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racing rim size 

 

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 Post subject: racing rim size
Posted: Tue Dec 08, 2009 8:34 pm 
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Hey guys, just a bit of advice on rim sizes when drag racing, what is best?

i have 19"s and last time i raced in them i got poor times..

should i go 15's all round or will i get away with 19's on the front and 15's on the rear?
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 Post subject: Re: racing rim size
Posted: Tue Dec 08, 2009 8:35 pm 
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FORDom wrote:
Hey guys, just a bit of advice on rim sizes when drag racing, what is best?

i have 19"s and last time i raced in them i got poor times..

should i go 15's all round or will i get away with 19's on the front and 15's on the rear?


if you could get some 17's that would be an ideal size.

 

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 Post subject: Re: racing rim size
Posted: Tue Dec 08, 2009 8:38 pm 
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you could go with wide low profile 15" tyres to get your tyre diameter smaller/ slightly faster launches off the mark..
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 Post subject: Re: racing rim size
Posted: Tue Dec 08, 2009 9:08 pm 
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why were the times poor, no traction?
if traction wasn't an issue they only way you'll improve is with ligher wheel/tyres...

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 5:00 pm 
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it's a gearing issue, your gears don't stop at the diff... hehe

increasing the diameter of your wheels will increase your top speed for the cost of acceleration, and smaller wheels will achieve faster acceleration at the cost of top speed.

thats why v8 supercars still run 17's and not blingin' 20's.

thats why cars with 20's drive you more than you drive them lol

and lighter wheels will work like a lightened flywheel (less rotating mass/inertia) theres an equation that compares lightening wheels to reducing body weight and it's something like 3 times more effective by memory. if that makes sense..... heh

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 5:20 pm 
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What sort of tyres do you intend on running? Full street, soft street, semi slick or drag radial? That should be the first thing to work out then go looking for rims to suit.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 6:19 pm 
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low_ryda wrote:
it's a gearing issue, your gears don't stop at the diff... hehe

increasing the diameter of your wheels will increase your top speed for the cost of acceleration, and smaller wheels will achieve faster acceleration at the cost of top speed.

only if overall rolling diameter changes.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 6:48 pm 
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Steady ED wrote:
low_ryda wrote:
it's a gearing issue, your gears don't stop at the diff... hehe

increasing the diameter of your wheels will increase your top speed for the cost of acceleration, and smaller wheels will achieve faster acceleration at the cost of top speed.

only if overall rolling diameter changes.



With 19s on an e series I'd be suprised if it didn't. The 20s I've got for my au are an inch taller than the standard wheels. Works out to be roughly 8-10%.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 7:00 pm 
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about as much difference as running with brand new tyres vs worn tyres :lol:

my point was, saying that 'gearing' is changed by changing wheel size is wrong, it's changing the rolling diameter that does it.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 8:10 pm 
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Steady ED wrote:
about as much difference as running with brand new tyres vs worn tyres :lol:

my point was, saying that 'gearing' is changed by changing wheel size is wrong, it's changing the rolling diameter that does it.


they're only car tyres not 35" muddies. The tread isn't that deep.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 8:18 pm 
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no s**t sherlock, i'm saying the difference in rolling diameter is sfa between 205/65 15s and 245/35 19s.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 8:32 pm 
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Steady ED wrote:
no s**t sherlock, i'm saying the difference in rolling diameter is sfa between 205/65 15s and 245/35 19s.



I don't care much for your attitude. :roll:

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 9:12 pm 
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Steady ED wrote:
no s**t sherlock, i'm saying the difference in rolling diameter is sfa between 205/65 15s and 245/35 19s.


but if you drop profile to 50 series 15" it could help! but not as much as changin the diff ratio..
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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 9:37 pm 
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ebxr82nv wrote:
Steady ED wrote:
low_ryda wrote:
it's a gearing issue, your gears don't stop at the diff... hehe

increasing the diameter of your wheels will increase your top speed for the cost of acceleration, and smaller wheels will achieve faster acceleration at the cost of top speed.

only if overall rolling diameter changes.



With 19s on an e series I'd be suprised if it didn't. The 20s I've got for my au are an inch taller than the standard wheels. Works out to be roughly 8-10%.


Be surprised then.

205/65/15 = 2034.2mm circumference
235/35/19 = 2032.9mm circumference
Thats 0.1% difference.

235/30/20 = 2038.9mm circumference
Thats 0.2% difference.

It really really really helps when you get the right size tyre fitted. Even if you use 245s the difference is still 1% for 19s and 1.2% for 20s.

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 9:51 pm 
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but with 20'z you only get a very small contact patch and very little side wall flex.
so putting 20'z on fro racing is not the best bet.
for drag racing get some M/T street slicks or what every they are called in 15's.
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