# Bicycle Mechanics - Largest cassete cog size for 105 deraileur?

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

john_iverson
11-17-06, 07:13 AM
I'm in the process of building up my first touring bike with an old Scott Pro-Racing frame. I have an all but new 9sp 105 rear deraileur (5501) in the parts box and am wondering how large a cassette I can run with that? I've had no problems with cassettes up to 27 on road bikes in the past but really want to go with 30+ if I can get away with it?

Thanks,
John

rmfnla
11-17-06, 08:31 AM
I put a 9sp 11-30 cassette on my wife's bike with an Ultegra RD and it works great (a 32T cog was too much) so the 105 should handle it, too.

Before you ask, I don't know where to buy an 11-30 9sp cassette; I made mine from a standard 12-27 Ulterga by dumping the 14T cog and adding a single 30T from an 8sp LX. Just make sure to use the 9sp spacer, NOT an 8sp one.

Flanderflop
11-17-06, 09:13 AM
Your answer depends on what you have for chainrings on your crank, and if you have the SS or GS 105 derailleur. The GS has a 37T total Capacity, and the SS has a 29T total capacity. To determine what you have on your bike you will need to do the following calculation.

Subtract the number of teeth on your smallest chainring from the number on your largest. (So if you have a 52/42 you would get 10)

Add this number to the difference between the smallest cog and the largest cog on cassette you want to put on. (If you are putting on a 12-27 the differance is 15 so you would need a total capacity of 10+15=25T, so this combination would work with any 105 derailleur.)

Also note that if you are running a tripple up front, you are more likely to exceed capacity.

As for the largest cog you can fit in, you probably won't find a road cassette with more than 28 T, and most 9 speed MTB cassettes have a 32 T or greater large cog which is probably (as noted above) too big.

HillRider
11-17-06, 09:27 AM
Another way of attacking the gearing problem is at the chainring end of things. Since this is a touring bike I can safely assume you have a triple. Most likely it came with a road triple with 52/42/30 chainrings.

If so, the easiest and cheapest way to get really low gears is to replace the 30T granny with a 26 or 24T chainring. You may not have enough rear derailleur "chain wrap" capacity to allow you to use the smaller granny with the smallest one or two cogs but that's no sacrifice.

A 26 x 27 low gear is slightly lower and a 24 x 27 significantly lower than a 30 x 30 low gear.

Sheldon Brown
11-17-06, 10:14 AM
Your answer depends on what you have for chainrings on your crank, and if you have the SS or GS 105 derailleur. The GS has a 37T total Capacity, and the SS has a 29T total capacity. To determine what you have on your bike you will need to do the following calculation.

Subtract the number of teeth on your smallest chainring from the number on your largest. (So if you have a 52/42 you would get 10)

Add this number to the difference between the smallest cog and the largest cog on cassette you want to put on. (If you are putting on a 12-27 the differance is 15 so you would need a total capacity of 10+15=25T, so this combination would work with any 105 derailleur.)

Also note that if you are running a tripple up front, you are more likely to exceed capacity.
This is all the straight Shimano Party Line, but it ain't necessarily so. See:

http://sheldonbrown.com/capacity

As for the largest cog you can fit in, you probably won't find a road cassette with more than 28 T, and most 9 speed MTB cassettes have a 32 T or greater large cog which is probably (as noted above) too big.

We have sold hundreds of our Century Special 13-30 cassettes for just this application, this is one of our most popular products.

See: http://harriscyclery.com/9

Talk about "road/mountain" cassettes is just marketing bs, implies a difference that doesn't exist.

In my experience Shimano "road" rear derailers will almost always work with a 30 in back, generally not anything bigger. Fortuntately, derailers are dirt cheap, so it's a big mistake to allow a \$40 part keep you from having the gearing you need!

Sheldon "Gears" Brown

+-----------------------------------------------------------+
| Always listen to the experts. |
| They'll tell you what can't be done, and why. |
| Then do it. --Robert A. Heinlein |
+-----------------------------------------------------------+

john_iverson
11-17-06, 11:54 AM
Thank you Mr Gears--you're right, I've seen plenty of 11-13/30 cassettes out there. I'm trying to build this up without having to starve my children in the process so I'll likely go with the 105 since it's already in the garage. Flandertop, you make things WAY too complicated!!!! I don't have a crank yet, (the old Shimano that was on it originally is pretty far gone and the arms are a little long for my tastes anyway) but I'm thinking something like 48-28-26 or thereabouts.... Hillrider, this is/was an ~1990 Mtn bike, one of Scotts best. It was all XT equipped although only 7 speed--nice ride for it's time!
Which brings me to my next question: I'm using the original wheels/hubs, (XT M732) for the rear as they are still very straight and smooth for being older than my son! Can I fit an 8 speed cassette on this hub? I know 9 won't work but I have some 8 speed barcons as well I would like to use...

Thanksall!

John

Sheldon Brown
11-17-06, 12:31 PM
...this is/was an ~1990 Mtn bike, one of Scotts best. It was all XT equipped although only 7 speed--nice ride for it's time!
Which brings me to my next question: I'm using the original wheels/hubs, (XT M732) for the rear as they are still very straight and smooth for being older than my son! Can I fit an 8 speed cassette on this hub? I know 9 won't work but I have some 8 speed barcons as well I would like to use...

Actually, any Shimano hub that works with 8-speeds does work with 9- or 10-speeds too!

You can't fit an 8-/9-/10-speed cassette on your present Freehub body, but you could replace the Freehub body with a newer, wider 8-/9-/10-speed for \$20-30.

See: http://sheldonbrown.com/k7.html#transplant

By the way, if you still have the original XT rear derailer, that would be a better choice than the 105 if you want to get wide-range gearing.

Sheldon "If It Ain't Broke..." Brown

john_iverson
11-17-06, 01:01 PM
Mr. If'n it ain't broke,
I actually poached the old XT deraileur about 18 months ago to fix one of my daughter's friends' bikes after a bad crash--That's what you get for being a nice guy :-)
Funny thing, I just finished reading your transplant article before I read your post--small twisty world we live in...... Doesn't sound too hard to replace the freehub body but I'm a little concerned about the "redishing" part. The frame is 135mm and the axle is plenty long but I'm a little intimidated by having to do more than a little minor wheel truing. Can this allignment issue be taken care of by say, shortening the fixing bolt on the new freehub or is it really not that damn hard to adjust the spokes???

Thanks for all your help and I now have your website bookmarked--what a great resource!!!

john_iverson
11-17-06, 01:06 PM
P.S. Just to rub it in a little, I have the afternoon off (hence the internet hovering), the sun is out, it's 55degrees and my road bike works just fine thank you! I'm going for a spin.