Melvang

So, over the winter, I have de a full groupset upgrade from 15 year old Tiagra 3x9 to current gen 105. The new set is standard full size chainrings and a 12-25 cassette. I went with the chain rings because I didn't want to add another 6-9 months additional lead time. Apparently this groupset in silver is pretty low priority on the production schedule. And I wanted as close of ratios on the cassette as feasible.

Around home, this will work just fine. But, the wife and I are planning some seemed trips to areas that the hills are steep enough, the car doesn't want to up shift. So, I am figuring I will need more low end range.

I will probably get a different cassette. The main issue, is the rear derailleur I ordered is a short cage, and Shimano lists max tooth count for that as 30. Though some say, I can run 32 with a B screw adjustment.

I guess my current options would be the following.

30/32 tooth cassette and adjust B screw
34 tooth cassette and medium cage derailleur (no idea unless time for this with wanting silver)
34 tooth cassette and potentially swap the smaller chainring, is this even an option for R7000 105 crankset?
34 tooth cassette and hanger extension from somewhere like Wolf Tooth

Like I said, this is only for a couple weekend trips throughout the year, and potentially RAGBRI.

What would you guys suggest?

DeadGrandpa

I'm not sure that defining your ride as a "weekend trip" is the critical criteria for selecting a gear train combo. For me, it's the terrain that necessitates the gear range I'm going to want/need, not the number of days on the bike for the trip duration.

I've used both the Tiagra and 105 components, and the Tiagra is quite serviceable. More expensive parts are a bit lighter and sometimes work a little better. Is the 105 crankset equipped with the same size chain rings as your old group and did the old group get the job done? That's the question. Gear ratios are gear ratios. See Sheldon Brown's website for a gear calculator. If you're climbing steep hills with luggage, you need a low gear in the area of 17 gear inches, from what I've read and experienced.

Or maybe I misunderstood the question.

Melvang

Not defining gear needs on "weekend trip". But where these trips are going to be has vastly different terrain and much steeper hills than what I have locally.

I have nothing against Tiagra as a groupset. But the old groupset was 11-28, and a weird ratio Cannondale triple from 2005 era. It worked fine around home. I have drove where we want to take these trips at, but never cycles it. A lot of hills in the 15%+ range. Hardly anywhere flat.

I have a reasonable estimation where I want to be with gear ratios. I guess my biggest question, hope for the best with a B screw adjustment and try and squeeze a 32 tooth cassette, get a longer cage rear mech and a 34 tooth cassette (unknown lead time), or to with the 34 tooth cassette and a derailleur hanger extension.

The extension would be the easiest to aquire, and be the least amount of hassle for prepping the bike for that area. Mostly, it would eliminate extra cable damage from removing and reapplying end caps to the cable, unless I could solder it.

HTupolev

What kind of gradients are you dealing with right now, and how low are the gears that you're using on them?

For example, if the steeper hills in your area are 7%, and you ride up them at ~80rpm in your 39-25, then you're going around 9.8mph.
At the same power output, on a 15% hill, you'd likely be doing only around 5mph. In your 39-25, this would mean pedaling with a lot of torque at 40rpm. And typically, when people are that badly bottomed-out, their power output drops significantly and they end up being even slower.
In this case, even switching to a 34T rear cog only gets you up to a still-pretty-painful-for-most-people 55rpm, assuming you're still holding the same power.
In this situation, in order to comfortably pedal at the same 80rpm as before, you'd need a roughly 49T cog on your cassette.

The point being, big differences in gradient can require big differences in gearing if you're trying to avoid bad gearing bottom-out. If you're not doing anything close to 15% right now, and if you're using your lowest gears already, switching to a 32T big cog might only cover a small portion of the difference.

Melvang

Honestly, I have not rode the bike yet with the new 105 setup. Still waiting on rear mech, crankset, and BB. But the old tiagra was 11-25 and a 52-40-3? odd ball cannondale setup. Most of the hills are pretty tame and short enough I can just treat as a quick interval. I am also not opposed to swapping to a smaller inner chain ring in the front. But like I said, I ordered the full size crankset to avoid an extra 6-9 month lead time for silver.

