Rebuilding stairs question

HI all,
I have a couple of questions about redoing our interior stairs.
The house is 100 years old and the existing treads and risers are quite worn and some of the tread nosing has been broken off. The risers and treads are 3/4" pine boards. I have no problem replacing these, will use 1 inch oak for the treads and most likely 3/4' poplar for the risers. Will paint the risers and stain the treads to match the hardwood floors.
The stairs are about 40" wide with two stringers made of 2 by 12 (true 2 inches thick and 12 inches wide) and one middle stringer made of 3/4 inch pine.
My concern is the span and the middle stringer; I would like to replace the middle stringer with a thicker one as the stairs are a little wobbly.
First is replacing the center stringer overkill? Or should I replace this with a good piece of 2by lumber
The treads are on the narrow side (about 8 inches) I read in an old construction book (circ 1940) that treads should not extend more than 1 3/4 inches beyond the riser. So to widen the steps a little I wanted to have a 1 3/4 inch overhang on each tread. Is that too much for a 1 inch oak tread?
I tried to find out stringer spacing requirements on the web but no luck, only thing I found is a rule of thumb of 32 inch span between stringers. Any suggestions?
Thanks, Dave M
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" snipped-for-privacy@yahoo.com" wrote:

Check that there's not a significant difference in the riser height for the first/last step when changing the tread thickeness (obviously they'll be the same for the intermediate). While you're only change ~1/4" on the thickness, if there's already a slight mismatch, you could be making it worse, thus making a trip hazard (and failing code in the process)...

Wouldn't even have to replace it--just put a 2x in beside the existing one if it's tough to get the existing one out. Otherwise, I would definitely add a center riser--use the existing one for the pattern (assuming it's well cut to match the two end ones)...

May create more of a trip hazard by adding overhang than you cure by the slightly wider step. The stength of a 1" oak tread will be fine (assuming it's either a glued on nose piece or one piece, not just nailed-on bull nose). I don't have the code at hand to look up what is allowed and don't recall, but sounds a little too much to me.
Could possibly reduce the potential problem by using a small crown mould return under the lip to help prevent the "toe-under-overhang" catch...

As noted, I'd beef up the center and you'll definitely be fine. W/ 1" oak you could probably get away w/ doing nothing. Depending on the size of the existing 1x, you could possibly just use a 2x6 along it and stiffen it enough to make a difference. In reality I would just go ahead and add the extra stringer but if I were trying to save labor and/or money I'd lay a few of the oak treads down and try them out.
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I think adding a 2x4 nailed and glued to the existing stringer will give you as much added stiffness as doing all the work of replacing it.

I wouldn't make the treads deeper. In the older houses (I grew up in one) the stairs were pretty steep, and extending the tread will make each platform deeper, but won't change the pitch of the stairs. Try the experiment of walking up and down the stairs a few times. Going up, your weight is on your toes, and the heel really doesn't need support. So a shorter tread won't hurt. Going down, you would like to have a wider target to plonk your foot onto, but you won't because the space between the end of one tread and the end of the one below it is the same as it was before. And the additional protrusion does indeed make tripping more likely. Current standard is no more than 1" projection.
Good luck on the project. Should look nice with stained oak treads.
BTW, I'm assuming that the ends are not exposed and there are no balusters mortised into the treads. 'Cause if there are, you really have a JOB to do.
Walt C
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Thanks for the responses, as per the recommendations I will keep the one inch overhang and sister 2by on the center stringer.
My wife has a request which would create more work one side of the stairs has a partial open stringer, she hates this because the dust and dirt accumulate behind the balusters (The are just nailed to the treads) She wants to convert the open portion into a closed stringer with a knee wall.
As the balusters are right over one of the stringers I may have to add an additional stringer and build the knee wall over the old stringer. Trying to convince her that that is too much work, but if she gets something in her head...
Thanks Dave M
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