Gear ratios & double or triple chainset?

Membrane

I'm looking at a used roadbike with a double 39/53 Ultegra chainset, rear cassete 11-25. I'm concerned that it won't go down low enough to comfortably tackle steeper gradients.

My current hybrid has a triple 22/32/42 chainset, combined with a 13-28 cassete it goes very low, and I'm not ashamed to say that I encounter gradients on which I need the lowest gear if I want to remain seated and do ~80RPM cadence.

I'd like to get some feedback on what others are using, and on the above double chainring ratios.

hunnymonster

I'm using a 50x42 chainring and 12-27 cassette. I moved from a triple about this time last year and no problems. The only thing I would say is that it feels like there is a lot of overlap. I tend to double shift a lot. I've never had a problem with running out of gears. Then again, I am a cruncher and will happily climb on the big ring with lower cadence much to the annoyance of the real cyclists around me.

Google gear ratios and have a read of the information out there.

kincsem

52/42/30 with a 12/26. I'm building a new bike, and will have Shimano Ultegra, but will try to swop in a 46/36/26 (from their MT range) with a 12/27.
You seldom need the top gear on a bike. Often downhill pedalling will not add anything to freewheeling, but you certainly need the low gears going uphill. I can get away with my present gears, but there ain't much spinning done going uphill, more like a slow grind.

Trojan

I'm getting 34 to 112 gear inches from a double compact (Ultegra10). I find it just fine to spin up Howth Sutton side in lowest, but can imagine running into trouble on steep uphills if fully loaded (I'll get a replacement cassette for that).

This cassette is 28-11 but I can't remember what the chainrings are. Cranks are 172.5 if that helps.

blorg

I'm 52/39/30 with 12-25 on my road bike, and I definately use both top and bottom, although I could live without the lowest on the back and that would include the Wicklow mountains. Interestingly this gives me ~32-114.5 gear inches which is not that far off Trojan's compact. (Indeed ~34.5 min if I drop from 25 to 23.) I don't think I'd be up for a standard double yet myself.

You can figure these things out on Sheldon Brown's site. Your current hybrid is going to give you a range of ~21-87 while this new bike would be around ~42-130. That is a fair difference. On the other hand the new bike is likely to be a hell of a lot lighter. Are you planning on cycling a lot of mountainous routes?

You may be able to change either the cassette to something bigger (prob only to 27) or the smaller chainring to something smaller, although there may well be compatibility issues that I'm not aware of. AFAIK these should not be expensive modifications at all.

Membrane

blorg wrote:

Your current hybrid is going to give you a range of ~21-87 while this new bike would be around ~42-130. That is a fair difference. On the other hand the new bike is likely to be a hell of a lot lighter.

13kg for my hybrid vs an advertised 7.8kg for the road bike, but the latter is without pedals and other references to this bike list it as 8.2kg.

I already assumed that I would no longer need the very small 22 granny that I have on my current hybrid, but road triples typically have a 30 granny, that seems about right to me in relation to the lower weight.

blorg wrote:

Are you planning on cycling a lot of mountainous routes?

Exclusively, I have an old fashioned roadster that I use for the city.

blorg wrote:

You may be able to change either the cassette to something bigger (prob only to 27) or the smaller chainring to something smaller, although there may well be compatibility issues that I'm not aware of. AFAIK these should not be expensive modifications at all.

I looked into that, but Cycle Superstore only lists a few seperate chainrings, none suitable for Ultegra. They do list complete Ultegra chainwheel sets including crank, but those are expensive and IIRC there are only 2 sizes available, the smallest one is only slightly smaller than the one on the bike I was looking at.

There are also triple Ultegra chainwheel + crank sets available, but changing a bike from a double to a triple would also require changing the front derailer, and possibly the shifter. This would be far too expensive for me.

For the cassette, again only small variations in size are listed with as you say the largest being a 27, not enough of a diference with the 25 mounted on the bike to make a real difference.

Looking at what is mounted on new bikes it seems that pretty much all high end bikes (the ones with Ultegra kit) use double chainrings, triples seem to feature only on low or mid end models.

Trojan

blorg wrote:

I'm 52/39/30 with 12-25 on my road bike, and I definately use both top and bottom, although I could live without the lowest on the back and that would include the Wicklow mountains. Interestingly this gives me ~32-114.5 gear inches which is not that far off Trojan's compact. (Indeed ~34.5 min if I drop from 25 to 23.) I don't think I'd be up for a standard double yet myself.

Aye. I worked out the gear inch range in the shop when deciding on the groupset because I really wanted to go for a triple, for touring reasons. When they showed me I'd be getting the same range with the compact I was happy to go for that, because moving to a triple would have caused headaches...

Membrane wrote:

There are also triple Ultegra chainwheel + crank sets available, but changing a bike from a double to a triple would also require changing the front derailer, and possibly the shifter. This would be far too expensive for me.

... exactly. Actually I believe the root cause is that you'd need a long cage instead of short cage rear derailleur to take slack from smallest chainwheel. (I might be off the mark here cos it's late - snooker was great).

Membrane

Trojan wrote:

I'm getting 34 to 112 gear inches from a double compact (Ultegra10).

I hadn't spotted the Ultegra double compact as an option. It does look like a viable alternative for a triple, thanks for the pointer.

blorg

Changing to a triple would also require a bottom bracket change (triple is wider) as well as (likely) front _and_ rear derailleur changes (you arguably need a long-cage rear.) AFAIK levers actually probably wouldn't need a change as modern Tiagra/105/Ultegra can deal with both double and triple. Which is as well as the levers are _very_ expensive.

AFAIK changing to a compact might also still need derailleur changes, depending on the range.

At the end of the day - especially if you are buying second-hand - you are probably better off waiting until you find something that suits (e.g. triple or compact.) I wouldn't have thought that triple or compact is that rare an occurence.

Membrane

blorg wrote:

At the end of the day - especially if you are buying second-hand - you are probably better off waiting until you find something that suits (e.g. triple or compact.) I wouldn't have thought that triple or compact is that rare an occurence.

I quickly concluded that modifying a used bike would be unpractical and too expensive. But I now have a much better idea what to look for in a used bike. I'm in no hurry, it may well be winter before I find something suitable to buy. Thanks to all for the info.

blorg

On the other hand, just tried a lunchtime ride up to Glencullen without using the small chainring and found I probably wouldn't miss it if I didn't have it - more standing than ususal maybe but quicker too. So you never know, double might be OK.

Membrane

blorg wrote:

On the other hand, just tried a lunchtime ride up to Glencullen without using the small chainring and found I probably wouldn't miss it if I didn't have it - more standing than ususal maybe but quicker too. So you never know, double might be OK.

Haven't tried the climb from Kilternan up to Clencullen on my current bike yet (have done it on my 23KG roadster years ago). I love climbing whilst standing on the pedals, but it is a habit I'm trying to get rid of. Sheldon Brown compares low cadence climbing with power lifting, tiring you out. In contrast he compares low cadence climbing with swimming, something you're able to maintain for much longer. I'm trying to extend my range, so I'm aiming to only stand for short durations (to get over short humps), longer climbs I aim to stay in the saddle and do 70 -80 rpm.