My experience changing final gearing for better mileage (14-43 -> 16-41) - Yamaha R3 Forum
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post #1 of 9 Old 09-02-2019, 01:49 PM Thread Starter
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Post My experience changing final gearing for better mileage (14-43 -> 16-41)

I bought my R3 not because I wanted a racing/sport bike specifically but rather because I wanted a motorcycle and I heard the R3 was a good bike to learn on. It's also popular enough that I hoped spare/aftermarket parts would be cheap and abundant, and I found a pretty good deal for a new-old 2016. No ABS unfortunately, though I know opinions on ABS are mixed.

So you can have some perspective on who's writing this, I don't have super high performance expectations. For example, even if I didn't know about the break-in period I doubt I'd ever have gotten the engine above 7000 RPM. I pretty much just take it easy.

Why I wanted to do this:

My immediate concern was that first gear felt useless; I felt like I needed to shift into second before I was even through an intersection. This instinct led to some hair-raising experiences where I shifted with the bike leaned a bit while turning left from a stop. Not a good idea apparently.

Another thing I hoped to improve was my gas mileage. Unfortunately I don't have a record of my gas mileage before the sprocket change. My hope was to reach ~80 MPG at 80 KM/H (50 MPH), which would also help to extend my range without a backup gas can. My gearing changes should hopefully (?) also be easier on the engine and drivetrain, extending lifespan somewhat.

Using Gearing Commander I found that if I remove a tooth in the rear for every tooth I add in the front, I don't need to unnecessarily replace my factory-new chain. A 16 tooth front sprocket was the biggest I could find so I went with a 41 tooth rear sprocket. The rear axle is still in roughly the same place as it was originally, maybe off by 1mm or so.

B]The parts I purchased:[/B]

- JT Sprockets 520 Front Sprocket 16 teeth
- JT Sprockets 520 Rear Sprocket 41 teeth
- Speedo Healer V4.0 Control Unit
- Speedo Healer V4.0 Harness (SH-H05)

As it turns out, the 17 tooth front sprocket I'd originally hoped to buy would've been a mistake anyway. A 16 tooth front sprocket is a hair too big and it causes the chain to rub against the plastic cover for the front sprocket. I've put ~800 KM (500 miles) on it since changing the sprocket and I don't hear a rubbing noise anymore; I expect it's "worn in" by now. When I said it's a hair too big, it really is just a hair. It barely touches it, at least with the sprocket I got.

I'm really sorry I'm hazy on this, but I remember using a dremel at one point. This was over a month ago and I've done a lot of other work on the bike and around the house since then, so I don't remember what specifically I did with it. Sorry. It probably would've been cutting out a spot where the chain would rub, likely at the top or bottom of the cover where the chain enters/exits. I know it was a tiny adjustment, a millimeter or two... so have a dremel on hand, you'll figure out quickly what needs to be done.

The rear sprocket was fine, no issues at all besides rookie mistakes and it being a PITA to get the rear brake caliper to cooperate while putting the wheel back on. Watch for those spacers. Have something on hand that you can put beneath the rear wheel to help you hold it in place while you put the axle back through, some books or something.

I replaced the sprockets with very minimal mechanical knowledge only aided by YouTube videos (STG has everything you need), so I highly recommend this as a beginner-intermediate mod. It took me a few hours since I was unsure of myself; I could do the same job again in less than an hour. For the rear axle IIRC you'll need a 19mm and 22mm socket, while the front sprocket's giant nut will require a 29mm socket and an extra-long handled rachet for better leverage because it's on there tight from the factory. You'll need rear spools and a spool jack thing, not expensive. Use a torque wrench to re-tighten all bolts/nuts to factory spec. IIRC you need locktite on the front sprocket's bolt. Be careful with routing the cables that go near the front sprocket, they need to go back where they started when you put the cover back on.

Speedo Healer is a device that adjusts the tachometer & odometer to account for the different gearing. Without it (or something similar) your speedometer and odometer will give inaccurate readings. It's a little tricky to install without instructions but I think STG has an install guide video on YouTube. I found I needed a 10% offset from the factory calibration to get it GPS-perfect but you should check this for yourself. Speedo Healer is difficult to find in Canada. Bayside Performance sells them, though I found them to have pretty miserable customer service and false stock listings on their website (which still hadn't been corrected when I checked back months later).

Results:

I used to be able to get into 6th gear while just cruising around town at ~55 KM/H (34 MPH) without lugging the engine, while it's now more comfortable at around 70 KM/H (43 MPH). That, in my mind, is the sort of speed a 6th gear should be for.

First gear now feels much more useful and there's no longer something in the back of my mind telling me I should be shifting into second even before I'm out of an intersection, which is a huge safety thing (for me as a beginner at least). If I need to accelerate quickly I can hit ~30 KM/H (19 MPH) at around 5000 RPM in 1st gear, which isn't obnoxiously loud.

