Switching from BWR?

[ukoldschool]

I've had my little S6 brommie for just over a year now, commuting to and from the station at both ends of the journey, and it has been a great little thing and very reliable.

A while back I was taking a route to the station that involved a brief downhill stretch, followed by the inevitable uphill afterwards, and in an effort to stop myself spinning out in top (and to enable me to carry greater speed back up the other side) I changed my rear sprockets from the standard 13/16 to 12/15. The 12 tooth is a standard bromton part from the single speed bikes, the 15 was a single gear Shimano, this gives the same gearing as changing the front sprocket to a 54t, but is considerably cheaper (£15 as opposed to £40) as you don't need to buy a new chain.

I'm happy with the gearing as it stands, but now note that I never ever use the first 2 gears, and quite rarely the 6th. All my journey is spent from 4th to 6th, and to that end ive been giving though to swapping out the heavy BWR hub for a 4 cog rear casette hub like the one from brombacher in Korea:
http://en.brombacher.kr/product/bro...4s-shift-kit/339/?cate_no=106&display_group=1

Anyone know the weight of the 6 speed BWR rear hub or the weight of the wheel compared to the weight of the 2 speed wheel (which I believe this conversion uses)

I will need to change the front sprocket to something bigger to get similar gearing, so does anyone know the easiest way to do this with say a 60t chainring? does it mean I have to change the cranks?

Thanks

 

[Kell]

The weight of the BWR on its own is given as 2lbs 1 oz whereas the hub for the single/2 speed is given as 11 oz.

Can't help you on the other bits.

 

[12boy]

Even if you get a 60 tooth chain ring, a 12 tooth sprocket yields about 80 gear inches, while your current set up can go over 100. I've looked for a compatible 11 tooth without success. 349 wheels without the bump upwards of an IGH hub just can't get that high. Even a 70 tooth chain ring only gets to 94 gear inches. The product you referenced won't get you there either. I use the Sheldon Brown gear inch calculator which is handy for different combos and unlike some others, has an option for 1 3/8 " 349 wheels and tires. My current combo is 12/17 cogs with 2 chain rings...58 and 38. This yields 77 and 55 and then 51 and 36 gear inches for the 58 and 38 chain rings. It's true I spin out fairly quickly at 77 gear inches, but I like it for most levelish riding as long as the headwind isn't too stout. I would love an 11 tooth sprocket but can't find one as I've said, and I was I'd expect it to wear out pretty quick.

 

[ukoldschool]

I dont really understand inches, I work in metric.

Currently my 'go to gears' are in 'Metres development':

3rd	4.40
4th	5.50
5th	6.90
6th	8.62

Using the gear calculator set up as 'no inetral gears' for 21/17/13/11t gears gives the following with a 60t chainring which doesn't seem a big difference (given that I don't use what is currently my 6th gear very much)

21	3.77
17	4.66
13	6.09
11	7.2

by comparison the standard Brommie BWR 13/16 gearing which I was happy with other than the spinning out looks like this:

3rd	4.13
4th	5.08
5th	6.47
6th	7.96

But I guess if you can go higher that a 60T this doesnt have much legs unless I can stomach a lot of spinning out?