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Discussion Starter · #1 ·
My wife will be doing the Whiteface hill climb with me for the first time this summer. I want to make sure her bike is well setup and the most cost effective solution would seem to be new cassette and chain.

Currently she has a compact double (50/34) and a 9-speed 11-25T cassette. The shifting in the rear is managed by a Tiagra 4500 rear derailleur.

The derailleur specs say not to go more than 27t on the largest cog, so I was thinking of getting a 12-27t cassette.

Now is the extra two teeth worth it? Do you think I could safely go to a 28t or 30t rear cog despite what Shimano says?

I would really like to avoid swapping derailleurs and/or cranksets if possible.
 

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I'd say the 27 is worth it for a hard, sustained climb, but I'm not your wife.

As you alluded to, you'd need a new derailleur to handle bigger in the rear.
 

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I'll bet your can easily take a 28t cassette, but you might need to screw the B-tension in a bit.

And if your frame has an effectively long derailleur hanger (this depends on both the frame and hanger combined), then it'll take a 28t no problem.

If your wife has a 25t and you're wonder if she might need a 27t or 28t, then go with the 28t cassette. Better to overgear than undergear.
 

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I guess some of it depends on how good of a cyclist she is, but if it were me, I'd look at buying a longer cage RD (even second hand) and perhaps putting a 32 on her bike if you think she might struggle at all. The fact that you are asking the question would suggest that you think she might.
 

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I put a 32 on the back of my bike and WOW, what a difference! Had a 28 before. I temporarily kept the same RD and just avoided cross chaining. Worked just fine for the lap around Lake Tahoe, but I had the shop swap the RD first chance I had after that.
 

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Discussion Starter · #7 ·
I've done the race twice before, it isn't easy, but she has never trained at the level I have before, right now she is mirroring my training. I know she will be in much better shape than she has been for climbing, but to answer the question, yes I am a bit worried that the 34t up front and 25t at the rear is not enough.

I have a triple and 30t up front and 25t at the rear is what is available to me, but I rarely use the last gear in the casette. I was thinking maybe 27t would be enough for her, but felt like 30 would put us into that "extra comfort safety zone" if I can call it that.

What kind of derailleur? I see the new Tiagra 4700 GS can go right up to 34t, but it's a 10-speed, will it work with 9?
 

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The 30t will work. I've used it with 7800 and 7900 derailleurs (also Sram Red). It's been done by many people.

9sp and 10sp Shimano road rear derailleurs have the same cable pull and will interchange. The shifter will determine the number of gears so a 10sp derailleur will be 9sp with 9sp shifters.
 

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I'll defer to others on the derailleur compatibility, but be sure the chain is long enough before you try that big/big crosschain combo :)
 

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if you're already on a 50-34, you probably don't need it, but if you feel you are maxing out and need a lower gear go for it. If you want to save some money and get a better sense of it, instead of asking us, why not pick a smaller hill in your area and do repeats on it and see for yourself.
 

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My wife will be doing the Whiteface hill climb with me for the first time this summer. I want to make sure her bike is well setup and the most cost effective solution would seem to be new cassette and chain.

Currently she has a compact double (50/34) and a 9-speed 11-25T cassette. The shifting in the rear is managed by a Tiagra 4500 rear derailleur.

The derailleur specs say not to go more than 27t on the largest cog, so I was thinking of getting a 12-27t cassette.

Now is the extra two teeth worth it? Do you think I could safely go to a 28t or 30t rear cog despite what Shimano says?
Find her vertical climbing speed at the duration of interest in meters per second. Strava can tell you.

As an alternative, find her maximum power at the duration of interest. Multiply by 90% for the fraction being used to overcome gravity. Divide by total mass in kilograms of her + bike + extras. Divide by gravity 9.8 m/s^2.

For 1.5 hours in good shape I manage 210W. My bike and I total 70kg. 210W * .9 / 70kg / 9.8 m/s^2 = 0.28 vertical m/s.

Divide by grade to get forward speed.

With Whiteface reported at 8%, .28 / .08 = 3.5 meters/second.

Double check whether that's feasible. 11 miles is 17600 meters, divided by 3.5 meters/second is 5028 seconds, or 1 23 48. OK.

Multiply by 1000 mm/meter, multiply by 60 seconds in a minute, and divide by tire outside circumference to get rear wheel RPM.

3.5 * 1000 * 60 / (3.14 * (622 + 25 * 2)) = 100 RPM

Divide target crank RPM by wheel RPM and multiply by small ring tooth count to get big cog size.

I can comfortably make the same power seated below 60 RPM and have a triple with a 30 ring, so

60 / 100 * 30 = 18

or

60 / 100 * 34 = 20

Adjust in other situations where it's not a nice uniform 8% grade.

I like having a 30x26 low gear to get me up grades pushing 10% at an endurance pace, although this is a race where you don't need to stay fresh for the following 200 miles.
 

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Discussion Starter · #12 ·
Thanks guys, I'll have to go with a 12-30t cassette and new chain, some say it has worked with their 9-speed Tiagra derailleur, so I will try it out. I feel with 34/30, she should be in a good position to finish the race 34/27 or 28 seems a bit risky. If it doesn't work, I will just upgrade the derailleur and so be it.
 

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Shimano is conservative with their specs. it is possible that a 29 or even a 30 cassette works, but you'd have to try. there are 3rd party companies making compatible cassettes.
 

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if you're already on a 50-34, you probably don't need it, but if you feel you are maxing out and need a lower gear go for it. If you want to save some money and get a better sense of it, instead of asking us, why not pick a smaller hill in your area and do repeats on it and see for yourself.
He was asking for his wife, not him.
 

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I would think the 28 will work for sure, the 30 will probably work on most bikes but it depends on the length of the derailleur hanger...the longer the better.

A 'longer cage' derailleur won't get you anywhere, it has to also be designed to work w/ a larger large cog. The old 'long cage' triple derailleurs of years past had the exact same large cog spec as the short cage derailleurs of the time. 27t. The new 'medium' cage road derailleurs actually have different movement geometry from the short cage units to allow them to clear a 30 or 32.
 

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I've had a 34-29, and it's great on those long steeper climbs. I think your 34-30 is really helpful for this 8 mile, 3500 foot climb. She should be able to stay seated most of the time, much better than having to stand with a 34-25.
 

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Definitely wise to go with more than 27 in the back. I don't know your wife, of course, but I've climbed Whiteface a few times and ride with a few women who've done really well in that and other hill climb races and while I don't know exactly what they use for gearing on Whiteface I know it's considerable more than 34x27. I'd guess by looks they have 34x30 and no offence intended but it's almost certain these women are a lot stronger than your wife.
I'm not saying they need more than 34x27 to survive and not have to walk, but to race it efficiently they definitely greatly benefit from more.
 

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How heavy is your wife? If she's around 100 - 110 lbs, I'd say go with 28 on the back. If she's around 130 - 150 lbs, get the 30.

EDIT
 
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