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Zurichman

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Reply with quote  #1 
I need some info and ASAP on my Raleigh Roker Comp

It is in route via Bike Flights so I can't see what front gearing it has.

I am guessing a front sprocket of 42 tooth but not sure.

I just signed up for the Bootlegger 100 and have read that it is super hilly and the toughest gravel race some folks have done. For that reason I want some lower gearing for a back up.

I know I have 11 x 42 on the rear and they make a 11 x 44 for the rear.

somebody mentioned a 38 tooth for the front but that seems like a big drop down from the 42 if that is what the bike has. I am not a gear head or know much about gearing as most on here know. I will sacrifice some top end speed for some better climbing but I still want to keep as much top end speed as I can for the down hills.

I know I read about 3-4 riders on here that had the 2017 Roker Comp. Maybe they can chime in here as to what the exact front sprocket is.

I do appreciate any and all help.


Thanks
Zman

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drwelby

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Reply with quote  #2 
It's supposed to have a 42.

Dropping to a 38 drops the gearing by just under 10%. In the low gears, each shift between cogs on that cassette is between 14-17%, so switching to that size ring will drop the gear by less than "one shift". If you want it to change by something closer to one shift you'd want a 36 tooth chainring.

You could also swap to an 11-46 cassette (Shimano or Sunrace depending on how you want the gears distributed), but 42 to 46 is also about 10% lower. The rear derailleur is officially rated only for a 42 but others here have used it with a 46 without problems.

Changing the chainring is the easiest - all you would need is an allen wrench. It's possible you might need to shorten the chain.
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Zurichman

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Reply with quote  #3 
drwelby I think I am getting what you are saying.

If I just change out the front sprocket only to a 36 if will give me a 1 shift lower gear. If I switch out to the 38 I get less than 1 shift lower gear. Do you happen to know how much this changes out my top speed with the 2 different sprockets.


Thanks for you reply/help
Zman

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drwelby

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Reply with quote  #4 
At the top end you'd also lose one gear. 36 x 11 (first cog) is almost the same as 42 x 13 (second cog).

Here's the comparison
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NoCoGreg

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Reply with quote  #5 
Zman - The difference between gears on your cassette vary between 12% and 18%.
42/36 = 16.7%
19/17 = 11.8%
13/11 = 18.2%

So if you split the difference and say there's an average of 14% difference then to get one gear lower you'd need to buy a 37t chainring:
42/1.14 = 37t 

If you want 2 gears lower you'd need to get a 32t chainring:
37/1.14 = 32t

Conversely going to a 44t cassette will only get you about a third lower gearing:
44/42 = 4.8%

To get a full gear lower by moving to a larger cassette you'd need to get:
42*1.14 = 48t

Note that if you do get a smaller chainring (say 38t), you'll may be spending more time in the smaller cogs on your cassette, which is where the gear-to-gear changes are larger.

Also note that you may need to shorten the chain if you go for a 38t chainring. A shop should be able to guide you on this.  If you think you'll want to move between setups you can get a 2nd chain and masterlink (Shimano chains use a special pin that is expensive to replace, instead consider consider SRAM, Wipperman or KMC chains - all are good quality and have master links).  

Hope this helps,
Greg


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Zurichman

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Reply with quote  #6 
Quote:
Originally Posted by NoCoGreg
Zman - The difference between gears on your cassette vary between 12% and 18%.
42/36 = 16.7%
19/17 = 11.8%
13/11 = 18.2%

So if you split the difference and say there's an average of 14% difference then to get one gear lower you'd need to buy a 37t chainring:
42/1.14 = 37t 

If you want 2 gears lower you'd need to get a 32t chainring:
37/1.14 = 32t

Conversely going to a 44t cassette will only get you about a third lower gearing:
44/42 = 4.8%

To get a full gear lower by moving to a larger cassette you'd need to get:
42*1.14 = 48t

Note that if you do get a smaller chainring (say 38t), you'll may be spending more time in the smaller cogs on your cassette, which is where the gear-to-gear changes are larger.

Also note that you may need to shorten the chain if you go for a 38t chainring. A shop should be able to guide you on this.  If you think you'll want to move between setups you can get a 2nd chain and masterlink (Shimano chains use a special pin that is expensive to replace, instead consider consider SRAM, Wipperman or KMC chains - all are good quality and have master links).  

Hope this helps,
Greg




Thanks for this info Greg. This is a tough/hard learning curve for me coming from the roadie end where I have triples and all you do is change out the cassette on the rear for lower gearing.

If I am reading this right a 37 front would work and then Dr. Welby posted above that I could go to 46 rear with no problems. Now all I have to do is find a 37 front gear.

Where I am coming from is I plan on doing the Bootlegger 100 in Lenoir NC in April and have read/heard it is one of the toughest climbing/descent gravel races out there. With it being so early in the season and being up North here I am not going to get a chance to be in late season form so hoping to get all the help I can get.

