jasandalb

So...I want to upgrade my original crankset.
Currently the original Truvativ Isoflow Triple is on it. Bottom bracket (from what I found on the mfg's site) is a sealed cartridge.

My question(s) are:
1. The bottom bracket...is there a specific size I am looking for or can I just look for a "sealed cartridge" bottom bracket (as opposed to a square or tapered?)
2. Can I go from a triple to a double with effecting the shifting? I rarely am in either the top ring or bottom ring (no hills in florida)
3. Should I be too concerned with crank length? Current length is 175mm (measured from insertion in b.b t to pedal hole)

Or ... can I just replace the bb and the cranks and leave the chainrings alone?

Sorry this is so long, but I am relatively new at the upgrade parts and looking for help.
I appreciate EVERYONE'S feedback....

Beaker

1. Don't know the answer, will leave that to someone who does

2. Shifting normally improves between triple and double. From my limited knowledge, I believe you'll need to check if your shifters will be compatible with a double - e.g. some Shimano shifters are a bit fussy about that. I went from 105 triple to a compact double crank - my shifters were OK, but the corresponding Ultegra and DA shifters are specific for one or the other.

3. If your 175mm cranks work, then why change them?

To your final point, why would you want to replace BB/crank arms without changing the chainrings?

Walter

There is a specific size you'll need. Depends on whether the bike is English or Italian threaded and whether it's a triple or a double. Doesn't matter whether it's square taper, ISIS, Octalink and etc. (I don't have, yet, experience with outboard bearing set ups).

Shifting may improve but you'll be changing bottom brackets and possibly front derailleurs.

I'd stay with the crank length you're used to but if you go a little longer (170-172.5) I don't really believe it'll make a difference. Chainrings will come with your new crank if you decide to swap. 53X39 is more than fine for us Floridians.

jasandalb

Shifters are "shimano 8spd triple"...sora's maybe(sti)...
I didnt know if there would be a benefit to go with a diff crank size.

How would I be able to find that out?

Current is 30/42/52.... but judging by what Beaker was saying I should probably stay with a triple to avoid messing with my shifters...

ridethecliche

Triple shifters/fd work with double cranks.

kenshinvt

1. you need to look for a bottom bracket specific to the new crankset you will be using. e.g., if you are using a shimano octalink crankset you will need an octalink bb. it is the interface you are looking for (e.g., ISIS, octalink, square taper, etc). it will also need to have the correct shell width for your frame. you also need to take into account the chainline that results based on your new crank length. this may not be a big issue but look up chainline for more info.

2. if you swap from a triple to double you will need to replace the front derailleur (double front derailleurs have a narrower cage) and likely your shifters (at least the left one, doubles have to click detents instead of three for triples). although, the shifters should still work if you dont mind an extra detent. I'm not sure if this is what you are asking but if you wanted to know if you can just put a double on there and it will shift fine, then no. at the very least you are going to have to fix the indexing.

3. look up some fit resources online that talk about crank length.

This can be a lot of work, as you can probably see from above, so make sure you definitely want to swap over. Double shifting is far more responsive and easy to keep precisely indexed.. but its a project on a bike that is already set up as a triple.

stapfam

Several cost problems you will encounter. The brifters may not be compatable with a double so new Brifters may cost. The front derailler will need changing to the correct type- there is a difference between a triple and Double.

I have just put a triple on one bike from a Compact double but this bike is going to be for the mountains. So for a new Double crankset- I would go for the newer type that has the outboard bearing. unless you have a weird manufacturer or it is a very old bike- There would be no problem in fitting these.

Walter

BB shell is either 68 or 73mm. It's probably 68 as Italian threading is less and less common and you don't seem to be describing an Italian racer.

68X108 is the size for doubles with 68X113 or 118 for triples. When (if) you break yours down your BB should be marked though I'd guess its 68X118.

As far as shifters go I have minimal experience with Shimano. Campy left shifters work with either doubles or triples but Shimano might be different.

You're right in that you don't need a triple here in FL but it might not be worth swapping a crankset out either.

Walter

Just to clarify: Obviously you need to make sure the BB matches the crank e.g. square taper crank and square taper BB. However, the size of the BB will be as I listed above regardless of the taper. If it's an English threaded BB on your bike (as I'm pretty sure it is) you'll need a 68mm BB assembly. 68X? and the type of taper will be determined by what crank you buy.

Beaker

One question here - what is it you're trying to achieve with this switch? That might help us understand what might be a good way to go.

Re the shifter question, you might be fine, you should just be aware that this can be an issue. For instance, I went from triple to compact double with Shimano 10sp 105 and they were fine. You might want to ask the specific question around your shifters (once you've identified them) in the mechanics forum to get a better answer. Either that our your LBS.

stapfam

Wheras 105 has one brifter for Double or triple- 8 speed sora does show a different brifter for triple or Double.

So it gets more expensive to go double as the details become apparant.

You are now looking at a new crankset with bottom bracket- New front derailler and new brifters. If you are going this route- you might aswell get a new bike- Unless you can find a buyer for your old gear.

ericm979

At least for 9 and 10sp Ultegra and Dura-ace, the triple shifters will work on a double. The cable throw for the outer two chainrings is the same. I suspect that Sora is the same. I do not know why Shimano makes triple and double shifters when the triple ones work on a double.

"Sealed cartridge" just refers to the bearings. They make sealed cartridge square taper BBs. Newer Octalink, ISIS and outboard bearing BBs all use sealed cartridge bearings. If you have anything other than outboard bearing, you will need a new BB with a shorter spindle to fit double cranks.

I am not sure what you are going to get out of "upgrading" to a double. A double may be up to 1/2 lb lighter, but 1/2 lb makes very little difference. Frankly, lightening a bike with Sora components is pretty silly. The shifting on a well set up and maintained triple is nearly as good as the shifting on a well set up and maintained double, and much better than the shifting on a poorly set up or unmaintained double. And of course you will lose your low gears and have fewer gear ratios to chose from.

jasandalb

Looking for less weight and a little better performance. Will not be changing from Triple to double...cant afford to replace brifters now.....And yes, I know my brifters look beat down. I assume that when I replace the crankset I just need to find that appropriate bb that goes with it.

Here are pics of the brifters:

jasandalb

further follow up.... I was just asking about the triple to double because I rarely use the top chain ring, was not planning it UNLESS it was feasible and not too difficult.