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In 2011, I bought a cheap bike from Walmart. It's done fine by me on the ride or two I take per year, but I'm looking to enhance my home gym a bit and was looking to grab a direct drive trainer. The big thing here is I'm more concerned with being able to work out at home than I am with having a nice bike, and I'm looking to avoid the mounting costs of getting both a trainer and a bike.

The direct drive trainer I have my eye on has says it supports 9 / 10 / 11 speed cassettes - my bike only has 7 speeds on the rear wheel. I was planning on buying a 7 speed cassette and just using spacers, but the LBS said that I might have issues with a freewheel vs freehub if the bike was that old and cheap. Turns out he was right - I have a freewheel on the bike.

So here's my question - with a direct drive trainer, does it matter what the rear wheel has? I'm taking it off - my thinking was that as long as I get a 7 speed freehub cassette with spacing the same as my current setup, it should be fine.

Is that correct?

  • That sounds reasonable - the gotcha might come on the Overlocknut Dimension (OLD) which is the width in MM between the insides of the two dropout faces, and is the same as the outside locknut dimension of the hub. 7 speed stuff is old enough to be harder to find in shops, so look at ebay or used, and get a rear hub + spares that way. – Criggie Nov 16 '17 at 3:59
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    The direct drive trainer most certainly has a cassette interface which is very likely to take 7-speed cassettes as well 9/10/11-speed, You'll probably just need the correct spacer(s). It's worth a try. – Carel Nov 16 '17 at 11:44
  • As a follow up question - if I were to get a 7 speed cassette, would I need to ensure that I get the same size cogs that I have on the current bike? It seems like my rear wheel cluster has 14 teeth in the smallest cog, and 29(?) teeth on the largest one. It doesn't seem like they make that size cassette, as best I can tell – btoconnor Nov 16 '17 at 13:20
  • Shimano have a 12-28 teeth 7-speed cassette. If you search the net you'll find plenty of sellers. Or since you mention your LBS take the trainer (and the bike) to the store and have them fit a cassette with the correct spacers. And you may fit any cassette that is compatible with the range of your rear derailleur. – Carel Nov 16 '17 at 17:16
  • I have successfully used two different 7 speed wheels in a bike. One has 7 speed cassette on a spacer on an 8/9/10 speed freehub, and the other has a high quality 7 speed freewheel on a Mavic hub. Friction shifters would make it easy, but I have indexed stem shifters cos that's what I had. – Criggie Feb 4 at 3:08
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Yes the Direct Drive Trainer (DDT) should work fine with your bike and yes you're on the right path...

  1. You will need a 7 speed cassette and 4.5mm of spacers for a 7 speed cassette to fit on a freehub designed for 8/9/10 speed cassettes. If the DDT has an 11 speed freehub you would need an additional 1.85mm spacer and maybe a 1mm spacer. Yeah, lots of spacers...

  2. Before buying your DDT make sure it supports your bike's rear wheel spacing: 130mm and 135mm are the most common. BUT some of the older 7 speed bikes also used 126mm. An inexpensive Walmart bike likely has flexible tubing in the rear triangle so even if yours measures 126mm it could be forced to fit 130mm. But just to be safe, remove the rear wheel and measure the inside distance between the dropout faces. If the bike isn't 130mm then you should also see if it is easy to pull apart the dropouts 5mm. If the frame is made of aluminum frames tend to be much less flexible than steel frames.

Also note that since you're going to want to reinstall the rear wheel at some point you're not trying to permanently bend (aka "cold set") the frame but rather just coercing the frame to fit the 130mm trainer. Steel in particular is very forgiving so flexing it a bit won't do any damage.

Yes the number of teeth in the largest cog does matter. If the new cassette has a lot more teeth then the chain may be too short and need replacing. Alternatively you can use the too short chain and just make certain to not shift onto a rear cog which is too big. Doing so typically causes the rear derailleur to bend and get forced into the rear wheel. Never a happy ending...

7-speed cassettes and freewheels have the same pitch: pitch = width_of_cog + width_of_spacer

So whatever shifters you have on your bike should work fine with the 7-speed cassette instead of freewheel.

The adjustment for shifting may be off a bit so don't be surprised if you have to do some derailleur adjustment.

There are bicycle co-op's and other similar bicycle advocacy organizations which recycle and rebuild donated bikes. If you have one nearby they should be able to provide a very inexpensive used cassette and maybe even some spacers.

  • Would the downvoter like to comment ? – Criggie Mar 5 at 6:51

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