A conversion, is it possible?
 

I have a Cannondale touring bike and I want to make it into a bit faster. I can't afford a nice road bike. Right now it has an 11-28 gear in the back, and 7 speed STI RSX shifters, a triple crankset of 22-32-42, and a deore LX rear deralieur. What I wan't to do, aside from narrower tires, is put more teeth on the crank set, say a 53, 42, and whatever for the granny. I have a shimano 105 deralieur to replace the mountain bike deralieur. All the parts I have are in very good shape, some like the 11-28 have never been used, and all I would have to buy is a new crankset. Is what I propose possible, and able to work well together, or is it an impossible mismatch of parts? Changing the gearing, and putting the 105 derailieur with 7 speed RSX shifters. Would a 53, 42 work with an 11-28? I am concerned because of the 11 in the back, will it work with an older 105 derialieur?

As far as I know, 105 is neither 8 or 7spd compatible. Maybe 8spd back in the day but I don't remember coming across a 7spd 105 ever. RX100 was 7spd though, pre 105 stuff. Anything is basically possible, I don't see any reason to get rid of the LX derailleur since you need a long cage for the triple anyways. Maybe I'm completely wrong on this one but I'm pretty certain all you need is a new chain and crankset.

What?? Derailers don't have speeds. There was 105 back in the perhistorical days of 6 and 7 speed. RX was not pre 105.It was contemporary with 7 and 8 speed 105 and was essentially 105 with a different finish.

Whether or not you can use the 105 rear derailleur will depend on the model. On the back there should be numbers, format RD-XXXX. Once we know the model, we can determine if it is 7 speed SIS compatible. 105 goes back to 6 speed, pre-SIS days, so there are 7 speed SIS compatible derailleurs. I believe I have one in my parts bins.

Another concern will be the total capactiy you're asking the derailleur to handle. It should handle the double chainring and cassette combination you propose, but once you throw in a granny gear, it will likely exceed the capacity. The 105 is basically a mid range derailleur with most models handling about 28T capacity and a 28T maximum cog. However there were some long cage versions that handled up to 34T capacitiy. Again, we'll know for sure once we have the model number.

How are things in Ottawa to-day? In very wet and windy, one hour south of you, in Brockville.

An 11 works with the 105 but it should be a long cage if you have a triple up front.If you change to a crank with a 52 or 52 big ring you will will need a road triple FD to handle the bigger rings. You likely need a new BB with correct spidle length for the new crank.

FYI, SIS index shifting started with 6 speed.

Yes, but 105 was introduced in 1983, as a friction shifting, 6 speed group.

So what's your FRONT derailleur?

Right now, you have a mountain bike crankset (42, 32, 22). If you replace it with something that has a 52 tooth big ring, you might find that you have interference with the chainstay and you will definitely have a front derailleur issue.

The crankset determines what bottom bracket spindle you need. Obviously the bottom bracket has to match the hole in the crankarms. The crankset also determines what spindle LENGTH that you need. If your chainline is wrong, it may rub your chainstay or it may create all manner of shifting woes.

Your current front derailleur will have a cage that has an arc that roughly matches your 42 tooth big ring. If you change to a 52, the arc diameter will be too small and it will rub on the back of the cage. If you raise it up so it doesn't rub, it won't shift as well and it will look goofy. If you switch to a 52 chainring, you'll also need a road front derailleur.

Now look at how the cable is routed to your front derailleur. All road front derailleurs route the cable under the bottom bracket. Most mountain bikes route the front shift cable along the top tube and down the seat tube. Not having cable stops where you need them is a pain. I'm told that cyclecross guys have a gizmo that reverses the derailleur cable pull, but I've not seen one in real life.

Retrogrouch makes good points about the front derailleur and clearance. Which got me to thinking about chainring bolt circle diameters. If you are running a 32T middle chainring, then the BCD would be less than 110mm (which accommodates a 33T or 34T minimum, depending on the source) and you may have trouble finding chainrings as large as 52T with the correct BCD. Someone may be making them, but I haven't seen any. Anyone else know a source for these?

I know for sure that my deraillieur is 7 speed STI sompatible because I have used this exact same deraillieur before on a 7 speed STI. The thing that causes me concern is that I always used it with a 12-21 not an 11-28. I am not sure that this will work. I do not know the model number of the deraillieur because I can't find it right now, my appartment is in disaray right now, but I am not too worried because this is a bike that will not touch the road until may.

The reason I mentioned the granny is because the shifter I have for up front is made for 3 chainrings, I do not like the fact of having a granny gear because I will never use it, I have never used it in the past, even for fully loaded touring. I think what I would like best is to use the shimano 600 and try to block the granny option and go with a double chainring. I am not to worried about dropping the chain because I rarely shift into my big ring, more than once a week. So dropping the chain is not too much of a concern for me. By the way the front deraillieur is a deore, so you see I have 2 cices with the front deraillieur.

Things are real crappy here in Ottawa also, I rode home on Thursday and I almost froze my feet off in the cold temps. I am definitly not properly equipped for cold wet weather riding. Cold yes, wet no. And the out look is much the same for the next while.

I do not need to use a triple, the 105 rear deraillieur is pretty short, actually I would prefer not to use a triple, but like I mentioned earlier the RSX shifter is made for a triple. If it means having to be careful on the rare time I will be going from my 52 to my 40 something that is no problem, because I avoid using the granny like the plauge, and I would rather have a double than a triple chainring.

Deore LX but I hope to switch it to a shimano 600

I am not to worried about this since I think I am due for a new cartridge anyways, so I will probably have to buy a new one anyways.

If worst comes to worst I could probably trade my shimano 600 front derailliur for something that may fit. If I can't do that I do not thin that the cost of a new deraillieur will be too prohibitive, I have until May, it would be nice not to have to spend that money though.

My cable routing in that respect is the same as any road bike, under the bottom bracket.

I think in this respect I will just have to buy a new crank set, this would be my treat, I have always favoured 105 for cranksets, and I would be delighted to have a bike that was sporting a new one, in this instance I think I could scrape up the cash, but my resources are very limited, I do have till May though.

Your rsx front shifter shifts a double or triple. use the ganny and middle ring positions if using it with a double.

That sounds better than what I was originally thinking, my way would have stretched the cable too much.

Thank you everybody for your help.