Compact 50/34 28t to Double 53/39 32t difference and maths help please?!

[raleighnut]

I wouldnt bother to swop in all honesty . Its a lot of hassle and expense for a marginal gain . According to this http://www.machars.net/bikecalc.htm and assuming 700c wheel size and 23 mm tyres
50 x 11 at 100 rpm will give you 37.7mph
53 x 11 at 100 rpm will give you 35.6mph
so just over a 2 mph difference . Just think how often you actually spend in 50 x 11 .

errr You may have posted the speeds wrongly there.

 

[paraffinlamps]

errr You may have posted the speeds wrongly there.

Excellent spot . My bad . Edited now

 

[smokeysmoo]

I won't be swapping but as you mentioned it I do have a new 10 speed grey Ultegra F6750 compact that was gonna go on a bike but just checked it out and annoyingly it's a 175. If any good make me a sensible offer!

Sounds perfect as I use 175's but sadly my funds situation means the only offer I could make was the one to swap, the story of my life goes on it seems

 

[Ajax Bay]

Looking to change things up to a double from compact but with a 32t cassette.
Main reason is that I am spinning out a lot down hill. [but]
Rarely do I encounter hills that require the 34 / 28 but when I do I do need it!!

Increase your 'threshold' cadence by 6% (with the 50/11) and you'll spin out at 37.7mph (see @paraffinlamps amended figures above).
Going to a 11-32 will widen the steps between the gears, which would adversely affect me more than the occasional 'spin out'. Pedalling above 30mph is wasted effort (probably applies to above 25mph). Improve the suppleness of your pedaling so you can maintain that increased cadence and perfect your aerodynamic tuck.

 

[ColinJ]

I still can't see how 50/11 isn't high enough!

For years I was riding with a top gear of 52/14 and used to pedal that gear up to about 33 mph on steep(ish) descents. If I wanted to go faster I just stopped pedalling and got my chin down on the bars and soon I would be doing 40-50+ mph (assuming no headwind). There is no way that the average rider is going to pedal even a 53/11 at 50+ mph!

So, if the hill is steep enough that a 50/11 can't be pedalled fast enough, getting aero should do the trick.

Ah, which is pretty much what Ajax Bay just posted - I got distracted by the Giro highlights from yesterday and didn't read his post!

 

[Ajax Bay]

I still can't see how 50/11 isn't high enough!

I absolutely agree Colin, but some people just want speed. The only time I'm pedalling at those speeds (52/12) is if I know there's someone on my wheel ish) and as the hill slackens, if I don't pedal they'll have to 'air'(body) brake. At 110 cadence that'll allow me to maintain 38mph (with a stonking and straightish downhill). OT - Had the inception (intimation?) of a speed wobble at close to 50mph (when I dared to look down) this weekend a couple of times so my aerotuck swiftly included a knee on the top tube).

 

[Bonacentral]

I appreciate all the replies guys!

I think part of the problem is that I live on a semi steep hill. Everytime I get about 200 metres down it I am spinning out. There is no point in aero as it's a built up area with a lot of traffic.

If I was as decent as I think I am downhill then I'd be grinding the 50 / 11 on the flats - I'm really not haha!

Perhaps I should just wind my neck in and realise that I am damn unfit and just enjoy the ride going downhills?!!

Appreciate all the technical gubbins though - still can't understand it and bigger cassette is gonna weigh more - when I need that 34 / 28!!

Sounds perfect as I use 175's but sadly my funds situation means the only offer I could make was the one to swap, the story of my life goes on it seems

Sorry can't be swapping a used for new - the wife wouldn't be up for it! Sadly don't buy any used parts anymore after buying a chainset described as "very good, light dry use" and it turned up as a shed.

And Paypal found in that conman's favour with my pictures to prove it wasn't!!

I'm probably going to get a 5800 52 so if you are interested could do it for £100 and £7 postage?

 

[smokeysmoo]

I'm probably going to get a 5800 52 so if you are interested could do it for £100 and £7 postage?

