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Replacement parts on trek 7.5 fx disk

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Replacement parts on trek 7.5 fx disk

Old 05-23-14, 02:34 PM
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harryracer
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Replacement parts on trek 7.5 fx disk

Hi, I have a 7 year old trek 7.5 fx hybrid bike that is in need of some serious maintenance as I haven't used the bike for the past 2 years. Having recently got the bug again it has come apparent that a lot of parts needs replacing of which I want to do myself.
Its spec is currently

Crank

Shimano M443 Octalink 48/36/26

Cassette

SRAM PG950 11-26, 9 speed

Im still happy with the current 9 speed so was looking at currently replacing the cassette and chain and will replace the crank later.

Im looking at having a Shimano Ultegra Hollowtec II triple but in order to use this can I still put in a 9 speed cassette and chain and if so which ones do I look for? I thought 9 speed would all be the same and chain as standard? Not sure just what is supposed to go with what?

My gears Shimano Deore 9 speed that work fine so dont want to mess with this beast just yet.

Any advice would be welcome
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Old 05-23-14, 02:44 PM
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jimc101
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You need to research if you front derailleur will cope with the increased ring size of the Ultegra crank, this will be 30/39/52.

Also, you need to check the BB shell size, road are standard at 68mm, if yours has a 73mm, the Ultegra won't fit., Also, Shimano road cranks don't come with BB's so budget for this.

Would look at the gear ratios using a calculator (like this Bicycle Bike Gear Ratio Speed and Cadence Calculator) to see if its worth changing.

If you FD can cope, the crank will run fine with 9 speed, even though it's spec'd as a 10 speed.
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Old 05-23-14, 03:01 PM
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harryracer
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I guess that the front derallier can be replaced if needed. I know that its a 68mm BB, does this have an issue with the derallier then if the crank is set further out or in?
If I change the cassette as 9 speed again then the 10 ultegra would still work on this with 9 speed deore shifters?
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Old 05-23-14, 03:09 PM
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Originally Posted by harryracer View Post
I guess that the front derallier can be replaced if needed. I know that its a 68mm BB, does this have an issue with the derallier then if the crank is set further out or in?
If I change the cassette as 9 speed again then the 10 ultegra would still work on this with 9 speed deore shifters?
You will need a flat bar road front derailleur for that setup. But first you need to determine if the chainrings will clear your chainstays, road chainrings are bigger and mounted further inboard.
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Old 05-23-14, 03:32 PM
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It is your bike, and you should feel free to upgrade whatever you want, but you asked on a public forum, so here I go getting all opinionated.

Unless the parts were worn out before you parked the bike, or you parked it out in the elements, all I would do is replace the chain and ride... and that would probably be more than it needs.

Changing the crank won't buy you much... With either crank, once you spin out, you are probably going down hill, so you can tuck in and go faster than you can pedal anyway. I hit 38 mph down hill on a recent ride with the same high gear you have (Trek 7.3 FX) by doing just that... Well almost, I periodically stabbed the brakes because it was an unfamiliar road, and I didn't know what was around the corner.

At 80 rpm the difference between 48x11 and 52x11 is 28.0 vs 30.4 mph. And, I think 28 is a reasonable top speed for a hybrid. If I am riding over 28 mph, I am tucking, because I deserve the free ride since I paid the price climbing to the top of the hill the other side of where I am descending.

Concerning the FD, it might need to be a road derailleur to accommodate the large ring, and if so, it won't be compatible with the front shifter since Shimano decided that front derailleur cable pull should be different between their mountain and road groups, even though the pull is compatible for RDs.
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Old 05-23-14, 04:04 PM
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Hi Thanks for your comments , the cassette, chain and middle ring of chainset are heavily worn and need replacing. If you think that the I have had the bike for 7 years with 5 years solid use approx 100 miles a week commuting it has had no service!!!!
Yes I agree the speed of excess 28 mph probably isnt going to occur often so I'm not so fussed about that. But I thought that as I am replacing the cassette and chain I might as well go for a bit of an upgrade as well.











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