I've been looking at some bikes on the interweb. Head angle figures are always put up but how are these actually measured? is there a standard or are they all measured differently – what I mean is when it says 68.5degs, one brand could mean with a 100mm fork and another could mean with a 130mm fork. If so how do you compare?

Some firms (ragley for one) will tell you how the head angle is calced – with a typical fork of X travel and Y% sag.

Some others give unsagged static figures, which are pretty pointless for comparision purposes.

Usually the manufacturer will specify the fork and/or axle-crown measurement that the angle presumes. They should also state whether it's taken sagged or unsagged. The angle is useless without this information, and it is rather annoying when so many places don't give you all the details.

And even then they're often not what you get in real life. A few of the mags do their own measurements and they're always different to the manufacturers published figures.

What tron and pedalhead said.

I've ridden on bikes with a "70 degree" head angle before that felt slack, and ones with a "68 degree" HA that felt steep. The problem is there is no real standard as such, just some manufacturers measurements are more reliable/appropriate than others.

If it's a BFe you're referring to, I'm of the opinion the way Cotic measure their geometry is pretty accurate and paints a good picture.

the diameter of the tyres, headset cup height e.t.c will all have a bearing on the measurement too.

It makes a mockery of the whole HA calculation thing then.

Mboy – it is but also wanted to compare it to the Bottlerocket I rode the other night as that was very different.

AAGH! can of worms HT V FS comparison, factor in rear sag too 😯 😯

badly?

it should be clear if it's sagged or static, and with what fork, but forks vary by 10mm between brands so there's 1/2 a degree variance.

add in the fact that framebuild tolerances mean batches can vary by up to half a degree and it does make a bit of a mockery of HA obsessions.

I've seen mags test quote 4 or 5 bikes in a test (one of ours was included) and there was no mention of how they measured them – if they actually did. the figs varies a lot from what they should be and our bike was said to feel nicely slack, but they listed it as 70 degrees – and a better ride than a bike that was listed as 68-69 from memory.

it's hard to use printed HA figs to compare bikes between brands unless you know what fork length the angle was measured at, not just the travel. fork length cancells out brand variations, so what you need is "68 degrees at 520mm" etc to make comparisons.
weight distribution and front-centre also affect the handling feel in a similar way as head angle but no-one seems mentions that very often, basically it's all interlinked so you need to ride or measure the bike to really tell and that's the tricky part.

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

Does this make it rocket science then?

Yup it's Bottlerocket science…. 😀

http://www.dirtrider.com/tech/141_0908_tech_tips_motorcycle_rake_and_trail/index.html