maddmaxx 

Indeed, the magic question. This math only points to a starting point. As most have noted in this thread, adjustments from that starting point are an artform, not science. As you noted, the ratio points you toward smaller but the amount you are going to figure by yourself. I would think that going to a shorter than norm top tube would be part of the adjustment to bigger/smaller that the ratio points to. On the other hand, you may go down a size and look for a longer top tube. (this is where the art kicks in)

I think for purposes of discussion here frame sizing is the seatpost method and based on a traditional geometry frame. Compact frames have to be converted to traditional by using the virtual top tube length.

stapfam

I have two frames One a Giant Compact frame and that is a 46.5. The Boreas is called a "Sloping Tube" and is a 51. Top tube length on both is similar at 535mm for the TCR and 530mm for Boreas. 5 mm is less than 1/4" so They are extremely similar. However- One of the critical Measurementsd for set up of any bike- that most people do not realise- Is the seat tube Angle. This will affect the Fore and aft position of the saddle which can limit the Position of the Knee over the pedal position. A Lesser angle will put the seat further back than a greater angle. To me- this is one position I like to get correct for pedalling efficiency and is one of the reasons I would go for a smaller frame every time. The larger the frame size and the Lesser that angle is- hence putting the saddle further back on the bike. The TCR is a 73.5 deg and the Boreas is 74.4. Doesn't sound a lot but if that angle was 73 or less- then I would not be able to get the knee far enough forward for the position I like. And that is with an inline seat post and not the laid back form.

So as I said - Sit on the bike and see if it fits.

Having done the Measurement-I should be riding a 50.92 frame so Boreas is correct with the second calculation being 2.18. And the TCR compact frame equates to a 51 to 54 cm frame so I guess I am just on the Lower limit of this frame. Both these bikes were bought without any measurements being taken- just sitting on the bikes and adjusting to fit.


All I have to do now is Put an extra 3" into the ride position on the Tandem to get the theory to work. (Tandems are in a world of their own to get right so throw the book and theories out of the window and just ride the things)

Tom Bombadil

Visited a couple of bike shops and stood over several bikes in an attempt to find an optimal standover height. Found a couple where they felt just right, where I felt just a bit snug. Looked up the geometries on-line and found that they were 75.4 and 75.5 cm. That's right about where my measurements were, but it is easier to confirm over a bike than trying to use a tape measure and a book.

On a traditional geometry bike, that's a frame size of 49-50cm.

However when trying out a number of bikes, the ones that put me into my best riding position, according to the judgement of multiple LBS staff, were those with an effective top tube of 55-56 cm. Typically a 50 cm standard geometry bike will have a top tube of around 52-53 cm. My top tube optimal size requires a bike of around 55-57 cm.

So I fit the vertical size of a 49-50 cm bike, and the horizontal size of a 55-57 cm frame. I would need a custom made bike for a good fit in a traditional, non-sloping top tube design. But there are a number of stock bikes with compact geometry that provide a good fit.

solveg

Tom, after I get the CCM set up ( seatpost:52 cm x TT:56 cm), and after I get the information I need from it, why don't you borrow it for a couple months and play with it. It's about as close to a custom fit that you're going to get, too. I only need it for my fit tests.

Tom Bombadil

I've already got three bikes waiting to be ridden. And who knows if I'll buy a fourth anytime soon.

What's a "CCM?" And does it have foul drop bars?

solveg

If you borrowed it, you could put any bars you wanted on it.

It's the top road bike a mediocre canadian company put out in the early 80's. It's not low end...it's, well, think Japanese Bike boom. On the level of my Bridgestone 200. It has pretty lugs, I like it. It's just not a valuable bike, except to me because of the weird sizing.

If I find some huge, amazing handling difference, then I'll know that some day I'll get a custom bike. I suspect I won't be able to tell the difference. But I can set this bike up EXACTLY to my fit dimensions and know once and for all.

Big Paulie

Any thoughts about the ideal stem length, in terms of handling? I've always thought that 11 CM produced the most natural handling...assuming that's it the correct length for the frame you are riding.

I've had both 12cm and 10cm stems that were the right length in term of my reach, but the bikes didn't handle as well as 11cm.

solveg

For me, the Fit Kit gave me these dimensions. Would they work for you, Tom? If you're interested in riding the bike, we can meet sometime when you come to MN and I can hand it off. I can put some compromise bar we both agree with on it.

