|   Brant - a thought provoking question wrt e-BBs | SS_MB-7
Feb 13, 2002 7:30 AM | | Brant,
I'm considering a new custom singlespeed 'cross/fixed-gear frame with the Phil Wood flip/flop fixed/free rear hub. I'm also thinking of using an eccentric bottom bracket and vertical dropouts instead of horizontal dropouts. Although the frame will not be using discs (although, I did think about using Avid road discs), I believe the e-BB solution still offers several key advantages:
1 - no need to adjust the brakes with chain stretch or gear ratio changes; and
2 - no chance of rear wheel slippage in the dropout under heavy torque.
I noticed on your Il Pompino, that you are using a set of BMX chain-tugs to prevent wheel slippage.
But, I am wondering about the effective BB height. Since I'll be using this bike as a fixed-gear, the BB height is critical during high-speed turns -- whack a pedal and you get launched! With the e-BB and for a given chain-length, there are 2 positions the e-BB can be in within the shell: one high and one low. Obviously, the higher location will provide more ground clearance, but will it affect stability. The lower position would provide increased stability, but will there be enough groud clearance.
So, have you thought about using an e-BB on a non-disc singlespeed framesets?
Are there any other issues I should consider?
Ride Hard,
Mike B. |
| I know this was directed to brant but... | vulture
Feb 13, 2002 7:49 AM | | heres my two cents. Dont be afraid to run your bottom bracket on the high side. Common sense calls for a low bb for center of gravity but most of the gravity of a bike/rider is the rider, reasonably high to begin with. Some say that you can comepare it to balancing a broom on you hand, the longer the broom the more stable. One issue Ive noticed with high bb's (Ive ridden from 11 inches to 14.375" with 26" wheels) is seat heighth. Higher the bb higher the saddle. The bike with the 14.375 bb was hard to get on and off. sorry for butting in. |
| Hey, butt out! ;) just kidding, thanks for the info (nm) | SS_MB-7
Feb 13, 2002 7:59 AM | | |
| Few points off the top of my head | Brant
Feb 13, 2002 8:02 AM | | 1) I've never adjusted the brakes to take up chain slack (I don't think)
2) I would be interested to see if fixed put any extra hoopty loads on the e-bb. I wonder if it would tend to try and rotate it a little more than a standard freewheel would.
3) I like high BBs
4) The difference between high a low position is AT THE MOST - half an inch. And is often a lot less.
5) Certainly a much more expensive way of doing things.
I would go with horizontal dropouts and chaintugs I think. Dunno though... you've got me thinking! |
| I told you it would be though provoking.... | SS_MB-7
Feb 13, 2002 9:02 AM | | Now, I'll try and address some of your valid points:
1) I've never adjusted the brakes to take up chain slack (I don't think)
Since I will be using it as a 'cross and fixed gear bike, the difference in gear ratio will be extreme -- 36:18 for 'cross and 50:13 for fixed. Depending on how these fall in the horizontal dropouts, it may or may not require a brake adjustment.
2) I would be interested to see if fixed put any extra hoopty loads on the e-bb. I wonder if it would tend to try and rotate it a little more than a standard freewheel would.
I can't see how it would since, in both instances (fixed or free), you are still exerting the same amount of pedal pressure/torque on the e-BB. I have just over 1 year on my Bushnell e-BB and it hasn't slipped yet.
3) I like high BBs
No comment.
4) The difference between high a low position is AT THE MOST - half an inch. And is often a lot less.
Agreed. But, this could still make a difference in terms of pedal clearance and center of gravity.
5) Certainly a much more expensive way of doing things.
Not really. The only difference is the price of the e-BB (~$50US).
Ride Hard,
Mike B. |
| Pull/push or rather pull/pull | Brant
Feb 13, 2002 9:13 AM | | I worry that the fixed drive MIGHT pull one way under no-load, then the other way under load. Know what I mean... I haven't seen any problems - inspite of me spending a while calculating the optimum position for the bb to be in... |
| Errr.............. | Mike T.
Feb 13, 2002 9:49 AM | | .....you're thinking of using 50/13 for road use? That's a 103" gear!!! Either you're world class and going for the hour record on the track or you're off a touch in your teeth. That gear's good for about 30-35mph (50-60kph) at efficient pedaling speeds.
Also, track racers, even the oh-so-powerful sprinters and kilo guys use regular track ends and they don't pull wheels over. Of course they use track nuts and not puny QR spindles though.
Just a thought. |
| Ya, 50/13! You gotta problem with that MT? ;).... | SS_MB-7
Feb 13, 2002 9:58 AM | | Oops, that should be 50/18 (73.0 gear inch).
Ride Hard,
Mike B. |
| FffweeeeEwwww.............. | Mike T.
