Why Drop Final Ratio From Stock?

I'm about to replace my 02 VFR drive chain, and was considering dropping down a tooth on the front sprocket from the stock 16T. However, I'm not sure I understand the benefit.

What am I gaining by lowering the final drive ratio that simply downshifting a gear is not going to accomplish? Obviously, in 1st gear, downshifting is not an option, but I don't spend much time in 1st gear (and would spend even less in 1st if I dropped a tooth).

It seems to me that dropping a tooth on the front gains me some improved acceleration in 1st gear, but is noisier (no rubber damper for 15T F/sprockets), screws up the speedo (unless I want to spend even more money for a Speedo Healer), and potentially raises the engine RPM at crusing speed.

What are the other benefits of smaller front (or larger rear) sprockets? Thanks!

hlf, Oct 4 2006, 07:27 PM
I'm about to replace my 02 VFR drive chain, and was considering dropping down a tooth on the front sprocket from the stock 16T. However, I'm not sure I understand the benefit.

What am I gaining by lowering the final drive ratio that simply downshifting a gear is not going to accomplish? Obviously, in 1st gear, downshifting is not an option, but I don't spend much time in 1st gear (and would spend even less in 1st if I dropped a tooth).

It seems to me that dropping a tooth on the front gains me some improved acceleration in 1st gear, but is noisier (no rubber damper for 15T F/sprockets), screws up the speedo (unless I want to spend even more money for a Speedo Healer), and potentially raises the engine RPM at crusing speed.

What are the other benefits of smaller front (or larger rear) sprockets? Thanks!

Sounds 'bout right, in summation. Spend $$$$, be one of us. LOL.

hlf, Oct 5 2006, 12:27 AM
r (no rubber damper for 15T F/sprockets),

You may find Honda use a 15T on something that will have the rubber and the correct pitch / width. blink.gif
Possibly CBR600F2, can anyone else verify?

The bike will accelerate/pull better in every gear in all situations. It's the best, simplest, & cheapest performance mod you can make period. Depending on how you ride or the type of riding you do, you may or may not like it. It will make the speedo read another 8% higher than it already reads and at cruise(hwy) you'll be at a rpm 8% higher than normal.
I myself love this mod and will never go back, I do mostly twisties and have over 40k miles with this mod. wheel.gif

PS, if your changing front & rear sprockets and chain anyway, going up 2-3 teeth on the read.

baileyrock, Oct 4 2006, 07:51 PM
The bike will accelerate/pull better in every gear in all situations.

I agree that lowering the final drive ratio will produce better acceleration in every gear. But if I downshift to a lower gear, I'm going to have better acceleration with stock gearing than you will in a higher gear with a 15T front sprocket (or 3 more teeth in rear).

The change from 16T to 15T on countershaft sprocket is going to give you roughly 6% better acceleration. Downshifting a gear is going to give approximately 15% better acceleration due to change in transmission ratio. (I'm simplifing this to assume relatively constant engine torgue over the RPM range we use for spirited riding, so acceleration is proportional to the combined transmission and final drive ratios).

Unless we're both in 1st, or I've reached red line in 5th and am forced to shift to 6th (not very likely on the street), I think I'm always going to have better acceleration by simply downshifting.

hlf, Oct 4 2006, 08:36 PM
I agree that lowering the final drive ratio will produce better acceleration in every gear. But if I downshift to a lower gear, I'm going to have better acceleration with stock gearing than you will in a higher gear with a 15T front sprocket (or 3 more teeth in rear).

The change from 16T to 15T on countershaft sprocket is going to give you roughly 6% better acceleration. Downshifting a gear is going to give approximately 15% better acceleration due to change in transmission ratio. (I'm simplifing this to assume relatively constant engine torgue over the RPM range we use for spirited riding, so acceleration is proportional to the combined transmission and final drive ratios).

Unless we're both in 1st, or I've reached red line in 5th and am forced to shift to 6th (not very likely on the street), I think I'm always going to have better acceleration by simply downshifting.

If I downshift too, I'll leave you in the breeze!
In the same gear the 15t will always pull the 16t and you'll most likely have a higher top end if you care.
Think of two VFR's pulling away from a stop, one w/15t one w/16t. The 15t bike will always be accelerating faster the the other in every gear. fing02.gif
It's a easy mod to change, just run a 15t when you replace everything for a little loop and decide. If you don't like it you can recover most of the cost of buying a 16t by selling the 15t here. Takes about 15 min. to change.

Plain as day, if you want better accel. from your bike than you currently have, make the change. Otherwise forgetaboutit! tongue.gif

Bailyrock is right, I will put my pink slip up racing a stock bike setup.

Chisel these sentiments in granite. I went up 2 in the rear rather than 15 in front.

