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Tyre fitter/ Wheels & Tyre expert.

Started by Gen1Jack, Aug 21 2013 08:21 PM

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#61 Robert

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Posted 03 July 2014 - 12:00 PM

I have 215/45/17 on mine and my speedo shows
100 when I'm doing 104 roughly

#62 Barbbachello

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Posted 03 July 2014 - 12:01 PM

I have 215/45/17 on mine and my speedo shows
100 when I'm doing 104 roughly

I've got the same tyre but mines bang on 100

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#63 Robert

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Posted 03 July 2014 - 12:03 PM

Yeah I don't get it.

So would going to a 225/45 bring it back down to 100 for me?

#64 Barbbachello

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Posted 03 July 2014 - 12:45 PM

Maybe. I get confused about how size affects the speedo lol

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#65 Robert

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Posted 03 July 2014 - 12:46 PM

Yeah me too Hahah.

#66 allpaw4

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Posted 05 July 2014 - 06:52 AM

Got 225/45/17 on my B4 and speedo is smack on. Different cars will get different results because every speedo is out by a certain amount. Specs on new cars is now 0% less, 20% faster, ie speedo is not allowed to show you going slower than what you actually are, and a 20% allowance to show you going faster. My brand new ranger is 7k out at 110.
Specs on the older cars were 10% allowance either way.

MY00 Red RX, a nice daily that was sold off once the B4 became reliable...
MY02 Blue B4, aka 'The Project' - v8 JDM STi engine package and assorted other 'goodies' - Sold, then bought back for parts. Stripped and crushed.
MY03 Blue RX, the newer old daily, pretty well more B4 than RX now... In the process of being converted to the track toy... Watch this space!
MY02 Silver Wagon, H6 conversion, full blue/black leather and almost full black interior to go with it.
MY03 White/Silver H6 Outback, donor car for silver waghoon.
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#67 migoreng

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Posted 05 July 2014 - 03:40 PM

215/45/17 on my Liberty B4 overeads by a few kph.

 

When speedo is on 110kph, my Samsung S4 phone GPS is about 107kph


#68 Liberty

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Posted 11 July 2014 - 07:09 PM

With regards to tyre pressures, I remember reading somewhere (I'm pretty sure the Bridgestone website or something) that whatever your placard says, it's a good thing to add about 4 PSI (when your tyres are cold obviously). If I'm not mistaken, my front tyres are inflated to 37 PSI and my rear tyres are at 40 PSI.


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#69 RX25SE

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Posted 12 July 2014 - 08:32 AM

Maybe. I get confused about how size affects the speedo lol

 

Yeah me too Hahah.

 

 

My GenIV is 9% under according to the GPS.

109 on the speedo = 100 on the road

 

To correct it I need to turn the tyres slower at the same road speed.

A larger diameter tyre will turn slower to maintain the same speed.

 

So, for example, if I swap my 215/45-18 for a 225/45-18 the new tyre has a wider tread but the same sidewall profile then its overall diameter will be larger therefore it will turn slower for the same speed.


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#70 Adam

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Posted 13 July 2014 - 05:23 PM

Still confused how width affects diameter??

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#71 Barbbachello

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Posted 13 July 2014 - 05:31 PM

The profile is a % of width so wider with the same profile will be taller


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#72 Adam

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Posted 13 July 2014 - 06:46 PM

ok. So say a 45 tyre wouldn't actually be 45mm sidewall?


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#73 Robert

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Posted 13 July 2014 - 06:50 PM

45 percent of the width of the tyre

Ie 215/45r17

Would have 96.75 mm side wall

My understanding anyway

#74 Adam

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Posted 13 July 2014 - 06:51 PM

SEEN!


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#75 Cracktastic

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Posted 29 July 2014 - 12:52 PM

Found the page Adam! :P 17x7 +42 what size tyre would i need?


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#76 Harry88

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Posted 29 July 2014 - 01:01 PM

17x7 +42 what size tyre would i need?

 

215/45/17

 

Same size are stock WRX wheels.


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#77 Cracktastic

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Posted 29 July 2014 - 01:52 PM

could i go any wider?


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#78 nickknack

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Posted 29 July 2014 - 01:54 PM

225 should be fine, no wider though

#79 Cracktastic

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Posted 29 July 2014 - 01:58 PM

225/40/17??


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#80 Harry88

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Posted 29 July 2014 - 02:08 PM

225 should be fine, no wider though

 

You could get away with a 225 but when I had 17x7 wheels I stuck with the 215


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