Little review - 18T upgrade

[twocool]

OK... right...so if the max HP is at 8500...and WOT in sixth gear gives you 8500, the gearing is just about perfect...........(unless you want to use 6th like an overdrive and cruise at relatively high speed with lower RPM........Again "performance" and "economy are at odds.

Once you get the bike moving from a stop...you can upshift at any RPM you desire..this is why the "middle gears" don't really matter.....

The power curve is kinda flat up there around 8500 ...so a bit more or less RPM really doesn't matter........

yes you want to be way above the max HP RPM when you shift up...so that you are still in the power band once in the new higher gear........

There are many articles on this....some conclude that you should run all the way to redline before shifting.

If you shift and the rpm drops to 7000...you are too low on the power band.....You want to be close to 8500 AFTER the upshift........but this is for max acceleration.....

I shift anywhere between 5000 and 6500 unless I'm in a hurry.......I have never had my bike anywhere near redline....since I have nowhere to go, I don't need to get there fast..

Cookie

For the fastest possible top speed, flat out.....we need the engine to produce the max possible Horsepower....This comes near or at redline..........

By theoretical top speed I am guessing you mean redline RPM in sixth gear.........This would be disregarding the aerodynamic drag (and other drag)

If the bike hits 108 mph flat out in sixth gear...  but can't get past 8500 rpm.....then the gear ratio is too high for max possible top speed......A (slightly) lower gear would allow the engine to spin up to redline, thus producing more horsepower and (slightly)more speed.........)

Max HP comes just a little before redline, I believe.......for max acceleration you should SHIFT at redline though..

I'm talking about a stock GS500 which does hit the approx 108 mph top speed at the max HP which is the point I was making, Suzuki got it right, and it is as you said:  For the fastest possible top speed, flat out.....we need the engine to produce the max possible Horsepower.  But this happens at 8500 rpm on a stock GS500 long before the 11.000 rpm redline and so max acceleration can be had shifting at 9-9.5k rpm.  Doing so drops the rpm about 2k rpm to the top of the torque curve at approx. 7000 rpm.  That's why I refer to running at 7-9k rpm for max performance on stock GS shifting up and down to keep it there.  Typical dyno curve for a stock GS looks like this:



Do a good job of modifying intake, exhaust, and jetting and you can extend the power peak close to the redline like John did on Annie's GS:

[prmas]

You are correct of course GSJACK. For maximum acceleration you should up-shift at the point which will place the engine just a little before peak torque when the next higher gear is selected. On a close ratio gearbox this will likely be near the same revs each time but on a gearbox with "tall or short" intermediate ratios the shift revs will be quite different for each gear. Having an overdrive 6th gives relaxed, almost vibe free cruising with slightly improved economy. If it is hilly or I have a headwind I use 5th gear which is now roughly the equivalent of my stock 6th. As I have said on another similar thread recently I have been using 18/37 for 2 years and like it very much. With standard tyres this gives me 4950rpm at a "true" 100kph/62mph. I have recently recalibrated my speedo to eliminate the inbuilt 10% error. 

Macka

[twocool]

Well...i think if you do a little reading on the internet...you will see that upshifting to peak (engine) torque is not the best  for acceleration....Upshift to peak HP....so you have to run your RPM past peak HP in order to shift to peak on the next higher gear.......

Some confuse engine torque with real wheel torque...rear wheel torque is AFTER you figure in the gearing.......max rear wheel torque (at a given ground speed) is going to come at peak engine HP.........

Remember HP is torque times RPM..........so torque is only part of the power equation........max HP is max HP...at max engine torque...you are producing significantly less than max HP... which means in order to get max acceleration you need to keep the engine as close as possible to max HP rpm........This is the whole reason for gears in the first place...in theory..if you had more gears...or "infinite gears"...you would just run the engine at best HP RPM and leave it there...and let the gearing go up continuously as the bike speed increases......

Cookie

You are correct of course GSJACK. For maximum acceleration you should up-shift at the point which will place the engine just a little before peak torque when the next higher gear is selected. On a close ratio gearbox this will likely be near the same revs each time but on a gearbox with "tall or short" intermediate ratios the shift revs will be quite different for each gear. Having an overdrive 6th gives relaxed, almost vibe free cruising with slightly improved economy. If it is hilly or I have a headwind I use 5th gear which is now roughly the equivalent of my stock 6th. As I have said on another similar thread recently I have been using 18/37 for 2 years and like it very much. With standard tyres this gives me 4950rpm at a "true" 100kph/62mph. I have recently recalibrated my speedo to eliminate the inbuilt 10% error. 

