Indoor bike - buy new or new groupset?

I have a spare full-time indoor bike just for the trainer.
Looking for 2 sets of advice - whether I should abandon my current setup and go for a cheap new bike, or whether I should just go for full/partial new groupset on the current frame.
If the latter, the bigger question is how creative I can get with the drivetrain.

Current setup is a 2nd hand Specialized Allez on a Kickr Core.
Tiagra shifters, crankset (50/34), rear derailleur. Claris front derailleur. I think either 105 or Ultegra cassette (11-34) - whatever I could get at the time.
The ride is not great, not smooth, and it is prone to dropping the chain when I’ve been on the small ring and moving back up. Its ok, but has never felt smooth on the trainer as much as it does if I try another of my bikes (hence, not a problem with the trainer). I use the appropriate spacer for 10sp on the trainer hub.
The Allez if I put back on its original wheels, feels fine on the road. Hence I’d thought it was a matter of indexing the gears, but I took the whole kit to a store for that, who spent an hour on it and told me it was fine - I’d just some chain rub on front which I knew about (either very top or very bottom gear rubs on the front derailleur chain guide a touch, regardless of screw adjustment).
Also no matter how much I cleaned the bike when purchased, and put on new cassette & chain, it still has dirt and residue on the drivetrain meaning its black and minging - which in theory ought to be avoidable with a purely indoor bike.

So I find myself considering a new bike, for fresh drivetrain, for clean drivetrain, and hopefully start fresh and get a smooth ride from it.
I can get a Specialized Allez for £650 just now with Claris, or £989 for the Allez Sport with Sora.
Trek Domane same specs for about £700 / £1,000.
Decathlon options, at £850 for a Triban RC520 with 105 seems great, but my size hasn’t been seen for a while (6 months+).
50/34 and 11-32 gearing sees me lose a bit off the climbing gears - currently I have 34:34 for when I face the Alpe du Zwift.
I’ve also never had less than Tiagra on a bike in years. I borrowed a bike with Sora on holiday a few yr ago and it was rough shifting, but the bike wasn’t well looked after so had a few issues.

Should I just get the new cheap bike and accept only 8 or 9sp gearing and less gear ratio? Will I notice significant drop in shifting quality?

So then I wondered - the frame, stem etc is fine. Possibly even the shifters are salvageable (though they’re old and scuffed) and I don’t care about wheels or brakes. A new drivetrain or even partial drivetrain is probably the cheaper option.

But then I further considered I could get creative with gearing. I’ve always felt on Zwift I could power a higher gear. I struggle more with leg speed but I’m a big guy (102kg) and for years on the road I used to ride what I think was referred to as the “pro’s compact” - a 52/36. AND I ride 170mm cranks on my current road bike so changing to get close to my current main outdoor setup makes sense I think.
So I was then trying to figure out, if I bought a Tiagra or 105 52/36 crankset… could I then buy the Medium/Long cage rear derailleur and put an 11-34 cassette on the back?
Giving me 52:11 4.73 to 36:34 1.06 gear ratios, new/clean drivetrain and 10 speed?

I’ve been to 2 bike shops about this. One said yes, one said no.
The guy who said No, said it was due to 52/36 and wide cassette exceeding the Tiagra rear mech maximum tooth count (though I’d never have reason to ride in that gear, and he specified Tiagra, it occurs to me maybe a 105 mech has wider range?)

So ultimately its new bike or new groupset… and if the latter, whats the best gear ratio setup I can get without paying silly money?

Other notes:
Bottom bracket has “BC1 27x34” printed on it which I think means its a BB-RS500 cartridge unit, I’m guessing that would need to be replaced.

What I can say is…
Mixing an matching lines may be working but is always risky. Crossing lines of the same generation will have more luck (esp if more recent ones.) It just takes a tiny cable pull distance difference on the shifter to make a the derailleur ‘never right.’

Lower line develop more “play” over time. To keep the prices low manufactures use less expensive materials and lower manufacturing tolerances. Unless extremely well maintained they will develop a lot of “slop.” What you are calling ‘rough.’

If the frame isn’t too old, I’d upgrade the group set. If you want new then look at 105. I’d buy everything used. Talking to local shops, you might find a “take off” set — when someone buys a frame with a high spec group set and the shop needs to sell of the “used” but never ridden group set. All bike parts are hard to find these days…but 105 is the most often upgraded to Ultegra — making 105 used pretty common. Keep everything the same series (generation.)

Modern 105 was also designed for a wider gear range to work in the “Age of Gravel.”

Just one persons thoughts.
Collect several more.

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Two quick thought: in the current market, a new bike with a new groupset might be easier to get than just a new groupset.

Regarding your gear ratio debate. I don’t use zwift anymore, but I thought there was a setting “trainer difficulty”, which is a bit like a gear ratio adjustment. Maybe try playing with that, so you can keep a gokd cadence with the gears you have.

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Yeah, the default is 50%. Personally, indoors, I would use as small a cassette (corn cob) as possible. I’m using a 11-25, just because it was cheaper than 11-23.

