Author Topic: BMX  (Read 7417 times)

John Henry

BMX
« on: August 08, 2012, 08:31:47 pm »
We should probably have a thread about it, shouldn't we?

I miss the individual pursuit, but I must admit that of all the cycling disciplines I've watched this Olympics, the BMX is the one which I'd most like to have a go at myself rather than watching other people do. It did look fun.

Anyway, apparently our people have made a 'solid start' according to the BBC.

Re: BMX
« Reply #1 on: August 08, 2012, 08:44:31 pm »
I watched it.  Out of all the events we applied for, and didn't get a single ticket, I was most disappointed to miss this.
This afternoon was the seeding runs, an individual time trial on the track to determine which heat you go in and gives you a practice.

Shanaze Read is 5th and Liam Phillips is 12th.  Seeding is done to keep the fastest riders apart until the final.

So, off to a good start but the racing has to start properly yet.  A woman crashed out in their event and a man crashed out in theirs.  The racing is an entirely different prospect to the seeding runs as you can't necessarily choose the line you want as there is another rider in the way!

Should be good, like ski cross in the Winter Games! :)

Re: BMX
« Reply #2 on: August 08, 2012, 09:06:04 pm »
I watched some of it and it was cool. Would love to have a go!

Interesting seeing just how much difference riding the bumps smoothly makes to a time. Unfortunate really, as I'd like to see them getting maximum air and showing off in general  :P
Those wonderful norks are never far from my thoughts, oh yeah!

Re: BMX
« Reply #3 on: August 08, 2012, 09:13:29 pm »
really enjoyed it but why are the bikes geared so low? Some of them looked like they were spinning a bit high

Re: BMX
« Reply #4 on: August 08, 2012, 09:32:27 pm »
I don't know, but I know they spend an awful lot of their training time purely on improving their pedalling. One would assume at this level they do more than just slap on some random gear!
Those wonderful norks are never far from my thoughts, oh yeah!

LittleWheelsandBig

  • Whimsy Rider
Re: BMX
« Reply #5 on: August 08, 2012, 09:38:12 pm »
I used (2 decades ago) to work with a bloke who'd won the BMX world champs a couple of years before. Spinning 180mm cranks at 200 rpm while standing up seems to be essential to win, though I don't know why. It was hard enough to get him to try SPDs.

I'm always impressed how they start pedalling while both wheels are off the ground. I've never been able to do that.
Wheel meet again, don't know where, don't know when...

John Henry

Re: BMX
« Reply #6 on: August 08, 2012, 09:39:06 pm »
really enjoyed it but why are the bikes geared so low? Some of them looked like they were spinning a bit high
I've just looked at the UCI roolbook for gnarly BMX action. No rule on max gear ratio, and in fact multiple gear systems are allowed. But they seem to prefer to spin.

citoyen

  • Cat 6 Racer
BMX
« Reply #7 on: August 08, 2012, 09:55:21 pm »
I may be wrong but I thought smaller chainrings were preferred for reasons of clearance. Lower gearing would be a side effect of that.

d.

John Henry

Re: BMX
« Reply #8 on: August 08, 2012, 09:56:57 pm »
I may be wrong but I thought smaller chainrings were preferred for reasons of clearance. Lower gearing would be a side effect of that.

I just had the same thought. I suppose there's going to be a minimum feasible size of sprocket, a maximum practical size of chainring, and hub gears probably aren't the thing... so your gear is limited and spinning it is.

Re: BMX
« Reply #9 on: August 08, 2012, 09:58:02 pm »
I may be wrong but I thought smaller chainrings were preferred for reasons of clearance. Lower gearing would be a side effect of that.

d.


I think you can go right down to a 9 tooth sprocket on modern BMXs with cassette style hubs, so they should be able to get a reasonably high gear (if they wanted one) with a fairly small chain ring...

Edit: It's 8. And the smallest available chainrings are 22. So by my reconing that's about 55"

Edit 2: Actually nearer 60"
Those wonderful norks are never far from my thoughts, oh yeah!

Re: BMX
« Reply #10 on: August 08, 2012, 10:07:34 pm »
Some Googling turns up that 43/16 or 46/17 is pretty common - so not a small ring at all really...

More here



Those wonderful norks are never far from my thoughts, oh yeah!

citoyen

  • Cat 6 Racer
BMX
« Reply #11 on: August 08, 2012, 10:17:52 pm »
Ah, thanks for that, bobb. So the low gear is for fast acceleration out of the gate. Makes sense.

d.

citoyen

  • Cat 6 Racer
BMX
« Reply #12 on: August 08, 2012, 10:28:39 pm »
Thinking about it, the small chainring thing might be for freestyle bikes. My son's BMX has a tiny chainring and one of those silly 8t sprockets. It's mechanically quite interesting - the sprocket is built into the outside of the freewheel mechanism. I'd never seen anything like it before he got that bike.

d.

