Measuring seat angle - correct tool?

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landsurfer
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Re: Measuring seat angle - correct tool?

Postby landsurfer » 27 Aug 2017, 4:56pm

I level it up by eye.
If its uncomfortable then I move it until it's not ....
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brynpoeth
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Re: Measuring seat angle - correct tool?

Postby brynpoeth » 27 Aug 2017, 5:04pm

Heath Robinson machines, or Dr Edywilly?

I saw an article somewhere about several simple machines that are simply gr8: block + tackle, archimedian screw, the rollers used to move the Stonehenge stones, plumb line... Why, Leonardo da Vinci sketched something very like a cycle..

Why do you want to determine the angles (head tube too?), how accurately, what will you do with the information?
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horizon
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Re: Measuring seat angle - correct tool?

Postby horizon » 27 Aug 2017, 7:22pm

brynpoeth wrote:Why do you want to determine the angles (head tube too?), how accurately, what will you do with the information?


Only the seat tube angle really. This allows you to calculate reach. Without the seat angle, the top tube length is meaningless as they just move the seat tube backwards and forwards.
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Brucey
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Re: Measuring seat angle - correct tool?

Postby Brucey » 27 Aug 2017, 7:37pm

there seem to be two sorts of person reading this thread

1) those who think that this has something to do with the tilt angle of the saddle

and

2) those who think it has something to do with the angle of the seat tube

I'm in the latter camp.

If you are interested in saddle setback, just drop the plumbline through the BB centre and mark the intercept with the top tube. Turn the bike 180 degrees and repeat. If the mark is in a different place then the floor wasn't quite flat and the average position Is correct. Measure backwards and forwards, sighting through the mark and the BB.

You can work out the seat tube angle but really there isn't much point provided you are comfy and the forward reach is known.

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horizon
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Re: Measuring seat angle - correct tool?

Postby horizon » 27 Aug 2017, 8:35pm

Brucey wrote:
I'm in the latter camp.



Me too.
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robc02
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Re: Measuring seat angle - correct tool?

Postby robc02 » 27 Aug 2017, 8:37pm

I'm also in the latter camp.

You can work out the seat tube angle but really there isn't much point provided you are comfy and the forward reach is known.


That's true, but it is very useful to know the seat angle of your favourite frame when looking for a replacement or N+1.

reohn2
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Re: Measuring seat angle - correct tool?

Postby reohn2 » 27 Aug 2017, 8:39pm

horizon wrote:
Brucey wrote:
I'm in the latter camp.



Me too.

And me
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Gattonero
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Re: Measuring seat angle - correct tool?

Postby Gattonero » 27 Aug 2017, 8:47pm

Interesting picture from american framebuilder R. Sachs. He doesn't seem to care about the seat angle at all, rather the seatback as paramount.

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tooley92
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Re: Measuring seat angle - correct tool?

Postby tooley92 » 27 Aug 2017, 8:49pm

For iPhone users go on the compass app and swipe right, this turns your iPhone into a very useful spirit level and inclinometer.
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horizon
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Re: Measuring seat angle - correct tool?

Postby horizon » 27 Aug 2017, 8:53pm

Gattonero wrote:Interesting picture from american framebuilder R. Sachs. He doesn't seem to care about the seat angle at all, rather the seatback as paramount.



The seat angle doesn't matter at all - you just move the seat forwards and backwards (within reason). But the length of the top tube does matter - it determines how far forward you have to reach to the bars. Again, you can alter the length of the stem but there are limits to this. But you don't know the real length of the top tube (whatever the brochure says or what you measure) unless the seat angle is known as well.
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horizon
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Re: Measuring seat angle - correct tool?

Postby horizon » 27 Aug 2017, 8:55pm

Brucey wrote:
You can work out the seat tube angle but really there isn't much point provided you are comfy and the forward reach is known.



Which I am not and it isn't.
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531colin
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Re: Measuring seat angle - correct tool?

Postby 531colin » 27 Aug 2017, 9:15pm

Gattonero wrote:Interesting picture from american framebuilder R. Sachs. He doesn't seem to care about the seat angle at all, rather the seatback as paramount.....

You can't buy lugs unless you know the angle.

Brucey
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Re: Measuring seat angle - correct tool?

Postby Brucey » 27 Aug 2017, 9:51pm

horizon wrote:
Brucey wrote:
You can work out the seat tube angle but really there isn't much point provided you are comfy and the forward reach is known.



Which I am not and it isn't.


Having marked the 'centre' of the TT above the BB as suggested, the forward reach can be known, without knowing the exact seat angle per se.

I happen to know that (with my preferred saddle and seat pin) I can't get the saddle in the right place unless the seat angle is 73.5 degrees or less. But I measure it in terms of the saddle nose being so many cm behind the 'centreline' of the bike. All my bikes have a centreline mark on the TT and using it works as well as using a gunsight does.

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horizon
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Re: Measuring seat angle - correct tool?

Postby horizon » 27 Aug 2017, 10:57pm

Generally the seat angle and (effective) top tube are given for most bikes. Many fewer give the top tube to head tube (?) that you suggest (I think Surly do to their credit but they give seat angle anyway). So it's mainly a matter of convenience - I've only got one bike (owned and prospective) where I don't know the seat angle but I would struggle to get the reach for all the others. Otherwise it's generally very simple to compare.

The other thing is that (for finding reach) the sloping top tube makes it harder to drop vertically to the BB and then horizontally across (I'll have to look again to see if that is right).
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JohnW
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Re: Measuring seat angle - correct tool?

Postby JohnW » 27 Aug 2017, 11:07pm

Brucey wrote:there seem to be two sorts of person reading this thread

1) those who think that this has something to do with the tilt angle of the saddle

and

2) those who think it has something to do with the angle of the seat tube

I'm in the latter camp.

If you are interested in saddle setback, just drop the plumbline through the BB centre and mark the intercept with the top tube. Turn the bike 180 degrees and repeat. If the mark is in a different place then the floor wasn't quite flat and the average position Is correct. Measure backwards and forwards, sighting through the mark and the BB.

You can work out the seat tube angle but really there isn't much point provided you are comfy and the forward reach is known.

cheers


...................and a third camp says that the angle of the seat-tube is critical because the seat-pin/saddle type combination can prevent you from getting the saddle far enough back - there have been several threads on this issue and I've experienced the problem........nothing to do with the tilt of the saddle.