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Old 03-29-2011, 09:15 AM   #1
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Default VTA Gearing question.

I'm running a TC4 in VTA and I'm wondering what final drive ratio I should be shooting for with the 25.5 Novak?
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Old 03-29-2011, 09:20 AM   #2
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This has been discussed many times in the Vintage Trans Am thread... most racers are finding that 4.00 FDR is a really good place to start with 25.5 gearing on most indoor tracks, then work from there with temps and infield performance. It might be a bit taller outside at LH, but most of us will probably look somewhere in that direction to start with.

Are you coming to the Nationals this weekend, Jerry? Good to see you got a 25.5 to come race with us.
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Old 03-29-2011, 10:27 AM   #3
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What is a good gear combo to do this? I never got a really good answer on that?

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Old 03-29-2011, 11:50 AM   #4
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It depends on the car. All cars have different internal gearbox ratios, so the path you take to get to a 4.0 FDR will be different for everyone. For example, to get there with my Losi JRXS-R, the internal ratio is 1.83, so to have enough space for the motor to move close enough to the spur, I started with a 104t spur gear. A 47t pinion puts me right at 4.049 FDR.

I will probably swap out a 100t spur at some point, to allow a bit more range of pinions up and down, but for now, it works.

Some cars require really small spurs to get the proper ratios (many shaft drive cars like the TC3/TC4, Pro4, etc). Some cars with really low internal ratios (some Xrays are at 1.7, which is great for low turn spec motors) can get away with larger spurs and more modest sized pinions.

You can also change out pulleys in many cars to alter the internal ratios, too. Some cars like the Sakura Zeros and some Tamiya belt drive cars can really be dialed in for internal ratios, too, which can be a nice tuning aid for the really tall ratios we need for 21.5 and 25.5 motors.
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Old 03-29-2011, 11:56 AM   #5
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BTW, there is an old XLS spreadsheet I made in the first year of the USVTA for figuring out proper FDRs for various cars. It hasn't been updated in 3 years so there are some newer cars not on the list. I'd be happy to update it if someone else wants to do the legwork for newer car internal ratios.


I'm going back to the original VTA thread... if you have more questions, as them there.
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Old 03-29-2011, 01:48 PM   #6
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Being a newbie to VTA and RC in general I had the same question. I have a TC3 which has the same 2.5 diff gearing that your TC4 would have. I ended up using a 50t pinion with a 80t spur gear in 64 pitch, this results in a perfect 4.0 FDR. I just chose some numbers out of a hat that came up to this ratio.

My first race was at the 1000 enduro we had at Thunder RC and this combo seamed to work good. Since it was an enduro we stayed out longer than the average 8 minute race, usually about 14-16 minutes (if my driving wasn't so bad that I broke something 5 minutes in). My Novak SS 25.5 was about 160 degrees after most stints, so in an 8 minute heat I would say it should be about 120 or so.

Good luck man.
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