IntoTheWild

Does anyone know what exactly is involved in converting a 2012 model Trek 820 to an 8 or 9 speed drive train? I've read that some of the newer 7 speed bikes use an 8speed freehub with a spacer, so in such cases it should be easy to just throw an 8 speed cassette on. I'm sure a new shifter would be needed, not sure about the derailleur though.

JiveTurkey

The cassette, chain, and rear shifter must match in speeds. It's ideal if the FD speed matches.

You need to determine if it's really a cassette or freewheel you have. If freewheel, you'll also need a new hub (though a whole wheel will be easier).

Pretty sure the 820 has a freewheel. This upgrade would cost so much, you're better off selling the bike and getting a different one.

IntoTheWild

I didn't think multispeed freewheels had been used on bikes in a LONG time.

JiveTurkey

Any department store bike and shop bikes with lower-end components will have a freewheel. The 820 fits the latter category.

jimc101

The 820 comes with a Formula FM31 rear hub, which is a freehub (should read freewheel)https://www.formulahubs.com/en/formul...=detail&aid=41

For upgrading to 8 or 9 speed, as JiveTurkey the easiest and probably cheapest option would be to sell the current bike, and get a bike with 8 or 9 speed already installed.

Would look at what you are getting into if buying 8 speed, as in all but the lowest groupsets, it's obsolete and you may have issues trying to get spares for anything less than 9 speed.

IntoTheWild

Hmmm... well if I leave it 7 speed, can I use a 9 speed rear derailleur on it?

JiveTurkey

That's not a freehub. It's a standard hub that takes a screw-on freewheel.

JiveTurkey

The RD doesn't care how many speeds the rest of the system is. It goes where the shifter tells it to, as long as it has has the same cable-pull ratio, which all indexed Shimano RDs and rear shifters adhere to except old Dura Ace and the new 10-speed Dina-Sys.

If you do replace the RD, make sure it is a long-cage MTB (SGS) so it can handle the triple crank and 32T or 34T largest cog.

IntoTheWild

Wasn't sure if the pulleys were compatible with the 7 speed chain. If I do replace the rear derailleur, I'll probably buy a new IRD screw-on 7speed freewheel, too. Interesting to find out it takes screw-on freewheels.

fietsbob

says FREEHUB ;Shimano TZ31 14-34, 7 speed
https://www.trekbikes.com/us/en/bikes.../sport/820/820

as usual , ask yourself what gear ratio specifically is not offered in those 7.. ?
I toured thru Europe with a 14-34t, 6 speed 50/40/24 crank. carrying my camping gear along.
you can add a cog and not gain a useful ratio at all ..

It's a decent entry level mountain bike.. want a 9 speed ? go shopping for an upgraded bike
for more $, sell the one you started with.
such as : https://www.trekbikes.com/us/en/bikes...ries/4300_disc

FastJake

What's your end goal here? An extra speed or two on a MTB really isn't much to go after IMO.

+1 that it would cost more than the bike is worth to upgrade to 8 speed, and even more-so if you want 9-speeds. For 8 speeds you'll need a new right shifter, 8S cassette, and a new rear wheel with a Freehub. If you want 9 speeds you need all of the above plus a new chain, and possibly a new crankset and front derailer if the front doesn't play well with the narrower chain.

IntoTheWild

JiveTurkey is right...the picture is of a hub that takes a screw-on freewheel. It's definitely not a freehub.

IntoTheWild

To replace the rear derailleur with a low-normal model. But all the low normal models are made for 9spd drive trains. I know they'll work on 8, but I've never tried one on 7. However, if it'll work on 7, then sticking with 7 will be fine.

fietsbob

the 'speeds' is detents in the shift lever..

the RD is a parallelogram, just has 2 limit screws ,
a B screw around the mounting bolt,
and a cable clamp screw. and a return spring to take up cable slack.
it has no 'speeds' , it shoves the chain back and forth .

want a low normal RD go for it,
buy local and you might be able to return it if it doesn't work
or have the LBS, your Trek dealer, put it on.

IntoTheWild

lol...as if any local bike shop would ever carry a low normal rear derailleur.

fietsbob

they have distributors, and those UPS trucks, you just say what you want
and it will be there in a week .

maybe 2 since the season has slowed down.

FastJake

Well, 7 and 8 speed are basically the same. The width between cogs is a little different, but the RD doesn't care about that, the shifter does. I bet a 9S RD would work just fine on a 7S drivetrain.

If your current shifter won't work with a low-normal RD, you could find an old 7-speed thumb shifter and run that.

JiveTurkey

Why would you want a low-normal RD?

IntoTheWild

True, although I'd feel terrible returning a product that I asked someone to special order. I just assume order unusual products online. I go to the LBS to bike complete bikes or to buy common accessories that I know they'll stock.

I'm sure the standard 7 speed shifter would work fine. It pulls the cable the same amount, it's just the derailleur spring runs backwards.

The same reason I type on a Dvorak keyboard layout...because I've used it for a long time and it gives me a warm fuzzy feeling.

dscheidt

It might say that. It's dead wrong. The TZ31 is a screw on freewheel. In fact, any bike sold in the last few years with seven speeds has had a freewheel.

reptilezs

current 820s are freewheel. specialized has some hard rocks with 7 spd cassette. op should just buy an 8spd bike

joejack951

Man, some of you buys are really downers about upgrading a bike. With MTB's at least, increasing speeds is a relatively cheap endeavour if you search out parts wisely.

Deore shifter/v-brake set, $40: https://store.icyclesusa.com/shimano-...ed-p49870.aspx
Deore Cassette, $28: https://www.niagaracycle.com/product_...oducts_id=6298
Alivio front derailler, $28 (check pull/swing): https://www.niagaracycle.com/product_...ucts_id=509138
Deore/SUN CR18 rear wheel, $47: https://www.niagaracycle.com/product_...oducts_id=5105
9 speed chain, $20: https://www.niagaracycle.com/product_...oducts_id=2441

That's $163 not including the low normal rear derailler which isn't necessary. I don't think that's too bad for a complete bike makeover. Even added to the retail price of the 820, it's not a bad deal for a 9 speed MTB, especially when the purchase price is sunk cost and selling the bike will only lose the OP even more money.

reptilezs

free shipping? free labor? you think the op is capable of doing the work? 820 is a crappy bike

joejack951

So add $25 for shipping (probably won't even be that much). The OP didn't ask about molding a carbon fiber frame in his basement. Swapping shifters/deraillers is fairly basic stuff. I'm sure he can handle it. The 820 looks like a fine bike to me. If he has the money and the bike fits him well, I think it's worth it. He can make his own decision though. I laid out some prices at least rather than making the blanket statement that it's not worth it.

IntoTheWild

Haha...if only I had a basement. In any case, I can do most work other than build a frame from scratch or build a wheel from scratch. I wish I could do the latter.

The 820 seemed like a nice project bike...one of those things you can do a little to at a time. I imagine when I finish with it, it'll have as much money in it as a Fuel. The 2012 820 would look sweet with a Fox Fork =)