Vraar

Hello
I did those measurements 3 times,with 2 different people and once solo,always got same results so this is not a mistake.
I'm 178 cm (5′10″) height with 79 cm ( 31") inseam.
Top Tube Length 56.8 - 57.2 Cm
Seat Tube Range CC 52.0 - 52.4 Cm
Seat Tube Range CT 53.2 - 54.0 Cm
Stem Length 9.8 - 10.4 Cm
BB Saddle Position 80.8 - 82.8 Cm
Saddle Handlebar 52.5 - 53.1 Cm
Saddle Setback 1.7 - 2.1 Cm
Seatpost Type Not Setback

I want to buy 80's or 90's Merckx Corsa.Should i go for 55 cm square or smaller/bigger one??
Thank You.

AnthonyG

Your short inseam is throwing a spanner in the works for the fit calculator and I don't think its giving you good advice.

A saddle setback of 1.7-2.1 cm is ridiculous. That's a time trialling position. It will be VERY uncomfortable to ride and distance as there will be a LOT of weight on your hands and shoulders.

Based on your inseam of 31" (787mm) I recommend that you should be riding 165mm cranks maximum. This is based on a recommendation that crank length should be in a range of 20-21% of inseam. 165mm is 21% of your inseam. The fit calculator I suspect is assuming 170mm or 175mm cranks and then theoretically positioning you for KOPS (knee over pedal spindle). This is just silly.

With 165mm cranks fitted to your bike you should be sitting higher and further back which will be more comfortable, and it should improve performance.

I recommend you buy a set of 165mm cranks, fit them to your current bike and then experiment with saddle position, either KOPS or slightly behind/in front of KOPS.

Anthony

Vraar

Thank You for You recommendations,will try 165 mm crank if i get a chance.
My current bike i bought few years ago when i had no idea about bike fitting.It was on sale and i guess they just wanted to sell it

I have a chance to buy Merckx Corsa 54cm square or 55cm Moser Leader but without trying it first so i have to at least somehow rely on calculators.

Took measurements again this morning in case im doing something wrong but results are almost the same,using spirit level to be sure.
Top Tube Length 56.2 - 56.6 Cm
Seat Tube Range CC 52.4 - 52.8 Cm
Seat Tube Range CT 53.9 - 54.4 Cm
Stem Length 9.7 - 10.3 Cm
BB Saddle Position 79.4 - 81.4 Cm
Saddle Handlebar 52.3 - 52.9 Cm
Saddle Setback 2 - 2.4 Cm
Seatpost Type Not Setback

Actual Inseam79 Cm
Trunk 67 Cm
Forearm 32 Cm
Arm 63 Cm
Thigh 54 Cm
Lower Leg 56 Cm
Sternal Notch 144 Cm
Total Height 178 Cm

Here are my measurements fit into wrench science
Road
Frame Size Center-to-Center: 51
Frame Size Center-to-Top: 53
Handlebar Width: 42
Overall Reach: 67.50
Saddle Height: 69.76

AnthonyG

Cranks change everything. A fitting that works with one length of cranks doesn't work the same with a different length of cranks. I wouldn't trust ANY fitting data that has you with only 2-3 cm of saddle setback or even less. I would trust even less any fitting data that DOESN'T quote a saddle setback figure.

Shorter cranks will lead to MORE saddle setback. The small saddle setback distances quoted by the fit calculators is a major red flag to me that something is drastically wrong.

My gut felling is that you need a larger frame fitted with short, 165mm cranks, which is an unusual way of doing things and to be honest, I haven't worked it out any better than the calculators. I suggest you fit 165mm cranks first to your current bike as a test bed and then see what is needed.

Speaking of your current bike, what size is it and what do you wan't to change about your fit?

Anthony

trailangel

I say 170mm cranks are fine. You are 5' 10".
No smaller than 55cm frame.. would go 56 or 57.
Your torso is longer than you legs and you will fit better with a larger frame... just lower the seat a little.. handful of seatpost.
If you were 5'10" with longer legs I would say smaller frame like 55cm.

fietsbob

What are You Measuring? rather than use trouser inseam to cuff, use the absolute highest distance that you can stand over.

pull a book up between your legs, barefoot, and mark the wall where you get it pulled up to.

jyl

Your measurements are similar to mine: 5' 11", 32" bike inseam (not pants inseam, see fietsbob's post). I am most comfortable on 56 cm to 58 cm (center to center) bikes, this is traditional/old-school frame geometry with top tube roughly same length as seat tube ("square"). I have to use seatpost with set back, slide saddle toward rear, and longer stems to get enough saddle-to-bar reach.

To give you some concrete examples, one bike is 58 cm CTC, set back seatpost, 120 mm stem, long modern brake hoods; another is 56 cm CTC, very set back seat post, 120 mm stem, and long modern hoods; another is 58 cm CTC, set back seatpost, 140 mm stem, short vintage brake hoods.

If you prefer a more upright position, you might not need as much reach. Bottomline, I think you should lean toward 56-57 cm seat tube center to center for a "square" frame, just make sure you can stand over the top tube with a bit of crotch clearance (lightly brushing the hanging soft bits is okay in my book).

Edit: If you're going to use the bike for short fast rides, you could certainly go for a smaller frame. I have a 53 cm (52?) road bike that I ride with a looong seat post, it is great for short rides, feels fast, maneuverable, etc - but around 40 miles my back starts to hurt from the cramped position. One of these days I will find a very set back post and a super long stem for that bike, also switch it to modern brifters with looong hoods, and see if that works better.

