Diff article research & questions

[Amoeba]

Gang,

I'm in the process of writing an article for RCNT on Diff setups/fliuds and how they affect handling and performance. I'm working with some of the R&D guys at Team Associated and other vendors but figured I'd pose some of the questions to the crew here for additional input. This assumes standard spider diffs, not ball diffs. Please take a look:

- Is there a mathematical formula or guideline that can be followed to determine how different oil thicknesses change wheel spin? i.e. 5k weight changes %age of torque applied and available to spider gears before wheel slip/power to loose wheel breaks free, vs 10k, 30k etc. Is this a measureable aspect outside a lab or trial & error?

- Do Diff oils follow API service rating or SAE weight designations like motor oil or is there another standard unit of measure?

- Are there benefits or drawbacks between various diff oil products or is oil oil?

- How much does weight bias of a chassis influence differential setup? For example, is there a significant difference between a 5-5-5 setup on a buggy (centered weight bias) vs. 5-5-5 on a MT or Truggy (rear weight bias)

- How large of a role does chassis weight play in affecting diff setup & response? All other things equal, what differences would there be (if any) on a 7-5-3 on a 6lb. buggy vs a 7-5-3 12lb. buggy?

- What are some reasons why you wouldn’t just use a “locked” diff for front, rear, or center diff? What about locked center, diff’d front/rear?

- Does final drive gearing ratio play a significant role in differential performance? Are there other methods or changes (non-tire related) that can be made to noticeably modify wheel traction outside of diff oil weight?

- Many times I see suggested diff oil setups like 10-7-5, 20-30-3, or 10-30-5. Is there a rule of thumb or general guideline applicable (such as question #1 above)

- How large a role does diff setup play in handling and performance given varying terrain types?

- How large a role does the rotational mass of the wheels play? Given the same mass/weight, would a smaller wheel diameter (higher rpm) behave differently on diff performance than a larger wheel (lower rpm) in response to loose traction?


Thanks in advance everyone!

 

[MrClean]

Sorry I can't help, cause I need to know the answers to ALL those questions.

 

[LouisianaSwampbug]

Different track compounds(dirt etc...)will determine what diff oil to use. Also mixing the right tire with diff oil makes a big difference. Many people(including myself) recommend some kind of setup on diff oils. Most of the time it's what works best for that tracks conditions. By following what works well for one person may not work as well for someone else. Most manufactures give you a setup that the team drivers use. Those work well overall, but someone elses driving habits may warrant a different diff oil set up.

I have two truggys that I race, and believe it or not each one has a different setup on diff oils. Both are Losi 8t's but they handle different. So I had to change the diff oil setup on one of them to get them handle almost the same.

Now don't get me wrong... Diff oil, springs, tires, droop, and ride height play a big part.

On the buggys I race I find the setup is much more important. Buggys are not as forgiving as a truggy. I believe having some sort of guidelines to go by is a good idea.

Amoeba,
I think having a post about diff oils etc.. is a good idea. If you need any help just hit me up.

Tim