omni461

Hello, this is my first post. Kind of new to all this, but very interested in learning.

I am starting college in the fall and since its only a 17.5 mile round trip. On fairly flat land. I decided to try commuting. Last week my brother gave me his old specialized mtb. A vintage 21 speed rockhopper with 26" wheels and cantilever brakes. Using this bike I did the 17.5 mile trip in about 2 hours. I'll admit I missed a few turns and got lost a few times, but it was a fun easy ride. I was actually surprised at how much I enjoyed it.

Now, between buying a new bike or customizing the rockhopper I would rather build something. Plus if I'm going to be riding M-F for the next few years, I might as well get used to working on bicycles.

The only real changes I am planning are to the drivetrain. I'd like to go 1x7 with a 48t chainring and a 7 speed (13-14-15-17-19-21-23) cassette. Instead of the 3x7 thats on it now. This is where I am asking for your help. I found the parts I want. Which give me the gear ratio spread I'd like. Now I am just hoping these parts will work together. I believe my bb shell is 73mm. I can't measure it properly until tomorrow evening, when I pick up the tool to remove it at my LBS.

Sugino single speed 165mm Road 48t crankset
Shimano BB-UN54 73x110mm BB
Shimano 7-speed Cassette

Please let me know if I missed anything.
Thanks for the read.

10 Wheels

Moved from commuting

HillRider

What crank is on the bike now and what is the bolt circle diameter? You may be able to use it by removing the three current chainrings and adding a 48T single ring and single ring mounting bolts. Surly sells stainless steel chainrings in a range of bolt circles and these are "flat" rings so they do not tend to spill the chain in single use.

If you buy the Suguino crank, is the bottom bracket you show the correct length for it?

Little Darwin

Any single speed crank should be good for a 1x drive train, since the inner spacing of the chains are the same.

The BB should be ok, as long as your RockHopper has a 73 mm BB shell, but in a quick search, I see reference to 68 mm bottom brackets for RockHoppers, so it may vary.

The cassette will work for 7 speed. However, 7 speed on older bikes could be either cassette or freewheel. I suspect yours would be a cassette, but you should confirm. It is easy to tell. Freewheel or Cassette?

Also, I would consider a smaller chain ring, since if you need to climb a hill, lower gears are good, and if you spin out on a descent, you can still gain speed by tucking and coasting... but that is personal preference.

ClarkinHawaii

Yeah, really, it sounds maybe kinda over-ambitious. So you rode the route leisurely once on a nice day--what about when your legs/knees are sore from mashing and you've got that heavy bike with the thick (heavy) tires and it's pouring down rain (snow.sleet?) and you're bucking a 20mph headwind? I have made this mistake many times--assuming that the way something feels the first time I do it is how it's gonna feel a month or two down the line. Avoid expensive mistakes by allowing time for your body to adjust to the new grind.

omni461

@ HillRider - The triple chain ring which is currently on the bicycle is held together with rivets, unfortunately. The sugino crankset lists it's spindle length as "103, 110mm" and the spindle length on the bb is listed as 110mm. Im not sure what the 103 is referring to on that crankset.

@ Little Darwin - I'll pull the bb out and measure the shell with a set of calipers this evening before ordering the appropriate one.

I never bothered to check if I had a cassette or a freewheel. Thank you, that could have thrown a wrench in things. I just checked and it's a cassette.

As for the chain ring. I chose 48t after checking with this calculator. Sheldon Brown's Bicycle Gear Calculator Having ridden my friends single speed, which is set up at 65 gear inches, I think thats a good compromise between speed and intensity. Here in Sacramento, CA it's mostly flat. My commute being 70% secluded bike path and 30% city roads. With a 48t chain ring I can choose from 55 gear inches to 96 gear inches. That gives me room to push myself and hopefully grow as a cyclist, lots of room. haha

Thanks for the replies everyone. I'll hold off on ordering any parts until everything is sorted.

Edit:

@ ClarkinHawaii Hmmm. You have a very valid point. Hmmm.

trailangel

You would be better off changing to lighter weight tires.
I don't think that bike has a cassette.
Forget about the 165mm crank arm on a MTB.

Cross Creek

If the BB that's on the bike now is 110mm (as I think you said above), I'd mount the new crank on it before buying a new BB to see what kind of chainline you end up with. Best on a 1x to have the chainring line up with the middle cog on the cassette. Another spindle length might work better for that [I think the 103, 110 marking on the Sugino crank probably indicates a recommended range, depending on rear hub spacing (eg, 126, 130, 135) and frame design]. You can move the crank inboard to adjust chainline with a shorter spindle, so long as the chainring clears your chainstay (a smaller chainring allows the crank to be mounted further inboard and still clear). Even with perfect chainline, you may have problems keeping your chain from jumping off the crank with a 1x, where it might stay in place on a single speed with a less than perfect chainline. I converted a 2x9 to 1x9, then 1x7 because it's easier to shift with the friction shifter I wanted to use. My chainline is close to perfect, but the chain would occasionally jump off, so I installed a chain keeper (not a chainguard, which only keeps your trouser legs out of the works). It all works perfectly now. My rear hub spacing is 135 and my BB 68x107, btw. I'm running 39x13-28, and can manage 12mph at a knee-saving pace with that setup, plus I've got the gear range for some decent hills. I have a 42t chainring in my parts box as well, but I'm happy with 39t for now. Don't think I'll ever need to go as big as 48t, but then I'm 59 and maybe not as ambitious as I once was.

omni461

Yes, I have a set of 26x1.5 tires. They will make quite a difference.

