Bike fit question - completely stumped.

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diegogarcia
Posts: 571
Joined: Sat Apr 24, 2010 7:31 pm

by diegogarcia

Hi - I wonder if anyone can help with a bike fit issue. I changed from a Specialized S-Works tarmac to a Giant Defy SL 0. I am now 44 and not racing, just enjoying riding again after moving to different terrain hence moving to a 'comfort bike'.

I rode a 56cm S-Works tarmac with an inline seat post (short legs, long body) for for years and could ride up to 7 hours pain free. I now get severe neck ache a mere 1.5 hours into the ride on the Defy. The caveat being the Defy is on paper, technically smaller than the Tarmac with 56cm top tube and a 185mm head tube compared to the 56.5 top tube and 160mm head tube on the Tarmac. So in essence, closer and higher. Both bikes have 100mm stems and I have the stem placed akin to the head tube + conical and 2 x 10mm spacers on the tarmac on the Defy.

But I am stumped. The only thing I can think of is that the Defy is slacker in the seat tube by .25 of a degree thus rendering me further back, though surely offset by the slacker head tube 73.5 to 73. The neck ache is really stumping me and I cannot see the wood for the trees in so much maybe I suit a lower head tube, or a longer stem though I have no idea where to start any changes. I have no injuries to speak of on legacy issues with the neck / upper back. Any thoughts out there ?

As an aside, on paper, I measure up as a classic Medium fit rider at 5' 9", but a BG fit some 4.5 years ago advised the 56cm frame over 54cm due to the classic longer torso dynamic, hence going for the medium large Defy after comparing geo charts before purchase. I flipped the clamp on the Defy to, gaining -25 to -5 of seat position. The other aside is that my riding buddy says I should have bought a Medium Defy, but after test riding the bike it felt very small and rolled my spine rather than opened it up. Confused and dejected :unbelievable: Am I just getting old :noidea: :shock: :D

https://www.giant-bicycles.com/en-gb/bi ... /#geometry

http://www.specialized.com/us/en/bikes/ ... d#geometry

jeffy
Posts: 1325
Joined: Sun Oct 05, 2014 11:51 pm

by jeffy

0.25 degree will be only a few mm, and the chain stay/wheelbase differences will mean that there is greater difference in centre-of-gravity.
So once reach/stack comparison is made (and *some consideration* for HT Angle) I would start the saddle in the same position (relevant to centre of BB) as the tarmac and then just 'adjust to taste'.

M/L Defy
72.5 HT ANGLE
73 ST ANGLE
38.1 REACH
58.5 STACK

56 TARMAC
73.5 HT ANGLE
73.25 ST ANGLE
39.5 REACH
56.4 STACK

using http://yojimg.net/bike/web_tools/stem.php
(better stack/reach comparison tools are out there)

so tarmac is ~ 20mm lower and ~20mm longer (reach is added because of the higher stack on the Defy),

with the new Defy - using 20mm less spacers (than the Tarmac) and a 10mm-20mm longer stem (than the Tarmac) should get you in the ballpark of the Tarmac fit.

remember to take account of how much height the topcaps differ - stack is to the top of headtube, not the conical spacers/topcaps

by Weenie


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diegogarcia
Posts: 571
Joined: Sat Apr 24, 2010 7:31 pm

by diegogarcia

Jeffy - thanks. I was thinking perhaps longer required, but the inner bike fitter always assumes back and up to rid the rider neck of pain, but realise, like in this instance, not always the case. I appreciate your reply - it is something to work with.

DanW
Posts: 1243
Joined: Fri May 02, 2008 5:39 pm
Location: Here, there and everywhere

by DanW

http://bb2stem.blogspot.co.uk/

This is the best I have found for comparing different stem/ spacer combinations on frames with different stack/ reach/ HT angle (scroll to the right and use that section of the spreadsheet)

drchull
Posts: 376
Joined: Sat Jul 30, 2011 6:38 pm

by drchull

Also, are the bars the same width?

