new bits advice for Trek7300fx (circa 2006)

[Steveo100]

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[peetee]

The crankset you have is not divisible so it would have to be replaced as a unit rather than removing two of the chainrings. It’s likely too that the bottom bracket would have to be changed for one that matches the new crankset.
If changing to a two ring crankset you may well have to replace the front gear mechanism. Depending on what suits you may also require a new gear lever. If you have combined gear and brake shifters this might not be possible.
As you can see it can get rather involved and costly and knowing what you want is a prerequisite if you don’t want to avoid spiralling costs that would rival the expense of a more suitable bike from the second-hand listings.
It might be a better option to replace the cassette (I’m assuming here that the wheel does not have a screw-on freewheel) with a closely spaced set of ratios and leave the original crankset on the bike.
It would help if you could tell us why you are considering this change and which of the gears you presently use.

[Steveo100]

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[peetee]

If you are not using the bigger cogs on that cassette there is no reason why you cannot substitute with one with a narrower range; 12-25, for example. The idea being you have more gear choice for the range of speeds you do. The added advantage of this is that your use/mileage is spread across more cogs and the cassette lasts much longer.

[Steveo100]

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[peetee]

That would work. But bear in mind that some specific adjustments may be needed on the rear gear mechanism and the chain length which may not conform to the ideal set up for standard cassette/crankset combinations. An experienced bike mechanic would help. I fear that the tuition and knowledge gained by many mechanics in national retail stores would have them insist that “You can’t do that”.
But I do stress, without more knowledge of which gears you presently use I cannot say if this will be right for you.

[531colin]

.........This would be a simpler set up for me....

Just using the existing middle ring (or the big ring) would be the simplest. Would either of those work for you?

If you are not using the bigger cogs on that cassette .....

Yeah, but we don't know that is the case, and fitting a smaller cassette might mean he HAS TO change the front changer.

Oh Ok, sounds good. I like to buy from Amazon, but cannot locate one atm. eBay has this ?......

Great. do you know how to fit it? have you got the tools?

[Jamesh]

Was it the front chainrings that had worn or the rear cassette.

You should be able to get a replacement cassette either SRAM or Shimano or even sunrace which aren't bad

Count up the number of teeth on the largest ring to get something the same. If your rear mech is a long cage then you might be able to go up to a 36t cassette for easier pedaling.

As others have said I'd leave the front unless it's really well worn
If it is a cheap sunrace chainset can be had for £20


Cheers James

[Steveo100]

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[rotavator]

If you post close-up photos of the teeth on your crankset then we can give you an opinion/s on whether or not they are worn out. If they are OK, I would keep the crankset; there is no need to follow the 1X fashion IMHO.

[Jamesh]

Thanks again chaps,

I did contact a local bike shop, but they wanted me to bring it in (can't blame them either) it's been a long time since I worked on a bike. I do have an engineering back ground, but not with bikes I probably mainly use the middle chain ring, and maybe the first four or five sprockets. Yes have ordered tools, and worked out how to index them etc. ( YouTube is my friend ) Just not clued up on ratios & compatibility etc. Haven't ordered the cassette yet. Think this is the tool ? chain whip on the way too.
Screenshot_20210114-113942.png

That's the job and a big wrench...

Cheers James

[Steveo100]

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[Steveo100]

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[Steveo100]

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[531colin]

....... I probably mainly use the middle chain ring, and maybe the first four or five sprockets......

Is that the biggest 4 sprockets or the smallest 4?
Its probably obvious, but if you have (or use) fewer chainrings then you will have less range of gears. If we know what gears you generally use, and what gears you can do without, then we can make recommendations for the simplest way to get the gears you need. On the other hand, if that means messing about fitting a new chainset (and probably a new bottom bracket bearing unit to go with it) maybe its easier to stick with the chainset you have now, and use the front changer from time to time?

Yes, you need a chain whip as well as the tool you illustrate. If you have quick release wheels, you can take the skewer out and use the tool with the long rod, this goes in the hollow Q/R axle and holds the tool quite firmly. With a bench vice I find it easier to put the tool in the vice, put the wheel on the tool and turn the cassette with the chain whip to undo the lockring.