Using retul bike fit to help decide on frame size and model selection

Discuss light weight issues concerning road bikes & parts.
rynogee
Posts: 63
Joined: Sun Sep 05, 2010 2:11 am
Location: DK

by rynogee

TobinHatesYou wrote:
Fri Feb 16, 2018 6:51 am
silvalis wrote:
Fri Feb 16, 2018 1:42 am
TobinHatesYou wrote:
Fri Feb 16, 2018 12:13 am
With a saddle slammed forward on a zero-setback post you are really closing up your hips at the top of the pedal stroke and bending your knees too much...
Could you elaborate on this because I'm having trouble visualising your words.

Assuming the upper body angle to horizontal is staying the same (eg the bars are moving equivalent with the saddle) and assuming the cleat position isn't changing as well, then moving the saddle/hips forward relative to the bb in an arc will open up the hip at the top of the pedal stroke, not close it...
Two reasons:

1) Because when you move your hips closer to the BB along the horizontal axis, you are turning the full extension of your leg closer to a straight vertical line instead of a more natural diagonal. Think "|" vs "\" ... With more setback your pedaling involves less knee flexion, and as a result of that less hip flexion.

2) Because the OP is presumably trying to stick to a long and low stem/bar position up front because it looks "pro." He should move his saddle back to a normal position (lower and farther back) and use a shorter/higher stem/spacer/bar combo.
I guess you know what they say about making assumptions...

the frame is too large. I'm trying to decide how much smaller to go. (in order to get a better fit, not trying to look like anything).

short stems make a road bike handle poorly, there isn't much point having perfect hip angle if the bike handles like a dog as a consequence

RyanH
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by RyanH

I did a retul fit before I got a time trial bike. It helped a lot when it came to deciding which size I should go with.

If you're completely unsure of your size then I think it's a good starting place assuming the fitter is good. Retul is a tool, it's still going to come down to the fitter if any thing worthwhile comes out of it.
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pdlpsher1
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by pdlpsher1

I don’t know what your body measurements are but here are mine for reference. I ride a custom bike. My height 170cm and inseam 80cm. My saddle setback is 5cm and height is 70cm. I have a 110mm stem with 20mm of spacers.

What are your body measurements? If you are similar to me then you need to subtract about 5cm from your current reach so you can have a proper saddle setback.


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AJS914
Posts: 2005
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

rynogee wrote:
Sun Feb 18, 2018 8:05 am
TonyM wrote:
Sat Feb 17, 2018 4:32 pm
I used a Retül bike to determine the right frame size for my F10 disk (47, 50 or 51.5).

We change the Retül bike according to the 3 different size and also with different stem length etc....

That was very useful!

I did not pay for for it but I would have paid if necessary - considering the price for the frame/ bike and the importance to get the right frame size/ stem length etc....

thanks, I hadn't thought of putting in the geometry of the frames I'm considering to try them.

You can do this in one of the many bike frame stack/reach calculators. You plug in all the numbers of the frame, stem width, spacers, stem angle, stem length, etc. and the calculator will tell you your total reach and stack. This makes it quick and easy to compare two frame sizes and what it would take to get to the same reach/stack.

Do the Retul if you are unsure of your current fit.

DJT21
Posts: 183
Joined: Sun Mar 27, 2011 7:35 pm

by DJT21

rynogee wrote:
Sun Feb 18, 2018 8:11 am
TobinHatesYou wrote:
Fri Feb 16, 2018 6:51 am
silvalis wrote:
Fri Feb 16, 2018 1:42 am
TobinHatesYou wrote:
Fri Feb 16, 2018 12:13 am
With a saddle slammed forward on a zero-setback post you are really closing up your hips at the top of the pedal stroke and bending your knees too much...
Could you elaborate on this because I'm having trouble visualising your words.

Assuming the upper body angle to horizontal is staying the same (eg the bars are moving equivalent with the saddle) and assuming the cleat position isn't changing as well, then moving the saddle/hips forward relative to the bb in an arc will open up the hip at the top of the pedal stroke, not close it...
Two reasons:

1) Because when you move your hips closer to the BB along the horizontal axis, you are turning the full extension of your leg closer to a straight vertical line instead of a more natural diagonal. Think "|" vs "\" ... With more setback your pedaling involves less knee flexion, and as a result of that less hip flexion.

2) Because the OP is presumably trying to stick to a long and low stem/bar position up front because it looks "pro." He should move his saddle back to a normal position (lower and farther back) and use a shorter/higher stem/spacer/bar combo.
I guess you know what they say about making assumptions...

the frame is too large. I'm trying to decide how much smaller to go. (in order to get a better fit, not trying to look like anything).

short stems make a road bike handle poorly, there isn't much point having perfect hip angle if the bike handles like a dog as a consequence
What a load of nonsense. Short stems don't make a road bike handle poorly. Another internet myth that badly educated people regurgitate on internet forums.

A badly fitted bike is more likely to handle poorly. If a bike fits perfectly with a short stem then it will handle just fine.

However, a short stem is often a consequence of a poor fit.

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siauragama
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Joined: Fri Dec 30, 2016 9:33 am

by siauragama

DJT21 wrote:
Sun Feb 18, 2018 7:57 pm
However, a short stem is often a consequence of a poor fit.
What is a short stem? Shorter than recommended by frame manufacturer for given frame size?

