Oil vs. Graphite test

[4wheeldrift]

I've heard and read threads where everyone says oil is much faster than graphite.

I've got the 'secret oil' mix and use it sparingly (2 small drops on the axle) and yet when I do the spin test in comparison to a graphite prepped axle/wheel, the spin time is way less with oil.

Is this still a fair comparison between the two? I understand the oil will last a lot longer through multiple runs but still, it seems like the rolling resistance is greater with oil...no?

thx

 

[bracketracer]

I'm sure others with more knowledge will chime in here soon, but if you do the spin test as a comparison, what you're seeing is completely normal. On the track, however, oil will be faster and for longer without needing to relube. My car picked up about .030 sec. switching from graphite to the DD4H oil process.

 

[Resophonic Racing]

The spin test is not a good test. When oil is used in conjunction with the DD4H Bore Prep, Red Rocket Wax and jig-a-loo it will be superior to graphite on the track. If you just use oil with no wax or axle prep it will perform the same as graphite, sometimes slower. The thing you are mainly looking or listening for after you prep with oil and wax is a smooth quiet spin on the axles, almost as if it is floating. A good oil prep will be consistent and last for months.

 

[4wheeldrift]

Thanks for the follow-up post. I don't have the specific info as to John's process, but I've learned the steps from another forum regarding the use of jigaloo, wax, etc.

You're right though in that when doing the spinning I noticed there's a period of time where the wheel just seemed to glide and turn effortlessly (and silently). But it was the duration that I thought was odd cause they'd spin for 15 seconds at a time.

 

[kickaxe]

The graphite spins longer because it a better lube when there is no load (weight on the rubbing surfaces). The oil viscosity slows the wheel faster under non load bearing conditions. The oil is faster on the track than graphite due to the weight of the car pushing down on the wheel/axle system. The physics were discussed here http://www.pinewoodderbyonline.com/post/Secret-Oil-Process-6234852?trail=15

 

[jator359]

Kickaxe - an earlier post that mentioned graphite in the dfw and oil in the rears immediately came to mind. Which begs the question (at least for me), what are the respective weight thresholds for graphite when lubricity begins to tank and for oil when it begins to improve? Or am I going down a rabbit hole?

The graphite spins longer because it a better lube when there is no load (weight on the rubbing surfaces). The oil viscosity slows the wheel faster under non load bearing conditions. The oil is faster on the track than graphite due to the weight of the car pushing down on the wheel/axle system. The physics were discussed here http://www.pinewoodderbyonline.com/post/Secret-Oil-Process-6234852?trail=15

 

[kickaxe]

To my understanding, the graphite is not tanking the oil is improving. As pressure increases, hydronamics can create extremely low coefficients of friction. Graphite and other dry lubes perform well in all areas of load and lack of load. Graphite in the DFW could be faster than oil if the wheel had very little pressure on it. As far as the magic pressure conditions where the hydrodynamics begins to outperform graphite in derby cars.....I have no idea.

 

[jator359]

On a related note, I can measure the static load on each wheel by using 3 scales but how does that loading change (assuming that it does) on each wheel with the car in motion (I now regret not paying attention in high school physics)?

To my understanding, the graphite is not tanking the oil is improving. As pressure increases, hydronamics can create extremely low coefficients of friction. Graphite and other dry lubes perform well in all areas of load and lack of load. Graphite in the DFW could be faster than oil if the wheel had very little pressure on it. As far as the magic pressure conditions where the hydrodynamics begins to outperform graphite in derby cars.....I have no idea.

 

[Rocket car]

There is a way to test this. I think. The tipical wheel for SS is 2 grams . When I build my cars I usually have about 15 grams on the FDW. If there is a way to weight the wheel to 15 grams equally balanced. You could spin both and see which one spins the longest.

. That will tell you which one is better.

 

[derby freak]

Here is a easy solution to all your problems, get a set of wheels and axles and prep them with graphite then get a set and prep them with oil. First using a tune board tune the car to a known steer then run the car down the track with the graphite wheels 10 times then the same with the oil prepped wheels. Figure the average for the oil and the average for the graphite. the one with the best avg. time is the best. /images/boards/smilies/thumb.gif but I can already tell you this, I cannot build a car using graphite to beat a car I build using oil. Oil for me has run times about .03 faster and that is a big difference.

 

[bracketracer]

When I prepped and ran a car with the DD4H oil, I pulled it apart a few days later and it looked dry. Are you guys saying there are hydrodynamic effects going on in there even though it appears to be dry?

I'm thinking that since I don't want to "contaminate" my oil wheels with graphite, I should prep my DFW with oil and the NDFW with graphite, run the car, reprep the front axles only, and swap the wheels and retest. That should minimise the variables, no? My DFW load is similar to Rocket's.

