What does anyone think about the differences between these two bikes.
Which one should I get.
What are some other options?
Thanks
What are your plans for the bike?
mostly triathlons…just getting started in the sport, have done a bunch of sprints and a few olympic
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Why not get a tri bike?
I only plan on getting one bike…road bike is more versatile and more comfortable…I have a bad back.
I was told road bikes are better for someone like me.
True?
If you’re more comfortable on a road bike, that decision has already been made, I was just curious.
do you know anything about the two bikes I mentioned of any others that are similar.
If your back is am issue you may like the Roubaix better as it has a taller head tube.
thanks
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if only getting one bike go with cervelo S1 or P1. that way you can set them up as with tri or road. Neither the tarmac nor the roubaix will work real well as a tribike.
from what i gathered from a few years ago when deciding on a bike, Tarmac, the Tarmac is designed more as criterium/shorter distance road racer. The geometry of said Tarmac allows for quicker power transfer and solid road handling whereas the roubaix, if i’m not mistaken, is close to the same as the Tarmac but is design specific for comfort on longer road races/rides and so you have the longer head tube which allows for a more upright position. Granted upright on anything can be played with, that’s what spacers are for. I roAd both at the time and instantly knew that the Tarmac was for me, just awesome road handling but I got wider, 46 cm whereas it was offered with 42’s or 44’s, bars so as to allow for some room and comfort on long rides which is what i like and extended the 80 mm stem to a 110 as my knees would hit the bars when out of the saddle. In essence I turned my Tarmac into a long distance road racer with the ability of a crit bike so a two’fer.
Then came the Roubaix SL2 which I believe takes after the heart of the Tarmac, close if not exactly the same as the Tarmac and I never knew what was what any longer.
I , as would anyone, suggest you ride them both and decide after that.
I certainly hope I helped more than I think I confused myself. 
Good luck!
I own a tarmac expert and have ridden a roubaix expert for a week while on vacation. The roubaix is a smooth ride compared to the tarmac, but the tarmac is by no means harsh and I don’t find it uncomfortable in the least over longer distances. I acutally ended up riding it slammed with no spacers due to having to swap in a spare fork. After the first week or so I’d adapted to the position and now I greatly prefer it. In comparison I found the Roubaix (even with the stem flipped and no spacers) too upright and not as responsive. It was also a bit ‘soft’ in the rear triangle compared to the tarmac. YMMV obviously, but I find the tarmac a much better ‘all-around’ bike and a great bike for training and road racing. The roubaix is a nice smooth ride, but a bit boring.
In a nutshell -
Tarmac is a racing oriented bike.
Roubaix is a touring bike with more upright geometry good for comfortable distance rides.
If you have a tricky back, the Roubaix might be more to your liking.
have a read of burble here
http://forum.slowtwitch.com/gforum.cgi?post=2563296#2563296
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55 year old here with a 2009 Roubaix Expert and couldn’t be happier.
To call a Roubaix a touring bike is stupid and is probably said by someone who regurgatates what he reads on message board forums without any hands on use of either bike.
What bike was ridden by this years Paris-Roubaix winner?
Not everyone can afford,nor wants,a stable of bikes.
Go get the Roubaix it will do you fine at short course tris.
Igot
The difference is a matter of fit, more than purpose for the bike. One is not really a racing bike, and the other a touring bike. Get some fit coordinates and then see which one is better. Most companies have what specialized is doing here, which is to allow different people who cannot ride an extremely aggressive position, to ride a good position. Felt has the F and Z series, Trek has the Pro fit and the Performance fit, specialized has the tarmac and roubaix.
The Tarmac has a more aggressive geometry for road racing, while the Roubaix is slightly more slack (longer head tube, etc). It also incorporates more Zertz inserts to absorb vibrations. The Roubaix was designed for a much rougher road race and is the bike Cancellera used to win the Paris-Roubaix this year, so I also dispute the dismissive claim that the Roubaix is a tourer. 
If you’re looking for a race bike that you can also use to run Triathlon with, I would recommend the Tarmac.
I test rode both a lot before I decided and I went with the Tarmac and have been very happy with it. I think the 2 are like BMW and a Cadilac. One is built for speed and fun the other is built for a more comfy ride.
The difference is a matter of fit
Indeed!
It’s novel what bikes like the Roubaix are trying to do, but depending on the person, that extra tall head tube may be too tall for them. For example, I have a bad back. I prefer a slightly more up-right riding position on my road bike. I like the comfort options that the Roubaix would offer. But I have short legs and a long torso and if I was to ride on the right size of Roubaix for me, I would need to use a negative sloped stem to bring the handle bars down to the right position for me - this would look rather silly and defeat the purpose of the extra tall head-tube. If I was choosing between these bikes, based on my needs, I would choose the Tarmac.
all right all right, I get it - touring bike was a bad choice of words…