TMassimo

The Sirrus comes equipped with a 48/32T crankset. I checked hundreds of bikes spec. in the same category and price range and they all come with a 50/34T crankset. In fact, even most road bikes seem to come with a 50/34T. The Sirrus seems to be the only one having a 48/32T.

My guess is Specialised chose this set for the Sirrus as it makes the bike quicker and more responsive for city rides and commuting in general. I’m not complaining - I love how quick and responsive it is – it’s quite enjoyable, but I’m wondering if changing to a 50/34T would make the bike more efficient. Like moving farther for my pedal strokes and making longer rides seem shorter or less fatiguing, for lack of better words.

Has anyone here gone from a 48T to a 50T (or vice-versa) for this reason? What do you think?

Stormsedge

I have a bike with a 48 big ring (triple crank) and one with a 50 big ring (compact crank). I am not a fast rider and for my money I see very little difference between the two. That said, for me, the key is how long and at what cadence might I actually be able to push the big ring. If your answer, like mine, is "not very long", stick with what you have until you wear it out, then upgrade if you still want the 50/34. Also, you might take a look at the "Sheldon Brown Gear Calculator" to see what you gain with a 50 over a 48. If you know your normal cadence, you can view it in mph...I didn't calculate it as I do not know your cog set, but I suspect the gain to be small.

canklecat

Gear combos are gear combos. The gain ratios/gear inches can be achieved with many combinations of chain rings and rear cogs.

My hybrids have 28/38/48 triple with 13-32 freewheel, another has 30/40/50 with 13-28 cassette, and my road bike is 42/52 with 13-24 freewheel. They can all get roughly the same gain ratios/gear inches in the appropriate front/rear combinations.

Unless you're spinning out in the 48/11 combo, you probably won't gain much with another chain ring combo.

For me, it's almost never unless I'm on a long -3% or so downhill where I still need to pedal rather than tuck and cost. And we have some decent long downhill grades and flats where a seriously strong rider might spin out. My road bike's top gear is 52/13. At 80 rpm I'd be going 25 mph. With your bike's top gear and same cadence that's 28 mph.

And 80 rpm isn't spinning out for most riders with some experience -- approaching 100 rpm, sure, it's harder to do smoothly, especially without foot retention. I use platforms and regular shoes and can manage 100 rpm and over 30 mph on some flats and -1% downhill grades, although I can feel some inefficiency trying to keep the feet in contact over rough pavement.

If you're not spinning out but would like a bit more responsiveness at most city speeds -- mostly sprints from 10-25 mph -- lighter tires and possibly wheels might make more difference. I've kept the stock wheels on my bikes but tires made a bigger difference. It's always a compromise between lightness for speed and puncture resistance. If you go for lighter tires with thinner puncture shields, or none, be careful to avoid road debris and be prepared for more flat repairs.

Going clipless or with toe clips might help but I suspect it's the firmer contact between foot, shoe and pedal that matters as much as the retention system. I wear soft, comfortable walking shoes for bicycling with platform pedals. I can feel some efficiency loss to those compressible soles. My old Detto Pietro cycling shoes I wore 30 years ago had hard, rigid soles with no give. Even without strapping the cleats into the toe clips I was still getting more efficiency. But I'm not comfortable riding with foot retention in traffic, so I'd use clipless or toe clips only on my road bike in areas with little traffic. I'll stick with platforms on my hybrids.

fietsbob

48:12=4:1 just like a 52:13..

canklecat

There's a theory that the extreme angle of a small rear cog, like an 11 tooth, over a smaller jockey wheel, can cause some strain or inefficiencies.

So the theory is that a larger chain ring and larger rear cog to achieve the same gain ratio/gear inch, is more efficient.

No idea whether there's any data to support this theory. But if you're more comfortable using a larger chain ring and sticking with your existing cassette's 13 tooth cog and avoiding the 11T, it might *feel* more efficient, even if it can't be proven to be more efficient.

I can say that my old road bike's climbing gear combo doesn't feel efficient. The 42T chain ring and 24T largest cog on the freewheel puts the chain line at an angle. I can hear the chain noise and it feels a bit ... grindy. It's not quite cross-chained, but it doesn't look or feel quite right for serious climbing. But that bike was designed for triathlon time trials over relatively flat terrain where the rider would be a strong cyclist in top gear most of the ride. Presumably the designer was more concerned about maximum chain line efficiency in top gear, not for climbs.

TMassimo

Good info. Much appreciated

I get that you can achieve the same ratio with different gear combinations switching between larger and smaller chainrings, but how is that gonna work between a 48T and a 50T with the same 11-32 cassette. I haven't checked but I'd be very surprised if you can get the same gear ratio on all combinations or even on most...

TMassimo

that's one combination. Would it be like for others as well? Like:

48:13 like 52:14
48:14 like 52:15
48:15 like 52:16
48:16 like 52:17
and so on...

Pendergast

A 48/32 crankset makes more sense for recreational cyclists. I'm surprised it's taken so long for bike companies to figure that out.

