Sizing/geometry question

Camcycle1974

When looking at geometry of different bikes is top tube length (or effective tt length) more or less important than reach?

For example my Giant Defy which feels slightly too stretched is 560mm ETT and 380mm for reach. The PX Pro Carbon I am looking at is 547mm ETT and 385mm for reach. Basically will I feel even more stretched on the Pro Carbon than I do on the Giant despite the fact the TT measurement is shorter :?

mikenetic

Bear with me, this could be a bit complicated.

Reach is measured from the horizontal distance between an imaginary line drawn from the centreline of the top of the head tube and a vertical line drawn up from the centre of the bottom bracket.

ETT typically runs from the centreline of the head tube where the HT and TT intersect to the horizontal intersection with the seat tube centre line.

On two bikes with the same reach, a steeper seat tube angle would result in a shorter ETT (the ST is being tilted forward, in effect), so this angle affects the distance. However, you're going to want to sit at a fixed point behind the BB unless you can make your legs longer or shorter. In other words you may slide your saddle back or forward to compensate for the ST angle.

Presuming you're happy with where you sit relative to the BB, you will feel more stretched on the PX Pro, allowing for same bar/saddle height difference, stem length and angle. In effect nothing behind the BB changes, but the front of the bike has got 5mm longer.

Fundamentally ETT is a bit of a tricksy measure, as it doesn't account for how you set up your saddle position.

Cervelo have a great write up here: http://www.cervelo.com/en/engineering/t ... d-fit.html

Camcycle1974

mikenetic wrote:

Bear with me, this could be a bit complicated.

Reach is measured from the horizontal distance between an imaginary line drawn from the centreline of the top of the head tube and a vertical line drawn up from the centre of the bottom bracket.

ETT typically runs from the centreline of the head tube where the HT and TT intersect to the horizontal intersection with the seat tube centre line.

On two bikes with the same reach, a steeper seat tube angle would result in a shorter ETT (the ST is being tilted forward, in effect), so this angle affects the distance. However, you're going to want to sit at a fixed point behind the BB unless you can make your legs longer or shorter. In other words you may slide your saddle back or forward to compensate for the ST angle.

Presuming you're happy with where you sit relative to the BB, you will feel more stretched on the PX Pro, allowing for same bar/saddle height difference, stem length and angle. In effect nothing behind the BB changes, but the front of the bike has got 5mm longer.

Fundamentally ETT is a bit of a tricksy measure, as it doesn't account for how you set up your saddle position.

Cervelo have a great write up here: http://www.cervelo.com/en/engineering/t ... d-fit.html

Thanks for the explanation. Very clear. No wonder I am confused :? !

looking also at the Ribble 872 which is very similar geometry wise to the pro carbon.

mikenetic

The simple way to think about it is all other things considered, a longer reach will do exactly what it says.

Are you comfy on the bike? When you say you're too stretched is that manifesting as a sore back, shoulders, for example?

Camcycle1974

mikenetic wrote:

The simple way to think about it is all other things considered, a longer reach will do exactly what it says.

Are you comfy on the bike? When you say you're too stretched is that manifesting as a sore back, shoulders, for example?

Mostly ok except for a sore neck. Think I am too upright and it's putting my neck at a funny angle. Some tingling in hands too but back/shoulders are fine.

mikenetic

If you're too upright then a shorter reach might make things worse. Might be worth getting a decent bike fitter to take a look at you if there's one near you. When I had one I got a set of measurements so I could compare my fit to future bikes, so it listed saddle height, reach, stack, saddle to bar drop etc.

You can get a less upright position by lowering the bars, a longer stem, or a combination of the two. However, doing it yourself can lead to you hunting around, which potentially introduces money, discomfort and time.

Camcycle1974

Thanks Mike, which fitter did you use? My experience of them so far is not brilliant, having been stung by an unscrupulous one in the past. Could have a Retul as a present at some stage I guess. In Cambridge where you would think it would be easy to find a decent fitter.

styxd

Do you have any pictures of you sat on the bike?

Camcycle1974

styxd wrote:

Do you have any pictures of you sat on the bike?

No but i can get someone to take some. Might only be for future reference as its up for sale. 5 months in and as i can't get comfortable it has to go. Hence the reach/geometry questions. Reach on my defy is 380mm. Can't find a reach figure for the ribble stealth r872 but the tt measurement is less than the defy.

styxd

How tall are you?

You're probably to hunched up if you're getting neck pain, you need to stretch out a bit more I reckon!

Camcycle1974

styxd wrote:

How tall are you?

You're probably to hunched up if you're getting neck pain, you need to stretch out a bit more I reckon!

A smidge under 5"10. The sizing guide says m/l is for people 5"10-6"1.
Hoping the 872 will give me more room to get comfortable it.

styxd

Have you tried adjusting your postion with different stem/bars etc?

Camcycle1974

styxd wrote:

Have you tried adjusting your postion with different stem/bars etc?

Got narrower bars on which is another indication it is too big. Came with 44's and i changed to 42. Have a 100 stem so not much scope to go shorter. Could try a 90 i suppose.

mikenetic

Camcycle1974 wrote:

Thanks Mike, which fitter did you use? My experience of them so far is not brilliant, having been stung by an unscrupulous one in the past. Could have a Retul as a present at some stage I guess. In Cambridge where you would think it would be easy to find a decent fitter.

I used Le Beau Velo in Shoreditch, London. It was done by two people, Mal, who runs the business, and Jo - she's a corrective exercise specialist. About 10 mins walk from Liverpool St Station, so easy from Cambridge.

The pair of them working together means that you get a lot out of it. There's an assessment of any physical problems or areas that need to be addressed. You get a fitting on your current bike, and a set of standardised measurements that you can use to compare other bikes or if you wanted a custom frame built.

My missus also had a fitting there that's helped her out - she was using a stem that was too short, crunching her back up.

Check out the fitting service here: http://lebeauvelo.co.uk/index.php?optio ... &Itemid=37

Camcycle1974

mikenetic wrote:

Camcycle1974 wrote:

Thanks Mike, which fitter did you use? My experience of them so far is not brilliant, having been stung by an unscrupulous one in the past. Could have a Retul as a present at some stage I guess. In Cambridge where you would think it would be easy to find a decent fitter.

I used Le Beau Velo in Shoreditch, London. It was done by two people, Mal, who runs the business, and Jo - she's a corrective exercise specialist. About 10 mins walk from Liverpool St Station, so easy from Cambridge.

The pair of them working together means that you get a lot out of it. There's an assessment of any physical problems or areas that need to be addressed. You get a fitting on your current bike, and a set of standardised measurements that you can use to compare other bikes or if you wanted a custom frame built.

My missus also had a fitting there that's helped her out - she was using a stem that was too short, crunching her back up.

Check out the fitting service here: http://lebeauvelo.co.uk/index.php?optio ... &Itemid=37

Great, thanks. I will check them out. Will need a fit when the Ribble comes.

passout

Ribble have a fitting jig or whatever you call them, if you can make it to Preston. At least they did when I bought from them about 5 yrs back - might be worth asking them. I wouldn't travel the country purely to do this though!

Camcycle1974

Thanks Passout. Have to confess I clicked the buy button last night. Won't get it until September, just hope I got it right this time! Cue comments telling me I am mad to buy a bike without trying it first etc.