I think you lose a few MPH on top speed, but how often to you get near 150 MPH anyway?
The extra acceleration and perceived (not real) increase in power is worth the other trade offs too imho. beer.gif

I don't want to go back either. wheel.gif

VFR4Lee, Oct 4 2006, 10:16 PM I think you lose a few MPH on top speed, but how often to you get near 150 MPH anyway?
The extra acceleration and perceived (not real) increase in power is worth the other trade offs too imho. beer.gif

I don't want to go back either. wheel.gif

That is, only if you are redlining in 6th gear. If you can't redline in 6th, you may actually raise your top speed by lowering your gearing. wheel.gif beer.gif

baileyrock, Oct 4 2006, 07:51 PM PS, if your changing front & rear sprockets and chain anyway, going up 2-3 teeth on the read.

Good luck finding one made from steel for less than $100.

jeremy556, Oct 4 2006, 09:30 PM
That is, only if you are redlining in 6th gear. If you can't redline in 6th, you may actually raise your top speed by lowering your gearing. wheel.gif beer.gif

That is true, many bikes will actually also gain top MPH by dropping the gearing. With stock gearing most bikes can't pull redline in top gear. fing02.gif

I reckon that 15T is too small, and the increase in noise/chain wear isn't worth it. I went from 16T to 15 on my VTR, but that was only because the chain and sprockets were already nearly kaput, and it was a cheaper experiment than a new rear sprocket. Handily, the 'discarded' 16T from the VTR fit the VFR with only a small amount of grinding of one side of the flange required.

I've now run lower gearing on a VFR750 (bigger rear sprocket by 1 or 2 teeth, can't remember), the VTR1000 (down 1 on front) and the VFR800 (down 1 in front). It made a huge difference to the rideability of the VTR, which is WAAAAY overgeared as stock and felt like a new bike afterwards, and a significant improvement to the VFR800.

When/if the VFR's replacement cush rubber set arrives <sigh>, I'm buying a new chain and larger rear sprocket. Haven't decided about the countershaft sprocket yet, but I may go to 16T on that as well as 2-up in the back. Easy twiddle of the speedo corrector to adjust.

Incidentally - I get much lower fuel mileage now my speedo is correct, as my odometer is reading low. smile.gif

enzed_viffer, Oct 4 2006, 10:43 PM
When/if the VFR's replacement cush rubber set arrives <sigh>

You STILL haven't gotten that??? blink.gif I replaced mine like 6 months ago and you had already ordered yours. Offer still stands, cancel your order and I will get them locally and mail them to you, probably have them in a week (and half the price).

jeremy556, Oct 5 2006, 02:45 PM
You STILL haven't gotten that??? blink.gif I replaced mine like 6 months ago and you had already ordered yours. Offer still stands, cancel your order and I will get them locally and mail them to you, probably have them in a week (and half the price).

I really screwed up there. If I hadn't decided that I was going to get them anyway and put a deposit on them (which incidentally was more than the total cost via the US), I could've done that.
Mind you, even if I lose the NZ$30 deposit AND pay for some from ServiceHonda or whatever, they'll still be half the price they'd be from the dealer here.
If I ever get them!! pissed.gif
Maybe I'll just throw away the worn ones and fill the hubs with wood, or cement or summat. comp13.gif
Or do what I did with my VF500 and cut some replacement cush rubbers from solid rubber.

enzed_viffer, Oct 4 2006, 11:01 PM
I really screwed up there. If I hadn't decided that I was going to get them anyway and put a deposit on them (which incidentally was more than the total cost via the US), I could've done that.
Mind you, even if I lose the NZ$30 deposit AND pay for some from ServiceHonda or whatever, they'll still be half the price they'd be from the dealer here.
If I ever get them!! pissed.gif
Maybe I'll just throw away the worn ones and fill the hubs with wood, or cement or summat. comp13.gif
Or do what I did with my VF500 and cut some replacement cush rubbers from solid rubber.

Tell you what, next time I replace mine, I will send you my old ones to hold you over until your new ones arrive.

baileyrock, Oct 4 2006, 09:48 PM
If I downshift too, I'll leave you in the breeze!
In the same gear the 15t will always pull the 16t and you'll most likely have a higher top end if you care.
Think of two VFR's pulling away from a stop, one w/15t one w/16t. The 15t bike will always be accelerating faster the the other in every gear. fing02.gif

The acceleration we get will be proportional to the torque delivered to the rear wheel. (F=ma stuff...)

Here's a comparison of rear wheel torque using 15T vs. 16T:  VFR.htm ( 50.89k ) Number of downloads: 31


I've calculated the rear wheel torque of VTEC VFR for various road speeds. I've used typical engine torque curve (from a dyno output). The rear wheel torque is simply the engine torque multiplied by the primary gear ratio (1.939), the transmission ratio (varies by gear), and the final drive ratio (either 43/16 or 43/15). The gear ratio was picked by running the bike speed up in the lowest possible gear until we reach a constant "Shift RPM", at which point the next higher gear is used. This process is repeated until I reached 150 MPH. I've done the calculation for 11,500 and 10,000 shift points.

