Bicycle Mechanics - How many mm space do I need to put 8th cog on?

Geez, I have 5-6mm between dropout and cog edge. Does this mean a new shorter hub\shell, and or I can save the cogset, re-lace the wheel w\ shorter body\ original cogset+1 and put the new cog essentually to the inside of wheel? (next to spoke.)
The derailler is 8, just need a shifter.
This question, put differently is ' Does the extra movement go either way with the derailler? I believe it would move closer to the smallest cog and not further towards the wheel.
I would rather adapt this wheel as it is Mavick and Swiss DT on Shimano (o.k by me).

>jef.

and thanks.

Sorry, more info> I have 142 mm between dropouts. Am 'attempting' to add 10 tooth cog onto 12-28 set.

thinking more...do I just buy an 8 cluster, being closer together might fit, can I keep the hub body? just a chain replacement.

I'm feeling kinda stoopid about this.

>jef.

Where did you measure the "142 mm"? The width should be measured inside dropouts. Unless it's a tandem, it should be 135 mm (mountain, touring) or 130 mm (road bike).

Regarding cassettes, check data at http://sheldonbrown.com/k7.html

I'm not sure you could (technically) add an extra cog of whatever size and fit it besides what you have. It wouldn't be supported by the hub, so it would break loose very quickly. Besides, your shifter has only 8 clicks and even in friction mode, you would need to shift beyond the shifter's range.

On the other hand, the same hub is used for 8 and 9 speed cassettes. With 9 speed, each cog is marginally thinner and spacers are thinner, so the overall width of a 9 speed cassette is 1 mm more than the overall width of an 8 speed cassette.
As a consequence, it also means that a 9 speed shifter has closer clicks and that a 9-speed chain is narrower than an 8 speed chain.

So, in a nutshell, to go to 9 speed, you will need:
- new 9-speed shifter
- new 9-speed cassette
- new 9-speed chain

Finally, a last word: your hub can accept a 12-tooth small cog. It may also accept an 11-tooth small cog (see the illustrations of a Compact freehub body on Sheldon's page). But a 10-tooth cog is out of the question.

Where did you measure the "142 mm"? The width should be measured inside dropouts. Unless it's a tandem, it should be 135 mm (mountain, touring) or 130 mm (road bike).

Regarding cassettes, check data at http://sheldonbrown.com/k7.html

I'm not sure you could (technically) add an extra cog of whatever size and fit it besides what you have. It wouldn't be supported by the hub, so it would break loose very quickly. Besides, your shifter has only 8 clicks and even in friction mode, you would need to shift beyond the shifter's range.

On the other hand, the same hub is used for 8 and 9 speed cassettes. With 9 speed, each cog is marginally thinner and spacers are thinner, so the overall width of a 9 speed cassette is 1 mm more than the overall width of an 8 speed cassette.
As a consequence, it also means that a 9 speed shifter has closer clicks and that a 9-speed chain is narrower than an 8 speed chain.

So, in a nutshell, to go to 9 speed, you will need:
- new 9-speed shifter
- new 9-speed cassette
- new 9-speed chain

Finally, a last word: your hub can accept a 12-tooth small cog. It may also accept an 11-tooth small cog (see the illustrations of a Compact freehub body on Sheldon's page). But a 10-tooth cog is out of the question.


HEY, thanks..I was wondering if I asked the wrong question or my description was hard to follow.

First. 142 mm between. Tom Ritchey pre P-series prototype. The guy who sent specs to factories in Japan for R.M and T to build the common bike. Frameworks 1990-1? earliest sloped t-tube I've ever seen.
142, he was thinking about 8. Wasn't invented yet prob.ond.
Or its an axle load\ rear torsion experiment. 16 inch frame.

Second, 7-8 speed conversion.



Do I get 8mm less over all with pre built 8 over 7. HAHAA...this is way out.

Okay. HOW wide is a 8 speed cassette mtb. Second, can an 8th cog be added to an existing 7, is this safe?, how BIG willl it be, if stuck into a steel frame with 142 mm between dropouts, considering the space between the inside of the dropout and the edge of the cog is 6mm......___________. there are 9 and 7's in the house- no 8's to measure.

Maybe I should find a new wheel.

Pulled wheel, flexed the triangle- 140mm 'tween.

I could (steel frame) use spacers and go to 144 between. putting the edge of the current lockring, 6 mm away from the edge of the dropout, tooth to tooth is close to 3mm apart so my existing set would expand only 3-4 mm. leaving 2-3 mm clearnce for 7 speed chain.

