sprocket math help

[Sandy]

Why is the diameter of the front sprocket so important. Most of the chain/Sprocket kits I see in 530 are coming with a 16t front sprocket. I found an 18t on Z1 but am curious as to the why just for my personal knowledge base.

I certainly like the price on this and its quality components

https://www.ebay.com/itm/SunStar-530-Conversion-RDG-O-Ring-Chain-16-42-T-Sprocket-Kit-43-4571-for-Suzuki/321583437298?_trkparms=pageci%3A86b8d52c-199d-11e8-aa89-74dbd180ff74%7Cparentrq%3Ac9681ecb1610aa19ebf21ad2ffffac8a%7Ciid%3A1&_trksid=p2481888.c100675.m4236

I would just need to pick up new lock washers and a rivet tool.

The only.reason for the diameter being correct is so the top run of.chain doesn't contact the swing arm. If there's lots of clearance it doesn't really matter but better to err on the plus side.

[hannibal]

That's an aftermarket JT spocket: http://www.jtsprockets.com/catalogue/sprocket/JTR818. I guess that's pretty clear though...

[Brendan W]

Divide the back number by the front and get a number like three or thereabouts.
This tells you that the drive sprocket must complete three revolutions for every wheel revolution.
Wheel revolutions is road speed so the higher your particular back/front number the more revolutions the engine has to do to maintain the same road speed.
Let's say do the math for two possible combinations, a 3 and a 2.8.
In the 2.8 case the engine has only to make 2800 rpm to get the same road speed as 3000rpm using the 3.0 ratio.
If you want to talk fractional or percentage change from one ratio to a new one we can talk about the change from 3.0 to 2.8 and do something like (2.8/3.0)x 100 = 93% approx.
Then you can say that the new 2.8 set up will run 93% of the old tacho speed.
If the proposed new ratio is higher than the old, something like a 3.2 the fractional change is (3.2/3.0)x100 = 107% approx.
In this scenario the motor will have to run 7% faster to maintain the same road speed.
Note in both scenarios the new number goes on top of the old. Neither is meant to be a real situation, it's just to demonstrate the principle.
In general sprocket size is not a free choice, there are things like space and wear rates to consider so unless you have a very good reason, stick close to stock or a known working alternative solution.

[GRAND ROUGE]

Just a thought too re 530 conversion. Did so on my GS 1100. 630 originally a 15 /42 set up and 96 links. I had at some point installed a 40T rear sprocket.....suited my highway cruising needs.... I notice the 750 is a 15 /41 (Owners manual Bass Cliff site) but the important number too is 96 links.

I went with a 18 /48 set up...to closely maintain ratio I had with the 15 /40 .. and the number of links is 114. Boriqua, you mentioned earlier a conversion kit and chain is 110 links....Might be too short?

As others have noted......for sure the 18 tooth front sprocket....and choices are yours re the rear....

[Boriqua]

Thank you for the info!

I decided to go with a 18/47.
Give me a touch more pep around the neighborhood than what I am running now but sacrifice around 200 rpm to increase at highway.
Although I am still a touch on the fence about going to 48 for the rear.

I decided I am not going to buy a kit because they seem to be almost double the cost of me sourcing the individual components so my shopping list has a 120 link 530 and I figure I will cut it to length.

[Boriqua]

Thank you so much everyone. I was able to calculate all the different gear ratios and then the change in RPM based on the posts. I took it out on the highway for the first time today and it was dead on to my calculations. I went with 18 front and 48 back and that geared it down from where I was but still taller than stock 15 x 41

SO I got some pep back which makes it far more fun to ride around on but at 75 I gained about 250 or so RPM. I can live with that. At 80 mph I was pretty solid between 5400 and 55. at my normal highway speed of about 72 I was right around 51-5200.