I have an S1 56cm which I ride with an 11cm stem. The stem is down right down on-top of the conical spacer as I end up with it pretty low at the front, I'm 182cm tall.

 Im just about at the point of clicking 'buy' on an R3, which has the same geometry table as the S1 but I'm caught wondering whether to 'stick with a 56cm' OR go for a 54cm and put a 13cm stem on it (the extra 2cm making up for the 2cm shorter dimension of the top tube) ...then I'd also have 20mm less in the head tube on the 54cm so there's the possiblility of me lowering it when I put tri-bars on it for some club 10 stuff, which I've been doing on the S1.

Anyone got any opinions on whether the 54cm with a 13cm is an odd thing to do compared to 56cm with an 11cm stem.... yes, I'll have more seapost showing too, but Im not that long in the leg, if anything got a longer torso.

  Edit : looked at competitive cyclist bike fit calculator out of interest just then and it says this for me....

 

Measurements
-------------------------------------------
Inseam:                84
Trunk:                 69
Forearm:               35
Arm:                   67
Thigh:                 61
Lower Leg:             55
Sternal Notch:         148
Total Body Height:     182


The Competitive Fit (cm)
-------------------------------------------
Seat tube range c-c:   54.4 - 54.9
Seat tube range c-t:   56.1 - 56.6
Top tube length:       55.9 - 56.3
Stem Length:           11.6 - 12.2
BB-Saddle Position:    74.0 - 76.0
Saddle-Handlebar:      55.2 - 55.8
Saddle Setback:        5.4 - 5.8

 ...so with a top tube length of 565mm this confirms that 56cm is correct and I should stick with that?? ...I haven't much looked at the other figures to check them out, is there anything else this should be telling me? (I always seem to want to be a bit forward on the rails saddle-wise too.)

I have a 56 RS frameset for sale in mint condition. See my post of 11/4. Even with the CC sale, it will be a lot less.

Interested?

 RS will have an even longer headtube so it will be wrong for me as thats one of my concerns, keeping that down. Ta for pointing me though.

My dimensions are similar to yours. I'm 5'9" (175cm) with a 84cm inseam. I rode a 56cm R3, with a 120mm stem. (my position is unusual compared to many) I think the CC fit calculator is bogus - at least for me.There is nothing wrong with a long stem: it makes your steering more stable.The shorter the stem the quicker it is. Stable steering is good, especially in pack riding. You see racers on 120-140mm stems all the time. If they didn't like that it would have changed a long time ago.

Yes, you will have more post showing on a 54 but not much more,they would both look normal seatpost wise. 

A 54 with a 130 is getting a little long, shifting more weight to the front end, especially if you do run a TT front end with the same length stem.

How do you look/feel on the 56, do you feel you can stretch out a little more, or do you feel that you can shorten up a little, or does it feel just right.  And if the bike does feel just right, then why are you considering switching sizes. 

If you run the 54 with 20mm spacers to give you the same saddle to handlebar drop then the change in reach would be 14mm so a 120 stem would be 4mm shorter and a 130 stem 6mm longer.  If you change the saddle to bar drop it will change the reach also, more bar drop=more reach, less bar drop=less reach.

so i would look at my bar drop, and look at the change in reach after deciding on the drop, and if i could use the 120 then nothing wrong with the 54, but i dont think I would run a 130 if you really need to go to a 130 then stick with the 56 and just get a more negative stem if you need more drop.  THis is of course assuming you need a little more drop, if you are needing 4cm more drop then another whole discussion then maybe the 54 with 130 is better.

Have you consulted a fitter in your area, The online stuff is sh## by the way

sam:

If you run the 54 with 20mm spacers to give you the same saddle to handlebar drop then the change in reach would be 14mm so a 120 stem would be 4mm shorter and a 130 stem 6mm longer.

Probably best to skip down to where I wrote EDIT ***  below....

Umm... I thought the reach would be 20mm shorter on the 54 cos the top-tube is 20mm less (with the same length stem) as a starting point...but cos Id need 20mm of spacers (for same height again as a starting point) to raise the bars up to be the same as my current drop then this would mean that the bike would be getting EVEN shorter (as more spacers brings bars back a bit yeah). Id expect that reach to go more than 20mm shorter on the reach difference not less like the 14mm you say ?? ...so, stay with me here cos I might be getting right confused... i thought that by having a 130mm stem instead of a 110mm stem then Ive added 20mm to top tube that Ive lost between the 56 and 54 but then I'd LOSE a little more because of the bars being closer cos of the 20mm extra spacers?? BUT... you're saying a 130mm stem would be 6mm LONGER?? than Ive got it at the moment? Are you sure??

 Another way of putting it... you're telling me if I have 20mm of spacers extra (having bugger all on my 56 at the moment) on a 54 frame and I run a 120mm stem then I'll have 4mm shorter reach overall with the same drop as I have at the moment?? Not sure that I understand why as you can probably tell!!! BUT... that sounds like a good proposition to me with regards to how I feel on the bike at the moment.

***** EDIT: Maybe this is simpler...!!! If you said 14mm then you're saying if you add 20mm of spacers under the stem it effectively shortens the reach by 6mm? On that logic the 54cm frame is 20mm shorter in the top tube than the 56 but also will be an extra 6mm shorter reach-wise when these spacers are fitted... a total of 26mm shorter in reach ??

 On that logic if I then have a 130mm stem on a 54 instead of a 110mm stem on the 56 it'll be somewhere like 6mm less on reach overall?? (of course, there are angles in the stem too but my brain would burst if I tried to take them into account too) 6mm shorter would be fine, as long as 130mm stem on this kind of bike is in a good 'normal' range??

