Bicycle Mechanics - 7sp cassette, 8sp STI

I recently got a bike with a 7speed cassette with down tube shifters. I have a pair of STI levers for 8 speed. Will they work together? I realize there would be an extra click but is the spacing the same for 7 and 8 speeds?
If they won't work, what are my options for putting indexed shifting on the handlebars for my 7 speed bike. I noticed bar ends only go to 8 speed.
Thanks

Check out Sheldon's Alternate Cable Routings section, as it's what you want:

http://sheldonbrown.com/derailer-adjustment.html

Excerpt:

Shimano originally publicized an alternate cable routing which placed the cable slightly closer to the pivot, making the derailer move slightly farther for each click. This adaptation makes newer Shimano derailers work with older Dura-Ace (http://sheldonbrown.com/dura-ace.html) shifters, but it is also useful when you want to use a 9-speed cassette with 10 speed shifters, or 8-speed cassette with 9-speed shifters, or a 7-speed cluster with 8-speed shifters.

Maybe the 'centeron' pulley slop sideways will cover minor mis synch issues..


I noticed bar ends only go to 8 speed...
you mean you didnn't find the"Dura Ace' 9 speed bar end shifters?
look around more, there are 9 speed too..
but that requires more stuff to by to run 9 speed , and the extra ratio may not really matter.

Generically a 8 speed adds a gear to the spacing of a 7 speed ,
so a leftover shifter klick should not be an issue.

Ihave tried to use 7 speed shifters on 8 speedcassettes iin the past. The result was barely acceptable - extra concentration and effort required to get between certain gears. Others have said they got it to work perfecty. IIRC, 8 speed has a 4.8mm/gear spacing and 7 speed has 5 mm/gear spacing. The result is that over 7 gears you can be as much as 1.4mm out of alignment, which doesn't sound like much but it is 28% of a step.

I have had moderate success changing a 7 speed hub over to a 8 speed freehub body to use a 8, 9 or 10 cassette, although this changes the spacing of the rear axle.

I've had good luck mixing 7 and 8 speed shifters and cassettes/freewheels. Setup is more finicky but I've always gotten it to shift fine.

If the 7 speed cassette doesn't index to your satisfaction, get an 8 speed cassette and lose one cog. Then it will work as intended. Alternatively, you could tear apart both cassettes and use the 8 speed spacers on your 7S cassette.

Alternatively, you could tear apart both cassettes and use the 8 speed spacers on your 7S cassette.

8spd cogs are 0.05mm thinner; this would introduce an error of up to 0.3mm. Not much, but if you have the 8spd cogs, it just makes more sense to use 7/8.

I'd just get hold of an old 8spd cassette body and re-dish the wheel so I could use all 8.

I like the ratio set of the 7 speed Shimano K cassette. a practical combination.