Ride UK Tech Columns
#58 Euro/USA Bottom
(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
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
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
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
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
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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