Effective top tube difference vs. height?

[shortieforlife]

Hello lovely ladies,

I just joined the forum and I'm also trying to join the world of cycling. I've been looking for my first road bike for 2 weeks now, and I'm just getting more and more impatient about the matter. I want to bike for a month at least before it get's all snowy icy here in my State..

I'm only 4"11' which doesn't make the problem any easier. I really want to get Bianchi Nirone7 in 44cm frame (has effective top tube of 510), but not sure if I can fit on the bike. I can't find one nearby to test ride..

However, the ones I did test at my LBS are..

Specialized Dolce (Claris, basic model) 44cm Effective tube top 498 - perfect fit

Specialized Dolce 48cm, ETT 506 - a failure, couldn't even get on the bike without help, the brakes were too far. Although handling and riding was alright once I established my balance.


I don't know if it was the big frame size that messed up the fit or the effective tube top of 506... Is there anyone around my size with experience with Bianchi 44cm model? Any thoughts or advices would be greatly appreciated.

Thanks!

 

[lisamatjessie]

Hi
I am the same height and have had loads of issues getting bikes to fit. Currently I ride specialised Amira s works 44 frame and cannondale supersix 44. I find the cannondale easier to get on drops. I have had two professional bike fits which have helped. Cannondale has longer crank I tried shorter crank for amira. Prefer the bigger crank to be honest. How did you get on with your final bike choice what did you opt for

 

[alfeng]

FWIW. This may be long-after-the-fact as a beneficial comment for the OP, but a shorter-or-longer stem is often used to tweak a bike's fit ...

So, if the Specialized Dolce (498mm Effective Top Tube) with the "perfect fit" has a 100mm (?) stem ...

Then if the Bianchi Nirone7 (510mm Effective Top Tube) is fitted with a 90mm stem and/or the TERRY handlebars (which have a shorter forward reach ... and, which I presume are still sold) then (if the saddle is oriented the same relative to the pedals) you could adjust the Bianchi to have the same effective reach as the Specialized.

At the extreme would be to use a stubby 50mm Downhill stem (there are also slightly longer DH stems).

Raising-or-lowering the stem/handlebar will also have an affect on the effective forward reach.

The fact that the sales person did not mention that you could change the stem with one which has a different length is inexcusable, IMO ...

Unfortunately, in the retail world, sales of one item over another are often promoted based on the profit margin and/or possibly the commission which the sales person might receive ...

So, caveat emptor should be heeded in more ways than one might think.

 

[BrianNystrom]

The "effective top tube" length (ETT) cannot be taken in isolation when comparing bikes. It is the combination of the seat tube angle (STA) and the ETT that determines whether the bike will fit you or not in reach. You want your body to be positioned properly in relation to the bottom bracket (BB) first, which is the primary concern when fitting a bike. From there, the other measurements effect the fit as follows.

If you were to take two small frames with the same ETT, but one with 74 degree STA and the other with a 76 degree STA (a common range for your size frames), the fit would be very different. Let's look at a couple of examples:

• If the bike with the 76 degree STA puts you in the proper position relative to the BB with the saddle positioned in the middle of the rails, the bike with the 74 degree STA would force you to slide the saddle forward to position yourself properly over the BB, effectively shortening the top tube length.

• Conversely, if the bike with the 74 degree STA puts you in the proper position relative to the BB with the saddle positioned in the middle of the rails, the bike with the 76 degree STA would force you to slide the saddle backward, effectively lengthening the top tube length.

This is why bike manufacturers have started quoting a measurement called "Reach". This is the distance between vertical lines passing through the BB and top tube/head tube intersection. If you take two bikes with the same Reach measurement, as long as you can get your saddle positioned properly (by changing the amount of seatpost offset or position or by sliding the saddle on the rails) they will both fit you in terms of reach.

It helps to know how much of a difference a degree in STA makes at the saddle, which varies depending on your saddle height. My girlfriend is 5'1" with relatively short legs and rides the same size frames that you do. A 1-degree change in STA is ~7mm at the saddle for her, so that would be a good guide for you.

You also really have to take manufacturer's stated frame sizes with a grain of salt, as they don't all measure them the same way. Some are measured from the center of the BB to the center of the top tube-seat tube junction (commonly called "center-to-center" or "C-C") and others are measured from the center of the BB to the top of the seat tube (known as "center-to-top" or "C-T"). Some with sloping top tubes use an "effective seat tube length". It's a mess and it can even vary within the same brand or bike model. In my girlfriend's case, her new 46cm Cannondale SuperX is actually slightly smaller than the previous year's 44cm bike. Go figure.

The bottom line is that when looking at frame geometry, you should concentrate on either the Reach or the combination of ETT (which you are doing) and STA, then check the "Standover Height", which determines whether you'll be able to straddle the bike comfortably. As I'm sure you know, that latter dimension can be a real deal-breaker for petite people.

I hope this information is helpful. I may have given more of an explanation than necessary, but I have no idea how familiar you or others who may read this are with frame geometry terms and their meanings.