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post #21 of 159 (permalink) Old Sep 24th, 2013, 8:10 pm
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I did the 15 / 42, loved it, now trying 14t front

I did the 15 / 42 and loved the pull out of corners, and enjoyed being able to use 6th gear for the first time ever. Even easier to shift smoother with the lower ratio, engine stays in the power band easier.
But with the larger rear sprocket, you lower the rear ride height and change the wheelbase. I kept the 108 chain which reduces wheelbase. If you go with the 110 chain that sprocket center recommends, you increase the wheelbase.
I changed several things at once on my bike and after everything was done, the bike felt squirrely.
I was convinced that the ride height and wheelbase changes had messed up my bike.
I went back to stock gearing, bike still felt squirrely.
Turns out my PR3s were feathered / cupped.
New tires and my bike is back.
But I miss the lower gearing.
So I am going to try the 14t. To get the chain slack correct, the ride height and wheelbase will be almost unchanged from stock.

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post #22 of 159 (permalink) Old Sep 24th, 2013, 11:20 pm
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Ride Height?

Hard to believe this is detectable: given the swing arm would be approximately horizontal when you're sitting on it, wheel base is probably the only change. Even then, surely we're only talking "a bee's dick" or two?
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post #23 of 159 (permalink) Old Sep 25th, 2013, 4:14 am
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I did the 15 / 42 and loved the pull out of corners, and enjoyed being able to use 6th gear for the first time ever. Even easier to shift smoother with the lower ratio, engine stays in the power band easier.
But with the larger rear sprocket, you lower the rear ride height and change the wheelbase. I kept the 108 chain which reduces wheelbase. If you go with the 110 chain that sprocket center recommends, you increase the wheelbase.
I changed several things at once on my bike and after everything was done, the bike felt squirrely.
I was convinced that the ride height and wheelbase changes had messed up my bike.
I went back to stock gearing, bike still felt squirrely.
Turns out my PR3s were feathered / cupped.
New tires and my bike is back.
But I miss the lower gearing.
So I am going to try the 14t. To get the chain slack correct, the ride height and wheelbase will be almost unchanged from stock.
Wouldn't proper chain length correct any influence from short or long "chaining"?

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post #24 of 159 (permalink) Old Sep 25th, 2013, 9:34 pm
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I think the ride height change is about 4 or 5 mm

I am not saying I can detect it in the handling of the bike, I think my problem was tires all along. But with the stock sprockets and stock chain, the eccentric is at about the 6 o clock position. If you install the 42 tooth rear, you either keep the stock 108 chain in which case you have to move the axle about 8mm forward, which raises the axle about 4 or 5mm, or, you install the 110 link chain, in which case the axle moves back about 8mm and up about 4 or 5. I'm not good at math, but its easy to see when you play with it on the bike. You have to rotate the eccentric a lot to get significant fore-aft axle movement, and as you are rotating it away from 6 o clock, the axle is moving up also. It could be a real effect to ride height depending on where the ideal original eccentric position was. I am not sure if the original position was truly 6 o clock or not. If you had perfect chain adjustment with the axle at 4mm to the rear of 6 o clock, and you installed the 42t and kept the 108 chain, your wheelbase would decrease by 8mm but your ride height wouldnt change.

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post #25 of 159 (permalink) Old Sep 25th, 2013, 10:02 pm
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Hard to believe this is detectable: given the swing arm would be approximately horizontal when you're sitting on it, wheel base is probably the only change. Even then, surely we're only talking "a bee's dick" or two?
Ride height will change about 7mm from eccentric full fore or aft - to full vertical.

The wheelbase will change more (up to 14mm) depending on whether the eccentric is full fore or full aft of centre.

On my 848 race bike I have modified the brake caliper mounting plate so I can get the eccentric completely horizontal. I then chose gearing and chain length to suit - which as it happened is 15/40 - exactly what I wanted

The idea is to get the longest wheel base possible, which improves high speed stability.

When I go to the 42 rear on my MTS I'm gonna use the 110 chain for this reason.

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Last edited by oleary; Sep 25th, 2013 at 10:18 pm.
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post #26 of 159 (permalink) Old Sep 25th, 2013, 10:20 pm
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Hard to believe this is detectable: given the swing arm would be approximately horizontal when you're sitting on it, wheel base is probably the only change. Even then, surely we're only talking "a bee's dick" or two?
How much is that compared to "a blond one"?

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post #27 of 159 (permalink) Old Sep 26th, 2013, 8:56 pm
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Hard to believe this is detectable: given the swing arm would be approximately horizontal when you're sitting on it, wheel base is probably the only change. Even then, surely we're only talking "a bee's dick" or two?
I bet it is ..detectable - We'll see

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post #28 of 159 (permalink) Old Sep 26th, 2013, 10:31 pm
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I bet it is ..detectable - We'll see
I'm with you, mate.

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post #29 of 159 (permalink) Old Sep 27th, 2013, 10:17 am
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For high speed sweepers and powering out of turns I am sure the longer wheelbase is better. I dont ride fast and try to ride on twisty stuff where you meet your ass going around corners, shorter wheelbase should be better for that, right?

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post #30 of 159 (permalink) Old Sep 27th, 2013, 10:47 am
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Adding 2 teeth to the rear sprockett and 2 additional teeth to the chain... the wheelbase should remain the same my friends... Think about it!
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