18 t-front sprocket and 130 / 90 rear tyre - dropping approx 1600 rpms each gear

[lin]

hello dear GS-Fans,


i am looking for a 18-Tooth Front Sprocket. Where to buy it?    I have a GS 500 (version 1999).

Does anybody have made any experience witht this sprocket.

i allready have heared about a  change to

130 / 90  from
130 / 70

The new tyre should lower the RPMs  about 1000 x in each gear - is this true!?
Just tell me your opinion, your ideas and - if you have got - your experiences -

just look forward to a very fruitful discussion...


love to hear from you ...

greetings
lin 


see this topic here .... ;
http://gstwins.com/gsboard/index.php?topic=21803.0

I was in the same boat abot two years ago when I first went from the stock 130/70 rear
tire to a 130/90 which effectiavly drops 1000 rpms for each gear.   for me it was easier
to find tires in taller sizes than a new sprocket.   #
instead of going to a 18 tooth sprocket you may want to try going to a 80 series rear tire.

that means that it is a very very effectiv way to choose a new rear tyre - which effectively drops 1000 rpms for each gear.
Well - how does this big tyre change the bike  - is it more difficult to ride such a tyre!?

[Roxtar]

tire math time!

diameter of a 130/70-17 tire = 17inches + 2*(130mm*.7) = 17 inches + 182 mm = 24.17 inches
diameter of a 130/90-17 tire = 17inches + 2*(130mm*.9) = 17 inches + 234 mm = 26.21 inches

circumference = pi * diameter.
stock tire = 75.93 inches around
90 profile = 82.34 inches around
82.34/75.93 = 1.08441986

this means that you'll be traveling 8.4% faster at a given rpm with the 90 profile tire.

stock, 5500 rpm in 6th is ~70mph.
with the 90 profile tire, 5500 rpm in 6th = ~70*1.084 = ~76mph... meaning that 70 would be ~5000 rpm.
you save around 500 rpm at cruising speeds.

how does this change the ride? well, the taller tire effectively gives you a taller final drive. the engine has to do more work with the torque it has available. getting going from a stop will be harder. you'll struggle more on hills and in passing. acceleration will be slower.

check this site out:
http://www.gearingcommander.com/

[gsJack]

130 / 90  from
130 / 70
The new tyre should lower the RPMs  about 1000 x in each gear - is this true!?
Just tell me your opinion, your ideas and - if you have got - your experiences -

No, not true.  Change in rpm is proportional to change in speed/change in tire dia/change in gearing so it's not so simple as that.

4730 rpm @ 60 mph with 130/70 in top gear with stock GS500
4730 x 24.2/26.2 rpm = 4370 @ 60 mph with 130/90
4730 x 80/60 = 6307 rpm @ 80 mph with 130/70
6307 x 24.2/26,2 = 5825 rpm @ 80 mph with 130/90
5825 x 16/17 = 5482 rpm @ 80 mph with 130/90 and 17T
5825 x 16/18 = 5178 rpm @ 80 mph with 130/90 and 18T

So 130/70 to 130/90 change will reduce engine speed 360 rpm @ 60mph and 482 rpm @ 80 mph.  A 130/70 to 130/90 plus a 16-18T sprocket change will reduce engine speed 1129 rpm @ 80 mph, less at lower speeds and/or in lower gears.

I ran a couple 130/90 rear tires about 10 years ago for about 35k miles, my reason was to use long milage touring tires available in the 130/90 size.  Only difference I noticed regarding 130/90 tire was the noticeably quicker steering of my otherwise stock GS.  It raises the rear of the bike about 1" and decreases the rake about 1 degree.  I liked the difference, others might not.  I didn't like the low traction of the touring type tires but tires are available in that size in most of the good sport touring tires with their better traction.

Ref:
http://img.photobucket.com/albums/v443/jcp8832/CalcTireDims.jpg
http://img.photobucket.com/albums/v443/jcp8832/GS500gearing-rpms.jpg

[lin]

good day dear roxtar and GSJack

many thanks for the postings. They include quite  alot of informtation - i have to re-read them at the weekend.


@gsJack - i love the huge amount  of information - you have made lots of experience.


@ roxtar: many thanks for the hint to the geringcommander - great tool!  Incredible.

BTW - does anybody run a 18 tooth - sprocket!? That would do a good job - if it fits nicely!?  I did not test it  untill now....

love to hear from you 

update:

hello - again me: have you have had a closer look at the very interesting thread here:

beRto talks bout the different gearing here: 
http://gstwins.com/gsboard/index.php?topic=41297.msg589310#msg589310

he made a Gearing Calculator: http://cgi.stanford.edu/~sanjayd/gs500/Main/GearingCalculator


Well, this is good data to compare against the gearing calculator I made! (the gearing calculator can be downloaded from the wiki:
http://cgi.stanford.edu/~sanjayd/gs500/Main/GearingCalculator)

The following was calculated from the spreadsheet for 6th gear:

    16-tooth sprocket, the theoretical engine speed at 65 mph is 5096 rpm
    18-tooth sprocket, the theoretical engine speed at 65 mph is 4529 rpm


new questions that arise:

what about the change of the

front-sprocket to 18 and the rear sprocket
from 39 to - let us say 36 teeth

[prmas]

