Runtime
 

one 3500kv motor geared for 40mph..

and

one 4600kv or 5700kv motor geared for the same speed "40mph"..


does give the same runtime or .. ?

If the motors are on the same battery setup AND have the same efficiency rating.......then YES.

They all will have the same runtime in the same vehicle.

With the same battery and driving style- in principle, you will get a longer run time. Higher motor speed with lower gearing will reduce current draw and therefore give longer runtime, but there are an awful lot of variables and 'what ifs?' to think about:

Lower kv motor & higher voltage with the same gearing would be best and certain to give better runtime- you didnt mention your voltage....

No change in voltage, just kv and gearing. It really depends on what motor it is and where the most efficient RPM range is.

Anyone know what it is?

"Awful lot of variables and what-ifs?"

Higher kv and lower gearing is what the original question was, and yeah, that would yield better runtimes (not massively though I expect).

Going with lower kv and higher voltage would yiled the best results- the whole 4s & 2000kv vs 6s & 1600kv thing. :yes:

ok .. so a 3500kv motor on 3s 11.1v give more runtime then a 3500kv on 2s 7.4v geared for the same speed ?

Yep. A stop watch is a handy thing to own though for sure :wink:

You're also forgetting one important factor in this equation, the battery capacity.

We all know 2 & 3s is 7.4 & 11.1v respectively, but, are you just changing kv & gearing to keep at your 40mph to determine if your runtime will remain the same?

As Neil said, get a stop watch. Don't take anyone's word for it as we all use different packs, motors & gearing & they all perform differently.

Do the testing yourself & then you will know.

I've done my testing to get my cars to where they are. Yeah, it may have cost me money to buy the motors, but, I just sold what I didn't want & got a decent price for them.

I learnt a lot doing it too.

Good luck what ever path you choose.

whats give me more runtime in :

lower tooth spur gear and lower pinion

or

higher tooth spur gear and higher pinion


geared for the same speed ..

The smaller gears should weigh less, so you'll waist less power spinning them, but unless there is a really huge difference in gear size, I don't think it will make enough difference to notice a change in runtime.

Yeah- the difference in rotating mass will only get you about 30 seconds more runtime.

I dont think he means rotating mass though, does he?

If you gear higher (smaller spur and/or larger pinion), you get less runtime but more speed upto a point- more time to hit top speed though.

If you gear lower (larger spur and/or smaller pinion), you get more runtime but less speed- better acceleration though.

But he said "geared for the same speed", so ratio would be the same, meaning rotating mass would be the only difference I would think.

Ah, touche.