Speed Runners, Diff Oil..??

[GMballistic]

I've read what you've written @Mr.Duke several times over before writing this.
My understanding is that a centre differential divides power between front and rear. If the centre differential is removed and a spool added or the differential was locked then the motor provides equal power to the front and rear.

The front and rear standard differentials are still in play which is what divides power between the left and right sides of the vehicle so AFAIK one wheel on one side of the vehicle could spin up during a loss of traction if for example one wheel was on mud and the other opposite wheel on solid ground.

If I'm wrong then I'm wrong and I will put my hand up but that's how I believe the mechanics of the differentials work so it is possible that one wheel could "spin" up.

 

[Mr.Duke]

With a spool,
The front and rear center shafts are locked and turn equal revolutions per minute, which means the front and rear differential pinions are always in sync as far as rpm is concerned. If the left front tire breaks traction and the front differential pinion climbs in rpm as a result, what rpm is the rear differential pinion turning? The same rpm as the front. For the spike in rpm to happen in the front diff pinion, the same spike has to take place on the rear differential pinion. This means that one of the rear tires has to break traction at the same time. Whether it’s both left front and rear tires, or opposite corner wheels breaking traction, it has to happen to both at the same time. The point in all of this is to show that it’s much less likely to be a factor than what we traditionally experience when running a center differential that allows some degree of slip.
With a spool, you can only spin all 4tires at the same rpm or 2 on opposing axles, never just 1 or 3. Thats the mechanical advantage that a spool offers over an oil filled center diff.

 

[jondilly1974]

I don’t understand where the idea that only 1 wheel can lose traction when running a center spool comes from. Can we all acknowledge that its not mechanically possible as long as the front and rear center driveshafts are locked together and turning the same rpm? The only way you can experience a spike in rpm from the left or right side of the vehicle is for the opposing axle to lose traction on one side or the other at the same. There’s never a time where only 1 wheel diffs out (spikes in rpm in relation to the other 3).

I hate to be that guy, but I found a way ??‍

 

[BashingBrian]

So after even more reading and debating I've given up..!! ?
Was going to use 100k originally, Phil uses 10k so I though I'd split the difference (sort of) lets see how it goes.....
I've built both diff's with 50k..??

 

[parcou]

So after even more reading and debating I've given up..!! ?
Was going to use 100k originally, Phil uses 10k so I though I'd split the difference (sort of) lets see how it goes.....
I've built both diff's with 50k..??

Good luck and let us know....as I stated and you did as well it's a pain finding numbers because we all are different... You are doing speed runs...I am not but your numbers are close to mine now.

60/100/30 f/c/r

Mine is that way for drifting.... I can see as I read this over again...Infraction comes with less OEM and if just doing a straight line feels to me all about power and diffs not make much difference if all straight-line power is equal to the wheels. Me I need more front pull cuz I am certainly going sideways and not straight

Post your results and enjoy!!

 

[Tony Ripper]

So after even more reading and debating I've given up..!! ?
Was going to use 100k originally, Phil uses 10k so I though I'd split the difference (sort of) lets see how it goes.....
I've built both diff's with 50k..??

How’s the 50k going?

 

[Taztaz]

In my typhons i run 1 mill front, 100k rear.
limitless 100k front and rear.

 

[Notorious J]

Just found this thread and I'm glad I did. Since starting my "true" speed runs in August, I had left my f/r 60/30 which was my original bash set up. 5 months later and after reading countless posts from different groups, I just switched to 100/100 with a center spool. I also learned that the steering DR needs to be turned down so that inputs are less dramatic. Unfortunately, we just received a brutal blast of snow last night, so testing will have to wait. I know at least two local guys running stretched Typhons, both into 130+ territory, and both run much higher than 100k. One drops silicone ear plugs in them. Infigure that experimentation is easy in this department as dif fluid changes take no time at all. Hopefully I'll be able to report back sooner than later with real time results.

 

[jondilly1974]

Just found this thread and I'm glad I did. Since starting my "true" speed runs in August, I had left my f/r 60/30 which was my original bash set up. 5 months later and after reading countless posts from different groups, I just switched to 100/100 with a center spool. I also learned that the steering DR needs to be turned down so that inputs are less dramatic. Unfortunately, we just received a brutal blast of snow last night, so testing will have to wait. I know at least two local guys running stretched Typhons, both into 130+ territory, and both run much higher than 100k. One drops silicone ear plugs in them. Infigure that experimentation is easy in this department as dif fluid changes take no time at all. Hopefully I'll be able to report back sooner than later with real time results.

I have Scorched RC spools in the F/R diffs in my Typhon turned Infraction.

 

[LibertyMKiii]

Just found this thread and I'm glad I did. Since starting my "true" speed runs in August, I had left my f/r 60/30 which was my original bash set up. 5 months later and after reading countless posts from different groups, I just switched to 100/100 with a center spool. I also learned that the steering DR needs to be turned down so that inputs are less dramatic. Unfortunately, we just received a brutal blast of snow last night, so testing will have to wait. I know at least two local guys running stretched Typhons, both into 130+ territory, and both run much higher than 100k. One drops silicone ear plugs in them. Infigure that experimentation is easy in this department as dif fluid changes take no time at all. Hopefully I'll be able to report back sooner than later with real time results.

I think because yours is stretched with the Kraton wheelbase it is somewhere in between the Limitless/Infraction setups and the Typhon setups.
The short wheelbase of the Typhon makes it a difficult car to master.

