New cannondale SYSTEMSIX road frame!

Discuss light weight issues concerning road bikes & parts.
TobinHatesYou
Posts: 3306
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Are you saying the setback is functionally 40mm relative to the line drawn at STA from BB-c, or relative to the center of the post itself? Damon said previously the seatpost was 25mm. I’m trying to eyeball the offset of the ST vs BB-c, and it does look like the “25mm” is relative to the seatpost’s own centerline and not the BB’s centerline...which does look pushed forward of the ST by about 10mm.

by Weenie


DVR
Posts: 15
Joined: Tue Jun 05, 2018 5:48 pm

by DVR

refthimos wrote:
Wed May 15, 2019 5:00 pm
"New bikes are being spec'd with the "less setback" post.
Thanks for your feedback!

If I understand your post correct you purchased the seatpost that is shown on the new eTap AXS bike, true?
That seatpost should have a setback of around 15 according to Damon.

I have a setback of 25 on my Dogma F8 and have moved the saddle forward as much as possible within the tolerances marked on the saddle rail.
So I think the new 'less setback' post should be just fine for me too (I hope).

Do you have a photo of your bike with the new post? Would love to see how it looks with a 76 saddle height on our 56 frame.
Cannondale SuperSix EVO HM eTap
Cannondale SuperSix EVO HM Disc Ultegra
Cannondale SystemSix eTap AXS
Colnago C60 eTap
Pinarello Dogma F8 eTap

TobinHatesYou
Posts: 3306
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

DVR wrote:
Wed May 15, 2019 8:44 pm
refthimos wrote:
Wed May 15, 2019 5:00 pm
"New bikes are being spec'd with the "less setback" post.
Thanks for your feedback!

If I understand your post correct you purchased the seatpost that is shown on the new eTap AXS bike, true?
That seatpost should have a setback of around 15 according to Damon.

I have a setback of 25 on my Dogma F8 and have moved the saddle forward as much as possible within the tolerances marked on the saddle rail.
So I think the new 'less setback' post should be just fine for me too (I hope).

Do you have a photo of your bike with the new post? Would love to see how it looks with a 76 saddle height on our 56 frame.

I'm still betting the seat tube has 10mm of its own setback, turning the 15mm post into a 25mm equivalent...and the 25mm into a 35mm equivalent.

refthimos
Posts: 234
Joined: Fri May 25, 2012 6:02 pm

by refthimos

DVR, check first post here:

viewtopic.php?f=10&t=156100
EVO | 5.37kg
SystemSix | 8.01kg
TCR Advanced SL Disc | 7.35kg
P5 | 9070 Di2 | SISL2 SRM | Enve 7.8 | Alto Disc
T1 | P2Max Type S | Rolf Prima FX58/Zipp Super 9 Disc

DVR
Posts: 15
Joined: Tue Jun 05, 2018 5:48 pm

by DVR

Thanks but confused , those are photos picturing the stock high setback seatpost.
Anyway, no worries. Soon I'll see the bike for myself with the new less setback seatpost.
Cannondale SuperSix EVO HM eTap
Cannondale SuperSix EVO HM Disc Ultegra
Cannondale SystemSix eTap AXS
Colnago C60 eTap
Pinarello Dogma F8 eTap

BigCol
Posts: 27
Joined: Tue Apr 07, 2009 10:03 pm
Location: UK

by BigCol

refthimos wrote:
Wed May 15, 2019 11:53 pm
DVR, check first post here:

viewtopic.php?f=10&t=156100
That's the original high set back post isn't it?

willmac
Posts: 135
Joined: Thu Aug 25, 2016 11:33 am

by willmac

TobinHatesYou wrote:
Wed May 15, 2019 9:08 pm
DVR wrote:
Wed May 15, 2019 8:44 pm
refthimos wrote:
Wed May 15, 2019 5:00 pm
"New bikes are being spec'd with the "less setback" post.
Thanks for your feedback!

If I understand your post correct you purchased the seatpost that is shown on the new eTap AXS bike, true?
That seatpost should have a setback of around 15 according to Damon.

I have a setback of 25 on my Dogma F8 and have moved the saddle forward as much as possible within the tolerances marked on the saddle rail.
So I think the new 'less setback' post should be just fine for me too (I hope).

Do you have a photo of your bike with the new post? Would love to see how it looks with a 76 saddle height on our 56 frame.

I'm still betting the seat tube has 10mm of its own setback, turning the 15mm post into a 25mm equivalent...and the 25mm into a 35mm equivalent.
If you look at the Cannondale geometry charts, seat tube angle is drawn from the centre of the bottom bracket to the screw looking thing at the centre of the top of the seat post. If you use that as reference, then the 25mm seems accurate. Interesting thing is that seat post angle changes significantly between sizes

TobinHatesYou
Posts: 3306
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

willmac wrote:
Thu May 16, 2019 12:30 pm
TobinHatesYou wrote:
Wed May 15, 2019 9:08 pm
DVR wrote:
Wed May 15, 2019 8:44 pm
refthimos wrote:
Wed May 15, 2019 5:00 pm
"New bikes are being spec'd with the "less setback" post.
Thanks for your feedback!

If I understand your post correct you purchased the seatpost that is shown on the new eTap AXS bike, true?
That seatpost should have a setback of around 15 according to Damon.

I have a setback of 25 on my Dogma F8 and have moved the saddle forward as much as possible within the tolerances marked on the saddle rail.
So I think the new 'less setback' post should be just fine for me too (I hope).

