Ride UK Tech Columns

#58 Euro/USA Bottom Brackets

(This article first appeared in Ride UK issue No. 58 and is reproduced here by kind permission of Ride UK.)

BMX is a great big multi headed hydra of a beast. Rearing up on ugly great legs with lots of heads to snap at you and lots of tails to whack you round the face as you try to retrieve the golden fleece of freestyle….

OK, maybe not, I never was very good with metaphors; what I was working up to in my very laboured way, is that there are many, many strands to BMX these days. We have magazines, videos and websites; street, dirt, park, ramps and flat; there are multi-million dollar training camps and skateparks; shoes and clothes.
Most of these get their fair share of coverage but what about the actual bike you ride?
It has never been very “cool” to spend too much time thinking about your bike but surely it is crucial to your daily ride? None of us would like to go back to the bikes of the ‘80s, at least not for serious riding. Can you see Stephen Murray doing a double back-flip on a super-burner?
Technology has come on a fair bit in 20 years but we had to dodge some bullets in there too. Answer suspension forks anyone?
As long as BMX is big, and lets face it, it IS big now, there will be a businessman seeing a profit to be made. Just because a businessman is also a rider doesn’t mean that everything they say should be taken as gospel.
The aim of this column is to discuss some new and coming innovations that may be on your next bike, and to see if they are genuine improvement or a marketing gimmick. I say discuss because there are two sides to every argument, as far as possible I will try to present the case for and against with balance. But bear in mind that I am just another rider trying to screw a few quid out of the kids…..

The obvious target for the first column is the heated controversy that surrounds European bottom brackets.
First; some background.
A long long time ago before freestyle was invented all bicycles were different. A lot of them were French and had one big wheel and one little wheel. These pennyfarthings never had a bottom bracket, instead the forks had a “bearing” at the bottom of each leg for the hub to run in with a crank arm on the end. Very simple, no balls and lets face it, not very good. Eventually people got sick of smashing the shit out of their faces from 10 feet up whenever they stopped or hit a stone so the “safety” bicycle evolved. Every manufacturer had their own way of doing things so there were no standard parts.
Manufacturers sought refinements that they could make to put their product ahead of the pack so they started using ball bearings instead of a brass bush and pneumatic tyres etc.

Slowly a standard started to emerge for bottom brackets, a tube approx. 3” long with an inside diameter of just under an inch and a half. Unfortunately there was still a lot of incompatibility, the French, British and Italians all had different threads and you had to get the right cup for your frame.
Over the years a standard did eventually emerge and today all road and mountain bikes use a bottom bracket which is threaded internally, one and three eighths inch diameter and 24 threads per inch, strangely enough the same thread that a normal 16tooth freewheel uses. It still comes in two sizes, 68 or 73 millimeters wide, though.
THIS is the Euro BB that is causing so much controversy.
At some point a bike manufacturer realised that cranks were one of the most expensive parts of a bike to make. Highly loaded in multiple modes of bending and torsion they needed to be made in several parts and the parts needed to be quite accurately made. So, some bright spark came up with the idea of making the whole caboodle in one bit. Just forge a single bent piece of steel to act as crank arms and spindle. Trouble is it would never fit through the small bottom bracket shell of a normal frame. The obvious solution was to make a whopping great big one that it would fit through. The cash rolled in and the standard became common, common enough that when the pioneers of BMX were building the first bikes they adopted it for convenience.

One of the most technologically competitive areas of BMX has always been the very young racers’ bikes. Whilst a few ounces extra on the weight of the bike doesn’t make that much difference to a big racer weighing 150lbs, it can be crucial to a young 50lb sprog, and more importantly his dad! It may just be my biased and cynical view, but I am guessing that a lot of proud dads watched their kids come second week after week at the local track and desperately wanted to help. Whatever the truth, in their search for the winning edge the little guys bikes became far more “techno” than their full size counterparts. Aluminium, titanium and carbon fibre were soon commonplace on the little guys bikes, saving weight and in little danger of breaking under such little riders doing such small jumps they soon gained popularity, as did the small european bottom brackets. It seems that the few ounces they saved were crucial to many dads’ dreams of glory.

In the last year or so there has been an undercurrent of dissatisfaction in our neck of the woods. Some riders have started thinking that their 40 pound street bikes are a little on the heavy side. Its pretty understandable, as someone who has had a peg half way through his right hand when his bike landed on it from 4 feet I too wouldn’t mind loosing the odd pound off mine. 8 pound frames have lost popularity, 6 or 7 is much more acceptable, people are switching to 36 spoke wheels to save a measly 2 ounces worth of spokes despite the huge loss of strength, and sleeved pegs can save you a few more ounces for as long as they last. 
I guess it was only a matter of time before someone looked at the whole crank and bottom bracket area. With Profile cranks now pretty popular with mountain bikers, you can buy cups to fit either Euro or BMX bottom brackets. The BMX version most of us use weighs 6.8 ounces while the Euro version weighs 4.6 ounces.
Look at the shell as well and while a 2.5mm thick BMX bottom bracket shell weighs 7.7 ounces a Euro shell 2.5mm thick weighs just 5.4 ounces.

