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Franken-drivetrain Problem(9 posts)

Franken-drivetrain ProblemTWD
Mar 18, 2003 4:04 PM
Can any of you velo-gurus help me out with cx drive train problem.

Here's the deal, I'm currently running 2 wheel sets on my cross bike (one for winter road riding and 1 for CX racing/offroad adventure type rides). The bike shifts fine with one wheelset, and horribly with the other.

The stock setup that came with the bike was 9spd 105 STI shifters, an 11-32 Sram 9 speed cassette, and an XT long cage rear derailluer. This is my off-road setup and the bike shifts fine.

When I swap to the road wheels, I'm running a 12-25 shimano 9 speed cassette. Bike shifts like crap with this setup. The shifts are innaccurate, delayed, and no amount of fiddling with the adjuster barrel can get it to shift correctly. Upper and lower limits are fine for both cassettes. Adjusting the B-tension screw didn't seem to do much either way.

What baffles me is that when the bike was new, I never seemed to notice any shifting problems when I swapped over to the road cassette.

The only thing that I can think of that has changed is that I'm running a differnt crank (24-34-46 triple vs. 36-48 double that came on the bike)with a slightly different chainline.

I've got my chain as short as I can get it, so that isn't an option.

Any other ideas, or is running a road cassette with XT derailluer not going to cut it?

Thanks in advance
Is the chain brand spanking new?Ahimsa
Mar 18, 2003 4:46 PM
Or did ya put a few miles on it with the off-road cogset?

I'd say that it might be differing wear patterns on the two cogsets.

Just a thought.

Cheers!

A. (Non-guru)
re: Franken-drivetrain Problematpjunkie
Mar 18, 2003 4:54 PM
could be the chainline going from double to triple but I think it may be chain length. A chain that is set up length wise properly for a 11-32 is going to be too long for a 12-25. It may be flappin and slappin in certain positions and this problem will be amplified by the triple set up. Swith the offroad cassette to an Ultegra 12-27 set the chain length up for it and you should be fine. You really don't need a 24-32 anyway. 24-27 should do ya fine.
re: Franken-drivetrain ProblemTWD
Mar 18, 2003 10:35 PM
Thanks for the input, I kinda figured it was a chain length issue.......and that I would get the "ya don't need a 24 -32" :-)

Not so sure I can ditch the 32 though. Under normal riding conditions no.....I wouldn't need anything close to a 24-32 combo.

However, my idea of a normal ride goes something like what I did last saturday - 60 mile hilly road ride with the local club (i.e. hammerfest). Stopped by the house for a bite to eat, then picked up the family and headed out for an off-road ride.

The off-road ride went something like this - 10 miles of flat to rolling pavement to the trailhead, then immediately start a 4 mile fire-road climb (average grade = 8.5% with several pitches nearing 20%)on loose gravel. Oh yeah, forgot to mention I was pulling my son in a burley trailer (total weight = about 50 lbs). I weigh about 220 myself without riding gear, so total weight of about 280 with trailer, water, tools, light system and battery etc (yeah, this finished up as a night ride).

I grunted up that stinking climb in my 24-32 most of the way except for two spots where it eases a bit. The cross tires just won't bite into the loose gravel on grades that steep lugging that kind of weight, so I had to remain seated pretty much the whole way. Even seated, it was hard to keep the front wheel on the ground on some parts.

I made it though, got to soak in a nice view, then turned around and headed the 14 miles back home, all downhill or flat thank goodness.

My philosophy is "Hey, I'm a clydesdale, I might as well be pulling something right?"

I'll have to post a ride report with photos, since the cross board has been kinda slow as of late.
re: Franken-drivetrain Problematpjunkie
Mar 19, 2003 1:13 PM
I'm a Clydesdale as well. 230 right now. will be toting a trailer later this year. good to know. My race bike is a double 48/36 with a 11-30 XT 8sp Cassette. My commuter/adventure bike/Racer is 48/36/26 with a 11-27 9 sp rear. Do stupid rides like yourself (no offense)
but sans trailer and kid. I may have to get a cassette like that this summer.
You may just need to knock out about 3 links of your chain when you switch to that road casssette or switch it to a 12-27 and then your chain lengths are more similar. Then it's only a 5 tooth gap vs a 7 tooth gap. I wish Shimano would make a 11-30 9sp. then we'd be set.
Follow up thoughtTWD
Mar 19, 2003 4:25 PM
Hmmmm,

Just had a thought, my wife's got a 12-27 cassette on her cross bike, and I have had to steal her wheels for a day in the past. If I recall, I don't think it shifted any better, however, my chain length was still the same.

Here's how the three cassettes compare tooth wise:

Sram 7.0 (11-32) 11, 12, 14, 16, 18, 21, 24, 28, 32
Ultegra (12-25) 12, 13, 14, 15, 17, 19, 21, 23, 25
Ultegra (12-22) 12, 13, 14, 15, 17, 19, 21, 24, 27

The 11-32 shifts fine in all gears throughout the range.
Looking at the 12-25, theres no more than 1 tooth difference from the 11-32 in the five smallest cogs.
So, you would expect my shifting troubles to come in a the largest three or four cogs of the 12-25 cassette.

Oddly enough, most of my shifting problems occurr in the middle of the cluster.

I guess the real problem is that with the chain length set to handle a 32 (in reality I've shortened it so that I can't really get into the 32 from the big ring anyway) it can't handle the shifts between cogs that are only 1 tooth apart. In other words, on the 11-32, shifting from my 14T up to the next bigger one is a 2 tooth jump to a 16T. On the road 12-25 or 12-27, going from the 14T up to the next bigger one is a 1 tooth jump to a 15T.

Must just be more finicky towards chain length making the smaller jumps.

So, as you suggested, I could run a 12-25 on one wheelset and 12-27 on the other and shorten my chain a bit more.

But running a 12-27 on one and a 11-32 on the other won't gain me anything.

Does that make sense to you?
Follow up thoughtatpjunkie
Mar 19, 2003 5:13 PM
makes sense. I would think the middle would be the problem just from extra chain length. This is where shifting problems usually arise. It's that length of chain that seems to be the problem. Just for an experiment, set it up for a 12-27 with one extra link so you can easily get it into a your big chainring, big cog(27). set it up so it shifts smoothly. Now throw on the 11-32 and see how it goes. just don't go big chainring big cog. The extra chain should handle the 28 and this may work. Like I said, Hey Shimano wheres the 11-30? I have an 8 sp version I love.
Follow up thoughtTWD
Mar 19, 2003 11:54 PM
Yup,

I ran 11-30 on the mtb for years and still do on the tandem and on my wife's mtb.

I'm waiting for my STI levers to die, then I'll think about scrounging up some 8 spd bar ends and going back to the trusty old 11-30.
11-30atpjunkie
Mar 20, 2003 6:54 PM
Yup. and I run a 1997 era XT rear der. still the most trusty der. shimano ever built. Run bar ends on both my crossers, couldn't be happier. 9sp on one 8 on the other.