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Chris Livengood
Joined: 24 Jul 2001
Posts: 2432
Location: United States, Pennsylvania, Da Burgh
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Tom Sekey
Joined: 25 Jan 2004
Posts: 1077
Location: United States, Palau,
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 Posted: Tue Dec 07, 2010 7:17 pm Post subject: |
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| Mike Goebel wrote: | | Tom Sekey wrote: | | Ran both on our PCR. If the track had low grip the 17's were faster. If the track had medium + grip the 25's were faster. 17's flex 25's don't. |
Tell me how much each flexes under a 100-200 lb load.
Mike G. |
400 lb kart pushing 2 g's in a turn. What makes you think spindles are not flexing? |
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Dan Haynes
Joined: 17 Sep 2007
Posts: 2372
Location: United States, Pennsylvania, Ellwood City
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| Posted: Tue Dec 07, 2010 7:54 pm Post subject: |
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Chris, on the Arrow the spindle is the same, you just change the shaft. it's a 2 piece spindle, so i don't see how the geometry could change. maybe other brands might. don't know.
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Blaise Haynes
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Mike Goebel
Joined: 28 Jul 2001
Posts: 5766
Location: United States, California, Winnetka
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| Posted: Tue Dec 07, 2010 8:14 pm Post subject: |
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| Tom Sekey wrote: |
400 lb kart pushing 2 g's in a turn. What makes you think spindles are not flexing? |
Ok we will use some engineering instead of guessing. Lets say that 400lb kart has a 60% - 40% balance. The front has 40% so that's 160 lb on the front total. Divide that by 2 and you get 80lb per wheel but since you think that 2 g's are possible that translates into double the force on the front wheel and we will go for that. That makes one front corner 160lb at 2 G's. That is still less than the 200lb I did for a back of the envelope calculation, which resulted in a .004 deflection. Lets for the fun make it 2 times that load, which is 320lb on one front wheel, (almost as much as the entire kart and driver). The deflection on the 17mm spindle is linear and that equates to .008in. WOW that's a lot 
Mike G.
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Chris Brunnemer
Joined: 13 May 2009
Posts: 582
Location: United States, Indiana, McCordsville
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| Posted: Tue Dec 07, 2010 9:59 pm Post subject: |
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| Mike Goebel wrote: | | Tom Sekey wrote: |
400 lb kart pushing 2 g's in a turn. What makes you think spindles are not flexing? |
Ok we will use some engineering instead of guessing. Lets say that 400lb kart has a 60% - 40% balance. The front has 40% so that's 160 lb on the front total. Divide that by 2 and you get 80lb per wheel but since you think that 2 g's are possible that translates into double the force on the front wheel and we will go for that. That makes one front corner 160lb at 2 G's. That is still less than the 200lb I did for a back of the envelope calculation, which resulted in a .004 deflection. Lets for the fun make it 2 times that load, which is 320lb on one front wheel, (almost as much as the entire kart and driver). The deflection on the 17mm spindle is linear and that equates to .008in. WOW that's a lot G. |
I wondered how much that deflection resulted in camber gain and taking Mikes deflection numbers i got this. .008 deflection resulted in a .001* camber gain. and .004 resulted in .0005 camber gain. so a camber gain theory is out. that would be a negative camber gain btw |
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Jeff Field
Joined: 02 Dec 2007
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Location: United States, Delaware, Wilmington
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| Posted: Wed Dec 08, 2010 9:47 am Post subject: |
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I agree that the deflection from the assumed load on the spindles is negligible. But, boy do they make the kart (GP in my case) feel different (better in my case).
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Mike Goebel
Joined: 28 Jul 2001
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Location: United States, California, Winnetka
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| Posted: Wed Dec 08, 2010 10:03 am Post subject: |
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| Jeff Field wrote: | | I agree that the deflection from the assumed load on the spindles is negligible. But, boy do they make the kart (GP in my case) feel different (better in my case). |
I believe that.
Mike G.
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Chris Livengood
Joined: 24 Jul 2001
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Location: United States, Pennsylvania, Da Burgh
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Dan Haynes
Joined: 17 Sep 2007
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Location: United States, Pennsylvania, Ellwood City
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| Posted: Wed Dec 08, 2010 11:22 am Post subject: |
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Chris, the Arrow X1 spindles are two-piece. The yolk is the same and only the shaft changes (removable shafts). Both shafts are the same length and insert to the same depth, so on the X1, the scrub radius will remain consistent between the two.
