27 versus 28 tooth cassette

Paul Hough

I'm doing St Croix on 6 May.   It's well known for the hill called the beast (see description below).   I'm taking my compact crank with a 12-27 cassette.  Would a 28 cassette make much difference?   Despite the hype, this hill doesn't sound any more imposing than Sugarloaf Mountain (right here in central Florida) which is a half-mile climb at 19% grade.  An older review I read states that the average cyclist is taking 7 to 8 mins to get over the top of the beast.   It doesn't seem worth it to me to buy another cassette for one more tooth but I would like to hear what the experienced climbers say.  What about IM St George...would a 28 be preferable to a 27?

Twenty-one miles into the bike, The Beast is a 600-foot climb in a stretch of highway 7/10 of a mile long with an average grade of 14 percent and a maximum grade of 21 percent. 

 

mgraffeo

take a look at this quick site

http://cycleseven.org/bicycle-gear-inch-calculator

difference between 34/27 and 34/28 at 90 RPM is about 0.3mph. Or, at the same speed, (8.54 mph), you'd be at 90 RPM in the 28, 87 RPM in the 27...

save your dough...

Cary Blanco

Paul,

I bet you'd totally be fine with a 27. However, if you had a 28 and were going up the hill and had to switch back to a 27 right before you were going up the steepest part you probably wouldn't be a happy camper. But I think you'll be fine.

If you were looking to upgrade from a say Ultegra to a Dura-Ace or PG to OG then it might make sense.

Also - have a look at this gearing comparison tool http://public.tableausoftware.com/v...cleGearing

GMAN 19030

I say man-up and ride a 54/42 with an 11-23.



I agree that one tooth isn't going to be worth the $$$ from the charts shown above.

mgraffeo

Thanks for that link, Cary! I was looking for that one, and couldn't find it. Great tool for visualizing these types of questions.

Paul Hough

Thanks guys. I guess I'll save the money since the difference seems to be that I need to go at least 8.87 mph on the 27 versus 8.55 mph on the 28. Just for grins, I put in Bob's real man gearing and see that you would have to hold 12.86 mph on the 40/23. I wonder how far up I would get before I would fall over?

GSmith821

Is speed the right measure for going uphill? I would look at it from a power perspective, that is, do I have to create substantially more power in 27 vs 28 for this hill. I realize the 27 and the 28 are just one tooth...but the SRAM 12-27 has a 24 and 27 and the SRAM 12-28 has a 25 and 28 which to me is 2 more "easier" gears than the 12-27. Sure it may not be worth the $$ but I have never heard anyone say "I just had to too many gears going uphill." Just another thought.

Cary Blanco

George, agreed on the "too may gears" point, but ... the race Paul is referring to has one big ass steep hill that Paul is concerned about. We're recommending against getting a new cassette with only one more tooth for just that one hill. If Paul was doing IMSG, IMMT or IMLP we all might be singing a different song as the amount and length of the hills and the it's impact they'll have as the day goes on, etc.

cgres123

@ Cary, that link just saved me a Bucks... Thx

Bob Irwin

What about IMC? I need a new cassette and was debating between the 12/27 and 11/28. I know with my power the 11/25 isn't going to do it on those long long climbs.

imc1792

@Bob, i have done IMC 4 times, the first with an 11-25, the 2nd with a 11-26 and i felt i still needed one more and went with 12-27 for the last 2 turns and it was perfect for me. 28 seems excessive as the climbs are longish and not so steepish. As mentioned numerous times on EN forums with respect to finding z4/TP intervals easier to hold going uphill than trying to hold on flats, I prefer a slightly lower candence than high rpms up.