Macka

[twocool]

http://www.sportrider.com/tech/146_0402_art/

Here's a nice article which explains it better than I ever can......

Note shift points are at the overlaps...sometimes at redline...sometime less than redline.....

Cookie

[prmas]

Sorry Twocool, as I read the article it pretty much confirms what I said but in a different way, therefore I disagree with you. There is no point upshifting so that your next gear places you at peak power as both torque and power are decreasing from that point on. As the article says, you have passed your best point. You will still have acceleration but less than you would have "in the torque/power band". If you get the "surge" on upshift as in the artlcle you have obviously shifted too late. It should feel like a pretty smooth curve but it will depend on gear ratio spacing and the characteristics of the engine. Sometimes on a standard gearbox that will lead to troughs in acceleration. That is why racing bikes use cassette gearboxes with the ability to change intermediate ratios quickly and easily to suite the track of the day. I agree that the engine is most efficient where the torque and power lines cross. It is interesting in the dyno sheets that GSJACK put up that after modification there was a very worthwile increase in power at the top end but quite a dip in torque between about 3500 and 5000 rpm. This shows that the engine has gained overall but has become more "peaky". It would feel a little flatter at city speeds in higher gears relative to the top end than when standard. If that is what you want , great. Not for me though.
Macka

[twocool]

Look at first and second gear in that article

you gotta go to redline  (this is true for any gearing where the power curves don't touch each other...

Later gears which are closer spaced.... you shift where the power curve lines cross..so you don't go all the way to redline...

But engine horsepower is what you want......producing the most hp at the engine will always give you the best torque (drive force) at the wheel.

Again...if you had "infinite" gears...there would be only one smooth curve...it would approximate the six little curves you see on the charts.......if you made a smooth curve touching the little curves where each one crosses the next.........

If max HP comes at 8500 then that infinite transmission would keep the engine at 8500 the whole time..........

Since we have 6 finite gears...we have to approximate that curve with 6 little separate curves........

I grant you that in the higher and closer spaced gears...you don't want to run all the way to redline...because you would actually get more torque (driving force) to the wheel in the next higher gear........

The charts show that with some bikes..one gear curve actually crosses the next two gears....so you could actually go up two gears at once.


But remember what we are trying to do is get max torque at the rear wheel...not max engine torque.......

Max rear wheel torque come at peak engine HP.........

Sorry Twocool, as I read the article it pretty much confirms what I said but in a different way, therefore I disagree with you. There is no point upshifting so that your next gear places you at peak power as both torque and power are decreasing from that point on. As the article says, you have passed your best point. You will still have acceleration but less than you would have "in the torque/power band". If you get the "surge" on upshift as in the artlcle you have obviously shifted too late. It should feel like a pretty smooth curve but it will depend on gear ratio spacing and the characteristics of the engine. Sometimes on a standard gearbox that will lead to troughs in acceleration. That is why racing bikes use cassette gearboxes with the ability to change intermediate ratios quickly and easily to suite the track of the day. I agree that the engine is most efficient where the torque and power lines cross. It is interesting in the dyno sheets that GSJACK put up that after modification there was a very worthwile increase in power at the top end but quite a dip in torque between about 3500 and 5000 rpm. This shows that the engine has gained overall but has become more "peaky". It would feel a little flatter at city speeds in higher gears relative to the top end than when standard. If that is what you want , great. Not for me though.
Macka

[twocool]

you can see on Jack's charts..that at peak torque...you're producing about 34 Hp at 7000 rpm

while the max HP comes in at 38 HP at 8500   but the curve is still pretty flat up to 9000..........

so after an up shift...if you're down to 7000...you are 4 HP short.........

the closer you keep the engine to 8500 the faster you will accelerate...

Cookie

[Janx101]

i do find this interesting...  ... specially prmas 18/37 combo ...

as for the gearing vs torque vs hp bit ... cant help myself ...



.... and this is my preferred seating ..