I don't know anything about short cranks, I have 172.5 cm mostly. I can see the reason for trying shorter ones, but just haven't, mostly because they are not that easy to get.

Vraar

Highest possible without bib shorts is 82 if i push really hard

My current bike is pretty old and used up, it's 55 c-c effective top tube and 46 c-c ,51 c-t seat tube.
I want to start riding more and this time get best fitting frame i can get.
And i fell in love with 80's-90's steel frames .I will try to test 165 mm and see how it feels.

Ok thank You for advice.I will go to bike shop tomorrow and do some test rides on different frames.

fietsbob

Lots of bike frames have sloping top tubes now , throwing off the size numbers,

but going to a shop and physically standing over the bikes

will resolve the conflicts in numbers and their actual meaning.

Vraar

Thank You very much a lot of great info.

My main problem and why im using calculators is that i will be buying new-old bike via ebay prolly ( cant get any old steel frames where i live).
It will be classic geometry prolly Merckx Corsa. From answers here i think something like 55 or 56 cm square should be ok.Thank You for help.

fietsbob

My RB1 is a 56 level top tube 565 long I m not short legged or long either ..

I can still do a stand over on a 58 too .. thats about my touring . Max..

Road Fan

In that case the proper inseam to use is 82. We also usually measure to the millimeter if possible. You need to get the upper measurement point to approximate the position of the saddle top when your weight is on it. You NEED to push really hard!

In any case, if you think this is not correct, find a bike with a flat top tube that measures 55 cm c-c for the seat tube, and stand over it in bare feet. If you feel a lot of pressure, 55 cm is likely too big based on likely interference with your body when you stand. I find your cycling inseam of 78 cm to be implausible. It's off by nearly 2 inches in your first measurement, and this is a big error in frame sizing/fitting.

The best way to apply upward pressure is for you to hold the piece of wood or whatever and pull it up, while your friend makes sure it's level and your legs are straight, and makes the measurement. It SHOULD be at the maximum physical height, and if you feel painful pressure against your skeleton, that is a sign you are getting it tight.

A smoothed 2x4 about more than 2 feet long makes a really good tool for this. Measure with a tape that shows at least to the ⅛", estimate the 1/16" in between the marked eights, and then convert to millimeters using a calculator - 1" is equal to 25.4 millimeters.

Road Fan

Vraar, the fit calculators often give pretty decent results. You really should try it again with the 82 cm inseam and see what happens. Your seat tube guideline should increase.

Anthony says the setback number is too small, and I can't argue, but I also don't use KOPS as a fitting criterion at least for myself. I tend to set back my saddle to get my center of gravity so I'm more nearly balanced over the BB and don't have excessive hand pressure. It's probably not good for a maximum power position, but it works for me over long hauls. I'm 5'6", 185+ these days, and I have cycling inseam around 81 cm. My best seat tube length usually works out to 53 or 54 cm on vintage frames, with TT up to 54. However, I like a laid back seat tube (71 to 72.5 degrees) to enable adequate saddle set back.

Yes, I need to lose weight and strengthen my core, but until then I have a bike or two that works well.

AnthonyG

If your actual inseam is about 820mm rather than 787mm then yes, you can use longer cranks than 165mm. 170mm would be good although 165mm may still work for you well.

Also I don't think that KOPS is a golden rule of fitting yet it is still a very useful measuring point. You can be behind KOPS if you like or in front of KOPS if you like yet KOPS is still a very useful reference point. Were I get a bee in my bonnet regarding KOPS is the fact that so MANY recreational bikes have the rider positioned in front of KOPS where I would have all recreational riders behind KOPS for better comfort. Being in front of KOPS is only for high performance riders who know what they are doing. Placing recreational riders in front of KOPS just because the builders couldn't be bothered to do better is infuriating. It just puts recreational riders off riding.

Anthony

Vraar

I was following instructions at competetive cyclist calculator and it said "INSEAM Wear your cycling shorts , and take the measurements in bare feet." Thats why the difference in those 2 measurement,first one was in shorts and 2nd without and with a lot of pressure.
I think i will go for something like 56-57 top tube frame.And few days ago i was looking at 52-53 cm frames.
Thank You guys for advices,it really made my frame size choice much much easier.

AnthonyG

Well, maybe in this case you would be better off with 165mm cranks. The shorter cranks will enable the saddle to be set further back for the KOPS position, which will take the weight off your hands and shoulders and make it easier to adopt an aerodynamical position.

Longer cranks may give you a tiny bit more torque when the pedals are level but then its slightly harder to get through top dead centre of the stroke. Shorter cranks make it easier to go through top dead centre but at the cost of a little maximum torque.

Shorter cranks will smoothen out your power delivery and help to make the bike more comfortable.

Anthony

Road Fan

I think the shorts would have to be armor plated to add more than 2 or 3 millimeters of thickness buildup with your weight on the saddle.

With cycling inseam, you are trying to measure the distance from the foot's bone surfaces that support your weight to the pelvis' bony surfaces that form your support points while on the saddle. That number is then multiplied by a factor to get the target saddle height. The multiplying factor allows for adding margins for pedal shape, shoe buildup, and perhaps shorts thickness. That's how the traditional methods work. Whether Competitive Cycles has them programmed accordingly I could not say. But I still can't see the shorts making a difference more than 3 mm. NOT 3 cm.

Vraar

The big 3cm difference is because i didnt put enough pressure while measuring for the first time.So i guess my correct inseam is 82cm.I have a chance to buy 57 cm top tube Merckx Corsa ,i hope it will fit.
Thank You very much for help.