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Discussion Starter · #1 ·
I'm going to be ordering a new Surly Cross-Check, but I can't decide between a 54cm and 56cm. I've heard that the Surly's run large, so I'm looking for some assistance here.

Here's the rundown of my current bike, with a 110mm stem and 4cm spacers:
Head Angle: 73.8
Seat Angle: 73.5
Eff Top Tube: 56cm
Seat Tube: 56cm
Standover: 31.2

54 cm Cross Check:
Head Angle: 72
Seat Ange: 73
Eff Top Tube: 56cm
Seat Tube: 54cm
Standover: 31.2

56 cm Cross Check:
Head Angle: 72
Seat Ange: 72.5
Eff Top Tube: 57cm
Seat Tube: 56cm
Standover: 31.9

Just going by the numbers, it looks like the 54cm would be the best fit, but I don't know how the different frame angle effect the fit of the bike. Thanks in advance for any help!!!
 

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head tube length???

Why would you think Surlys run large, when the numbers are there to review? That standover height tells you how tall the frame is.

What is missing is the head tube length. Since your current frame requires 4cm of spacer, the frame is either too small, you've got the wrong stem angle, or you just want your bars up real high. On a new frame you certainly don't want a shorter head tube.

You should also be sure that the BB drop is not significantly different than the frame you have now, when comparing head tube lengths. If the BB is higher, the head tube needs to be longer.

As for the fit differences, the 54cm will have about a 5mm shorter reach and the 56 will have a nearly identical reach, once the saddle is set in the same position relative to the BB.
 

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Discussion Starter · #3 ·
Well, I think the Surly's run large because a 54cm bike has a 56cm top tube....I'm 5'10.5, and it seems like I'd be riding a 54cm bike. To me, that's a big 54cm bike. Plus, I don't really know what any of these numbers mean besides TT length (I know what they mean, I just don't know how to interperet them), and I know different head and seat tube angles can have an effect on fit as well. I've also been told by the shop that I'll be buying the bike from that Surly's run large.

As for having a lot of spacers (I remeasured, and it's acutally 3 cm), the reasoning for this is because I have short legs (31.5 inseam) and a long torso. I was professionally fitted on this bike, and this is how they set me up. It's very comfortable, and there is still a 1.5 inch drop from saddle to bars.

Anyways...here's the head tube and BB info

Current:
HT: 14.1
BB: 26.8 (I don't think this is drop....it is the distance between the bb and the ground, it was the only number referencing BB on Trek's website)

54cm Cross-check
HT: 12.1
BB Drop: 6.6

56cm Cross-check
HT: 14.1
BB Drop: 6.6
 

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Hoopy Frood
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Assuming you have the standover clearance

You could probably fit either the 54 cm or 56 cm.

The 56 cm Cross Check has a slacker seat tube angle than both the 54 cm and your current bike. That will reduce the effects of the slightly longer top tube.

If you can comfortably stand over both sizes, it's more a question of how much saddle-to-bar drop you like and whether you notice/prefer handling differences with shorter or longer stems. If you run a larger drop from saddle to bars, you might be better with the 54 CM due to the shorter headtube. However, since you have a lot of spacers now, you might be better with the 56 cm (but that could be misleading since you're on a Trek and they seem to have short head tubes in relation to their top tube length so require more spacers).

I agree with C-40 - all things considered, I don't think the Surly Cross Check fits bigger than it is.

- khill
 

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tradeoffs...

If you've only got a 31.5 inch CYCLING inseam, then you have hardly any clearance with a 31.2 inch standover. With a 31.9 inch standover, you'd have none. Are you quoting a pants inseam?

From a head tube standpoint, the 54cm would be too short, unless you can increase the stem angle by about 12 degree. For example, if you have an 84 degree stem now, you could flip it to 96 and raise the bars about 2cm.
 

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Discussion Starter · #6 ·
C-40 said:
If you've only got a 31.5 inch CYCLING inseam, then you have hardly any clearance with a 31.2 inch standover. With a 31.9 inch standover, you'd have none. Are you quoting a pants inseam?

From a head tube standpoint, the 54cm would be too short, unless you can increase the stem angle by about 12 degree. For example, if you have an 84 degree stem now, you could flip it to 96 and raise the bars about 2cm.
I have a cycling inseam of 31.5. Maybe wearing shoes I'd be closer to 32...not sure.

So basically, I need a 54cm with a flipped-up stem?
 

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Are you quoting a pants inseam?
Perhaps it's time to give the term "inseam" back to the clothing industry. The human body has no inseam - cycling, pants or otherwise. In my opinion, "inside leg length" or "pubic bone-to-floor height" would make these fit discussions less confusing and the expert advice more accurate.
 

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cycling inseam...

dez182 said:
I have a cycling inseam of 31.5. Maybe wearing shoes I'd be closer to 32...not sure.

So basically, I need a 54cm with a flipped-up stem?
http://www.coloradocyclist.com/bikefit/

The link above shows how to measure cycling inseam. If yours is really only 80cm, then your saddle height from center of BB to top of saddle will only be about 70cm. Is your saddle that low? If so, you've got some really short legs for someone 5'-10.5 inches tall. I'm 4 inches shorter and have an 83cm inseam.

One dimension that may be critical is the fork length. I assumed your old bike was also a cross bike. If not, road bikes have much shorter forks and you need to compensate for that when figuring handelbar height. The Surly has a 40cm fork length, whereas a typical road bike is only about 36.7cm. A cross bike could have quite a bit shorter head tube and still produce the same bar height as a road bike.

Personally, I wouldn't buy a frame with that little standover clearance, but if that's what you've got now, I guess it's working for you.

Another way to measure cycling inseam is to block up the wheels on your current frame, standing over the bike in bare feet, wearing cycling shorts. Increase the blocking until the TT produces saddle-like crotch pressure, then measure from the floor to the top of the TT. This is your cycling inseam.

Unlike Wim, I have no problem with the word inseam. Any website with fitting instructions tells how it's measured.
 

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Discussion Starter · #9 ·
C-40 said:
http://www.coloradocyclist.com/bikefit/

The link above shows how to measure cycling inseam. If yours is really only 80cm, then your saddle height from center of BB to top of saddle will only be about 70cm. Is your saddle that low? If so, you've got some really short legs for someone 5'-10.5 inches tall. I'm 4 inches shorter and have an 83cm inseam.

One dimension that may be critical is the fork length. I assumed your old bike was also a cross bike. If not, road bikes have much shorter forks and you need to compensate for that when figuring handelbar height. The Surly has a 40cm fork length, whereas a typical road bike is only about 36.7cm. A cross bike could have quite a bit shorter head tube and still produce the same bar height as a road bike.

Personally, I wouldn't buy a frame with that little standover clearance, but if that's what you've got now, I guess it's working for you.

Another way to measure cycling inseam is to block up the wheels on your current frame, standing over the bike in bare feet, wearing cycling shorts. Increase the blocking until the TT produces saddle-like crotch pressure, then measure from the floor to the top of the TT. This is your cycling inseam.

Unlike Wim, I have no problem with the word inseam. Any website with fitting instructions tells how it's measured.
Yep, my legs are really that short. Distance from top of saddle to center of BB is 72.5 cm (I know...I'm a mutant).

I talked to the guys at the shop and went through all the different measurements, and I ended up going with the 54 cm. The longer fork will add around 4 cm (as you just mentioned). Also, I didn't take into account that my current bike has an integrated headset and the cross-check doesn't, so the stack height of the headset will add another 3.5cm or so.

Thanks everyone for your input. I'll post pictures when it's done!
 
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