Feb 13, 2002 11:13 AM | | ....y'either had me worried or impressed there for a while MB. An hour's ride on the road since I posted (1/2 in a snowstorm) didn't change my thinking - "He's either sump'n else or he pedals slow". |
| i got that 56T-110mm ActionTec Ti ring i been saving... | DeeEight
Feb 13, 2002 5:30 PM | | that should look good on an eventual SS-cyclocross bike. |
| I took some Bushnell e-BB measurements and... | SS_MB-7
Feb 14, 2002 4:47 PM | | I just took some measurements from Bushnell e-BB to determine what the maximum difference is between the upper and lower positions. By my calculations, the difference is 14.0mm (0.55").
For reference, the oversized shell has an inner diameter = 54.5mm. This is also the e-BB outer diameter. At it's lowest point, the centerline axis of the e-BB is 20.25mm from the bottom edge of the oversized shell. Therefore, the difference between the upper and lower positions is:
54.5 - 2(20.25) = 14.0mm.
Ride Hard,
Mike B. |
| A properly bolted on Phil Wood hub won't slip (nm) | BitterChan
Feb 13, 2002 11:24 AM | | |
| Yes, you are probably right.... | SS_MB-7
Feb 13, 2002 12:16 PM | | According to Brent @ Phil Wood when asked about wheel slippage:
"Not with our hubs, arrogant huh? We use a much larger washer made out of stainless along with the oversized endcaps."
So, the slippage might not be an issue, but what about the brake adjustments? By changing from a 36:18 to a 50:18 gear ratio, this will most certainly place the wheel in a different location in the dropout and, therefore, require a brake adjustment. Now, will I be swapping gears so often that brake adjustments will drive me nuts? Hard to say.
Argh! decisions, decisions.
Ride Hard,
Mike B. |
| Do you really need to.... | toothpick
Feb 13, 2002 12:30 PM | | adjust the brakes if you're switching to a fixed gear? I'm just running a front brake on my fixie with a 49/18 and never felt the need for a rear brake. I'd just let the brake pads in place for when you're using a freewheel.
toothpick |
| It depends.... | SS_MB-7
Feb 13, 2002 12:38 PM | | Yes, you are right. Technically, I don't even need a rear brake when riding fixed. But, I'm not about to remove the rear brake when changing applications -- too much hassle.
However, depending on where the rear wheel is with respect to the pads, the brake will likely need adjusting in order to avoid brake-rub, etc. But, as you mentioned, I wouldn't need to worry about alignment -- only that they are clear of the rim and tire. Hmm.
But, then again, I'd likely align the rear brake for emergency stops.
I guess I need to evaluate how often I'll be switching from 'cross to fixed-gear. During the summer, I'll likely stay fixed for training, but during the fall/spring, I'd be toggling back and forth.
Ride Hard,
Mike B. |
| Final solution.... | toothpick
Feb 13, 2002 12:44 PM | | I guess the only thing you can do is get 2 new bikes instead of 1 so you don't need to worry about this. oh the hardships we put up with to ride our bikes.
tooth |
| what chainstay length? | BudhaSlug
Feb 14, 2002 8:05 AM | | I was just thinking that since you know your gearing (50/18 and 36/18 right?), and I imagine you had a chainstay length in mind, you can figure out exactly how much your rear wheel is going to be moving when you flip the wheel over, and this will tell you whether you are going to need to do much, if any brake adjustment. I would suggest grabbing a copy of the fixed innovations software from:
http://www.peak.org/~fixin/fixmeup.html
Its very possible that the difference in positioning will be small enough that it will work without the E-bb.
As to the issue of wheel slipage... don't worry... I've been riding a fixed/free cross bike for over a year now, locking the rear wheel up at 25mph occasionally to avoid getting killed, and my wheel has never slipped a bit. The only thing to watch out for is thick paint on the dropouts... if you can, have the painter just apply a clear coat to protect from rust... something nice and solid though.
The point brant made about different forces on the E-bb from fixed might be true... the fact that your legs are trying to be pushed at an approximately constant rate as they make their way around the pedal stroke might do strange things. I don't know what physics might say, but I do know that climbing on a fixed gear can be done in a very different way than on a freewheeled bike... One of my favorite ways to stretch out while climbing is to lean my entire body forward about 45 degrees... I end up in nearly a standing position, just leaned over. This allows me to spin quite fast without becoming unballanced, but it depends entirely on the fact that the bike is always pushing against me and lifting me up. Hard to explain, very weird to watch or do, but it seems like it might put weird stresses on an E-bb. Locking up the rear wheel to skid also likely puts a good bit of stress there since you effectively stomp down on the cranks while suddenly reducing their speed... its an effect you can't achieve on a freewheeled bike... kinda like the force you would put on the BB if you could accelerate from 0 to 20mph instantly.
