Cannondale size advise for rider which measure 5 feet 8 inches

Discuss light weight issues concerning road bikes & parts.
wingguy
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by wingguy

themidge wrote:
Tue Jul 24, 2018 10:35 pm
The whole thing is based around the bottom bracket (as you said, it has to be) and as such, to 'manually control BB drop', as in change it to the same as the other frame, would affect the rest of the bike.
Oh boy.

If you don't have stack and reach values available (as on the Mares), BB drop needs to be accounted for in your calculations to ensure that comparisons you make using HT, TT, ST, fork length etc. actually work. This is why BB drop is a listed value on both of the geo charts you have access to for these two bikes. So when I say control BB drop on the spreadsheet I don't mean change them both to be the same, I mean control them seperately for each frame so they are what they are supposed to be. I would be surprised if that is not an option, because it's fairly fundamental to what the tool is trying to achieve.

(Though as it happens on these frames listed BB drop is only a few mm apart, so the crude option of making them both the same would get you very close to the right answer. Certainly much, much closer than you have been so far.)
Indeed, it would be useful if you could see the comparison with the wheels on the same level,
No, not really. Having a comparison with the BB as reference is the accurate way of comparing rider positions between bikes - but only if you can use the measurements you have to properly model the bike. Lining the wheels up instead doesn't help you do that, it is in fact introducing yet another inaccuracy into the process.

Once again; if you don't understand these issues and how they relate to each other yet, you should probably avoid trying to give geometry chart based advice until you've spent more time learning about it.

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themidge
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by themidge

BB drop is accounted for, or at least, I can only assume it is seeing as you have to enter it into the spreadsheet.
Image
(^that's a screenshot of the values of the bikes you start off with, not the ones from this thread)
The spreadsheet is taking the BB as its point of reference (as you can see from the scale on the graph), so I'm not sure what the problem is. Please do explain exactly what is wrong if it is.
As far as I can tell (CIIR), the spreadsheet takes the BB as zero, and then counts up to the level of the hubs using the BB drop value. From there, presumably, it uses the wheelbase, chainstay length, seat-tube length & angle, fork length, and head-tube length & angle values you put in to draw out the rest of the bike. It can do this without stack and reach because when you have BB drop and chainstay length, you can work out the distance along the other side of that triangle. From there, (presumably, I don't know how else it could do it) it finds out how far away the front hub is from the centreline (vertical line bisecting BB) by subtracting the rear - centred distance from the wheelbase. Once it has the front hub placement, I can only assume that it uses fork length, rake, and head angle to find the bottom of the head-tube, and then the head-tube length to find the position of the top of the head-tube. Then, using the seat-tube length and angle it can draw out the top tube and seat-stays, and join up the heatube and bottom bracket with the down-tube (not that the down-tube is particularly relevant).
That was all speculation (please, if it doesn't do it like that, do tell) but it would seem to me to be the best way.

You're right, clearly I don't fully understand how everything works with bike geometry (otherwise I would have noticed the fork length error in the first place), but perhaps by explaining how the above is wrong, you can help me understand it all better.

by Weenie


wingguy
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by wingguy

themidge wrote:
Wed Jul 25, 2018 12:54 pm
BB drop is accounted for, or at least, I can only assume it is seeing as you have to enter it into the spreadsheet.
Image
(^that's a screenshot of the values of the bikes you start off with, not the ones from this thread)
The spreadsheet is taking the BB as its point of reference (as you can see from the scale on the graph), so I'm not sure what the problem is. Please do explain exactly what is wrong if it is.
Why are you showing me the BB values of bikes we are not talking about? Show me the screenshot of the values that correspond to the second set of graphs you posted and then I can tell you exactly how wrong it is.

In fact, just look at the edited graph you put into your post and compare it to the original graph that I quoted in my reply. BB drop was not properly controlled for the second one, nowhere near. You shouldn't need me to explain that, you just need a functioning pair of eyes. :noidea:
As far as I can tell (CIIR), the spreadsheet takes the BB as zero, and then counts up to the level of the hubs using the BB drop value...
.
.
That was all speculation (please, if it doesn't do it like that, do tell) but it would seem to me to be the best way.
Yes, that's what it should do - but it is not what it actually did. I don't know how that spreadsheet is supposed to work, but again I'd assume you simply didn't use it properly. I would suggest starting from scratch and inputting all data including fork length and BB drop into a fresh sheet rather than trying to edit your first attempt and deal with more potential knock on errors.

