BicycleBicycle

Hello all.

Right now I have a SSCX bike (No fixed cog) and I was thinking about gearing down juuuuuust a hair.

Because I'm not running fixed right now, i'm a little more flexible (don't need to worry about how fast my legs will be spinning in relation to my speed).

Please keep that in mind when I ask this.


So, currently i'm running 42/17 which gives me a 2.47 ratio.

This is actually quite perfect for normal day to day riding.

I actually like this quite a bit and I can make it up most of the hills I need to around here (san francisco).

However, there are times when I could make up those hills a little bit faster, and after three nights of riding 6-7 hours a day sometimes I wish I had a slightly smaller gear.
I also want to avoid uneccesary stress on the bearing surfaces of my knees (I start and stop more often than not, so a lower gear would help).

It would also help on the longer climbs (slight gradient, but for like a half mile or so).

Also, even after some pretty fast descents, I am still able to spin and gain a tiny bit of (or maintain) speed on my bike.

In the past few months, i've probably only been in a situation where I get total spinout (completely unable to apply power to pedals) like 2 or 3 times?

Being that I rarely go this fast, it probably means that I can gear down and it won't be a big deal.


I was thinking about gearing down to 40/17 (2.35).

or 37/17 (2.18)


Now, my question to you guys is.

At what point will I actually feel the difference? '

Will I notice a significant difference for a gear down of 2.47 to 2.35?

Will 2.47 -> 2.18 be a very dramatic difference?


Going too low also results in not being able to climb efficiently due to spinning to fast in relation to how i'm climbing.

I can climb pretty comfortably now after getting stronger, but it's still pretty slow, and this gear, if anything, will probably hinder strength gains as i'm just pushing really hard slowly instead of more intensely.


What do you guys reccommend?

Thanks.

mtbikerinpa

You will likely notice a more dramatic feel change by changing the rear gear compared to the front. If you have access to a multispeed bike of comparable front end you could use it to compare feel between gears and map out what feels best. That way you could get a more real-time feel than simple prediction.

phobus

Try a calculator like this one: BikeCalc.com - Speed at all Cadences for any Gear and Wheel

Plug in the cadence range that's comfortable for you, your current chainring/cog combinations, plus any others you think you might change to. You should be able to tell what the right amount of change will be.

BicycleBicycle

Anyone here know if the difference between 2.47 and 2.35 is unnoticeable?
2.47 and 2.18?
I could have just asked this, but I was hoping someone else with similar experiences could offer better advice.

BicycleBicycle

I'm not trying to go a ton lower..
I just want a liiiitle more, and it would be absolutely perfect.

fietsbob

Get a new cog? , F/W , 1 tooth number (18) larger ?
or a 41 t chainring, 1 t smaller

I Could find my way around the hills, there..
but that's where the main streets are, by now..


How about a multispeed IGH rear wheel?

Peers all into other stuff? shame of more than 1 gear frowned on?








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BicycleBicycle

If the gear ratio is the same on paper, does it feel the same on the road?
eg. if i could get a 2.25 by just changing the front gear, or by changing both front and rear, then it's exactly the same gear right?
I think this is true because of talk of redundant gears on many multi speed bikes.

20t

..

hay

Mikefule

1t difference makes a bigger percentage difference at the rear.

For a rough guide, look at the range of sprockets on a typical geared block. On a road block, you will see something like 10, 11, 12, etc. showing that with this size of sprocket, 1t makes a difference.

Once you get to a 17t sprocket on a block, the next one is likely to be a 19t.

On my fixed, I've recently gone from 18t to 20t. The difference is easily perceptible on hills without a huge loss of top speed. On that basis, I'd suggest you go for a rear sprocket 2t bigger.

fietsbob

OK, but my 3 speed IGH has 3 distinct gears 0.75, 1. & 1.33.. Sturmey Archer..






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phobus

Either will be noticeable. Whether it's a big enough change for you, depends on you. Again - check that calculator I linked above. If you're just looking to play with different gearing setups, it'll be cheaper to pick up a few different size cogs.

