Speed gains to be had from 15t? - Wrist Twisters
 
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post #1 of 29 Old 07-29-2010, 09:47 AM Thread Starter
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Speed gains to be had from 15t?

Outside of a higher propensity to pull the front end up, are there actually any speed gains to be had from going down a sprocket up front? Does anyone have any track experiences to back up that claim?

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post #2 of 29 Old 07-29-2010, 09:52 AM
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you will most certainly accelerate faster, regardless of if the wheel is on the ground or not. you will give up some cruising rpms though

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post #3 of 29 Old 07-29-2010, 09:55 AM
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Top speed will be slightly reduced, but you can accelerate faster.

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post #4 of 29 Old 07-29-2010, 10:32 AM
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yup... u loose a theoretical 7ish % top end, but your VERY unlikely to actually get to the revlimiter in 6th WOT with a 15tooth or a 16tooth front.

you definitely rev a lil higher cruising... but tbh i feel as though the 919 is smoother at 5.5k with the 15t vs the 4700ish rpms with the 16tooth.

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post #5 of 29 Old 07-29-2010, 11:04 AM Thread Starter
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I want 1/4 mile times!

I need proof, haha.

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post #6 of 29 Old 07-29-2010, 11:27 AM
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Quote:
Originally Posted by brickonwheels View Post
I want 1/4 mile times!

I need proof, haha.
just get a 15tooth off ebay and enjoy the hooliganism


... ps hooliganism is an actual word... WTF!

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post #7 of 29 Old 07-29-2010, 11:39 AM
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Dropping a tooth in the front raises cruising rpm by 6.6% but will not change the top speed as much as many seem to think. From the reports I've read here and elsewhere the 919 really flattens out for the last 1,000 rpm in top gear. A 15T may get the same top speed by decreasing the load on the motor thereby leaving more power in reserve to fight the wind.

Go to a roadrace track or drastrip and look in the pits for a team that knows their stuff. Invariably you will see a stack of front and rear sprockets. They know that there is no ideal final ratio, and careful selection of gearing will make the difference between finishing 2nd or 10th.

A 15 tooth sprocket has a neat "WAHOOO!" factor, but it begins to wear a bit thin after a while. That explains why the same 15T has been on at least 5 different WT bikes. That's a guess, but it wouldn't surprise me.

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post #8 of 29 Old 07-29-2010, 11:49 AM
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15 tooth made launches too difficult for me, best times came with 16 tooth.

All I ever ran was the 8th

Before I sold the bike, went with a 17 tooth, eventually returned to the 16.....

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post #9 of 29 Old 07-29-2010, 12:17 PM
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Just put a 15 tooth on about half an hour ago. Will be going for a ride tomorrow. My niggle is why don't Renthal put the rubber on the sprocket to reduce noise like Honda do on the standard sprocket.

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post #10 of 29 Old 07-29-2010, 01:43 PM
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Quote:
Originally Posted by Pob View Post
Just put a 15 tooth on about half an hour ago. Will be going for a ride tomorrow. My niggle is why don't Renthal put the rubber on the sprocket to reduce noise like Honda do on the standard sprocket.
ull like it to mess around with... i like the 15t for the tight twisty local stuff... but i like the 16t for the longer trips with more sweepers.... so its a toss up.... altho i must say i can be smoother with the 16t which i am finding is the overwhelming factory in riding faster is being smooth.

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post #11 of 29 Old 07-29-2010, 06:15 PM
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I went 15/45. Im interested in other options down the road....but I have zero complaints about my current count and cant imagine it being much better across the range

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post #12 of 29 Old 07-29-2010, 08:11 PM
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Quote:
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I went 15/45. Im interested in other options down the road....but I have zero complaints about my current count and cant imagine it being much better across the range
15/45 is the hooligan set up.

I'm runnin16/45 an I'm gonna go 15/45 for sure(rubbing hands with a mischevious smile from ear to ear).

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post #13 of 29 Old 07-30-2010, 04:53 AM
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how is the 16/45 combo? im thinkin about this as i dont quite want to go to the 15t but would like a little added snap

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post #14 of 29 Old 07-30-2010, 05:03 AM
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I'm running a 16/45 and love it, just a little more pep. It's my understanding 1 down in the front is roughly the same as 4 up in the back. I didn't want that much so I opted to bump up a little in the back. Something I learned after the fact is a smaller front sprocket bends the chain at a sharper angle and makes it wear faster.

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post #15 of 29 Old 07-30-2010, 05:49 AM
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nice i may have to try that. stock is 16/43 right?

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post #16 of 29 Old 07-30-2010, 08:03 AM
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Yep.

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post #17 of 29 Old 07-30-2010, 08:33 AM
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My Hooliganation titer must be a bit low. I went with the 17, and still get surprised by the front wheel leaving the earth unexpectedly at times. 15 would be too much snap for me....