Sal Bandini

You're not using the 48:11 combo anyway so why bother looking at 50?

twodownzero

Remember also that it may have to do with the derailleur setup. Every derailleur can only "take up" so many teeth.

That said, 48 is plenty on the front for most riding. As I was bombing down a mountain yesterday on my Surly Disc Trucker, I found myself without gear to accelerate. I was in the drops/sprinting position, my back was basically flat, and when I looked down, I realized I was going 33 mph. Its top gear is 48x12. According to Sheldon Brown's gear calculator, 48x12 is good for 35.5 mph at 120 rpm and 29.6 mph @ 100 rpm (with 26x.1.5 tires, which is as close as I could get to mine). Do you think you'd need much more than that on your flat bar bike? I don't.

I highly doubt you'll see 33 mph on a flat bar bike of any kind.

fietsbob

Do the math..

castmasterflash

^ I literally top 33MPH on my Sirrus every ride on my morning loop - not just sometimes, and definitely not never. I changed my gearing out to a 50/34 and 12-25 in back. I'm not saying gearing is everything but with that and 700x30 tires I have sustained speeds at 30ish and top out down hills around 38-40. (Those are down hill, total average on 20mi is 18.5-19.6).
I love the closer ratios and bigger rings and actually once in a while wish I had one more gear to grab but wouldn't go with bigger rings than what I have.

twodownzero

Well the good news for you is that a 700c is bigger than a 26, and so the same gearing gets you even more speed with 700c.

TMassimo

48:12 = 4:1...........53:13 = 4:1
48:13 = 3.7:1........53:14 = 3.9:1
48:14 = 3.4:1........53:15 = 3.5:1
48:15 = 3.2:1........53:16 = 3.3:1
48:16 = 3:1...........53:17 = 3.1:1
48:17 = 2.8:1........53:18 = 2.9:1

kinda close.

So, does that mean that a 48T on a 12t sprocket will function and generate the same amount of force as a 53T on a 13t sprocket and will feel exactly the same whether cycling uphill, downhill or flat?

djmcnz

Yep, there's science and maths behind it but you need to cover off the obvious, prima facie particulars first.

How often do you use 32x32? If it's a fair bit then you'll suffer going to a 50/34.
How often do you spin out at 48x11? If it's hardly ever then you're not going to benefit from a 50/34.

I also have a 48/32 2x11 Sirrus. The only real problem I see is the lack of sub-compact chainring options currently available. Your front derailleur will suit either.

I found this article interesting: https://cyclingtips.com/2016/11/sub-...-bike-gearing/

TMassimo

I ride on the 48T 95% of the time and only used briefly 48-11 a couple of times.

Very interesting article. I thought the difference with these cranksets size would be more significant. On paper seems to be very small. However, in practice, I'm still not totally convinced.

I really like them Praxis Works' cranksets...

djmcnz

Agreed and Specialized have started to use them on their '18 Sirrus lineup.

MRT2

You might have your doubts, but the math is there. At 90 rpm (a cadence any decently trained road cyclist should be able to maintain) riding the 48 - 11 gear combination, your speed would be 31.5 mph. Switch out to a 50 tooth big ring and your speed goes to 32.9 mph. If you went down to a 46 tooth big ring, your speed would still be an impressive 30.2 mph. While these differences might make a difference in road race, especially at a sprint finish, I challenge anyone riding a hybrid to maintain speeds in excess of 30 mph on flat ground or rolling terrain for any length or time.

I agree with the above posted article that more manufacturers should be equipping both flat bar road bikes and endurance road bikes with subcompact gearing. It isn't hypothetical. I know many avid cyclists over age 50 who seldom hit a top speed above 30 mph, yet who need something close to 1:1 gearing going up climbs. To this end, a 48- 32 subcompact, or even a 46 - 30 subcompact mated with an 12 - 30 or 12 - 32 cassette is close to ideal.

TMassimo

I might be missing the point here, but would it be fair to assume that a bike with a 50T will travel ~1.4 miles faster than the same bike with a 48T? I'm not interested in speed - if there existed a cassette with a 13 or even 14-32T I'd buy it immediately. I'm more interested in the velocity as in the distance covered. For example, would one full spin (360) of the crank on a bike with a 48-12 combo cover the same ground as the same bike with a 53-13 combo? If the answer is yes then I rest my case.

I even spoke to a bike fitter about this. He thinks 48/32T is a good idea. In fact, he uses it on his road bike (go figure). He says it allows you to spin easier and faster whereas a 50T would feel like dragging something in comparison (or something like that).

Anyway, my desire to change crank has probably more to do with the look of them Praxis Works than anything.

Sal Bandini

You need to look at it as percentage. Going from 48T to 50T is about 4% difference. That's hardly noticeable.

Edit: And to answer you question, yes 48-12 is almost the same as 53-13. Divide the numbers, that's all that really matters is the ratio.

MRT2

Gear inches X cadence = speed. Gear inches isn't subjective. Is is an objective measurement. So if the gear inch calculator says 48 : 11 is the same as 50:12 or 53:13, that is what it is. I agree with your fitter. Going up to a 50 tooth gives most riders fewer usefull gears.