OPs shifting problems sounds like it needs more time at a mechanic to check all the basics, drop out alignment, derailleur hanger alignment, etc.

Also, if the wheel is fine, but the trainer isn’t, it could be that you need 2 spacers. Some Shimano 10 speed cassettes require the 1.0mm spacer that usually comes with the cassette, and the 1.85mm spacer to put it on a 11 speed hub.

It could also be dropout width, but make sure you have the 2 spacers. Some Shimano 10 speed cassettes need 2 spacers, when going on an 11-speed freehub.

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I did read back when I set it up that some needed the 2 spacers - but it was horrendous with 2.
It wasn’t even great with the Wahoo ones the trainer came with, I ordered Shimano ones instead.
Ultimately I went with whatever the thickest one was of the options I had (same as what goes on it when on a regular wheel with shimano/sram freehub).

I’ll see if another store will have a look, but I’ve had it in 2 now and one of them spent at least an hour on it checking out the cassette, hub, gear indexing. The other didn’t look much at the current setup (bit of a waste of my time hauling a heavy trainer into them) and just advised going for the new groupset as cheaper option.

I seem to be able to find either Tiagra or 105 with 52/36 and 11-34 cassette (all mix n match bits). On Merlin cycles for example, you pick the bits you want.
£614 though for 105 - when I can basically get a new bike for that.

Any thoughts on whether 52/36 and 11-34 is viable?

This is a setup/adjustment issue that could be solved. Or, get a chain catcher so it never drops.

I’m assuming that you are using wax to lube. Getting a drivetrain sparkly clean takes an enormous amount of effort and steps - multiple baths of different solvents, scrubbing, boiling, alcohol rinse, etc. Even after all that your wax might be a touch grey after a little grease works it way out of the chain.

This sounds like the issue is with the alignment on the trainer cassette. If that is the case, a new drivetrain for the bike won’t help you.

You also say that your other bikes are fine on the trainer - going by that, there is something odd about the Allez and the gear alignment.

Apart from the cassette spacers, is the axle length correct?

There are specific sizes. The actual brand doesn’t matter. IIRC, Wahoo ships with the 1.85mm. I use off-brand spacers, that I buy on e-bay/Amazon. Whatever is cheapest. I just measure them with my calipers.

The Shimano cassettes, some of them, use 1.0mm spacers. So you would have 2.85mm of spacers. 1.0mm + 1.85mm spacer, depending on which cassette you are using. Some Shimano cassettes don’t need the 1.0mm spacer.

What wheel do you have to works fine? Is the KICKR set up with the same dropout spacing (130mm/135mm/142mm)? There’s no logical reason why there would be shifting issues on a trainer but not on a wheel. You may hear more clicking, but some of that is due to chain maintenance, and possibly worn components (cassette on wheel) vs the new cassette on the trainer.

Your front shifting issue is a byproduct of something else. It’s hard to say without knowing specific part numbers of every bit of the drivetrain on the bike.

What year is your Allez? Disc or Rim brake? AFAIK, the Allez never came with SCS, so you wouldn’t have odd issues like older Crux’s.

I just don’t buy the drivetrain working in one way, but not another. That’s just not really possible, there’s always an explanation and it’s usually something small.

Sometimes people just can’t hear clicking on the road,

No. It’ll turn black, always. It’ll be just like a normal bike, and still need cleaning the chain and lube. The chain wears and that’s what’s coming out as black, when the fine metal particles are mixed with lube.

A new bike will help, of course, but that’s like throwing the baby out with the bath water.

With the derailleur, the issue I believe is that its the Claris derailleur and its ever so slightly not quite right tolerance. Hours of my own trial and error with the adjustment screws, same by a bike shop, where it is now is as good as we could get it.
And when I rode it on road/with wheels for a handful of times, never had the issue.

I’m actually not using wax - is that an issue? I figured since the crankset was already used outdoor I’d give it as good a clean/brush as I could on the bike, but I then used wax-based lubricant, and then latterly have just used dry lube.

I figured if I get a whole new groupset then a full wax dip might be a good option?

The cleanliness isn’t really the main issue though, the roughness in the ride is more than just a little lube difference.

From my personal experience, wax is a PITA. I wax, and I’m constantly having to vacuum and brush off the wax that gets flung around the trainer. It even gets on to the other side of the trainer, just from the wax flakes flying around. Lube, though, might have splatter onto walls, etc., if you lube and have too much on.

But, I find waxing to be massively more maintenance than lube. It’s at least an order of magnitude more, and it doesn’t last as long between lubrications.

I’d check 2 things first. The dropout alignment, and the derailleur hanger alignment.

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It would be easy enough to source the correct derailleur.

For cleanliness, I don’t think it’s going to matter whether you get a new groupset or use the old one. A chain is always going to turn black if you use an oil based lubricant. It just turns black slower when used indoors.

