JohnnyC

I'm buyiny a road bike.

It will have an Ultegra compact (50/34) fitted. The cassette choice:

11-23
12-25
12-27

My current hybrid is 48/36/26 with a 12/26 cassette fitted.

I'm not sure on what cassette to get, I was thinking 12-27 or 12-25. What do you guys suggest?

I currently cycle 80 miles a week on rolling roads/hills. Will the 12-25 suffice? Fitness is ok (ish) I can cycle 15 miles at a 14.3 mph average - no problems.

I'm planning on increasing my 25 mile runs up to 40 miles - rolling hills.

doghouse

A little more information would be helpful.

Are you able to make all your hills on the middle and/or big chain ring? If not, then how often do you use the small chain ring on your current ride? Do you ever have to use the 26x26 to climb your rolling hills? Have you ever really needed the small ring to get home on a bonk or windy day?

If you answered yes to either of those last two questions, then even that 39x27 is going to be a strain, I think.

By the way, 54x39 is not a compact crank size. A 52x39 is usually the standard road crank. A 50x34 would be an example of a compact. BTW, road triples are usually either 52x42x30 or 52x39x30.

Hope this helps some.

JohnnyC

Ooops my mistake - it will have a 50/34 fitted.

On my hybrid - I rarely use the small chainring. When I have been really tired on a windy day - I have used the 26x21 to get up steepish hills, usually use the 26x19 for hills. Will I survive on 34x27?

CliftonGK1

My previous geared roadie had a 53/39 crank with a 12-27 cassette, and the rolling hills started to wear on me pretty seriously on rides over 60 miles. Even for shorter 30-40 mile rides with moderate (2000-2500') climbing I found myself wishing for some lower gearing.

With my new bike, I have a 48/34 compact crank with an 11-32 cassette. The gear jumps aren't as tight as you'd get with a 12-27, and it requires double shifts to move up by the smallest gear-inch increments, but I can hammer away on the hills all day long with that 34--32 combo if I need to drop that low.
If you use your 26t ring on the hybrid, consider either a road triple with that 27t cassette so you have a 30--27 gear; or think about a compact crank and a rear derailleur to handle larger than a 27t cassette.

TrumpetMurph

Yeah, I agree with Doghouse--the biggest thing is to decide how well you handle the rolling hills. If you don't have any problems right now with your middle chain ring on your hybrid, then the 34 on the roadie with an 11-25 shouldn't give you any trouble. But, if you use that small chainring quite a bit, the step up to a 34 from a 26 will be tough.

Not sure what your budget looks like, but since you're looking at Ultegra, I'll assume money isn't your main concern. Have a look at the Bianchi Axis. An '07 on closeout at Jenson USA is under $1000, so you'd have money leftover to upgrade shifters and deraileurs to Ultegra. The crankset is a 34/50, and the cassette is an 11/32.

https://www.jensonusa.com/store/produ...ee+Kit+07.aspx

Little Darwin

Just to add a vote to get the largest cog you can get...

If you are ever needing to drop to the small chainring on your current cassette, I would say you need the largest cog you can get.

If 26-21 is the lowest gear you ever need, then the numbers show you should get a 27 or 28 cog for your 34 low chainring...

26-21 = 33.4 gear inches

34-27 = 34 gear inches

34-28 = 32.8 gear inches

This assumes the same sized wheels and tires. If you are at the same time moving from 26" to 700c, then you need an even bigger cog to keep you where you are. I always like having a bailout gear lower than I need... you may want to consider if the extra gear on the bottom increases your comfort as well.

Bill Kapaun

Something to keep in mind also is CRANK LENGTH.
If your current bike, for example, has 175MM cranks and the new bike has 165's you'll want to gear lower and make up the difference in a faster cadence.

Check out the link-

https://sheldonbrown.com/gears/

JohnnyC

Ok - lots of things to take in...

The cranks on my hybrid are 175mm.
The wheels are 700cc.

The bike I'm looking at getting is a titanium frame from planet x bikes - with a full ultegra kit. A little treat for myself. I went for the titanium - because at 256lbs I'm too scared to risk carbon!!!

rollerdavem

My all time favorite cassette was Boston, Third Stage. I would crank that up to eleven!

