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racing rim size 

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 10:10 pm 
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krisisdog wrote:
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.



Then explain to me why when traveling next to my mates car at 100km/h with my 16s on both cars sit side by side but with my 20s on and speedo at 100km/h he needs to do 110km/h to sit level

 

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 Post subject: Re: racing rim size
Posted: Wed Dec 09, 2009 10:14 pm 
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You have a bigger sidewall on your 20s than what you should have then, or, the 16s arent quite right either.

 

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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 9:13 am 
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Or one car has the wrong speedo gear, or a cluster out of spec, etc.
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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 10:32 am 
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krisisdog wrote:
You have a bigger sidewall on your 20s than what you should have then, or, the 16s arent quite right either.

The 16s run the factory spec 225/50 tyres and the 20s run 245/40 tyres. Both cars run the appropriate diff ratios and speedo setups. His car runs the factory spec tyres also.

 

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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 10:35 am 
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ebxr82nv wrote:
krisisdog wrote:
You have a bigger sidewall on your 20s than what you should have then, or, the 16s arent quite right either.

The 16s run the factory spec 225/50 tyres and the 20s run 245/40 tyres. Both cars run the appropriate diff ratios and speedo setups. His car runs the factory spec tyres also.


Maybe tyre pressure, tread wear, fuel level and weight in the boot make up the rest of the difference ;)

 

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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 2:09 pm 
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ebxr82nv wrote:
krisisdog wrote:
You have a bigger sidewall on your 20s than what you should have then, or, the 16s arent quite right either.

The 16s run the factory spec 225/50 tyres and the 20s run 245/40 tyres. Both cars run the appropriate diff ratios and speedo setups. His car runs the factory spec tyres also.


Like I said, helps when you run the right sized tyre, your 20s are incorrect.
They're out 8.7%.
They should be 245/30 (1.2%) or 245/35 (4.9%) - or better still 235/40 (0.2%)

I thought I explained this to you previously?

 

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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 4:27 pm 
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ebxr82nv wrote:
The 16s run the factory spec 225/50 tyres and the 20s run 245/40 tyres. Both cars run the appropriate diff ratios and speedo setups. His car runs the factory spec tyres also.


225/50/16 is actually an undersized tyre compared to the 205/65/15 eseries came out with.

fair enough the xr's had 225/50/16 from the factory, but i assume Ford wasnt concerned with the speedo reading 3kph higher on the safe side?
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 Post subject: Re: racing rim size
Posted: Thu Dec 10, 2009 4:32 pm 
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actually xr's with factory 16" wheels use the black 23 tooth speedo gear and the xr's with 15 " wheels use the grey 22 tooth speedo gear...
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 Post subject: Re: racing rim size
Posted: Fri Dec 11, 2009 4:27 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.



true... considering how inebriated i was when i wrote that i'm surprised i did that well lol

can krisisdog shed some scientific light onto the rolling MASS side of things.i'm far too lazy.

 

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 Post subject: Re: racing rim size
Posted: Sat Dec 12, 2009 2:55 pm 
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What kind of track work is it? Circuit/quarters/drifting etc

 

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Cramping in the hand from having it on your Wang for an excessive period of time is a definate con.
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 Post subject: Re: racing rim size
Posted: Sat Dec 12, 2009 6:52 pm 
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Its for 1/4 runs.
low_ryda, I could, but I CBF. The basics are pretty simple though, heavier wheel = slower lol. If you add 3kg per wheel (easily the difference between 2 types of 17/18" rim), its the equivalent of adding around 50kg weight to the car overall.
At speed the weight difference effects are minimal, its during initial acceleration and take off where the difference will be made. You can generally shave a few tenths off a 1/4 run with lighter wheels.

 

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 Post subject: Re: racing rim size
Posted: Sun Dec 13, 2009 1:14 am 
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Ohh sweet.

Get the lightest 14/15in rims for the rear you can that will allow you to fit a decent tyre (or even widen stockies if you must). Then play with tyre pressures, I would start at around 30psi just to get a starting point then lower it down everytime you hit the track and see what works for you.

 

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EVL098 wrote:
Cramping in the hand from having it on your Wang for an excessive period of time is a definate con.
Seriously do people google "f**k up modifications for Fords owned by Jews" and get linked straight to this site nowadays?

AU,factory fitted tickford kit/IRS, t5,Sports ryder/KYB: gone.

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