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Downgrading from 9 speed to 7 speed...

2831 Views 4 Replies 4 Participants Last post by BruceBrown, Jul 13, 2004

BruceBrown

Discussion Starter · Jul 13, 2004 (Edited)

I know, I know. It sounds wild, doesn't it?

However, I am preparing to give away an old steel Trek 820 (vintage 1989) frame that has been set up as a commute and "kick around the streets" bike for the past 2 years with a full 9 speed XT drivetrain. That drivetrain and XT components have now been moved over to a two niner and I figured I should do something with this old frame with the parts I had around the garage.

I am going to give the bike to the son of one of my friends as a gift as they are not able to swing a bike financially at the moment. So I want to outfit it right and set it up as something he can be proud of and enjoy while commuting around town and to college as his campus bike next year.

I had the original Altus derailleurs and 7 speed shifters along with a brand new "bought it at the bargain bin" Shimano Megarange (11-34) 7speed freehub cassette. (I wish they would have had those Megarange cassettes and freewheels about 10 years back....) I also picked up a sale priced SRAM PC-48, 8 speed chain which works with 6, 7 and 8 speed drivetrains. Since I spaced the frame from 130mm to 135mm, in order to use the 135mm rear Shimano hub laced to an Alex rim, I have mounted a spacer on the hub and put the Megarange cassette on it. I had a brand new set of V brakes and levers from my own son's bike to use for this project (due to a disc brake upgrade).

The only thing that remains to finish this bike is a crankset. The original had the rings riveted together onto the driveside arm and the rings had worn out, so it got tossed 2 years ago since there was no way to replace the rings. I have both an Octalink BB available and the original square taper BB to choose between - so I just need a crankset. However, if memory serves me right with 9 speed cranksets, the ramps are a little different than older cranksets. Can I get away with running a 7 speed set up using the PC-48 chain (6/7/8 speed specific) with just about any crankset (that fits the BB), or do I need to get something that is 7/8 speed specific (Altus or Alivio)? I think Speedgoat has the Shimano M440's for a decent price (and Jenson has the OEM square taper version of this set). That's a 9 speed crankset, but the price isn't bad and either one will work with the two BB's I have laying around.

Any illumination would be greatly appreciated so I can finish up this gift and get it to the boy so he can start riding.

Thanks.

BB

Here are a few pictures of the downgrading "project".

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chuffer

· #2 · Jul 13, 2004

sorry, no info re: the cranks, but that is a fine thing that you're doing!

how about a single up front? since it is a commuter afterall.

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logbiter

· #3 · Jul 13, 2004

go for it

you can run 9spd rings with 7/8spd stuff. The rings are narrower, so you don't want to run a 9spd cassette w/ 7/8spd rings or chain.
Good work donating to the cause, hope he gets some passion for biking! The rig looks good, almost too good for campus *wink*
I do like the simplicity of a single ring up front (and less desireable for thieves), depending on the hilliness of campus/town.

BruceBrown said:
I know, I know. It sounds wild, doesn't it?

However, I am preparing to give away an old steel Trek 820 (vintage 1989) frame that has been set up as a commute and "kick around the streets" bike for the past 2 years with a full 9 speed XT drivetrain. That drivetrain and XT components have now been moved over to a two niner and I figured I should do something with this old frame with the parts I had around the garage.

I am going to give the bike to the son of one of my friends as a gift as they are not able to swing a bike financially at the moment. So I want to outfit it right and set it up as something he can be proud of and enjoy while commuting around town and to college as his campus bike next year.

I had the original Altus derailleurs and 7 speed shifters along with a brand new "bought it at the bargain bin" Shimano Megarange (11-34) 7speed freehub cassette. (I wish they would have had those Megarange cassettes and freewheels about 10 years back....) I also picked up a sale priced SRAM PC-48, 8 speed chain which works with 6, 7 and 8 speed drivetrains. Since I spaced the frame from 130mm to 135mm, in order to use the 135mm rear Shimano hub laced to an Alex rim, I have mounted a spacer on the hub and put the Megarange cassette on it. I had a brand new set of V brakes and levers from my own son's bike to use for this project (due to a disc brake upgrade).