Derailler spec says 7 or 8 speed. I may mbe able to find travell distance (no manual.) I'll have to look for 8 shifter around the house.

Help me out guys, I'm pretty bold, what am I overlooking? This thing still will be way under an 9 cogset size?

Sure, there is a usual way of running 8- why would this fail? Maybe the travell won't be far enough to the outside- I could spacer it 1-2 mm out, totally play out the screws.

Tell me it can't be done...

Please.

Jef. :(

Jeff,

I think you have a bike with non-standard spacing. Nothing wrong with it per se, but it's hard to tell you exactly what to do without knowing all the details.

Ref. http://www.sheldonbrown.com/k7.html

First of all, as I said earlier, current specs (standard anyway) are:
135 mm (mountain, touring) or 130 mm (road bike).
Back when 7-speed freewheels (1982-1988) and cassettes (1988-1994) were the norm, spacing was 126 mm.

Meanwhile, the standard spacings for tandems has been and is:
130 or 135 mm (can't remember) back in the 6 and 7-speed era
135 and 140 mm with 7-speed cassettes
140 mm a little while after (is it for Campagnolo or the 1st 8-speeds?)
145 mm : current 8/9 speed standard (would also work with 10 speed AFAIK)
160 mm : current 8/9 speed Santana standard (ditto -- also used by a few other makers)

Apart from tandems, there are one or two makers who design singles with tandem spacing, as it makes a stronger wheel. The Co-Motion Americano (designed to tour the world) has been designed that way. Obviously (I assume it's a single bike, but the same reasoning would apply to a tandem), your frame has been designed with wider tandem-width dropouts to allow for a stronger wheel.

Going from that, you need to determine what is/was the original width of your hub.
You might have a tandem hub (140 or 145-mm width), which would have been widened or narrowed with washers on one or both sides, or you could have a recent single hub (135 mm) widened with washers, or you could have a "vintage" 7-speed hub widened with quite a few washers. It is possible to play with these and re-centre the wheel, but depending on its current design, you may end up with a very strong wheel... or a much weaker one.

As for "adding an 8th cog" or even going to 9 speed:
- If it's a freewheel (though I doubt), you replace the 7-speed freewhieel with an 8-speed freewheel and, if necessary, move the washers/redish the wheel accordingly;
- If it's a freehub, then you have two options:
Go with the "8-of-9-on-7" that Sheldon Brown describes at the bottom of hils k7 page.
Or, since you seem to have plenty of space left, go for a real 8-speed or 9-speed; in that case, you will need a new freehub (the ratchetting "core" onto which the cogs are attached -- $20), because your existing freehub isn't long enough to attach an extra cog.

In any case, unless you want to operate them in friction mode (assuming the shifters you have work in friction), you will need new shifters anyway, because your 7-speed shifters don't have enough "clicks" for 8 or 9 speeds. I would then suggest you go all the way to 9 speeds, because the shifters are the most expensive part, and you'll need them anyway)

With a 140mm O.L.D., I hope you have a cassette, Jeff, because an axle that long would be subject to extremely high breaking stress at the right-side bearing cone. Assuming you have a cassette, go for 9 speeds, per Michel's recommendation, and use any shifters you like, as long as they have a friction mode.

140-between hub locknuts, 20mm in spacers non drive side, the frame has not been bent to fit.
Pro build wheel old, Shimano Deore DX FH M650 (new condition, why I want to keep) hub body? Don't want to change the body, re-spoke.

I run a tandem axle, weird. Thanks for the link, lots to digest.

As I said before, there are factors to suggest I have a non-production frameworks.

Cool bike. And being huge rear....like I know buying an 8 chain, 8 space and # of cogs cluster is way easier.
-BUT, someone must have built up this way. 7 spd chain, 8 cluster in 7 spacing with 8 shifter, derailer.

It's really bugging me. I have a 10 t cog and the lock. No spacers.

My wheel was dished to run ballanced mid axle...my mechanic said it was to the side.
Wonder if to compensate for the 20mm spacers on the non drive side axle.

I'm still in flux.

And perhaps outreaching my bike modification abilities.



>jef.

C'mon Fixer, you said no and removed your post.

I'm an idiot or I will do. Scared, to be associated with this crazy notion?

Really, science is not my long suit, design is.

How'd they figure to go up? Was the 123456789 progression a new cogset every time? NO...?

I bend metal, do wierd stuff to bikes. No big.