Really depends on tire OD as they are not the same. With large OD HPI X-Pattern tires 3.25 FDR and with shorter touring sized tires 3.14 FDR with full timing on the can, Tamiya 417x.

WOW, I'm way off from that. I've been running it at a 3.56fdr with Jaco blues and 20* on the can. Thanks for the info!

Yeah, totally surprised me to. I started with 3.6 - 3.7 and the motor was constantly overheating due to over revving. A fellow racer with a track star motor was beating everyone with a 3.25 FDR. So I geared similar and the motor came alive finally. Same story for another racer with the Tekin Gen 2 motor. These 21.5 motors take a lot of gear we are finding out. Good luck! :)

What are you guys running as a fdr with the reedy sonic 21.5?

I been wondering about that because mine has been coming off around 150*, at 20* timing and a Yeah Racing Tornado fan on it:eek: I will throw some gear at it next weekend. I'm pretty sure that no one at the track is running anywhere near that kind of gear in GT

Same story here, with a Tornado fan and trying lower timing settings the motor was slow and always coming off the track hot. Gearing fixed my issue and a few others in the USGT class. I hope it works for you too! :nod:

I went down to 3.3 in matts car but wasn't sold on the idea . Seemed to loose more infield punch than it gained on speed (D3.5 21.5 full timing /extreme stock HW)...

What did the temps do tho? Thats what my main concern is. My car is capable of running with anyone in the class there. You turned great times when you drove it 2 weeks ago.

USGT
 

We have 3 guys running GT and so far 4 different motors. Ballistic, shurr, reedy sonic, and trackstar. We started at 3.7 as others did with the same results. Too much heat and not enough speed. We are all geared between 3.3-3.5 FDR on a 60x30 track. The cars run greatand no one is having heat issues with one fan.

Mike

He has a SAIS fan in his car and @3.75 it's coming off @130-140 wasn't any hotter geared to 3.3 .

I take the same system in GT as with VTA...I start at 4.0 FDR and center motor time and test from there...

I will say Im nowhere near 3.3-3.5 FDR...Im not sure how thats working out for you guys...? but I know my car is as faster than most, and thats on HPI Xpaterns...turning 30 laps and fast laps in the high 11's

It's working great for us as I explained above on a somewhat large track (compared to others talked about) approximately 50' x 80'. We run laps from 10.9- 11.3 if you are one of the fast guys turning 32 laps or so in 6 min.

The reality is the guys running on small tight tracks might get away with something like 3.7 as they are not "revving out" for very long before slowing at the next corner, thus not building up the heat. Where open tracks like ours that has an 80' straight + 50' sweeper and another 20' before the first u-turn it just does not work at all. That's 130' of wide open throttle where an under geared motor revving out for so long most definitely will overheat, it has been proven.

I would say the heating effect is definitely track related but it looks like Miket3 has seen the same scenario at their track, so we are not making this up nor are crazy. Heck I run 3.3 FDR in both off my VTA cars with the Ballistic 25.5 @ 43°-44° timing, it just flat out works at our track. Granted the drivetrains are super free and the cars carry excellent corner speed which is a must to run such tall gearing. But if you don't you will be left behind in no time.

yeah Im at 3.8-3.9 at Thunder 92x50ish and Im the fastest GT car from both Nationals held there 2011 and 2012 ...but if the lower fdr are good for you, great, Ive never had any luck going that low

I also keep the same FDR at Hotshots,Track Harbor Hobbies,One Lug, and others, I just adjust my motor timming...all different size tracks and layouts

Hotshots Summer 2012 TQ and Win
Hotshots GORC TQ and Win
Thunder Jam V TQ and Win
USVTA Southern Nationals 2012 TQ(didnt run mains, promo)

same setup and FDR

Thats just the thing tho Myron, I'm worried about the heat I'm getting from the D3.5. I don't care about the speed as there is no speed in a burned up motor. My T3'12 gets broken down every week, bearings cleaned and oiled, everthing checked for binding issues. Its EG's old TC chassis so you know its good, has the Boca Orange Seal Ceramics kit on it. Its a very free rolling chassis. I been running with the timing backed down to 10* in order to keep temps 130*-140*.

I can throw a 3.44 fdr @ 45* timing at my vta and it will stay around 140*

SS is right.

The Tekin Gen 2 I have was running 150+ after 6 mins at about 3.8-3.6 FDR. I was worried getting lower in FDR would heat the motor up, so geared and temped motor after each minute... Once re-geared to ~3.3-3.2, temps came down ~130 (No Fan yet).

And the car felt like it had more "pull" out of the corners, which seemed to contradict what I thought should happen.

But hey I tried it and like the feel... if you try it and don't like it always just gear it back to what it was.