Txchemist, a graphited dfw is something I've been pondering for a while now. I'm thinking of sending a test car to nationals with a graphite dfw. I wonder if there would be an issue with graphite shedding to the rear wheel contaminating that bore.
Drilling the DFW
- Thread starter GravityX
- Start date
I think this happens because when you spin the oil prepped wheel and it "hangs down" the clearance between the axle and bore increases at the bottom allowing the oil to puddle there and not at the top where the contact point is. The wheel is now spinning "dry" and on top of a puddle of oil and not on a thin oil film. I'm guessing the oil does not grab enough to climb the wall of the bore for ideal lubrication.
With the weight of the car resting upon the axle and bore, clearance is negligible with a stopped car. Oil will still puddled at the bottom of the bore, but once the car starts rolling a very thin film of oil is spread out and now puddles in front of the contact point and this prevents the axle from climbing the wheel bore as the wheel turns. In my opinion, making it slipperier. Hope this makes sense, best way I could explain it.
Graphite sticks to everything and remains in place unlike oil.
With the weight of the car resting upon the axle and bore, clearance is negligible with a stopped car. Oil will still puddled at the bottom of the bore, but once the car starts rolling a very thin film of oil is spread out and now puddles in front of the contact point and this prevents the axle from climbing the wheel bore as the wheel turns. In my opinion, making it slipperier. Hope this makes sense, best way I could explain it.
Graphite sticks to everything and remains in place unlike oil.
txchemist said:Now think about this- why is it that when you spin a wheel prepped for oil, you do NOT get a low friction time at all, 6-12 sec is not unusual where spinning a graphite wheel can hit 26 sec or longer. You need some weight on that oil wheel to drop the friction. Find a way to make that wheel super light, and the friction will increase dramatically.
If anything, if you could make the car nose push down a little more, it would drop the friction on an oil wheel. Now how about a car with back wheels oil, and make the com aggressive and the front wheel very light, so use a graphite wheel on the front?
Mud flaps. But in this case, graphite flaps.
Sorry, I couldn't resist that.
I think I can hear people saying Noooooo.....
I think I can hear people saying Noooooo.....
down4derby said:
The DFW wheels of the top three cars in the April SS race all look to have been drilled to achieve very low front ends. And what is that white strip on the back 1/2 inch of those cars?
you have to look closely at the pictures to see how the NDW is mounted. They put the NDW at a 45 or more degree angle, i.e. almost on top of the front of the car. This was done several ways. the fastest cars still mounted the wheel in such a way that it still acted like a pin. Others actually used a pin in addition to the NDW wheel. They also covered both the NDW fender (which was also at a 45 degree angle) and the wheel in such a way there was almost no drag. In some cases this covering (lets call it a skirt) was Monokote, and with others it was a very thin piece of balsa. The workmanship of these cars was flawless, especially the guy from Idaho.
In person the cars do not sit low at all, I would say almost the opposite. They look a little higher.
pony express said:
I hope the NDW is not on more than a 45º angle, because it would be against the rules.OPARENNEN said:
Rocket car said:I hope the NDW is not on more than a 45º angle, because it would be against the rules.OPARENNEN said:Looks like about 60º degree angle from the race footage, but that can be discieving.
PM DD4H. He copied the idea on this own unpainted car.
The right rear wheel (if using the right as DFW) should have 0 toe in. The left is up to debate. Toeing in both gives you more high speed stability, but I saw loss of speed with equal toe in on the rears. You can experiment with the right rear, but I've tried different cants, levels and other drilling options and had one of those experimental cars that you could adjust the toe on and lock it in place. I would then remove the axle and place a 6 inch drill bit and measure the best toe options. The right was always zero toe.
This is a little off subject of the thread, but it was also brought up by Txchemist on wheel spin (see below) in this thread. It was stated that wheel spin times are typically shorter with oil, 6-12 sec. Now, I'm not sure if I stumbled across something or just getting above average results. After prepping my wheel bores and axles, no Jig (yet) and DD4H oil, I'm getting approx. 16-17 sec. spin times. Thinking it was simply a fluke, I snapped it again between my thumb and finger 10 times and averaged 16 sec. spin times. I'm going to try this with Jig sprayed on the axles next to see what happens, but that is for tomorrow. Should I be excited about these results or not? I know this is not really a scientifically controlled test, but what are you guys seeing for times?
