Measuring saddle Fore/Aft on Different Bikes

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Mick F
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Mick F » 10 Sep 2019, 3:08pm

Off topic :oops:

Nice kitchen!
Where's the dog?
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Witterings
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Witterings » 10 Sep 2019, 4:03pm

Mick F wrote:Off topic :oops:


Where's the dog?


Dog was a bit tied up at the time ..... doing what she seems to do best at the moment .... busy testing her new bed for comfort levels whilst
supervising :lol:
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Mick F
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Mick F » 10 Sep 2019, 4:52pm

:D :D
Wonderful!
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fausto99
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby fausto99 » 10 Sep 2019, 5:43pm

Witterings wrote:Has anybody found any reliable way of measuring saddle Fore/Aft so if you get a position on 1 bike that's really comfortable and is friendly to your knees etc. you can easily replicate it on another bike and also where do you measure from / to on the saddle ... the nose or the rear.

I've tried using plumb lines but where the middle of the bottom bracket is further out from the line of the top tube it makes it difficult and holding the line against the nose of the saddle it doesn't drop straight down without hitting / being deflected on various parts of the frame so you end up tilting the bike which I'm not convinced helps give an accurate reading.

If anybody's got any "bright ideas" I'd be really interested in hearing them.


I have 4 bikes set up so that they feel as near identical as I can tell. Here's my method (assuming you can duplicate the "sit bone" to pedal distance easily enough):

1. Do not use the nose of the saddle as a reference point. Even if you have identical saddles on both bikes the nose is irrelevant. Stick a strip of masking tape across the saddle. Draw a line across from the two indentations made by your "sit bones". This is your reference line.

2. Rest a straight edge from the above sit bone line to the handlebar/stem joint.

3. use a very large set square (make it out of timber 3:4:5 for a rt angle) on the above straight edge and slide it along until is in line with the BB.

4. Measure along the straight edge the distances from sit bone line to BB and from BB to handle bars.

5. Move saddle fore and aft and change stem to achieve identical measurements on both bike.

Job done - have a cup of tea!

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Mick F
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Mick F » 11 Sep 2019, 7:02am

What happens if it's a new saddle?
No indentations.

Also very hard Brooks Pro, and even though on Mercian with 40odd thousand miles ridden with the saddle, there isn't much to show where my sit bones are.

I used the saddle nose. Set the saddle at the same angle and move it fore and aft to get it into the correct position.
Mick F. Cornwall

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Re: Measuring saddle Fore/Aft on Different Bikes

Postby philvantwo » 11 Sep 2019, 7:52am

Didn't you lower your saddle the other day Mick F?
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fausto99
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby fausto99 » 11 Sep 2019, 8:01am

Mick F wrote:What happens if it's a new saddle?


You can sit on the saddle and feeling where your sit bones are stick some tape down the sides level with them. Get off an tape across then draw a line. The nose position is completely arbitrary.

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fausto99
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby fausto99 » 11 Sep 2019, 8:02am

fausto99 wrote:
Mick F wrote:What happens if it's a new saddle?


You can sit on the saddle and feeling where your sit bones are, stick some tape down the sides level with them. Get off and tape across, then draw a line. The nose position is completely arbitrary.

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531colin
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby 531colin » 11 Sep 2019, 4:02pm

I can't see how Fausto's method will work unless the drop from saddle to bars is identical for each bike. Maybe you forgot to mention this?
I agree that the saddle "nose" is unimportant; but by the same token its pointless measuring from the handlebar/stem clamp unless the bars (and even brake hoods) are identical on each bike.

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Re: Measuring saddle Fore/Aft on Different Bikes

Postby 531colin » 11 Sep 2019, 4:22pm

Its readily possible to get far too hung up on all this stuff.
As somebody mentioned up-thread you generally won't get handlebar stems in increments of less than 10mm, so your "reach" is an approximation.
Where in the bum-bone dent do you measure? Do you guess the centre? In any case, I move back or forward on the saddle as occasion demands.
Do you measure saddle height above the BB vertically? Along the seat tube? LeMond's "method" for saddle height measures from the BB axle to the bum bone dent, this is probably most "accurate". (ie best way to reproduce your position on bikes with different seat tube angle or seatpost/saddle)
I take a bit of care over saddle angle; I like them horizontal or the nose can be a maximum of 3mm up......done with spirit level and plastic packing pieces of known thickness (Screwfix, etc) But if the saddle doesn't have a flat(-ish) top, all bets are off.
I notice small differences in saddle height...as in I adjust saddle height by about 3 or 4mm for different shoes; I can't measure saddle height this accurately, I have to do it by "feel" until I learn what different shoes do.
Saddle setback, handlebar height, handlebar reach; I doubt I would pick up an "error" of +/- 5mm in any of these, so these measurements don't have to be "spot on" they can be "near enough"....maybe the skill lies in knowing how near is "enough".

