lwrncc

This is mainly a question about flat bar vs drop bar reach.

Using Roubaix an the Sirrus have pretty much the same geometry, the only difference being the bar styles.

If I fit a 52cm (537mm ETT) Roubaix perfectly, would that mean that the Sirrus in 52cm (also 537mm ETT) would have a shorter reach and I may need a stem that is 2-4cm longer than the Roubaix to compensate for flar bar reach vs reach to drops?

I read several post in the FG/SS forums advicing people to choose the same size bikes as their road bike even though it is a flat bar bike. This doesn't seem right, please enlighten me.

I know the best way is to go to the bike store and try, but I need to satisfy my curiosity now!

Tapeworm21

Never read FG/SS forum for advice. Rule 1. They'll recommend a 650c wheel on the front at the drop of a hat. (Dude... it allows clearance for bar-spins, yo).

Get a drop bar. If you're under the age of 35, look into a Tarmac or Super Six. So many things your LBS should say to your choice....

lwrncc

I already have a road bike with drop bars, I'm wanna build a flat bar bike as well.

Menel

Why bother with an inferior system?

lwrncc

Why is it inferior? I want it for around town build, seems like flat bars would work well too.

Campag4life

For town riding...forget a road bike and I love road bikes. Get a 29er...either rigid or one with a shock. I agree...a flat bar...I prefer riser...in town makes the most sense. I have close to road bike speed on my 29er if I set it up with skinny 700C tires just over an inch wide. The nice thing about a mtb with 700c wheel dia is the ride is fantastic and can't be beat in town. Great for curb jumping...stonger wheelset than a hybrid...they can be built very light with Ti or carbon and much stronger than a road bike derivative with a flat bar like a Sirrus and more comfortable as well.
29ers are fantastic and without question my favorite overall bike. Nothing matches a carbon road bike out on the open smooth road though for speed and fun. They each have their place.
My 29er below:

revchuck 

It'd work fine for that. You can get "campus" pedals for it as well, which have one side you can use with regular shoes, and the other side is set up for MTB cleats. My very first bike (since I started riding again) is a Giant FCR3, and it works well in that mode.

I've read that a huge proportion of the gas we use is consumed in trips of less than two miles. Especially with gas prices going haywire again, having an "around town" bike makes a lot of sense.

lwrncc

Very nice setup, I won't be needing front suspension though. Could you tell me the reach difference between your 29er and road bike (tip of saddle to center of handler bar). I know it is not a fair comparison due to the different geometry, but I would just like to know.

lwrncc

I plan to use MKS Sylvan track pedals, my around town biking is generally less that 2 miles, with lots of traffic stops. Don't think I need any form of clipping in.

Campag4life

An asute question and pretty relevant. Rule of thumb, road to mtb...mtb will have about a 50-60mm longer top tube. In my case the tt on my road bike is 575mm and on my 29er 622...with a bit longer stem on the 29er. Both have a fairly slack sta of 72.5 deg...I have long femurs which works out well and still ride a Thomson setback post on each.
The reason why a mtb has a much longer top tube of course is the bars move back with some modest back sweep...in my case 9 degrees and road bikes as you know move forward with generally 80-100mm of reach with hoods in front of stem clamp centerline. Rider position isn't dramatically different...some ride quite aggressive on their mtbs but in my case my torso angle is more upright on my mtb because I prefer not to have too much pressure on my aging hands and wrists due to jarring off road. The Moto Fly Ti rides like butter off road for a hardtail...amazing ride...helped with Reba race shock and Easton carbon riser handlebar.
Cheers.

lwrncc

Thank you! That's what I wanted to know. Should have phrased my topic better, but the literature eludes me.

In that case, using my first example of the Roubaix vs the Sirrus is it a safe bet to assume that: Since I fit a 52cm Roubaix perfectly, I would probably need a 54cm Sirrus (11mm longer ETT) and a relatively longer stem?

Campag4life

11mm longer ETT?...did you mean 11 cm? 11mm is less than 1/2 inch and therefore isn't enough difference.
For the best answer...if you want to try for a good response...post geometries of both bikes here...or you can do a fit analysis for mtb with one of the on line calculators. I don't want to diss the Sirrus because you seem intent on it...but I am not a fan of effectively a road bike with a flat bar...better known as a hybrid...too close to a road bike in nature and without the rough and tumble strength of a mtb if you want to ride on rough roads. A 29er has a more robust frame and if you go Ti about as light with much better ride comfort. The wheelset is naturally stronger on a 29er. Its the same argument between a Cx bike compared to a 29er and why 29ers vastly outsell Cx bikes.