I really don't want to be one of those people that wakes up the neighborhood, so the generally lower RPM (about a 16.6% reduction) is nice for that.

I can't say for sure - it might only be due to gaining experience - but I find the bike is now more forgiving when starting from a stop. It's more tame and feels easier to leave a stop sign with a measured pace rather than either stalling or accelerating overly fast. Again, this could easily be down to gaining experience. I CAN still accelerate fast if I want to, but it's not something I do by accident. I like how it feels better, in any case.

If I'm going 80 KM/H (50 MPH) in sixth gear (for reference now ~4200 RPM on flat), I can slowly accelerate while going up a quite steep hill. As I understand it, 4200 RPM is well below the bike's power band, so if I was moving at highway speed (~110 KM/H / 68 MPH, 5800 RPM), I'd probably still be good even considering greater air resistance.

With my previous gearing, if I needed to quickly pass someone on a highway I'd ideally be in 5th to have the best acceleration past 120 KM/H (75 MPH), while now 4th is where I'd want to be.

I spend probably 60% of my time on county roads doing 85 KPH (53 MPH) or so. At best I'm now getting 3.8-3.9 L/100 KM (72-75 MPG imperial, 60-62 MPG US). Yamaha estimates 63 MPG imperial (56 MPG US). That was before the first service, which I've heard may improve mileage. I just did my first oil & filter change yesterday and haven't had it out again since then.

I can't speak for how sporty it feels now since I don't really have a point of comparison. It's my first bike and I only rode it a couple hundred KM with the original sprockets. Without riding like a complete dick I can still easily leave an intersection before anyone else has reached the half-way point, sometimes before they've even passed the crosswalk. I'm not a racer, so if the only thing on the road faster than me is another motorcycle, that's more than good enough in my book. I doubt I'll be doing any wheelies with this gearing, I've never tried it and don't intend to.

When it's time to get a new chain/sprocket set I'm planning to go even further and try a 110 link chain (stock is 112 and would be too long I think) with 16/38 sprockets (a further 7.3% RPM reduction) to see how that feels. With 16/38, I'd be running around 3300 RPM in 4th gear around the city at 50 KM/H (31 MPH), 3900 RPM in 6th on county roads at 80 KM/H (50 MPH), and 5400 RPM in 6th on the highway at 110 KM/H (68 MPH).

Any truth to what I've heard about MPG improving after the break-in period? Due to a surgical procedure (thankfully unrelated to motorcycling) I can't ride for another week or so, so I'm curious what I might find.
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post #2 of 9 Old 09-02-2019, 08:06 PM
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Interesting, as I'd expected that driving economically you'd get better mileage than that. I can't remember precicely what my R3 used to get, but my MT07 sits consistently on 4.0L/100km and that's pure commuting with and without traffic, up to 70km/h max. And I blast it open every chance I get.

It might be a break in thing for you as well, but I also thing you might have picked the wrong bike if pure economy was your thing. If you think about where the engine is operating most efficiently, this is where the engine it as peak torque. The R3 is quite a revvy little thing so peak torque happens moderately high in the RPM range. At casual street cruising RPM, the engine is below this point and not operating in it's efficiency zone. This would explain why my MT07 gets roughly the same fuel consumption, as this engine has peak torque lower in the RPM.

I reckon you'd get much better mileage out of a CBR300 or possible even a CBR500 as these bikes run stronger at lower RPM.
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post #3 of 9 Old 09-04-2019, 01:49 AM
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The law of diminishing returns is in effect here. Making the revs even lower probably won't return much, if any, further improvement in fuel consumption, and there are foreseeable mechanisms that could make it worse. Lugging the engine down under heavy load (caused by gearing that is too tall and asking it to go uphill) may put it into a speed and load regime that uses full-load enrichment and/or delayed ignition timing to forestall detonation.

My R3 is only ever below 7000 rpm when puttering around in the paddock and on the cool-down lap, and just from that, it feels juddery and rough when under load much below 5000 rpm. It is not really designed to operate under load down there. (In fairness, I also haven't really tuned it to optimise operation down there.)

Best BSFC (brake specific fuel consumption) on typical gasoline engines usually happens somewhere near peak-torque RPM and that's north of 7000 rpm in this case. That doesn't necessarily mean you will get best gas mileage by always keeping it up there, but it does mean that lugging it down under load below that isn't necessarily doing yourself any favors.

Due to my racetrack use of the bike I have a handy-dandy little spreadsheet for working out gear ratios.

Stock gearing with a 150/60-17 rear tire (not stock! although rolling diameter is not far off) gives 3891 revs per km in 6th gear (this is actual speed and actual RPM, not what the instruments say). So 100 km/h in 6th would be 6484 rpm, and 110 km/h would be 7133 rpm. This is basically the bottom of the RPM range where the engine makes decent torque. (The actual peak is around 9000 rpm, there is a pretty significant ramp-up between 6000 and 7000 rpm, below that it's only making about 80% of peak)

Your current set-up gives 5410 actual RPM at actual 100 km/h. It's only making about 18 horsepower at that point ... you're probably using about 12 to do that. In terms of BSFC that's actually a pretty good situation. Half of rated RPM and two-thirds of rated torque usually lands pretty close to the best-BSFC "island" on the operating-conditions map.