Moisture

Personally I think I'd stick to the 12-25 unless you really do need the extra couple teeth, that is a really good ratio spread.

If you have something like a 34t for the front chainring granny gear, I think you'll do just fine.

My lowest gear right now is 38t front, 30t rear and I would sometimes use 34t rear when climbing a moderate hill, loaded, in windy circumstances. If you're not dealing with heavy wind, you'll managed with 34t front and 25 rear.

Melvang

Thats part of the problem. To avoid an exceedingly long lead time on the crankset, I went with a full size, 53-39. If I could swap the inner chainring, I think that would help a lot by itself. Couple that with a 30 tooth rear for the occasional hilly weekend, I think that would work out fine.

DeadGrandpa

Ok, I have a Shimano Sora triple crankset with only 46/30 chain rings mounted, running a SRAM 10-42 cassette, long cage RD, again SRAM. That gets me up most climbs. When I was riding in Alaska, the front chain rings were 38/26. I never missed a third, largest chain ring. Depending on your smallest front chain ring, I don't think an 11-34 or 11-36 is low enough, even if your short cage RD works. Sorry, but you definitely will need a new shifter cable to make a good install. No point in being cheap and causing yourself problems.

Melvang

I have been looking around, and it seems I can get replacement chain rings for 105 for a bit over half the price of a full crankset. Right now, I am considering cassette with roadlink so I don't need a new rear mech, and getting a 50-34 set of rings for the front. Though, I am assuming I would need to move the front mech up and down for this.

canklecat

My various short cage rear derailleurs handle cassettes and freewheels with 28T big cogs just fine. I've used mostly 13-28 on my 7-speed freewheel bikes, and 12-28 on my 7- and 8-speed cassette bikes, with various short cage RDs: older Suntour GPX, Shimano 600 Tricolor/Ultegra, Dura Ace, one or two others. I have one wheelset with a 13-25 but that mostly gets used on the trainer. And I have a Dura Ace 10-speed 11-25 but haven't used it for a couple of years.

My chainring setups range from 52/42 on one 1990s era bike, 53/39 on my most recent bike, and 50/38 on my 1989 steel bike. Vuelta makes good 38T chainrings for 130 BCD cranks, affordable and good quality. I lucked into some Vuelta plain and ramped/pinned chainrings for around $10 via Amazon warehouse sales, but those usually cost $25-$50.

I'm 63 (150 lbs), not a strong climber, but these combos are fine on our roller coaster terrain. No long serious climbs. A few longish grades that average 2% over 10 miles or so, mostly rollers with hillettes in the 5%-12% range that last for up to 400 yards at a time, followed by comparable downhills, etc. The only continuous climb I can think of in my area that lasts for at least a mile of around 5% without any false flats is at least 25 miles west of me (D/FW area).

The only tricky bit is cutting the chain short enough to minimize chain slap against the chainstay, but long enough to avoid damaging the rear derailleur in the big/big combo. It'll happen eventually, usually when we're exhausted, trying to keep up with a group, or the ambient noise level is so loud we can't hear the telltale crosschaining sound. So it's best to be sure the chain is long enough to handle that 53/28 crosschain combo. I've seen a couple of friends claim they'd never shift to that big/big combo so they cut their chains a bit short. Aaannnddd they shifted into the big/big and tore off their RDs, usually on fast group rides in noisy conditions. Helicopter tape or something similar over the chainstay will minimize paint/carbon fiber damage from a chain that's just a link or two long.

If we had serious climbs I'd switch my lightest carbon bike to a compact crankset, probably 50/34, and 32 big cog. And a medium cage or long cage rear derailleur. But there's nothing long and steep enough to need that here.

With a heavier bike, touring bike, etc., granny gears are good. My 30+ lb Univega hybrid has a 30T small chainring and I've switched from the original 7-speed 13-28 to 8-speed 11-32, and occasionally use that 30/32 combo on a couple of hills with double digit grades of 11%-%16 for about 50-200 yards. Especially when I'm hauling stuff on the rear rack or in the handlebar bag. But that Univega has a long cage RD and does run more smoothly in big cogs than forcing a short cage road bike RD beyond its design limits.

