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Discussion Starter #1
What are the effects of changing to a 14t sprocket?
I expect to have the improved power on the low end (which is what I want.)
What about on the top end? What should I expect to lose? I am not a 100 mph+ junkie, so that is really useless and I dont mind losing it.
How does it effect cruising RPM and fuel economy?
 

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Loki,
it'l accellerate Harder, Round town cruising is heaps better, more prone to wheelies, fuel economy...........can't smell the diffence, awesome.......Do It!

Oh & you'll probably only get 205kph at 8,500 (14/39) but eh, still plenty fast enough.

I think a sprockets only 30 bucks & it takes 15mins to change, same chain also! ;D

Cruising RPM for me 14/39 in 6th is 80k-3,000, 100k-4,000 & 120k-5,000
 
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Just upped 2 teeth in the rear from sprocket specialists and got a new gold DID chain. Less clutch grabbing in traffic which is beautiful. The bike feels more suited to my needs. Hoewver, expect your to speed to be lowered, although not missed; un monster-like.
 
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Oh, I could make many rude comments, but I'll save them for later.

You should have about a 7% decrease in top speed, by the numbers, but that's assuming the bike had enough power to reach top speed with the stock gearing.
 

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Herb,
without going into the science of the whole thing. :-/

What should the stock top speed be & what do you think the top speed should be with a 14/39 or 15/41 setup?

I am at max, nothing left at say 8,400 in 6th at 200kph (14/39)

If I lean right down on the tank i might get 205 or 207kph at 8,500 or 8,600.

But the bike easilly goes to 9,000 plus in 1st, 2nd, 3rd & 4th.

Wind resistance??
Engine running outa Balls?
past the torque curve at WOT RPM?

Was actually going to bolt a 15t sprocket back on for interest sake & see what WOT bringeth!! ;D
 
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I'll go out on a limb here. Ideally, You'll reach top speed, in top gear, at top RPM. Since you don't reach redline in top gear, that would typically mean that adding a tooth or two to the rear sprocket would get the RPM up, but you may not go any faster, due to the deeper gearing. You've probably done all you can do to push your aerodynamic "brick" to it's terminal velocity. A more streamlined bike would certainly have more top speed.
 
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I went -1/+2. I rarely go over 100mph, and with that gearing I can still get there (probably get there quicker). If you do a lot of around town riding, I highly recommend it!!! The bike is just smoother all around. If you do a lot of top end speed stuff don't do it. My RPM at 70mph in 5th are About 5100, with the stock gearing it was like 4700. Scott Nelson posted somewhere the formula for what your RPM will be and loss of top end if you want all that scientific crap.

ps Herb I'm impressed by your seriousness! but I like the JackAss better, we have enough technical Guru's here!
 
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i ordered a 14T for my little duc. I'm hoping it tames the low end and makes it a big more aggressive off the line.

I got stuck in bumper to bumper friday on the way to work. I swear the bike isn't too happy in first gear at around 3mph.

my hands felt like they were beaten when I finally got to work.
 

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Loki,

Best and easiest mod I've done. 30 min, and a whole lot more grin factor and the chugging and clutching slipping from a start is gone....
 

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Loki: Do yourself a big favor and make the gearing change!

My analysis suggests that you go for about a 10% overall increase in numerical final ratio.

This would give a 620ie the following benefits:
0-60 time would be cut by abou 1/4 second
0-80 time would be cut by about 1/4 second
0-100 time would be cut by about 1/3 second
Horsepower available in top gear at 60 mph would increase by about 14%.

RPM at 60 would increase from about 4500 to just under 5000.

Top speed would NOT be reduced (the bike is overgeared form the factory).

There are a couple of ways to do this:

(1) Change rear sprocket from 48T to 53T (if 53T available), for a 10% change

(2) Change countershaft sprocket from 15T to 14T (7%) plus change rear sprocket from 48T to 49T (2%) for a mathematical total of slightly more than 9% (you multiply, not add, the ratios)

(3) Change countershaft sprocket from 15T to 14T (7%) plus change rear sprocket from 48T to 50T (4%) for a mathematical total of slightly more than 11.5%

The 620ie is a REVVER. Do not be frightened to let it rev. When I test drove one, I deliberately disregarded the tach when cruising, and found that I always ended up at 4500 to 5000 rpm even around town where the power requirements don't require it. It LIKES to rev. Let it.

Jim G
 

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Discussion Starter #17
Well, it is done, and all I can say is WOW! I only got to ride her for a mile or so and cant wait to get off work to open it up on the freeway. I got on the throttle no more than I used to and didnt really appreciate the difference until I looked at the speedo. One other thing I noticed is that she gets up in the higher RPMs alot faster. She never wanted to in first or second before, now it is very natural feeling.
 

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Loki: Glad to hear you like it! Which variation of gearing did you actually implement? (front sprocket change, rear sprocket, or both?)

Jim G
 

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Discussion Starter #19
Loki: Glad to hear you like it! Which variation of gearing did you actually implement? (front sprocket change, rear sprocket, or both?)

Jim G
I just did the front for now (14t) maybe at the 6000 mile service I will go up on the rear and get a new chain while I am at it. Clip ons are in the near future right now as well. Well shoot, while I am at it, they have the Matrix 998 in the showroom too.... :p
 

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All this gearing talk made me re-think my purpose for being.. so last week I ordered a 14T from Chris K, and last weekend I slapped it on... (actually, he was out of the standard 14T so he sent me one for a 916/996 race version (fro more $) ... it's got holes drilled in it for reduced mass (from AFAM)... which makes it cooler than most).

My reactions are like LOKI's... "WOW" Except, I added a ".. ..ie, Wow, wow...!". So it's more like:

"Wowie, Wow, wow..!"

It's a quicker bike for sure.. which helps since I've put on 10 lbs in the past 6 months ! haha..

LOKI did you you have to back the Clutch Slave out a bit to get the sprocket and chain off? I did.. could figure out how to do it without...

I also noticed the chain is flying awefully close (if not touching) the little plastic guide/guard on the swingarm.. so I'll keep an eye on that..

It's a damn good and cheap mod.
 
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