So who are you going to have build it? I'm currently riding a surly cross check, but when I get the money together I'll be replacing the frame with something nice and custom... just haven't really decided on who since there are so many good/great builders around (Right now the list includes curtlo, kelly, true north, TET, Igleheart (I have a great road from from him), etc, etc).
Peace and Light,
Ben |
| Ya, I thought of that, but... | SS_MB-7
Feb 14, 2002 8:51 AM | | That is an excellent idea, and I had thought of that, however, my gear selection is not necessarily limited to 50/18 and 36/18. Depending on the terrain, I may opt for a slightly harder/easier gear ratio. Without some form of chain tension, this would not be possible.
I'm going to have a local builder (True North Cycles) design and build the frame/fork. It was a toss-up between True North and Curtlo. Both are very keen to build this frame, but I opted to stay local. Doug Curtiss (Curtlo) is a great guy and I wouldn't hesitate ordering from him. Just read the reviews!
I've read very mixed reviews about TET -- some very good, others very, very bad. With such favourable reviews of True North and Curtlo, I went with the sure-things.
With regards to brake adjusting, since you ride both fixed/free, do you find this to be a pain-in-the-ass? What are the two gear ratios you use for fixed and free?
Ride Hard,
Mike B. |
| RE: Ya, I thought of that, but... | BudhaSlug
Feb 14, 2002 11:01 AM | | With the fixed innovations website I wasn't suggesting that you go with vertical dropouts and a standard bb... I was suggesting that you could figure out what pairs of fixed/free combos you would be easily able to run without adjusting the brakes if you decided on horizontal drops. You'd still be able to run any other combos as usual, but they might involve brake adjustment.
True north is near toronto right? Thats almost local to me (close as I'm likely to find since I'm in Rochester, NY). I've seen some of the pics you've posted of Hugh's work, and it really is beautiful stuff. As to gearing, my current is 42/16 fixed and 42/18 free. I'm going to be getting a 20t freewheel when I get around to it (during the winter its all fixed gear for me). I don't really use it much for trail use or as a SS, although occasionally, and the 42/18 has been too high for real trails. The 42/16 is great for long rides and commuting, but I've also got a 46t which is good for short sprint rides (10mile fun time trials), and for use with the 18t freewheel when my knees aren't in the mood for fixed.
I really don't flip the wheel around all the time, and so brake adjustment hasn't been much of an issue. I've found that with the 42/16-18 I've been able to get one brake set up that works for both... just sorta place it inbetween. Plus I'm using some old Onza cantilevers (Dan's Comp BMX store online for $10/set!!!) which are about as simple and quick to adjust as you can get, so its not much of an issue at all even if I did have to adjust when I flipped the wheel.
I hadn't really thought about doing an E-bb until recently. Since you are going to be riding it both road and cross, fixed/free, assuming the E-bb isn't really a potential problem for fixed, it might be a great idea to go with it, especially if you can get hugh to really think through the geometry and set it up so that you effectively get two slightly different geometries depending if you are setting it up for road or cross/ fixed or free (i.e. it would be tuned a bit towards cross with the E-bb in one position (lower, further forward maybe) and tuned a bit more for road when its in the other position (higher, further back maybe). I imagine the effective differences are only about 1/2" and at most 1/2deg, but its something that might actually be nice if its carefully planned. If you really go with this idea, you might even want to go with something that seems odd at first, an E-BB and horizontal dropouts... you use the E-bb for geometry adjustment, and possibly for tension, and the horizontals to adjust chainstay length, and complement the E-bb (I'm just babbling here, its probably more trouble than its worth, but its a thought).
When you get it built, you should take a ride cross the border and come down to rochester (not that there is actually anything to see here, and little good riding).
Peace and Light,
Ben |
| Yes, True North is just outside Toronto... | SS_MB-7
Feb 14, 2002 11:48 AM | | Ya, True North is in Kitchener which is just outside Toronto.
Ah, now I see what you mean wrt the fixed innovations. And, in looking at the results for a vertical dropout and 50x18 and 36x18 gearing, the difference is only 0.3cm in chainstay length. I'd imagine this would not require to much brake adjusting.
Ya, I've seen Hugh's work first-hand (several of my racing buddies have True North's) and they are gorgeous! The pictures don't really do his frames justice.
Hugh and I are only just beginning the designing phase. Still much to decide.
Ya, I could be up for a road ride across the border come spring/summer. I'll meet at the border ;)
Ride Hard,
Mike B. |
| 50x18, chainstay = 42.7cm & 36x18, chainstay = 42.4cm | SS_MB-7
Feb 14, 2002 10:08 AM | | According to the FixMeUp program with vertical dropouts, 50x18 will require a 42.7cm chainstay length and 36x18 will require a 42.4cm chainstay length.
Ride Hard,
Mike B. |
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