I'm currently running a 50/34 with an 11-28 (105) on one of my bikes. On long, gradual descents I find that I'm starting to spin out, so I'm toying with the idea of swapping over to a 52/36. If I swap to a semi-compact, should I also swap the cassette to an 11-30 to keep the lowest gear relatively similar? The area where I live is hilly, not mountainous, however. Mostly rolling, with several 3 and 4 category climbs dotted around, but I don't think anything much bigger than that. Advantages and/or disadvantages to making the swap? If I swap, should I keep the 11-28 on the back and see how I get on?

Unless you are racing down hills, can't you just keep what you have and work on your cadence and/or aero tuck??

what is your cadence when you spin out?

I’m approaching 40mph before I spin out a 50x12.

Coast? Definitely a serious cyclist, BTW.

Not sure of cadence, but hitting 40mph easily, and my legs can't go any faster

going from 50t to 52t will get you about 1.5 mph at 120rpm.

I wouldn’t bother making the changes.

Fair enough, what I was looking for. Thanks

Tuck and enjoy life.

but if you want to make thebchange, then sure swap the cassette too so you have a similar bailout ratio.

Pedaling up to 120 rpm briefly to get up to speed is OK, but keeping it up for long is a big waste of energy. Here's a speed calculator.

BikeCalc.com - Speed at all Cadences for any Gear and Wheel

Sure, but so is pedaling at 40+ on long downhills.

Unless you are in a race, just tuck and enjoy the ride.

EXACTLY!!!!! I get tired of hearing some folks say you don't need higher gearing until you've spun out. Maybe he doesn't want to be spinning 120.

how often are you riding at 40mph, and for how long?

i want my bike to have ideal gearing for 98% of my ride, not the 2% of the time that I could go 2-3mph faster on a DH.

I just did this exact thing a week ago. Changed from 34/50 to 36/52, keeping the 11-28 cog set. Changing the rings was dirt simple; 4 Torx screws had to be removed and the rings lifted over the pedal. You will have to lift your front derailleur a bit to clear the bigger chainring, possibly add a link to your chain and maybe even tweak your indexing to get everything back to smooth shifting.

Did it change my world? A little bit.
Was it worth it? No idea yet.

Pro's
Coming out of a tuck, I can start to put the power back on at a higher speed.
If your body is used to pedaling at a certain cadence, you'll be a few %age points faster at the same cadence
Hills are really no harder than they were before, even on the lowest gear; you really only added 4 or 5% to it and the body seems to adjust OK to that.

Cons
Costs money
You have to relearn your shifting, I'm still getting used to having to stay on the small ring for an extra gear before hopping up the large. Its weird to have to think about shifting, it was pretty ingrained and now I've changed it all

I'd say do it if you really find yourself spinning out lots and you have the legs to push the big gears; you really don't make up much time on the down slope, but being able to get back on the power a bit earlier is a good way to carry the speed further. Otherwise, if you're not a total clock watcher/strava addict (I may be one, the other or both), there really may not be much advantage to it.

Yes
And forget that nonsense about whether you are actually spinning out or not. If you have to spin - at all - to accelerate to 35mph+ on a negative grade, you need a bigger chain ring, and you're probably strong enough to manage your climbs with a mid, too. A bit of mashing at the top of a descent pays such nice dividends. Why anyone thinks its OK for a geared bike to require one to spin on normal descents is beyond me. Maybe they just don't like to go fast.

That comment essentially makes my point. I just want the ideal gearing at my preferred cadence for the situation. I use my 52-11 a lot more than I use my 36-28. In addition, I use the 52-11 a lot more than I use 52-22. Point of that rambling is that the 52-11 increases the % of time that I'm riding at my preferred gearing and cadence.

This is what folks miss who always rant "you haven't spun out yet". I want to limit excessive spinning and excessive grinding.

Are you drunk?

What percentage of your ride is at 40mph?

I hit 40mph for a moment on every ride, but I don't choose my gears to optimize that moment.

You're the drunk one. I've just finally heard enough of this crap & decided to reply.

Again, why must I ride 40mph in the 52-11. What if I prefer a cadence of 80 while riding in a group & not pulling? That would be about 30mph. Or maybe spin 95 on a descent - 35mph.

Why can't you understand that you don't have to spin your big gear at high cadence.

Really more of an issue of what gradients you're on. If you're doing climbs that are steeper than 10-15% then I would say stick with compact. But if you're regularly on ramps below that then go for 52-36 with an 11-28. At least that's my preference in hilly Marin County.

On some of the 20-28% grades in SF, my 50-34, 11-32 gravel bike is far better even though it's heavier. Sounds like OP may be more concerned with spinning out on descents, but seems the climbs should be the first priority.

What part of the OP's question are you having trouble with?

I would say there's a difference between actually being spun out and not wanting to spin at a high cadence. A lot of times people say one thing when they really mean the other. I would also say a lot of people would be better off not pedaling at all in an aero tuck which would be just as fast if not faster

OP you can mix and match whatever rings you want up front. as long as they fit. but a 2 teeth difference up front is less than 5% difference in gearing. if you went to a 55 it would at least have been 10%, and thats a difference.
unless you try it you will never know.

same in the rear. a 28 and a 30 is close. but you will feel the difference.

Personally I'm on 1x. thats all i need. i run a 42 or 44 up front. and a 40 for the winter/snowbike.

It's hilly where I live, but not mountainous. Quite a few 3 and 4 cat climbs, and while challenging, aren't killing me. One in particular goes on for a bit. It ramps up at the beginning, hitting a 24% gradient for a short spell, before levelling off to a slight uphill for a couple of miles. Average gradient over the entire 3.1miles is 4%. There is another, similar, climb that I tend to do the same ride, but it's not as windy, but slightly steeper (max 25%, average 5%, similar distance, higher elevation). Again, it's not a struggle, and I've seen all manner of bikes do this hill, including folders, as it features on the most popular local sportive. Most people make it up from what I've seen. These are two of the iconic climbs in the area I live, but by no means the most difficult. But they are typical of what hills I do ride.

Because its not always just about a focus on spinning out in the small cog on descents. I found when I had a compact that I'd spent most of the time in the bottom 2 or 3 gears on the rear cassette, and by moving to a semi compact I had a much better chain line and more efficient drive train for the gears I was in most of the time. I also found the jump between the two front chain rings just felt too big on a compact, and as a result I found myself cross-chaining more in the small ring too.

To the OP I would say go for it, if you can get up the hills around Bristol without too much strain on your current set up, you will be fine on a semi compact. My sister lives in Bristol and I visited her and cycled around the area, I've only got bikes with semi compact and regular 53/39 and don't have any cassettes with bigger than a 25 on (and I'm an 85kg pie eater), so you'll be fine with the 28.

And depending on your crank you may just need to only change the rings. I had a compact Campag one that allowed you to just fit new 52/36 chain rings to the same crank, sounds cheaper in theory but of course it was Campag so it was anything but, LOL, think I got compatible TA ones in the end.