Does anyone know how much difference dropping 2 teeth off the chain rings would make and roughly how many cogs I'd drop down on the cassette if I went from a 48/32 to a 46/30 and also how easy would it be to do.

I've only recently gone to a gravel bike from MTB so am getting used to higher gearing but for the riding we're doing there are fairly regular short bursts when I'm on the 48t on the front and one of the 2 lowest gears / biggest cogs on the cassette compared to being 3/4 down on my MTB and if I could drop it down a couple of cog's would be nicer and help avoid cross chaining.

It's a FSA Gossamer Pro 48/32 on the front with a 105 - R7000 ... 11 - 34t on the rear.

I don't have the answer for you. What happens when you go to the 32 up front and run a smaller ring on the cog.??

I would think there is a combo on your rings that would work for you. You just have to find it and be prepared to lock in before you need it. Sometimes it's all about knowing what gear you need in advance and timing it just right. You say it's a short burst so I'm not so sure changing rings will solve your issue.

No offense here, I don't know you but, another way of looking at this would be strength and endurance. The stronger you are you can drop the chain down the cog out back and use strength to get you where you want to be.

Also, you have a great group set. But, the cog has 11 gears, I do believe, so it's relatively wide. From what I've read about that cog, it doesn't get much better. Lots of bike companies will put on an Ultegra group set and use that 105 cog in the back. They last forever and people love them. So I don't think you have to worry about cross chaining for short bursts on the cog. The chain, well.... I don't know.

These are my thoughts. Others with much more experience will chime in soon, I would suspect.

https://www.calculatorsoup.com/calcu...calculator.php

Simple math made easy thanks to the web!

Going from 48 to 46 is a 4% difference.

Going from 32 to 30 is a 6.5% difference.

I found going from a 53t big ring to a 50t ring fit me alot better. This is because I'd find I was spinning a little too fast on one gear but upshifting had me putting out more torque at a lower cadence then I wanted. After the 15t cog your gear spacing is all about 11% apart up to the 34t.

48T is only about 4% bigger than 46T. Rear gear shifts on your cassette range from about 8% to 18%. So the number of cogs you could drop down on the cassette is... about half to one-quarter of one cog, depending on where you currently are in the cassette.

If you're going to try and shift your position on the cassette significantly with a chainring swap, you'll probably want to be looking at a new crankset which supports tiny subcompact chainring sizes. Even if you went all the way down to a 42T big ring, your top gear (42-11) would still be higher than your current second-to-highest gear (48-13), and you'd only move your position on the cassette by about 1 shift.

Pheew..... I told ya the experts would chime in. My heads spinning. Is yours.?? Math.....

Try shifting to the 32 chainring and adjust the rear cassette from there.

48x11 at 80rpm is 27.7mph on 28mm tires.

old 53x12 gearing, what was run by some back in the day for racing, is 28mph at 80rpm on 28mm tires.

you arent giving up anything. If riding gravel, I've found a 46t large ring is excellent. 46x11 at 80rpm is just so fast for me on gravel and unsustainable for a long time due to resistance that I don't need more.

with 40mm tires, the 46x11 gearing at 80rpm is 27.5mph.

as a tire gets bigger/wider, speed increases relative to a smaller tire at the same rpm.
so with gravel tires, a wider tire offsets a smaller crankset, to a degree.

all the more reason why 50x11 with 40mm tires is overkill. Thats 30mph at 80rpm.
hardly anywere close to spinning out, and going 30mph. At 90rpm you are going over 33mph.
its simply rare that riders need such a setup. I've found very few who need 50x11 with a 40+mm tire on gravel. There are people that do need(benefit) it, and they are the elite among us.

I've read through all the replies and a lot of it's gone straight over my head, I started cycling a lot more seriously about 1 1/2 yrs ago and have learnt an awful lot overall including bike maintenance etc. but as it was all on the one bike where the gearing happened to suit the riding we were doing so it's not an aspect I've needed to learn about until now.

I know the obvious is to shift to the smaller ring on the front which then also has the subsequent required shift on the rear as just changing the front on it's own is too much of a drop in gearing and you're just spinning out. The changes as mentioned are often for relatively short patches and you very quickly want to drop to higher gears / smaller cogs on the cassette and given that you can't use the 3 smallest cogs when on the small chainring on a 105 set you'd just be constantly changing the front ring with the associated changes on rear which I'm sure most would agree isn't ideal.

