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Anyone try a modern 17.5 brushless in a older 2.25 stealth transmission. I would be really curious to know how it went. It should be a lot easier to gear because of the lower transmission ratio. Please let me know if you have done this, how it felt on the track.

nikos2002 wrote:Anyone try a modern 17.5 brushless in a older 2.25 stealth transmission. I would be really curious to know how it went. It should be a lot easier to gear because of the lower transmission ratio. Please let me know if you have done this, how it felt on the track.

I think I just found someone will finally be able to explain to me why different IR (not talking FDR but really IR as this is your question here) would "feel" different on the track, as I have yet to find a proper justification for this

Thanks!

Paul

Smartest question I have read in the last 3 days on the web.

Somedody explain please ?

My 10T shortcourse ran all last season with a viper 17.5. Tekins going in this year but I had no issues as long as the diff was tight.

Bigjeepzz was running a 10.5 brushless last time I saw him.

Lonestar wrote:

nikos2002 wrote:Anyone try a modern 17.5 brushless in a older 2.25 stealth transmission. I would be really curious to know how it went. It should be a lot easier to gear because of the lower transmission ratio. Please let me know if you have done this, how it felt on the track.

I think I just found someone will finally be able to explain to me why different IR (not talking FDR but really IR as this is your question here) would "feel" different on the track, as I have yet to find a proper justification for this

Thanks!

Paul

i wanna know what he's saying

I've got three race nights on mine, (one night with a 10.5 and two with an 8.5) I'm using a V2 B4 slipper. zero problems, diff is smooth.

farmer wrote:

Lonestar wrote:

nikos2002 wrote:Anyone try a modern 17.5 brushless in a older 2.25 stealth transmission. I would be really curious to know how it went. It should be a lot easier to gear because of the lower transmission ratio. Please let me know if you have done this, how it felt on the track.

I think I just found someone will finally be able to explain to me why different IR (not talking FDR but really IR as this is your question here) would "feel" different on the track, as I have yet to find a proper justification for this

Thanks!

Paul

i wanna know what he's saying

Who Nikkos or Lonestar?

I have been running a 17.5 & 13.5 in the open mod (against 10.5's and lots of 8.5's) with the 2.25 stealth all year-

I don't think there is much of a difference in the car or motor with the lower IR- it's not quite like a turbo 4 cyl that has such a narrow powerband etc. But, given that the BL motors are all about torque instead of sheer RPM as the brushed variations were- theoretically it might keep the motor in a lower RPM state

A friend of mine likes to describe the differences in gear ratios this way: In drag racing, you sometimes see cars do a better ET even though they didn't have as high a top speed. Sometimes the gear ratios let the car spool up faster. The majority of it is the gear range however.

My question is - why does IR matter when it really seems to be FDR that determines "performance"?

In other words - what difference does it make to have a FDR of 8.0 (8 motor revolutions needed per wheel revolution) coming from:

( spur that has 80 teeth and a pinion that has 20 - ExtRatio 4.0) & (top gear of 15 and diff gear of 30 - InternalRation 2.0)

vs

( spur that has 60 teeth and a pinion that has 30 ER 2.0) & (top gear of 10 and diff gear of 40 - IR 4.0)

OF course there's the positioning of the motor vs. the axle, but that shouldn't impact "motor" performance. Is it an efficiency thing, where bigger gears actually have better mechanical characteristics? Is it about harmonics, where you don't want numbers to divide to not always "hit" the same teeth and have the system resonating? I can understand that the newer transmissions should have high IR's to accomodate the low FDR's needed by the newer "stock" BL's which put out crazy torque, but then again why should the car "feel" different on the track???

for years we were told that this internal ratio is so much better than that internal ratio... I have yet to find someone who can explain it to me the past few years... Hope the question is clearer now...


Paul

the FDR should be the ultimate target, regardless of internal ratio vs external ratio. I can tell you that the larger OR more closely match gears in diameter offer a better interface efficiency because the tooth profiles are either exact or very much closer. So for instance, an internal ratio that is lower allows you to run a higher external ratio, and you don't need to run a tiny pinion which has a more compromised tooth profile. We're not talking about a lot though, fractions of a percent probably. Having a lower internal ratio also allows you a great flexibility in external ratio to give you a wider ratio range, OR allows you to run a much taller tire, in the case of a truck.

jwscab wrote:the FDR should be the ultimate target, regardless of internal ratio vs external ratio. I can tell you that the larger OR more closely match gears in diameter offer a better interface efficiency because the tooth profiles are either exact or very much closer. So for instance, an internal ratio that is lower allows you to run a higher external ratio, and you don't need to run a tiny pinion which has a more compromised tooth profile. We're not talking about a lot though, fractions of a percent probably. Having a lower internal ratio also allows you a great flexibility in external ratio to give you a wider ratio range, OR allows you to run a much taller tire, in the case of a truck.

Thanks Joe in other words, it shouldnt "feel" different on the track, all pther things being equal... :

Paul

I'm running both a 4600kv castle (about 12T) and a 5700kv castle (about 10t) in my gold pan runners with no trouble on the stealth.

I ran a 17.5 blinky in my gold pan/stealth. I felt that the car had better acceleration off the corners than the B4s and other cars I was racing at the time. I was geared 33/72. I am a mid level driver and easily qualified for the A main at a pretty well attended race (almost 300 entries overall, 30+ in blinky buggy). It was noticable enough that my car was taken to "tech" after the race and I was asked to pull the battery out and show it was a ROAR pack.

I've run a 17.5 in a TRX3 (same fdr as the stealth) and JRX2 with the LRM (fdr of 2.18). All feel great on the track, with the right tires and such.

What about rotating mass since both the diff gear and the motor pinion are going to be smaller for the 2.25 stealth?