Stelvio gearing (11-28 vs 11-30)

Not sure I've much to add to this other than to agree with the others. You didn't say specifically at what point the Stelvio appears in your schedule but with multi-day, multi-climb tours, it's always worth erring on the cautious side. You might have a bad night's sleep, dodgy dinner, the weather might be bad, etc. It's not like a Sunday ride where you can skip it, shorten it, change the route or time...

I did the Stelvio from Bormio about 3 years ago, I think I would put it down as my favourite day ever on the bike!

I'm 80 kg, have a 52-36 and 11-30, I would have been 55 then.  Stick with the 11-30, you'll be using it!  The hardest thing I found about the Stelvio was the top, the last 3-400 m of altitude nearly broke me.  I'm lucky enough to be able to do the Blockhaus in the Apenines quite often, which tops out at 2100m.  I'd never really thought about the thinner air going up there, but it seemed much more noticeable at the top of the Stelvio.

Take lots of kit.  I did it at the end of August, after a fortnight on the Adriatic beaches regularly at 35 degrees.  The Stelvio in Bormio was 6 degrees first thing in the morning!  I went in shorts and short sleeves, thinking I'd be climbing for 2-3 hours and would warm up, which was about ok.  I assumed by the time I came back down the day would have warmed up too, but it didn't.  I took about 45 minutes to descend, teeth chattering all the way...

Also, the weather can be horrendous.  I tried to do it 2 years before, they have Stelvio day at the end of August, no cars after 8 am.  When the weather is nice, 10k plus ride or run or skate up.  The first time I tried, it rained all day the day before, and was actually snowing on the day itself.  They closed the road to all traffic about a third of the way up, but still circa 2000 folk braved the elements to go that far. 

I'm on the tools.... and sort a lot of Challenge bikes out ... it depends on your ablilty plus if you have the route with the hills profile fot the route....  Then assess your ability and then check a couple of scenario's on     http://www.gear-calculator.com/?GR=DERS&KB=24      including the tyre/wheel sizes. 

Input the fields with your proposed gearing's and go from there. It's easy to say go this or that cassette but sometimes dropping a front ring down say fro 52 to a 50 does it better......  Hope you find the answer

I've often regretted not having a lower gear to click to, I have never regretted having one and not using it.

I am currently using the Ribble OSPW with a 53/39 chainset and 11-30 cassette with an R8000 medium cage rear derailleur. It works fine for me.

Many of us olepharts have ridden such climbs on the long ago standard bottom gear of 42X21 (or at best, 24). It can be done, although you do get geet big quads and glutes, as it's weight training via pedalling.

The requirement to be able to do this was no doubt a decent FTP (although no one measured such a thing in those days) but also a big dollop of what was then called stamina. With long days out and a long series of extensive climbs, the ability to go for hours at a decent power output is more important than just a good FTP.

Now I yam old and decrepit, I enjoy the lower gears on the climbs .... and even the sporadic help of an electric motor!  But all climbs are still possible as much because I can push pedals for hours as well as quite powerfully when needed.

So ..... I'm sure you'll have enough power to go up nicely graded Continental climbs with even 39X28. But 34X32 will be kinder to your sinews and joints, especially if you haven't trained for years with a 42X21 lowest gear.    What you really need, though, is that stamina - the ability to do many miles, every day with most of the time spent going up. (It takes only a minute or two to go down, or feels like it).

Me, I'd forget the big jockey wheels (a useless fad) and install a 13-32 cassette with a 48/34 chainset. No silly big gears are needed as downhill and flat bits are where you need active rest in preparation for the next monster hill.

What you might also find efficacious is a close ratio cassette - as many one-tooth jumps between sprockets as possible - to enable you to find your exact cadence sweet spot as you labour for 30 minutes up a perfectly graded Continental climb.

I've done similar multi day mountain events and I'd want the lowest gearing I could. The few grams saved on the pulley or lighter groupset will make no difference. 
 

When I did Stelvio I had a 34/11-32 and was very grateful for it, particularly after a long day and a few days in the saddle.  The Stelvio is high and cold which saps your power. 

I'm 65kg on an FTP of around 280 at that time. I generally run an 11-25, a 28 was fine in Mallorca but I will be putting the 32 back on for an upcoming Geneva-Nice. 
 

The Stelvio is very long, and it goes to very high altitude. That altitude will knock a chunk off your power output which will only get more pronounced the higher you go. This is not the moment to be thinking of how your bike will look. This is instead the moment to be thinking how to get the lowest gear possible because you will absolutely use it.

Get an 11-32 or even better 11-34 and swap your 36 chainring for 34. With your w/kg, the length of the climb and the length of your cycling journey in particular, you will be very grateful for 1:1 gearing, should you need it (newsflash: you will).

Unless of course you love cycling at 60 rpm, switching between sitting and standing every 30 seconds for the last 45 mins of the climb!

This is coming from someone at 83 kg, 340 FTP, who rides 50/34 and 11-32, and who lives in Switzerland.

I did this in 2019, aged 50, 85kg and FTP of 235W.

It wasn't a cycling trip as such (long story, family holiday tour via France, Belgium, Netherlands, Germany, Switzerland, Italy and back via France - the quid pro quo for my wife insisting on going to Venice was us entering Italy via the tunnel near Livigno, a stay in Bormio and me putting my bike in the van), I was bike fit at the time as just 3 months before, I had completed the multi-day N2 Challenge, a north->south 738km traversal of Portugal in 5 days.

My bike had 52-36 and 11-32, this was not so much in preparation for this climb, more that at home in Dorset, the local climbs are fairly challenging. However the sheer length of Passo dello Stelvio from the Bormio side, if I were you I would prefer all the help I can get. Although most of it is around 6-7%, it's over 20km distance, with a short 12%ish bit in the middle, and then the last few km are around 10%.

So my advice would be take the 30, leave the OPSW at home and enjoy the ride. Maybe even sell the OSPW and put the funds towards a 11-32 cassette. 

Anyway, that's just my $0.02 worth, buona fortuna and all that and let us know how you get on.

Here's a gratuititous photo op - top one is a view back from around 2/3 of the way up, and the bottom one is the descent that awaits you if you're going over the top (I rode back to Bormio, if I do it again, I'd want to do both sides!)

I'd try the OSPW with the 30t cassette; the difference in radius between a 28 & 30t ring is minimal and guidances are always conservative (shimano being famous for being a good 4t under whats viable) you may find you get looks and gears that way.

Also; never tried OSPWs myself but supposedly they arent as good at changing under load - which maybe something to consider if youre going up a lot of mountains.

I've only ridden the Stelvio on the trainer but as a man of about your weight (though quite a bit older!) I'd say take every extra tooth you can get! How much weight will the new jockey wheels save you, 30g maybe? Take an inch less in your water bottle for the same saving...if in that impressive list of climbs you've done you never needed your lowest gear then maybe but Stelvio is fearsomely long, I think you'll probably be grateful for every gear you've got by the top. 

If you really want to use the new system, have you checked it won't work with your 30T cog? Manufacturers usually state a maximum limit a few teeth below the real world limit, my Ultegra derailleur is only rated for 30T but it runs 32T quite happily and I'm told by the LBS that it should run 34T when necessary (sometime about the middle of next week if my knees keep deteriorating the way they are at the moment...).

Good luck on your ride, sounds awesome.