Yes.

Mikefule

This is one of those "everyone has an opinion" questions.

The simplistic answer is that if the ratio is exactly the same, then the gear is exactly the same and it should feel exactly the same.

However:

• A larger chainring and sprocket combination, with a slightly longer chain is very slightly heavier. More metal.
• A larger chainring and sprocket combination is very slightly less aerodynamic. Chainring has bigger frontal area.
• With a larger chainring and sprocket combination, the chain has to bend less, and the torque is applied across more teeth. There's less friction and the transfer of power is more efficient.

Apart from the very extremes, most of us would not notice any of this in normal day to day riding.

Examples:
39/13 is exactly a 3:1 ratio.
42/14 is exactly a 3:1 ratio.

I doubt anyone could really tell the difference in day to day riding.

18/6 is a 3:1 ratio. It would be noticeably lighter, and the aerodynamics may even be noticeably better in a headwind, but it might feel bit strange to pedal. However, this is a "ridiculous extreme".

Similarly if you made up a ridiculous extreme like, say 90/30, you might notice some difference.

But within the normal range, for most of us, identical ratios will feel pretty much identical to ride.

As chain rings are (usually) bigger than sprockets, 1 t difference on a chainring makes a small percentage difference to the ratio, and 1t difference ont he sprocket makes a bigger percentage difference.

The human body is very adaptable, and will compensate for very slight differences between ratios (e.g. 49/17 and 48/17). My gut feeling is you learn to ride the ratio you have. If you find it uncomfortably hard on your biggest local hills, then gear down around 10%, or maybe a little more. If you have a flip flop with 2 different ratios, then a 2t difference is sensible, and means that the wheel doesn't need to shift too far forwards or backwards when you flip it. (This is particularly important if you have a rear brake fitted.)

bmwjoe

To answer your original question... I ride fixed ~5000 mi/year. My low gear is 42/16=2.62. If I have a long flat ride I change to 50/18=2.78. This is only a 5% difference. I can feel this. Subtle, but noticeable to me. I get a little more speed on the flats and I have to work for the hills a bit more. Changing from a 40 to 42 chain ring will have about the same percentage effect. I would start here and see what you get.


For the City to Shore ride (175 miles flat) I decided to gear up a notch to 53/18=2.94 or a 12% shift from my original gearing. I could still grunt up the local hills, but I was cruising at a higher speed. 100 rpm = 22 mph. I was able to hold my own in the pacelines that formed on the ride. I made the right choice. I went back to the original 42/16 for the Bike MS NYC ride as it has 5700' of climbing. It worked well for me.

AlmostTrick

I run 1 tooth difference on the rear cogs and can easily tell the difference.

Try an 18 tooth cog/freewheel. If you have a flip flop hub, run both the 17 and 18. Based on all you wrote, I suspect you'll be happy with this set up and it won't cost a lot.

TimothyH

My experience is 100% in line with @AlmostTrick.

48x16 vs 48x15 is a 7% difference. It is noticeable when riding.

Keeping cadence from dropping too low is more of a challenge with the 15 tooth cog. I really know I've been riding the next day.


-Tim-

63rickert

Flip flop hub has same threading both sides, fixed side just adds the left hand lockring thread. Depending on brands you could end up with a slight difference in chainline spacing but it will be trivial. Since 42x17 has worked so well for you, keep it. Only choice is do you want an 18T on other side (you will feel the difference)or do you want to go lower for hills.

EdwinHeadwind

I'm running a 39 X 17 these days (freewheel), which, at somewhere around 60 gear inches, is pretty spinny. I love it on climbs, but I get spit out the back on flat sections. In your case, I think the 40 X 17 would definitely be noticeable, and it would achieve what you're aiming for, in terms of climbing comfort and knee health.

But putting a freewheel on both sides of a flip/flop hub would give you the option of switching back and forth. 42 X 18 (61.2 gear inches) is essentially the same as 40 X 17 (61.8 g.i.). Run a 17T on one side and an 18T on the other, and the chain should still fit fine.