Thanks again
Zman

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Zurichman

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Reply with quote  #7 
NoCoGreg, drWelby or others. Sorry but I don't know how to read gearing charts. So I ordered a 38 front tooth Sram Force 1x-Sync from Art's Cyclery. Looks like Sram doesn't make the 37 tooth.

To get the 1 gear lower or maybe more than 1 lower gear do I need to order the 44 or 46 for the rear. I will try and look at the gearing jumps but what would be the difference there in the top end gearing/speed then?

Any help is greatly appreciated.

Thanks
Zman

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Skldmark

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Reply with quote  #8 
Zman, what you need is the IVCV Transmission- Infinitly Variable Constant Velocity.
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dangle

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Reply with quote  #9 
Narrow wide rings (used for 1x systems) have to be evenly numbered so there's always a narrow, then a wide tooth. You would have to choose between 36 and 38 and it looks like you chose 38.

I'm 93% sure nobody makes an 11-44 cassette, but even if they did, that 44 cog would be the only difference and it would be less than 5% lower than a 42......which is why nobody makes one.

The 11-42 and 11-46 from Shimano are identical, except they throw a 46 on instead of the 42. It's 10% lower. It's really up to you to decide if spending nearly $100 to have a slightly lower bail-out gear is worth it. A 38 front and 42 rear is already really low. If you were pedaling in the 38/42 at a cadence of 70, you're approaching walking speed.

"Run what ya brung." and "Don't try anything new on race day." come to mind here.

Enjoy!

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NoCoGreg

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Reply with quote  #10 
Zman - if you go to the gear calculator link below it's setup to show a 38t and 42t chainring and 700x40c tires.
http://www.gear-calculator.com/?GR=DERS&KB=42&RZ=11,13,15,17,19,22,25,28,32,36,42&UF=2240&TF=90&SL=2.6&UN=MPH&GR2=DERS&KB2=36&RZ2=11,13,15,17,19,22,25,28,32,36,42&UF2=2240

Additionally the calculator shows speed at a 90 rpm cadence.  With the 42t chainring and11t cog, you'll be going about 29 mph.  Going to a 38x11 you're at 26 mph.  In first gear, the 38x42 combo, you'll be moving between 6 and 7 mph at 90 RPM.  If it's really steep and you're in diesel mode at 60 RPM you'll be down to 4.5 mph.

I took a quick peek at the course on Strava and some ride reports and yes this ride sounds brutal.  With 10,000+ ft of climbing over 100 miles you'll have a nice long day.   

IMO to decide how low of a gear is needed, find out how long the steep sections are and see how you do on similar grades in your area.  Yeah, you'll be more tired when you hit steep sections late in the ride but one can usually zig-zag across the road to reduce the effective grade.  There are stages of the Giro and Vuelta where the finish has been on hills with long 25% grades and all but the strongest climbers will be winding their way up the grade.  Standing on a long grade can do wonders for resting the quads before returning to "the grind".  I'll always shift up a gear or two before standing as I prefer a much lower cadence while standing.

Back to the cassette options, a 46t is 9% lower than the 42t - this difference is 2/3 of the other gear jumps.

If your derailleur can handle an 11-46 cassette, then using the 11-46 cassette should eliminate the need for adjusting the chain length as the 4t larger cog will compensate for the 4t smaller 38t chainring.  You can enter the 11-46 cassette cog sizes in the above calculator to see how it compares.

Greg

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Zurichman

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Reply with quote  #11 
Quote:
Originally Posted by dangle
Narrow wide rings (used for 1x systems) have to be evenly numbered so there's always a narrow, then a wide tooth. You would have to choose between 36 and 38 and it looks like you chose 38.

I'm 93% sure nobody makes an 11-44 cassette, but even if they did, that 44 cog would be the only difference and it would be less than 5% lower than a 42......which is why nobody makes one.

The 11-42 and 11-46 from Shimano are identical, except they throw a 46 on instead of the 42. It's 10% lower. It's really up to you to decide if spending nearly $100 to have a slightly lower bail-out gear is worth it. A 38 front and 42 rear is already really low. If you were pedaling in the 38/42 at a cadence of 70, you're approaching walking speed.

"Run what ya brung." and "Don't try anything new on race day." come to mind here.

Enjoy!



Thanks Dangle and NoCoGreg I have a good month to try and get the gearing worked out. I have A 7-8% 3 mile mt. gravel bike ride I can do hill repeats on and a 2-3 mile roadie climb with 15% for the last 300 yards or so that I could train on. The kicker is the weather just isn't cooperating too well here and that is what has me scared that I can't get enough training in on time. Today in Pa. was 34 deg. F with 12 mph winds making it a wind chill of 26 deg. F. I can't ride in those kind of temps anymore. I will try the 38x42 before I go with the 46 rear cassette as I could climb my local mt. with the stock gearing so with a little bit of luck and hopefully some training should be able to make it through this ride. I just don't want it to be a death march. It probably isn't worth it to spring extra money on the rear cassette also as hopefully I can get myself in better race/riding shape this summer.

