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Mixing SRAM 1:1 and Shimano 2:1 for a certain effect - - possible?

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Mixing SRAM 1:1 and Shimano 2:1 for a certain effect - - possible?

Old 02-18-11, 01:41 PM
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Mixing SRAM 1:1 and Shimano 2:1 for a certain effect - - possible?

OK, I know you cannot mix the two in a normal situation but bear with my thinking for a minute please:

Lately, a lot of downhillers are shaving weight/simplifying their drivetrains by removing cogs from cassettes and, in effect, creating five-, six- and seven-speed drivetrains - - still with the 8- or 9-speed cog-spacing (basically removing the inboard couple or three largest cogs and inserting spacers in their place). The reasoning is, you are lightening the cassette and eliminating extraneous gear selections.

That got me to thinking: could you REALLY lighten and clean things up by mixing a SRAM 1:1 shifter with a 2:1 Shimano rear derailleur to make a shifting setup that would move the derailleur two cog spaces for each shift - - allowing you to eliminate every other cog in a 9-speed cassette, giving you five speeds? In other words, take, say, an 11-34 cassette and use 11, 13, 15, 20 and 26 cogs all spaced two cogs apart on the cassette body. Could it work?

I can imagine downshifts might be a bit notchy; but, since most DH shifting is upshifts, that would not be an insurmountable issue. Am I way off-base here?
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Old 02-18-11, 02:21 PM
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The ratios aren't exactly 1:1 and 2:1. They're just convenient integers close enough to differentiate between them.

I just measured a Shimano RD - it moved 30mm with ~17.6 mm of cable, very close to 1.7:1. That's based on shifting high to low on a Shimano 7 speed HG cassette, which Sheldon Brown says has 5 mm spacing (6 steps x 5 mm = 30 mm) The ratio I measured fits with the 1.7:1 figure given here for Shimano. According to this table, SRAM is actually 1.1:1

So, I wouldn't expect it to work at all.
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Old 02-18-11, 02:46 PM
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I did this several years ago with a Shimano 9 speed setup. I rode the bike to commute and only needed 4 gears. So I used spacers on the inside and out to put those 4 gears into the middle of the hub. I then moved the limit screws in as far as they would go, but it wasn't far enough.

Only once did I overshift the chain onto the spacers. After that, it was just a matter of being careful.
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Old 02-18-11, 03:42 PM
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Originally Posted by mike_s View Post
The ratios aren't exactly 1:1 and 2:1. They're just convenient integers close enough to differentiate between them.
Ahhh . . . OK. Makes sense; thanks for the info and the actual measurement.

Originally Posted by 55/Rad View Post
I did this several years ago with a Shimano 9 speed setup. I rode the bike to commute and only needed 4 gears. So I used spacers on the inside and out to put those 4 gears into the middle of the hub.
Now why didn't that occur to me? That gets rid of the unused cogs but still keeps the stock spacing (and is better than the setups I've seen with just the inside cogs removed). Dumb question: can you get more limit adjustment by changing the length of the limit screws?
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Old 02-18-11, 03:59 PM
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THere is at least one other reason why the 2:1 ->1:1 conversion won't work: If you space the cogs out much farther then the chain can get caught in between.

Also, it seems sort of silly to be removing cogs without any other changes... having an extra two or three or four cogs doesn't slow anyone down - least of all downhillers. THe best reason I can think of for running less cogs is to allow a wheel with less dish... and simply removing cogs and adding spacers does not do this - you would need a narrower freehub body.

How many people are actually removing cogs from their downhill bikes? It can't be too common to lose that much practicality for 3 oz of weight savings.
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Old 02-18-11, 04:06 PM
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That got me to thinking: could you REALLY lighten and clean things up by mixing a SRAM 1:1 shifter with a 2:1 Shimano rear derailleur to make a shifting setup that would move the derailleur two cog spaces for each shift - - allowing you to eliminate every other cog in a 9-speed cassette, giving you five speeds? In other words, take, say, an 11-34 cassette and use 11, 13, 15, 20 and 26 cogs all spaced two cogs apart on the cassette body. Could it work?
Why not just put on a 6 speed freewheel hub? Use the wide chain?


Jtek shift mates are a cable pull conversion pulley.
like Travel agents are for running road bars/brifters and V brakes..

I can see supplanting the 2 outer cassette cogs with discs
that keep the chain from running off the ends of the cassette
and jamming the wheel up.

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Old 02-18-11, 04:45 PM
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Originally Posted by LarDasse74 View Post
How many people are actually removing cogs from their downhill bikes? It can't be too common to lose that much practicality for 3 oz of weight savings.
Believe it or not, they're doing it - - so save (especially unsprung) weight. Now that the sub-40-lb quest has been conquered by so many, they're trying to go lighter and lighter. Not saying I'm doing it, but . . . .

It serves another purpose too, in that you don't really need all those tightly-spaced gear ratios for DH; so if you boil it down to a wider-spread set of five or so and shed some weight to boot, why not?
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Old 02-18-11, 04:51 PM
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Are you kidding me? This is crazy - to think people tell me I should rebuild my 5,6 & 7 speed bikes for more modern drivetrains, and now people are going backward to save weight?
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Old 02-18-11, 05:00 PM
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Originally Posted by dminor View Post
Believe it or not, they're doing it - - so save (especially unsprung) weight. Now that the sub-40-lb quest has been conquered by so many, they're trying to go lighter and lighter. Not saying I'm doing it, but . . . .

