vane171

I've looked at some threads related to gear calculations, looked at some external sites with calculators, but I don't find my gear options there and also it looks like not what I am after.

I ride a bike for many years and the top gear for hills on that bike is 40/23 which I find rather difficult going on bigger or longer hills.

Now I got this bike with the lowest gear on it 39/25 and I am wondering how much of a difference it will make. I can't ride the new bike in my usual ride area yet since I have to take it with me to Europe after this crazy virus dies down.

Just using common sense, one tooth on the front I take it makes little difference, probably negligible, compared to one on the sprocket. Probably can look at it as just two cogs extra sprocket on this new bike.

I looked around and found the same brand name and make crankset but with triple rings 52/39/30 (to replace my current 53/39) and assuming it will work on this new bike (most I worry about chain slack on 30T which might prove too much for the RD I have), I wonder if that won't be too easy gear now. I mean if that is too easy for a road bike. I don't talk about huge hills, no Alps or Pyrenees LOL, only shorter ones 10/12% or longer at maybe 5% on which I sometimes end up walking the bike, especially when I don't want to get too sweaty. At six decades of life behind me, I don't see much point staying in the saddle with 40/23 gear.

That old bike actually has one more sprocket 26T but can't shift to it because then the RD is hitting wheel spokes. I replaced most of its parts in 1990s and put on it the best what I had around, including that 8spd sprocket. The frame was built I think for 6spd or so in 1970s, had to push the rear stays apart quite a bit to mount the wheel with it.

If that new tripple crankset wouldn't work on the new bike (either not enough space for the third ring next to the frame or more likely that chain slack - with Ultegra RD-6600), I believe I should be able to mount it on that old bike. Without that option, I might not have risked buying that triple crank on blind.

Crankycrank

Here's a good one. BikeCalc.com - Bicycle Gear Ratio Chart

HillRider

Actually you are comparing bottom (i.e. low) gears, not top. The calculation is quite straightforward to get the gear ratio for any combination of chainring and rear cog. Most commonly here in the US we use the term "gear-inches" and the calcualtion is as follows:

Wheel diameter in inches)x (chainring tooth count)/(cog teeth).

For a 700c wheel or a 27" (ISO 620) wheel the wheel diameter is conventionally chosen as 27". As an example your original 40x23 calculates to 27x40/23 = 46.9 gear-inches and your 39x25 calculates to 27x39/25 = 42.1 gear-inches. The same calculation can be used for any chainring and cog choice.

shelbyfv

The triple crank will also require triple compatible shifters and front and rear derailleurs. Your simplest and least expensive path to significantly easier gearing will be a "compact" crank, usually 50-34, and a larger cassette. You can probably use a 28T or 30T w/o changing your rear derailleur. Plug those numbers into your calculator and see if it gives you what you want.

vane171

Thanks, that calculation is handy to know, even if one doesn't know how it translates to real use feel, so to speak.
What worries me more is what shelbyfv says. The old bike has ordinary shift levers on the down tube, no indexing on those just friction and feel for it that you develop, some gears need compensation after you shift (I must say, I am kind of tired of it). This new bike has the indexing I believe, it sort of clicks when I move the levers - the bike has TT style handlebars with shifter levers on those center bars, forgot the names for them, so it is not the classic levers behind brake levers on drop bars.

So you are saying that the FD (FD-6600, same Shimano Ultegra edition as the RD-6600) may not shift to that third chainring even if I adjust the limit screw on it? Or is that the mater of the levers on the handlebars? I am new to this indexing tech. I really need to read up on it.

If it turns up I can't make that Ultegra FD shift to that third ring, I am sure that tripple crankset would work on that old bike.

Bill Kapaun

40/23=1.74
39/25-1.56
1.74/1.56=1.12.
40/23 is 12% "harder".
It's simple arithmetic. Compare one ratio vs the other ratio.

Amt0571

This.

I run a 50-34 crankset with a 11-32 cassette on my road bike. You have to check what's the maximum cassette your RD can take though.

dsbrantjr

Here is a good calculator which lets you compare two different gear trains side by side, with numeric and graphic depiction: https://www.kstoerz.com/gearcalc/compare/

xroadcharlie

If your rear derailleur on your new bike will handle a 14 - 28 freewheel. for less then the cost of breakfast for two you can buy a Shimano 6 speed 14 - 28 freewheel. That will provide you with about 38 gear inches (GI) to start. Lower is easier for climbing. Your old bike had 47 gear inches. No wonder you had trouble climbing. Changing the freewheel alone will give you a 20% advantage over your old bike.

The next, More expensive step would be to swap out the crankset with a 50/34 T unit. That would bring you down to under 33 GI. That is low enough to climb some pretty challenging hills considering I just got back from my morning ride which includes climbing a pretty steep trail with soft gravel and lose stones with my 33 GI sprockets. So pavement or hard packed gravel should be a breeze, and might be doable with just the 14 - 28T freewheel change. If you still need more, I recommend keeping the bike as close to original as practical to insure compatibility. IMO you don't need a triple crank.

My old mountain bike had a 14 - 34 6 speed freewheel that was good for climbing, But the gears are too far apart for normal riding. A 14 - 28 IMO is a fine range for a road bike with 6 or 7 speeds.

cyccommute 

I prefer this calculator. It’s a but easier to use. For vane171’s problem it’s especially easy to compare because it allows for comparing a single gear and is also easy to export.

vane171

Thanks all, nice discussion. As to swapping out crankset, I would like to keep with the GXP bracket and hollow tech axle (GigaX Pipe) and that limits what's available out there, in used department that is. I don't think this type is being still sold as new, looked at bunch of online shops, in US or Canada and nobody sells this technology anymore. The bike is Trek from 2007 and since then, they make quite different cranks. Also the bike looks really nice and even other parts on it belong to a brand set, like both shifters and brakes are Shimano 6600, cassete Shimano 12-25 HG (Hyperglide) as is the chain HGX, wheel and cranks Bontrager...

The chain is also not for sale anymore it seems but for the mileage I put on bike, it should last many years yet. I like to go for an hour to hour and a half not too long but fast rides, sort of time trial style riding but on an amateur level. Usually 15 to 20 mi twice or three time a week, or 25-30 mi on longer rides. I think I will end up putting that tripple crank on the old bike and keep this one as is, don't really need to take it into the hills.

davidad

https://www.jbarrm.com/cycal/cycal.htmlhttps: