Abe_Froman

The title pretty much asks it all...but I'll elaborate for the sake of discussion.

I'm in the market for a new bike. Pretty much have decided on a disc brake, 105 or Sram 1X equipped cyclocross bike. I'll be using it for CX racing, nice weather commuting, fast (ish...) road group rides, solo road and gravel rides.

I'm just wondering what the actual losses are vs a proper road bike, specifically from the frame/component design.

I've seen some research, but everything seems to evaluate the bikes as a whole. IE....knobby tires on the road rather than using equivalent wheels/tires.

Just wondering what everyones experience are using CX as a road bike. And I'm looking for the little differences...I'm fully aware there is nothing dramatic about a CX bike slowing it down relative to a road bike. Also...the only hills I'll ever see will be in a CX race anyway...so not too concerned about the weight differences of the bike categories.

woodcraft

Maybe if it's flat, but I'd be hard pressed to keep up on fast group rides

with 40-11 top gear.

fietsbob

The body of the rider on the saddle is the biggest aerodynamic drag.., next may be the rolling resistance of the tires..

'faster' ? slick , light, expensive & debris puncture vulnerable..


you will have to do the science yourself, maybe U of Chicago will help.

Abe_Froman

Yea, if I went the 1X route I'd probably get a 42 or 44 chainring just to make sure I had all the gearing I needed for group rides. Though honestly a 40 would probably be fine.

Seattle Forrest

Obviously it's going to depend on the two specific frames. You can't really compare something as specific as aerodynamics between two categories of bike. Sorry for being a pedant.

Get a Cervelo C3. With 105 not SRAM, especially not 1x. It's a fast and incredibly nimble bike. It has clearance to around 35 mm which is more than you're allowed in CX.

fietsbob

N+1 again, want an aero frame, get a time trial bike..

Abe_Froman

Laws of fluid dynamics don't cease to exist when you're not on a time trial bike...

caloso

There are guys on the local A ride all the time with CX bikes. A Cat3 teammate of mine uses a Trek Boone as his only bike, CX and road. He just swaps wheels. It's not holding him back on the road in the least.

Dean V

Surely the aerodynamics of the CX bike will be very similar to a traditional road frame? eg. Giant TCR. Plenty of people racing on bikes like that and still doing ok.

fietsbob

but, reduced to just the frame , they do all that wind tunnel testing to get the drag down within the constraints of what the UCI lets them use..

Out side of UCI demands for what a bicycle can be..
but to hit the 80+ mph measured flying 200 feet, record,
they even eliminated the window,, relying instead on a camera and a tablet screen, in the recent Battle Mountain speed meeting.


86.65 mph.
https://www.ihpva.org/home/ a Velomobile, makes the whole thing slip the the air with less drag,



6-Hour Men's, Standing Start: 234.13 miles, 376.79 km at an average speed of 39.02 mph, 62.80 kph.

Abe_Froman

I think I would want more than 35mm clearance. You're not restricted on tire size for amateur races.

THe 3T Exploro is an interesting bike. I doubt it would be great as a CX racer...but it's interesting. https://www.3t.bike/en/3t-bikes/exploro-2.html

fietsbob

But as a sales hook , it looks good , just difficult to throw on your shoulder for the run up sections..

no longer "screwed and glued", but they kept the style homage to that era..

HTupolev

What's "not dramatic" to you? A 4% difference in overall speed? .4%? .04%?

Abe_Froman

I'd say anything measurable in a wind tunnel. Which I assume would be probably around 0.4%. Certainly more than 0.04%, certainly less than 4%. Good enough?

Campag4life

My question is...when is a Cx bike ever considered in an aero manner?...aside from a more aggressive geometry.

Now maybe Cx bikes are starting to be designed with aerodynamics in mind...as are more conventionl and non aero specific more round tube road bikes.

But I don't know which brand of Cx bike have aero tube shapes as a priority.

Does anybody know of a given brand and model Cx that advertises an aero advantage? If so, please post.

So, lets take aero specific bikes off the table completely because they clearly will be more aero than any Cx bike. But even non specific aero bikes, like the Spesh Allez or the new Tarmac disc with aero cues, they will be more slippery than any Cx bikes.

Maybe first OP identify any Cx bikes advertised with an aero advantage as a starting point. I don't know of any but maybe there are a couple out there. Lots of road bikes will be more slippery.

Also, the close cousin of a Cx bike aka gravel bikes also aren't known for being specifically slippery either. Pinarello came out with a dogma based endurance bike that is more slippery than normal...a first I believe of the endurance genre.

Seattle Forrest

I test rode a Santa Cruz Stigmata that's a lot like that bike. It was a fine machine. I went on to buy the C3 instead. I did a test ride, and knew before I left the parking. Depends what you value in a bike, if it's clearance, you're looking in the right direction. I love being on a nimble bike.

