Bike geometry - judging comfort without sitting on it

Discuss light weight issues concerning road bikes & parts.
mike001100
Posts: 67
Joined: Sun Dec 04, 2016 10:26 am

by mike001100

Hi,

trying to figure out how to judge if a bike will "fit" me without sitting on it...

I have insofar had only one bike that due to geometry felt uncomfortable - I felt cramped on it, like my knees were on level with the stem bolts - the Giant TCX, size M. Geo for this bike is here:
Reach: 375, Stack: 556, Top tube: 545

I borrowed a SuperSix Evo 2015 recently which I felt comfortable on, geo:
Reach: 384, Stack: 526, Top tube: 535

The difference in reach (which I assume did the "cramped" feeling) is 9 mm... is this 9 mm really such a huge difference between feeling cramped and feeling like there is room to move?! Or am I missing something?!

Thank you.

TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

If your knees are close to the stem bolts, your saddle fore/aft and height might be all wrong. Could you tell me what your saddle height and setback are? Between 5-10cm setback is typical depending on the length of the saddle. The fact that you don't feel cramped on such a compact bike as a 52cm older SuperSix Evo but do feel cramped on a bike that has a longer effective top tube and higher frame stack is bizarre. If we lowered the stack on the TCX to 526mm, it would probably have a reach around 390mm.

Also how tall are you and what is your inseam? A photo of your current set-up may also help.

by Weenie


Hexsense
Posts: 326
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

you may also need stem and handle bar height/reach. and probably saddle position too.

if it is just 9mm difference in reach, 10mm longer stem will fix it easily.

alcatraz
Posts: 587
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

My guess would be the to compare seat tube angle and the length of the head tube. The other measurements can kind of be dialed in with the seat position and stem. Also not to forget the compliance/carbon layup of the frame.

A quite good balance berween comfort and stiffness can probably be found on trek frames with the isospeed decoupler.

Depending on how WW you are maybe an H1 domane or an H2 madone could suit your taste. H2 is the longer head tube version. H1 is aggressive short.

I'm not a bike fitter.

/a

alcatraz
Posts: 587
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

.

istigatrice
Posts: 756
Joined: Sat May 12, 2012 8:32 am
Location: Adelaide, Australia

by istigatrice

mike001100 wrote:...is this 9 mm really such a huge difference...


Some people are really sensitive, Apparently Cadel Evans could notice a 2mm difference in how high his shifters were.

But judging by the shorter stack of the C'dale it could be a longer effective reach to the bars since they're lower. The reach is 9mm shorter and the stack is ~30mm lower so that could result in the bars being 31mm 'further' from your shoulders. This is assuming both stems were slammed, had the same angle etc.
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TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

istigatrice wrote:
mike001100 wrote:...is this 9 mm really such a huge difference...


Some people are really sensitive, Apparently Cadel Evans could notice a 2mm difference in how high his shifters were.

But judging by the shorter stack of the C'dale it could be a longer effective reach to the bars since they're lower. The reach is 9mm shorter and the stack is ~30mm lower so that could result in the bars being 31mm 'further' from your shoulders. This is assuming both stems were slammed, had the same angle etc.


Changing my saddle fore/aft 2mm in either direction turns a Retul report from all green to all red. It's interesting how micro-adjustments have huge effects.

As far as the reach on the two listed bikes is concerned, it is already baked in. The only reason why the Cannondale has a longer reach is because the head tube / stack is shorter. The effective top tube lengths are telling. The TCX is the equivalent of a more relaxed 54cm while the Cannondale is racy 52cm. If the TCX had the same reach as the Cannondale, but also a taller stack, it would need a much steeper head tube angle or longer wheelbase to compensate.

This is why I suspect the OP's saddle position might be slammed forward. Unless he's over 6' or has really long legs, his knees shouldn't be coming anywhere close to the steerer/stem.

lone wheeler
Posts: 481
Joined: Mon May 22, 2006 11:34 am
Location: Dubai, UAE
Contact:

by lone wheeler

Have to agree on the fore/aft 2mm, if my saddle height isn't just so it feels like a completely different bike, hate it.

TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Okay having reviewed the OP's post history, he has been to a Retul fitter. The report indicates a saddle height of 706mm and a very short setback of -38mm. He also has 35mm worth of spacers+headset cover on a medium Propel with 552mm frame stack. His handlebar reach is only 502mm and his handlebar stack is 629mm.