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post #18 of 29 Old 07-30-2010, 09:06 AM Thread Starter
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My fat ass must be way up on the tank. The front end doesn't usually loft much at all. Granted, I don't whack open the throttle from a standstill. I will launch then be WOT by 3/4 of the way through the gear.

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post #19 of 29 Old 07-30-2010, 10:21 AM
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rob, what do you think about my theory that the ECU just pulls more and more timing out as needed to prevent accelerating past 142 mph?

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post #20 of 29 Old 07-30-2010, 11:06 AM
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Quote:
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rob, what do you think about my theory that the ECU just pulls more and more timing out as needed to prevent accelerating past 142 mph?
id believe it..... considering my chevy truck ust to have a "reckless driving mode" where if you got into it at WOT it would retard the timing to hard that there was no dif between half throttle and WOT..... not the case any more... damn truck chirps the tires between first and second... and has no motor work done to it past a cold air intake and the new tune hehe. (6.0L gasser btw)

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post #21 of 29 Old 07-30-2010, 12:29 PM
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Hooligans......hrmph! You guys are all criminals! Nothing more!

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post #22 of 29 Old 07-30-2010, 12:35 PM
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Hooligans......hrmph! You guys are all criminals! Nothing more!
no its the fuckin retards riding their 600cc sportbikes weaving in and out of traffic and gutter running past everyone at a stoplight that give us normal bikers a bad name.

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post #23 of 29 Old 07-30-2010, 12:53 PM
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no its the fuckin retards riding their 600cc sportbikes weaving in and out of traffic and gutter running past everyone at a stoplight that give us normal bikers a bad name.
tru dat. i almost wish the US would put in a step license like the UK does, it would weed out a ton of squids who wouldnt find it worth it to ride a 250 and a 500 before they could get their gixxer 1000

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post #24 of 29 Old 07-30-2010, 05:31 PM
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tru dat. i almost wish the US would put in a step license like the UK does, it would weed out a ton of squids who wouldnt find it worth it to ride a 250 and a 500 before they could get their gixxer 1000
That would be great, while we're at it lets adopt their gun laws. (won't work now but would've if it had been in place)

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post #25 of 29 Old 07-30-2010, 06:53 PM
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Quote:
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That would be great, while we're at it lets adopt their gun laws. (won't work now but would've if it had been in place)
No prob with the step lic., but what's withthe gun laws? There's ABSOLUTELY NO REASON we shouldn't have our boom toys....

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post #26 of 29 Old 07-30-2010, 06:54 PM
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That would be great, while we're at it lets adopt their gun laws. (won't work now but would've if it had been in place)
Never mind, I get it now (haha)

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post #27 of 29 Old 07-31-2010, 12:42 PM
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Over here getting to a full unrestricted bike licence is not easy. It's also complicated and expensive. I think around 750 for everything to pass is normal now. You can't go to a full bike licence till your 21 over here now either without passing and having to have a probabtion period restricted to 33BHP for 2 years. In fact all our driving tests are harder, you can't start driving lessons in a car until 17 and a truck is 21.
By the way now running 16/45 gearing on my 900 after trying 15/43.

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post #28 of 29 Old 07-31-2010, 05:30 PM
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Quote:
Originally Posted by brickonwheels View Post
I want 1/4 mile times!

I need proof, haha.
If you are dragging it, then drive line shock is more of an issue. Better to add teeth at the back than drop at the front. The theoretical angle of wrap remains the same, but the radius of curvature is better with the 16 than a 15.
Theoretically speaking of course.
And yes, the smaller 15 front and therefore smaller rear means reduced radius as far as fourth moments of interia are concerned, and reduced chain mass as well, but I'd still go for the larger radius of a 16 front and play at the back to get the overall gearing I wanted.

As for "speed", put a 15 on healthy 919 at sea level with rear left as stock, and your top speed can only do one thing, at that is go down. Maximum top speed with a healthy 919 at sea level is going to derived with stock gearing, or one tooth more on the rear.
No stock or near stock can get anywhere near the rev limiter in 6th with stock gearing.

There's about

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post #29 of 29 Old 08-01-2010, 08:28 AM
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Get the 15. I've heard they are slower int he quarter mile due to wheelie control issues but I'm skeptical of that. Especially if you are a big boy keeping the front down is easier and you could use the extra torque multiplication.

As for highway. Its not that big a deal. Yes it revs higher. But thats why you have an L4 anyway right? Instead of staying between 4500 and 5k on the slab it will rarely be below 5k. Sometimes up around 6 while cruising.

For me I' loved the 15t front. Way more pep. Way more fun. And little sacrifice in mileage. Top spead changes slightly up or down who cares. How often are you racing someone to absolute top speed. Ever? I bet you'll do top gear roll ons next to someone, or a quick blast through 1st and 2nd gear at a red light much more often.

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