I'm new to oval racing. I raced RC cars about 15 years ago and this year I started racing again but I've been racing outdoor off-road nitro stuff. I just bought a Racetech Macattack and I have yet to turn a lap with it. I've been reading as much as I can and I will be going to York, ME on the 14th.

I'm a programmer and I like to "what if" stuff, so I wrote a Rollout Calculator application for my PocketPC. I've made one that let's you figure out Rollout, Pinion, Spur, or Tire Diameter. You just leave one field blank, fill in the rest and it provides the answer for the blank field. This is just something I am doing to help me visualize the various combinations.

I'm adding a function that if you leave the pinion and spur blank it will list all the pinion/spur combos that get you within some threshold of the target rollout.

My questions are:

1. What is the range of the most common pinion and spur gears that are used? Pinion 25? to 35? Spur 100? to 120? My Racetech came with a 120 Spur no pinion.

2. What is a reasonable threshold for matching your target rollout? For example if you want a 1.80 rollout is 1.82 good enough or is 1.85 good enough?

My goal is to display something like this:
Target Rollout: 1.80

114/29 = 1.8011
110/28 = 1.8022
106/27 = 1.8034
102/26 = 1.8048

http://dirttwister.com/rc/images/rollout_calc.gif

Thanks,
Bruce

My questions are:

1. What is the range of the most common pinion and spur gears that are used? Pinion 25? to 35? Spur 100? to 120? My Racetech came with a 120 Spur no pinion.

2. What is a reasonable threshold for matching your target rollout? For example if you want a 1.80 rollout is 1.82 good enough or is 1.85 good enough?

My goal is to display something like this:
Target Rollout: 1.80

114/29 = 1.8011
110/28 = 1.8022
106/27 = 1.8034
102/26 = 1.8048

Thanks,
Bruce

Bruce, I did a similar deal, only in basic, not fancy like yours..
I had the final rollout carried out 2 decimal places, which is fine.
It is also what everyone deals with. You hear 1.86, more often than
1.8639.
and had it so the pinion number was a whole #. There isn't much sense
in having a 27.3 pinion answer. 27 is what you'll run.
The tracks that you will probably run on, York or LRRCS,
a range of 1.75 to 2.25 should be more than sufficient.

If you are trying to get a 1.80, a 1.82 will be fine.
A 1.85 may be stretching it.
By having your answer round off to 2 decimal places, your answer should
round off to the closer of the two options.

I think your gear selections are reasonable.

Hope this helps.... good luck with the Mac Machine....
sounds like a BOJO rig?

I did get it from BOJO. I'm anxious to try it out.

My program isn't fancy, it's just that using a GUI forces you to have a prettier interface then just text. It only took 30 minutes to do it on my Pocket PC while I was waiting for my daughter's Saxophone to be repaired. That's programming it with the stylus, tapping on the on screen keyboard.

Thanks,
Bruce

100 to 128 spurs, and I run as small as a 17 tooth pinion to obtain, a .98 rollout, well .9786 LOL. Don't forget about the mod guys :thumbsup: .

Nice program :thumbsup: .

Later, Bret

Please bear with me, or at least a little...lol
I just got back into racin again a little over a year ago, was moving, sold everything, went back about 8yrs later, and left with some stuff. wnet to the local dirt track, heard they were closing, went to another track that was almost open. ened up getting a T/c, ran it some. but not enuff for me, got me a used pan car, some hotshoe was smoking everyone in 6cell spec, i got the car, beat em alot, he sold everything. 6 cell spec was gone, had to go to stock, did alright, batteries killed me, (anyone want to sponser me?)lol
got a novice stock started, then i heard peeps talking about rollout....huh?
at first they were saying to go with 178 to 184......now thay are saying to go with 168 to 172....my question is .....why????
and how does rollout interact with the car? motor? speed?
my head is about to burst....someone help me please
Jimmy JAM

forgot to mention......newly crowned
ROAR Region 3 Oval champ Novice stock that is
thanks again...

Okay, here goes, I will try to explain as if you are a total newbie. 175 is a rollout number, actually 1.75. What that means is that for every revolutin of the motor, your car will travel foreward 1.72 inches. To illustrate that, make a mark on your rear tire and roll the car foreward until the mark is back to its orig. place, and you can measure the 1.75".
So the next question is, how do i know what rollout to run, and how do I apply it to the car? Make a few runs without paying attention to rollout, and write down the pinion you used for each run, especially the run that you felt you were the fastest and most competitive. when you get the cars speed to where you are happy,divide the pinion by the spur,multply by 3.14, then multiply by tire size. Not as difficult as it sounds, after awhile you will be doing it in your head! example: 32\128 x 3.14 x 2.24 in =1.75
If foam tires didnt wear none of this would be important. the reason we keep track of rollout is to compensate for our foam tire wear, and make sure the car stays FAST! Otherwise the car would go slower and slower as the foam tires wear down. I use the RR tire to measure tire size, others use both RR and LR, it doesnt matter as long as you do it the same every time and use the same tire as the reference every time you measure. The higher the rollout number, the more TOP END the car will have. It is possibble to overgear, or use too high of a rollout number. Every track has one perfect rollout number, the trick is to find it. That is the single most important way to win races, assuming your car is up to snuff. Oh yeah, EVERY motor has a different rollout number it runs best with. Have fun, hope this helped...

thanks mayhem,
that helped alot. I did not realize that the rollout was used for the mesurement for the car. ie, 1.75= 1.75in traveled..
and i kinka thought the higher rollour would mean more top end....and to me means binding or bogging in the corners, of which I have heard you want to keep the momentum going in the corners......
thanks again mayhem
Jimmy JAM

Here is what my calculator currently does. I'm curious if anyone would be interested in it. If so, I can make it available for download. It is for a PocketPC 2002/2003.

Features:

Computes rollout, spur, pinion, or tire diameter required to achieve a certain rollout. You just leave the field blank that you want to figure out. If you leave the spur and pinion blank then two buttons appear that let you display a list of gear ratio combinations that come close to the desired rollout. One display lists the best gear combinations and how close they come to the desired rollout (plus or minus). The other display lists your gear combinations sorted by spur gear and also shows how close it comes to the desired rollout.

Bruce

http://dirttwister.com/rc/images/rollout_calculator.gif

Okay, here goes, I will try to explain as if you are a total newbie. 175 is a rollout number, actually 1.75. What that means is that for every revolutin of the motor, your car will travel foreward 1.72 inches. To illustrate that, make a mark on your rear tire and roll the car foreward until the mark is back to its orig. place, and you can measure the 1.75".
...

That isn't exactly correct...

You would want to mark your pinion gear, and revolve it one time,
to see the car move 1.75".

If you rolled the car one revolution of the tire, and it moved
1.75", that would be one small tire....

Ah yes, I always get it confused. I think maybe it can be described that the car moves foreward 1.75 inches per each revolution of the motor??? Some describe rollout as "inch gear" instead.