Wowbagger

  • Dez's butler
    • Musings of a Gentleman Cyclist
Re: BMX
« Reply #13 on: August 08, 2012, 10:34:08 pm »
I saw both the crashes and they made me wince horribly. Exciting stuff, but it doesn't appeal to me as something I'd ever want to do.
Eating's a serious business. Don't bollocks around wagging your tail.

citoyen

  • Cat 6 Racer
Re: BMX
« Reply #14 on: August 08, 2012, 10:48:39 pm »
The thing that really made me wince was not the crashes we saw today but when they mentioned that one of the first choice American women had to pull out before the games started because of a "lacerated liver".

 :sick:

d.

Re: BMX
« Reply #15 on: August 09, 2012, 08:23:54 am »
Fingers crossed for Shazza. Her seeding time was very disappointing - nearly a second off the leaders. She won't be happy with that. 
<i>Marmite slave</i>

Re: BMX
« Reply #16 on: August 09, 2012, 11:50:01 am »
Shanaze always does better in the races than the seeding runs, so don't panic yet!

The small gear is for sprinting out of the gate as mentioned above.  BMXers get most of their speed by pumping the bumps and practise on specially designed "pump tracks", which are basically a loop of bumps where the aim is to get round as many times as possible without pedalling.  A quick Google will turn up quite a few videos.

I enjoy watching BMX but I don't have the cojones to do it.  The spinning power BMXers have translates well to the track: Jamie Staff started in BMX and Shanaze has been known to partner Vicky P. in team sprints.

Re: BMX
« Reply #17 on: August 09, 2012, 03:08:43 pm »
On commentary just now, Ed Leigh said "We've had a lot of tweets about the gearing of these bikes...." then Jamie interrupted him and nothing more has been said on the matter!

Ha! Last heat the entire field went down except for one rider!
Those wonderful norks are never far from my thoughts, oh yeah!

tiermat

  • According to Jane, I'm a Unisex SpaceAdmin
Re: BMX
« Reply #18 on: August 09, 2012, 03:19:31 pm »
Lots of crashes in today's semis, the latest (I think) lost 7 of the riders on the first bend, only the race leader at that point avoided it....
I feel like Captain Kirk, on a brand new planet every day, a little like King Kong on top of the Empire State

Re: BMX
« Reply #19 on: August 09, 2012, 03:39:15 pm »
Quarters today, but yeah - it's carnage.  And why they do 3 runs, rather than 1 :)

Regulator

  • That's Councillor Regulator to you...
Re: BMX
« Reply #20 on: August 09, 2012, 03:53:51 pm »
Can I commit heresy and suggest that BMX is a prime candidate for this thread?

Quote from: clarion
I completely agree with Reg.

Green Party Councillor

tiermat

  • According to Jane, I'm a Unisex SpaceAdmin
Re: BMX
« Reply #21 on: August 09, 2012, 03:56:58 pm »
The favourite, a Kiwi, is out, he has just been carried off the track, for some reason he came over a bump and just appeared to throw his bike away!
I feel like Captain Kirk, on a brand new planet every day, a little like King Kong on top of the Empire State

Re: BMX
« Reply #22 on: August 09, 2012, 04:01:05 pm »
Can I commit heresy and suggest that BMX is a prime candidate for this thread?

If you must. Miserable old git  :P
Those wonderful norks are never far from my thoughts, oh yeah!

tiermat

  • According to Jane, I'm a Unisex SpaceAdmin
Re: BMX
« Reply #23 on: August 09, 2012, 04:01:48 pm »
Oh, hang on, the Kiwi is back, lets see if he throws his bike away again :D
I feel like Captain Kirk, on a brand new planet every day, a little like King Kong on top of the Empire State

Wowbagger

  • Dez's butler
    • Musings of a Gentleman Cyclist
Re: BMX
« Reply #24 on: August 09, 2012, 04:02:39 pm »
Can I commit heresy and suggest that BMX is a prime candidate for this thread?

The more I watch it the more I think it's an excellent olympic sport.

It's accessible in that loads of kids have BMX bikes and many towns have purpose-build obstacle courses.

It seems as though it's the one olympic event with greatest chance of personal injury.

It's exciting to watch.
Eating's a serious business. Don't bollocks around wagging your tail.