MAK

I currently have a 30t SLX crank and 11-42 SLX cassette with an SLX rear derailleur on my mountain bike. I'm thinking about changing the cassette to a SLX 11-46 for more climbing range. I expect that I'll need a new chain. Will I also need to replace the rear derailleur? I'd like to stay with an SLX. Are there different SLX models? If so, which is preferable?

Thank you

cobba

What model SLX derailleur do you currently have?

RD-M????

jimc101

New chain yes, on the basis you have an M7000, read the specs

taken from CRC

Shimano SLX M7000 11 Speed Rear Derailleur

The rear SLX M7000 series derailleur was totally redesigned to incorporate premium features from XTR and Deore XT. The SLX RD-M7000 rear derailleur features Shimano's Shadow RD+ technology and a refined geometry for increased stability.

SLX series Shimano Shadow RD+ derailleurs use adjustable stabilisers for either maximum stability or lower shift effort.

Features:

• Shifting Action: Shadow RD+
• Mount Type: Direct attachment (Conventional)/Direct mount compatible (w/o bracket spec available)
• Maximum Sprocket: 42T(2x11-speed); 46T(1x11-speed)
• Minimum Sprocket: 11T
• Front Difference: MAX 10T
• Total Capacity: 41T
• Average Weight: 323g
• Shadow design with optimised, shallow slant angle, low profile design
• 20% reduced shift effort
• Chain stability improved
• Improved driving and shifting stability
• Adjustable clutch tension
• High efficiency pulleys
• 1x11 and 2x11 compatible

MAK

I believe that it's the M7000 but I couldn't find anything on the derailleur itself indicating the exact model number.

MAK

Although it doesn't say on the derailleur itself, I believe that it is the M7000. From the spec sheet you sent, it appears that the 46T cassette will fit the 1x11. Thank you.

base2 

Another thing you should ask yourself: Is 1.8 gear inches worth it?

Based on 29'er 42 wide tires (622x42) you go from 20 gear inches to 18.2 gear inches. It seems to me that on any terrain requiring such gearing is too steep to get traction, the wheelie factor is too high, or the goings are too slow to stay upright.

Regardless of tire size, It's up to you whether ~10% lower bottom gear in this case is worth the marginal utility. I'm not sure it is in actual practice.

Retro Grouch 

I didn't take the time to calculate the ratios, but I believe that could be right. If you are a digital thinker, you will probably fret endlessly over that 1.8 gear inches. 18.2 is definitely lower than 20 but not enough different to matter to me.

Retro Grouchery is good.

tyrion

Not in my experience. Lower gearing allows me to deliver power more smoothly hence retain traction that I couldn't with higher gearing. Sometimes 18.2 GI vs. 20 GI is the difference between pedalling and walking.

MAK

I hear what you're saying. FWIW...The tires are 27.5+ x 2.8. I'm at work so I had little time to research. Sheldon Brown's Gear Calculator doesn't list my size tire and the few I Googled weren't helpful. I will look again tonight. I'd really like to get exact numbers to make an informed decision.

base2 

Arguing individual experience or minutia of local conditions is a fools errand. I was merely suggesting it may be a good question for the OP to ask him/herself.

In my experience on non-pavement surfaces there is a point of diminishing returns. Only the OP knows whether such a setup is suitable for where he/she rides.

I have a mountain bike that bottoms out at 15 gear inches. It's so ridiculously low as to be completly unusable on steep grades with anything less than perfect traction. Even with good traction there isn't enough purchase with every pedal revolution to get meaningful foreward movement. The wheel base is too short for the delicate balance between traction & wheelie for all but the shortest climbs. The bottom gear on that bike is essentially wasted insurance against a set of conditions that so rarely exist off-road it's not worth having.

My touring bike with 20 inch stays & 15.3 gear inches on the otherhand has been proven more than useful on pavement. 70+ pounds of gear up 22% grades 3.5 mph at a passable (80rpm) cadence.

We don't disagree, as far as I can see. Surely theres no problem with asking someone to consider whether the proposal will meaningfully solve their perceived problem. The OP'S intended use, local conditions, as well as other factors should be considered.

Maybe there is 1 specific hill the OP thinks the new cassette will help with.
Maybe he/she never intends to go off-pavement.
Maybe leg strength/cardiovascular ability are part of the equation.
Maybe he/she just likes spending money or someone told him lower gears is always better.
Maybe an e‐mountain bike is in the picture...I dunno & neither do you. The OP never specified.

Dropping $80 to not solve a problem is something I know I'd regret. I know. I've done it enough times to recognize & appreciate when someone asks me to hit the pause button.

Will it fit? Yes.
Is it a good idea? It depends. There are use cases where in can be appropriate & some where it might not. It's worthy of thought. Thats all.

Cheers!

base2 

Something like this?

tyrion

Of course not. Neither are anecdotes of said proposal solving problems.

base2 

Of course not. Like you, citing one anecdote where it was appropriate, I shared one where it was appropriate, & one where it wasn't.

This is why I rarely frequent BF anymore & just ride my bike. Quit trying to make an argument over nothing but well wishes & advice shared in good faith.

Sheesh.

tyrion

Lol.

tomtomtom123

I surpass all of youuuuuuuuSSSS! I've got 14 gear inches. Beat that.


So, 46/11 = 418% range. Seems ok. If you assume 26 inch diameter tires, and a 30T chainring, that would be 17 to 70.9 gear inches. But you'll have very wide gear spacings.
42/11 = 383%

I have a 10 speed 12-34T cassette, and 24/44T double chainrings on a 20" wheel, effective diameter of 19.8". It gives me 519% range. 14 to 72.6 gear inches.

Closer spacing at high gears, and big 6T jump at the bottom. I'd like to reduce the 13.3% by inserting a 16T, but it ruins the rest of the spacing at the bottom. I'd then have to settle for a 30 or 32 cog which would increase my lowest gear to either 15 or 16 gear inches.



Oh, I missed the post where you said 27.5". Opening a spreadsheet and typing in formulas is the easiest way to figure out how to modify your drivetrain. The formula is easy Chainring / Cog X tire diameter = gear inches. Once you've got a table, you can copy and paste it over and over again, and enter different cog/chainring sizes to compare how you like each of the different setups. If you don't have Openoffice, you can simply use Google Sheets.
The best way to get accurate numbers is to roll your bike while sitting on it, and measure the distance of maybe 5 revolutions. Divide by 5 and 3.1415 and you get the effective tire diameter. Air pressure and amount of load on the bike will affect the measurement.

My normal easy riding speed on flat, smooth, level ground is around 60 gear inches. Sometimes I run out of gears at the top at 72.6 gear inches, pedaling at 90 RPM, at 31.2 kph, while going downhill, but it lasts only a couple minutes per hour and I simply coast down. I'd only lose a few hundred meters of extra distance per hour by not having the higher gear. But having the low gear makes the difference of whether or not I have to get off and push.