Rear Dropout Spacing?
 

So on my frame that I built 2 years ago I used 130mm spacing. I had built my wheels up on Shimano 600 hubs that are like new. The bike I am currently building,for my wife, will use the same Shimano hub wheels as I built. (These are currently in use on her 1981 Miyati mixte)
Am I being short sighted by stay with 130 vs. 135?
What is the down side?

Follow up information.
My wife's bike is using an 8 speed cassette.

Are you building your wife a frame from scratch? If you plan to use the old 130mm spaced rear hub then that is for a rim brake build. Not sure what you would be trying to achieve with 135mm spacing.

If you are asking about being short sighted I'd think a better answer would be to look right past 130, past 135s and build her a proper disc frame with 142mm through axle rear dropouts or disc and forget about the Shimano 600 hubs. But if you are dead set on using the 600 hubs then just build a 130mm spaced rim brake frame. You're not talking about a tandem are you?

I guess I fall into the "old school"! Yep,rim brakes and center pull at that!

Set the rear end at 132.5 and the 2.5 either hub width (130/135) won't matter. If this was for me I'd go 135 and respace/lengthen the rear axle length to 135 too. Andy

Tom, the reason I suggested you build your bike with a rear spacing of 135 is because there is less dish on the wheel and therefore it is a stronger wheel. This assumes of course that you have a 135mm hub (or can change a present hub to 135mm spacing). When I recently built my wife a new bike I bought a White Industries hub with 135mm spacing.

A 130 rear wheel is pretty severely dished. The reason manufacturers didn't make it wider when more rear cogs were added is so that they didn't make prior hubs and frames obsolete. Not because it was superior engineering. If Tom can find or make a 135 hub that is his best option using rim brakes.

Through axles with disc brakes are not a great combination for a beginner builder with minimal equipment. It demands accuracy or the wheel is not going to center nor the disc brakes properly positioned. It is hard enough for those without really good fixturing to get even vertical dropouts positioned so the wheel is centered. In the midwest, recreational riders that like to ride in good conditions don't require disc brakes. Neither do they benefit from the heavy steel fork blades and chain stays required to withstand the forces of using disc brakes.

Edit: If I understand the intent of your question correctly, I think you might be asking if using the hub/wheel you already have will work fine or it you need to go to the bother and/or expense if getting something other than what you already have. Of course the hub you already have will work fine. Millions of miles have been risen on 130mm rear hubs even though they require a lot of dish. In a perfect world when using rim brakes, a 135 rear wheel is stronger (less likely to go out of true) than a wheel with 130 spacing. Only you can decide the risk reward. I made my wife's bike 135 because everything was going to be new so there was no reason to make it 130. If there is a wheel problem, I don't need to find a convenient and much more common 130 spaced replacement wheel. Others may be in different situations and therefore choose other options. I mentioned 135 spacing to you because sometimes those that aren't custom builders don't realize they don't have to follow all the most common rules.

The last two frames I have built have been spaced to 135 simply for the reason Doug has stated above. Spoke tension is perfectly even between drive and non drive side, which made building the wheel easier, and should add to its durability over the long term. The first frame I still use a 130mm hub in it with the axle spaced to 135, the second frame I use a 135 hub.

Doug, I have knees that do not like Q-factors over 145. I did a lot of work to bring my TiCycles 9-speed to 143. My knees really appreciate it. I have an inner chainring close to the chainstay and a left crank just as close. Now, the bike is ti with straight chainstays, so either steel or curved stays could address that with wider DO spacing but a 135 hub that moves the cassette outboard means a poorer chainline if I keep the cranks in for my knees.

What my knees really love are the Q-factors around 135 on three of my bikes. So I see the irony of riding fix gears because they are knee friendly. My TiCycles stayed on the wall for many rides over the years until I revamped it with an old Sugino triple, absolute minimum width Phil BB and a mishmash of chainrings to get the gears and 9-speed compatibility. Looks funky now but my my body doesn't care.

Edit: Yes I do love little or no dish. The fix gears! But dish allows me to keep riding (derailleur) geared bikes.

Thanks Doug I do recall that conversation. I kinda like Andy's suggestion of 132.5. We have ridden lots of miles on the current wheels on both pave and rough gravel,my preference!, and every time I put the wheels in the truing stand they are still right on. I credit that to the other bike mechanic who taught me how to build wheels!

I build my rim brake frames with 130mm spacing. I just checked to see if my preferred brand of hubs comes in 135, and it does.