SoftrideSam

Hello All,

I'm new to riding again after about 10 years. My bike is an 8 speed with a 53/42, but I need some more gears for the hills around me. Can I convert my 42 to a 36 and get the help that I need? Are there any drawbacks to this set up? Sorry for sounding like a newbie, but I am.

Thanks,

Sam

moxfyre

Yes, you could do the conversion in theory, but it might be complicated. 53/36 is a very large gap between the two chainrings! Your front shifting will be slower and more difficult even if you get this change setup as well as possible. It may require replacing one or both rear derailers, and possibly the crankarms.

Rear derailer: the rear derailer must have enough capacity to wrap up 6 more links worth of chain, in theory. In practice, your current RD should be fine.

Front derailer: the front derailer must have a deep enough cage to accomodate a 36T chainring. The difference in radius between a 36T and 42T ring is about 1/2 inch. Does your front derailer look like it has 1/2" between the bottom of the cage and the chain, when using the small chainring? If so, you can probably use the current fr, if not you may need to change it.

Cranks: if you have a double crank with 53/42, it is probably 130 mm BCD (the diameter of the bolts that hold the chainrings on). The problem is that such a crankset cannot accomodate chainrings smaller than 38 teeth. How to figure out your BCD: https://sheldonbrown.com/gloss_b.html#bcd If you do have a 130 mm BCD crank, you'll have to switch to a different crankset, maybe one with a 130 mm BCD.

Okay, that's complicated Instead of using a 53/36 up front, why not just get a wider range cassette in back? What is your current cassette? Cassettes up to 12/32 are easily available, and MUCH cheaper than all the changes you might have to do to get a 53/36 working. (You might need a new rear derailer if you change the cassette, but maybe not)

SoftrideSam

Thanks for the input. Would going to a 39 with a new cassette be easier?

Applehead57

What a great answer! You got a star today.

moxfyre

Yep, almost certainly. A 39T chainring will fit on that crankset fine. I don't know of any triathlon-specific front derailers, so I'm 99% sure you won't have to change the FD. Again, you may have to change the rear derailer to accomodate the wider gearing, but maybe not. If you tell me what your current rear cogs are, what your current rear derailer is, and the rated capacity of the RD, I'll be able to give you a pretty good guess about whether or not you'd have to change the RD.

I just noticed your username. Sounds like you have a triathlon bike, and that's why you've got a 53/42 instead of the usual 53/39 for a road bike. I'm guessing your largest cog is either a 23 or a 25... I can see why those high gears would give you trouble on the hills...

John E

I vote for something like 50-39 or 48-38 up front, with a 26T low gear cog in back (or a 27 or 28, rear derailleur permitting).

Another option is a 110BCD crankset, with something like a 48-34 combination.

SoftrideSam

I have a Shimano 105 RD. How do I check the size of the cogs? Also, would I be better with a 39 and a 9 speed cassestte. What else would I need to change if choose that option?

Thanks for the help.

Sam

SoftrideSam

Just checked and the largest cog on the back shows 21T the smallest one is is an 11T.

phidauex

Yeah, your bike is geared really high!

A lot of road doubles are 52/39 up front, and the 105 derailleurs should have no trouble with that. You could probably go 38 up front as well without trouble. They don't make 36t chainrings in the 130bcd size that you almost certainly have.

11-21t is also very high gearing on the back. If you want to keep your high gear the same, but wanted a 'lower low' you could go to an 11-28t rear, which I know is available (and I think is on sale from Nashbar right now). If you wanted an even lower low, you could go to a 38 or 39t front and an 11-28 on the rear.

I suggest playing with Sheldon Brown's gear calculator: https://sheldonbrown.com/gears/

Plug in lots of different combinations to see their effect on your ratios, and then choose the cheapest configuration.

For me, I upgraded a road bike from a 7 speed 13-26 to a 12-25 to get a higher high gear, and I'm going to change the front from a 52/44 to a 52/39 to get a wider range. Your solution may end up being similar.

peace,
sam

phidauex

If you go to a 9 speed cassette you'll need new shifters (unless you use friction shifting), a new cassette, and a new chain. Your 105 derailleurs and chainrings will work fine with a 9 speed system. So basically, if you are planning on swapping cassettes anyway to find a better gear ratio, then add to that the cost of shifters (not too bad for barends, very expensive for aero levers), and the cost of a chain if you want to go 9 speed.

peace,
sam

SoftrideSam

I don't know if it makes a huge difference, but my bike has 650 wheels. I just ordered my 39 chain ring and am looking for the cassette. REI has the SRAM 12-26 for $30. I'm not sure if I want the 11-23, 12-25 or 26. Suggestions??? Thank you all for the help.

Sam

phidauex

650c wheels make a small difference. If you and I were in the exact same gear ratio, but I had 700c wheels, and you had 650c, you'd be in a lower effective gear. Sheldon's gear calculator takes this into account if you specify wheel size.

If I were you, I'd wait till you get the chainring, put the chainring on, and then ride for a while and see what you think.

You need to ask yourself two questions...

How low do I want to go? The bigger the biggest gear is on the rear, the lower your gearing. Ride for a while with the 39, and if you still feel like you need a much lower gear, then you know to look for a cassette with a larger big ring. If you feel close, like you are just a click or two away from being 'optimal', then you don't need such a big ring on the cassette.

Second question:
How high do I want to go? Right now your highest gear is 53/11. Do you ever use it? If not, then don't worry about keeping an 11t on the rear, and go with a 12-something. If you find yourself using that high gear sometimes then you may not want to sacrifice it, especially since you are racing. You can extend the range of your gearing by getting a smaller small chainring and bigger big cassette cogs, and the only thing you give up is fine control, since your ratios will become farther apart. But if you give up that 11t on the rear, you are giving up top speed. If you never use it, no biggie, but if you use it, you may want to keep it, for race purposes.

But anyway, just change one thing at a time. Give yourself a few good rides before changing something else. Its easy to get 'change happy' and then lose sight of the original goal. If your original goal is satisfied with the smaller chainring, then you've saved some money.

peace,
sam

Al1943

Try a 12-25 or 12-26, it will make a huge difference compared to an 11-21, especially when you add in the change from the 42 to a 39 chain ring.

John E

I concur. 42/21 is a 54-inch gear. Even the Tour de France riders use something a bit lower, typically a 39/21. In contrast, 39/26 gives you a 40.5-inch gear, which is as low as I ever need on-road, even on a steep climb or at the end of a long ride.

John E

For better shifting, I would recommend 50-39 / 12-26. Otherwise, consider 52-39 / 13-26, which still gives you a high enough top end for all "normal" purposes.

moxfyre

I second this advice. (Actually, phidauex's advice is always excellent!)

Go for the 39T chainring (or 38T if you want...) and ride around on that, see how it feels. If you still need lower gears, go for a wider range cassette. The chainring is a very simple replacement.

The cassette replacement is also very simple, but may be made more complicated if you have to replace the rear derailer as well... though since your bike is currently geared SOOO high, I'd bet money that you can fit a 12-25 cassette on there without changing the rear derailer.

Al1943

You definitely do not need to change the rear derailleur. What you need is an 8 speed cassette to work with your 8-speed shifters.