So by switching to the new standard you can keep your standard Profile cranks and still save 4.5 ounces, just over a quarter of a pound. Many frames have super thick bottom bracket shells so the savings could well be even more. Add to that the fact that the cups are calmly and smoothly screwed into the frame like a precise ballet of precision technology (rather than being belted in with a hammer), then locked in place at the correct position with a lock-ring; and it looks even more attractive.

So, that’s that then yes? We should all rush to adopt the new standard as soon as possible? Maybe not. Let’s look a little deeper.

Some of the kids that used euro bottom brackets on their mini-racers have grown-up by now and are still racing. Presumably they all took the technology with them for that vital edge in weight on their full size bikes? NO!? Why on earth not? They could be saving a quarter of a pound off the weight of their bike! Surely that’s an edge they want?
It seems that the majority of pro-racers don’t think that a Euro bottom bracket is good enough for them to race on! They complain of a less stiff frame amongst other things.

So what are the drawbacks?
Well a euro bottom bracket has an inside diameter of just 35mm compared to a BMX bottom bracket inside diameter of about 50mm. Into that space we need to fit an axle and bearings. A normal Profile axle is ¾”  (19mm) diameter, so with a euro bottom bracket we have a gap of 8mm to fit the bearing and that nice adjustable threaded cup into. Not surprisingly there is a distinct shortage of bearings, to suit this tight gap, ‘off the shelf’, so manufacturers are forced to get ‘specials’ made up. These specials are typically rated at around 250kg of force. This is pretty inadequate so the usual solution is to put in twice as many.
The BMX bottom bracket has no such problems. A normal profile spindle sits in there with over 15mm gap each side of the spindle, into which you can fit a whole range of standard ‘off the shelf’ bearings. The R12 which is typically used can take a load of nearly 500kg of force so only one pair is needed.
Still, this is no big problem is it? 4 special bearings instead of two common ones; big deal, we have saved a lot of weight and lost nothing except a little extra cost and maybe gained a bit more friction?

Well, yes you have, as long as normal Profiles are strong enough for you. Speaking personally they aren’t strong enough for me. Even with a very good build quality and one of the strongest materials available, I tend to twist spindles. So years ago I stopped using standard Profiles, which are after all, designed for race use. For people like me who have broken the standard version, Profile makes SS cranks. With a 7/8” (22mm) spindle and big fat arms, SS Profiles should be able to take anything. It is even possible to fit these monsters through the euro bottom bracket, but with only 6.5mm for the bearing and cup things are looking a little dodgy.
Add to that the fact that if you NEED SS cranks you are probably putting some big forces through those bearings at times, and you have a few problems on the horizon.

OK so lets assume you are a smooth rider who is quite happy with normal Profiles, the euro bottom bracket is still an attractive option right? Well maybe,
IF you like working on your bike and are happy to buy the right tools.
Happily euro bottom bracket cups seem to have moved to a standard spline-drive. Simply insert the special splined tool into the recess in the cup and screw it in or out. The left hand cup is a normal right hand thread and the right hand is left handed. Like pedals but opposite.
Sounds sweet, much more satisfactory to the mechanic than wailing away with a hammer or bunging everything in a vice. Once the cups are in place you just set the bearing cups at the right spacing and lock them in place with the lock-ring. This position needs to be spot on or you risk overloading the bearings, and of course lock-rings never cause any problems or come loose as we all remember from threaded headsets and one-piece cranks.
Trouble really starts after a few months or years use. Suppose you have bashed your bottom bracket on the odd grind, any damage will have deformed the threads quite considerably and they may be seized. With luck you will be able to get it out and take the frame along to a local shop to have the threads cleared out with the special taps.
If you simply try to tighten it back in you risk cross-threading and rendering the frame completely useless.
Wailing on the cups with a hammer suddenly looks quite attractive.

Finally, what of the future? Personally I like the idea of saving some more weight, so surely the Euro bottom bracket is bound to be good in the long run? We can look forward to needle roller bearings and other innovations making it practical for everyone cant we?
Well yes, maybe we can, but what could be done if we stayed with the BMX bottom bracket? With all that space to play with, it is only a matter of time before we move to a bigger hollow spindle. In the same way that 1,1/8” aheadsets allowed us to have lighter and stronger forks, a 25 or 30mm crank spindle would let us have cranks far stronger than those available today for less weight. Bottom bracket shells can be much thinner if they don’t need threads on the inside, my current fame has the bottom bracket shell from an old Hutch trickstar, just 1.6mm thick, it only weighs 5 ounces and has stood up fine for the last 3 years. By sticking with the BMX bottom bracket, we could, quite simply, have our cake and eat it.

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