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Sizing question: 51 vs 53cm.....(12 posts)

Sizing question: 51 vs 53cm.....SS_MB-7
Feb 6, 2003 5:57 AM
OK, now I need your opinion on sizing.

Originally, I was all set to go with the 53cm Bianchi Pista based on Bianchi's claimed standover height of 30.5" and top tube length of 53.5cm. But, I later found out from two independent '03 53cm Bianchi Pista owners that the standover was actually 31.25" -- a difference of 0.75" over the claimed. So, I dropped down a size to the 51cm, but this is pretty short in the TT at 52.5cm relative to my current road bike (54.1cm).

Last night, I measured my '02 54cm (c-t) Fuji Track. It's claimed standover is 77.6cm (30.6"), but it's actually 78.4cm (30 7/8"). I find the Fuji to be too stretched out with a 55cm top tube (c-c), so I'm looking for something around 54cm -- like the 53cm Bianchi Pista.

I decided to mount some wooden shims under the wheels of my Fuji to give a standover height similar to the 53cm Pista (31.25"). With my riding shoes on, I was able to straddle the top tube and could pull the top tube up a little bit. Or, I could flex my knees slightly before resting my crotch on the top tube. Barefoot was a little too painful.

FWIW, my custom road bike has the following specs:
seat tube (c-c) = 50.5cm
top tube (c-c) = 54.1cm
standover = 78.1cm (30.75")

What do you think? 51cm or 53cm?

Unfortunately, this bike is not available in Canada.

Ride Hard,
Mike B.
I'd go with the 51cm, but I'm assuming....bent_spoke
Feb 6, 2003 6:46 AM
there is no 52cm frame and that you can adjust the reach with a longer stem. The 53cm sounds like you don't have alot of leeway with the standover, so the 51cm seems to make more sense to me. However, if you already use a longish stem, then increasing the stem length might not be your best option. At this point, you might consider a different frame, one that gives you a better overall fit. fwiw
the 51cm..C-40
Feb 6, 2003 9:25 AM
It doesn't make sense to pick a frame that you can barely standover.

You also don't mention the stem length or total reach that you use.

Don't forget to account for differences in seat tube angle when you compare these frames. Is the STA is not the same, you can't compare the TT lengths directly.
More info....SS_MB-7
Feb 6, 2003 9:44 AM
The complete specs of the Pista are here: http://www.bianchiusa.com/site/bikes/19_Pista.html

The 51cm has the following specs:
seat tube (c-t) = 51cm
top tube (c-c) = 52.5cm
stem = 90mm x 17
head tube angle = 74
seat tube angle = 76

The 53cm has the following specs:
seat tube (c-t) = 53cm
top tube (c-c) = 53.5cm
stem = 105mm x 17
head tube angle = 74
seat tube angle = 75.5

My current bike has the following specs:
seat tube (c-c) = 50.5cm
top tube (c-c) = 54.1cm
stem = 100mm x 0 (90).
head tube angle = 73
seat tube angle = 74

Ride Hard,
Mike B.
accurate comparison...C-40
Feb 6, 2003 2:54 PM
Using your road bike at the standard for comparison, 2.4cm must be added to the top tube length of the 51cm Pista, due to the 2 degree difference in the seat tube angle. The effective top tube length becomes 54.9cm, assuming that you place your knee in the same position relative to the bottom bracket. This also assumes that you would be able to get a seatpost that would permit this amount of additional saddle setback. If you don't use the same KOP positon on your track bike as your road bike, then this comparison is not valid either.

The steep seat tube angles used on these track bikes suggests to me that the intent is to use a more forward position relative to the BB to promote a higher cadence.

Do you know the exact geoemtry of the Fuji track bike that feels too long in the top tube? This would probably provide a more accurate basis for comparison.
Here are the Fuji details...SS_MB-7
Feb 6, 2003 4:53 PM
'02 54cm Fuji Track:

- seat tube (c-t) = 54.0cm; 50.4cm (c-c);
- top tube length (c-c) = 55.0cm
- head tube angle = 73.5
- seat tube angle = 73
- stem = 90 x 10

And for reference, here's a pic of me during a local race:



Ride Hard,
Mike B.
the comparison...C-40
Feb 6, 2003 6:08 PM
If you want to compare your Fuji to the 51cm Pista, there is a whopping 3 degrees difference in the STA. This makes the Pista TT length about 3.5cm longer, or 56cm, which is even longer than your Fuji, IF you can get the saddle back to the same KOP position. You would almost certainly need a seatpost with a larger amount of setback if you want the same KOP on the Pista. Now you can see why it's not wise to look at TT lengths without taking into account the STA.