DanW
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Joined: Fri May 02, 2008 5:39 pm
Location: Here, there and everywhere

by DanW

Also, bar reach, different hoods.... ?

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Saddle setback is the main determinant for how much work your legs can do to support your torso - not enough setback and your arms and shoulders have to carry your upper body.

Could this be a factor?

diegogarcia
Posts: 571
Joined: Sat Apr 24, 2010 7:31 pm

by diegogarcia

Thanks all ....

I am running the Defy with the cock pit aligned to the Tarmac as best as possible. The bars are the same width, reach and drop also. Hence being stumped. I think it is something to do with the slacker geo at the back, but from my understanding, it is not a huge amount at .25 of a degree and of course I have 'reversed' the seat post clamp to add 2cm of reach without affecting the look and feel at the rear of the bike. Could just be one of those things. Worth fettling and it'll get there as the slacker head tube, offsets the slacker seat angle. I suppose what puzzles me is that transitioning from a 'race' bike to a 'sportive/endurance' bike, my neck and shoulders have hated it. Here is the bike, all looks proportionate though should have zoomed the lens to compress the image and flatten the bike so it looks 'real'. Below is the set up from my tarmac, which fitted like a glove.

Image

Image

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Both setups don't look very neck-achey to me actually. The defy has more setback, so the position should unload your arms.

Could it be external factors? Colder temperatures?

User avatar
ALAN Carbon+
Posts: 294
Joined: Mon Dec 26, 2005 9:21 am
Location: Canberra, Australia

by ALAN Carbon+

Looking at the two set ups you look like you are more on top of the bb with the tarmac. It might be a combo of the slightly slacker seat angle plus the extra setback from the topper (given the tarmac is using a zero setback post) that might be worth looking into.

Maybe start with getting the saddle setback the same as the tarmac, then adjust the reach and drop of the bars.

Sent from my 0PJA10 using Tapatalk

DanW
Posts: 1243
Joined: Fri May 02, 2008 5:39 pm
Location: Here, there and everywhere

by DanW

Different saddles to factor in too. It can be hard to replicate fore-aft when your sit bones might be in different positions relative to the nose and/ or tail so you have to think about where you are relative to the BB rather than where the saddle is if that makes sense?

Wingnut
Posts: 2196
Joined: Sat Jun 23, 2007 12:41 am

by Wingnut

Agree with DanW...difficult to replicate when saddles are different...

AJS914
Posts: 5399
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

You can just drop a plumb line from the some point on the knee to the pedal axle and reproduce that on both bikes.

Looking at the pictures, it looks like the seat on the Giant is much farther back which would increase reach. I agree with your friend, the Defy frame looks too big.

On my new bike I went with a shorter top tube and more drop (lowered my stem). I'm finding it a lot more comfortable.

diegogarcia
Posts: 571
Joined: Sat Apr 24, 2010 7:31 pm

by diegogarcia

Thanks all - I agree with all in the most part. I cannot fathom how a 'smaller' bike can feel so much bigger than my previous machine, but it does and I hope to remedy it by in the mid term changing down to a medium frame and fettling the cock pit to suit. I am not a big fan of short stems and what not as usually a barometer of the wrong bike at the wrong time. I've always had to compromise fit as short legs, big body and a former high level rugby player which makes the upper body as far removed from what a pro cyclist looks like as possible.

Still, my girl loves the guns so its all good :mrgreen:

Thanks again one and all :thumbup:

DanW
Posts: 1243
Joined: Fri May 02, 2008 5:39 pm
Location: Here, there and everywhere

by DanW

It doesn't look at all like the Defy is "bigger" from the geo. I'd forget the cockpit for a second and get the saddle in the right position. As ALANcarbon+ says, you've got an inline post on the Tarmac and setback on the Giant. That could be a good 20mm or so right there. New saddle also an issue as I've already mentioned. Don't move the saddle for "reach". Get the saddle in the right position first and then adjust the cockpit for reach.

by Weenie


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