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How usful is re-gearing for drag applications?

  • Thread starter Thread starter rallygabe
  • Start date Start date
R

rallygabe

Guest
1978 GS750base
So I really enjoyed the dragstrip last weekend and got to thinking. What effect would re-gearing (to a higher numeric) have on a bike? I was topping out third right around the 1/8th so I don't think I would gain much because of time lost shifting? Is that accurate logic on a motorcycle?

Thanks for the thoughts and opinions!
 
rallygabe said:
1978 GS750base
So I really enjoyed the dragstrip last weekend and got to thinking. What effect would re-gearing (to a higher numeric) have on a bike? I was topping out third right around the 1/8th so I don't think I would gain much because of time lost shifting? Is that accurate logic on a motorcycle?

Thanks for the thoughts and opinions!
Click to expand...

From what I hear, you can gain quite a bit and you have the top end to still accelerate to the 1/8" mile finish. You will need to keep the front wheel down which will become the limitation.
 
I believe the best gearing would result in topping out your highest gear just as you cross the line, not sure if this is correct for 1/8 mile.

There are some drag racers here that will know more.
 
What did you run and where did you take it to? I don't use my clutch when I want to shift faster. I think the stock gearing is alright.
 
You could try changing to a 17 tooth front gear. I believe the stock one is 15. That will change it enough to see if it will make a difference without to much time or money spent. Shouldn't have to much problem keeping the front wheel down either. You should shoot Rapid Ray a message I'm sure he could help out more than most.
 
heathen said:
You could try changing to a 17 tooth front gear. I believe the stock one is 15. That will change it enough to see if it will make a difference without to much time or money spent. Shouldn't have to much problem keeping the front wheel down either. You should shoot Rapid Ray a message I'm sure he could help out more than most.
Click to expand...

17? How about 13?
 
heathen said:
You could try changing to a 17 tooth front gear. I believe the stock one is 15. That will change it enough to see if it will make a difference without to much time or money spent. Shouldn't have to much problem keeping the front wheel down either. You should shoot Rapid Ray a message I'm sure he could help out more than most.
Click to expand...

going up in the front would result in him not getting out of 2nd gear.

I would recommend going down 1, 3 up in the back. Hold on tight.
 
By gearing it higher like droping a tooth on the front sprocket your mph may still be the same but your ET can drop like a rock. Anytime you can get out of the hole faster to the 60' and 330' is a good thing.

If you break down your timeslips you'll notice your 330 to 660 & 660 to 1320 time will most likely be close to each other. It's the time to the 60 and 330 that will make the most differance on your ET.

Test and tune is great for trying different gearing combo's to find out what works best for your bike and how much you weigh.

If that was your first time you'll be surprized after you get 50 runs under your belt your ET's will fall by the tenths. Add some gearing and they fall even more.
 
Like Jake posted above re gearing will make a difference. Get some runs under your belt and learn the bike better first. Then try gear changes. A smaller number of teeth on the front sprocket will for sure give you quicker times, as will a larger number of teeth on the wheel will also. I would go with a 2 teeth change smaller on the front for starters. Then experiment with the rear.
 
And keep a detailed log of every single factor you can think of on the racetrack. Tire PSI, humidity, ambient temp, dew point, cloud cover, engine temp, A/F ratio, launch RPM, shift RPM, track conditions, everything you can think of, even your mood and fatigue level. A good old fashioned spreadsheet can help keep track of this stuff. Record every run, every time. Pour over the data when you get home from the track, and figure out what helps you go fast. When testing, only change ONE variable at a time, otherwise, you won't be able to tell which change made which difference.

At least, that's what we did when I was bracket racing cars, and it worked out pretty well.
 
I have had the best results gearing the bike to almost redline in 4th gear right when you reach the 2nd MPH marker for the 1/8th mile....The time you lose shifting from 3rd to 4th will very minimal because of the momentum........Billy
 
i have to also ask. Is the bike going to much street riding? if you gear for 1/8 mile it will suck on the highway or long town driving
 
Also note what which gearing does to your wheelbase. (shorter/ longer)
I like to run "quickly" around town and run a 14T FRT. with a 42T RR.

For the highway, I like to stretch the gears to 16T FRT. and 40T RR. (85 cruise)
With a 750, 16/40 might be a bit tooo much. Lot's of clutch to get going. ;)
I used to run 15/38.

NOTE: my engine is now 1085 cc's W/ more cam, carb and compression. :)

Eric
 
Yes, gearing down in front and up a bit in back is what you need to do.

The easy way, and least expensive would be down 1 up front and up 2 in back so you can retain the stock length chain, unless you are planning on a new chain anyways then gear however you would like.

Yes, its all in your 60' so remember if you can't keep the front end down when you launch you are not helping your 60'.

My friend back home has an 06 GSXR1000 and was running 10.40's @ 138mph 1.6s 60' with stock gearing, now after 1down 2up gear change he cannot keep from spinning (launching at 7.5 to 8k) and lost a .10/.15 on his 60' and cant make it up in the 1/4 knocking his et's to high 10.50/60's, and lower MPH. They just had their last race of the year so he hasn't had another chance to get it under control, the bikes a wheelie machine now going down the 1/4.
 
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