If you do your proposed change, it will only be doing 5014 actual RPM at actual 100 km/h and only making 15 horsepower. And it will be in that RPM range where it's going chugga-chugga-chugga-chug. I do not think you will be happy with that ... And it won't be appreciably better in terms of BSFC; if anything it will be falling off the bottom in terms of RPM and falling off the top of that best-BSFC "island" in terms of torque.

If you're happy with what you've got, I'd say leave well enough alone. I wouldn't like it, but I'm not you. Changing it further, in your proposed direction, isn't going to accomplish what you are looking for and it will be worse in other aspects.





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post #4 of 9 Old 09-04-2019, 03:33 AM
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I'm afraid that GoFaster is absolutely correct in his analysis. That were my immediate thoughts as well when I read the article.
Learning to ride properly and understanding the basics of your R3 might have been the wiser decision, especially as there is nothing wrong with using higher revs every now and then.
You wrote that you mostly spend your time on country roads at around 85 kph and I wonder what benefit a longer transmission should bring there. If you spent most of your time on motorways at or above 150 kph I would be able to kinda get your point but not for the speed range you are using.

I have a stock 2016 R3 and even though I go somewhat faster than you on country roads - where I spend about 80% of my riding time - my fuel consumption is considerably lower than yours. Not sure what you actually gain from your modification but I know what you lose and that is acceleration perfomance which sometimes is an essential safety factor - not just when overtaking other vehicles...
Anyway, as GoFaster wrote: "I wouldn't like it but I am not you"... Keep enjoying your R3 and take care!
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post #5 of 9 Old 09-08-2019, 05:48 AM
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My R3 is completely standard and I always get 78-80mpg UK measures, confirmed by both the dash display and fuel receipts. This is over a mixture of in and out of town and touring miles. I don't specifically ride with economy in mind and usually change up at or before 7000 unless I feel the need to hurry.
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post #6 of 9 Old 09-09-2019, 02:25 AM Thread Starter
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Thanks for your responses, very educational. If I understand correctly then, I'm likely better off running it at ~7000 RPM for best milage? That's much higher than I would've guessed, but obviously I'm barely even an amateur. I'd assumed until now that lower RPM is simply better for milage, like it is with a car. Counterintuitive. Could someone explain why that isn't the case with bikes?

In any case, I should still be able to run the engine in that efficient zone now, just maybe in a lower gear, right?

I'll definitely not go with the 16-38 experiment if it's not going to be beneficial at all.

When it's time to change sprockets or if I'm feeling bored one day then I'll try the originals again to see what I think of them now that I'm a little more comfortable with riding in general.

My feeling right now is, I do prefer having a more usable first gear, especially for wide left turns from a stop at intersections. Shifting to second at a lean was hair-raising. And this is strictly a personal preference thing, but I do prefer having the option to make my bike a little bit quieter around town. I really don't like it when people with loud exhaust come down my street early in the morning and it's become a pet peeve of mine I don't want to reproduce for others if I can help it.

I'm writing this on a phone so I can't refer to the replies directly but I remember someone saying 5000 RPM feels like the engine is lugging to them. That's not my experience, it feels smooth to me down to 3500 RPM even in sixth. Maybe I just don't know what less severe lugging feels like though.

It's definitely possible/probable I didn't go with the ideal bike off the factory floor but I've really enjoyed making the customizations to it that I have, in order to make it the ideal bike for me. Stuff besides just the sprockets I mean. I'm planning on welding together a custom luggage rack next! Lots of fun and I'm learning a lot.
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post #7 of 9 Old 09-10-2019, 08:40 PM Thread Starter
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On your advice I switched back to my OEM sprockets for now. It's rough going back to the first gear being so useless. I'll at least leave them on for the rest of the season though to give them an honest try.
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post #8 of 9 Old 09-11-2019, 09:25 AM
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The BSFC map is not that simple; just because the best-efficiency "island" is probably in the 7000 - 9000 rpm range doesn't mean that's the best RPM range all the time. The best-efficiency "island" on the BSFC map is also contingent on being (generally) around two-thirds to three-quarters of rated torque, and being "off the island" in terms of being below the torque range is worse than being off in terms of being below the RPM range. If only a small amount of power is being demanded then it's better to turn the engine slower but with greater torque ... up to a point.


I think you'll find that with the stock gearing compared to what you had, there will be little real-world impact on fuel consumption. Remember to correct your odometer when establishing this (compared to what you had before, which would have under-reported your actual driving distance).
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post #9 of 9 Old 09-11-2019, 09:27 AM
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Here is a link to a thread on another forum that gets into this topic.


https://www.eng-tips.com/viewthread.cfm?qid=363722
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