Any question answered...

Since we're comparing 24mm steel with 30mm aluminium, there's about 20% difference in torsional and bending stiffness for the same length spindle with the same ratio of OD to wall thickness

On 24mm steel spindles I can detect 0nm defection due to spindle flex. Whatever percentage it is, x% of nothing is still nothing.

Well yes and no. I switched from a 110bcd 105 crankset to a 110bcd praxis works crankset. So yes it was the only thing I changed, didn't expect any change, got loads of it.

But I have to say, praxis works is known for their stiffness, so maybe not the most fair comparison with a 105 crankset.

x% of nothing is still nothing

Yes, which is why I doubt @Jaap 's claim to have felt anything, particularly if he's claiming that changing from 24mm steel to 30mm aluminium was felt as "more stiff". The cranks make more difference than the spindle anyway, most of pedal deflection is actually the crank arm twisting about its long axis.

Interesting stuff
http://blog.fairwheelbikes.com/reviews-and-testing/road-bike-crank-testing/

Shows there is quite some difference between drive side and non drive side deflection, implying there is noticeable flex in the spindle, right? Especially since the difference on 24mm spindle cranksets is bigger.

Air compressors for home workshop

What’s good, what to look for? Belt drive etc?

Car and bike tyres
Possibly spray painting and air tools

what to look for?

Quiet would be nice if you're working right next to it

Apparently even 30mm spindles fit BB86: http://rotorbike.com/catalog/default/rotor/road/bottom-brackets/bb86/bb86-press-fit-4130.html

Apparently

If you like very thin section bearings. It's a desperate move to get around a problem nobody in his right mind would give himself. We stopped using Octalink/ISIS because the bearing section was that thin.

The next Aldi/Lidl offer?
The 3 year warranty is unmatched at the price level.
I thought the 'cool kids' were all into airless spray for painting these days?

I've got a SIP 3hp 150 litre belt-drive compressor in my workshop and a Clarke 100l 3hp belt drive compressor at home. Both are good. Get the largest and most powerful you can, but avoid oilless or direct drive as they're bogging noisy.

Can be done, but the normal 30mm BB30 spindle is too narrow for a BB86 shell width, the recent BB30a spindle/BB386/etc. may fit as they're wide enough.

As @mdcc_tester quite rightly said, the bearing is smaller and thus more prone to wearing out sooner than later (look at American Classic's hubs that use smaller bearing).

Shows there is quite some difference between drive side and non drive side deflection, implying there is noticeable flex in the spindle, right?

Measurable is not the same as noticeable. Changes in neutrino flows are measurable. They are not noticeable.

there is quite some difference between drive side and non drive side deflection, implying there is noticeable flex in the spindle, right?

There's a lot of difference between left and right cranks besides the tube joining them together in the middle. If you want to know how much the spindle winds up when driven by the left crank, you need to measure the spindle wind up, not the total deflection of everything in the load path from chain to pedal bearing.

I've been trying to help, but you don't seem to be taking the hint. Steel is about 2.5 times as stiff as aluminium. A 24mm tube with 2.5mm walls (HT2, pilot bore for M20×1.0 bolt) is about 0.4 times as stiff as 30mm tube with 3.5mm walls (BB30, pilot bore for M24×1.0 bolt) if the material stays the same. I think you can see where this is going (0.4×2.5=?)
The advantage of aluminium 30mm over 24mm steel isn't that it's stiffer, it's that its about 60% of the mass and uses bigger bearings.

I've been trying to help, but you don't seem to be taking the hint.

Hey I'm just curious and trying to gather information. Nothing personal.

Of course the outside diameter of the spindle is only a very small part of the story. I just found some deflection data that seem to confirm my feelings :)

@danstuff, agreed.

Nothing personal

Ditto, I just thought I'd try to limit your embarrassment by being more explicit, since you keep claiming that 30mm aluminium is noticeably stiffer than 24mm steel

found some deflection data that seem to confirm my feelings

Yes, data which confirms our bias is the best kind. Best to ignore any which doesn't :)

since you keep claiming that 30mm aluminium is noticeably stiffer than 24mm steel

You're right, my bad. I shouldn't have used the words steel and aluminium. You are better than me.

You are better than me

Seems unlikely.

Whatever you think you noticed when you changed from 105 to Praxis, it seems equally unlikely that the BB spindle diameter played any part in it.

The problem is that there is so many factor to take in account, frame material, thickness, wheels, quick release skewer, big chainring, tyres pressure etc. to name but a few.

Testing in labs does not always translate to the real world.

That was kind of the point I was trying to make, real world performance can be very different from just calculating performance of fictional tubes/spindles. But I really don't want to be embarrassed any more, so I take everything back that I said.

you bin scobl_estered

One for the mathematicians. Imagine a 19x10k made of 1k squares. You have to ride through every 1k square, no minimal distance for each square. How would the theoretical route with the least distance look?

Why is this like this:

Does it tension OK with the wheel stopped? If so, I'd be looking for excessive drag in the freewheel to explain the slack in the top run.

No, same with the wheel stationary.

Could it be chain wear?