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8-speed cassette compatibility road/mountain.(9 posts)

8-speed cassette compatibility road/mountain.rtyszko
Jul 22, 2002 4:50 AM
Hey all. I would like to know if I can switch out my current 12-25 road cassette (Shimano) for something with a higher tooth count (12-28, 12-34)and have it work. Essentially, I'd like to gear out my road bike (Shimano 105 triple 8-speed group circa 1997)to do a lot of steep climbing. Does my rear deralleur cage length matter? I measured them, and my LX cage is definitely longer so I was wondering if that matters. Also, what are the cog numbers that are included in the higher cassettes from Shimano?

Any help would be appreciated,

Bob Tyszko
It'll work, just be careful of rear der. capacityOffTheBack
Jul 22, 2002 5:28 AM
In other words, don't shift into 53x28. When you install the cassette, just check which gear combinations would over-stretch the rear derailler (or cause it to go slack, like maybe 39x11) and don't use those combinations.
It'll work, just be careful of rear der. capacityrtyszko
Jul 22, 2002 6:06 AM
off the back,

So if I spin the higher tooth count in my granny gear up front is should work? I really don't intend on running say a 53 to 34 combo anyway.

BT
Rear derailleur capacity.Spoke Wrench
Jul 22, 2002 7:29 AM
There are two different factors.

The first is largest rear cog. Shimano rates all of their road derailleurs for 27 tooth largest cogs. Some guys say they have been able to cheat a little with this, but I personally havn't had good luck in that respect. The issue is that the upper jockey pulley rubs against the largest rear cogs. The solution is to use a mountain rear derailleur which is rated for 32 or 34 tooth cogs.

The second is chain wrap up. Shimano road derailleurs are rated at 29 teeth for the short cage version and 37 teeth for the long cage. Mountain derailleurs are rated from 33 to 45 teeth. If your derailleur doesn't have enough wrap up capacity, you will either have a slack chain in the little/little combination, or twist your derailleur cage into the spokes in the big/big combination. I wouldn't worry about a chain that is a little too long if I had a triple in front. You'll never accidentally shift into the little/little combination if you have a granny ring.
I'm not planning on shifting out of the granny ring up frontrtyszko
Jul 22, 2002 8:04 AM
Thanks for the input. I'm not planning on shifting at all in the front. I just purely want to stay in the little ring up front and have access to two to four rings out back. Literally I just want to sit and spin much of the assent. Would chain wrap then matter? I could always shorten my chain to solve the other problems (but I doubt I'd have too much chain slap to bother) Any further thoughts?

BT
I ran 8 speed ultegra with an 11-28 cassetteOffTheBack
Jul 22, 2002 10:35 AM
on my rain / beater bike for a long time and never had any trouble. That was with a regular short-cage ultegra road derailler and double crankset. Of course, a triple crank with a tighter cassette is a better setup since you can get closer spaced gear ratios, but if you're on a budget, this way works. Good luck!
Plans...grzy
Jul 23, 2002 5:54 PM
Plans are made to be broken. Or something like that. As much as you tell yourself you'll never shift into a big/big combination with too short a chain you'll be right 99.9% of the time. However, that 0.1% when you forget it's going to cost you. Get yourself a long cage rear deraileur and put your mind at ease.

Another issue is that you typically need to install a 1.1 mm spacer bewteen the cogset and the freehub or else the whole cogset is left loose and sort of floats around on the hub body. This makes for really poor shifting. It's a subtle thing and it depends on you exact components, but the problem you're looking for is the lock ring bottoming out on the freehub body, not the cogset. You can actually feel the play in the cogset with your hand.
re: 8-speed cassette compatibility road/mountain.louiemtb
Jul 23, 2002 5:43 PM
I have been using an eight speed 11-30 XTR cassette with a 39-53 ultegra crank (6500), ultegra short cage derailler (6500) and have had no problems, works great.
Louie
Thanks, what I tried is workingrtyszko
Jul 25, 2002 1:35 PM
So I tried it. I'm running a 105 triple up front (53-42-30) and a 12-28 out back and it works fine. I do hear a bi of chain rub in the big-big set up but it shifts fine. I have not noticed any play in the cassette, but I'll check it tonight. The spacer idea seems like a sound one. Thanks again all. It's great to have a forum like this.

BT