Sorry, but its stacks of money! ..and I wanna get it ordered while the pricing is good.

I will try to explain the reach in a way you can visualize, then explain in bike terms

Take a piece of paper, and draw a big V on it, on top of that V put 2 dots, and lets say the one dot on top of one side of the v is your saddle, and the dot on the other end of the v is your handle bars.  And draw a line between the two legs of the v towards the bottom of the v, it is going to be your top tube, now draw another line towards the upper part of the v, it is the top tube of the bigger bike.  The two top tubes are different lengths, but your saddle and bar positions never moved, so your reach stayed the same.  So top tube length really has nothing to do with reach ( in a matter os speaking )

 Now a bike is not a perfect V, in the case of 54 and 56 the difference in reach is 14mm, 6mm of the top tube length is being negated by the V affect.  because the TT of the 56 sits higher up the v it is 20mm longer, but only really 14 mm longer for your purpose

If you look at the geometry charts, and look at stack and reach, Those are the only 2 numbers that are going to tell you the actuall difference in fit.  The difference in reach is 14mm, if you set up the two sizes with matching X and Y cordinates, x and y being the realationship of the saddle versus BB, and the handlebar versus BB.  Or more simple put, if the saddle is set at the same height on both bikes, and set at the same for/aft on both bike.  Then you put your bars at the same drop on both bikes, In this case would be by adding 20mm or actually 19mm of spacers on the 54.  Both using the same length stem, Then the difference in reach would be 14mm.

http://www.cervelo.com/content.aspx?t=Company&i=WhitePapers#1  look at the presentation of geometry, it goes a little bit into the subject

I dont have my laptop at the shop today, that is where I keep my custom frame design program when building someone a custom bike.  If I had it I would plug in a few numbers to give you some more examples

 Ahh... that's great of you thanks explaining all that... well this might have changed things for me because I think 4mm shorter running on a 120 stem might be the exact answer for me. There's just the cosmetics of running 20mm of spacers under the stem thats all to consider really on the look of it but it would mean I could get it a fair bit lower when I put my clip on bars on it for club 10s and stuff and that could be a good thing. Thanks. Got some more thinkig to do now!

why would you use an r3 for time trials?

that should not be a consideration at all unless you do your time trials up alpe d'huez (or some such other purely uphill TT).

 Looked at that presentation... only thing now confusing me is this ... http://www.cervelo.com/slideshow.aspx?id=5 (go along until you see figure 8, don't think the link jumps you to the right bit of it) ...see where the reach is measured on each, well, the reach is stated at 14mm less on the 54 than the 56 but there's still 6mm less reach again cos of the 20mm of spacers?? If so, thats a straight forward 20mm total less reach I can expect and 20mm I need to add to the stem? ...or have they put the arrows on here a bit wierdly, is it really measured from the center of the top of the headtube back to a dropline through the crank center on each frame??

jordan:

why would you use an r3 for time trials?

that should not be a consideration at all unless you do your time trials up alpe d'huez (or some such other purely uphill TT).

Well, only for club run events, mucking about socially, not competition, if I was properly into that I'd buy a dedicated TT bike as well but I have just been clipping on some TT bars on my road bike and riding them a bit yeah... and it would be nice to be able to get a little lower for that, but thats not the use of the bike no.

 Another factor: on your 56, how close can you get your knees to the underside of the handlebars? When out of the saddle pushing forwards? Because they might be the same distance fore/aft from the saddle, but they'll be that little bit lower. You don't want to be tapping the underneath of the handlebars with your knees...

 

greg66:

 Another factor: on your 56, how close can you get your knees to the underside of the handlebars? When out of the saddle pushing forwards? Because they might be the same distance fore/aft from the saddle, but they'll be that little bit lower. You don't want to be tapping the underneath of the handlebars with your knees...

 

Umm... dont think thats an issue really as im first just trying to replicate the exact position (or maybe bring bars back about 5mm or so) and then have the option to drop the bars down should I want to. Im riding my 56 as high as I could want, what I mean is any higher and it would be no good, which is fine as it is but the stem is directly on top of the conical spacer at the moment with an 11cm stem you see, so Im thinking getting smaller would give me the option to lower them a bit, just weighing up the pros and cons. What I REALLY need is cervelo to make another size in-between like a 55cm with a 150mm headtube... that would be smack on.

Sorry, I think I should not answer questions when having a bad day at the shop.

But I spoke backwards, the difference in reach is 14 mm, but adding the 20mm spacers will negate that and make the reach 20 mm.  Sorry bout that.  I am usually having a conversation with someone comparing 2 different brands, with different angles and such, so had that way of thinking on my mind, I am sitting here at midnight designing a frame that is close in demensions to a 54cm cervelo and made me think about this thread, took a break to look at the forum, and now that I am not stressed out can think a little more clear.  So never mind what I say, i might just be nutz.

 

My own feeling is that you cannot go wrong with a 54. It's good to fit on the smallest frame that will fit you, and your stem is all the way down on the 56, so there is no risk of the 54cm frame being too small. You will approximate your old position with a longer stem, but it will feel marginally different with the smaller size. Many riders are on 12cm stems and like it. Even a 13cm is fine. You might want to try both. I had a 13.5 on my R3 for a while, and I use a 15cm on my townie (with upright bars) and the steering is fine.

I don't know how old you are, but we don't get any bigger once we're fully grown, in fact we shrink and get less flexible as we get older. I used to ride with a 13.5 and now I'm on a 12 for that reason.