Converting 105 chainset to 48/32 or 46/30

[Rusty Nails]

I have just bought used gravel bike with 105 2×11 compact groupset, and think that I will struggle on the rides I like with that set-up.

I like the look of the new GRX gravel group set but am loathe to spend a lot extra at the moment so was just thinking of the idea of getting two new smaller chainrings for the 105 instead.

a) will this work OK?
b) if so any specific recommendations for make of chainrings

 

[CharlesF]

Look at Spa Cycles Chainsets

I visited them and explained what I wanted, sorted out in a few minutes. I’m sure you would get the same with a phone call to them.

 

[neil_merseyside]

I have a Spa Elan 2x11 50/34 and it's full105 (with a medium cage rear) and a 42T as my biggest cog, shifts well and is a good low gear at 34/42, so a 22" bottom gear. So in gear inches the range is from 125 to 22".

 

[Sharky]

If you are talking about a standard 110 bcd chainset, I think a 34 ring is about the smallest available.
What options have you looked at with the rear cassette? One or two extra teeth at the rear will have the same effect.

 

[Rusty Nails]

If you are talking about a standard 110 bcd chainset, I think a 34 ring is about the smallest available.
What options have you looked at with the rear cassette? One or two extra teeth at the rear will have the same effect.

I have a 32T rear cassette so could go up to 36T.

@neil_merseyside. Interesting, I am surprised that a 42T cassette works well with a medium cage rear mech., I thought it would need a long cage.

 

[Venod]

I have 46/34 with 11-36 cassette, medium cage deralleur on one bike, works in all gears should you inadvertantly find yourself in 46 front 36 rear

Does 50 front 42 rear work ?

 

[Deleted member 23692]

The 110mm BCD on a 105 will not let you go below 34t sprocket. 30t on a 104 BCD is difficult, so you're looking at either changing the chainset or upping the cassette (or both), which then leads you into the question of max capacity your present rear mech can handle.

Have play with this... http://gear-calculator.com/ ... and explore the gearing options.

I had the same problem and swapped for an ultegra RX800 rear mech and a Praxi Works 48/32 crankset, and kept my 11-32 cassette (for now). Still deciding on the cassette

 

[carlosfandangus]

I have recently swapped crankset on my bike, 105 to GRX double 46/30, I was going to swap the rear cassette to a 34 instead of the existing 32 as some of the trails home and the hills are steep (not young or fit enough), however I have 2 X 32's in stock and I managed to get the GRX for about £90 (cant remember who from) the cassettes are worth about £70 so when these get used up I may go 34

 

[CXRAndy]

Smallest inner chainring is 33t. If you dont want to spend GRX prices look at FSA adventure crankset. You will need a new BB too. They do 48/32 or 46/30

Example of prices

https://www.tredz.co.uk/.FSA-Tempo-Adventure-JIS-Chainset_201080.htm

 

[carlosfandangus]

£84.99 from Singletrackbikes 175 mm 46/30, just checked my emails from them 30/10/2019 made more sense to me than going for a bigger cassette, however this may not be the best route to take, I bought the cassettes using Tesco clubcard vouchers before the Evans take over so they worked out at half price.

 

[Rusty Nails]

I have recently swapped crankset on my bike, 105 to GRX double 46/30, I was going to swap the rear cassette to a 34 instead of the existing 32 as some of the trails home and the hills are steep (not young or fit enough), however I have 2 X 32's in stock and I managed to get the GRX for about £90 (cant remember who from) the cassettes are worth about £70 so when these get used up I may go 34

I have looked at the GRX double chainset, which seemed ideal, and there are some good offers around, but was concerned at possible compatibility problems as I read the chainset was offset compared to regular chainsest. I must admit to being confused by Shimano's compatibility charts.

Did you use the 105 L/H shifter and front mech? My bike has a fixed front mech fitting and I wondered if it catered for smaller chainrings. I would not want to change either of these because of the price, especially a hydraulic disk brake/shifter.

I have a press-fit BB, and assume that the alternatives would be suitable.

I am also interested in the FSA and Praxi Works smaller chainset.

 

[neil_merseyside]

I have 46/34 with 11-36 cassette, medium cage deralleur on one bike, works in all gears should you inadvertantly find yourself in 46 front 36 rear

Does 50 front 42 rear work ?

Well sort of, it will just 'go in' but as it's right on the limit of 116 chain links I suspect actually using even just the once will probably kill the chain for stretch in a couple of revs! More links might not self destruct but too much chain sag and ponderous shifts methinks.

 

[PpPete]

I have Absolute Black "sub-compact" oval chainrings on the 105 cranks. The 46/30 setup which says it is only compatible with DA & Ultegra 9000/8000/6800 works just fine with 7000 series cranks. Assume the 48/32 option will work as well, but not tried that.
https://www.tredz.co.uk/.absoluteBL...-for-9100-8000-9000-6800-Chainring_118319.htm
They may have an option for older series cranks but I've not investigated yet.

Or get a second hand triple crankset on a well-known auction site and just use the 74mm BCD inner / 130mm BCD middle positions for whatever teeth rings you fancy (subject to derailleur capacity). Chain ring bolts will need replacing with shorter, or fit a bash ring / or some spacers. (Spa have all the necessary bits)
The chainline won't be quite right, but a couple of spacers (if external BB) or longer axle (if square taper) will sort that.

 

[carlosfandangus]

I used the 105 brifters, front and rear mech, the only thing from a 105 groupset that I couldnt use were the flat mount calipers, I ended up fitting some Deore post mount, no problems so far.
with hindsight a full GRX groupset would have been bought, however I decided that a 105 compact was the way to go, I never considered GRX at the time

I have looked at the GRX double chainset, which seemed ideal, and there are some good offers around, but was concerned at possible compatibility problems as I read the chainset was offset compared to regular chainsest. I must admit to being confused by Shimano's compatibility charts.

Did you use the 105 L/H shifter and front mech? My bike has a fixed front mech fitting and I wondered if it catered for smaller chainrings. I would not want to change either of these because of the price, especially a hydraulic disk brake/shifter.

I have a press-fit BB, and assume that the alternatives would be suitable.

I am also interested in the FSA and Praxi Works smaller chainset.

 

[rivers]

I just swapped to an FSA omega 46/30 chain set on my tiagra equipped cx bike. I needed a new bottom bracket as the old one was shot, but that's it. I think it was £130ish.