5 arm cranksets versus 4. Which is better and why?

Question

I'm looking to buy a Sora triple crankset. Shimano make two types, one eith 5 arms, and the other with 4 arms1. Which should I get and why would that be a better choice? I'm a slow-ish rider. I'm 50 and speed is not a priority. But I'm planning a long ride in Asia and Africa next year. Which of the two chain-ring types would be a better choice for spare parts and any other considerations? Note: the 5 arm crank has a P.C.D. of 130 compared to 110 for the four arm crank.

Editor's note: The 4-arm R3030 crankset, below, is described as having a 110/74mm BCD.

The 5-arm R3030-CG, below, is described as having a 130/74mm BCD.

Answer 1

With a triple crank it matters more what the inner most PCD is. 110 and 130 both refer to the larger rings only and the length of the crank arms themselves may not suit you and it may not be compatible with your bike immediately either. I have played with bikes for over 40 years and ridden most Shimano PCD types and arm lengths and 4 of the bottom bracket standards too. You may need new bottom bracket bearings installed at the same time, the different standards don't interchange at all. The newer the better from every angle if you need it and the price is right for you. Sometimes the bike is better to be replaced if you know enough to understand what you need and more than a few things need to be replaced at once on a mediocre older bike.

Your described style of riding tells me you need the model that comes with the smallest number of teeth on the smallest ring of the crankset. This selection will provide the easiest effort to you regardless of most other things. The other gears are almost always properly spaced to provide 3 separate ranges of gears you can use for riding comfortably uphill, downhill and more level ground. Practice using all you gears to learn when you may wish for just that particular effect on your comfort and your efforts.

Just like your brakes it is important that your gears work just as you need them to when you need then to.

I have used middle and inner ring minimums on 48/34/20T with 94/58PCD and 54/39/24T with 130/74PCD and others in between. Your tyre size, terrain you ride and what you will carry on it really sets your gearing needs the most. If you learn to enjoy using more effort and sweating when you ride your gear needs may also evolve.

I've not seen or heard of less than 20T on a crankset. If both cranksets have the same lower number, then, the wider of the other 2 gears would be my recommendation. You can usually change just the inner ring very cheaply if you need a change but it can only go so small with each PCD.

Bike parts are usually so reliable as metallurgy has improved greatly in our lifetimes, thinking about ongoing costs is not very relevant apart from maintenance of the chain. Keep it clean and dry lubed following the directions is the biggest money saver you can make. It is possible to have a chain last many 1,000s of kilometres with regular care.

Edit: Only now that I've returned have I actually seen these 2 crank set images you referred to. I'd select the 5 arm Shimano with a new BB, the 2 piece design was introduced 20years ago and lots of spares and a 24T is possible in place of the 26T if needed. Bending any axle or crank arm is likely with enough force regardless of the system.

Answer 2

Seems to me the main difference is that the 5 arm version has a chain guard. The larger PCD is different but both come with a 50t large chainring per default, so that in itself doesn’t make a functional difference. I can't find a weight for the 5-arm chainring version, but I suspect it to be heavier.

Chain rings generally last >10Mm, so I don’t think spare part availability matters much. An unexpected failure is unlikely, with a broken tooth on the big chainring being the most likely. But then you can still continue on the smaller chain rings without much of a problem.

If you don’t need the chain guard, I’d just go for the 4 arm version.

Answer 3

I'm looking to buy a Sora triple crankset. Shimano make two types one has 5 arms and the other only has 4 arms. Which should I get and why would that be a better choice?

The one where you can reasonably rotate the chainrings in the best possible manner.

Normally, that would mean 4 arm. However, the Sora 4 arm crankset has an asymmetric bolt circle. It means you cannot rotate the chainrings to get maximum life out of them. Not only that, but sourcing these asymmetric chainrings is a major burden.

So the 5 arm is better in your case. The rotation to even out wear life is not perfect (a 4 arm crankset allows you to rotate the chainring exactly 90 degrees, the maximum possible rotation, whereas with 5 arms you get 72 degree rotation).

However, the 130 BCD doesn't allow a compact gearing. I looked at the cranksets and today it lists 110 BCD double and 130 BCD triple for the 5-arm designs. The 110 BCD double is the best bet for slow riders as you won't want a triple due to its unoptimal chainline on the big ring.