You are here

BB Shell Type and Cranksets

Most of my time on the bike consists of riding around Omaha. The terrain is very hilly. On the residential streets, I encounter many short (three blocks or so) climbs of 12-15%. On the main roads, there are many longer uphill grades of 5-7%. I have the standard triple 48/36/26 that comes with the bike. I need lower gears and do not use the highest-speed combinations.

Requirement: 165-170mm crank arms.

(1) Since I already have a Shimano Hollowtech triple, can I simply replace it with a double and have no problems?
-----I was thinking that a 38/24T up front would work with the 11-36t on back.

(2) Could I go as low as 22T for the small ring?

(3) What exactly is the bottom bracket shell size and type?
-----I would like to know what other cranksets could be used (if I cannot find a Hollowtech). In my upright (younger) days, I had a 44/32/22 SRAM crankset on my mountain bike that worked very well for getting around town.

Hi again Hank-
The Lightning bikes have ordinary english threaded 68mm wide bottom bracket shells that will accept a very wide variety of bottom brackets and cranksets. However, I think you are jumping the gun in buying a substitute crankset. Your present crankset - equipped with a smaller granny gear - is likely just fine.

The first step is for you to determine the BOLT CIRCLE DIAMETER of the Shimano crankset you already have. Look on the back of the crankarms close to the pedal spindle hole. You should find the Shimano part number of the cranks you presently have. If you type this part number into GOOGLE you should be able to find out the BOLT CIRCLE DIAMETER of your present crankset. A phone call to Lightning should also supply this information. Once you know the BOLT CIRCLE DIAMETER, you should purchase the smallest "granny gear" that will fit the crankset you already have. You presently have a 26t granny gear. You can likely go lower. A 24t, or maybe a 22t. Granny gears are cheap. You can find them on eBay, from Nashbar, Jenson, etc. JUST MAKE SURE THE GRANNY GEAR YOU PURCHASE has the CORRECT bolt circle diameter to fit your crankset. The smaller granny gear might be enough to solve your problem.

If it is not enough, the next step is to get another rear cassette with a LARGER biggest cog. There are some newer cassettes that have 38 and 40t big cogs, larger than your present 36t. The number of cogs on the cassette should match what you already have. Again, you can find cassettes on eBay and the like. Between getting a smaller granny gear up front and a larger largest rear cog, you should get better gears for the tough climbs. I would keep the triple crankset you already have, and if you have problems adjusting the chain length and derailleur adjustments after getting new gears, consult a good bike mechanic for help.

Best wishs, and safe riding,
Joel

Thank you for the kind reply.

I thought of that. The front derailleur is a Shimano Deore LX FD-T671-3. It has a capacity of 22 teeth. The 48/36/26 crankset fully covers that range. I figured that changing the small would require changing the others. I was happy with the 44/32/22 triple when I had my mountain bike. It also worked well when I had the Tour Easy. I used the 22T ring a lot.

The crankset itself is a Shimano XT FC-T8000 3x10. I've not found rings for this. But I've written a few stores to see if they have rings that will fit.

Since I don't like the chatter when I use the largest ring, I thought that changing out one Hollowtech (double) for another (my present triple) might be a good idea. Don't even have to mess with the BB... Especially if the cost of buying three new rings added up... If the double was a mistake, I could put the triple right back on the bike.

Getting on the gear calculators and figuring things, I would only lose the 48-13 and 48-11 (100 & 118 GI, respectively) by going to a 38/24 (or better yet, 22T) double.

BTW, your advice in a previous thread was correct. Replacement of a part(s) in the headset assembly solved everything. I had not thought to question this because the problem existed when I received the bike new. Just thought it was the "twitchy" about which I had read. Now I realize that there can always be a bad little part involved. Now the bike feels safe at high speed. The low-speed handling has always been great.

Hi again Hank -

I poked around Google a bit regarding your problem. Your present Shimano XT triple crankset takes chainrings with a 4 bolt pattern. The two outer chainrings have a 104mm bolt circle diameter, and the little granny gear has a 64mm diameter. I think that the smallest granny gear available in the 64mm size is 22 teeth. So the first thing you should do is buy a 64mm bolt circle diameter granny gear - with 4 bolt holes in it. These should be available cheaply just about anywhere. I find cheap bike stuff on eBay. The switch from your present 26t granny to the smaller 22t granny might do the trick.

If you do this, and still crave lower gearing, the next move should be a rear cassette with a bigger largest cog. Something bigger than 36t. I would keep your present crankset, front and rear derailleurs, and so on. Don't switch to a double crank. Even if the official specifications for the Shimano derailleurs say you will run out of range, you can probably do just fine with the smaller granny and larger rear cassette cog. Some rules are meant to be broken. The Shimano components on your bike are of very high quality, and you should not dump them unless absolutely necessary. I think that you can get them to work well for you with the proper adjustment to your future smaller granny gear - and possibly to your future cassette with a bigger largest cog.

Let us know what you try, what works and what does not. Get the help of a bike mechanic if the shifting does not go smoothly. Maybe the same person who helped you with the badly adjusted headset, or whatever it was that made you shaky at speed.

Good luck,
Joel

I picked up an FSA 24-tooth ring (10-speed, 64 BCD) on E-Bay. Although listed as Shimano/SRAM drivetrain compatible, the chain (KMC X10.93) badly hung up on the ring. Didn't work at all.

Hello Hank,

That sounds odd to me. Do you have a bike mechanic who can help you out? Maybe something is not adjusted correctly? I have been playing with bikes for many years, but I still sometimes make boneheaded errors when working on my bikes. A fresh pair of eyes might help.

Safe riding,
Joel

It's just changing the small ring. Unless installing the ring backwards, it's impossible to screw up. Imprinted words facing up with steep side of teeth doing the work. The ring simply didn't work.

Navigation

User login

Powered by Drupal