The 51cm has the following specs:
seat tube (c-t) = 51cm
top tube (c-c) = 52.5cm
stem = 90mm x 17
head tube angle = 74
seat tube angle = 76

The 53cm has the following specs:
seat tube (c-t) = 53cm
top tube (c-c) = 53.5cm
stem = 105mm x 17
head tube angle = 74
seat tube angle = 75.5

My current bike has the following specs:
seat tube (c-c) = 50.5cm
top tube (c-c) = 54.1cm
stem = 100mm x 0 (90).
head tube angle = 73
seat tube angle = 74

Fuji
- seat tube (c-t) = 54.0cm; 50.4cm (c-c);
- top tube length (c-c) = 55.0cm
- head tube angle = 73.5
- seat tube angle = 73
- stem = 90 x 10
Please explain how you came up with these numbers....SS_MB-7
Feb 6, 2003 7:07 PM
I'm trying to figure-out how you determined that the 51cm Pista has an effective TT of 56cm.

BTW, those stem angles for the Pistas and Fuji should be -17, -17 and -10, respectively. That is, just slightly below parallel with the TT on the Pistas and a slight rise on the Fuji. Not sure if that has any bearing on your calculations.

Ride Hard,
Mike B.
explanation...C-40
Feb 7, 2003 5:53 AM
The TT length of a frame is measured from a fixed point, the intersection of the centerline of the seat tube and the top tube. If the seat tube angle is different on two frames, then this fixed point of reference is not the same horizontal distance behind the bottom bracket. Frames with a steep (76) STA must have the saddle moved further back to place the rider in the same position relative to the bottom bracket. When the saddle is moved back, this effectively increases the TT length by the amount of the saddle movement. The formula to calculate the difference is: saddle height x (cosA-cosB). For example, say that your saddle height, measured from the center of the BB to the top of the saddle, parallel to the seat tube, is 72cm and you need to compare a frame with a 76 STA to a 73 STA. 72cm x (cos73-cos76) = 3.6cm. The 3.6cm is added to the TT length of the frame with the 76 degree STA to compare these two frames with the saddle in the same position relative to the bottom bracket. This assumes that your geometry information on the both frames is correct.

To get the same total reach to the handlebars, the stem length must be adjusted to correct for the difference in effective TT length. In the comparison with your Fuji, the 51cm Pista was shown to have an effective TT length that was about 1cm longer than your Fuji. The stem on the Pista would need to be 1cm (10mm) shorter on the Pista than the Fuji to produce the same total reach. As I noted, finding a seatpost to permit this much rearward movement of the saddle might be tough. The Pista is obviously designed for the rider to be positioned in a further forward, relative to the BB. Since you feel that your Fuji is too stretched out, why don't you just try a shorter stem?
Gotcha! Thanks....SS_MB-7
Feb 7, 2003 6:35 AM
So, if I reduce the 51cm Pista's stem from 90mm to 80mm, this would yield a similar reach to the 54cm Fuji. And, since I find the Fuji too long, I'd need to go even shorted on the 51cm Pista.

I've already sold the Fuji. But, in looking at Fuji's 2003 site, it appears they now have a 52cm with the following specs:



seat tube (c-t) = 52.0cm
top tube (c-c) = 54.0cm
head tube angle = 72
seat tube angle = 74
stem = 90 x 0

This is pretty close to my current ride:

seat tube (c-c) = 50.5cm
top tube (c-c) = 54.1cm
stem = 100mm x 0 (90).
head tube angle = 73
seat tube angle = 74

I guess I had my heart set on the Bianchi Pista because it has nicer components, looks nicer, etc. But the '03 52cm Fuji Track might be the better bike for me. What do you think?

Ride Hard,
Mike B.
virtually identical fit...C-40
Feb 7, 2003 8:36 AM
The 52 Fuji would fit the same as your current bike. Just change the stem to a 100mm and get the saddle adjusted to produce the same KOP.
I owned the 51cm Pista...Quack
Feb 6, 2003 10:28 AM
I'm 5'8" tall with a 30.5" inseam measurement and have owned the 51cm Pista. I'm not an expert on fit but the track bikes that I have ridden have all tended to be shorter across the top and have higher BB than standard road bikes. The 51 worked great for me once I got used to the tighter cockpit and narrower bars.

Larry