Best Gearing for the quarter?

plattey

plattey

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Was wondering what's the best suggested gearing in the rear for the quarter mile. Does the stock 17/34 do pretty well with the stock displacement or would 36 in the rear do better?:shrug:

Last fall the car club went to the drag strip and I went with the xs with the big bore kit, mikes 2 into 1, and 17/30 gearing and the fastest run with that setup was 13.513 seconds at 96 mph. I'm back to stock displacement due to a bad crank and scored pistons, but would like to maintain or beat that time.

Here's a vid of me getting absolutely spanked by a built Kawasaki H2 (that thing was a beast! Expansion pipes, wheelie bar, air shifter, rear slick and still street legal?! If I remember correctly, he was running in the low 11's most of the day)!

http://s1112.photobucket.com/albums/k485/plattey/?action=view&current=MOV01917.mp4
 
The 36 on the rear will give some quick acceleration. I had a 36 on mine for the first season, and it was great fun around town but too many rpm's for the open road. I changed over to 33, and very happy with it for both town and open road riding.
 
Retiredgentleman, thank you for the quick response! Going back to near stock gearing would probably be more favorable? Once it's warm enough, I'll be doing a lot of riding back and forth between school and home (3hr ride on freeway). The 36 rear would just cause a lot of discomfort on the freeway?
 
I'd like to know the answer too. How many shifts do drag racers like to use in the quarter?
 
With the 17/30 gearing, I was just shifting into 5th at the traps and spinning about 6k rpm. A friend told me that the best setup would be that you would be close to running out of rev's in top gear at the end of the quarter. I found this from xs650garage.com:

www.amckayltd.com/xs650revs.xls

Plugged in:
36 rear
75.5" for rolling distance
100mph for the speed calc

....and got 7,238 rpm at 100mph
 
Last edited:
plattey said:
Retiredgentleman, thank you for the quick response! Going back to near stock gearing would probably be more favorable? Once it's warm enough, I'll be doing a lot of riding back and forth between school and home (3hr ride on freeway). The 36 rear would just cause a lot of discomfort on the freeway?
Click to expand...

The 17/30 would be great for driving the expressway. The 17/36 is great for snappy acceleration around town. That's why I use 17/33.................just like the goldylocks story.............not to hot, not to cold.............just right.
 
plattey said:
With the 17/30 gearing, I was just shifting into 5th at the traps and spinning about 6k rpm. A friend told me that the best setup would be that you would be close to running out of rev's in top gear at the end of the quarter. I found this from xs650garage.com:

www.amckayltd.com/xs650revs.xls

Plugged in:
36 rear
75.5" for rolling distance
100mph for the speed calc

....and got 7,238 rpm at 100mph
Click to expand...

Your friend is 100% correct, You dont want to shift right before going thru the traps at end of 1/4, hopefully you can have it geared to where your right at rev limiter at traps. that would be perfect. Thats all going to be be subject to bike rider and what ya done to bike. You have to run it see where your at going thru traps.
 
by the sounds of it, 17/34 or 17/33 is going to offer the greatest all around gearing for what I would like to get out of the bike:D
 
Theres not much way to beat that H-2 with a xs650, even with a big engine. I had a 74 H-1 that ate every thing on the street for lunch. The H-2 was even more so.
I think your calculations are off a bit. your 75.5 rolling distance seems off. A 120/90-18 has a 83.2 inch distance. A 130/90-16 has 79.1 inch distance. What size rear tire do you have?
In my gearing chart with everything stock, 130/90-16 rear tire redline is 110 mph.
33 on rear is 113.6
32 is 117.2
31 is 123.7
30 is 125.0
The 110/90-18 is a about 3 mph faster.
The 130/90-16 with the 36 on back will get 105 mph with 7561 rpms, or 104 at redline.
Those are calculated speeds, not real life speeds. You won't reach those speeds because of to much wind and lack of horsepower.
At the track take a selection of rear sprockets and try them. Find which works best.
I don't think you will beat the 750 kitted engine with a stock engine. The extra HP of the 750 wins every time.
On my 75 the 17/32 with a 139/90-16 gives good all around performance. For mostly highway a 17/30 works well but you loose some low speed performance. Mostly around town the 17/34 works well, good low speed performance, reasonable highway.
Leo
 
H2 750 Kawi, Ring a ding ding!! Music to my ears

flagman.gif
 
xsleo, I just guestimated what I thought was right just to get some numbers :laugh: It's got a 130/90-16 in the rear at the moment. miss the big bore, had that thing up to 115 once and it still had a little bit of steam left to go, but then heard a dense knock from the bottom end several weeks later. after a tear down, the left con rod was waaaay out of tolerance in side to side play...the crank was cooked.
anyway, if the 650 won't beat the 750 time, it'll be a decent time for stock displacement hopefully:)
 
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