
Seth Higbee
Hastings/Ionia
Widening the distance between your feet increases the likelihood of pedal strikes. Pedal strike is definitely bad, widened weight distribution below the c.o.g. is questionable good.
In fact, I think it could be bad for handling. I used to ride an old BMW boxer motorcycle. Fans of that engine all claim the weight down low & wide makes you really stable. But it's nimble as a bean bag.
- wider bb shells are a solution for wider tyres close to the cranks in a MTB situation.
- A wider tread can be accomplished by simply getting cranks with a bigger Q-factor such as mountain bike cranks. some cheapies like alivio etc are astonishingly wide. I feel like i'm riding a horse. also the old race face square taper ones are pretty wide.
- Leaving the BB shell at 68mm gives more flexibility in crank/bb configuration.
- Shimano MTB outboard bearings come with a set of spacers which are used to ensure that the bearings end up the same distance apart regardless of bb shell width. This is because the spindle is a fixed length and the left crank arm has to press up against the left bearing with about +/-0.5 mm to spare. What this means is that the tread is the same regardless of bb shell width. using a wider shell just lets you put the chainstays further out but limits your bb choice.
- my favourite solution for better stability is slacker headtube angle. I use a very small tread on my polo bike and feel incredibly stable. short wheelbase makes it nimble. i'm making a new one which will be even shorter and a lot lighter.
alright, here is what I found out, unless you want to drop $200-400 on Mtb outboard bearing cranks, i.e. DeoreXT, XTR or the fucking awesome SAINT series, (oh so fuckin sexy and they come in 165 UUUUUUUUUUUuhHHHHHHHHh!) then square taper mtb or bmx with the wider profile is the way to go. Special goodness is on the right track about outboard bearings being stiffer. though I don't think I would rock road cranks of the outboard variety on the polo court personally. Do what you want and they will be cheaper, but I just don't trust em with impacts is all. Scottles has a great solution in increasing the head tube angle, this can be accomplished for those of us without a frame building shop by doing a little fork rake to head tube angle math and finding an appropriate fork length to rake ratio to slightly increase trail and slacken up the head tube angle there by increasing handling. Warning! if you increase your rake more than 2-3cm your bike may handle like a boat with its anchor down blowing in the wind.
call it!
for my polo bike i got a tiny old 24" (wheel size) road frame and stuck a early/mid 90's mtb fork on. slapped in 26" wheels and the bb's well clear of the deck. head angle's back to 69deg, 42mm fork offset giving 82mm trail (unstable over 45km/h!), seat tube angle also at 69deg which puts the seat almost above the rear axle when extended to the right height. super slack head angle slowness is offset by miniscule wheelbase and just more use of your body to turn, it's incredibly stable though, even with one hand on the handlebar I can throw the bike around like crazy with total confidence, or even get hammered by lachlan riding full tilt at the sydney 2x2 and still stay up. Re cranks: i use old sugino gt cranks (170 long) with a nice kajita bb. they're incredi-stiff, far stiffer than the frame, so i'm not thinking about changing to outboard bearings any time soon.
I just started running Stylo 1.1 myself and I love everything from the spindle to the self removable crank arm bolts. I moved up to a 170mm and see little difference in pedal stroke and have no pedal strike. I think they are quite resonable price wise and I like the bearing system quite a bit. Plus a stock bashguard is pretty nice with room for a beefier upgrade. Plus you get gearing options up front which is something i have desired for a while because of varying court sizes.
I am interested in seeing how the power spline compares to square tapper. Nearing the end of the life of my MKE pologuard/ sugino my non ds crank was coming loose weekly until i filed down the inside of the arm to get clearance for a tight squeeze without butting up against the bearings. Since the pologuard is compatible with other cranks arms with similar bearing system as my stylo's, i might try a different crank arm variation.
Stylo 1.1 looks like a great deal! I'm curious to learn about durability. Susan had something similar for a while ... probably/hopefully an earlier design. The bolt on the non-drive side came loose under susan's smashing acceleration ... letting the spindle edge out of the drive side - splines and all. For that - clean the bolt and spindle threads and locktite the fumo before munging the splines. Wouldn't travel too well.
I really like shimano's newest integrated drive side + spindle design. The hollowtech II (more expensive ... 105 and up I think) are a feat of engineering and production wonder. And the whole damn assembly comes off easily for shipping. Be warned though - got to check the ft-lbs on those two ~5mm allen bolts that pinch the non drive side onto the splined spindle. Especially when you're smashing like polo player.