[Soloratov]

Lol, Janx. I'm more confused how we got there! All I am trying to do is present data, in an objective way and then share my opinion based on those numbers and my experience. Especially considering by increasing the gearing I am effectively going the wrong way in the higher torque argument.

Either way. I added the Speed/RPM graph and corresponding gears information for the 16T sprocket. I will be recreating this graph for the 18T this weekend.

[Janx101]

'how we got there' ... pffft .. easy ... classic case of "my engineers sliderule is bigger and shinier than your engineers sliderule!!" .. happens all the time...

.... nevertheless .. i AM going to re-sprocket my bike with a 17 or 18 up front... and either a 39 again or 37 on the back .. gotta get the funds together tho 

thinking of getting all the bits .. and over time trying them out... so then i can 'grunt appropriately' yes/no in these kind of discussions..

probably going to get a clip link chain too!!! .. ooooeeeerrrrr gasp goes the crowd!!  .. so i can pull the chain out easier and give it a proper clean when it needs it... cleaning a chain on the bike never seems to get right into the nooks and crannies!!

of course this will mean i need to actually learn to do spanner-ish type things on the bike .. but sacrifices must be made in the name of "cos i can"

really a torque/hp comparison "hoedown"  is pointless in this thread... no offense meant... its about how you feel with your change in cogs .. every other person is going to have a different view anyway .. love it or hate it ..

looking forward to your reports/charts .. will give some more good baseline checking info for later!! 

[gsJack]

you can see on Jack's charts..that at peak torque...you're producing about 34 Hp at 7000 rpm

while the max HP comes in at 38 HP at 8500   but the curve is still pretty flat up to 9000..........

so after an up shift...if you're down to 7000...you are 4 HP short.........

the closer you keep the engine to 8500 the faster you will accelerate...

Cookie

so max acceleration can be had shifting at 9-9.5k rpm.  Doing so drops the rpm about 2k rpm to the top of the torque curve at approx. 7000 rpm.  That's why I refer to running at 7-9k rpm for max performance on stock GS shifting up and down to keep it there.

That's why I say upshifting at 9-9.5k will give max acceleration on the stock GS since it is a full 2k rpm drop on the 2-3 shift but it's an increasingly lesser drop on the 3-4 and the 4-5 shifts.  If you look at a 2k drop from 9.5k to 7.5k rpm on the dyno chart you will see near equal amounts of HP below max HP above and below the 8.5k max rpm point.  And at the higher 3-4-5 gear shifts the best point will drop closer to the 9k.  Here's a chart showing the speeds in mph of the GS at 7k and 9k rpm in all gears for your amusement, we've been here before in such a similar almost silly discussion:



And now I will take Janx's astute advice and withdraw from the field of battle with apologies to Soloratov for my part in the hijacking of his thread.   

'how we got there' ... pffft .. easy ... classic case of "my engineers sliderule is bigger and shinier than your engineers sliderule!!" .. happens all the time.........................
........................really a torque/hp comparison "hoedown"  is pointless in this thread... no offense meant... its about how you feel with your change in cogs .. every other person is going to have a different view anyway .. love it or hate it ..

[SAFE-T]

Given the difficulty of finding an 18tooth front sprocket I would really look at a 17/36 combination if it was available.

[gsJack]

http://vortex-sprockets.com/categories.php?category=Suzuki-Sprockets/GS500-89%252d08&sort=featured&page=1

http://gstwins.com/gsboard/index.php?topic=62854.msg738503#msg738503

[Soloratov]

I also added link to an 18T with hub

[mister]

I have nothing to add to this thread.

[SAFE-T]

36tooth rear sprocket in steel ? Bueller  ?

[prmas]

My front shoulderless 18t sprocket (on my K9) is steel but the rear 37t is alloy and shows no wear after 11,500km. If it is kept clean and lubed it should give good service. I bought the alloy one as an experiment but it has exceeded expectations. 

Macka

[Soloratov]

Added Tank 2 stats for the day. So far, a marked increase in fuel mileage is obvious, but more so is the dramatic decrease in RPM that I can say has made a great difference in my riding comfort.

[twocool]

Increase?

Added Tank 2 stats for the day. So far, a marked increase in fuel mileage is obvious, but more so is the dramatic increase in RPM that I can say has made a great difference in my riding comfort.

[Soloratov]

woops, typo.