Can I use an 8-speed cassette on a 7-speed hub?

Question

I have a spare tire with a 7-speed cassette, but I want to put an 8-speed cassette on it with a set of 'slick' tires for pavement. Can I just toss an 8-cog cassette on, or do I need to replace the hub (I know you can put a 7 speed cassette on an 8-speed hub by adding spacers, but I wasn't sure if the reverse was true or not). Thanks!

Answer 1

Unfortunately, that is out of the question. 7speed cassettes only interchange with the old 6 speed freehub. 8 speed only interchanges with 9 speed on the freehubs. Let me explain with the Shimano example. 6 speed came first. Then, Shimano fit 7 spockets on the existing 6 speed freehub body by narrowing the space between sprockets. 8 speed came along shortly after which required a longer freehub body. So, what happenned? Shimano decided to add 9 sprockets by narrowing the space between sprockets. For these reasons, there is no easy solution.

Answer 2

Two options:

You can get an LX 9 speed cassette and a 12t lockring. Discard the 11t. This will put 8 into the space of 7. But, a 9 speed shifter is required.

You can also do the exact same thing with an 8 speed cassette. Remove the 11t and buy a 12t lockring. However, you will need some sort of small spacer, such as stuffing a non-top position 9s gear onto the back of the cassette (like a 13t/14t) Add however much aluminum stove pipe tape is required for correct spacing.
Now you've put 7 speeds onto a 7 speed hub, but with compatibility to an 8 speed shifter.


Oh, but I've got a huge question over the "slick" tires. While barely functional on pavement, due to the lack of tread making for 100% contact of the sticky rubber to contact the road for a big slowdown and being unable to stop on the wet pavement, there's only one real use for mountain bike slicks.
The lighter weight makes for extra speed up hills. However, the typical slow nature does usually make for lower average speeds than if you just kept the knobbies.
Okay, Tioga's slick really is fast, but it has put a few people in the hospital from slipping out on corners and simply wrecking in the wet.

But there are fast tires for the mountain bike:
And, you can stop.

For $9, there's Kenda Kross Plus (plus version is lighter weight and always has the big yellow label on the side. Inferior versions don't have the yellow label).
Works so very well on gravel and is very fast on pavement.

Schwinn Typhoon Cord (available in all black) is wildly fast on flat ground and easily keeps up with racing bikes as long as the front tire is about 40 pounds and the back tire is about 60 pounds. This is more than the label recommends, but mine have just over two thousand miles so far. At 980 grams, they're not so hot on hills--until your speedometer passes 44 on the way down the other side. ;)
Featherweight high performance XC racing inner tubes help a lot.


Panaracer Pasela Tourguard Folding at 26 x 1.25 (plus the specialty inner tubes for that size).
They do have some tread and do stop on wet pavement. They're also pretty darned quick. Not as fast as the Schwinn Typhoon on flat ground, but still a very high performance tire. At an extreme light weight bracket, climbing hills is very fast, unlike the majority of mountain speed up products. The Pasela is a real road bike tire.

The Pasela goes only onto an XC racer with XC rims (the narrow mountain bike rims). It should also be used on a bike with the optional XC road race gearing. That is an 11-32 cassette plus a 28-38-48 crankset for racing gears that are high and tight. Why? The 11-32 has narrower gaps for better road use. The 28-38-48 crankset is high enough to make up for the fact that you have installed a much smaller tire.

Note: Nashbar has a sale on a black Shimano 105 crankset that can be operated with an LX (made for 48) front derailleur. This is a good replacement for a 22-32-44 crankset because the 105 9 speed has far lighter weight and efficient alloy chainrings. Yet, there's almost no real advantage to replacing a 28-38-48 if you happen to already have one in place.

With the XC road system (or your own version) performance can be identical to a 650 road race bike. That's because authentic road tires fit the XC and there's not much difference in the bike.
In fact, drop bars that fit mountain bikes are available and don't cost much. Controls go cyclocross-style, very close to the stem. Even better areo plus great comfort is available with the extra narrow 19" alloy version (Nitto) of "North Road" 3 speed looking bars if they are installed upside down, wrapped like drop bars, and have the controls across the front (time trial style). The "wilted arrow" is far and away faster than drop bars, but never caught on because it is homely. Leverage for hills is gained by angling the backswept portion downwards a bit, which is also a more-natural wrist angle. There's something else normally seen on a 650, but your friends will think you're weird. ;)

Anyway, should you enjoy your mountain bike and not want to turn it into a road bike, just get a pair of the gravel-and-pavement-loving Kenda or the super-fast flat-free Schwinn tires. They're both big and won't reduce your gears. I've tried both, and hey! They're fast and they don't remove features from your mountain bike. Unlike moutain bike slicks, you'll think that 22mph is bad news, like the brake must be rubbing or something. ;)

Answer 3

7 Speed Hub

Answer 4

NO. Why would you?

Answer 5

NO!!!!!!!!!!!!!