If you got the compact road version I think the MKE 110 pologuard could be your outer ring. For a standard road double (130) you could probably use your old MKE guard as the outer. Saving $100 on conserving that guard (do they really have an end of life?!) would be a big influence on me.
Funny thing that you mention the MKE Pologuard, I was spec'ing out the SRAM line and found that Red, Force, and Rival all have 110bcd which should allow for the guard to fit on a higher end road crank with SRAM Spindle. I haven't tried it yet, but i'll be sure to do it after madison for shits and giggles.
Also, I have seen the end of a pologuard. Greg Ya'll from chicago scorched his really bad at ESPI's. The teeth are completley worn down and his chaine made this awful set of grooves all around the inside of the bash guard. BUT that was the first edition, which I can only imagine they improved upon. We'll have to wait to see the wear on their newer pologuards.
Maybe his chainline was off...
Also - just noticed this at Ben's Cycle's. Check out the 35tooth 110bcd PINK pologuard ... last one ... wish I had a benjamin to throw at it.
"NOTE – It is no secret that chains and chainrings wear with each other. Chain stretch is the number one reason chainrings go bad. So if you want this all-in-one to last you as long as possible, change your chain every year (if not twice a year) before the chain stretch ruins the teeth. If you want to make things really easy on yourself buy a Park CC-3C Chain Wear Indicator and check your chain frequently."
Why the short, 165, cranks? Is that so there isn't as much open space for people to shoot goals through? Longer cranks give much quicker acceleration. You must, of course, have the right height BB and or shorter pedals to avoid the tripod.
Pedal strike when taking sharp turns.
what do people think of the MID bb system? cheap, easy, and strong so far as I can tell. Tucker?
uhhhh...well...
no doubt when the Mid BB became popular in and around 2004 it added some benefits the "american" bb bearing press fit system. It seemed to be a response to the english threading introduced by Standard around 2003-04. Now there is the BB30 or Pressfit 30 threadless systems that are being utilized by a few component companies, but is wieghted towards the higher end crank sets. Which is better? I couldn't tell you off the bat other than breaking it down into installation and durability. I always disliked bearing pressfit systems because they were easy to tweak the wrong way and mess up your cadence, and I didn't always like using my bench vise or rubber mallet as my primary tools (mind you i was 14 at the time). Another thing to consider is your parts availability, which for mid isn't so bad with the bmx and MTB companies that have bearing systems that are compatible. These parts are going to be strong as hell but my question would be wether or not the single bolt sprocket system seen on most bmx cranks is strong enough for the high torque output required to play polo, though great for sprocket grinds and hitting ledges, where your sprocket would be cashed in a month or two any way. then you just rip it off and replace.
If I may call it like i see it, i'd stick to threaded bb's. If you ever want to get fancy, I'd check out some of the newer Outboard bearing systems. The can be pretty cheap, and are super easy to work on.
I don't want to be the Guru on this one, someone else contribute.
In my experience Euro BMX bottom brackets don't last nearly as long the larger sizes. Just last night i had mine go out on me for the second time this year (terrible grinding and loss of smoothness; eastern brand bb). Now i haven't ridden a mid or spanish bb in more than few years, but i do seem to remember them lasting a lot longer than 4 months. or maybe polo is just that hard on parts..
Press fit seemed like a bad idea to me with the BB30 or the terrible trek bb90. I don't see a need to go with a press fit style, be it spanish, or mid. Its the reason euro bbs because the standard, I feel the standard threaded bb offers the most versatility to the users.
I like the idea of the outboard bearings because it makes it stiffer, especially because the two contact points are spaced further apart with out affecting the q factor or the frame design. It doesn't make sense to me. every other application seems purpose oriented where euro bbs seem to allow for vast customization.
http://www.bikefit.com/img/Prod20mmPedalSpacer.jpg
You could always just use something like these +20mm pedal spacers rather than moving to uncommon bottom brackets and other parts which will wear out.
I thought you were
coming close the full release of the Fleetvelo Joust Polo Bike. Our website is due shortly, and you'll be able to order from Fleetvelo.com via paypal.
You'd think the bottom bracket would be decided on for something that is a month away from an unveiling.
That said: I vote for 68mm, pretty much just because of the commonality of spare parts. I hear your technical arguments for a 73 but don't see them outweighing cheap and abundant replacement parts. Also I think (but admit I'm only talking theory) that a lot of the torque issue you are concerned about is mitigated by the very low gearing most of us use.
Chicago Bike Polo 2003-2008
St Louis Bike Polo 2008-fun
Wanna buy some polo stuff?
http://www.fixcraft.net/stcago