Technical Forum Query

[lemmy]

I tried to post a query about gearing on a Kalkhoff Agattu on the technical forum but it tells me I do not have access privileges.

Can I try here and it be transferred?

I'm contemplating changing the gearing to an 18 tooth cog (7 speed shimano) but anxious not to lose too much range or hill climbing abilty. My steepest hill is Broomfield Hill in Richmond Park, about 20%/ 1in 5/ I think.

If I fit the 18 tooth, will I need to retension the chain? Secondly, if I would lose range and hill climbing, would a change to a 20 tooth be worth while?

Any experiences? Also, does anyone know a bike shop in SW London who understand hub gears? LBSs at New Malden and Morden don't consider them 'proper' gears and don't do them.

 

[flecc]

The Technical forum is intended for more permanent items, most questions best asked in here. I have included some advice on this in my Extra page in my Kalkhoff Agattu review.

You will lose range, the amount roughly pro rata to the amount of the sprocket teeth change. The 18 tooth on an Agattu will probably drop the range by about 15 to 20%, a 30 mile range becoming around about 25 miles for example, but gaining assistance to around 18 mph. A 20 tooth will make less difference, about 10 to 15%, but you won't be gaining much by that change of course, the assistance only to about 16.5 mph.

There are many bike shops who will change a sprocket on a hub gear and you must be very unlucky around there. Try a branch of Evans if you have one. I don't know the dealers in your immediate area, but in South Croydon there's Bike Plus on the Brighton Road who will do that for you.

The chain does need to be adjusted after the change, two complete links removed for for the 18 tooth sprocket, one for the 20 tooth. The setting of the idler arm on the motor unit is the thing that determines the amount to shift the rear wheel for the fine adjustment, as shown here:

Chain wrapper adjustment

You can get lots of other advice on my website here:

Panasonic Unit advice website

You will still be able to climb 1 in 5 with either of those changes
.

 

[lemmy]

Still finding my way around but getting there!

That's most helpful - thank you.