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How important are Stack + Reach vs. Top Tube Length and Standover Height?

14K views 10 replies 6 participants last post by  joeinchi 
#1 ·
So I currently ride a 49cm Allez (Specialized Bicycle Components) and I like the way it fits.
I'm looking at this frame (GreatKeen Bike Sport Equipment Co.,Ltd) and I'm just a bit confused as to what I'm supposed to be looking for in terms of compatability.

I'm stuck between the 48cm and the 51cm on the second bike. The 48cm has a smaller horizontal top tube and standover height. The standover height on my Allez is just right. However, when I was trying out the 52cm Allez at my lbs, they told me it would fit me just great if the top tube was a bit shorter.

Now, the stack on the 48cm S5 and my Allez are both 505cm. The reach on the S5 is a bit smaller.

Final Questions: Does Reach counteract a longer top tube? Would I be more comfortable with a slightly longer top tube and shorter reach?
Thanks!


**Yeah, I know the best thing to do is try the S5 frame out, but there are no Cervelo dealers near my current location :/
 
#5 · (Edited)
Let's see ...

View attachment 283892

So I currently ride a 49cm Allez (Specialized Bicycle Components) and I like the way it fits.
If you like the Allez, the short answer is to go with the 48cm S5. Aside from a 6mm shorter top tube, it's virtually the same size. You can compensate for this difference with a slight saddle adjustment.

The stack difference between the 48 and 51 S5 is due primarily to a taller head tube, 114mm vs 134mm. This variance not only raises the standover but moves the top tube closer to your upper body ... something you'd notice when you get out of the saddle to climb or sprint, i.e. your knees will have less clearance.

I'm assuming your Allez fits well without the use of an unusual setup, stem or seatpost. A pic of your Allez and/or you riding it would be great.

Final Questions: Does Reach counteract a longer top tube? Would I be more comfortable with a slightly longer top tube and shorter reach?
The 48cm S5 will probably use the same stem length as you use on your Allez to achieve the same fit (or reach), maybe 5mm longer. The difference in handling would be negligible.

As for comfort, that's more a function of seatpost and stem adjustments. The top tube length merely gives you a starting point. From there, you'd fine tune saddle and bar position to get comfy.

Questions?
 
#6 ·
Let's see ...

View attachment 283892

If you like the Allez, the short answer is to go with the 48cm S5. Aside from a 6mm shorter top tube, it's virtually the same size. You can compensate for this difference with a slight saddle adjustment.

The stack difference between the 48 and 51 S5 is due primarily to a taller head tube, 114mm vs 134mm. This variance not only raises the standover but moves the top tube closer to your upper body ... something you'd notice when you get out of the saddle to climb or sprint, i.e. your knees will have less clearance.

I'm assuming your Allez fits well without the use of an unusual setup, stem or seatpost. A pic of your Allez and/or you riding it would be great.

The 48cm S5 will probably use the same stem length as you use on your Allez to achieve the same fit (or reach), maybe 5mm longer. The difference in handling would be negligible.

As for comfort, that's more a function of seatpost and stem adjustments. The top tube length merely gives you a starting point. From there, you'd fine tune saddle and bar position to get comfy.

Questions?

OMFG YES!
This is exactly the kind of information I was looking for :D
And yea, I'll try to post a picture of my bike setup. The only thing I did was flip the stem so that my neck wouldn't be as sore after long rides.
 
#11 ·
More to ponder. The design differences between the two bikes make it a challenge to use some of the specs to determine the right size.

For example, the aforementioned seat tube angle. While the Allez employs traditional design (where the seatpost continues along the same angle as the seat tube), the racier S5 seatpost takes a steeper angle as it exits the frame. See pic.

Also, notice the low-profile headset on the S5. Stack measurements only apply to the frame but use of headsets with different top cover heights changes the effective stack spec (and reach to a lesser extent).

The bike in the pic also has a cut steerer and minimal, if any, spacers; a new bike will probably have a longer tube and spacers but it's something you'd want to confirm.

Finally, the top tube shape and its connection point to the headtube can also affect knee clearance ... something not reflected in the stack measurement. As you can see, the S5 top tub is relatively straight and connects near the top of the headtube, whereas, the Allez top tube bends down and meets the headtube a bit lower. It's probably negligible but, yet, another reason why a test ride is probably the best way to determine which size to go with. :(

Damn sexy bike, though! I can see why you're eager to pull the trigger.
 
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