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Discussion Starter #1 (Edited)
Have you ever had your car running great, had good speed, and the handling is "right on", then you change your tires and you find it just have the "punch" it did before? Then you've run into the dreaded "roll out" problem.

Not everyone knows that if the new tires you put on are a different diameter then the old ones are, you need to adjust your gear ratio to make up for the difference in tire size.

I've made an easy to use chart that helps you find what gear ratio to use to make up for this.
Here is a small piece of the rollout chart. It is written as a Microsoft Excel spread sheet. If you do not have Excel, you can download the Excel file reader here.

In this example, we were running a tire diameter of 1.80" and a gear ratio 2.15. This equals a rollout of 2.629 (the first red square). We then changed to a tire diameter of 1.90".

To find out what gear ratio we need to change to, we follow the numbers under the 1.90 tire size until we come to a rollout figure that is close to what we had before the tire change. In this case, that number was 2.629.

By using the chart, we see that we need to change our gear ratio to somewhere around 2.25 to 2.30 to keep the same performance that we had before the tire change.

The chart that you download here is zipped, so you will need to unzip it then view it in Excel or the Excel viewer. You can then print it out on your printer so you can carry it in your pit box. The About RC Vehicles Roll Out Chart has been sized so that you can change your printer setting to size your printout to "fit the page" and it will printout nicely. There are two pages included, so make sure you print both pages.

Now, don't waste any more time, download the HobbyTalk Rollout Chart and get a jump on the competition!
 

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Hankster,

The roll out chart is a great thing, but I run pan cars and don't have tires that big. Do you have another chart with smaller tires, say from 2.50 down...for the foam car tires it would really help.
 

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cwinters said:
I just posted a palm program for calculating the rollout. You can find it at http://home.comcast.net/~cwinters15/rc/rollout_0_1.zip

Enjoy!
Chuck

Chuck I have just installed the Rollout Calculator. 0 1 and it works great. tried the 0 2 but it would not work. had to delete both programs and reinstall 0 1. I am very happy with it thanks.:thumbsup:




palm os tm software v3.1 on a visor made by handspring
 

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Palm

I also downloaded the Palm program. Works great. Thanks. This beats carrying sheets of paper and a calculator. Now all I need is the Palm.
 

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well in pan car you can figure out roll out if you have a calipier messure tire size times spur times pie`divided by your pinion gear....now you have a quick and accurate way for roll out ....pan car 10th you want around 2.50 for roll out exp....2.10(x)spur 100 (x) pie` 3.1415926535897932384626433832795 ( / ) pinion any questions you can post under oval track dis... mt. pleasant or bay city if you need more help about roll out
 

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Thanks all for the feeback all. It's nice to know people have a use for the software.

Bob W.: What is happening with v0.2? Does it crash, or just not work correctly? I never tested on a Visor, so any info you could give me will help to fix the issue.

Everyone else: What version of the palm program are you using?

Thanks,
Chuck
 

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Chuck ......02 crashed on me. it also made the 0.1 crash after 0.2 was installed. I also tried to install 02 after removing both programs, but 0.2 still
crashed.

thanks again

Bob
 

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The Jet said:
Mike, grab a caliper...OD x pitch - 2, equals # of teeth

Example 1.905 (OD) times pitch (64) equals 121.92 minus 2 equals 120 tooth spur ;)
The above formula allows you to calculate the number of teeth of an unmarked gear.
 

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Where'd you get this from? OD of a pinion or spur doesn't directly relate to the number of teeth it has, even knowing the pitch. Robinson Racing and Losi pinions aren't the same OD for the same number of teeth. Hence another reason to use the same brand of pinions for one car. Now, if you wanted to specify that formula for a specifc manufacturer, great, but what you posted isn't 100% accurate.
 
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