Do you have a photo of your bike with the new post? Would love to see how it looks with a 76 saddle height on our 56 frame.

I'm still betting the seat tube has 10mm of its own setback, turning the 15mm post into a 25mm equivalent...and the 25mm into a 35mm equivalent.
If you look at the Cannondale geometry charts, seat tube angle is drawn from the centre of the bottom bracket to the screw looking thing at the centre of the top of the seat post. If you use that as reference, then the 25mm seems accurate. Interesting thing is that seat post angle changes significantly between sizes

You had me second-guessing myself, so I decided to dig deeper. Check this out...

Image

Looks like I was right. The bottom bracket does not line up with the center of the seatpost...it's more than 1cm offset. Counting pixels, the seatpost does have 25mm setback, but the seat tube is also set back an additional 13mm or so.
Last edited by TobinHatesYou on Thu May 16, 2019 1:17 pm, edited 1 time in total.

willmac
Posts: 135
Joined: Thu Aug 25, 2016 11:33 am

by willmac

Isn’t that irrelevant? Actual angle is in relaion to the bottom bracket, not where the seat tube joins the down tube. Cannondale drawings are close to yours but the red line should intersect the round thing at the top of the seat post, not be in front of it. Mtb’s have been doing this for ages to get linkage ratios to work effectively. It’s still an effective 25mm setback from whatever angle is stipulated in the geo charts

TobinHatesYou
Posts: 3306
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

willmac wrote:
Thu May 16, 2019 1:15 pm
Isn’t that irrelevant? Actual angle is in relaion to the bottom bracket, not where the seat tube joins the down tube. Cannondale drawings are close to yours but the red line should intersect the round thing at the top of the seat post, not be in front of it. Mtb’s have been doing this for ages to get linkage ratios to work effectively. It’s still an effective 25mm setback from whatever angle is stipulated in the geo charts

How is it irrelevant? I’m drawing the line parallel to the STA as any logical person would do. Different brands are using different techniques to label setback. Cannondale’s seatposts themselves are 25mm and 15mm setback, but the total setback is going to be more like 38mm and 28mm. A 0mm setback post would still provide ~13mm of setback relative to that red line. This is why refthimos indicated that his seatpost is more like a 40mm setback post...he was pretty close.

Trek on the other hand labels its seatpost setback relative to the red line. In the case of the Madone SLR, the center of seatpost inches forward of the red line. That’s why the 25mm and 5mm setback posts look like they have even more setback...to compensate for the seat tube being set-forward.

Image

The stubbier seatpost is what Trek labels 5mm offset, but clearly it is offset more than 5mm relative to the centerof the post.

willmac
Posts: 135
Joined: Thu Aug 25, 2016 11:33 am

by willmac

4B4601A6-7E6E-4A5C-A17F-1BD9A4B39E8D.png
Easy there. Cannondale’s geo chart clearly shows the reference point for the centre line of the seatpost and it’s not where you put it. It’s up to the individual to determine how seat tube angle and setback work in combination but the specs on a 56 look aggressive to me. Supersix is 73.5 seat tube angle and this is 74 so the setback should actually equate to less than a “normal” bike

DVR
Posts: 15
Joined: Tue Jun 05, 2018 5:48 pm

by DVR

Thank you Willmac, makes me even more convinced the 15 setback will be perfect for me.
The 56 SystemSix is steeper than my F8.
Cannondale SuperSix EVO HM eTap
Cannondale SuperSix EVO HM Disc Ultegra
Cannondale SystemSix eTap AXS
Colnago C60 eTap
Pinarello Dogma F8 eTap

willmac
Posts: 135
Joined: Thu Aug 25, 2016 11:33 am

by willmac

Without doing a bit of math and knowing your saddle height to determine the change in set back based on different angles to start with, I’d say a 15mm sounds like a safe bet

TobinHatesYou
Posts: 3306
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

willmac wrote:
Thu May 16, 2019 1:47 pm
4B4601A6-7E6E-4A5C-A17F-1BD9A4B39E8D.png

Easy there. Cannondale’s geo chart clearly shows the reference point for the centre line of the seatpost and it’s not where you put it. It’s up to the individual to determine how seat tube angle and setback work in combination but the specs on a 56 look aggressive to me. Supersix is 73.5 seat tube angle and this is 74 so the setback should actually equate to less than a “normal” bike
The geometry chart is a conceptual drawing. Also it’s still showing a line parallele to the ST. It makes no sense to draw a line from the BB-c to an arbitrary point on the seatpost. The 15mm seatpost doesn’t even have that circle in the same spot.

In order to determine setback via math, the line must be drawn along STA from the BB-c. You are correct that STA and saddle position will augment the total setback. Of course that’s true, but what I said is also true. The center of the clamp on the seatpost will always be its own setback plus the setback of the seat tube itself behind the BB-c in a line perpendicular to the STA. Trek would label the Cannondale 25mm post a 38mm post and the 15mm post a 28mm post.

by Weenie


willmac
Posts: 135
Joined: Thu Aug 25, 2016 11:33 am

by willmac

Tobin, I’m not going to get into an argument but at my saddle height, if you’re red line that you’ve drawn, vs the actual design calculations is wrong, which is highly likely as that photo may not be perfectly square, then you will get significantly wrong numbers. One degree is worth nearly 15mm so I will take the design engineers numbers rather than some work done in paint on a laptop somewhere

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