# Does you Tarmac measure as advertised?



## Rugergundog (Apr 2, 2011)

I have a Tarmac SL4 size 56cm

According to the geometry chart this model should have the following lengths

*Seat Tube 530mm
Top Tube 560mm*


Yet when i measure my frame my Top Tube measures only *544mm.* Seat tube measures correct.

Can anyone else measure their bike?


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## nis240sxt (Oct 6, 2004)

Did you measure actual TT or effective TT length? I see the 56cm as having TT measurement of 565mm on spesh website which is the effective length not actual.


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## PJ352 (Dec 5, 2007)

Rugergundog said:


> I have a Tarmac SL4 size 56cm
> 
> According to the geometry chart this model should have the following lengths
> 
> ...


I suspect you're measuring actual TT length rather that _effective_ TT length.

Use the illustration below (read and green = ETT) and see how it measures out. Using a level helps, and keep in mind point A to B is center-top of HT to center of seat *post*. 
View attachment 249309


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## Rugergundog (Apr 2, 2011)

I want this frame in the picture provided to fit like my SL4. From my calculations i needed to order a 54cm frame as the numbers on this chart match up with the numbers i measured off my 56cm SL4.

Does anyone have a drawing like this for the SL4?

So did i order the right size?


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## PJ352 (Dec 5, 2007)

Rugergundog said:


> *I want this frame in the picture provided to fit like my SL4*. From my calculations i needed to order a 54cm frame as the numbers on this chart match up with the numbers i measured off my 56cm SL4.
> 
> Does anyone have a drawing like this for the SL4?
> 
> So did i order the right size?


To get close in reach and drop, you need to take STA, HTA and HTL into consideration when comparing frames, not just ETT.

In comparing the geo of the bike you posted with the 56cm Tarmac, the 56cm is a closer match in reach (slightly shorter than the 56cm Tarmac). HTL is 10 mm's shorter, so all else being equal (stem angle, spacers) drop will be ~10mm's lower.


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## Rugergundog (Apr 2, 2011)

Thanks for the explaination, makes much more sense nowl. I was doing my measuring from the top of my stem to the center of the seatpost hole in the frame. I didn't think of the head tube angle tilting the stem toward the back of the bike causing the measured distance to be different.

So i did all sorts of measuring and pondering and remeasuring and such. I then prioritized what is important to me.

I decided on the 54cm frame. Ultimately i like the feel of a shorter seat tube and sense of the bike seeming lower. 

In doing so the 54cm frame has closer to the same seatpost length as my 56cm Tarmac. 540 on new frame and 530 on Tarmac.

Now to compensate for a 20mm shorter top tube. I "think" the "actual" measured length is only going to be closer to 15mm shorter as the new bike has a much shorter headtube. I suspect a 20mm longer stem and playing with my stack spacers will get my reach similiar while keeping the low seat tube i like.


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## PJ352 (Dec 5, 2007)

Rugergundog said:


> Thanks for the explaination, makes much more sense nowl. I was doing my measuring from the top of my stem to the center of the seatpost hole in the frame. I didn't think of the head tube angle tilting the stem toward the back of the bike causing the measured distance to be different.
> 
> So i did all sorts of measuring and pondering and remeasuring and such. I then prioritized what is important to me.
> 
> ...


Because I don't know your current headset configuration, fitness, style of riding (among other factors), I can't give you black and white sizing advice. However, I will say that with saddle height being a constant, I question your prioritizing STL. Beyond accommodating a riders saddle height via the seat post adjustment it's pretty irrelevant. 

Conversely, reach and saddle to bar drop are important fit parameters, so (IMO) the focus should be on those measurements. Speaking of which, you're right that the difference in reach between the 54cm bike and 56 Tarmac is closer to 15mm's, but it increases again because of the lower HT. So depending on your current stem length, figure on adding ~20mm's. 

The HTL on the 56cm Tarmac is 160mm's, the 54 bike is 135, so (depending on your current set up) that 25mm difference _may_ pose a problem. Of course, if you're now running no spacers and a -17* stem, the 135 will better suite you, but not many recreational riders have that much drop.

Just some things to consider...


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## Rugergundog (Apr 2, 2011)

Im actually a racer. This bike will be a ss training bike. I do suspect I fit the range of two frame sizes as do most people. I just feeo I will be more pleased with my fit on the 54cm. But I will see should have it in a couple days.


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## Rugergundog (Apr 2, 2011)

I ride a 100mm stem now. Gotta decide between 120 or 110mm.


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## PJ352 (Dec 5, 2007)

Rugergundog said:


> *Im actually a racer. This bike will be a ss training bike.* I do suspect I fit the range of two frame sizes as do most people. I just feeo I will be more pleased with my fit on the 54cm. But I will see should have it in a couple days.


Points taken. Just to clarify, as I mentioned (paraphrasing), I'm following best practices here and not second guessing on your sizing requirements. Even if I knew more, fit is too 'gray' to do that over the internet. 

Re: stem length, Whenever I've changed frames, as much as I've tried to hone in on stem length/ angle/ spacers to meet my reach/ drop preferences, it never works out perfectly on paper. You may get luckier, but I suspect you'll end up test riding both a 110 and 120 before settling on the 'better' choice. 

I'm curious to know how this works out for you.


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## Rugergundog (Apr 2, 2011)

Sure thing I will keep you posted. I am tall but feel better on the smaller bikes. Not sure if its a wheel base ordeal or what. On paper a 58cm cannondale was my ideal fit, however in person it felt huge to me. Same held true with the 58cm tarmac....thus the 56 sl4 im on. Now the differences in frame shape on this chinaman frame has me wanting to try the 54cm. It does have a 540cm seattube, 10cm longer than my sl4 so I suspect I will have plenty of seat post. Now im antcy for the bike to come in.


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## Rugergundog (Apr 2, 2011)

Sure thing I will keep you posted. I am tall but feel better on the smaller bikes. Not sure if its a wheel base ordeal or what. On paper a 58cm cannondale was my ideal fit, however in person it felt huge to me. Same held true with the 58cm tarmac....thus the 56 sl4 im on. Now the differences in frame shape on this chinaman frame has me wanting to try the 54cm. It does have a 540cm seattube, 10cm longer than my sl4 so I suspect I will have plenty of seat post. Now im antcy for the bike to come in.


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