Singlespeed & Fixed Gear - A spacer between the fork and headtube to allow barspins - true?

I'll preface this with a few things. I can't nor do I want to be able to do barspins, this is to settle a debate over whether such a piece exists. And I know that if a piece did exist, it would probably weaken the whole system. THAT BEING SAID: Is there such a spacer? All these people complain about wanting to do barspins, and it seems that going to a 650 wheel is not as easy as putting a 1" spacer in the system somewhere, maybe between the crown and the race?

Yes, it exists.

Stupidest **** ever.

Serotta used to make this thing called a "heads up" that went between the top of the headtube and the top parts of the HS to reduce stack height when using a threadless set-up. And, I think some companies copied this. Is there any reason something like that couldn't just be stuck on the bottom instead of the top?

But, before this turns into an argument over bar spins vs no bar spins, if your already putting a spacer and such in to virtually change the axel/crown length, it would probably just be easier to get a MTB fork that has a similar measurement...and that's what most people seem to be doing now.

Serotta used to make this thing called a "heads up" that went between the top of the headtube and the top parts of the HS to reduce stack height when using a threadless set-up.
...
Is there any reason something like that couldn't just be stuck on the bottom instead of the top?

Not used to-- they still do.
And yes, the heads-up is widely used at the bottom.
a simple spacer probably wouldn't work nearly as well; the heads-up is pressed into the bottom of the steer tube, and the bottom bb cup pressed into it.
that said, keep in mind that the piece is machined from titanium, not steel. it's being used successfully by trek y-foil owners to switch from the stock fork to newer forks, but riding in a triathlon is not the same as riding freestyle.
does it work?
yes.
can it hold up to a six step drop?
not sure. simple barspins and coming down from wheelies most likely won't be an issue.
i have the 1" one and it seems beefy enough for that.
http://www.serotta.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=SCB&Product_Code=HEADSUP&Category_Code=SSAMP

ed: i just looked at that link. looks like it's made from aluminum now, not ti. not sure if that means it's weaker...
kinda wack that they switched from titanium to aluminum but kept the price the same.

ahh ahh!! he said the "B" word!!! cover your ears!! earmuffs!! earmuffs!!

http://www.carytownbicyclecompany.com/images/headsup1.jpg
http://www.carytownbicyclecompany.com/images/headsup2.jpg
http://www.carytownbicyclecompany.com/images/headsup3.jpg

What's the height of the extension? I guess you don't have a "track geometry" frame anymore if you use it on a track bike.

nope. nor do you have a "track geometry" frame if you use 650c wheels on a 700c frame.
i don't think "track geometry" is the priority here, though...

the extension is, as per the above link, 20mm.

^ I was being cynical. Kids these days are buying crappy frames to have a "track bike," but if you add this, you have something more along the lines of a classic road bike with track ends. Yeah, I know, the geometry will still be different and the fork will still have less rake, but you know what I am talking about.

Thanks for the info on the extension height.

if barspins with 700c are important to you just get a rigid dirt jumping mtb fork...

http://farm4.static.flickr.com/3101/2864469444_2c6690661b_b.jpg

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sounds cool, but I like having the top bar on my bike parallel with the ground, not tilted upwards. Could work well on those road frames that are sloped down though.

^
fail.

sounds cool, but I like having the top bar on my bike parallel with the ground, not tilted upwards. Could work well on those road frames that are sloped down though.

no.

What the dicks

if barspins with 700c are important to you just get a rigid dirt jumping mtb fork...

http://farm4.static.flickr.com/3101/2864469444_2c6690661b_b.jpg

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I want to say that bike is dumb, but I love it.