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235/40/17's on the rear of Ef. How would it effect the speed 

 

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 Post subject: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Sat Jun 02, 2012 10:56 pm 
Getting Side Ways
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Got a set of rims here that have tyres on the rears that has a wall size of 40 instead of 45. They have to be the rears as they are a different offset to the fronts. I am waiting to put a new pair of rubbers on them ( 235/45/17's) but cash is short and the repairs are plenty. I am sick of waiting, the fronts are 215/45's and all tyres have plenty of tread on them...... so why not use them now and remove some of the rubbers on the rears before they go to the tip. My concern is the effect on the speedo, if I am doing 100km/h on the speedo with the 235/40's on the rear what speed am I actually doing? Cars a 94 ef Fairmont with factory fitted stock 15" all round
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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Sat Jun 02, 2012 10:59 pm 
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speedo will be in error by about 8%. I rund 245/40/17's I have a 10% error. speedo says I am doing 110, in actual fact I am doing 100. checked by GPS. also checked what the error amount would be via a website i cannot find right now.

 

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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Wed Jun 20, 2012 3:42 pm 
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Heres a calculator I found that might help =]

http://www.miata.net/garage/tirecalc.html

 

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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Wed Jun 20, 2012 4:05 pm 
Getting Side Ways
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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Wed Jun 20, 2012 4:26 pm 
Getting Side Ways
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Isn't 235 a bit wide for factory 15" rims in the first place? I'd be more concerned about the cornering ability (or lack thereof) with that wide tyre on such a narrow rim.

Might work good at launching off the line. Especially if you've only inflated them to 30psi.
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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Wed Jun 20, 2012 5:30 pm 
Getting Side Ways
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fiend wrote:
Isn't 235 a bit wide for factory 15" rims in the first place? I'd be more concerned about the cornering ability (or lack thereof) with that wide tyre on such a narrow rim.

Might work good at launching off the line. Especially if you've only inflated them to 30psi.


he's referring to 17" wheels/tyres unless i missed something?

 

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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Wed Jun 20, 2012 5:44 pm 
Getting Side Ways
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Very bottom of first message in this thread
"Cars a 94 ef Fairmont with factory fitted stock 15" all round"

Paint the death wagon blue and put it on blocks in my backyard.
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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Thu Jun 21, 2012 12:01 am 
Getting Side Ways
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yeah, i think the replacement wheels he's got are the 17's.

death wagon will die in my back yard :P
time to update the sig too!

 

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DTHWGN - EA GL Wagon, LTD Interior, Satin Black, 5.0, Turbo
RACER - EF Futura , 5.0, 5 Speed
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 Post subject: Re: 235/40/17's on the rear of Ef. How would it effect the speed
Posted: Thu Jun 21, 2012 12:55 am 
Getting Side Ways
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Yeah sorry they are Sparco racing Jap import alloys 17". All the details on the rims is in asian..... They are SUPER light weight with the rears having a different offset. Got them off ebay a few years ago from a bloke who bought them for a saloon show, did the show and then stored them. I am sure the rear offset will fit as I test installed them on my Xg when I had it. Calculators tell me if I go a wall of 45 ill be only out by about 0.6%, but about 6 or so km/h at 100 if I use the 40's. Going to get some other stuff done while I wait to get decent rear treads with a 45 wall
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