This basically confirms my suspicions. You have a very short reach and your fitter wants you in a more upright position. According to your Retul report you should probably be on a 52cm bike with a very upright endurance geometry like a Canyon Endurace or Trek Domane, not a SuperSix Evo, not a Dogma F8/10, not a Wilier Zero.6. With those bikes you'd have like 5.5cm worth of spacers. Even with the Domane you'd be running at least 2.5cm of spacers and with a small Endurace, you'd be running 3cm (all including a tall headset bearing cover.)

mike001100
Posts: 67
Joined: Sun Dec 04, 2016 10:26 am

by mike001100

Thank you for all the replies. I didn't mention the Retul fit on purpose, since it was done under specific circumstances - it was my first fit, the fitter was trying to make do with what I have etc. For example, before the fit, my saddle was moved back and about 3 cm higher - only during the fit did I learn a position I liked in terms of my legs. In order to reach the position, the saddle had to be moved all the way forward on the frame. The fitter did not judge my flexibility and adjust the stem at all - he said it would be best that I first got used to the new position and then came back (which I haven't yet).

Since that fit, time has passed and I have gotten more flexible, moved the stem down, changed the bars to a more comfortable shape for my hands, etc.

I temporarily owned the TCX as a winter bike, and the moment I sat on it, I felt cramped - I felt like I was on a mountain bike. All I did (iirc) was adjust the saddle height to my 70.6 cm and move the seat forward to achieve my setback, as well as install a 100mm stem (originally came with a 90). In terms of upper body (iirc) it felt fine, it did not feel fine in terms of my knees too close to the stem...

Ugh...

TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

The issue is setback doesn't change from bike to bike, and your setback is very bizarre. Either you have short femurs or the fitter ignored a lot of red and instead trusted how you say you felt in that slammed forward position. Either way I would put you on a 52cm in most brands since your saddle to bar reach is so short...

mike001100
Posts: 67
Joined: Sun Dec 04, 2016 10:26 am

by mike001100

Tobin, thanks - I'm trying to understand what you mean by "setback doesn't change from bike to bike"? Surely, different brands and different sizes will have different setback, no? I think I have both short legs and short arms - for example, I sit all the way forward in my car, I sit close to my desk, etc., etc.

I can't seem to make any sense of this... I decided to go out and try a Giant TCR at the LBS, specs are:
Reach: 383 (1mm to the Cannondale) Stack: 545 (2cm higher than the Cannondale), Top tube: 550

Now, clearly, something is going on somewhere, because what I can say for certain is that my legs were not aligned in the same way as they were on the Cannondale. The Cannondale had a 25mm setback seatpost (original), my legs did comply with "tibial tuberosity over spindle" with the saddle centered, and it felt great. The TCR has also has a 25mm setback seatpost (AFAIK), saddle was centered, yet I felt like I would need to move the saddle forward 1.5 - 2 cm to get the same alignment/feeling as on the Cannondale. How is this possible?!

Stack - felt like I could drop the bars at least 2 cm to get comfortable...

In terms of sitting on the bike, it felt different to the Cannondale, I feel there was a very fine line between "ok" and "I feel cramped", but that could just be in my head... I am not sure that shifting the seat forward to get proper alignment wouldn't cross that fine line...

As the TCR was set up, it felt much more difficult (i.e. in effect normal normal) to stand up out of the saddle compared to the Dale... on the Cannondale it felt much easier than anything I have ever ridden...

Is there any help for me in understanding bike geo? Or will I just have to go around and test everything out?

TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Saddle position is almost entirely determined by leg length (and smaller influences like sitbone width, pedaling technique, etc.) None of this changes when you swap bikes. It is a coordinate measured from the center of the bottom bracket.

mike001100
Posts: 67
Joined: Sun Dec 04, 2016 10:26 am

by mike001100

Yes, I understand that part... but how can I judge saddle setback on a bike from the geometry? I do not see any measurement that would relate to that, and it seems to be a crucial measurement... i.e.:

- Supersix Evo setback seemed good for me
- TCR setback doesn't seem so good for me

Yet both frames have similar reach...

by Weenie


TobinHatesYou
Posts: 617
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Saddle setback is the horizontal distance from the center of the bottom bracket to the tip of your saddle (has to be the same length saddle.) Hang a plum bob off the nose of the saddle and see how far back the line/string is from the BB.

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