Geometry question -Langster to System Six - Help!!

[JesseD]

Dear WW Agony Uncle

I have a problem and want to know what to do about it?

I have been riding a Cannondale system six in a size 58cm with a 120mm Controltech stem which I always thought fitted me well, the bike has not been without problems as ever since I have had it the bottom bracket has creaked or clicked. I am running Campagnolo UT and initially had the adaptor sleeve bonded in which developed a click, so I had it removed and bought the press in cups which were ok for about a week then started to creak like crazy. I have tried all manner of Loctite solutions to the point where I was actually going to buy a BB30 specific chain-set and see if that worked, but after reading reviews on the net it seems like the creaking is a common issue with BB30 frames such as this.

Through work I had the chance to buy a Specialized Langster VAT free (god bless the cycle to work scheme) so bought one in the closest geometry I could to the Dale (57.5 TT and 17.5cm HT) which was a size 58cm (56.9cm TT and a 17cm HT with a 110mm stem) and I must admit it has been a revelation!! The fit seems so much better (could do with a 120mm stem I think) and I feel more powerful despite the geometry actually not being that different to the Dale (TT is 0.6cm shorter and stem height from bottom of HT to bottom of stem is the same on both bikes with spacers @ 19cm). So this is where my dilemma has arisen on what to do with the Dale.

So….

Do I rebuild my Cannondale System Six and find a solution to the creaking BB as the fit will be as near as dammit to the langster?

Or

Do I sell it and buy something different with a closer geometry to the Langster (56.9cm TT and 17cm HT but 74 degree ST and 74 degree HT) like a Tarmac in a 56cm (56.5cm TT and 17cm HT but 73.25 degree ST and 73.5 degree HT)?

Does the slight difference in TT length make that much difference?

Will the angles of the HT and ST make that much difference?

Is the Dale in a 58cm comparable to the Langster in a 58cm?

Yours sincerely

Confused of Bristol

[Dammit]

Chuck a tape measure on it and see what the measurements are from tip of saddle to centre of bars, and tip of saddle to tip of shifter hood.

That'll tell you what the actual difference is in terms of reach between the two, you could then move the Cannondale closer to the Langster to see if it feels better for you- i.e. 575mm top tube plus 120mm stem at the moment, so swap to a 100 or 110mm stem etc.

Or, sell me the System Six frame and get an S-Works Tarmac in a 58.

[JesseD]

Bikes already stripped down so cant do that unfortunately, also dont really want to stick another stem on it as it has the original Control tech one on which is stiffer than a stiff thing, also i dont like the look of a normal stem on the beefy headtube.

So what i am thinking is:

'Dale = 57.5cm + 12 cm stem = 69.5cm

Langster = 56.9cm + 12 cm stem = 68.9cm

I cant see the 6mm making a massive amount of difference but will the HT and ST angles or is it all relative as tt and stem length are all that matter?

[stella-azzurra]

My one rule in buying a frame is to buy one size smaller. Now you know why JesseD.

ControlTech stems are cheap buy another.

All contact point measurements need to match to your Lagster.

Seems like a no brainer here.

[Dammit]

The System Six specific stems do come up on eBay fairly regularly, and generally not for much money.

It's usually American eBay that said, although German eBay is usually worth a look.

I have a 58cm System Six, with the 120mm Control Tech stem, and yes- 695mm total from the two.

I also have a Klein Quantum Race with a 595mm top tube and a 100mm stem- 695mm total.

The Cannondale is the best handling and most comfortable bike I've ever ridden, the Klein feels like a bike.

So, even if you get the reach the same, it may not feel right.

Therefore, you should sell me your Cannondale.

[JesseD]

Therefore, you should sell me your Cannondale.

I am getting the feeling you are angling for another system six you can have first refusal if I sell it.

Maybe the 56cm Tarmac is the way forward

My one rule in buying a frame is to buy one size smaller. Now you know why JesseD.

I tried a 56cm and the HT was too short, I have a pathological hate of spacers so wanted a higher head tube, I found I was resting on my hands to much which gave me numb sport and hurt my back, I am getting old now (39 in 2 months) so my back is not what it used to be.

[5 8 5]

I cant see the 6mm making a massive amount of difference but will the HT and ST angles or is it all relative as tt and stem length are all that matter?

The 1 deg difference in STA can make a big difference. You have to move the saddle further back on the Langster to account for it.
If your saddle height was 80cm the difference is 1.3cm. You have too short a stem on the Dale if you're thinking of getting a 120 for the Langster.

[daj]

Let's take the easiest two measures of a frame to compare the two: stack and reach. They can be found on the manufacturer's respective website. (cervelo has a nice explanation of stack/reach. Click on "geometry and fit")

The reach on the Langster is 409 compared to 399 for the Cannondale.

The stack on the Langster is 559 compared to 579 for the Cannondale.
(the difference in stack can be explained by the slightly lower head tube bottom bracket position, which is very high on a track bike).

So the Langster size 58 is both longer (10mm) and lower (20mm) than the 58 Cannondale.

[diegogarcia]

Don't forget that your Langster has 170mm cranks, which may make a difference if you are running 172.5 or 175 on the dale ?

[JesseD]

Running 172.5mm on the dale (or was until it was stripped), this is where my ignorance comes in, how does it make a difference to fit?

[diegogarcia]

Running 172.5mm on the dale (or was until it was stripped), this is where my ignorance comes in, how does it make a difference to fit?

To attain the same saddle height set up for a nice bend in the knee, you would have elevated your seat to compensate for the 2.5mm difference in crank length as well as fettled your fore and aft to get your knee over the pedal...?

Most people wrongly assume you lower the seat to accommodate the shorter arms, but no, you go up as it is how you fit at the bottom of the stroke (6 o'clock) rather then the top of the stroke.

Just thinking that the shorter crank may be mechanically better for you which in turn has thrown your fit off kilter - perhaps your reach is closer on the langster mate ?

Dont forget the conical spacer and 10mm spacers on the Langster too ?

[JesseD]

Pretty happy that my saddle height and fore/aft is good on both bikes, my concerns were more how much difference does the ST and HT angles make in relation to the TT and stem length.

On the langster I am using the connical spacer so from bottom of HT to botton of stem is the same on both the langster and 'dale, so am I now looking at reach and saddle to bars drop?

God this is bloody confusing.

[stella-azzurra]

All you needed to do was to measure all you contact points and transfer them to the Lagster. The bs about the HT ans ST are negligent between the two. #comonson.

[daj]

As I said in my previous post, stack is 20mm lower and reach is 10mm longer on the Langster.

To translate this into the handlebar position:
If you use the same spacers and stem on both bikes, the handlebars will be exactly 20mm lower and 10mm further ahead on the Langster, compared to the System Six.

To obtain (roughly) the same handlebar position, on the Langster you would have to use 20mm extra spacers, (and you might use a 10mm shorter stem, but it is not necessary).

Use the method of Lennard Zinn to measure the exact position of handlebar and saddle, relative to the bottom bracket, to obtain identical fit.

[JesseD]

Now I see, and all it took was a picture!

The reach on the langster with a 11cm stem is roughly the same as the dale with a 12cm stem, the langster stack is 20cm less than than the dale, which can be remedied with spacers.

So I can pretty much replicate the fit on the dale with some fettling and a tape measure.

Looks like I am scouring the bay for a groupset/wheels/finishing kit etc.

Thanks all