 

[GravityX]

Another idea into the equation, in my way of thinking, the DFW will be see its highest load through the transition of the track especially as it enters the curve. This is where the car starts to change direction. (I am sure Txchemist may have some insight on this.) The way I see it, the car's weight is now bearing down all of it's weight onto the DFW as it enters the transition of the track. As the cars moves through the transition, the weight on the DFW scales back to normal as the car exits the transition and onto the flat.

So... Is the load too great during this brief period of time that the benefit of graphite is lost to scrubbing speed (friction) or is it negligible for the moment? If you think about it, the car spends most of it's time on the flat and maybe the first second on the hill of the run, being pulled by gravity. So maybe graphite is better in that position as there is not really that much weight resting on the wheel, 15g (to use RC's info) most of the time.

Another thing, will this get the car moving faster off the hill? I've seen some races won the moment the gate pin drops, call it "reaction time" to when gravity takes full effect on the car. It's quicker on some than others, let's call it overcoming breakaway torque. Lower breakaway torque equals a faster "reaction" time to gravity. Now, by the sounds of things being said here about graphite it may have some advantage in this area.

Just one more thing to think about!

Maybe this is what the fastest guys are doing??? I may just give this a try on one of my cars and it will be the only change made so I'll see the difference, if any.

Graphite/oil mix anyone???

 

[kickaxe]

I feel ya GravX.....there seems to be a neverending assault of "what ifs and maybe's" in pinewood derby making. I guess this why we are so excited about it. There seems to be a an endless parade of new products and ideas that can slightly improve one's time.

Freaky, nobody can argue that graphite is faster than oil on the back axles, oil has been proven faster too many times.......but depending on the load of the DFW, it may hold true that graphite (or something better) exists for the DFW only.

Bracket, it may be that there are miniscule beads of oil that keep the hydrodynamic barrier intact....... or that I am completely wrong about how the oil process works.

 

[4wheeldrift]

I've seen that as well GravityX where at the drop of the pin another car seemed to have half a car length within the first foot (as seen on a pack video I took). I usually equated that to a lower moment of inertia and thinking their wheels were much lighter (saw that they were shaved down to even having no beads).

I know in talking to Greg who put on Mid-America, he swears that a graphite car can run as fast as an oil one. Maybe that's the case but I don't think it would have the long lasting consistency.

I also found when running graphite with highly polished axles and wheel bores it almost seemed like there was really no way that the graphite was sticking and staying. I'd pull the axle out and it appeared as if nothing was on it. Although spin times when touched with a padded wheel on a dremel were nearly 50 seconds! I think the difference though is what Kickaxe said in that it will behave differently with a load versus no load.

 

[bracketracer]

Gravity, I totally agree with you on the starting line topic. Anything you can do to get the car "out of the hole" quicker will pay you back in spades at the finish since the starting line is the slowest part of the track. I tried blowing on the back of my car a couple of times as I released the start gate to see what would happen. It lowered my times by about .020. Hardly scientific I know, but I was surprised it even made a measurable difference given the small volume of air I applied.

I can see I need to get to work on installing the incremental timers on my track. When I used to drag race I tuned the car off the short times and the top end mph, so when I was buying parts to build the timer for this track I bought enough extra sensors to string up timers about a foot off the start pin, at the bottom of the hill, and halfway down the flat. That first timer at the start might prove useful now. Have to wait until after the Nationals since my car is done and I'm not touching it!

 

[bracketracer]

Bracket, it may be that there are miniscule beads of oil that keep the hydrodynamic barrier intact....... or that I am completely wrong about how the oil process works.

I don't think you're wrong, obviously the oil is still working since the times didn't slow much. (I lose about .005 after it sits a few days and then stays there 'til I reprep). I just couldn't see liquid oil on the surface with the naked eye. I should have put the axle under the 'scope and looked closer. It did feel slippery to the touch but it didn't leave a shiney spot on my skin.

I did pull an axle after about 15 runs on fresh oil and there were tiny beads visible on the axle. Looked like water drops on a freshly waxed paint job.

 

[down4derby]

When I pull my wheels after getting my cars back there is always little droplets on the axles and in the bores never completely dry. As far as testing a graphite dfw if you have a track just prep a trued older wheel for oil first then prep it for graphite. Jumping out at the gate is something I've pondered as well, not only are you getting a head start and more momentum but you get slightly cleaner air.

 

[GravityX]

I've been thinking about this for some time now and was wondering if this would be of any use, because I do feel that if you knew the times as the car reached the transition (60 foot times in drag racing) it would give you an idea of how quickly the car reacted. You could then make adjustments to decrease reaction times. You could also compare times to the other cars on the track to see where times was lost or gained not only on the slope but on the flat of the track too.
Things could get crazy having that much information!

I can see I need to get to work on installing the incremental timers on my track. When I used to drag race I tuned the car off the short times and the top end mph, so when I was buying parts to build the timer for this track I bought enough extra sensors to string up timers about a foot off the start pin, at the bottom of the hill, and halfway down the flat. That first timer at the start might prove useful now. Have to wait until after the Nationals since my car is done and I'm not touching it!