mko123

Dear All,

I was wondering if you could kindly help me. I have a somewhat unusual situation, which I'll summarize briefly:

I own a Tern Link D8, which I purchased in 2015. Several years ago I unfortunately had to replace the rims, and that started a sequence of events which were:

-I (unknowingly) replaced the rear wheel with a freewheel hub, and even though my bike was previously an 8 speed (I believe using a cassette), I had replaced the rear wheel with a 7 speed freewheel.
-The 7 speed freewheel actually worked and still works fine, but I have recently wanted to replace it, as I'm often pedaling too fast when going down hill (which I attribute to the fact that it's a 14-28t design).
-I would prefer not to replace the entire rear wheel with a new hub that would allow me to install a cassette. Therefore, I was hoping that I could just upgrade from my 7 speed freewheel to an 8 speed freewheel. I have learned that these are hard to find, and may come with issues. Nevertheless, I did find one with an 11-34t design, from a company called DNP (posted on Amazon).

So, with all the above, my questions are: what issues (if any?) will I encounter if I switch to the 8 speed freewheel hub that I identiifed? Will the installation be as trivial as removing the existing freewheel, screwing on the new one, and possibly replacing the chain?

Thanks in adavance for your help.

Best Regards,

Mko.

fietsbob

Broken axles.. the hub bearing on the drive side is a long ways away from the dropout, so all that length is leverage, flexing the axle.

they break just inside of the cone.

freehubs moved that bearing close to the dropout, making it part of the freehub driver assembly.

Miele Man

How heavy are you?

An 8-speed freewheel is most likely longer overall than a 7-speed on. Let me check my Sacks 8-speed corncob one to confirm that.

Yes an 8-speed freewheel is longer overall. That means you might require a longer axle and that greatly increases the chance of bending or breaking the axle because the right hand cone is so far inboard of the axle end compared to a freehub. Incidentally freehubs were invented to cure the problem of broken axles. The heavier the load on the rear wheel the greater risk of breaking a rear axle.

Here's an image of a Shimano 7-speed freewheel and my Sachs 8-speed corncob freewheel. You van see how much longer the 8-speed freewheel is.



Here's an image showing where the bearings are located on a Freehub and on a Freewheel. The red dots are the bearings.


Here's an image of where a freewheel axle most commonly breaks.


Cheers

Homebrew01

What size is the chainring(s) on your crankset ?

mko123

Thanks Miele Man , much appreciated.

Just so I understand: if I choose to accept the greater risk of axle fracture, is the upgrade as simple as unscrewing the existing freewheel (with tool), screwing on the replacement, and possibly replacing the chain with an 8 speed chain? (Again, I already have an 8 speed shifter and derailleur on the bike). I'm not that heavy (175 pounds).

Homebrew01 I believe that the size of chainring is 52t.

Best Regards,

Marko

hermanchauw

You don't have to change to an 8 speed chain. 6,7 and 8 are interchangeable.

Because the 8 speed is wider, the hub would be further to the left, ie the rim would be also, so you have to redish the wheel.

A simpler way would be to keep the rear as it is and get a bigger chainring.

But in the long run, getting a freehub wheel would be better. Even 6 speed is risky. My mother had a bent axle and she is much lighter than you (asian average sized lady).

Miele Man

As another poster noted and the images I posted show, the 8-speed freewheel will be longer than the 7-speed one. therefore, unless your locknut on the axle is far out from the smallest cog on the 7-speed freewheel you'll most likely need a longer axle and also need to redish the rim. that means moving the rim back to center after installing a new axle if a new axle is needed.

If you're determined to use an 8-speed freewheel (plus a high chance of breaking an axle*) then I suggest fitting the 8-speed freewheel on the existing wheel and see if the axle and locknut protrude far enough out past the 8-speed freewheel so that a new axle is not needed.

Cheers

* How far away from home might you be if that axle with an 8-speed freewheel breaks? If the axle breaks do you have far to walk to get to alternate transportation, or will you be able to sit/wait in the shade whilst you call for a ride and wait to be picked up?

I really recommend that you get a new wheel and an 8-speed cassette if you can afford the There's a HUGE difference in the strength of a freehub wheel over a freewheel wheel. the freehub wheel is a LOT more worry free.

Sorry about the chain comment. I forgot that you weren't going to a 9-speed system.

Point

None other than Sheldon Brown himself advised me to avoid doing this due to the axle breaking potential. That was enough for me