TobinHatesYou
Posts: 1211
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

siauragama wrote:
Sun Feb 18, 2018 9:21 pm
DJT21 wrote:
Sun Feb 18, 2018 7:57 pm
However, a short stem is often a consequence of a poor fit.
What is a short stem? Shorter than recommended by frame manufacturer for given frame size?
FWIW, the OP seems to think a 110mm stem on a 54cm is short, which is laughable.

pdlpsher1
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Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

There's a growing trend to use a long stem and long seatpost. This is because everyone wanted to look like a pro. Pro bikes use long stems because they need a very small frame in order to achieve a significant saddle to bar drop. Most of us non-pros cannot ride in such an aero 'pro' position for a long time. Now it seems that a 120mm is the norm, which is unthinkable ten years ago. If you want a lot of seatpost showing you can choose a bike with a sloping top tube. When I had my custom bike designed I wanted a lot of seatpost showing. This is because I wanted to use a suspension seatpost (Canyon 'leaf spring' model) and that seatpost requires a certain amount of exposed seatpost for the suspension effect to work. So I opted for a 11 degree negative slope top tube which is the same as a Moots Vamoots RSL.

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silvalis
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Location: Aus

by silvalis

pdlpsher1 wrote:
Mon Feb 19, 2018 2:32 am
There's a growing trend to use a long stem and long seatpost. This is because everyone wanted to look like a pro. Pro bikes use long stems because they need a very small frame in order to achieve a significant saddle to bar drop. Most of us non-pros cannot ride in such an aero 'pro' position for a long time. Now it seems that a 120mm is the norm, which is unthinkable ten years ago.
While I don't doubt your comments on the growing trend, you are talking about a fraction of the cycling population though, not the 'norm'.

pdlpsher1
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Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

silvalis wrote:
Mon Feb 19, 2018 3:28 am
pdlpsher1 wrote:
Mon Feb 19, 2018 2:32 am
There's a growing trend to use a long stem and long seatpost. This is because everyone wanted to look like a pro. Pro bikes use long stems because they need a very small frame in order to achieve a significant saddle to bar drop. Most of us non-pros cannot ride in such an aero 'pro' position for a long time. Now it seems that a 120mm is the norm, which is unthinkable ten years ago.
While I don't doubt your comments on the growing trend, you are talking about a fraction of the cycling population though, not the 'norm'.
Very true. I was just thinking of the WW population here when I made the post.

dim
Posts: 222
Joined: Fri Oct 13, 2017 11:25 am
Location: Cambridge UK

by dim

I've just bought a new bike for Audax rides/long distance and which will also be used as my daily commuter. I'm really keen to have a proper bike fit, and Primo Cycles offer the STT 3DMA bike fitting system. They are less than 10km away from me and I will most probably have this done.

http://primocycles.co.uk/2017/12/07/why-stt-3dma/

and a video:

http://primocycles.co.uk/2017/12/07/why-stt-3dma/
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Hexsense
Posts: 418
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Since we discussing about appropriate stem length and bike size, Let me ask for an advice for my sizing then,
I'm 169cm tall, inseam 79cm. currently using a bike with (frame) stack=511 reach=378, 9mm headset cap, no spacer, -7 degree 120mm stem.
Looking at this geometry of potential new frameset
http://www.workswellbikes.com/PRODDUCT/ ... 5/177.html
based on this i could use either
size 49 =505mm stack, 380mm reach set up with 15mm cap (6mm taller cap) then -7 degree 120mm stem
or
size 52 =522mm stack, 384mm reach set up with 9mm cap then -10 degree 110mm stem
both will give similar stack/reach and both are fine.

the difference however is how it will handle, both have 43mm fork rake and similar wheelbase (+-1mm), however
size 49 have 71.5 degree head tube, will fit with 120mm stem.
size 52 have 72.6 degree head tube, will fit with 110mm stem.
i'd guess they handle differently, right?

billspreston
Posts: 367
Joined: Tue Jun 30, 2009 7:40 pm
Location: CA

by billspreston

The trail on the size 49 is 65mm while the trail on the size 52 is 59mm. The size 49 will handle a bit slower. This can actually be a preferred trait for some riders, particularly those who ride a lot of flowing descents. I believe Colnago C60 has quite high trail values and is consistently regarded as a great descending bike.

I do think you'd be fine with either, with a small difference between the two. If I was in your position I would pick the size 52. It sounds like you have long legs and would balance better on the bigger frame. Aesthetically I also prefer a 110 stem vs a 120 in these smaller frame sizes. The handling difference between 10mm of stem is negligible. If you do a lot of descending or prefer a slower handling bike then I might consider the size 49.

pdlpsher1
Posts: 1542
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

The reason why the size 49 has shallower HT angle is to avoid/reduce toe-overlap. You can clearly see this in the geometry chart where the size 44 has a HT angle of only 70.5. But ideally when you use a shallow HT angle you should also use a fork with more offset to compensate the shallow HT angle. You see this fairly common on many bike models where the manufacturer will spec. two different forks with different offsets depending on the frame size. As a reference point my current custom Ti bike has a fork offset of 48mm and a HT angle of 72. I find the handling of my bike to be prefect for my taste. I think the size 49 with a fork offset of 43mm will produce a handling that is too slow. Maybe you can provide your current bike's fork offset and HT angle to get an idea of what changes in handling the new bike will result in.

Hexsense
Posts: 418
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Thank you,
I'm currently using Hongfu FM-169 (Avenger R8) which their geometry is exact copy of Canyon Aeroad.
72 degree headtube. unknown fork offset but i estimate it to be around 43-45mm.

So WCB-R166 49 will give me slower steerer and 52 will give me faster steerer i think. In this case 52 seems like a nice try.

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