WhyFi

I don't know of any CX off the top of my head, but the previously mentioned 3T Exploro (gravel/adventure) is marketed as being aero.

Abe_Froman

I dont think they really exist. Though they will at some point i’m sure.

bbbean 

I use my CX bike as my bad weather/backup road bike. With good wheels (Rol Race SL) and road tires (Specialized Turbo in 26F/28R mm), I can keep up on fast group rides, and in a pinch I would ride it in a training race, but the gearing, more upright position, less-than-slippery aerodynamics, and extra weight mean its never going to be as fast as my road bike. It is also a lot more work to spin 46X11 at 30 mph than it is 53X11, and the extra 2 or so lbs on the CX bike are noticeable on a real climb.

With that said, if I didn't race, I could absolutely live with a light CF CX bike. I'd probably go with something more aggressive than my SuperX, but a good CX bike would be fine for an all around bike.

Note these are purely subjective impressions. I also have a mid-range CX bike and a mid/high end road bike, so some of the differences may be due to my road bike just being a nicer bike. But there's a lot to be said for a bike that was build for where you ride it.

BB

Campag4life

Believe you are right...not many now for sure. And there maybe at some point. And then the question will be, what true advantage would there be to an aero geometry Cx bike...as Cx bikes are typically ridden and raced at lower speeds and quite sure why companies so far haven't exploited aka played the aero card on Cx bikes.


But you are looking to go off the grid a bit which isn't anything new certainly. And yes, uber strong guys jump into the A group ride on a cross bike for the simple reason...because they can and have more engine than other guys who need every technical advantage just to keep up. We all know guys like that...even fixie riders...or guys who never ride in line because they don't need the aero advantage...or take monster pulls because again they can.


And on the subject Abe of cross bikes, if you cruise youtube and you may have, some guys use cross bikes as gravel bikes even though there are some fundamental differences.


But...if looking for an all arounder...IMO, if going a disc bike, if you have a second set of aero wheels for your Cx bike, you are good. If you choose an aggressive geometry, you aren't going to give up much to a road bike...certainly much more than say what I do which is ride an endurance geometry in the town's A group ride. I know I should own a more go fast slammed bike for the A ride, but I don't have one because it isn't very comfortable for my aging body. But I believe a dedicated go fast bike would help a bit...but not enough to make me as strong as the faster CAT riders in the group anyway.

Clem von Jones

This is a question I've been pondering over lately too mainly because more tire clearance gives you the option of running these new lightweight low-pressure tubeless tires like the 38mm Gravel King slicks.

These tires are 320 grams but no tube is required and you can probably use lighter rims too with low-pressure (45-60 psi) fatties. The point is there's no longer much of a weight penalty for these fat comfortable tires, and meanwhile the roads are falling apart. It seems to me we're at the cusp of another road bike revolution because of these factors.

Abe_Froman

Agreed.

If I weren't going to be racing CX...I wouldn't really require that much clearance, but it certainly would be nice regardless. And there is zero chance I would consider a dedicated road bike, even if I were buying 2 bikes, that could not take at least a 28mm tire with room to spare. 25mm tires at ~100 psi are brutal on the roads here. 28s at 80 psi feel pretty nice.

WhyFi

Going up to 38s on pavement is a bit overkill to me. That said, I don't think that I'll buy another bike that can't take 30s.

Abe_Froman

I’d have 35 or 38 for cross.

Probably 28mm GP4000s on the road wheelset. Though 40mm tires at ~45 psi are really nice on rough pavement

GlennR

I have 2 bikes, a Trek Emonda SLR, Sram eTap and Zipp 303 with 25mm Conti GP4000IIS. I wanted a less expensive, more robust bike for riding December through March. It needed to have wider tires, hydro disc brakes and I wanted Sram Rival 1x since it was simpler and cheaper to replace compared to Red.

I decided on a Cannondale SuperX CX Rival 1x. It came with 35mm knobby tires which are nice for dirt but not good for the road. So I added a set of Zipp 30 Course wheels and Bontrager AWS2 32mm tubeless tires.

I love the bike, it handles the potholes easily, after 2 winters no flats even with all the road debris and the brakes are great in the wet. It takes 2 minutes to swap the wheels and i'm ready for some off road adventures.

I'm about 1mph slower on the CX than the road bike. The longest ride on the CX so far was 40 miles. I have no problem hanging with others on road bikes during group rides.

Don't get me wrong, I love the Emonda and look at the Cannondale a just another tool.

It's like having a Porsche and a Land Rover. Each has it use and no one is the best bike for any situation.