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20" Tire not really 20"?

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thescreensavers

thescreensavers

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IMG_20120625_150030.jpg


This tire is listed as 20x7-13

I am trying to find the Diameter of the tire but it seems like it shrunk? I have a few other tires and they also not close to 20 either?
 
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96Firebird said:
Some drag slicks are measured this way...

http://www.hoosiertire.com/specdrag.htm

As you can see, the tire diameters are only approximates. Are they used tires?

Edit - Looks like they are FSAE tires, were the tires carrying weight when you measured them?

http://www.racegoodyear.com/tires/sae.html
Click to expand...

They have been used yes, but have plenty of tread.

Yep they are FSAE tires, It has weight on it, but we have a few other tires laying around and they also are not near 20"
 
Actually it might be close to it, I just took rough measurements of the circumference and its actually close, I need to measure it more precisely, but I got a bit over 62 inches / Pi = 19.74 inches.

So I guess ruler test isnt that good then, nevermind lol
 
Inflation pressure, weight on the wheel, and stretch/stuff from the wheel will all change the "dynamic radius" of the tire.

Also, what's with the FSAE car? Do tell! 😀
 
^ Yep, its actually fine now, there was weight on that tire but not enough to deform it with the PSI thats in there. I contacted goodyear, after right after I sent the email figured it out but they just got back to me and, just what 96Firebird said, they are approximates. They are actually closer to 19.5"

So yea I see your Avatar, actually I never really looked at until now and I believe you've had that avatar for a bit(I think) What was your role?

We use the GSXR 600 motor, only reason being that last years team used it, and we have experience with it. We really cant stray away from the 4Cyl since we do not have budget to allow composites to get the weight low enough to where it would benefit us to run a smaller engine. The Last car built was our 2011 car(#67 at MI) which weighed in at 498lb and put down 74hp with 36 ft/lb torque.

I joined in 2012, we are a small team(~10 people)I became engine Team Leader and started to look at the 2011 car, there are many things which can and will be improved, now I just nominated my self for Drivetrain since the work wasnt done and its connected to the engine so why not lol.(yea my grades are crying a bit which is not too good)

Our 2012 car failed because of funding, but we have majority of the parts already for our 2013. Its 2013 Car or Bust, if its not built this year we might not have one the year after.

Otherwise its going well started nice and early, this year looks very promising. Trying to lighten it up further and improve on the 2011 design since it did decent(except for overheating).

211117_121774884574372_6504809_n.jpg
 
thescreensavers said:
^ Yep, its actually fine now, there was weight on that tire but not enough to deform it with the PSI thats in there. I contacted goodyear, after right after I sent the email figured it out but they just got back to me and, just what 96Firebird said, they are approximates. They are actually closer to 19.5"

So yea I see your Avatar, actually I never really looked at until now and I believe you've had that avatar for a bit(I think) What was your role?

We use the GSXR 600 motor, only reason being that last years team used it, and we have experience with it. We really cant stray away from the 4Cyl since we do not have budget to allow composites to get the weight low enough to where it would benefit us to run a smaller engine. The Last car built was our 2011 car(#67 at MI) which weighed in at 498lb and put down 74hp with 36 ft/lb torque.

I joined in 2012, we are a small team(~10 people)I became engine Team Leader and started to look at the 2011 car, there are many things which can and will be improved, now I just nominated my self for Drivetrain since the work wasnt done and its connected to the engine so why not lol.(yea my grades are crying a bit which is not too good)

Our 2012 car failed because of funding, but we have majority of the parts already for our 2013. Its 2013 Car or Bust, if its not built this year we might not have one the year after.

Otherwise its going well started nice and early, this year looks very promising. Trying to lighten it up further and improve on the 2011 design since it did decent(except for overheating).

211117_121774884574372_6504809_n.jpg
Click to expand...

I was many things on Cooper Union's team (only 4 core students, ~9 total). I did detailed design on much of the car (i.e. the suspension guy came up with geometry, I designed all of the links/mounts), all of the welding (wrote and was qualified on 3 WPSs), some of the machining... up through driving auto-x and enduro. We ultimately placed 35th at Michigan in 2009 after finishing every event, up from 89th the year before.

We also used the GSXR600, it's a good engine, but it is worth every penny to buy an OTS dry-sump oiling system to keep reliability up. We had issues with heat rejection too, and wound up using all aluminum hard lines for cooling and using an aftermarket ATV radiator with ducted fan and an electric coolant pump. Never had an issue with that setup. I think we were around 70whp with a wide, flat, torque curve at the expense of maximum power.

Cooling system without fan. Note the fill cap on a long extension to put the fill point well above the engine. We added stick-on color changing thermometers on the hard lines to quickly and easily check coolant temps during testing.
cooling.jpg


Our 2009 car, my last one, was 479lbs. We made a real effort to drop weight from 2008, which was 574lbs. A Lithium Ion main battery was a huge help, so was a titanium exhaust, center-lug forged BBS wheels, and carbon bodywork. We also used a Microsquirt ECU and used CANBus to drive our dashboard (custom) dropped a whole bunch of wiring and gauges doing that... every ounce counts!

Good luck on your build and design! I'd be happy to consult on anything, I was one of the founding members on Cooper's FSAE team, so I've done a bit of everything.
 
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