Replacing 6 gear back set with an 8 set one

[nigelb]

Hi

I've just picked up another 2nd hand bike (after my last was stolen) and I need to sort a few bits. Back set is 6 gear, there's a poxy shift lever (7 gear!), and it has twist shift on the front set.

Am I right in thinking that I can fit an 8 gear indexed selector with the existing 6 gear back set, and it will work fine, then upgrade the back set to 8 as and when it needs replacing?

The bike is a Falcom Explorer hibred, but its had stuff changed (including the back wheel), everything still says "Shimano" but the back changer looks plastic/cheap. I'm not inclined to replace stuff that doesn't need changing, but the gear selector appears horrid so I want to do that sooner rather than later.

Plan of action anyway is to ride it for a week, and see what happens.

Nige

 

[shouldbeinbed]

are you sure you've got room for an 8 cassette between the rear drops and enough flex in the frame not to stress it. I tries a 5 to 7 upgrade years ago and it ended badly but it was a cheapy frame so may have had something to do with it.

 

[tyred]

You will need a different wheel, or at least a different hub. Six speed would have to be a thread on freewheel hub, eight speed would have to be a cassette hub and you will probably need to spread the drop puts to suit the wider hub. Is it a steel frame?

 

[tyred]

Thinking again, your gear selection issues could be due to a non-Shimano freewheel having different spacing. It could be worth trying a shimano freewheel on it. 5, 6 or 7 speed ones are cheaply available from ebay. Or the other alternative would be to fit a friction shifter and use the freewheel you have.

 

[nigelb]

Thanks guys, I'd like to avoid friction shifters if I can (lazy, prefer indexed gears). Gear selection appears ok at the sec, just a poxy little lever which I won't want to live with (its a botched replacement of the twist grip).

Yes, of course the back wheel willbe wrong, can't just accept an 8 speed set

I guess the answer is ride the bike for a week, as is, see what I can find that needs fixing, and make a call from there. If the bike generally feels like a "goer" I'll drop the back wheel out, and see what size gap I have between the dropouts.

How would I tell what the frame is made of?

really appreciate the help/ideas

Nige

 

[GilesM]

Think about what Tyred and Shouldbeinbed have said and then you will also need a new chain as the eight speed chain will be narrower than the six, this may mean that you also need new chainrings as the narrow chain may not run on the old chainrings.

Also be careful about trying to widen the gap between the rear drop outs, it's not really recommended and at the very least it can result in the frame tracking going completely out to lunch.

 

[nigelb]

Hi

Its an ali frame, 6061?

The chain should be the same, same for 6/7/8 speed if I understand it right? (Mind, the chain looks like it needs a clean at least, but again I'm going to give it a week, not going to do anything to start with apart from adjust the front brake which hardly works. Have just swapped a chain on another bike, so not scared of doing it as and when req)

As I say, once I've got 75 miles on it done (a week's commuting) I'll have a think, and see where I stand.

the gear change is similar to this

(Just older/more agricultural looking)

Nige

 

[tyred]

I wouldn't try and change the spacing on an alloy frame.

 

[nigelb]

Hmmm, sounds like I'm going to need to measure the spacing carefully, and consider my options.

Should I then stay with 6 speed?
Are reasonable indexed changers available (not twist grip), and am i likely to be able to get spares for the rear set for a while to come?

So many questions, sorry, but its really hard to Google for some of this stuff!

Nige

 

[tyred]

It's the range of gears that's important, not the actual number. Is the current lowest gear low enough to climb any hill you normally ride up? 12/18 gears should be more than enough (I would probably singlespeed it if it were mine but that's another story). The simple thumb type shifters pictured should work very well, are cheap and have little to go wrong.

Six speed freewheels and SIS derailleurs are freely available on Ebay for very little money and I would expect it to remain so for a long time to come. If you're worried about it, buy a spare now.

 

[cyberknight]

It's the range of gears that's important, not the actual number. Is the current lowest gear low enough to climb any hill you normally ride up? 12/18 gears should be more than enough .

+ 1 i use a 7 speed block and to be fair never use the biggest granny cog at the back .I could get away with a 6 speed or a closer ratio on the back(unfortunatly all the ones that fit my similar screw on freewheel tend to be the same ratio as i have )

 

[gbb]

You can get 8 speed freewheels, then if the dropouts will allow it, you may need a wider driveside spacer on the axle...maybe even a longer axle.

 

[RecordAceFromNew]

Hmmm, sounds like I'm going to need to measure the spacing carefully, and consider my options.

Should I then stay with 6 speed?
Are reasonable indexed changers available (not twist grip), and am i likely to be able to get spares for the rear set for a while to come?

So many questions, sorry, but its really hard to Google for some of this stuff!

Nige

+1 re measuring OLD carefully and know frame material before thinking about increasing gears at the back.

Is this what you are looking for?

 

[swee'pea99]

A little googling suggests that you have 18 gears all told - three front rings, six on the back. That's loads. As long as it all works, I'd stick with it as it is. It's not going to be a great bike, whatever you do with it. It was sub-£200 new, and that just doesn't get you great components. But it should get you around ok. Concentrate on the basics - a bit of oil, pump up the tyres, make sure your saddle's at the right height...

 

[nigelb]

Hi

Again, thanks for all the ideas.

Yup, was a cheapie new, not expecting the earth, just I thought if I was going to change the gear selector (which I'll need to if I stick with it, current one isn't comfortable for me) might be worth getting something suitable for back set changes etc.

Understood, its the range of ratio's which is most critical. I only have one short hill on my commute, I am sure the range will be fine. Have to say, though, on 24 gears, I was finding on one stretch I'd be stepping between two gears - each was slightly the wrong side of where I wanted to be (maybe this new set of ratio's will give me the one that's spot on!). Of course, it was also wind dependent ...

With the existing wheel on, the gap between rear dropouts looks to be 13 cms. Looks to me like the chain needs replacing (which is fine), back set don't look worn.

Result, there's a front light mounting that fits my light, and the back one will match too :-) Now, I really must get soldering, and make up the homebrew lights I was working on, and bolt those to the frame (the clip on ones are legal, currently I use 1W tesco's torch to see by).

Apart from the lights (and any emergency stuff I discover) I'll see how I'm doing after a week.

Really appreciate everyone's input, its such a help.

Nige