It still makes me scratch my head how the wheelbase plays such a big part in diff tuning. My Typhon 6s drove horrible until I locked up the diffs (I used silly puddy)
Yet the Limitless is running stock diff fluids and drives great. In general every one I have seen posting on the subject seems to agree that thicker up front is ideal if you don't go fully locked. When I ran the Kraton I had 500k rear and 1 million front. It drove very straight.

 

[Greengaunja]

Imho the reason it doesn't really matter for speed running whether you're running 10K or 1Million etc is because and this is the caveat, if you're driving the car correctly for a speed run; being progressive with the throttle, going in a straight line, running on a decent surface with good traction/from the surface & your tyres then the differentials should be doing nothing other than supplying equal power to all four of your wheels.


However, our cars have open/standard differentials, so if one wheel was to loose traction because for example it was on a slippery surface whereas the opposite wheel on the same axle still had good traction due to the way the differential works more power would be supplied to the wheel that has lost traction which just makes things worse in that scenario.
If we use thicker diff fluids or lockers then you can limit or stop altogether the differential working in that way meaning that power is supplied to both wheels on the same axle more evenly or as a constant regardless of surface conditions.

Personally I run 100K in my 6S Typhon front and rear differentials which has worked great for me thus far so I'm sticking to that. My Limitless which is as yet untested I have decided to go a lot thicker at 500K for the front and rear differentials.

Overall this is down to driver preference, ...what works for me with the cars I run, the set ups I have and the roads I run on may not work for the next person. That's why practice and testing is so important.

Also, location is important in determining an oil. Im an RC noob, but seasoned offroader, it doesn't take a genius to figure exterior temperatures play a role in how diff oil reacts. Warmer climates might have more success with higher weights whereas colder climates may find lower more idea. All oils and grease thickens or thins.

 

[rotauq]

My limitless still runs stock fluids, never had any reason yet to change it. I guess non-ballooning tires recover fast enough to cause problems due to F/R diff oil...

Should I throw in weight distribution as a factor as well
During my 1/8 HPI prototyping at some point i moved my batteries in front of the front axle, the rear needed 500k to keep it going straight and stable, whiles in the front it didn't make any difference.
I think the shorter wheelbase of the typhon is more sensitive to weight distribution. The longer 1/7 just wants to go straight, regardless of the weight distribution or diff oil.

Assuming always running a spool (that doesn't brake)

 

[Notoriousone]

Everyone does it differently it seems, 50,000wt front and rear diffs and a spool is what I run, many times into the 130 plus range with no issues. I am tempted to switch to 1 million wt in the front diff only to see if it locks it and if that improves, or stabilizes I should say, the car more under hard acceleration

 

[vwturbowolf]

I run 1 million in my gt limitless front and rear.

My open wheel limitless I had 1 million, tried 20million and didn’t like it, once it starts to lose control it’s almost impossible to correct it.
Changed to 1 million front and 500k rear

My vendetta runs 1 million front and rear
2nd vendetta I tried 20million and it was terrible. Extremely hard to control. So again changed to 1 million front and 500k rear. Haven’t tested this one yet

My gt limitless with 1 million drives straight as an arrow and has good control

 

[Notoriousone]

Couple months ago I made the switch to 1 mill wt. fluid front and rear in most of my speedrun cars, seems to help

 

[44Dan44]

The best reference I have is real drag cars which always run locked/spools in the differentials.



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I believe personally that this is where the confusion comes in along with all the mixed data on fluids. The word drag gets mixed with speed runs.

 

[LibertyMKiii]

I believe personally that this is where the confusion comes in along with all the mixed data on fluids. The word drag gets mixed with speed runs.

Those "comments" were from 2 ish years ago and I have since held the firm belief that a more open diff is a good thing.
Any time I tried really thick fluid or locked diffs my car drove terribly and would grab groves in the road and find itself in the ditch.

Right now my Hobao VTE is running the original diff fluid that the factory put in there and I have never had a car that drives so perfectly straight!

 

[jondilly1974]

Those "comments" were from 2 ish years ago and I have since held the firm belief that a more open diff is a good thing.
Any time I tried really thick fluid or locked diffs my car drove terribly and would grab groves in the road and find itself in the ditch.

Right now my Hobao VTE is running the original diff fluid that the factory put in there and I have never had a car that drives so perfectly straight!

I am going to try the stock diffs as well on my VTE2.

 

[44Dan44]

Those "comments" were from 2 ish years ago and I have since held the firm belief that a more open diff is a good thing.
Any time I tried really thick fluid or locked diffs my car drove terribly and would grab groves in the road and find itself in the ditch.

Right now my Hobao VTE is running the original diff fluid that the factory put in there and I have never had a car that drives so perfectly straight!

I am going to try the stock diffs as well on my VTE2.

Heard, I don't disagree with you, I'm saying speed run setups are different than drag setups. From the fastest guys here including yourself; "You need to roll into throttle for best results" Makes total sense. 132ft I'm pushing the gas pedal through the floor on the go light. Thicker wins here.

 

[jondilly1974]

Heard, I don't disagree with you, I'm saying speed run setups are different than drag setups. From the fastest guys here including yourself; "You need to roll into throttle for best results" Makes total sense. 132ft I'm pushing the gas pedal through the floor on the go light. Thicker wins here.

Yep I have done both types of racing and drag for sure needs thick diffs. In fact if you can find lockers that take the abuse, even better. I find that even 500k thins out after a few hits. You’ll start to see it wander off course as the diffs thin out due to heat.