Moisture

53/39 is a good option for most applications, especially downhill sprinting.

You wouldnt want a more than 14t different between the two front chainrings. You'll have this weird gap where you require something in between. When I was using a 34/50 chainring setup, i did find that the 34t ring was useful for windy climbs, but most of the time, I was left looking for something a bit taller. My new rings solved that. I like the small imperceptible change in ratios between 38/48.

If you really need to, use the rear cassette to compensate. Or try to find some used rings or crankset.

FWIW, the added efficiency of the biopace rings really helped ofset a lack of a serious granny gear.

Wildwood 

Just to clarify - if you have a crank with a BCD for 53/39, it may not be possible to just change the rings to 50/34. Check to make sure mounting holes and BCD match before buying replacement rings. 4 or 5 arm crank?

Melvang

It is R7000 Shimano 105. According to their website, they only list one BCD.

Wildwood 

Then that's what you have to work with - unless you change the crank. The used parts market is pretty active in most cities.

In my experience 38 is the smallest ring you might find for 130bcd.
But I've got ShimaNo on none of my bikes, so what do I know?

Melvang

the new R7000 105 has a 110 BCD. After talking with my LBS, I think i am going to go with 50 34 rings and an 11-30 cassette.

According to Shimano's website, Max front difference is 16 (at limit for compact), and 35 tooth max total capacity, again at the limit with 11-30.

Moisture

39/25 as your granny gear could be doable for lighter touring application if you are in good physical condition.

Once you factor in a real touring load, and steep hills, could be more less doable until you begin dealing with wind. In that case, you'll want a 11-34 rear cassette.

Melvang

Trying to avoid a 32 or 34 cassette so I don't have to change rear mech due to chain wrap limitations. But not really going to be touring much distance, mostly just sight seeing.

Troul 

I'd swap the crank gears & adjust the chain length before swapping the chain, rear der & cassette.

Moisture

After thinking about your question over today's ride, I can confirm that 39x25 as your granny gear will be tough, mainly due to wind conditions rather than a light touring load.

Elvo

I would recommend a 46/30 or 48/32 crank with 11-36 rear. This is doable with a RX800/810 rear derailleur

Thomas15

I think the whole discussion hinges on the riders conditioning, pain threshold, anticipated travel speed and what tackle they have strapped to the bike.

My suggestion is try a few hills before making any changes. 15% grade is a lot of hill unless you are used to it.

Germany_chris

wolftooth road link will fix the cassette issue

https://www.wolftoothcomponents.com/...ducts/roadlink

Melvang

The problem there is with a short cage, an 11-30 with 50-34 rings is at capacity for the derailleur. Adding a wolf tooth doesn't change derailleur capacity, only going to a medium/long cage will address that.

79pmooney

I'm not sure I see why it is so important to keep the small rear derailleur. The penalty for a derailleur with more capacity when used with your current gearing is almost zero. A couple of ounces. Derailleurs are easy to swap. Cables are cheap. Yeah, you need a new chain and if you have gone too long, it won't work with the old cassette. (Keep the old chain and use the two together.)

Once you've upsized the rear derailleur, you have more freedom with cassettes, chainrings and chain take-up. Life just gets easier.

I run a mid-sized old Campy derailleur with a 50-38-24 triple and anything from 12-23 to 14-28. (It's a Campy cassette. Loose cogs except a carrier of 3 cogs.) I use all sorts of combos and never have to change anything else. Usually have the large and small made up on separate wheels and just grab what I feel like riding.

Koyote

Swapping to a smaller inner chainring will likely not work well.

You can buy an 11-30 cassette and use it with your current RD. If you want even lower gearing, look for a 105 GS rear derailleur and an 11-32 or 11-34 cassette. But be forewarned that you will be limited on the high end to an 11-28 cassette with that RD, according to Shimano's specs.

Or you could just stick with your current gearing, which probably works just fine in Iowa, and push your bike up the steepest hills on your weekend getaway. That's be far less hassle and expense. I've pushed my gravel bike up some nasty hills while gravel racing out here, and my heart rate probably gets higher than when pedaling.