Hi Lin,
         I am currently running a 17t front and 37t rear with the original 110 link chain. This gives me about 4500rpm at an indicated 100kph/62mph. It has noticeably reduced the response in 6th gear and requires a little bit more clutch slip on uphill starts but otherwise I believe that it has improved the feel of the bike. I like the few extra kph in each gear, especially on the freeway on ramp. It has moved the slight but not unpleasant handgrip vibration just above our legal freeway speed here so the bike has a more relaxed feel when cruising. I am a gentler rider (nearly 60yo) except when I am in the twisties when I love to lay it over as much as I can so the slight loss of power at speed does not bother me. Fifth gear now is between the old 5th and 6th so is good for overtaking. I have fitted several extras but none to increase power. My fuel consumption has not changed greatly with the different gearing as most of my riding is not on the freeway but I expect that at a steady cruise it would be significantly better than standard. If you are interested my overall  fuel consumption average is 3.58l/100km or 65.7mpg (US) or 78.9mpg (UK) in 8500km. A couple of fast club runs in very strong winds has dragged the average the wrong way with a worst ever figure of 4.2l/100km but it is usually around 3.2 or 3.3. Head winds really do show up the loss of 6th gear power but 5th is fine. Regarding the 18t front sprocket, I have one on order from the US and it is due to arrive around the 3rd to 6th of July. I do not yet know if it will give enough clearance between the clutch pushrod and chain but I wanted to try it as an experiment. My calculations tell me that with the 18/37 combo and standard tyres it should give me about 4100 at an indicated 100/62. This would put 5th gear with an overall ratio almost exactly where 6th used to be (with standard 16/39) giving me almost a full extra gear (the equivalent of 7th gear). It will be an interesting experiment and I am expecting a further noticeable loss of response but my answer is just downshift when I need to! If it fits I will do a couple of runs and let you know how it feels.

Paul

[SAFE-T]

Had an 18tooth front sprocket on a 2007 GS500F. So it obviously fits. Gives the GS500 the same gearing as the SV650.

I don't understand why people think it will make the bike harder to ride ~ slower starts ? will slow down going up hills ? None of this was ever a problem with the 18tooth front, and I couldn't even tell the difference between 2nd through 5th. 1st was better because you could stay in 1st a little longer from a start, which I thought was a real improvement, and 6th was better because it lowered revs out on the open road.

If I couldn't find an 18tooth front sprocket, you could use a 17tooth front with a 130/90 rear tire although I think that estethically the taller profile is awful.

As far as using a smaller rear sprocket, I didn't think there was one for the GS500 ~ a link to what was used would be great.

The 18tooth AFAM sprocket I used is difficult to find; you may have better luck looking for a GSXR1000 520 conversion front sprocket which is apparently compatible, and perhaps even the same part as the one I had.

[SAFE-T]

A 1st generation SV650 throttle tube also improves the GS500 by reducing the throw of the grip. Like a bigger front sprocket, it improves the bike in little ways that are noticeable without completely altering the way the bike works.

[lin]

hello dear Safe-T and hello dear Paul

Many many thanks for the responses with the valuable asset of knowledge. your experience is very very intersting and valuable.


Safe-T i am going to have a look where i can get a 18 t-sprocket. I live in Europe - so i can have a look whats going on in Europe -- probably i can find a 18 Teeth sprocket here in Europe. - IF so - i will let you know.

It will be an interesting experiment and I am expecting a further noticeable loss of response but my answer is just downshift when I need to! If it fits I will do a couple of runs and let you know how it feels. Paul

sure thing - i like your ideas - and i think that it is a very very interesting experiment.

my calculations result i the following data:  if you use a 18/36 combination  (with the stock tyre) then you get the ratio 1/1.22222 

that means that you drop the egnine speeed in the last gear about 1000 rpms at the same speed.


comparison:;

16/39 : 5000 rpm
18/36 : 4090 rpm

well i think that it is worth to give it a go



by the way : a German Dealer told me that i can use this rear-sprocket (with 36 teeth): http://grobmotorik.org/grob_int-1152845.htm

it has to be re-worked in the middle - but that is no problem here...


what do you think - i look forward to hear from you
and i look forward to a fruitful discussion

greetings
lin

[Roxtar]

I don't understand why people think it will make the bike harder to ride ~ slower starts ? will slow down going up hills ? None of this was ever a problem with the 18tooth front, and I couldn't even tell the difference between 2nd through 5th. 1st was better because you could stay in 1st a little longer from a start, which I thought was a real improvement, and 6th was better because it lowered revs out on the open road.

I don't have any personal experience with altered gearing on the GS. My comment was more general knowledge. making the final drive ratio taller (via taller tires, more front sprocket teeth, or fewer rear sprocket teeth) reduces your "torque multiplier". Imagine a geo metro (suzuki swift) trying to turn over 44" super-swampers. you're going to stall every time because your gearing doesn't give you enough torque. Drag race cars with short (high numerically) final drive ratios sacrifice top speed in order to get the higher torque multiplier of the shorter final drive. this allows quicker acceleration. doing the opposite increases the theoretical top speed, but means the usable torque is decreased. This decrease in available torque makes high-load situations more difficult (starting from a stop, climbing hills, etc). How much more difficult depends on how drastic the change from stock is.

[prmas]

Lin, here's my post in another thread on this subject. Have a look as it will solve your problem

http://gstwins.com/gsboard/index.php?topic=59607.msg708424#msg708424

Cheers,
Paul (Macka)