What's the downside if any to switching the spool outdrives to the steel ones?

Broken shafts if you tend to hit stuff. Otherwise, they are pretty nice.
Since the car is typically under weight, the steel parts will add a little weight fairly low in the chassis. I ordered them to try. I already use the RSD aluminum pieces on my TC6.2.

If you want to add weight DONT ADD rotation mass. Add it onto the chass in the center l/r f/b as much as possible.

As for the benefit of running the steel ones they dont break when you hit the wall really hard. However your blades will break and you must watch and check every round. Having a missing blade could simulate something similar to tweak. Also its rotating mass so if you dont brake the stock ones its alright. However if you run mod it might be a good idea, because you can out motor the weight.

I'm running mod with 7.5 turn I've got the steel ones on order but will wait till I break the plastic

Well then when you switch check often for broken blades.

The steel spool outdrives do not require blades, so that is one less thing to worry about breaking. However it will put more stress on the actual CVA components. I still think it is a good trade off though.

sure - sorry, I mixed it up!

I just picked up a TC6 as my first entry into on-road. I'll be running a carpet track with the longest straight being 110' long. What would be a good place to start with gearing running an 8.5t non-boosted? The spur gear currently on the car is a 96t 64p.

Thanks!

I bought a tc6 to race vta.I'm new to on road racing and I was wanting to get a FDR of 4. I was wonder what is a good spur and pinion combo to get.I didn't want to buy some that give you the right FDR and they not fit.Done that once not fun!

For even relatively small on-road tracks, you'll want to be between 3.5-3.7 FDR, depending on the timing your motor needs to run its best. I'd recommend a spur of between 86 and 92 teeth. Pinion sizes between 46 and 52 teeth.

I'd have to agree that you want to have a lower FDR but to answer your question directly, use 96t spur with a 48t pinion 64 Pitch to achieve a 4.0 FDR that will fit.
There is actually a simple rule of thumb to go by to determine what will fit. I think it was between 140 and 150 total tooth count. I may be off a bit but if you stay around 145t total, you should be good to go.

The instruction manual has a chart in the back that shows what will fit.
If 4:1 is what you want a 100/50 looks optimum to me as it gives you the most up down range.

*delete

See I thought that too until, I went to a larger track, an average size track and I need to go down to a 96 to get the gearing I wanted. I agree with Yodog 96 48

The track I'm at is kinda small no real straight away just curve then corner.