Frame advice in respect of NOTICEABLE difference.

[night cycler]

My bike has an 18 inch frame.

Serious question.

What If I got a duplicate bike that was the same in every aspect except the frame size, (The 2nd bike has a 20 inch frame for example). Where would the actual differences be noticed when riding the larger framed bike?

For example: I would be sitting 2 inch further from the handle bars?

The frame would be 2 inch higher from the ground? The front wheel would be 2 inch further away from the pedal crank?

Can anyone advise please?

 

[vickster]

Which bit of the frame has been measured to give the ‘size’??

What sort of bike is it?

 

[simongt]

Frame size is measured from the centre of the bottom bracket ( the bit the pedals are mounted in ) to the top of the seat tube ( the tube that the saddle is mounted into ) to where it meets the top tube ( the 'crossbar' ). Generally, the frame will be proportionally larger all round, but not by two inches in each direction - ! A lot depends on the make, type and geometry of the particular frame, so it's hard to generalise. Larger frames tend to be less manoeverable in traffic / offroad, so it depends on what purpose you have in mind for the larger frame. If it's general roadwork, then as long as it fits your body dimensions, you should be okay. As an example, I'm a skinny 1.78m tall and my three main bikes are an 18" frame street bike, a 21" frame tourer and a 23" frame audax bike. So a lot depends on what you want to use the bike for.
Hope this helps.

 

[Cycleops]

It sounds like you mean the MTB you’re riding in the pic. The measurement is the seat tube from the B.B. to the top. A longer seat tube will put you higher. You will be sitting slightly further from the bars. The top tube will also be higher increasing the standover. Other dimensions on the main triangle will increase in proportion. Stem length may change too. The foregoing will vary when the manufacturer uses a sloping top tube.
MTBs will have a shorter seat tube length compared to a road bike for the same fit as they generally have a higher B.B.

 

[Spiderweb]

My Specialized Roubaix has a 49cm measurement from centre of crank to top of seat tube but is a 54cm frame so you can’t always rely on these measurements to determine frame size. Bikes with a compact geometry (sloping top tube) measure differently.

 

[Racing roadkill]

There are so many variables, the question is nigh on impossible to answer. There will be an envelope of overlap in the fit, dependent on the settings of all the adjustable components, which could well mean that with certain bits, of certain sizes, set certain ways, there would be no discernible difference to you as the rider.

 

[lazyfatgit]

Many manufacturers list frame geometry dimensions on their websites.

Foe example, here’s the sizing for my MTB.

 

[Vantage]

The simple answer to this question is that you woud be more stretched out from saddle to bars. As a result the bike will feel more cumbersome but won't actually be more cumbersome in itself.
You might have difficulty clearing the top tube when standing over it depending on how well the smaller frame fitted you.

 

[night cycler]

Thanks. There is more to this subject than I realised, but I will provide some detail and clarity of why I am asking.

The bike in question is my lightweight 18 inch (ROSE brand) road bike.

When my bike was in the workshop, I was without it for over a week. I found it very frustrating not being able to cycle for that time.

I want to buy another because I like the current one so much, and I won't be without a bike again.

(All the parts would be interchangeable too. Not that I intend dismantling it, but if it is ever written- off the parts are salvigable for the other bike).

Now to the reason for my original question.

Although my bike is great to ride, and 'it flies' when I want it to, I think it is maybe a tad small for me.

When the pedal crank position is forward, the first few inches of my foot (the bit that is not actually on the pedal) is at the side of the wheel If I am turning at that point, the tyre makes cotact with my foot. This is why I feel that maybe a 20 inch frame would be more suitable if I buy the same model again. (I am 5'8" and my arms are quire long).

What do you think?

 

[Cycleops]

I would have said 18” is a little too small for you, a 19” or 20” might suit you better. Did you not try it before you bought?

The foot overlap with the front wheel is due to the tight head angle of a fast road bike and might not be any different with a bigger frame. You can only try. The problem would be eliminated if you went for a hybrid or adventure/touring bike as the head would be more relaxed and the wheel base longer.

I see from the pic of you on the MTB it seems you have the seat very low. You need to have it so your leg is straight or thereabouts when seated with the pedal at six o clock. Having it too low might induce leg pain, straight will give you more effective power delivery.

 

[vickster]

I didn't realise modern bikes were still measured in inches? Which bit is 18" (45cm?) If the seat tube that seems small (unless it's some weird geometry)

What exact bike is it, Rose have a big range of roadbikes?

 

[night cycler]

Cycleops-Ignore the MTB, I will remove that avatar because it is misleading people. I no longer use it & I should get rid of it. The seat on my road bike is much higher.

Thank you for advising that my foot could still touch the tyre if I got the same model in a 19 inch or a 20 inch.

I would have liked to have tried the bike for size before ordering, but it was an online purchase from ROSE in Germany.

Vickster the model is the Rose multiroad Pro SL2000 with straight handlebars. (see new avatar).

 

[vickster]

Ah ok, so it's a flatbar not drop bar roadbike. I'm none the wiser as the sizes on the website are quoted in cms...which correspond essentially to the Top tube length (horiz.)

On that basis, I should think you'd need a 55cm probably if 5'8 and long armed

 

[night cycler]

Possibly. That is about 21.5 inches.

My bike was ordered as an 18 inch. Just been looking at the receipt and it says "shiny- black /grey-green 55+3" Not sure what the 55+3 referres to as 58cm is about 23 inch. Clueless

[ATTACH

 

[vickster]

You have a 55cm, I'd say the 3 bit is irrelevant and probably a SKU reference or something (same as below next to bike box)

Still none the wiser as to where the 18" comes from

Looks like it could cost you at least £100 more thanks to Brexit killing the exchange rate. It's quite a lot for an alu flat bar too

How does yours feel if you stick a longer stem on and push the saddle back on its rails?