due ruote 

Thinking about getting some new (smaller) chainrings for the Davidson to make the gearing more sensible for my terrain. The bike has a DA 8 speed group.

The bike is set up as I bought it, with 42/53 rings and a 12-21 cassette. I rarely ride in a gear larger than 80-85 inches, so for the large ring I am essentially relegated to cross-chaining to the inner cogs.

Of course I could change the cassette, but I like the small jumps, and being a flatlander, I don't need much range. So my tentative plan is to change the rings to 38/48, which will give me way more range than I need, while allowing me to keep the small jumps, and spend most of my time on the big ring with a decent chainline. Comments on this plan are welcome.

Assuming I decide to go ahead with this plan, I'm looking at 3 options at Ribble:

1. Stronglight Dural: these are 5083 alloy and the least expensive option; about $27 for the pair plus shipping. I've seen mixed reviews and wonder about their longevity. They are sold as 8/9/10 speed.

2. Stronglight Zicral: these are 7075 alloy and would be about $60/pr plus shipping. I gather from various reviews and from this comparison that they would last longer. I am also led to believe that they have a nicer finish than the Dural ones. These are listed as 9/10 speed. Would they even work with 8 speed? I don't have all that much experience with indexed anything.

3. TA: these are also 7075 alloy, and, at about $70/pr plus shipping, are the most expensive option. Are they better than Stronglight? They are listed as 8/9/10 compatible.

Are there other options I should consider?

Tim_Iowa

If those ring sizes will give you the gearing you want, then it's a decent plan. The only possible hitch I see is if you can't lower your front derailer enough. But it's not a big change, and friction front shifting is more forgiving, so it should work out.

The 7075 rings should last longer than the softer alloy ones. I can't attest that the TA ones would be better than Stronglight, but historically TA seems to be the premium brand.

10 and 11 speed -compatible chain rings are thinner than 8 and 9 speed ones. They should work fine with the wider chain, but the opposite (wide 8 speed chainrings with narrow 11 speed chain) doesn't work. If you stick with an 8 speed cassette and chain, you shouldn't have problems with 10speed-compatible rings on your DA crank.

Those prices on Ribble are pretty great; nobody in the US seems to carry replacement rings for reasonable prices. I know where I'm going when I wear out another set of rings on my Campagnolo crank.

ThermionicScott 

I've had good results with plain ol' Sugino rings (48/38 shown here):



They were described as "5000" alloy, which is undoubtedly softer than 6061 or 7075, but I don't wear out chainrings very fast, especially ones this size. If you know that you're going to like that combo and put a lot of miles on it, then might as well spring for the expensive 7075 ones. Although I can't help but think the $/mile probably comes out to a wash in the end -- the Zicrals would need to last a little more than twice as long as the Durals to be worth the price.

Thin chainring spacers can be used if the 10/11 speed rings end up too close together.

pastorbobnlnh 

What about just changing the chainrings? You don't mention the model crankset you are currently using, but if it is Dura Ace or another Shimano road crankset, the BCD should be 130. 38T and 48T 130BCD chainrings are available in a range of prices from many different manufacturers. Just another route to possibly travel.

due ruote 

Good point about the FD. This is my only bike with a FD tab and I hadn't thought about that possibility. I'll check it out but my gut says it will probably be OK.

The bike has STI levers, so no, it's not friction.

Pastorbob, changing the rings is in fact what I am proposing, although, having played around some more with a gear calculator, I'm thinking maybe just the big ring.

ThermionicScott 

My go-fast bike has evolved to a 48/42 double, which looks a little strange but is very satisfying to ride.

Tim_Iowa

STI shifters are more picky; they're kinda lazy and rely upon the ramps and pins on the chainrings to help.

That said, yours still should work fine with the 48T big ring if you can lower the FD a mm or two.

I bet you could find a used 39T inner ring for $5 or less, if you want a little lower range for cheap. They're extremely common in 130 BCD; 52/39 was (and still is) a popular double road crankset.

due ruote 

That's exactly what I'm thinking of doing. Thanks for the input.

bradtx

I would use this set to determine if a 38/48T chain set delivers what you're looking for. They won't last as long as the other two options, but they will last for many, many miles.

I'm also a flat lander and I've put my 7400 12-21T into the parts bin in favor of a 13-23T, low 70 GI to upper 80 Gi has me roughly in the middle of the cassette when using the 53T chain ring.

Brad

nfmisso

Consider a 13-26T 13-14-15-17-19-21-23-26 (very even jumps) cassette instead.

