|Topic Review (Newest First)|
|10-17-2019 11:44 AM|
Originally Posted by SparkyMJ View Post
Everything in life is a compromise. Gearing change is no different, you never get something for free, you have to lose something else (Thermodynamics, anyone?). I'm not trying to be argumentative or confrontational, you do you, I'm just trying to inject some physics into the discussion so other people can weigh their options. Plus, I just love physics. Note: I'm figuring out the details as I go, so until the end I won't actually know the results. It's not to say one is objectively better or worse, just to highlight the differences.
Torque and Horsepower are related through RPM. The torque we are interested in is delivery to the ground, so wheel RPM is what matters. At a given RPM at WOT, the engine will produce a certain amount of power (ignoring environmental effects, etc.). Dyno charts correlate Torque and HP to engine RPM at WOT. A dyno chart I found online gives a peak HP of 34.95 at 10860RPM and Torque of 18 at 8370RPM. Important to note that a dyno only measures torque, it then calculates HP based on RPM using the applicable formula, which we will discuss in a moment. For the below, we will assume WOT for all cases. HP delivery is not affected by gearing (there are losses in the system, however the dyno measures at the wheel so we can ignore those) so the HP at the wheel is related only to engine RPM. Your gearing increases the speed by 5% for a given RPM, but also reduces the torque at that RPM by 5% as the power remains constant (wheel RPM up, torque to the ground down). Let's assume you are at peak power in 3rd gear and someone with stock gearing is at the same speed in 4th. Your engine is 10860RPM, your wheel is 874RPM. The same wheel speed (therefore forward speed) with stock gearing in 4th gives and engine RPM of 9387. You're making peak at 34.95, he's making 31.30. HP and torque are related by P=T*RPM/5252, so you are delivering 210FTLBS to the ground and he is only getting 188FTLBS down. We're going 103km/h. Looks pretty clear in your favour, but remember we based these on your engine being at peak performance and he's matching your speed.
If we reverse the roles, for him at peak HP we have a wheel speed of 1011RPM and you at 12564RPM, basically at redline. Good, right? Well, your power output is coming down to 32.7. You deliver 170FTLBS and he's got 181.6FTLBS on the ground. Speed is 120 km/h. Somewhere between 103km/h and 120 km/h your advantage of being in the lower gear gets lost. Also you're just about to upshift, pushing you into the bottom of the 4th gear band, greatly dropping your torque delivery, and you're playing catch up until he has to upshift, and you again get a brief advantage until you shift again.
Bear in mind we are only looking at torque to the ground so this comparison is only valid for saying in general, he will outperform you in terms of acceleration only except for the couple thousand RPM he's past peak power and you're still building up to peak. He's going to use more gas to do it, and if you've got a long enough straight to max out the speed of the bike, you may have him beat for top speed, but as far as the twisties where acceleration is key, you've only have him beat in the narrow speed range where you can downshift to hit peak power and he's got to stay in the higher gear. I say narrow, because our example of 3rd and 4th, you've probably only got the advantage if we take the turns between 95km/h and 110km/h. Any faster and you're up a gear, any slower and he can kick down one to be higher up the power chart. In short, if you are in the same gear at the same speed, he will out accelerate you every time. A small range of speeds will allow you to put more power down due to being able to drop a gear sooner. If most of the time is spent in that range (there will be one range every space between gears, so total of 5 speed ranges, extremely narrow in the lower gears and widening slightly as we go through the gearbox), you've got a winning gear ratio, but outside of those ranges, you're lagging behind.
Originally Posted by SparkyMJ View Post
I'm sure you're talking GPS, but for those of you who want to know more:
Most displays are somewhere between 5%/10% optimistic, and some places even have laws governing the accuracy. For example, in Europe, ECE-R39 requires that the speedo NEVER under-reads and over-reads by no more than 110%+4km/h. This means that if you are going 100km/h, your speedo would have to read between 100 and 114. It would make sense that a vehicle manufacturer would find a calibration that meets global requirements so they don't have to make a Europe specific cluster that meets this standard, but the NA cluster reads differently, and it would make sense that the reading would be somewhere in the middle of the allowable range to give the most leeway for tolerances, meaning at 100km/h, you will likely read 107 on the dial.
Also, the display takes the reading at the transmission output, so a final drive ratio change will again impact the variance between the actual and measured speeds. This gearing change however, will have the effect of under-reading, so it might actually "correct" for the intentional "error" injected.
TLDR: Nothing is free, depending on the scenario, a gearing change can improve or reduce overall performance. Everyone should do whatever it is they want with their bike. If you like it and it works for you, just do it!
|10-16-2019 04:02 PM|
I geared up to 14/40, and it is quite pleasant to me. I found that yes, I lost torque overall, but it gave me more gears to use at higher speeds. So at the track, on the twisties, or even just freeway riding, I could more often downshift, which was important to me so I could get to redline more often and at high speeds. Thats my opinion.
I can get to maybe 105-110 mph depending on the altitude im at, my tuck, and any other weight changes.
It is a great ratio for all around usage though, commuting and sport riding alike.
|10-11-2019 10:28 AM|
The limiting factor on this bike as far as top speed goes seems to be overcoming air resistance with torque at the wheel. Taller gearing is going to deliver less torque at the wheel for a given power output, which with taller gearing would also correspond to a higher speed. For a given speed, your torque output would be much lower than OEM gearing. If by "top end" you mean actual maximum speed, you will likely find that taller gearing will lower your top speed. If you just mean for a given gear selection, you might find an increase in top end for the first 4 or 5 gears, but the only real benefit here is a lower RPM for a given speed, at the expense of acceleration. I'm not telling you not to do it, but I think the physics doesn't work the way you expect it to. I imagine you are not going to get the desired result. Please let us know how it works out for you, I haven't tried a gearing change so this is all theoretical.
As a point of reference, with 15/40, your 5th gear will behave almost identical to OEM 6th gear, and your 6th gear would be even more gutless.
|10-10-2019 11:12 AM|
Originally Posted by vanguard_desperado View Post
There is a point where the engine does not have enough power to overcome aerodynamic drag, and the gearing isn't going to change that - it may even give you lower top speed.
Some cycles with "tall" gearing even go faster in a lower gear (5th) than they do in top gear (6th). The reason being the engine is operating closer to it's peak power in the lower gear, so it can overcome the increased drag.
The big advantage to taller gearing is lower cruising RPMs, but even then it doesn't guarantee better mileage. Again, changing the gearing may put the engine in a less efficient range while cruising, which would require additional throttle opening to maintain speed.
It's all a balance, but just looking at the number calculations doesn't tell the entire story. The little Ninja's engine likes to be revved, and makes its power up high, so dropping RPMs can put it into a range where it's not as efficient.
|10-09-2019 05:39 PM|
Here are a couple of threads that discuss sprocket ratios in depth...
|10-09-2019 04:24 PM|
I already grabbed a 40t rear. It’s finalized, haha
I just want more “top end” and so that’s the specs I’m going with.
I just generally wanted to know if I do use 15t/40t you guys think I’d have to shorten chain length, right?
My teeth are bad hence changing them. Worst case I just put my old ones back. I’ll try to send pics of how bad they are though.
If I’m not being clear, I’m sorry.
I’ll let you guys know when I do it!
|10-09-2019 11:21 AM|
|Kennylxix||I've got a 15t waiting to go one one of these days. Im definitely curious to see how it feels.|
|10-09-2019 10:27 AM|
You'd probably be fine with just the 15T as far as chain length goes.
Depending on your size and riding type/style/location, you may find just going to a 15T is too much.
Search around here for opinions, but I though I'd read comments where people ended-up switching back to stock gearing due to the reduction in acceleration from gearing up.
|10-09-2019 07:02 AM|
|Kennylxix||That's a pretty big jump. I wonder if trying just the 15t first would be a good idea.|
|10-09-2019 04:55 AM|
Changing Drivechain! Help?!
This may have been posted somewhere and if it has can you please link?
I am changing my sprockets and my chain!
15t/40t front/rear and I was wondering... will I need to remove some links from my chain, or...
Can you please help? I’m not sure if I will have to shorten chain, though I’m assuming I will. If that is the case, I will just take the links off the same way you break the chain with the chain tool, correct?
Sorry again if this same question was posted elsewhere. I’m new!