Cyclocross - Soma Doublecross sizing

I'm having a lot of trouble with this. I'm interested in buying this frame to modify with S&S couplers (so don't suggest any Al alternatives!), but the sizing is really funky.

When they say these things run long in the top tube they aren't kidding.

Ordinarily I ride, in a road bike, a 52cm frame with a 535mm horizontal top tube measurement. Acknowledging that because the bottom bracket is higher on a cx bike, I would anticipate getting a slightly smaller frame. However, the Soma Doublecross 50cm has an eff top tube of 548! Good lord! I can drop down to a 48 (which no one carries apparently) and get a eff top tube of 540, but then the chainstays all of a sudden get small.

Typically, at least with road bikes, smaller than 50cm means that you can't fit 622 wheels (700c) without compromising the geometry of the bike.

This is giving me quite a headache. No one has any built up frames that I can simply test ride.

You can't just look at published frame size. HT length + fork length + BB drop gives a rough measure for the height of a bike. And keep in mind, cross forks run about an inch longer than road forks.

Also, 13mm isn't that big a difference, you probably can make up the difference with a shorter stem.

People think the Double Cross runs long, but if you account for the sloping top tube and higher headtube extension, they really fit pretty normal in the dimensions that count.

I'm fairly certain that when they give the "effective" or "vertical" top tube measurement that they take all those variables into account, and arrive thusly at the exceedingly long 548.

I'm not concerned about the height up front.

It's the geometry in back that I think may be compromised on a frame that short in order to run 700c wheels.

What other frames will you consider?

I don't know.

My criteria are:

Steel.
Disc and Cantilever mounts.
Vertical dropouts.

Gunnar makes some, but they'll cost a TON more to get both brake options, PLUS the $800 they'll charge for the S&S mod. If I could find a frame comparable to the Double Cross without the (in my opinion) really funky geometry, I would absolutely consider it.

so you'll be paying a framebuilder to add the s&s couplers to the soma? why not have them shorten the tt and dt length while they're at it?

or, go with the traveler's check and have a disc tab added... of course, surly's also have super long top tubes.

the voodoo wazoo (http://www.voodoocycles.net/wazoo.htm) is steel, has canti mounts, and has sliding dropouts with a disc mount.

you could also hunt down a disc poprad and have canti mounts added when you're getting the s&s couplers added.

all in all, it seems you have very specific demands. why even bother with modifying an existing frame when you could just go with a custom bike and have it done right the first time and painted once.

I don't know.

My criteria are:

Steel.
Disc and Cantilever mounts.
Vertical dropouts.

Gunnar makes some, but they'll cost a TON more to get both brake options, PLUS the $800 they'll charge for the S&S mod. If I could find a frame comparable to the Double Cross without the (in my opinion) really funky geometry, I would absolutely consider it.

Steel, disc & canti mounts, vertical drop-outs, break-apart. I see the challenge. Nothing to my knowledge except the Wazoo with the couplings added meets this, and the geometry is better also. If you would reconsider on the disc brakes, all kinds of options emerge.

Michael

so you'll be paying a framebuilder to add the s&s couplers to the soma? why not have them shorten the tt and dt length while they're at it?

or, go with the traveler's check and have a disc tab added... of course, surly's also have super long top tubes.

the voodoo wazoo (http://www.voodoocycles.net/wazoo.htm) is steel, has canti mounts, and has sliding dropouts with a disc mount.

you could also hunt down a disc poprad and have canti mounts added when you're getting the s&s couplers added.

all in all, it seems you have very specific demands. why even bother with modifying an existing frame when you could just go with a custom bike and have it done right the first time and painted once.

These are all wonderful points. Ones that I have considered...

If you think on it, shortening the top tube would require a downtube replacement, not just shortening. If you doubt, take a triangle, shorten one portion, and see if you can still make the triangle work by merely shortening another leg. You'll have to actually replace and move it to change the angle.

