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Rear sprocket size opinion needed

  • Thread starter Thread starter TheCafeKid
  • Start date Start date
T

TheCafeKid

Guest
Ok on my 77 750B i have currently mounted this GINORMOUS 52 tooth rear (41 is stock on this model year) 630 sprocket. Dunno if i want to swap over to 530 just yet, but i DO want to find a size inbetween the 52 and 41 that will still have good guts off the line but not wind out at 60mph. Anyone have any suggestions for a middle ground?

btw have the stock 15t up front.
 
Cafe,
Here is a caluclator you can use.
Sprocket/Speed Calculator

So you don't have to look it up, here are some numbers you will need to imput.

Primary reduction: 2.152 (99/46)
Final reduction: 2.733 (41/15)
Gear ratios:
Low 2.571 (36/14)
2nd 1.777 (32/18)
3rd 1.380 (29/21)
4th 1.125 (27/24)
5th 0.961 (25/26)
Top speed: 125 mph
Circumference of Rear Tire - 2090mm (my approximate calculation for an 18" wheel with a 130/80 tire)
You can input these values, then play around with new ratios to see what it yeilds.

Have Fun :-D
 
Thanks Kurt!! Thats a neat lil tool! Should put it up in a sticky somewheres...
 
By the way, the calulator offers six gears, so use the 5th gear ratio for 6th gear too, otherwise your totals may not work out right.
 
I did a little spreadsheet that I give out if you have excel. Just let me know if you want a copy.

Sproket size has way too many factors to just toss out a number.

If your drag racing, the goal would be to get an engine speed of 10 - 11,000 RPM at the 1/4 mile.
 
Split the difference with something around a 45-46 that would give you something in the middle. I went from a 43 to a 38 to get lower rpms on the highway, and I like it.
 
well its looking like im only gonna be able to do about a 43 tooth to have any top end left. Bummer. still runs at 105mph at 7500rpm in 5th. 72 at 5500 rpm...hrmmm
Not sure i like that. Maybe ill just stick with the stock 41
 
TheCafeKid said:
well its looking like im only gonna be able to do about a 43 tooth to have any top end left. Bummer. still runs at 105mph at 7500rpm in 5th. 72 at 5500 rpm...hrmmm
Not sure i like that. Maybe ill just stick with the stock 41
Click to expand...

How about going up a couple teeth in the front and keeping the 52 on the rear?
 
Josh the stock 550 rear sprocket is a 45 tooth. Don't know if it will bolt straight on to the 750 or not and its only 4 teeth up from your original sprocket. If you are thinking about changing the front sprocket check it out before you purchase anything because there is restricted space in there behind the sprocket cover. I know on the 550 a couple of teeth larger will interfere with the clutch pushrod.
Cheers
Don
 
Dardoonk beat me to it, look at going up a tooth or two on the front, remember that on the front, you will see more difference per tooth than the rear, so 1 or 2 teeth should do it, also it is not going to interfere too much with your get up and go outta the hole.
 
TheCafeKid said:
well its looking like im only gonna be able to do about a 43 tooth to have any top end left. Bummer. still runs at 105mph at 7500rpm in 5th. 72 at 5500 rpm...hrmmm
Not sure i like that. Maybe ill just stick with the stock 41
Click to expand...

Well, that is the trade off you get. There is only so much you can do with a gearbox and you have to choose where you want it all to work. Just how much acceleration are looking for? Adding a couple of teeth on the back is usually very noticeable on the road. If you want an 1100, buy an 1100. Your 750 is not going to pull like that because it is 68% of the displacement; there really is no replacement for cc's if you want acceleration.

If you can get a ratio you like by adding a tooth or two to the front with your 52 rear, that is a better option because the bigger front sprocket is easier on the chain.

Mark
 
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