GravityX said:I think this happens because when you spin the oil prepped wheel and it "hangs down" the clearance between the axle and bore increases at the bottom allowing the oil to puddle there and not at the top where the contact point is. The wheel is now spinning "dry" and on top of a puddle of oil and not on a thin oil film. I'm guessing the oil does not grab enough to climb the wall of the bore for ideal lubrication.
With the weight of the car resting upon the axle and bore, clearance is negligible with a stopped car. Oil will still puddled at the bottom of the bore, but once the car starts rolling a very thin film of oil is spread out and now puddles in front of the contact point and this prevents the axle from climbing the wheel bore as the wheel turns. In my opinion, making it slipperier. Hope this makes sense, best way I could explain it.
Graphite sticks to everything and remains in place unlike oil.
txchemist said:Now think about this- why is it that when you spin a wheel prepped for oil, you do NOT get a low friction time at all, 6-12 sec is not unusual where spinning a graphite wheel can hit 26 sec or longer. You need some weight on that oil wheel to drop the friction. Find a way to make that wheel super light, and the friction will increase dramatically.
If anything, if you could make the car nose push down a little more, it would drop the friction on an oil wheel. Now how about a car with back wheels oil, and make the com aggressive and the front wheel very light, so use a graphite wheel on the front?
You may have a super snap- I'll bet you could get 30 or more sec with graphite. The only good correlation of spin time to coefficient of friction on an unweighted wheel is graphite. The point is that at low loading, graphite looks slightly better with the same spin force. The mystery is what is the minimum loading to get superior speed from oil? I have not tried it yet, but a very good builder could just run his graphite and oil cars with zero weights in the body and We would know the answer. My tests are what Mythbusters would call "plausible", but not confirmed.
The "super snap" that's funny, I like it! Possible new car name.
Well I guess to validate this idea I need to assemble a graphite axle wheel assembly and test the snap. As mentioned previously a highly unscientific testing method, but it will make do for what I'm doing.
Well I guess to validate this idea I need to assemble a graphite axle wheel assembly and test the snap. As mentioned previously a highly unscientific testing method, but it will make do for what I'm doing.
txchemist said:
Just doing some reading and found this thread very interesting, especially with the couple of tuning threads that exits now. I was thinking about the air under the car and how to minimize it (that's not my only problem), but has anyone built an air damm or lowered the front such that it road between the rails? I know would have to be some thought given to this as you have to ensure the body does not touch the rail. We do this already with fenders to some degree (get them as close to the track as possible). I wish I trusted my build skills enough to determine if there is a gain to be had. Ehhh - I might do it anyway...OPARENNEN said:
You can thank me later for drudging up an old thread.
Air dam up front would likely not last long. Stop section would be rough on it as it uses the bottom of the car's surface to provide stopping power.
Duh! Looks like I picked the wrong day to stop sniffing glue.
(well, you saved me from ruining a block of wood)
(well, you saved me from ruining a block of wood)
Using the approximate value of a wheel width of 3/8", and a net axle bend of 3 degrees, it would raise the front of the car (at the axle) by 0.0196".
With a net axle bend of 2 degrees, the front of the car (at the axle) would raise the front of the car by 0.0131".
1/64" is 0.0156". So, you are looking at a raise (at the axle) of somewhere between 9/512" and 5/256".
Calling the raise at the axle 1/64" (kinda the average between a net 2 degree and a net 3 degree bend), that translates to raising the nose of a scout wheelbase car (4-3/8") by 0.0227" (a little less than 3/128").
And now that I've buried myself in numbers, I see the answer right there. Drilling the DFW ~1/64" higher should negate any raise of the nose due to the bend of the axle. YMMV.
With a net axle bend of 2 degrees, the front of the car (at the axle) would raise the front of the car by 0.0131".
1/64" is 0.0156". So, you are looking at a raise (at the axle) of somewhere between 9/512" and 5/256".
Calling the raise at the axle 1/64" (kinda the average between a net 2 degree and a net 3 degree bend), that translates to raising the nose of a scout wheelbase car (4-3/8") by 0.0227" (a little less than 3/128").
And now that I've buried myself in numbers, I see the answer right there. Drilling the DFW ~1/64" higher should negate any raise of the nose due to the bend of the axle. YMMV.
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