The Surly with disc tabs? I've considered. I'll also need to have vertical dropouts put on there, and the cost gets to be about comparable.

Custom builder? I've looked at Gunnar. Fastlane: $900. Canti studs: $150. S&S Couplers: $800.

Soma: Frame $320. S&S couplers plus re-paint: $800.

I know I have specific demands, and the Soma seems to meet all of them, but that length is really, really "off", in my opinion.

Just an fyi. This is the best deal out there: http://www.ritcheylogic.com/dyn_category.php?k=114347

This supplier builds the frames to spec, You could end up with custom geometry titanium frame, couplers, and disc brakes. It may be the best value... http://www.habcycles.com/cross.html

I'm fairly certain that when they give the "effective" or "vertical" top tube measurement that they take all those variables into account, and arrive thusly at the exceedingly long 548.

I'm not concerned about the height up front.

It's the geometry in back that I think may be compromised on a frame that short in order to run 700c wheels.You totally missed my point. When you have a sloping top tube which joins the headtube well below its top edge, then the length of the seat-tube (i.e. "size" of the bike) is meaningless.

Compare Double Cross and Cross Check dims, but ignore seattube and "size" numbers. Look at the seat and head angles, BB drop, headtube length, and effective top tube, and you'll see that the Cross Check frames are even more "exceedingly long" than the Double Cross.

These are all wonderful points. Ones that I have considered...

If you think on it, shortening the top tube would require a downtube replacement, not just shortening. If you doubt, take a triangle, shorten one portion, and see if you can still make the triangle work by merely shortening another leg. You'll have to actually replace and move it to change the angle.

The Surly with disc tabs? I've considered. I'll also need to have vertical dropouts put on there, and the cost gets to be about comparable.

i started thinking about the downtube dilemma after i posted. good point... but, if you're going that far...

i'm curious; why are you so insistent to have both brake style mounts?

seems like the steel ritchey breakaway cross frameset could be a great candidate for some disc tabs. or a great frame to just get and compromise your disc brake idea. disc brakes seem like overkill on a cross bike anyways. all the extra weight, further dished rear wheel, and extra rotational mass also don't seem worth the braking performance you get from cable actuated disc brakes. a well adjusted rim brake can be just as powerful.

Another idea is to run a disc brake on the front fork only and keep a cantilever brake on the back. Most of the braking is done with the front brake.

Michael

check out curtlo, rock lobster, and tet cycles. they are among the more affordable custom steel bike makers, that have great reputations. I have seriously considered getting a bike through them, but will be waiting until the spring.

i started thinking about the downtube dilemma after i posted. good point... but, if you're going that far...

i'm curious; why are you so insistent to have both brake style mounts?
seems like the steel ritchey breakaway cross frameset could be a great candidate for some disc tabs. or a great frame to just get and compromise your disc brake idea. disc brakes seem like overkill on a cross bike anyways. all the extra weight, further dished rear wheel, and extra rotational mass also don't seem worth the braking performance you get from cable actuated disc brakes. a well adjusted rim brake can be just as powerful.

I already have an Al cross bike, and two sets of wheels for it, both disc brake wheels with no braking surface on the rim. I'd like to just move all the parts over.

Personally, I like the discs. It actually doesn't further dish the rear wheel, it makes the rear wheel closer to symmetric and relieves the differences in spoke tenstion caused by the typical spoke approach angle on the non-drive side.

And again, like I said, I already have all the parts on another frame. But I want canti mounts just in case I ever decide to run non-discs. The versatility certainly doesn't hurt.

If you can do without disc mounts, the Surly Travel Check could work...

While I'm at it...

I'll have to get the Soma DC in a 48cm size to get the reach I need, and would normally get, on a 52cm bike.

When they get that small, Soma shortens the chainstays to 420mm, a length more normal on a "proper" road bike, but I'm wondering if it will adversely effect the handling of the bike, particularly given the high rider "perch" (from the high bottom bracket) and the slightly slacker headtube angle.

Thoughts?