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I have 7 speed freewheel on Carrera Zelos. I want to upgrade to 8 speed but can t find any freewheel. How do I do it? Its my first road bike as I normally ride downhills and wanted to mix it up especially commuting to and from work and feel it needs better gears/ brakes. It has the shimano tourney set with a TZ500 freewheel.

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    First you replace your bike frame, then you get a new hub and spoke it to the wheel. Apr 19 '20 at 2:21
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Long story - freewheels died off, with the 7 speed freehweel being about the last you could get. 6 and 7 speed freewheels still exist because they're cheap and suit low-price bikes.

However as cassettes got wider, the 7 speed was more likely to bend its rear axle on an impact like a pothole or a driveway ramp. The 8 speed design with a freewheel would be worse.

https://en.wikipedia.org/wiki/Bicycle_wheel#/media/File:Labeled_Bicycle_Hub_Comparison-en.svg
from https://en.wikipedia.org/wiki/Bicycle_wheel

In the second image, notice how far inboard the bearings are on the drive side. Whereas a more modern freehub has the load spread across the bearings more evenly, with less leverage on the axle.

Your only real option to get more gears are to replace almost the entire transmission. That could cost more than a new bike, so not recommended. You will need:

  • cassette
  • chain
  • freehub-based back wheel hub + rebuild of your wheel onto this new hub OR
  • a complete new back wheel
  • replacement right-hand shifter
  • inner and outer cables for rear shifter

Additionally you might need:

  • rear derailleur that matches the number of gears
  • bartape

Probably you won't need to replace the chainrings or front mech, though some people can't stand having unmatched brake/shift levers on their bike.

Add all that up, and it could easily exceed the cost of your bike... consider that your bike retailed last at Halfords for £275 - and even if you spent that much, other parts would still not be new.

I would suggest you ride the Carrera as it is, and look to buy an entire new bike. Keep this as your N+1 spare bike, or sell it on to the next person as-is.

The only time this kind of upgrade is financially reasonable, is if you have a donor bike with adequate components already. Then you have to make sure the donor has the same OverLocknut Dimension as your existing frame, and so on. It starts getting quite complex.

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