3x10 vs 2x10 for the below average Mtb rider

[River Rat]

On the notties to himeville race my SRAM X7 front dérailleur decided to give up the ghost. It would not downshift onto my granny gear, I understand from my Lbs that the springs do weaken overtime so this is not unexpected.

 

Finding a SRAM 3x10 front dérailleur direct mount is virtually impossible ( to fit a specialized epic 29er) as it would seem that SRAM are moving towards 2x10 exclusively. In fact, chain reaction inform me that do not stock SRAM 3x10 in a direct mount configuration anymore.

 

This got me thinking of changing to 2x10 and I tried to simulate the top speed and lowest speed (climbing) of my current set up. I found an interesting link that allows you to compare different chainring and cassette combinations http://home.earthlink.net/~mike.sherman/shift.html. The results surprised me and really questions the move to a 2x10 configuration for the average rider.

 

Top speed - the max size for a chainring that can be accommodated by SRAM is 42t while Shimano gives 44t. The smallest cassette I could find is 11t, so to get the same top speed on my bike by getting a Shimano FD this is achievable. But what is significant (for me) is the difference between a 42t and 44t is 5% in top end.

 

Lowest speed - the key variable here is the maximum delta between the two chainrings which for both manufacturers is 14t. So if I maintain my 44t the smallest the small chain ring can be is 30t which means I cannot simulate the 22t x 32t currently on my bike since the largest gear for a cassette is 36t which would lose about 20% climbing ability. If the calc on the link is anything to go by. To get to the same climbing ratio with a 36t gear you would need to change to a 26/40t chainring set up, and this would lose you a whopping 10% top speed. (Even this combo would not quite simulate my current ratio at the low end)

 

So in conclusion if your riding is like mine where I struggle on climbs ( I have a chronic back problem so any potential improvement here is limited) and you try to make up for lost time on the downhills then a 2x10 configuration will not give you an optimal range. Fortunately Shimano still make a suitable 3x10 FD so I can continue with my current set up, SRAM's loss I guess?

 

Ps - it is also quite interesting to see the advantage a 29er gains over a 26er in top speed and what it loses in climbing ability when considering similar gear ratios. My experience is that the 29er makes up for it in terms of rolling resistance but this is an entirely different debate.

Edited April 22, 2012 by River Rat

[DJR]

For myself? On a 26er. Not a racing snake. Short answer?

 

The more gears and the wider the ratios, the better, especially as I ride everything on the mountain.

[Mellow]

On the notties to himeville race my SRAM X7 front dérailleur decided to give up the ghost. It would not downshift onto my granny gear, I understand from my Lbs that the springs do weaken overtime so this is not unexpected.

 

Finding a SRAM 3x10 front dérailleur direct mount is virtually impossible ( to fit a specialized epic 29er) as it would seem that SRAM are moving towards 2x10 exclusively. In fact, chain reaction inform me that do not stock SRAM 3x10 in a direct mount configuration anymore.

 

This got me thinking of changing to 2x10 and I tried to simulate the top speed and lowest speed (climbing) of my current set up. I found an interesting link that allows you to compare different chainring and cassette combinations http://home.earthlin...man/shift.html. The results surprised me and really questions the move to a 2x10 configuration for the average rider.

 

Top speed - the max size for a chainring that can be accommodated by SRAM is 42t while Shimano gives 44t. The smallest cassette I could find is 11t, so to get the same top speed on my bike by getting a Shimano FD this is achievable. But what is significant (for me) is the difference between a 42t and 44t is 5% in top end.

 

Lowest speed - the key variable here is the maximum delta between the two chainrings which for both manufacturers is 14t. So if I maintain my 44t the smallest the small chain ring can be is 30t which means I cannot simulate the 22t x 32t currently on my bike since the largest gear for a cassette is 36t which would lose about 20% climbing ability. If the calc on the link is anything to go by. To get to the same climbing ratio with a 36t gear you would need to change to a 26/40t chainring set up, and this would lose you a whopping 10% top speed. (Even this combo would not quite simulate my current ratio at the low end)

 

So in conclusion if your riding is like mine where I struggle on climbs ( I have a chronic back problem so any potential improvement here is limited) and you try to make up for lost time on the downhills then a 2x10 configuration will not give you an optimal range. Fortunately Shimano still make a suitable 3x10 FD so I can continue with my current set up, SRAM's loss I guess?

 

Ps - it is also quite interesting to see the advantage a 29er gains over a 26er in top speed and what it loses in climbing ability when considering similar gear ratios. My experience is that the 29er makes up for it in terms of rolling resistance but this is an entirely different debate.

 

I suggest sram 24/38 rings and 11-36 cassette. I think less than 1% of your riding time will be in 38/11

[River Rat]

 

 

I suggest sram 24/38 rings and 11-36 cassette. I think less than 1% of your riding time will be in 38/11

Mellow, on most technical routes I can't fault your thinking, but on Sabie Classic and Notties I found that 30% of my race was either climbing or descending. This is why I am using this in my comparison. I am getting the bike ready for Sani which I'm assuming will be similar.

[awesme]

Been noticing also allot of 2x10's. I got a Shimano XTR front, and XT read in a 3x10 configuration.

