lowering Shimano 105 gearing

[Kajjal]

On a mountain bike.

 

[lpretro1]

Yes fine on an mtb with 42-32-22t but not on a triple road

 

[Kajjal]

Evenin all, the lycra gear police are on patrol

Just use the gearing that suits your riding. I have been through the strava man phase and now just enjoy the riding on or off road.

 

[Ajax Bay]

This is nothing to do with @Kajjal 'lycra' or 'road' looks. Assume you have an RD-5500 GS. With your chainset (52-42-30) this has sufficient capacity (ie to wind up the chain when small/small) for a 12-28, just about. But whether a RD can operate with a large sprocket depends on where the RD hanger on a bike is placed. The hanger placement is roughly (for which read 'not') standardized on bike frames. Your RD will certainly work with a 27 sprocket and OK with a 28. I have exactly this set up at present (ie same chainset, RD and cassette). Maybe you'd be OK with a 30; just maybe. B screw would need full use. The issue is the clearance between the top jockey wheel and the bottom of the large sprocket. The diameter of your 25t sprocket is 101mm. The diameter of a 28t is 113 and a 30t is 121mm. When the top jockey wheel has the chain on your 25t sprocket, is there 10mm (half of 20mm) spare space there (probably not)?

If you need a longer gear than those sprockets will give you (on 52-42-30), then unless you change the RD (probably to an MTB type), you'll have to change the chainring(s) or the whole triple. @Smokin Joe has advised that it's not worth putting on a 28 chainwheel (vice the 30 at the front), and I agree. And if you did you'd need to swap out the 52 for a 50 to stay within the RD's capacity. There are other relatively recent (ie 2016) threads where this has been discussed, and a variety of advice offered.

Technical Service Instructions SI-5TK0D
Shimano 105 RD-5500-GS
Total capacity: 37 teeth or less
Largest sprocket: 27T
Smallest sprocket: 11T
Front chainwheel tooth difference: 22T

 

[sidevalve]

I just fitted a 30 to the rear and it is on the limit - 25 to a 30 is a BIG difference you really will feel it. [I did and I only went from 28 - 30]

 

[Banjo]

I had a 10 speed 105 triple road bike with 52 42 30 up front and 11 to 28 on the back it worked fine with a GS mech.

Great when meeting a big climb on tired legs.

 

[potsy]

Ignore the numpties, if you need to lower YOUR gearing then don't be put off by the stupid comments from a certain section on here.
When my 9 speed bike was still in my fleet I changed to a 12-27 at the back as there wasn't much chance of getting anything larger on there, I also changed the granny ring from 30t to 28t, it certainly helped on some of the very hilly rides I did at the time.

You may only need that gear occasionally but when you need it you will be thankful you fitted it.

 

[Smokin Joe]

Ignore the numpties, if you need to lower YOUR gearing then don't be put off by the stupid comments from a certain section on here.
When my 9 speed bike was still in my fleet I changed to a 12-27 at the back as there wasn't much chance of getting anything larger on there, I also changed the granny ring from 30t to 28t, it certainly helped on some of the very hilly rides I did at the time.

You may only need that gear occasionally but when you need it you will be thankful you fitted it.

^^This^^

Anyone who tries to dictate to others what gear ratios or how many of them go on what type of bike doesn't understand the principle behind variable gears. They are there to compliment the power output of the "Engine" and turn that into an acceptable speed and will vary from engine to engine.

 

[Ajax Bay]

Changing the largest sprocket from 27 to 28 gives you 3.7% 'better' gearing. Changing the small chainwheel from 30 to 28 gives you 6.7% better gearing. The capacity of the RD is stated as 22 on the chainwheels so 'just saying' it implies swapping out the large chainwheel (52 for a 50) as well. But the move from 25t to 28t at the back will have given you 12% already. I think this may make the difference you implicitly seek and is a better option than swapping the 30t for a 28t chainwheel. @Banjo implies this. @sidevalve has said go for a 30 on the back; and if your RD will manage it, fine. @lpretro1 has given advice from a technical standpoint too (OK for 30+ with an MTB RD but not the road RD-5500 the OP has).

Not sure to whom @potsy is referring to as 'numpties' (is that an inarticulate word for naysayers?) and 'stupid' (again an adjective which displays lack of vocabulary and fails to recognise some comments made in jest eg @Racing roadkill 's ) comments, but if directed at me I'd appreciate understanding what irrational or unreasoned comments he thinks I've got wrong. Please note my 9 speed bike is still in my 'fleet' (unlike his) and it is running 52-42-30 with 12-28.

Finally I'm unable to comprehend why people interpret advice offered as 'dictating to others' @Smokin Joe . It's the OP's decision and the advice they receive should allow them to make a better informed decision. Edited to add: I think your advice given at the beginning of this thread was on the money, but only if technically achievable.

Putting a 28t inner on the front won't make much difference, it's on the rear you'll really notice it. I'd go for a 30 or 32t sprocket on the back. Believe me, five extra teeth on the largest rear sprocket will make a massive difference.

 

[Mr Celine]

My winter / commuter originally had the same set up as the OP. I found it overgeared and spent most of my time on the middle ring, which wore out. I swapped the chainrings for 28 39 50 and the cassette for 12-28 which I found to be a great improvement.