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themidge
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by themidge

Here's the main part of the spreadsheet, where you enter all the values:
Image
Notice the differing fork travels, do go look at it yourself but as far as I can tell, the only way you can get different fork lengths is by changing the fork travel, and editing the corresponding length in the fork data sheet.
Image
A bit crude, and open to flaws, but seeing as the fork sag is left at zero it should be fine.

wingguy
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by wingguy

themidge wrote:
Wed Jul 25, 2018 7:30 pm
A bit crude, and open to flaws, but seeing as the fork sag is left at zero it should be fine.
Should be, but isn't. Don't know what it's doing and what data it has priotised but clearly it's ignored the bb drop values as they were entered, and as such the result is totally buggered. There is a fork length field in the "output variables" section, can you not use that?

Champ5000
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by Champ5000

Hi all

Thank you all for your input and comments.

I recognize that a rider with a height of ~ 5 feet 8 inches and an inseam of ~ 2 feet 8,7 inches can actual ride a Cannondale bike from 50 to 56 cm. depending on upper body.

I am targeting a 120 or 130 stem, as I find bikes with this length stems more aesthetically pleasing – maybe this sounds weird?

In order to get a proper position on my Focus Mares I have to run the bike with a zero set back seat post and a 100 stem.

I passed an authorized Cannondale dealer yesterday who happened to have a Caad 12 50 cm. in stock (women specific – however identical geometry to men’s Caad 12).

I tried the bike with center BB top saddle 74 cm. which is the right height for me – pictured in the below.

Image

Image

Image

As you can see on the pictures, the saddle height is quite up in the air and as also stated running a -17 degree stem would just look wrong. I guess that I would need a 130 steam, 6 degree and I would prefer to slam it.

What do you think – I lean towards that saddle beeing too much up in the air.

I browsed the new Cannondale 2019 catalogue at the dealer and saw a silver gray (colour name: sage gray) Caad 12 disc with black decals, thru axle front and rear, Ultegra 8000 version with HollowGram Si w/ OPI SpideRing crankset.

They should be able to deliver within a month or two. That would be the one I will go for.

I might find it difficult to target the 6,8 with disc brakes, 1500g. wheelset, and carbon seatpost and cockpit?

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themidge
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by themidge

^Looks okay, but a little small. How did the reach feel on that bike? To be perfectly honest, I don't think the Caad12 is really going to work without some kind of compromise. Going off stack and reach (my bike-comparator needs some scrutiny it seems :D) it looks to me that when it's tall enough, it's too long, and when it's short enough, it's too low. You'll probably end up with a shorter stem than you want (100mm maybe, it doesn't look so bad even on a 56) or a few spacers, I would choose the former.

wingguy wrote:There is a fork length field in the "output variables" section, can you not use that?
On the wee info thing that pops up when you hover over the cell, it says the values are from the 'fork data' sheet, which is what I changed to get the different fork lengths in the first place. So I think that 'fork data' sheet is all there is to work with.
I think I'll stick to comparing bikes with similar fork lengths from now on :? .

mrfish
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by mrfish

Yes. 50 looks too small.

To avoid errors calculate stack and reach of the focus by putting the back wheel against a wall, then measure horizontally from wall to stack point and vertically from floor to stack point. Now do the same for the B.B. and subtract the measurements. Job done and comparisons are fairly easy.

@midge, try building a frame sizing spreadsheet from scratch. Then cross check with measurements from a few bikes of different types. Otherwise you will keep making errors because you didn’t fully understand the assumptions the other guy made.

wingguy
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by wingguy

Champ5000 wrote:
Wed Jul 25, 2018 10:35 pm
I am targeting a 120 or 130 stem, as I find bikes with this length stems more aesthetically pleasing – maybe this sounds weird?
It's not weird (we all want stuff to look nice) but it may not be compatible with having a bike that fits properly and is pleasant to ride. You need to decide which is more important to you.
What do you think – I lean towards that saddle beeing too much up in the air.
I lean towards it having a monstrous amount of drop. If you can't deal with being any longer on the Mares I doubt you'll deal well with being that low on the Caad.

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