The chart shows road speed, with gear, engine RPM, engine torque, and rear wheel torque for each countershaft size.

The far right column gives the percentage torgue advantage of the 15T configuration vs. the 16T. A negative number means that the stock 16T setup will have more acceleration than the 15T.

At low speeds, when both bikes are in 1st gear, the 15T setup is pretty clearly the winner.

For speeds over about 45 MPH, however, there is no clear winner. When the 16T configuration is in a lower gear (at same speed), then it will accelerate faster. When both bikes are in same gear, the 15T bike will tend to accelerate faster. To some degree, the shift point influences the results; the lower the shift point the more the 15T setup may benefit.

I think the 13% advantage shown for the 15T bike at speeds below 30 MPH is overstated. I did not attempt to model clutch slippage (which we would most certainly be doing at these low speeds to get good performance). A lot of the 13% advantage is simply due to the increased torgue the 15T setup would have due to running higher engine RPM than the 16T for the same bike speed. (I modeled the low RPM torque as a simple linear ramp from 0 torque at 0 RPM to 42 ft-lbs at 5000.) Assuming we both slipped our clutches to something near 5000 RPM, we would have similar engine torque output, so the 15T setup would have just a 6% advantage.

So, 15T has something on the order of 6% advantage below 45 MPH, and it's a wash above that speed. You should win the drag race from a dead stop. I don't see you've got any advantage once were moving (I assume you are not below 45 much of the time on your mountain roads).

baileyrock, Oct 4 2006, 09:48 PM
It's a easy mod to change, just run a 15t when you replace everything for a little loop and decide. If you don't like it you can recover most of the cost of buying a 16t by selling the 15t here. Takes about 15 min. to change.

Excellent point. fing02.gif It is a cheap test, only $25 for a front sprocket. It will be entertaining to experiment.

hlf, Oct 5 2006, 02:14 PM
The acceleration we get will be proportional to the torque delivered to the rear wheel. (F=ma stuff...)
Excellent point. fing02.gif It is a cheap test, only $25 for a front sprocket. It will be entertaining to experiment.

Don't tell me, Your another Engineer! blink.gif schla15.gif laugh.gif

hlf, Oct 4 2006, 05:27 PM

...but is noisier (no rubber damper for 15T F/sprockets)...

What are the other benefits of smaller front (or larger rear) sprockets? Thanks!

I didn't notice any increase in noise when i went to a 15T, of corse with the TBR Pipe and earplugs in, It's all good!

I like the fact that VTEC kicks in at lower SPEED, that means that I can ride along in VETEC mode more often while on ~30 MPH tight twisty roads, and I can pull better in 2nd on the downshifts so I don't accedently downshift into 1st like I did a few times before.

I don't notice any difference on the highway, but the speedo affect is anoying. I didn't figure the cost of a speedo healer into my sprocket change... dry.gif

6% is a huge advantage. Seems like a pretty great price/performance ratio.

Just imagine how much it costs to get 6% more horsepower. wheel.gif

hlf, Oct 4 2006, 04:27 PM
What are the other benefits of smaller front (or larger rear) sprockets? Thanks!

Since replacing my front sprocket with a 15, I've detected a substantial, yet sustainable, elevation in the grin factor. tongue.gif

Laney, Oct 5 2006, 02:52 PM
Since replacing my front sprocket with a 15, I've detected a substantial, yet sustainable, elevation in the grin factor. tongue.gif

+1.gif
Pretty much says it all, it improves the FPG(Fun per Gal.) of the bike!

hlf, Oct 5 2006, 02:14 PM
The acceleration we get will be proportional to the torque delivered to the rear wheel. (F=ma stuff...)


snipped the math stuff

Excellent point. fing02.gif It is a cheap test, only $25 for a front sprocket. It will be entertaining to experiment.

Holt,

You're right (I think) on the math. The engine neither knows nor cares what gear the transmission's in. All it sees is the mechanical advantage provided by the reduction offered by the transmission. Any given gear ratio will result in the same torque multiplication whether that ratio is avaible in 2nd gear (say with stock gearing) or in 3rd (regeared).

I've played with alternate gearing a bit (not on this bike) endurance racing. I think a couple of things are at work in this debate. First, if you regear the bike (down) you will be impressed by how hard the bike pulls in every gear, because IN THAT GEAR it accelerates harder than it has "in that gear" in the past. This leaves one with the impression that "DAMN, that thing runs like a scalded canine with the smaller front sprocket." In this case there may be more psychology than physics at work.