Ah I didn't realise it was a new one you had, I simply can't justify spending so much for the amount I use it, thanks anyway

I'll stick with the double unless something crops up. I can plan my routes to avoid the monster hills, but there are a lot of them around here so can mean a lot of planning

 

[Ajax Bay]

I appreciate all the replies guys!
Appreciate all the technical gubbins though - still can't understand it and bigger cassette is gonna weigh more . . .
I'm probably going to get a 5800 52

Thank you for saying you appreciate the replies, but since you "still can't understand it" and are going to get a 52/39 chainset 'anyway' the advice you've received seems to have not been understood, or ignored, or both. The difference in the weights of an 11-28 (105 5800 - 276g) and an 11-32 cassette (an 11-32 Ultegra 6800 11 speed cassette = circa 290g) is minimal.
By choosing to go 52-39 and 11-32 you're:
1) Adding weight (also the double's chainrings (52-39) will be heavier than the compact (50-34)
2) Spending for minimal gain (4% more speed at a given cadence before spin out)
3) Establishing a wider %age step between gears.
Swapping out the 50t on your compact for a 52t (BCD 110mm) would cost £16 (much more if looks or groupset integrity are important to you) and you'd then keep the 34/28 low gear ratio you need (if you turn up the hill at home, not down it) as well as the closer ratios of the 11-28 cassette. The FD would handle that, just, (though would need to slide the FD up a tad).

 

[Bonacentral]

Thank you for saying you appreciate the replies, but since you "still can't understand it" and are going to get a 52/39 chainset 'anyway' the advice you've received seems to have not been understood, or ignored, or both. The difference in the weights of an 11-28 and an 11-32 cassette (an 11-32 Ultegra 6800 11 speed cassette = circa 290g) is minimal.
By choosing to go 52-39 and 11-32 you're:
1) Adding weight (also the double's chainrings (52-39) will be heavier than the compact (50-34)
2) Spending for minimal gain (4% more speed at a given cadence before spin out)
3) Establishing a wider %age step between gears.
Swapping out the 50t on your compact for a 52t (BCD 110mm) would cost £16 (much more if looks or groupset integrity are important to you) and you'd then keep the 34/28 low gear ratio you need (if you turn up the hill at home, not down it) as well as the closer ratios of the 11-28 cassette. The FD would handle that, just, (though would need to slide the FD up a tad).

Thanks Alex- that is the real world kick up the ass I need!

Persuaded me I don't need to change my compact and also that I need to kick myself up the ass and ride a bit harder - thanks!!

Have said I'm not good enough this whole time!!

Cheers

 

[si_c]

Thanks Alex- that is the real world kick up the ass I need!

Persuaded me I don't need to change my compact and also that I need to kick myself up the ass and ride a bit harder - thanks!!

Have said I'm not good enough this whole time!!

Cheers

You say you're spinning out, but just out of curiosity, do you know what your cadence is? I'll quite happily spin at 110rpm on the downhill, which is about 40mph, I can go faster, to maybe 120 or 130rpm, but I'd rather enjoy it and I'm not racing.

 

[Bonacentral]

You say you're spinning out, but just out of curiosity, do you know what your cadence is? I'll quite happily spin at 110rpm on the downhill, which is about 40mph, I can go faster, to maybe 120 or 130rpm, but I'd rather enjoy it and I'm not racing.

Good point. I'd rather enjoy it and not come off! Think my average is around 90 but will check. I'll be needing a 32 to be able to get up hills which will obviously be more weight. I'll keep the compact on my everyday bike but think I may go for it and build a 7KG bike. Just need to get a frame. Considering the Planet X pro carbon - simply because of price. Not keen on the exposed cables but not the end of the world!

Thanks for your response

 

[S-Express]

Not keen on the exposed cables but not the end of the world!

There's a lot to be said for the simplicity and servicability of external cable routing.

 

[Bonacentral]

Yes there is. Absolutely fine on my Allez. Simply an aesthetic point. Should probably be patient and see what comes up on ebay or hope that Westbrook get some more Scott CR1 pros that they feel like selling off cheap again!