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Blaise Haynes
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Larry Hayashigawa
Joined: 21 Oct 2001
Posts: 400
Location: United States, California,
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| Posted: Wed Dec 08, 2010 2:47 pm Post subject: |
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It doesn't make sense that such a small deflection could make a such a difference. Therefore the deflection has to be higher.
I think there is very large moment working on the spindle that is being overlooked. The large moment is generated by the effective cornering force working at the center of gravity of the kart w/ driver and the contact patch of the tire. This moment arm is more like 2.5 ft and the cornering force is 800 lbs (2gs x 400 lbs) . So the moment is closer to 2000 ft-lbs realizing that this moment is distributed between the rear axle and the front spindles. Nonetheless, the moment at the front spindles it is a lot more than 400 lbs x 6 inches = 200 ft lbs being used in the earlier estimates.
A 25 mm spindle is about 4.7 times stiffer in bending than a 17 mm spindle.
Does this make sense?
Larry
Last edited by Larry Hayashigawa on Wed Dec 08, 2010 4:23 pm, edited 1 time in total |
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Colin Edwards
Joined: 30 Sep 2009
Posts: 87
Location: Australia, Not USA, Melbourne
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| Posted: Wed Dec 08, 2010 3:33 pm Post subject: |
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Larry,
Makes perfect sense to me. We ran an X1 for a couple of years in a Yamaha Class at 160kg with 17mm spindles. Recently ran the X1 in Rotax at 170kg. Did significant back to back testing between 25mm and 17mm spindles. Reliable results as the spindle change over can be done very quickly - not much need to factor in track and environment changes. In ALL cases the 25mm spindle was on average 1.5 tenths quicker. Temperature spread across tyre was better. More feedback to driver during initial turn in and from there in to corner apex. It could be more of a driver feedback thing than basic tyre grip improvement. In ALL testing, new 17mm and 25mm spindles were used. Toe and camber was checked at EVERY change to ensure no geometry variation had been introduced. The 25mm spidles are hollow / lighter - maybe that needs to be factored into the equation as well. At the end of the day - if something is faster we,ll use it!
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Tom Sekey
Joined: 25 Jan 2004
Posts: 1077
Location: United States, Palau,
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| Posted: Wed Dec 08, 2010 4:33 pm Post subject: |
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| Larry Hayashigawa wrote: | It doesn't make sense that such a small deflection could make a such a difference. Therefore the deflection has to be higher.
I think there is very large moment working on the spindle that is being overlooked. The large moment is generated by the effective cornering force working at the center of gravity of the kart w/ driver and the contact patch of the tire. This moment arm is more like 2.5 ft and the cornering force is 800 lbs (2gs x 400 lbs) . So the moment is closer to 2000 ft-lbs realizing that this moment is distributed between the rear axle and the front spindles. Nonetheless, the moment at the front spindles it is a lot more than 400 lbs x 6 inches = 200 ft lbs being used in the earlier estimates.
A 25 mm spindle is about 4.7 times stiffer in bending than a 17 mm spindle.
Does this make sense?
Larry |
Yep, makes sence. Also take into consideration front width on the stubs. We have run as little as 42" and as much as 47.25". There is going to be a huge difference in the flex of the stub axle.
Mike, can you figure out for me how it works under heavy braking too? What about if I set up 45% front weight. I don't bother trying to figure out the exact geometry and weights involved because it is dynamic on the track. To many factors to get perfect numbers. |
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Dan Haynes
Joined: 17 Sep 2007
Posts: 2372
Location: United States, Pennsylvania, Ellwood City
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| Posted: Wed Dec 08, 2010 4:50 pm Post subject: |
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too smart for my dumb**s. i just bought them because the guy said they're faster
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Blaise Haynes
#3 Arrow X1-CIK
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Mike Goebel
Joined: 28 Jul 2001
Posts: 5766
Location: United States, California, Winnetka
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| Posted: Wed Dec 08, 2010 7:37 pm Post subject: |
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| Dan Haynes wrote: | | too smart for my dumb**s. i just bought them because the guy said they're faster |
No prob man. I once put a a cat turd on my fairing becasue the guy that beat me had one
Mike G.
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Mike Goebel
Joined: 28 Jul 2001
Posts: 5766
Location: United States, California, Winnetka
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| Posted: Wed Dec 08, 2010 7:40 pm Post subject: |
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| Larry Hayashigawa wrote: |
Does this make sense?
Larry |
NO! but I need to get sober before I answer.
Mike G.
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