It serves another purpose too, in that you don't really need all those tightly-spaced gear ratios for DH; so if you boil it down to a wider-spread set of five or so and shed some weight to boot, why not?
Why not? Because it will have exactly ZERO positive effect on performance. The amount of weight saved is negligable especially compared to the heavy DH tires and rims. THat much weight is less than what will get caught on the the tire on a muddy ride. THis reminds me off mountain biking in the early 90s when the trend was to cut handlebars down as short as possible - ostensibly to fit between trees better, but the drop in comfort and practicality was never worth the dubious benefits.
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Old 02-18-11, 05:07 PM
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weight is a benefit , going Down Hill..
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Old 02-18-11, 05:39 PM
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Originally Posted by LarDasse74 View Post
Why not? Because it will have exactly ZERO positive effect on performance. The amount of weight saved is negligable especially compared to the heavy DH tires and rims.
True that. But keep in mind that these are kinda the 'weight weenies' of the DH world who are doing this. Lightest rims that will still hold up, single-ply versions of the DH-cased tires, etc, etc. But they must have more money than I do to buy spares when they trash something.

My sled, on the other hand, tips the scales at 45 lbs. I didn't set out on purpose to build a porker; but I chose parts that I knew I could pound on mercilessly all season long and then some without having to worry about it failing. So I gave up and few grams here, a few ounces there and . . . damn . . . it added up. But I haven't DNFed a run from a mechanical in four seasons plus.

But I, too, can understand the quest for every advantage - - especially when the difference between making or not making the podium comes down to a couple hundredths of a second sometimes.


BTW, I'll scutter on back to MTB where I belong; just had to touch bases with folks 'in the know' who I knew could quickly shed light on my query. Thanks all.
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Old 02-18-11, 05:51 PM
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Originally Posted by corkscrew View Post
Are you kidding me? This is crazy - to think people tell me I should rebuild my 5,6 & 7 speed bikes for more modern drivetrains, and now people are going backward to save weight?
This IS crazy. Nuts, even. Insane.

In all seriousness there's a good chance that the modern drive train will be lighter, overall, than the old one. I took all the crap off this old Raleigh and, minus cables, bar, stem, saddle, seatpost, chain, and levers. . . weighs around 3 kg (over six and a half pounds) and another 3 kg for the wheels (including tires [27 1/4])
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Old 02-18-11, 06:49 PM
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Originally Posted by dminor View Post
Believe it or not, they're doing it - - so save (especially unsprung) weight. Now that the sub-40-lb quest has been conquered by so many, they're trying to go lighter and lighter. Not saying I'm doing it, but . . . .
That's counter productive going down-hill since reduced sectional density cuts your terminal velocity.
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Old 02-18-11, 07:04 PM
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Originally Posted by Drew Eckhardt View Post
That's counter productive going down-hill since reduced sectional density cuts your terminal velocity.
That applies when free-wheeling, but not necessarily when under power. Reduced unsprung weight may allow more power to the ground, more than offsetting any speed gain from weight.
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Old 02-18-11, 07:45 PM
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Originally Posted by mike_s View Post
That applies when free-wheeling, but not necessarily when under power. Reduced unsprung weight may allow more power to the ground, more than offsetting any speed gain from weight.
Pretty unlikely that would have any practical or noticable effect on suspension performance, IMHO.
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Old 02-18-11, 07:50 PM
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Perhaps two swalllows carrying it together. . .
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Old 02-19-11, 12:11 AM
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^^ Let's not get into ground speed velocity and laden swallows . . . it's tough enough to figure out with air speed velocity and UNladen ones.
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Old 02-19-11, 06:11 AM
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going down: more mass => good
going up: less mass => good
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Old 02-19-11, 10:56 PM
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IMO the unsprung weight reason may not be quite as silly as it sounds...

But yeah, I wouldn't bother unless it was part of a mission to seriously reduce dish.
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Old 02-20-11, 09:54 AM
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Doing it to reduce dish would seem interesting, but how would that work?
I can see where 8 out of 9 on a 7 would have less dish than using an 8/9/10 speed hub body, but beyond that wouldn't you need a shorter hub body? Does anyone make a shorter Shimano compatible hub body?
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Old 02-20-11, 02:32 PM
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Shorter than 7? No.
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Old 02-20-11, 11:20 PM
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Originally Posted by LarDasse74 View Post
How many people are actually removing cogs from their downhill bikes? It can't be too common to lose that much practicality for 3 oz of weight savings.
I did it not because it made any sense, which it didn't, but because I wanted to see if I could. That and I was able to customize the exact gears for a route I rode 6X per week.

Here is a photo of the setup. Can't see the cluster but it was 4 gears and a bunch of spacers with a 53 front.

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Old 02-20-11, 11:51 PM
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You could use a 6spd Uniglide cassette body if you filed the odd spline in the cogs... then it'd be worth it in terms of reducing dish.

You'd also need a Uniglide small cog to use for a lockring, which would be pretty fugly... I guess you could turn it down and put a couple of notches in it.
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