Thanks again
Zman

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Zurichman

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Reply with quote  #12 
Kind of last gearing question I hope as I hope to get the bike set up the way I want it when spring breaks here and get some training on it before The Bootlegger 100.

This is what I see.

Sram PG-1130 cassette now with Sram PG-1130 chain

stock 11-42
11-13-15-17-19-22-25-28-32-36-42

Shimano 11-46
11-13-15-17-19-21-24-28-32-37-46

Shimano 11-42
11-13-15-17-19-21-24-28-32-37-42

I see that the Shimao you can by in
XT CS-M8000 most expensive
or
SLX CS-M7000 less expensive and can buy it for $53.27

When I was reading the comparison between the two I read this. Available with 110mm/148mm boost option what is that?

For only $53.27 I can justify buying the Shimano 11-46. The higher gears look better than what I have on the bike stock right now. Yes the lower gears have some big jumps in them but I won't be mt. bike with the bike that often so this should work. In the future probably over next winter I will be buying a lighter wheel set but not int he cards right now.  

The Shimano 11-46 will work on my Sram bike right. If I read the post right above sine I would be switching from 42 - 38 up front and then from 11-42 to 11-46 on the back I shouldn't have to change out the chain. No big deal if I have to though. I think I did ead from drwelby that the rear derailleur is only rated for 11-42 but the 11-46 would work.

Thanks for all the help on this forum to the newbie rider.

Zman

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AlanEsh

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Reply with quote  #13 
Quote:
Originally Posted by Zurichman

When I was reading the comparison between the two I read this. Available with 110mm/148mm boost option what is that?

Boost spacing refers to the width of your frame or fork, or how much space there is between the dropouts. Roker won't have boost spacing.

Quote:

For only $53.27 I can justify buying the Shimano 11-46. The higher gears look better than what I have on the bike stock right now. Yes the lower gears have some big jumps in them but I won't be mt. bike with the bike that often so this should work. In the future probably over next winter I will be buying a lighter wheel set but not int he cards right now.  

I wouldn't count on that cassette working out of the box, you might need to add a wolftooth Roadlink or something to reposition your RD. With a new bike and limited time for modification testing, you're better off leaving your 1-42 on and going with a 36t chainring for that 10,000 feet of climbing. You'll be gasping and coasting down the hills so who cares if you spin out at 20mph rather than 22mph? 😃

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clarksonxc

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Reply with quote  #14 
Totally agree with Alan's second suggestion there, toss on a smaller chainring and leave the cassette and RD alone.  WolfTooth makes some nice elliptical rings!

The other statement caught my eye.  Why would a cassette be advertising a Boost/non-boost spacing option?  What does the dropout spacing have to do with the cassette width?  Does the Boost spacing allow the largest cog to not be dished, and require an 11sp road freehub?  I haven't heard any details on this before, so I'm curious.
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dangle

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Reply with quote  #15 
Quote:
Originally Posted by clarksonxc
The other statement caught my eye.  Why would a cassette be advertising a Boost/non-boost spacing option?  What does the dropout spacing have to do with the cassette width?  Does the Boost spacing allow the largest cog to not be dished, and require an 11sp road freehub?  I haven't heard any details on this before, so I'm curious.


There's no such thing as a Boost spaced cassette (yet). There's Boost "spaced" chainrings for 1x applications that moves the chain line slightly. It's not relevant for this conversation though.
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Zurichman

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Reply with quote  #16 
Quote:
Originally Posted by dangle
There's no such thing as a Boost spaced cassette (yet). There's Boost "spaced" chainrings for 1x applications that moves the chain line slightly. It's not relevant for this conversation though.


Yeah looks like my bad Dangle as I was looking at chain rings and cassettes and must have become mixed up as always. Thanks for that clarification.

Zman 

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neutered10mm

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Reply with quote  #17 

I ran the AML400 (417 miles because I made a run to Covington, VA about 5 miles off route on night 3 for a hotel room vs. camping) back in April/May of this year on a SunRace 11-46 rear & 38T chainring. Bear in mind I never ran out of gear except in one section, which was hike a bike anyways and I was left on day one with the bike packed down to the tune of 63 pounds! I can vouch that you are hard pressed to descend an 8% grade in excess of 42 MPH 😃

I'm going to be running the AMLX in October (yo-yo route with much more forest roads and more elevation - 502 miles, 46-47K of elevation) and I'm currently look at getting a new lighter GX MTB Crankset with a direct mount 36T chainring as it has steeper sections 14+% in parts. I'm currently researching the chainline differences out of the box vs. getting an offset direct mount chainring.

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