 

(42..32..23) Front Chainring

(36..11) Casette rear

 

Interesting enough, I think I've used the smallest chain ring maybe 2-3 times the last 6 months, could explain why I'm dead after any all uphills.

 

been pushing myself to shift down more, increase my cadence on the uphills.

 

G

Edited April 22, 2012 by awesme

[Mojoman]

Out of interest how many K's did you do with that SRAM derailer?

[Mellow]

Mellow, on most technical routes I can't fault your thinking, but on Sabie Classic and Notties I found that 30% of my race was either climbing or descending. This is why I am using this in my comparison. I am getting the bike ready for Sani which I'm assuming will be similar.

River Rat, ask yourself. if there was a 53t front ring will you use it ? Why not? its not what you can put on but what you use. like i say you will spend less than 1% of a race in 39/11 if any time. go test it with your current configuration.

 

edit : sorry i should have started with - you are right. you will lose some gear ratios and probably top end gears. as you said, the smaller ring is more important. i found that losing some top end gears did not really bother me and the weight saving and shifting performace of 2x10 is quite nice.

Edited April 22, 2012 by Mellow

[EZRider]

 

River Rat, ask yourself. if there was a 53t front ring will you use it ? Why not? its not what you can put on but what you use. like i say you will spend less than 1% of a race in 39/11 if any time. go test it with your current configuration.

 

edit : sorry i should have started with - you are right. you will lose some gear ratios and probably top end gears. as you said, the smaller ring is more important. i found that losing some top end gears did not really bother me and the weight saving and shifting performace of 2x10 is quite nice.

 

+1 on the shifting performance.

 

Just changed to 2 x 10 and tested it up a very steep gradient. On my Merida 26" with a 36 cassette my cadence is not much lower than granny on my 3 x 9.

 

River rat, don't think about the speed the gears will give you but rather your cadence on the climb.

And if you are in your biggest ring front, smallest back and have a high cadence on the steep Sabie descents then maybe you should be in downhill!

[River Rat]

Out of interest how many K's did you do with that SRAM derailer?

 

About 4000kms which also matches what I got from my SRAM x7 on by 26er, which I changed to an x9 when it failed. The x9 performs significantly better even after about 3000kms.

[River Rat]

 

River rat, don't think about the speed the gears will give you but rather your cadence on the climb.

And if you are in your biggest ring front, smallest back and have a high cadence on the steep Sabie descents then maybe you should be in downhill!

 

Hey TZmtb this is what I did on Sabie until I buckled my front rim and that left me limping to the finish. I guess its a case of too much weight + not enough talent , too much speed + too little brains or any combination of the 4. At the back of the field very few pass me on a downhill which is not he case on the uphill where 90% of the back markers nail me. So I need all the help I can get!

[Cejay]

Hi River Rat,I'm not one for a lot of calculations,I ride a 2x10 on both my 26er and 29er.I did the Notties and last year the JB2C will start it on Friday again.

 

My configuration 26/39 upfront and 11-36 at the back,I spin quite easily up the hills the 3x10 brigade does not leave me going up nor going down the other side.Guess what I'm trying to say is ride and then make up your mind.in Afrikaans we have a saying"papier is geduldig"meaning I can justify anything on paper.

 

My guess is once you have ridden it you will not go back

[EZRider]

 

 

Hey TZmtb this is what I did on Sabie until I buckled my front rim and that left me limping to the finish. I guess its a case of too much weight + not enough talent , too much speed + too little brains or any combination of the 4. At the back of the field very few pass me on a downhill which is not he case on the uphill where 90% of the back markers nail me. So I need all the help I can get!

 

Ha ha, more speed than talent can hurt!

Stick to 3x10 if you like it. The new shimano 2012 XT group is really good in both 3 and 2 ring versions.

[River Rat]

Cejay I'm sure you're right and it clearly works for you. As it stands I have a problem on hills and I can't see the adavantage for me taking into account my type of riding to change to a 2x10. I know this is a typical engineering approach but these calcs confirm my experience on where the advantages are between the 29er and 26er when it comes to top speed. So I tend to rely on them.

 

Good luck for Joberg2c, are you riding your 29er?

[River Rat]

Cejay just looking at the gear ratios you used on Notties I can see why you could see no difference between on the uphills. A 26 front 36 back gives a Gain Ratio of 1.55 compare to a conventional 22f and 34 b which has a Gain Ratio of 1.48 not too much of a difference. However when it comes to the big blade your 39f and 11b has a Gain Ratio of 7.63 vs 44f and 11b Gain Ratio of 8.61 which is quite large.

 

So according to the calculations you would have been at a disadvantage on the 13km downhill, was this actually the case?

[Falagar]

If you use 42/32/24 chainrings with 11/32 cassette you get exactly the same range as a 42/28 with an 11/36 cassette. In effect all you lose if you go with the second option is the diiference between the 44 and 42 chainring.

[VincentBikes]

Or you can simply buy my X7 FD off my specialized epic 29'er which has about 100k's on it.

 

P.S. It is not only about gear ratio's but your final drive ratio.

 

See the link below which takes your wheel circumference into account as well..

 

http://www.sportsdigest.co.za/gearcalc.shtml

Edited April 22, 2012 by FeO