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| FordAUte |
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Im just about to go pick up a set of 20" rims for my FG, but was wondering if there was a cheap easy way to adjust the speedo to suit the different diameter tyre... or if i will just have to live with it...
cheers in advance for any help... *CURRENT: Stock XT alloys Front 215/60R16 -Cir. 2086.6mm Rear 215/60R16 -Cir. 2086.6mm *NEW: High Speed AS wheels (black spokes polished lip) Front 225/35R20 -Cir. 2090.4mm (+0.201%) Rear 275/35R20 -Cir. 2199.8mm (+5.434%) Good site to compare tyres... plus gives a list of brands/models to suit that size. handy little online tool to use... http://www.1010tires.com/tiresizecalcul ... ion=submit
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| TROYMAN |
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nope, only via flash tuner , speedo signal is read via abs sensors/ wheel speed..
and afaik changes made via flash tuner only give you the option to change by diff ratio only not %, i could be wrong though... |
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| FordAUte |
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And very dumb question, but read from sensor on the rear wheels right?
Hmm... So with a change of 5% in circumference, at speedo 100/hr I will actually be doing 105km/hr? Just another excuse to buy a flash tuner :p haha
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| phatba |
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i think you have your sums wrong. your proposed rim has on the fronts 225/35r20 and rears of 275/35r20.
yet you show a difference in front to rear circumference. both tyres have the same rolling diameter, all that changes is the width of the tyre. the 225 and 275 numbers are how wide the tyre is. the 35 is the profile, or how high the tyre sits on the rim. the 20 is the diameter rim the tyre goes on. so you can change from a 17 to an 18 to a 19 without an effect on rolling circumference by opting for a smaller profile. you will be going from a rim with a diameter of 16 inches and tyre height/profile of 60, to a rim with a diameter of 20 inches but a profile of 35. using the calculator on their site a 275/35/20 tyre sits 17.272mm higher on the rim than a 225/35/20 tyre, id suggest asking another tyre company...... |
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| FordAUte |
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Whoops typo, rears are 275/30R20...
But aside from that, isn't the second number (30, 35, etc) a percentage of the tyre width. Eg the profile is 30% of 275mm width? Or have I been dreaming things up lol
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| Cobra427 |
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Have a look at this. Mighty car mods did a spot on a cheap way to adjust speedo reading. These guys do some cool s**t... http://www.youtube.com/watch?v=bMs7w72QTVM&feature=plcp
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| FordAUte |
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Those guys have gotten a lot more professional since I last saw them lol
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| TimmyA |
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Pretty sure Ford's diagnostic gear has some provision to recalibrate speedos, but this may only be on police enabled vehicles...
That kit wont work because the ABS sensor looks at the tone wheels and then sends the via canbus to the pcm and computer and such... In the data wires it isn't just a square pulse you're modifying like on E series or equivalent... You are right, first number is the width in mm second is percentage of the width in the side wall and next is the diameter of the rim... Attachment: I just jammed this together real quick... Don't take it as gospel... May have errors in it... But it shows the stages you do to work out tire sizing and then compares it... you sure your tire sizes are right? Massive difference in those tires... Remember this is perfect world... Tires actually squash with weight on them and the rolling diameter is different from the theoretical diameter and will vary with tire pressure... The spreadsheet assumes you're doing 100km/hr and then says if you had a GPS and the wheels were in perfect world this is how much real life (copper radar gun) speed change you should expect... Cheers, Tim
_________________ 93 Red ED 5spd Manual Build Thread |
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| FordAUte |
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Now I'm all confused... I'm standing in front of the tyres now, so this is what I'm reading off the tyres... No typos...
Fronts 225/35 ZR20 93W Achilles ATR Sport Pretty much new. Tyre is narrower then rim.  Rears 275/30R20 97Y Dunlop SP Sport Maxx Pretty much illegal tread. Tyre as wide as the rim. 
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| FordFairmont |
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Posts: 6113 Joined: 8th May 2007 |
phatba wrote: i think you have your sums wrong. your proposed rim has on the fronts 225/35r20 and rears of 275/35r20. yet you show a difference in front to rear circumference. both tyres have the same rolling diameter, all that changes is the width of the tyre. wtf man, your completely wrong to the op, 225mm tyre on a 9"-10" wide rim looks stupid and may even be dangerous. Im wondering do those front wheels even fit properly with the correct sized tyre on there like a 245? |
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| FordAUte |
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Yeah I thought it looked dumb... That's how I bought them though. I didn't put those tyres on...
Thinking of selling the tyres when I take them off to do repairs on the rim. Then putting decent width tyres on. The fronts are narrower then my au xr wheels :/
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| FordAUte |
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And yeah need to seriously investigate some guard rolling...
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| TimmyA |
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I was more curious about if your sure your 16" tire size is right? I had 225's on my 15's. Seemed a bit skinny. And I second the stretched tire look being gay.
Cheers, Tim
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| FordAUte |
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215/60R16 99V Pirelli P7's all round. Yeah they are narrow :/
Well the guy I got them off had a v8 VL and a jdm s13 (I think), the Silvia looked like a full on drift pig. He took these rims off the BA and replaced them with stock 16 skyline rims lol
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| TimmyA |
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Ahh...
So have you gps'd these wheels at 100km/hr to see if they're over/under? Maybe they're 5km/hr under std? What's the tire placard say it was fitted with? Cheers, Tim
_________________ 93 Red ED 5spd Manual Build Thread |
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