If you can get all the parts squeeky clean, then a wax dip would probably keep black grease from forming. As I said, squeeky clean is not easy to achieve and wax dip is a whole thing unto itself.

I use a drip wax (Smoove) and it still turns grey/black and flakes off. It’s not greasy though. The best lube for an indoor only bike might be a good topic for the forum.

Off topic, but I use squirt and it’s very easy. It doesn’t flake off either for me.

OT, yeah. I’m using Silca, both the drip and hot melt. Both drop flakes, all my my rocker, trainer, and bike.

+1.

For the rear, I don’t think it’s the derailleur. 8 speed should be fine. Definitely check alignment first. It does wonders when everything is pointing where it should. You will need some special tools. Bike shops should have them, or some more anal DIYers. (I have both drop out aligning tools and derailleur alignment).

For the front, though. I would, for sure, get the Tiagra or an 11 speed 105. The rubbing is probably from the front derailleur having a smaller width compared to 10 speed, as it’s just a hair narrower (I think). I find front derailleurs to be pretty finicky. They work, but annoy you at the same time.

I’d go for the cheaper option.

You don’t need such extreme gears on an indoor trainer. I would advise you to ditch the front derailleur and get something like a 11-32 (not 11-34) cassette or a SRAM 11-36 cassette.

Here is the thing: if you use erg mode, you could get by with one gear in principle, but 3–4 gears in practice — you would just use gear shifts to quickly change your cadence. And in erg mode you should not use hard gears, i. e. you should not use your big chain ring because your trainer will have a very hard time to hold a steady power output.

Even if you use your trainer in resistance mode at times (I do), you don’t need a large spread of gears. After adjusting the resistance properly, I am in my second-lowest or third-lowest gear during off intervals at 40 % FTP. And when I am doing sweet spot, I am in gear 5–7 depending on the cadence I shoot for. When I do VO2max, I don’t think I am beyond gear 8 much. I only use the other gears for out-of-the-saddle efforts and ultra-low cadence drills (think 50–60 rpm).

So you should be fine with a 10-gear 1x setup. I’d recommend a 40-tooth chain ring. With a big-little 1x-specific chain ring, I don’t think you will be dropping any chains (in the front). You would also only need one functional shifter, the other one would just function as a grip. You’d have less maintenance (just one cable to take care of and one shifter to adjust).

Even for Zwift, I think a 1x setup (perhaps with a 11-36 SRAM cassette with a 40-tooth chain ring) would probably be fine. Just to give you an idea: my top-end gear on my aero road bike is a 42:10 = 50:12, and I top out at 65 km/h, which is plenty. And I am fairly fit.

As the others have said, you have to be careful mixing Shimano groupsets. Depending on which generations you are talking about, the pull ratios of the rear derailleur might be the same or different. AFAIK the current-gen Tiagra RD has the same pull ratio is its 11-speed brethren, which makes it incompatible with e. g. 10-speed Ultegra or DuraAce gear.

Thanks for the reply.

Though I’m not sure I really understand parts of it.
I’m using the turbo almost entirely on Zwift, I’m not doing vo2 max and FTP training (I know what these are, I was a semi pro athlete in a contact sport in my 20s so used to get vo2 max tests on treadmill etc).
But these days it’s mostly using the competitiveness of races/crits on Zwift to get me going. And on those I find the 50 - 11, I could turn a harder gear. Maybe I could adjust the trainer settings somehow, but I don’t really understand how that works.
Conversely when riding the Alpe du Zwift, which I do every 4 weeks as a baseline endurance/fatigue guage, I need the 34-34. I could probably get away with the 36 front ring or 32 cassette. But my road bikes last few years have all had either 50/34 and 11-34 or my Bianchi has 46/33 and 10-33. So I am used to having a 1:1 climbing gear.

Frankly I only use maybe the 3 highest and 2 smallest gears on the trainer, I’m either grinding away in the high gears or needing the climbing gears.

This was not obvious to me. Since you posted here, I thought you were primarily using TR and doing Zwift on the side. Hence, my suggestions were aimed at optimizing your setup for TR.

That seems like an oddly high gear on an indoor trainer without a driven flywheel. What is your self-selected cadence?

I have never self-selected a cadence?

I just ride. Largely the reason I abandoned specified training for Zwift events is that personally I found it’s more closer to real-world riding than how I found specified training.
I am in the 60s a lot of the time.
I’m a big lad, 102kg and was a rugby & American football player - when I’m spinning on a slightly lower gear I just can’t retain the same Watts output. So at 64rpm I’m generally putting out 300 Watts, if I drop the gearing and ride 85rpm I’m spat out the back of groups.

60ish rpm is really low and could be bad for your knees if you maintain that for a long time. I’d try to lift your cadence to at least 80–85 rpm on the (virtual) flats.

I’d definitely make an effort to lift your cadence bit-by-bit. Also, the fact that you are spat out when you lift your cadence indicates that your cardiovascular system is your weak link. (Generally speaking, if you lift the cadence but keep the power constant, you shift the burden from your muscles to your cardiovascular system.)