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You guys that still race, what final gear ratio should I have for a brushless 17.5 (2270kv) motor?

That would depend on other variables you haven't mentioned; at the very least, what car you're racing, as that determines what your internal gear ratio is. Another factor like tire diameter can also play a role in calculating a suitable final gear ratio & rollout ratio.

For my 6 gear Lars, I have a non-boosted (blinky) 17.5 geared 87/23, and the timing turned up just a couple tics (half way to "hot"). The FDR is 1.87 x 3.78 = 6.9.

I just noticed the Classic manual page 20:
The call the internal ratio at 1.83 (I thought it was 1.87 ). They also say you can run 5.49 at the rear wheels with an unadvanced speed control and a 17.5.

So it's whatever works I guess...like Coel said.

Thanks Brian, just the answer I was looking for! Recommended 7.80:1 and you are down to 6.90:1, this will be good starting point for my Turbo Scorpion at the Nordic Indoor Vintage Challenge

Coelacanth wrote:That would depend on other variables you haven't mentioned; at the very least, what car you're racing, as that determines what your internal gear ratio is. Another factor like tire diameter can also play a role in calculating a suitable final gear ratio & rollout ratio.

I will run slick tire that are 83mm in diameter, a standard indoor tire in Sweden on my Turbo Scorpion

Hcp22 wrote:Thanks Brian, just the answer I was looking for! Recommended 7.80:1 and you are down to 6.90:1, this will be good starting point for my Turbo Scorpion at the Nordic Indoor Vintage Challenge

So I suppose you have your own gears in there? Aren't the stock options up at around 9-11ish because of the car weight and roughness of the tranny bitd. I suppose you don't have nicads but lipo, and are a lot lighter than it used to be. Please post whatever you work out, as I would like to see it for mine.

I use original gears, but I sorted out the problem with different FDR with my Tomahawk R for the VONats sins it was handout Tamiya Sport Tuned motors that was spouse to have a FDR 9.3:1. The Scorpions have the choice of 10.72:1 or 6.70:1 and there is a third that are almost impossible to find.

Pinion's with 1.0 module as the Scorpions are dam hard to find other then 12T or 16T. Then I found out that 1:8 sort course trucks use 1.0 module as the Scorpion. Those pinions fits only 5mm axles, buts there is adapters for 3.18mm motor axles... problem solved

You can't fine tune with 1.0 module, but this is a huge improvement compared with only 10.72:1 and 6.70:1 to chose between.

Hcp22 wrote:

Coelacanth wrote:That would depend on other variables you haven't mentioned; at the very least, what car you're racing, as that determines what your internal gear ratio is. Another factor like tire diameter can also play a role in calculating a suitable final gear ratio & rollout ratio.

I will run slick tire that are 83mm in diameter, a standard indoor tire in Sweden on my Turbo Scorpion

That's good...do you know the Turbo Scorpion's internal (transmission) gear ratio? I could research it but if you know, it would save me time. Note; the RC10's numbers aren't going to be the same as the Turbo Scorpion and therefore ideal gearing recommendations would be different.

Lars, is that an exerpt from my gear ratio calculator spreadsheet? Glad it's getting put to good use!

Coelacanth wrote:

Hcp22 wrote:

Coelacanth wrote:That would depend on other variables you haven't mentioned; at the very least, what car you're racing, as that determines what your internal gear ratio is. Another factor like tire diameter can also play a role in calculating a suitable final gear ratio & rollout ratio.

I will run slick tire that are 83mm in diameter, a standard indoor tire in Sweden on my Turbo Scorpion

That's good...do you know the Turbo Scorpion's internal (transmission) gear ratio? I could research it but if you know, it would save me time. Note; the RC10's numbers aren't going to be the same as the Turbo Scorpion and therefore ideal gearing recommendations would be different.

Lars, is that an exerpt from my gear ratio calculator spreadsheet? Glad it's getting put to good use!

That is actually my own, but you help me with the internal gear ratio and I did it more visible.

Cool, I like it. I just mentioned it because the Excel cell colors were similar.

On my TLR 22, I run 33/72 @ 2.43 = 5.30 FDR
On my Atomik I run 33/69 @ 2.60 = 5.43 FDR (same for my B4)
On my RC10 CE I run 31/75 @ 2.25 = 5.44 FDR

I havent gotten my Ultima done yet, I havent run a 17.5 in my JRX2

Thanks guys!
6.7:1 will be a good starting point, don't you think?