Author Topic: First time at 1/4 mile  (Read 157 times)

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Offline BTraci

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First time at 1/4 mile
« on: July 31, 2020, 05:52:22 PM »
Last night did first-time 1/4 mile test and tune.  2003 Road King, 117", 127hp, 140tq, TW408G cams.  21 tooth SE primary gearing.  Clutch is a Rivera-Primo with VPC plate--The 60 foot time is horrible, not the 1.60-1.70 that it should be.  With the trap speeds, I expect that the bike can do high 11's if I get the launch down, but did 12 runs and was stuck at 2.0-2.1 60 foot times most the night. 

With the 21T comp sprocket, 1st gear was very hard to use--either too gentle, or spin the tire, and the 1-2 shift really quick and seemed too early.  Was near the limiter in 5th at the top end.  Shifting that often seemed to sap momentum, and with a flat torque curve seems excessive.   Would it be better to revert to stock primary gearing, both to have less shifts during the run, and to have a more usable 1st gear to launching thru the 60'?  Anything aggressive on launch just spun the tire in first.  Track was very well prepped every hour and extremely grippy, so that wasn't the problem. I set the stock air shocks at 20 PSI and tried various rear tire pressures.  Since I have the original FLHRCI wire wheels with tubes, I didn't want to drop too low, but it didn't like the low 20s, preferring (with my minimal experience and poor riding) high 26-28 psi, but I admit I probably wasn't launching right.   

Thanks for any help or advice on how to get closer to the bike's true potential.  Any tips on what ET goal is realistic, and other than lots of seat time practicing, what changes I should make? Trying to trim weight within reason.  Any recommendations for a better rear tire that fits a MU85/142mm?

Thanks all!


Offline Racepres

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Re: First time at 1/4 mile
« Reply #1 on: August 01, 2020, 05:27:14 AM »
Like you say... the MPH is quite good... heavy Bike tho..
I have personally had best luck geared for "all in" at the traps... tached out... have consistently gotten the very best 60 footers that way..
I always give the Same advice tho... Until you bring me 4 or 5 Identical time slips in a row.. keep learning to Ride it!!
Then we can make 1 Change...see what it does..

Edit; Something interesting going on on those 2 Runs..checking the 1/8 mile... which is all one needs to know the Rider is doing their job... I may recommend Not using 5th gear...
My FXR does the best without fooling with 5th gear... Unless I change Gearing!!

Offline JW113

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Re: First time at 1/4 mile
« Reply #2 on: Yesterday at 08:20:00 AM »
I don't drag race, so my opinion is worthless. However, you did not say what brand of tire on the back. The Dunlops that come on baggers are about as non-drag race as it gets. They are made to get max miles on a heavy motorcycle, not to stick on hard acceleration. Try an Avon Cobra on the rear. It won't last, but they sure have more bite.

"Free advice is worth every penny you pay for it"

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline vafatboy1

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Re: First time at 1/4 mile
« Reply #3 on: Yesterday at 03:25:16 PM »
I played around on the track with a 2004 FatBoy 95” Andrews 37b cam, big boyz heads and 2-1 fatcat.  I got it dialed in to a 13 second 1/4 mile. Never got into 5th gear with 3.37 gearing.  I took a one day course with the track owners son for chit and giggles.

He stressed dialing in one skill at a time until you built the muscle memory. 
During test and tune time work on throttle and clutch work only until your satisfied, then on to 60’ time and so on. 

This approach really helped with consistency.  Having street tires on I couldn’t get consistent “launch”.  I worked out getting just enough heat in the tire and did a “softer” launch that got me hooked up quickly. This provided the most consistent 60’ times for me.   

Definitely an amateur here, but I got consistent working at it.