Second, (IIRC) one of the side effects of dropping the final drive ration is the reduce the interval between ratios in the (unmodified) transmission. The effect of this is real. Engine RPM will drop less between shifts, planting you more squarely in the fun part of the powerband in the next gear. What you have is built a poor man's close(er) ratio gear box.

I suspect most of us would find that both of these effects enhance the "grin factor."

I shy away from doing these things to the viffer because I like having 6th gear exactly where it is on long runs at low warp slab speeds.


Now, one of the engineers on the board can come back and tell me I'm FOS. tongue.gif

hlf, Oct 4 2006, 06:27 PM
I'm about to replace my 02 VFR drive chain, and was considering dropping down a tooth on the front sprocket from the stock 16T. However, I'm not sure I understand the benefit.

What am I gaining by lowering the final drive ratio that simply downshifting a gear is not going to accomplish? Obviously, in 1st gear, downshifting is not an option, but I don't spend much time in 1st gear (and would spend even less in 1st if I dropped a tooth).

It seems to me that dropping a tooth on the front gains me some improved acceleration in 1st gear, but is noisier (no rubber damper for 15T F/sprockets), screws up the speedo (unless I want to spend even more money for a Speedo Healer), and potentially raises the engine RPM at crusing speed.

What are the other benefits of smaller front (or larger rear) sprockets? Thanks!

pretty much for wheelie improvement!

I'm content with stock gearing for the street

baileyrock, Oct 5 2006, 03:41 PM
Don't tell me, Your another Engineer!

Yup! idea3.gif

Brown81, Oct 5 2006, 03:44 PM
6% is a huge advantage. Seems like a pretty great price/performance ratio.

Just imagine how much it costs to get 6% more horsepower.

6% torque gain could help you at all speeds. 15T helps you below 45 MPH, and only if you're willing to keep it in 1st gear to that speed. The shift to 2nd negates the advantage.

If you're spending a lot of time below 45, I'd be looking for a supermotard! cool.gif


I'm not for a second dismissing the "grin factor" here, even if it is largely psychological. A love of motorcycles is prima facie evidence that emotions are significant! (Which is why I'll probably try the 15T sprocket, at least for a little while!) Thanks all! beer.gif

My experience...
I went as far as minus two on the front as my dealer couldn't get a minus one. Yes, acceleration much better. The trade-off is in highway comfort - More vibration, and sounds like 100 at only 80. And extra cost for Speedo Healer. And worse gas mileage. Next chain I'll go minus one, for sure.

On my '96, I felt it was a noticable improvement to go -1 tooth on the front. It was a hassle in that my bike aquired milage faster and no longer lined up with the dozens of route sheets my sport touring club has used for a decade.

I would do it again, but only if I could afford a speedo healer. My '02 has a relatively new chain and sprocket, so for now, I won't be modding that.

because we are reposting this whole subject, up two on the rear is approximate of one on the front and you keep the rubberized gear. the rear sprocket change has to be a lot faster than the front. either sprocket change should allow for the use of the stock length of chain. vortex makes rears from 38th to 50th for vfr.
wheelie a lot of fun..............

I have teh Vortex 520 conversion kit. I originally went up 2 teeth on the rear. I did not notice much improvement in the accelleratoin dept. It did make it a little easier to get the front wheel up in 2nd. I thne decided to try going -1 in the front (15T) along with the +2 in the back. All I can say is I noticed a big difference. Much quicker accel and much easier to wheelie in 2nd (less effort to get it off the ground), and as long as I am comfotable after getting the wheel up, I can shift to 3rd and even shifted to 4th once. It allows for longer carrying distance.



NOTE: Wheelie at your own risk. I will not be accountable for you looping your VFR backwards and teh resultant destruction of plastic and metal and any injury sustained from said accident.

I'd love to see a Refridgerator on the back wheel in third wheel.gif fing02.gif

Good science HLF. Another point that can be made is that going up two on the rear sprocket (three requires an extra link in the chain) makes for a shorter wheelbase, as the axle needs to be moved further towards the swingarm pivot to allow the chain to get around the sprocket.

On a 750, this shortens the wheelbase by 10mm. Doesn't sound like much? Well Honda made a big deal about how the side-mounted rads and crankcase-pivot swingarm on the 5th Gen allowed them to shorten the wheelbase by 10mm... it does help to make the bike more nimble in tight cornering.

The bigger rear sprocket will also extend chain life as opposed to the little front sprocket (the tighter radius makes the chain work harder). However, the extra 2000-6000 miles you *might* gain is offset by the higher price of the rear sprocket - so replace them as a set and do it as part of a group purchase to get the price down. We did that on OzVFR and ChainGang gave us 10% off and free freight; a good saving on a $2500 order!