Bar back sweep matters when it comes to dialing in cockpit reach. Bars are easy to change on a Sirrus as well but you want to start with the best nominal top tube length for your size and riding position preference. My suggestion is you don't have past mtb or flat bar bikes to extrapolate from...go ride a few at one or two local bike shops or you run the risk of making a sizing mistake. Google is your friend for seeking the right size...type in your proportions. The big deal breaker for me which is derivative of old english 3 speeds..where roadbike meets flat bar...is the cockpit length on many road bikes converted to flat is just too short for comfort. Riding like Mary Poppins isn't comfortable or speed efficient for energy transfer to the pedals or aero.

While you are investigating, go ride a Gary Fisher 29er at your local shop or equivalent. If you want speed, put slicks on it and you are good to go. Below is a pic of a 29er converted for urban riding which is a far better solution to riding a Sirrus for commuting or out on the open road...niner carbon fork with Ti Lynskey frame and hybrid width tires. Very fast and comfortable and relatively bullet proof.

badger1

FWIW, I'll second Campag4Life's comments/suggestions: take a look around, and whatever you do don't buy before you try!

I ride a (2010) Sirrus as my 'road bike.' I also ride a 'roadified' hardtail. My Sirrus has a 560mm ett (74 degree s/a), and a 100mm stem. With bar-ends, works out perfectly for me. But, my Giant mtb has a 594ett (73 degree s/a), which -- with a 90 degree stem and risers (9 degree back-sweep) also fits perfectly!! I'd ride either a 52 or 54 Roubaix. You see where this can go!

As a rule, one would want certainly at least a 2cm longer ett if using actual (minimal backsweep) flat bars; more if using bars with backsweep. My take is you don't want to rely overly-much on stem length to get there (unbalanced handling and all that).

One example of a company that's kind of tried to do it right: Giant's (alloy) Defy and Rapid are in essence the same bike. A medium Defy has an ett of 545mm, a medium Rapid 565mm -- all else is identical.

lwrncc

Thank you very much Campag4Life and badger1 for taking the time to explain it to me. Nice 29er commuter! Anyway I wasn't getting a Sirrus, I was just using it as an example because it had the same geometry as the Roubaix. badger1's Defy/Rapid comparison made sense to me as well.

In the end, the best way was to try out the bike (it is a steel single speed).
Here's the result:

Current drop bar road bike:
ETT 54cm
HT/ST angle 72/74
Stem 90mm 17 degree rise
Tip of saddle to centre of bars 51cm
Drop ~3cm
Regular anatomical drop bars, not sure wad the reach is but it's definitely not compact

Flat bar single speed:
ETT 56cm
HT/ST angle 74/74
Stem 110mm 10 degree drop
Tip of saddle to centre of bars 54.5cm
Drop ~4cm
Riser bar, slight sweep maybe 6 degrees, 540m length

So therefore, I have learnt that for myself, 5'9.5", average torso/inseam (measured, right in the middle of the bell curve), slightly longer arms and good flexibility. I need roughly 3-4cm more reach going from drop bars to flat bars, assuming regular reach drop bars. I guess with compact bars it may be 1cm less.. Also different saddle as well. Too much theory crafting. It just safe to say I need at least 2cm more on the ETT, let the stem take care of the rest.

Still better to try the bike, but for some people buying off ebay/cl, it's good to know.

Campag4life

Its pretty easy to go try a bike even if it isn't the bike your want at your local shop. This way you will know what the difference is and again if you look at the industry...mtb's by and large have a 40-50mm longer top tube compared to their road bike equivalent. This isn't hard to conceptualize. Mountain bike bars sweep back from the stem clamp centerline and road bike drop bars sweep 'WELL' forward of the stem clamp center....bar forward sweep = 80-100mm + hood length.

Take Trek for example...what Lance rides both road and mtb...he competes on both. He rides a 580mm top tube size Large Madone road frame and 625mm top tube size Large mountain bike...a carbon fuel dually which is an awesome bike btw. Btw he rides a long stem on each...130mm on his roadie and 120mm on his Fuel. I pretty much ride the same size he does even though I am a fair amount taller....but lance has long arms and legs as well. Lance being a world class racer rides more stretched out than me to be sure and I am an average road biker.
So test some bikes. At the end of the day...analysis will only get you so far.
Cheers.

NormanF

A Sirrus is basically a "townie" road bike. Not all of us race for a living so for relaxed day rides, you may want to set up your road bike with North Road bars and wider tires. You won't go any slower and you will have a comfortable ride.

Nothing wrong with the comfort road bike category since Specialized invented it in 2004 with the introduction of the original Roubaix. Nowadays, it seems every major bike manufacturer offers such a model.