The fit kit said I should take a 52.7 cm bike, a 56 cm top tube, a 105-115 stem length, a 40 cm bar, and a crank length of 170-172.5 with a seat height of 85.2 to 88.1.

Tom Bombadil

Can't recall a reference to a "Fit Kit." Exactly what is that?

solveg

I think it's a serotta thing. They put you on this fake bike, measure you all up, adjust the bike, and look at you a lot. Once they like what they see, they modify your bike to the same measurements. It's half numbers and half art.

My problem was that I walked in with a 59 cm bike. He started out saying how huge the bike was for me, and how it may be that we couldn't adjust it enough. But when I got on it, he said that I had set it up in an unorthodox way, but that it looked great. All he did was lower the seat a smidge.

Here's my fit kit measurements as opposed to the bike I tried to set up myself.

The fit kit said I should take a 52.7 cm bike. My bike was a 59. I told him I had a bike that was 55 and that it felt a little small on me.

Fit kit said I should have a 56 cm top tube, the Mondonico was 57.

Fit kit said a 105.115 stem length, mine was 60.

Fit kit said a 40 cm bar, mine was 46

Crank length-- fit kit: 170-172.5; mine 172.5

Seat height: fit kit was 85.2 to 88.1, mine was 88.5

Road Fan

Tom, the book method should give you an inseam value that's larger than the standover height you got. The book is supposed ot get pushed up to simulate the presence of a saddle, and it sounds like you were more comfortable than that!

Are you of a long torso as well?

Road Fan

solveg

It sounds like he's almost exactly like I am.

stapfam

Can't have two Toms on the forum- Don't think I could stand it!!!!

This is why I have never bothered about what the books say Tom. I have short legs and that shortness is in the Thigh bone- Hence me wanting a bike with a Seat tube further forward than most. This generally means that I have to go for a smaller frame and a long seat tube- and possibly a longer stem than most would use. Most small bikes have a stem length of 70 to 80 mm and I find that just a change of stem to a 100mm and the bike will fit.

Certain Manufacturers were noted for their long Top tubes and Kona was one of those. Coupled with the sloping top tube aswell and Konas always used to fit me. Don't know if they are still the same but since they went away from using round or Oval Tubes and went to Bent plate welded into a tube- I have not looked at them.

I still think there is only one way to check to see if a bike fits and that is try it out. Shop assistants don't know how I like to set up a bike and they do get annoyed when I do not conform to their ideals. Luckily -My LBS know me so they can normally set up a bike for me.

Tom Bombadil

I got 75cm using the book method last week. On the bikes with 75.5 cm standover, the tube was pretty close to simulating the presence of a saddle. Definite upward pressure in the nether regions.

Long'ish torso. But slightly shorter than average arm length.

I'm all messed up!

Tom Bombadil

+1000

fthomas

Mine calls for a 56cm frame, which I have!

It does explain why all of my pants are so HIGH WATER!

I learn so much from you guys

Road Fan

Have we unwittingly discovered the cause of fredness? frames that are just a bit too tall?

fthomas

Oh, that hurts Road Fan

I am the Fred's Fred!

Signed
Fred

solveg

maddmaxx 

I don't know about freds but thats how we get the high voiced section of the chior.

Road Fan

Can't agree! My voice is moving from baritone to tenor, and I don't have any French fit frames!

Road Fan

Road Fan

I wasn't saying you were the cause, F Thomas!

I need some new Bermuda shorts with a pad for next year, tho! I'm fixed good for white socks.

taxi777

this link really changed completely the way I set my bikes. I spent all week remeasuring and adjusting and I'm really happy with the results
https://www.competitivecyclist.com/za...LCULATOR_INTRO

I like the Eddy position

fthomas

Just joking Road Fan

I am the Fred of Fred's I'm afraid! Just being honest!

Note: Still no clear picture of a "True Fred", but I'm probably close.

Tom Bombadil

So Solveg, did you pay in the neighborhood of $200 for your Serotta dealer fitting? That's what they charge here. I think that would be worth it if someone were paying $1500+ for a bike and was having a hard time getting a good fit.