I have some questions about gearing. I know ratios vary per rider weight and bike. I'm wondering is how changing tire R.O. affects gearing. i.e- 15-40 71RO to a 82RO.
Tranny is a 5spd. Ratios are.

1st: 2.416
2nd: 1.733
3rd: 1.333
4th: 1.100
5th: .909
primary is 2.142


There are no aftermarket trannies, gears or shafts available.

I have the tranny cut 1-3 over ride with 2-5 back cut.

Launching in 1st has very bad 60ft with poor ET's. The motor is ported, Alky (45 Lectron) fuel pump, single cylinder.

How is changing the tire RO from 71 to 82 affect gearing? And would be launching in 2nd be better? Thinking of trying 15/43 launching in second, while I WAS using 15-40 and launching in 1st. 15/40 seemed to go through the lights before it quit pulling. Which is good. Id rather it be on the up side of the power curve then the downside. I dont want to hit the max RPM at or before the lights b/c I would think the@ maw RPM the motor would have already came off the power curve. I swapped to a 12t on the front and it let the bike wind out faster and around the lights. But the bike was still having jetting problems. <<<<Thats for a later time.

I would like to be launching in second and be going through the lights in fourth.

Old bike was the one I was running the 15/40 gearing with 71RO 10 paddle EXT sls. Stock chassis.

New bike is Roidzilla chassis with 82RO 12 paddle EXT sls.

Can you guys make sense of this at all and maybe give me some advice??

Thank you,
Chris

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1987 LT250r
1988 LT500r
Roidzilla

Going to the bigger tire will make your overall gear ratio taller. I can't give you specifics on how much taller it will end up, but it will be noticable going from 71-82RO, especially considering the 82 has more paddle. On the flip side though, using the bigger tire will put more load on your engine which might help with traction on the line, but it will also be more weight to turn on the other end. Also, changing the chassis will affect how your bike leaves the line and hooks up throughout the pass. Being that you're changing the tires and chassis, it's really hard to say what direction you need to go, it may already be where you need it.

Finding the perfect gearing is not easy, lots of trial and error. It's a combination of your chassis, tires, gearing, clutch, and track conditions that make it all come together.

Thanks for the input. The stock frame is running now and the roid chassis will be running soon. I will be running both bikes. Just trying to get a notion on gearing and tires so when the other comes around I will be ahead.

changing the tire RO from 71 to 82 is like going from a 15 tooth front gear to a 16-17. more paddles the more load the engine will see.

biggest thing would be what rpm at 300' you are looking for, for what gear u want to finish in. then you have the question will the engine pull that set-up?.

Have you tried to leave in second on the stock frame with the 71ro tires? If so, what did it do?

I was thinking you are switching from one chassis to another, didn't realize you were going to run both setups.

Well to tell you the truth I have never had it on a dyno. So I dont know what its full potential is. And I dont have a tach on it either. I have no idea what RPM's it is even making. I would say in the range of 7500-8000 maybe. I dont know. And maybe around mid 80's on HP.

When I launched in second it felt real good. The best time in the 400lb bike plus rider was 5.00. I know it can go faster than that. That was with the 14-40 gearing and stock tranny. So far I have had the top end freshened up and got the cut tranny.

That's good, do you remember where you were (in which gear, 4th/5th) when you crossed the finish line, leaving in second?

Heck that was this past June or July. Im going to say in the top of fourth. Cant really bang that many gears in that short of a distance. I know i did get into fifth a few times, but that was a NEWB racing error there. I really am going to start launching in 2nd on both bikes.

Are the stock tranny ratios ok? And launching in 2nd and ending in 4th?

with that high of a primary you will never pull 5th in the 300 feet 4th either for that matter, at a 22 inch tire you would be pulling 113 mph at 9000 rpms in high gear fourth would be 94 mph,,, yikes that gear is way out in right field are you sure that is a 2.142 primary

to pull 80 mph with your gears and a 71 ro tire I would think a 14-49 or 48 would be in the ball park to hit 5th starting in second

5th on a banshee is 1.045 and the primaries are 2.86

you want it done right at the line