Front Sprocket

[Hitman]

at 15/41 my rpm to speed is 1000:10mph.

So running 8500rpm at 85mph on the speedometer.

Saves me alot on gas for freeway travel.

[Tony B]

Move to the UK, our gallons are bigger ....

[Alex]

[ratlab]

a tight chain won't wear out suspension but won't allow the rear shock to do it's job-it won't allow full stroke -dangerous

[Tony B]

A tight chain will also put extra pressure on the bearings .......

[Tony B]

So, taking a look at the sprockets on my rat, and finding that I'm glad I did, the PO hadn't bolted two of the nuts up, they were close to the end of the studs and could have caught on something
The PO had put a new 'O' ring chain and sprocket set on, all looks good quality, but the sprockets were 13/39.
I did some maths, and just by dividing the bigger by the smaller I came up with this :

14 / 45 = 3.2
14 / 43 = 3.07
15 / 45 = 3
13 / 39 = 3
15 / 43 = 2.86

[Alex]

Yup - looks like you had the same ratio as the much more common 15/45 that many people land on with a ninjette. Glad you caught the loose nuts!

[coondog]

Originally Posted by Alex

People have gone even taller than that. This member went to 16/41, though it was on a new-gen. A whole bunch of 15/41 folks as well.

There had to be a "speciality" involved, with 07's and back you just never saw below 42's on rear with a bigger front. Experimentation like that yea, but change-back to 15-44 absolutely.

[Bosgarage57]

So is there an agreement out that says 15/43 is the best for MPG and rpm as a cruiser?

[Alex]

There is no best. Choose what you like, and if you don't like it, tweak it until you do.

[coondog]

Just looking at the last two posts means there would be divergent opinions, strong ones. Flatlands of Tennessee vs. altitude and hills of S.F. lets just assume. Personally I'm surprised Alex is so open minded but that's because i'm so close minded. Where i am and say Texans (FLAT FLAT FLAT) if you're into gas mileage and commute long distances go 15/41, help yourself. Just be happy with keeping the speed limit, and that should work into your "savings" plan anyway so you're set. I don't give a hoot about cost of gas or mileage, although this ethanol sh*t I'll listen to anyone. I also like 6th gear alot, and mods get you there with the mid range boot as well as 15/45 gearing (15/44). Everyone is doing what they're doing hopefully for the "specialty" they desire. I like to use all my gears to there maximum, don't give a hoot, and love 11k rpm = 90mph. We're as different as the gear we wear but ONE as cyclists regardless of reason. Yes Alex I was called to the Window.

[FrugalNinja250]

WRT gearing, acceleration is determined by the relationship of engine RPM to rear wheel RPM, or speed. So, if your engine is turning 8,800 RPM at 50 MPH the instantaneous acceleration will be the same regardless of what the various gear and sprocket ratios are between the crank and the rear axle.

Having taller gearing on the sprockets and downshifting more to get the RPMs where they were before means roughly the same acceleration. One thing that does change is the rate of RPM change per speed change. Taller sprockets mean that you spend more time in each gear before upshifting.

Short version? Down shift more, accelerate about the same as before, enjoy the lower cruising RPMs.

[Live2ride]

This is my post from the mpg thread. I figured it belongs here too.

Originally Posted by Live2ride

Ok, I finally filled my tank after installing the new 15t sprocket. I got between 48-50mpg on the stock gearing, now I'm getting 57.5 mpg. Do not let that statement fool you because I did ride more conservatively on the tank with the 15t sprocket. I found that, after installing the new sprocket, the bike is much more enjoyable to ride conservatively ,imo, so that's how I rode it. I will try to ride more aggressively (normal pace) on my next tank and see the difference. On the 57.5mpg tank, I only went WOT once and did 1 top speed run, other than that is was smooth sailing.

I found that I can now shift at 5k,6k, or 7k rpm without a problem and the bike seems to love it. After riding 230+ miles with the new sprocket I love it even more. It has consistently dropped my rpm down to 300-600 rpm above my speed (ie. 45mph is about 4.9k rpms) and it feels like there is so much more left in each gear even though it's a small difference. I'll post again once I find what my normal riding gets, mpg wise.

edit: I ride a mix of highway, twisties, and city on all my tanks.

[road_rascal]

I topped off my '04 yesterday and recorded 61.4mpg with the 15T sprocket. It's a keeper!

[Kevin2109]

Alex I remember you saying in another thread that the 15t wont raise gas millage? Can you comment on that?

[Alex]

Yeah, I don't believe the posts. Over time, if people continue to ride the same way they did prior, the difference will be negligible. If someone is trying to maximize mpg on the first tank after the switch, perhaps the initial jump looks more sizable. The bike just isn't that much more efficient making the same required hp at 8500 rpm compared to 9000 rpm. If it's a percent or two it's alot. Reports of 20% improvement simply cannot be attributed to the change; it's either a misrepresentation of true mpg, or the riding style changed drastically before/after the swap.

I could get down into the 30's mpg just as easily with a 15-tooth front as with the 14-tooth front on our pre-gen, it's all about how you choose to use the throttle.

[FrugalNinja250]

I keep detailed records of fuel mileage, and my 10-tank average went from 59.8 to 62.6 with the change, same commute and similar weather. Though your reasoning is correct, it doesn't take into account motor efficiency, more specifically, pumping losses. Gasoline engines suck air in past a restriction in the form of a throttle plate, and it consumes energy to do so. The general rule of thumb is that you burn less fuel for a given power output at lower RPMs and more open throttle. It's referred to as Brake Specific Fuel Consumption. Now, there are a lot of other variables involved, so lugging a Ninja engine like a low-end torque motor will not yield better efficiency, but the minor change in RPM with the 15T sprocket does help. The secondary benefit, at least for me, was the elimination of oil consumption at extended highway speed traveling.