The only thing that remains to finish this bike is a crankset. The original had the rings riveted together onto the driveside arm and the rings had worn out, so it got tossed 2 years ago since there was no way to replace the rings. I have both an Octalink BB available and the original square taper BB to choose between - so I just need a crankset. However, if memory serves me right with 9 speed cranksets, the ramps are a little different than older cranksets. Can I get away with running a 7 speed set up using the PC-48 chain (6/7/8 speed specific) with just about any crankset (that fits the BB), or do I need to get something that is 7/8 speed specific (Altus or Alivio)? I think Speedgoat has the Shimano M440's for a decent price (and Jenson has the OEM square taper version of this set). That's a 9 speed crankset, but the price isn't bad and either one will work with the two BB's I have laying around.

Any illumination would be greatly appreciated so I can finish up this gift and get it to the boy so he can start riding.

Thanks.

BB

Here are a few pictures of the downgrading "project".

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bulC

· #4 · Jul 13, 2004

megarange

If that's the mega range cassette that jumps from 24t to 34t, do your friend a favor and either customize it by mixing its useful cogs with some others to obtain some decent gearing jumps, or use something else. having to choose between 24 or 34 with nothing in between is an exercise in frustration on singletrack.
I have a box of loose cogs so I bought some of those on sale mostly for the 34s. I tried one on my cross bike, stock and the 10t jump was laughable. another example of shitmano putting it to the consumer.

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BruceBrown

Discussion Starter · #5 · Jul 13, 2004

To logbiter:

Thanks, logbiter - I was under the impression that things would problaby work. My main concern was about the ramps in the rings and if the extra width in the chain may hamper shifting up front due to those ramps being designed for a slightly narrower chain. I imagine the practical approach would to be get a low-end, or entry level crank that work on the square taper BB. I'll stop by an LBS to see what they may have sitting around.

I will provide him with one of our older cable locks in hopes that it deters a campus theft, but he doesn't go to college until a year from this August - so he will be able to park it in his garage at home while he learns how to ride.

To bulC:

The rider that will be getting this bike will not be going off road onto any singletrack for reasons not really worth discussing on this board. Suffice it to say that physical limitations are involved. The main use will be for transportation to and from school this year and then around the college campus come next year.

Even though there is a big jump to the largest cog (26T to 34T), it is really meant to be a bail out gear for exactly the kind of riding the recipient of this bike will be facing. That would be an occasional hill every now and then mixed into an area that is primarily flat. That bail out gear should allow him the ability to tackle those occasional hills without having to get off and walk the bike. The freewheel version of the 7 speed Shimano Megarange has the 10T jump from 24T to 34T, but the freehub version cassette which I bought is a tad less with the 8T jump going from 26T to 34T. I run a SRAM cassette with a jump from 28T to 34T between the two largest cogs and can manage the 6T jump with out want of another gear between on even the most demanding singletrack. Maybe the 8T jump would leave one frustrated in that environment, but I think it will serve his purpose on the streets and paths quite well with only the occasional hill requiring a bailout.

You can read what Sheldon Brown from Harris Cyclery wrote about the Megarange (first place I heard about it after it came out in 2001):

=====
* At first glance, many people look at the sprocket numbers 11-13-15-18-21-24-34 and wonder what Shimano's engineers were smoking when they came up with that setup, with a 10 tooth jump between the bottom two sprockets! In practice, this is actually a very nice arrangement, because the big jump to the 34 allows the jumps in the cruising range to be much more reasonable. If the jumps were evenly spaced, the user would often find that one gear was too low for cruising, while the next one up was too high. This type of freewheel, sometimes known as an "alpine" design, is intended to provide comfortable cruising, with the super-low gear for the tough hills. It works a lot better on the road than it looks on paper!
=====

If the 11, 13, 15, 18, 22, 26 and 34T Megarange that I picked up in the bargain bin ends up not being a good choice for my friend's son - then I will certainly convert it over to something else so that he can be happy on his "new" bike.

BB

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Downgrading from 9 speed to 7 speed...

BruceBrown

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