To answer the original question I measure setback with a plumbline with the bike on a known level surface. Cables and parts of the frame which can get in the way are a nuisance, but you can minimise their effects by squinting down the string. As above, I don't think saddle setback needs to be, or even can be millimetre accurate.

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Re: Measuring saddle Fore/Aft on Different Bikes

Postby pwa » 11 Sep 2019, 6:58pm

In the past it has occurred to me that if you are dealing with a leather Brooks-style saddle that lengthens as you stretch it, and you don't fancy trying to estimate the centre of the bum bone area, the back edge of the saddle makes a more constant place to measure from than does the nose.

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Mick F
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Mick F » 11 Sep 2019, 7:45pm

philvantwo wrote:Didn't you lower your saddle the other day Mick F?
Stack height issues.
That needs to be vectored into the whole thing.
By measuring as I suggested ....... and others too ........ no-one has addressed the stack heights, and thank you Phil for mentioning it.

Most? pedals are the same stack heights.
Fitting Speedplay pedals means a very low stack height, and it means maybe half an inch difference to normality. Hence the saddle needs to be lower.

Mercian and when I kitted out Moulton, they had the same pedals. It was after falling in love with Speedplay Frogs, that I had to lower the saddle by half an inch.
Very soon, Mercian will also have Speedplay Frog pedals, and will also have the saddle lowered by half an inch.

The rest of the geometry and measurements will remain .......... minus half an inch from BB to saddle. As I said, handlebar height isn't (for me at least) particularly important to be spot on.
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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Sweep » 11 Sep 2019, 8:31pm

Despite it being poo-pooed above, with regard to saddle and bars I measure from the NOSE of the saddle to the centre of the bars. All of my saddles are pretty similar so I can't believe it produces much error. If I then sit on something which feels odd I just change it by small increments. Similarly with height of saddle - I work on the pretty common idea that at the bottom of the downstroke your leg should be almost but not quite straight. So I set whatever bike up like that. Then ride it. I can always fine tune it as I go.
As Colin says the shoes do change things - I have two bikes which have pedals clipped one side and flat the other. Both are set up for clipped as that is what I use most of the time - if I'm using plain city shoes on one of those for a ride into London and back to swan round a gallery (10 miles) I just lump it - I'm not going to start going back to the dark dark days of O level trigonometry. The other two -sided pedal bike may be ridden in flats for longer rides so I just move the seat up/down as needed. No great problem.

When buying a bike you need more measurements of course, but it's only to get the right size of frame.

Must be doing something right. I bought a very nice bike from nice Paul Hewitt who has his own perfectly good ideas on how folk should sit on a bike. I went along with his fit but after a while he helped me tweak it back to how I, for whatever reason, like to interact with the bike. All my bikes now have pretty much the same measurements - but they have all essentially arrived at that happy situation by "feel" - which tells me that they are all set up right. Sod the theory.
Sweep

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Re: Measuring saddle Fore/Aft on Different Bikes

Postby Witterings » 12 Sep 2019, 12:10am

531colin wrote:Its readily possible to get far too hung up on all this stuff.


You're right it probably is ... but the inconsistencies trying to use a plumb line off the front of the saddle nose to the bottom bracket .... I can take a measurement one minute and go and double check it a minute later ... the bike's at a slightly different angle and my reading can be 10mm out ..

If you then take transposing that to the other bike .. there's potential for the same inconsistency so now we're potentially 20mm out which can make an awful lot of difference in comfort levels ... especially if you've the number of injuries and amount of surgery I've had.

If you really think it's "readily possible to get far too hung up on all this stuff" ... why did you create webpage dedicated to it???
That's really not a criticism .... just interested as one comment seems in contradiction to other???

https://wheel-easy.org.uk/wp-content/up ... -2017a.pdf

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Re: Measuring saddle Fore/Aft on Different Bikes

Postby pwa » 12 Sep 2019, 7:28am

When I double check my results they are usually within 5mm, so I'm pretty confident that I'm close enough. Obviously if one can't hold a spirit level steadily one has a problem. Spirit levels should always be checked for accuracy before use, but I have used them at work for decades and know how to get an accurate reading. An extra pair of hands may be useful.

How exactly you keep the spirit level from the bottom bracket vertical and steady will vary with the frame design, and will be simplest with a slim tubed steel bike. But you can use blu-tac to locate it on the bb shell (adding however many mm it is from there to the bb centre) and you may be able to fix it to the top tube with masking tape, just as an example. It doesn't have to be freehand. It helps if you have a selection of different size spirit levels too. You need a second one to reach to the saddle to get the height established, and that could have the two clashing where they meet so some playing around will be needed.

But as Colin says, the height and exact spots of the bum bone centres is at best an estimate. When all the measuring is done you still have to have a ride and make minor adjustments.

(A spirit level in good condition will read the same whichever way up it is. If it doesn't you can still use it but you have to take two readings, flipping it, and halve the difference. if that makes sense).