Frame Geometry Abbreviations

[BrumbyJack]

OK, some of them are obvious, some of the manufacturers give you a diagram/key, some of them tell you SFA!!!!

Here is a list, if I'm wrong please let me know and otherwise, can you help fill in the blanks please???

HA = Head Angle

SA = Seatpost angle

WB = Wheelbase (hope they all measure it centre to centre).

CS = Chainstay length???

Effective Top tube, Actual Top Tube and horizontal Top Tube, TTT all a similar thing, but I don't think they are comparing apples with apples???

BB = Bottom bracket height from the ground???

ST = Seat Tube??? ala measuring an XC bike frame????

What else do you need to check???

Here are some I have no idea... all Norco

FC = ???

RC = ???

HT = Height?? if so where?? I'm guessing standover.

FL = ???

RWT A = ???

RWT B = ???


Cannondale give a nice diagram and so many measurements it is confusing.

Norco give heaps of measurments, but NFI what most of them are.

IronHorse don't give many measurements, but I know what they are.

Some bikes SA and HA are the same, some are different, what difference does that make?? I know smaller SA puts your weight further back.

Head Angle, 66 deg or 67 deg.... which is best for DH and why???? and does 1deg make much difference??

So many questions... so much of a headache

 

[Daver]

HT would be HeadTube length?

 

[anthonyma]

FC = ???

RC = ???

HT = Height?? if so where?? I'm guessing standover.

FL = ???

RWT A = ???

RWT B = ???

FC - Front Center - horizontal distance from BB to front axle. Obviously changes with fork length.

RC - Rear Center - horizontal distance from BB to rear axle.

HT - Head Tube length.

FL - Fork Length.

RWT A/B - Rear Wheel Travel in different shock positions.

Head Angle, 66 deg or 67 deg.... which is best for DH and why???? and does 1deg make much difference??

I doubt too many people can categorically state that they can discern a 1 degree difference, as they probably haven't ridden 2 bikes that are identical except for that 1 change.

There are a number of factors to be considered in a frame design, and many of them have an effect on each other. For example, head angle has an effect on wheelbase. Shorter riders would probably prefer a really short top-tube, but then a steeper head angle will result in either long chainstays or short wheelbase, so they would prefer a slacker head angle. Ultra-tall riders might prefer a slightly steeper head angle to keep the wheelbase manageable lest the bike become a bit of a barge to turn.

Unfortunately it isn't quite as simple as 1 figure for 1 measurement being better than another, you have to consider the design as a whole. But, if you want to generalise, the trend seems to be moving more towards slacker head angles (possibly to compensate for the longer-travel forks to a certain extent).

 

[BrumbyJack]

Does slacker mean more upright, or more sloping back??? That is one of the things that is confusing me.... angles I can cope with, jargon confuses me.

 

[Carlin]

Slack is opposite to steep;

So therefore: slack is more laidback than steep.

 

[Dirt Devil]

Does slacker mean more upright, or more sloping back??? That is one of the things that is confusing me.... angles I can cope with, jargon confuses me.

DH bikes = slack. Better at high speed and in the steep stuff.
DJ/Park bikes = steep. Turns on a dime but can get a bit twitchy at speed.

 

[Dirt Devil]

Effective Top tube, Actual Top Tube and horizontal Top Tube, TTT all a similar thing, but I don't think they are comparing apples with apples???

As far as I know, the Effective top tube and Theoretical top tube (TTT) are the same thing. Imagine if you had the seatpost right up... run a horizontal line from the centre of the headtube (at the top) to the centre of the seatpost, this distace is the TTT. The actual top tube length is measured the same way but along the frame (not horizontally).

 

[BrumbyJack]

Thank you everyone

 

[bradh]

'Effective Top Tube', 'Theoretical Top Tube' and 'Horizontal Top Tube' indeed all refer to the same measurement, which Dirt Devil explained, and all are opposed to the Actual Top Tube measurement, which is measured centre-to-centre, and should otherwise be pretty self-explanatory.

Oh, also: Norco's 'RC' = everyone else's 'CS'.