Sprocket setup for 70-75mph

[blackapache]

Hey guys well its time to start thinking about sprockets and chains as Ive just about buttoned the engine all up.

Im looking for something that'll run at 70-75mph and higher freeway speeds but something thats not crazy high in the rpms.

i was thinking of getting the 31tooth rear to go with my 17tooth front or even an 18 tooth front but wondering if im gearing too low?

Im running a rephase with JE pistons 707cc, 34mm mikunis, custom intake with velocity stacks and straight through pipes no baffles.

Id like to see a bit of the grunt that's been forced into the engine build but rather have something that cruises well and has more get up and go at highway speeds and passing speeds.

any thoughts gentleman?

 

[angus67]

your motor should have more than enuf umph. Stay with the 17/31. Don't go 18, unless you are meticulous about adjusting your chain. Im running a 18, but I also use the skate board wheel tensioner from monstercraftman. It takes up slack pretty good, keeping the chain away from my clutch rod.

 

[blackapache]

your motor should have more than enuf umph. Stay with the 17/31. Don't go 18, unless you are meticulous about adjusting your chain. Im running a 18, but I also use the skate board wheel tensioner from monstercraftman. It takes up slack pretty good, keeping the chain away from my clutch rod.

yeah i was thinking i'd do the same with the tensioner.. are you running 520 or 530?

 

[angus67]

520.....

 

[angus67]

that doesn't matter though. The side plates are the same size. Its the length between rollers that make it 530 or 520. I went with a 520 because I wanted my bike to look slim. A chunky 530 was not in the cards.

 

[pamcopete]

Here is a Excel spreadsheet that yields RPM vs MPH for all combinations of sprockets, gears, wheels and tires.

MPH vs RPM

Click on the several yellow (orange?) cells to reveal the pull down for various select able values. This spreadsheet use rolling distance rather than tire diameter as those metrics are not attainable for a motorcycle tire. The rolling distance is the distance that the motorcycle will roll for one revolution of the rear tire.

 

[chizler62]

If you just put a fresh 707 piston set in I can't believe you'd see any significant difference that you'd find it necessary to change gearing.

Cam, porting, valves springs anything like that done to improve horsepower?

@pamcopete thats an great tool, lots of work. Am I miss a rear tire diameter parameter?

Posted via Mobile

 

[blackapache]

If you just put a fresh 707 piston set in I can't believe you'd see any significant difference that you'd find it necessary to change gearing.

Cam, porting, valves springs anything like that done to improve horsepower?

@pamcopete thats an great tool, lots of work. Am I miss a rear tire diameter parameter?

Posted via Mobile

ported, rephased, cam grind, velocity stacks, VM34's custom intake (ceramic coated) tuned length headers..

pamco ignition, iridium spark plugs.

its not so much the horsepower issue, but rather putting it where its usable for what I want. I want to have lower rpms at highway speeds of 70-75+ but keep as much pop at low speeds as i can.

 

[blackapache]

Here is a Excel spreadsheet that yields RPM vs MPH for all combinations of sprockets, gears, wheels and tires.

MPH vs RPM

Click on the several yellow (orange?) cells to reveal the pull down for various select able values. This spreadsheet use rolling distance rather than tire diameter as those metrics are not attainable for a motorcycle tire. The rolling distance is the distance that the motorcycle will roll for one revolution of the rear tire.

thats a great tool pete, angus i hear ya Im building this one pretty skinny too, im thinking 530 gonna look like a rappers bling with how big it is.

 

[fredintoon]

that doesn't matter though. The side plates are the same size. Its the length between rollers that make it 530 or 520. I went with a 520 because I wanted my bike to look slim. A chunky 530 was not in the cards.

Hi angus,
you must have mistaken this string for the Joke of the Day string, eh?
But to keep the gag moving, how wide is your backside?

 

[XSLeo]

The difference between a 520 and 530 is the width of the chain not the distance between rollers.
The 530 runs on 3/8's inch wide sprockets, the 520 runs on 1/4 inch wide sprockets. Everything else is the same.
On your sprocket sizes, dropping one tooth on the rear drops engine rpms at 55-60 about 100 rpms. So dropping 3 teeth on the rear nets you a 300 rpm drop at 55-60.
I've tried a 30, and 32 tooth rear with the 17 up front. On my last sprocket and chaoin replacements i've gone back to stock.
The loss of low to mid speed acceleration with the others isn't worth the minor reduction in vibes.
I might only go with the smaller rear on a bike I only rode at highway speeds. I don't ride at highway speeds often. I do much more at 40-50. At these speeds the vibes are fine.
If your engine is well tuned, you don't get much vibes.
The bike was designed and set up as a good all around perfformer. The stock sprockets do just that.
Leo

 

[pamcopete]

If you just put a fresh 707 piston set in I can't believe you'd see any significant difference that you'd find it necessary to change gearing.

Cam, porting, valves springs anything like that done to improve horsepower?

@pamcopete thats an great tool, lots of work. Am I miss a rear tire diameter parameter?

Posted via Mobile

I use rolling distance instead of rear tire diameter. The rolling distance is the distance that the bike will move forward with one revolution of the rear wheel. There is a pull down that you use to select your rolling distance.

 

[Jack]

ported, rephased, cam grind, velocity stacks, VM34's custom intake (ceramic coated) tuned length headers..

pamco ignition, iridium spark plugs.

its not so much the horsepower issue, but rather putting it where its usable for what I want. I want to have lower rpms at highway speeds of 70-75+ but keep as much pop at low speeds as i can.

who ported your head? stay with the stock gearing to keep the engine in it's powerband to delivery the best grunt down low and for passing. These engines don't have a long arm stroke,so keep that in mind when changing gearing.

 

[650Skull]

You have mentioned you bought a 76C in your first post, and nothing about what it really is. Tracker, bobber/chopper, cafe, or any weight reduction, through any transformation.

Weight loss is relevant to gearing as well, these engines will run at 5000 rpm all day and that is when it's reaching the power band. Gearing it to low, (17/30), and having to pull out and pass a car doing 60Kph you will have to lug it in 4th or change to 3rd and be in the high rev range. Will be riding the clutch on take off and a standard weighted XS650 will not like that. Also factor in the carrying weight, 1 up, 85-100kgs or occasionally 2up another 50-65kg's.

Try 17/33

 

[tonyc]

Right now I have 17-30 and have plenty of power for passing. Full gear I go over 200 lbs. I do have a 32 rear that I will use when I do the 5th gear swap.