1/4 mile gearing

[GSJimbo]

need some input on 1/4 mine dragracing gearing, 15/50,15/48,15/46 etc........what do you guys run???

[rosco15]

My dragbike is 15/48. I'm running 1100 SC gear and a slick. I'm going thru the traps at about 9600 in 5th gear. I did some math and figured a 50 on the back would put me right around 10,000 at the traps.

[GSJimbo]

going to try a 15/50 got a 48 coming,had a 15/46 didn't like it,....thanks

[lecroy]

If you want, send me a PM with your email and I will send you the same Excel sheet (setup with the stock ratios) I sent Ryan to calculate this. Its pretty simple to use.

I am currently using a 15 / 42 with stock 1100 gearing. I am also about 9600 RPM in the traps. Hope to improve on this Friday.

[Baatfam]

Hey Lecroy....you've got a PM from me for the spread sheet....hope ya don't mind:-D

Bob T.

[rosco15]

That spreadsheet is awesome.

[lecroy]

You should have it by now. How is that new transmission hold up anyway?

And... what R U using 4 your gearing?

[Baatfam]

Thanks....got it.
Trans is fine so far, but only has three runs on it since I replaced it....the 16th-17th will be the next time out.

I'm thinkin' I'm running 15/46? with stock gears. Sitting here at work, I really can't remember for sure.
I'll be checkin' as soon as I get home:-D

Edit: Correction...I'm running 15/43 right now....

[lecroy]

Sorry about the delay Jim.

[Baatfam]

OK....that is one nice spreadsheet...thanks Lecroy!:-D

I knew I wasn't using all of 5th gear....and this confirmed by how much. It appears I'm geared to go through the traps at 149 and I usually go through about 137-138....

So now what....do I go with a 45/46 on the rear and use all five gears or go down to a 39 and just use 4 gears?

And what about tire diameter in your spreadsheet....my tire says its 25", but at speed don't they grow?

Any thoughts guys?

Bob T.

[lecroy]

When Ryan got me the new wheel tub I was really worried about tire clearence so I called M/T and spoke with Kevin. (anyone think its strange, Kevin at M/T, FBG and MTC? LOL) I use a 26 10 15 motorcycle tire and Kevin said that up to 150 MPH the tire could grow up to 1.5 inches. After 150, there would be no more growth. Also, the tire will get more narrow as it gets taller. I thought that he said that the 7" tires had a lot less growth. Give him a call at:

1-800-222-9092 Ext.3169

I am not sure on the gearing. I have always ran all five. Is your auto 2-3 or full? I would think if your running a 2-3 your wold want it to at least hit 3rd before the 1/8. At least then if you did need to run it in the 1/8 your could be safe from harming that new transmission.

[Baatfam]

Thanks....
Yes, I have a 1-2-3 auto....
I'm thinking of going up to the 46 and running all five.
I'm going to run a different class at Byron this year, Pro400, which uses a 400 pro tree....
I'm thinking it may launch a little quicker with the 46 gear....

Bob T.

[lecroy]

Last year the finals (with all the other local IHRA tracks) were running the 1/8. A few of the bikes are full auto, but the ones we were using were also 2-3 (or 1 2 3, I guess you don't much auto shift to 1st, LOL).

I would think the 46 would be a better match than the 43, but you never know. It may screw up something else.

The pro-tree would be a lot of fun. 9.80 index class with throttle stops, or 8.90 and your stepping it up? Or something all different?