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

[Bonacentral]

As title.

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. I'm really not fit enough to be running a double with a 28 or smaller.

Was just wondering if someone could explain the difference in plain English please? I am crap at maths!

Rarely do I encounter hills that require the 34 / 28 but when I do I do need it!!

Can't consider a semi compact 52 / 36 as the 53 was much cheaper!

Thanks in advance

 

[gbb]

Your post seems a little contradictory
You're spinning out downhill on a compact with a 28 ?. Downhill, I'd expect to be at the other end of the cassette, say an 11 or 12T.
What is the smallest cog on the back and which chainring are you normally on the front when spinning out downhill.

 

[Pro Tour Punditry]

I am not sure what you are looking at but here's a gear calculator that will help you work it out

http://www.sheldonbrown.com/gear-calc.html

edit - to save you the bother, according to the calculator the answer is that 34/28 and 39/32 are exactly the same

2nd edit - I think

 

[ColinJ]

As dbb, it does sound like @Bonacentral is using the wrong end of the cassette for downhills!

I remember someone saying to me that 'big' = 'fast'. I had to point out that it should be 'big front and small back' = 'fast'. He'd assumed that the more teeth involved, the faster he would be able to go, whether they were on the front OR the back ...

 

[Bonacentral]

Your post seems a little contradictory
You're spinning out downhill on a compact with a 28 ?. Downhill, I'd expect to be at the other end of the cassette, say an 11 or 12T.
What is the smallest cog on the back and which chainring are you normally on the front when spinning out downhill.

As dbb, it does sound like @Bonacentral is using the wrong end of the cassette for downhills!

I remember someone saying to me that 'big' = 'fast'. I had to point out that it should be 'big front and small back' = 'fast'. He'd assumed that the more teeth involved, the faster he would be able to go, whether they were on the front OR the back ...

I have re read what I posted 3 times just to be sure and no, I meant exactly what I wrote haha!

"I'm really not fit enough to be running a double with a 28 or smaller" so a 39/ 28

"Rarely do I encounter hills that require the 34 / 28 but when I do I do need it!!" - so would struggle with a 39/28

 

[Bonacentral]

I am not sure what you are looking at but here's a gear calculator that will help you work it out

http://www.sheldonbrown.com/gear-calc.html

edit - to save you the bother, according to the calculator the answer is that 34/28 and 39/32 are exactly the same

2nd edit - I think

Thank you - I know that there are gear calculators out there - I just don't really understand the maths! Bit number dyslexic if that's even a thing?!

Just wanted to find out how much of a difference day to day it would be. And yes - it's an 11-28t with compact 50-34 running at the moment

 

[Pro Tour Punditry]

What's the range on the cassette with 32 top end?

 

[raleighnut]

I think you may need a medium cage (GS) rear mech to cope with the 34

 

[gbb]

I have re read what I posted 3 times just to be sure and no, I meant exactly what I wrote haha!

"I'm really not fit enough to be running a double with a 28 or smaller" so a 39/ 28

"Rarely do I encounter hills that require the 34 / 28 but when I do I do need it!!" - so would struggle with a 39/28

Maybe I'm (and ColinJs) missing something. You're spinning out downhill but you're on a 28 which is at the opposite end of cassette I'd have thought you'd be on.
You ARE struggling with going downhill ....you don't mean struggling to go uphill do you?

 

[Bonacentral]

Maybe I'm (and ColinJs) missing something. You're spinning out downhill but you're on a 28 which is at the opposite end of cassette I'd have thought you'd be on.
You ARE struggling with going downhill ....you don't mean struggling to go uphill do you?

Apologies for the confusion. "Main reason is that I am spinning out a lot down hill. I'm really not fit enough to be running a double with a 28 or smaller"

There is no mention of what the small tooth is (11). I'm not fit enough to be running a double 39 / 28 for uphill compared to what I already run 34 / 28

Maybe I should of put a space between sentences?

 

[smokeysmoo]

If you decide to swap it over I might be interested in going the other way, depending on colour

Mine's a standard double, (Ultegra 10 speed grey), and I could probably do with a compact these days

 

[the snail]

Seems straightforward to me, 50/11 is too low for downhill, doesn't want higher than 34/28 for uphill. 53/50=1.06, so you will be able to go 1.06 times faster before you spin out downhill. 34/28=1.21, 39/32=1.22 so bottom gear will be the same as before, more or less.

 

[Pro Tour Punditry]

Seems straightforward to me, 50/11 is too low for downhill, doesn't want higher than 34/28 for uphill. 53/50=1.06, so you will be able to go 1.06 times faster before you spin out downhill.

Would that not only be the case if the cassette with the 32 also has 11 on the other end?

 

[Bonacentral]

If you decide to swap it over I might be interested in going the other way, depending on colour

Mine's a standard double, (Ultegra 10 speed grey), and I could probably do with a compact these days

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!

Seems straightforward to me, 50/11 is too low for downhill, doesn't want higher than 34/28 for uphill. 53/50=1.06, so you will be able to go 1.06 times faster before you spin out downhill. 34/28=1.21, 39/32=1.22 so bottom gear will be the same as before, more or less.

Thanks for understanding and working it out. The numbers are all Greek to me but "more or less" the same does it for me

Cheers

 

[paraffinlamps]

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 35.6mph
53 x 11 at 100 rpm will give you 37.7mph
so just over a 2 mph difference . Just think how often you actually spend in 50 x 11 .

Edited as rightly pointed out by Raleighnut I had the speeds back to front