Interesting point I picked up on from GrainBrain's post .... generally for the same resistance through the peddles will smaller chainring and smaller cassette reduce your cadence for the same "feel" ... something else I've really noticed since having this bike is my cadence which used to be similar to the people I ride with is now considerably higher ... the others I ride with noticed and mentioned it even before I'd said anything.

Overall though and from Htupolev's comment .... unless I want to change the crankset to go much smaller on the front I'm probably not going to see a significant enough change to make anything else worth while which is a shame.

Gearing though is something I could obviously do with learning more about and what effect changes on the front will make vs changes on the rear etc. ..... does anybody know if there's a Dummies Guide to gearing anywhere as I' probably benefit from doing a bit of reading up on it.

Cheers for everyone's help so far!!!

A trick for researching the site here is typing bikeforums.net: search term into Google. This will search the posts alot better then the search feature here.

When I started tinkering with my gearing, I started to really pay attention to what gears I was using. Sounds like you've started as well. I went from mtb/hybrid to road and it took me a full season to work those different muscle groups before I felt like I was at the same fitness as the mtb.

Am I correct in assuming you only use the 48t ring with the largest two rear cogs on the cassette? Sounds like I'd drop to a 44t big ring then, or even a 42t! A 42t could probably be found used very cheaply. Going to a 42t from 48t is a 13% difference, which is a whole rear cog jump.

It sounds like you are using the 32t chainring almost all the time? How often do you use the lower cassette cogs on the 32? Like 32x34, 32x30, 32x27? If you say never, then I'd look at buying a 36t small ring. 32t to 36t is an 11% difference, which moves you one cog on the back so now you use the 27t rear cog when you didn't before.

Your front crankset is nice because you can cheaply find replacement rings. I have a big fondness for front chainrings with a 10 tooth difference or less between the big and small rings. This really improves front shifting imo.

I went from a 48 to a 46 on my touring triple. All three rings were worn. My LBS found me a matching set of RaceFace rings that look terrific, but the large was only a 46. It was actually a good move since I also use the bike to commute/run errands over mostly flat terrain. The slightly smaller big ring has caused me to "spread the love" around the rear cogs more. On the loaded touring side, I don't feel like I have lost anything since I am not a speed demon down hill. If I am descending fast enough that I would burn out of my 46x11 I am coasting anyway.

a 1" reduction in circumference, and thus diameter of circle is smaller..

1/2 of yhe gear ratio CR,t(a) '/, hub,t (b) or a:b

Calculating gearing doesn't involve a lot of math but it can seem daunting. Alternatively, you can follow the Dunham rule...as in someone has probably already dun 'um for you. This website has all the answers to your gearing questions and presents them in an easy to see formate. For example, going from a 48/32 chainring with an 11-34 cassette to a 46/30 chainring setup are compared here. You are going from a 120 inch gear (or 120" wheel with the cranks connected to the axle) to a 115 inch gear. It's not much of a drop. A 115" gear is still pretty high for dirt riding. It's a good gear for pavement.

If you were to go to a 44/30 tooth in the front, you'd drop the high gear to 110" which is more reasonable. The smaller gap between the chainwheels also gives you a slightly smaller gap between the two ranges...although it is still rather large in my opinion.

I suggest you play with this application and see what is possible. It's easier than doing some arithmetic

Just put a 44 or 46t big ring on and forget about the small ring, it's already small enough.

Trying to take all the relies into account .. [MENTION=468352]GrainBrain[/MENTION] ... I use the large chainring for virtually all of our ride ...... at the moment ... it's pretty flat and on the road am mainly mid cassette but we do some gravel which is quite "sinky" with a slight incline and kills any speed and this is where I use the larger cogs on the cassette .... there's the occasional part where I go to the smaller chainring and once in a while switching over is absolutely fine.

That said in the summer (before I bought this bike) our rides started going a lot further and we started taking in some steep hills which is where the bigger cogs would be used with the smaller chainring so wouldn't want to reduce that option at all.

Longer term I wonder if pushing the rear cassette up to a 36 and also going smaller on the front may be the answer to like either a 46 or 44 and a 30 or possibly even smaller if that's possible.

My 29er was running a 39/27 front and 12/36 rear .... I used the large chainring for about 95% of our rides pretty much mid range for most of it and only going to the small front ring when we were in hilly terrain and very seldom using the highest gear combination so would err to getting closer to that but not quite so extreme to lose all the benefits of more road orientated gearing.
[MENTION=21724]cyccommute[/MENTION] .... cheers for the link as well I'll have a look at that a bit later!!!!