48/12 = 4 ~ 53/13 = 4.1 ; a 52/13 would be exactly the same as a 48/12

38/21 = 1.8 42/26 = 1.6

I would not go with the Shimano 12-25 because of the 12-13-15-17-19-21-23-25 <> that 13 - 15 jump is not nice.

due ruote 

I was thinking the same thing about the Dural rings, then my thinking evolved toward only buying one, so I might just buy the better one and be done.

I also looked at the 13-23 cassette option. It mostly looks good, but there winds up being a rather large gap between the 19 and 17 cog, where I'd like to have another gear. This gets smoothed out with the 48t ring.

That said, I would still think about changing to a 13-23 when it comes time for a new cassette.

due ruote 

The problem for me with a wider range cogset like that is that, at least with 42/53 rings, I always seem to be cross-chained. Ideally, I like to have as many gears as possible between roughly 65-85 gear inches, and I rarely use anything outside that range. I also dislike having to do a lot of double shifting.

So for your example, if I was on the small ring, I would use the 14 - 17 cogs. On the big ring, I would use the 19 - 15 cogs. In both cases, in terms of an ideal chainline, I would be at the wrong side of the cogset for the ring (granted, not as bad for the big ring), and in both cases I would miss having a 16t cog.

I am starting to realize why I like the 1 x 6 drivetrain on my Raleigh so much.

nfmisso

Keep in mind that you can build up any combination you want for less than the price of three cassettes.....Miche has first position cogs up to 15T, and middle/last position up to 29T.

Gear Inches are practically meaningless without knowing what size tires you have.

16T with a 53T ring is the same as 14½T with a 48T ring.

Actually a 13-23 would probably make you very happy at much lower cost than new chain rings.

13-14-15-16-17-19-21-23 - giving you almost the same ratios as a 48T ring with a 12-21.

due ruote 

From Sheldon Brown's glossary:
Gear Inches One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches. Unfortunately, the handwriting is on the wall for all inch-based measurement systems.

Since the wheel diameter is part of the gear inch calculation, I don't see how GI can be meaningless. Sheldon's gear calculator (which is the one I typically use) calls for both the wheel diameter and tire size.

I addressed the 13-23 cassette option below at post #11 . I will probably switch to that when I need a new cassette, but I went ahead and ordered a 48t ring. It seems like the best option for what I'm seeking.

Thanks for the replies.

John E

Even though, as a scientist, engineer, and academic, I generally prefer the Metric system, I really like Gear Inches, because the system is nicely calibrated to percentages of what used to be the default top gear of 52/14 = 100 gear-inches. Thus, a 50-inch gear requires half the pedal torque of a 100-incher. It's easy and very intuitive. It is also easy to relate to the old English wide-range 3-speed bikes, which were typically geared something like 50-66-88.

As for your questions regarding chainring and cog sizes, all of my road bikes have top gears in the mid-90s. For this I use a top gear cog of 13 or 14T and outer chainring of 45 to 50T. 45-42T works fine on the Peugeot with an old Shimano Titlist front derailleur.

jimmuller 

An effective wheel diameter of X is the same regardless of the wheel size because it takes wheel size into account. Instead, the ratio of chainring teeth to sprocket teeth really is meaningless without knowing the wheel size. For most of us neither the wheel size nor the crank length varies so much bike to bike that it matters. A 26" wheel vs. a 27" wheel is equivalent to changing a sprocket from 27T to 26T. Compared to the overall range of available gears, this difference is (almost) trivial. Even more so for a 622 (700c) vs. 630 (27"). So effective wheel diameter is a good way to express effective gearing, though you could quibble with the use of inches instead of mm. (But hey, we use a mix of metric and English units for everything else on bikes, so why not gears?)

There is another, more subtle value in the use gear inches over tooth ratio, or any ratio whether corrected for wheel and crank size or not. It's a matter of how much comprehensible information is carried in the number. Most of us can visualize the difference between, say, 32" and 50" and 90". In fact, the first digit tells us most of what matters. However the corresponding approximate ratios 1.185 and 1.851 and 3.333 are gibberish.

I are a injuneer (and rather too highly educated in science to be useful to man or beast) so I'm quite at home with metrics of all sorts. But for sheer intuitive understanding, I stand by gear inches.

Now back to your regularly scheduled discussion of chainrings.

ThermionicScott 

I suspect that what Nigel meant to type was "gear ratios are meaningless without knowing the tire size" since that is the usual objection to discussing gear ratios in isolation.