As a side note, one of the reasons diesels have such better efficiency is that they don't have throttle plates, just a gaping hole with an air filter.

[Alex]

The key word here is slightly. The fuel consumption is much more closely related to the hp being produced by the motor, than the rpms used to produce that same hp. Yes there are pumping losses to consider, but a 1/15 change in revs just isn't going to be particularly significant. The differences in pumping losses are measurable when you are talking about cutting revs by a 1/3rd or more. Keeping the revs below a certain threshold on the pre-gens can be critically important for the oil consumption reason you point out, and that is reason enough to gear the bike a bit taller if one puts on significant highway miles.

Keep track of the next 10 tanks and see if it remains over 62 or dips below 59. Whether it does or not, attributing it solely to the sprocket change is really hard to do, even if one does their best to ride in exactly the same manner and in the exact same conditions. I do not disagree that over time one could determine it provides a very small uplift, but anything more than a mpg or two has less to do with the gearing change than all of the other factors that need to be taken into account.

For some unrelated yet still interesting reading, check out how BMW no longer uses throttle plates on their engines in the conventional sense, and relies solely on controlling valve lift directly.

http://en.wikipedia.org/wiki/Valvetronic

[FrugalNinja250]

Originally Posted by Alex

The key word here is slightly. The fuel consumption is much more closely related to the hp being produced by the motor, than the rpms used to produce that same hp. Yes there are pumping losses to consider, but a 1/15 change in revs just isn't going to be particularly significant. The differences in pumping losses are measurable when you are talking about cutting revs by a 1/3rd or more. Keeping the revs below a certain threshold on the pre-gens can be critically important for the oil consumption reason you point out, and that is reason enough to gear the bike a bit taller if one puts on significant highway miles.

Keep track of the next 10 tanks and see if it remains over 62 or dips below 59. Whether it does or not, attributing it solely to the sprocket change is really hard to do, even if one does their best to ride in exactly the same manner and in the exact same conditions. I do not disagree that over time one could determine it provides a very small uplift, but anything more than a mpg or two has less to do with the gearing change than all of the other factors that need to be taken into account.

For some unrelated yet still interesting reading, check out how BMW no longer uses throttle plates on their engines in the conventional sense, and relies solely on controlling valve lift directly.

http://en.wikipedia.org/wiki/Valvetronic

Sorry your gas mileage didn't go up with the 15T you installed, as it has for so many others. The consensus on the forums is that it increases mileage. My personal experience is that it increased mileage for me by nearly 5%. I did 10-tank averages before and after to compensate for filling variations and variations is daily driving regimes. With approximately 16,000 miles with the 14T and 12,000 miles with the 15T, across all seasons, the difference still holds true. Looking over my most recent 10-tank average I come up with 64.9, not bad. My last tank I got 68.3. I fill up at the same pump 94% of the time, and fill to the same level, about 1/8" up the bottom of the filler neck.

I don't question the validity of my data, and my long-term documented observations back up my conclusions on mileage increase with the 15T.

Parting observation: My mileage hasn't gone below 60 mpg since I installed the 15T sprocket.

[Alex]

Originally Posted by FrugalNinja250

The consensus on the forums is that it increases mileage.

The consensus on the forums is that it increases acceleration, improves fuel mileage, makes the bike 3.6 times more comfortable on the highway, and causes male pattern baldness to reverse. Its benefits are universally overstated. I appreciate that you are getting some great mileage on the bike, and it's gone up a few percentage points since you changed the sprocket, and I'm glad it's working out for you. Others don't see the same (or any) mileage benefit and are surprised at that fact, thinking that the sprocket change itself is a guaranteed significant uplift in economy.

[FrugalNinja250]

Originally Posted by Alex

The consensus on the forums is that it increases acceleration, improves fuel mileage, makes the bike 3.6 times more comfortable on the highway, and causes male pattern baldness to reverse. Its benefits are universally overstated. I appreciate that you are getting some great mileage on the bike, and it's gone up a few percentage points since you changed the sprocket, and I'm glad it's working out for you. Others don't see the same (or any) mileage benefit and are surprised at that fact, thinking that the sprocket change itself is a guaranteed significant uplift in economy.

Sarcasm noted...

Time to do a survey...

[coondog]

Been waiting for FrugleBugle to quiet down and put his charts away. I could say you're a bore but I won't, but you ARE wrong. Alex reminded me of driving long distances and no matter if we "averaged" 90mph or 55mph, as CrashDenver sang "by the end of the day another 500 miles is done." I don't want to chat, though in a chatroom (I do know that much) because I don't think anyone can figure it, even with all the obvious reasons to come up with. For ME, 500 miles a day avg. is always bottom line and it's a freak of nature in my life.

[boytoy101]

hello sir just a newbies question, did anyone try to used a 15teeth front and 47teeth rear...what do u think will happen if u have a set of sprocket like this...how will be the performance, fast start or fast top end?...

[Alex]

What would be the point? It's so close to the stock 14/45 ratio that it would change almost nothing.

[CynicalC]

Originally Posted by Alex

What would be the point? It's so close to the stock 14/45 ratio that it would change almost nothing.

Psh. Math is overrated.

[Jinx250]

The one thing I've found that has a direct and significant impact on MPG is how you ride. If you short shift and keep it under or at the speed limit, you will easily and consistently be in the high 50s / low 60s if not more. But I've still seen a jump in my MPG after the change. Maybe because I don't (have to) spend so much time at the upper limit of the rev range.

[FrugalNinja250]

Originally Posted by coondog

Been waiting for FrugleBugle to quiet down and put his charts away...

Plonk...