I just pulled the rear off, it is a cassette. I also measured the crank arm on the drive side from the center of the crank axle to the center of the pedal axle with calipers. It measured 170mm. Based on this website and their research, 165mm is optimal for my height of 5'7". Would you disagree with that?

I am going to trust the combined experience of everyone who has commented regarding the 48t chain ring. I may have been a bit over ambitious. So I'll go with a 46t crankset with a replaceable chain ring instead. That way if I need to change it, all I have to buy is a new chain ring instead of the whole crankset again. Also I hesitate to call the gradual slopes on my route hills. I used to run hill repeaters up in WA state for track. Those were hills. These are 2 or 3 gradual slopes. Overpasses pose more of a challenge.

Thanks for the tip on the chain keepers. I will look into it. I truly appreciate all of you taking the time to help me out.
@Cross Creek - That is some very good Information. It just took a moment for my head to wrap around it. 103-110mm might be the recommended range. I was going to wait until this evening but I might as well do it now. Im off to the LBS to pick up some tools.

ClarkinHawaii

Not to beat a dead horse, but since you're going to be using this for school, you'll have books, laptop, sports stuff, coolweather outerwear, plus pump, spare tube, biketool, lights, etc, etc. The weight all adds up. You'll very likely end up with a rack and panniers. My point: The bike could end up being MUCH heavier than it is now!

Not to mention the times when there is something big and extra and heavy that you'd like to take home. And what about taking all those girls you're gonna meet for a "little ride" . . . I can hear it now:

She: Oh Omni, take me for a ride on your AWESOME bike!
He : Mumble mumble mumble recovery day mumble

replaceable chain ring sounds good. If you can tell the difference (while riding) between 48t and 46t I would be very surprised-- I mean, it's a 4% difference!

HillRider

The crank arm length is almost always engraved on the inside of the arm and 170 mm is a very common length so confirm your measurement there.

The "optimal" arm length for almost any rider is what ever you like and find comfortable. All of those studies of "optimal' crank arm length correlated with rider height, leg length, etc. are so much guesswork and theory have never been shown to mean anything in the real world. If you are used to 170 mm there is no need to change. Some riders have a definite preference and claim to notice small differences. Others are pretty much agnostic and ride whatever is there.

Bill Kapaun

Why not stay with the triple for a while? Just keep it on the largest ring and see if that will be truly suitable after a couple months.

You didn't specify what year Rockhopper, so you might currently have anywhere from 42 to 48T. My 86 was 46T. My friends 87 is 48T. I think the latter ones were more in the 42/44T range.

ClarkinHawaii

best idea yet.

omni461

@ ClarkinHawaii I know all about recovery days lol

@ Hillrider - Thanks for the tip. You were right. It was stamped right on there, 170. You are also right in that I am used to the 170mm crank length. Before my brother officially handed it down to me. Ever since he purchased a new Specialized 29er from the LBS. I would take the old rockhopper out for rides quite often. I have felt no pain from prolonged riding (up to 32 miles round trip) anywhere except my palms, but I believe that to be due to the flat bar more than anything. So I might be ok with 170mm crank length. Incidentally those happen to cost a bit less.

@ Bill Kapaun - I never really checked that either. After looking at it, and double checking. It is indeed 48t on the big ring. Either way it needs to be replaced. A lot of the teeth are really worn down. Plus the bb is starting to make some funny noises.

Now that I looked at the gearing. When I am riding this bicycle I am usually in 48 in the front and 15 in the back when cruising and I drop down to 48x13 when I want some speed. Maybe I should keep the gearing as is, just replacing what needs replacing and work on my pedaling. I admit I want to go faster but maybe I am going about it the wrong way.

Retro Grouch 

That's what I was thinking too. An adequate lock for a commute to school bike might weigh 7 or 8 pounds by itself.

Truthfully, my general advice for commute-to-school bikes is to find something that you feel is semi expendable. That way you won't feel so bad after it's stolen.

Bill Kapaun

Compare to a NEW ring. They look like they have a lot of worn down teeth too!
It assists shifting.

omni461

Here is a picture of it. If it's still good I can donate it when I upgrade to a crank with replaceable rings. If not I'll just junk it.

Bill Kapaun

Apparently you insist on spending your money. Enjoy. The economy needs a boost!