Cool the engines!

RD

Little Darwin

Your new 700c tires will I assume be more narrow than your 700c on the hybrid, which leads to the gearing being a bit lower. Also with the bike being lighter it should climb a little better (I know as a clyde, that the bike is such a small part of the overall weight, but in climbing any loss in weight does matter).

The most important advantage is that when you get it, you will be psyched and be able to ride harder.

I would still suggest going with the largest cog you listed... You can always change to one with closer ratios as a reward later on as your power increases and your weight drops (if you have any to lose).

JohnnyC

The hybrid is about 35lbs (with rack and pannier - always attached). The road bike will be about 20lbs or so. I've opted for some stonger / heavier wheels. So I am hoping the 15lb difference between bike weight will help.

I'm currently 256lbs - looking to lose another 28lbs altogether.

I don't really think my average speed will rise much (0.5 - 1mph increase), but I am hoping that I'll climb a little bit easier.

The bike has a sportive / more relaxed geometry - so maybe this will inspire longer rides. My max is 45miles at the moment. Roll on delivery day!!!

Thanks for feedback so far - very helpful

piper_chuck

What speed can you go on the toughest uphills during your rides? What cadence do you maintain during these uphills and do you feel it's fast enough or would you like it to be faster?

Armed with this info, go over to the already recommended gear calculator https://sheldonbrown.com/gears/ and run some numbers. Input all your numbers and in the Gear units box, choose the MPH @ your desired cadence. This will tell you your speed at that cadence for each gear combination.

I ran the numbers on a 50/34 12x25 with 700x25 wheels and 80 rpm. It told me the lowest gear would give you 8.5 MPH. Changing to the 12x27 lowered the bottom speed to 7.9 MPH. It's up to you to decide whether the speeds you get at your desired cadence are in the right range, or if perhaps you don't mind a significantly lower cadence up the hills. For example, with the 12x27 if you drop your cadence to 60 RPM, the lowest speed will be 5.9 MPH.

I prefer to keep spinning as much as possible up the hills, it's easier on my knees, so I went with a setup that allowed me to keep my cadence up on the hills...

Bill Kapaun

Assuming a 9 speed, there really isn't much difference between the two 12's.
12-13-14-15-17-19-21-23-25
12-13-14-15-17-19-21-24-27
From 3rd gear up, they are identical. For that reason, I'd go with the 12-27.
On the 11-23, you have-
11-12-13-14-15-17-19-21-23
A 50/11 is a serious high gear that you'd only use on a downhill.
Personally, if I'm going downhill, it's REST TIME!

JohnnyC

Piper_chuck - that's a great way of putting it into perspective. I usually move uphill at anything from 8-13mph depending on how long or steep it is. I know I spin faster than 60rpm on hills - definately don't grind up them!

Looking at my current setup - I think I must spin at 90rpm on the flats and about 70-80rpm up hills.

doghouse

+1 on the Sheldon Brown link: https://sheldonbrown.com/gears/

Plug in each set of numbers and you will have your answers very quickly. Much better than all of us guessing for you. You know your riding conditions and topography better than any of us. (ie-Most times I run a 13x24 on a 52x42x30 triple.)

As an aside, Harris Cycles offers a "Century Special" cassette, 13x30.

Since I don't get to ride more than a day or two per week, and am too big a chicken to run downhill fast enough to need an 11 or 12, on the long really hilly rides this thing is a life saver.

Good luck.

Ray Dockrey

Either way you will have to get used to it so don't get frustrated with it at first. I went from a triple to a compact last year. I run a 12-25 cassette and have only missed the triple once. That was two hills a couple of weeks ago on a 33 mile charity ride. The best I could do was 5 mph and just had to grind it out. I weigh 280 down from 305 and ride about the same terrain as you and average about the same on my climbs. Even though I weigh what I do I climb well and I love the compact. You will also find that you will have to shift the front a whole lot more then you do now but you get used to it.

jaxgtr

I would go with a 12-27

Halthane

another vote for 12-27.

Unless you are on very flat land or really wanting to race you will not notice a difference between 12-27 and 12-25 except on the hills, where you might want the 27