BrianGT Posted February 17, 2012 Report Share Posted February 17, 2012 Real life example.....my TA22 with 13 inch wheels when doing a true 70mph my speedo actually read 77mph....because my speedo was wildly optomistic. Changing to 14 inch wheels when doing a true 70mph my speedo actually reads 70mph.... Link to comment Share on other sites More sharing options...
Gray Posted February 18, 2012 Report Share Posted February 18, 2012 This website is great as you can enter offset and wheel width to compare tyre stretch http://www.willtheyfit.com/ Link to comment Share on other sites More sharing options...
lankyalien Posted February 19, 2012 Report Share Posted February 19, 2012 (edited) bigb1970, you're correct, period Edited February 19, 2012 by lankyalien Link to comment Share on other sites More sharing options...
lankyalien Posted February 19, 2012 Report Share Posted February 19, 2012 As a general rule of thumb, just to through a bit of uncertainty in though, standard fit tyres tend to under read on the speedo to actual speed, usually to the tune of 10%. I have come across some accurate vehicles but not many. Also bear in mind that as a tyre wears your actual speed will reduce compared to engine revs due to loosing about 12mm diameter off your tyre from new to illegal (new tyre generally have 8mm tread, illegal 1.6 so say 2mm to be safe). If you drive with a sat nav or safety camera system, compare the indicated speed on this with your speedo.Whatever the percentage difference is between these, if the sat nav read higher by say 10%, you can choose a tyre with a 10% larger rolling circumference (3.142*diameter) before risking your licence. Just make sure you measure your tread depth first though and factor this into your calculations. Link to comment Share on other sites More sharing options...
Black Knight Posted February 19, 2012 Author Report Share Posted February 19, 2012 Well this question has generated quite a debate hasn’t it Thank you to everyone for all your advice. Definitely going to go 205/50 R16. Tyre calculators report that that will be 0.37% bigger than current meaning that at 70mph actual speed will be 70.26mph. Seeing as currently when 70 on clock sat nav shows 68 that should be fine Lankyalien. As for considering current tread depth that’s just too mind boggling for me to compute! All I can say is that at present all tyres have good levels of tread. Link to comment Share on other sites More sharing options...
johndps Posted February 20, 2012 Report Share Posted February 20, 2012 I thought gen 5 came with 14" wheels, gen 6 with 15" ? Link to comment Share on other sites More sharing options...
rpsmith79 Posted February 20, 2012 Report Share Posted February 20, 2012 I thought gen 5 came with 14" wheels, gen 6 with 15" ? Prefacelift 5 came with 14"s, facelift came with 15"s Gen 5 Pre-Facelift GT - 14 x 6, ET 45mm - 205/60R14 Facelift GT - 15 x 6, ET 45mm - 205/55R15 GT4 Carlos Sainz - 15 x 6.5, ET 39mm - 215/50R15 Gen6 ST - 14 x 6, ET 45mm - 195/65R14 LTD - 14 x 6, ET 45mm - 195/65R14 SR - 16 x 7, ET 45mm - 205/50VR16 GT - 15 x 7, ET 45mm - 205/55VR15 Cabriolet - 15 x 7, ET 45mm - 205/55VR15 GT-Four - 16 x 7.5, ET 45mm - 215/50WR16 Gen 7 16" 5 Spokes - 16 x 6.5, ET 39mm - 205/50R16 17" Alloys, 17 x 7, ET 38mm 17" Tech 5's 17 x 7, ET 38mm Link to comment Share on other sites More sharing options...
markjbutler Posted February 20, 2012 Report Share Posted February 20, 2012 this is amusing... everyone is effectively saying the same things and still arguing! Link to comment Share on other sites More sharing options...
Black Knight Posted February 21, 2012 Author Report Share Posted February 21, 2012 Gen6 ST - 14 x 6, ET 45mm - 195/65R14 Gen 7 16" 5 Spokes - 16 x 6.5, ET 39mm - 205/50R16 Now I dont really understand this ET stuff, but I do notice that its a fair bit different between the wheels. Does this mean I'm going to need spacers or anything to fit the G7 wheels to my 6? Link to comment Share on other sites More sharing options...
GreyRacer Posted February 21, 2012 Report Share Posted February 21, 2012 The smaller the ET number the further out from the hub the wheel will sit. Difference between ET 39 and ET 45 is 6 mm. So the ET 39 wheel will sit 6mm further out into the arch than the ET 45. The & wheel is 1/2 wider and the tyres are 10 mm wider. I think the seven wheels/tyres will fill out your 6 arches nicely without spacers. Link to comment Share on other sites More sharing options...
Black Knight Posted February 21, 2012 Author Report Share Posted February 21, 2012 (edited) The smaller the ET number the further out from the hub the wheel will sit. Difference between ET 39 and ET 45 is 6 mm. So the ET 39 wheel will sit 6mm further out into the arch than the ET 45. The & wheel is 1/2 wider and the tyres are 10 mm wider. I think the seven wheels/tyres will fill out your 6 arches nicely without spacers. Ahh cool, that makes sense now then, cheers. Of course the down side to that then is going to be even more mud fling up the sides of the car :rolleyes: Edited February 21, 2012 by Black Knight Link to comment Share on other sites More sharing options...
Monkey Boy 1 Posted February 22, 2012 Report Share Posted February 22, 2012 I originally thought this thread was about the US market with their "tires" rather than our "Tyres", (sorry Ian, being a bit pedantic here about spelling ) but after reading all the stuff about Axle speeds, revolutions of the wheel over X amount of millimeters, GPS measurements and speedo accuracy my brain has just exploded. I need a coffee or something a little stronger Link to comment Share on other sites More sharing options...
rpsmith79 Posted February 22, 2012 Report Share Posted February 22, 2012 Best bet is to have a read of this http://www.celica-cl...ents-and-terms/ Then have a look at the links about the Offset Calculators, these will tell you exactly what will happen when you fit different width wheels with different offsets Link to comment Share on other sites More sharing options...
Black Knight Posted February 22, 2012 Author Report Share Posted February 22, 2012 Best bet is to have a read of this http://www.celica-cl...ents-and-terms/ I did, several times, and got more confused each time!?! I originally thought this thread was about the US market with their "tires" rather than our "Tyres", (sorry Ian, being a bit pedantic here about spelling ) Sorry Simon, this mistake has been pointed out to me already and I can only hang my head in shame. Oh and its Iain…not Ian Link to comment Share on other sites More sharing options...
GTsillycar Posted February 22, 2012 Report Share Posted February 22, 2012 Enough with the jibber jabber, show us the wheels Link to comment Share on other sites More sharing options...
Biggy Posted February 22, 2012 Report Share Posted February 22, 2012 Enough with the jibber jabber, show us the wheels I think he has given up Link to comment Share on other sites More sharing options...
Black Knight Posted February 22, 2012 Author Report Share Posted February 22, 2012 Now now boys, calm down. Good things come to those who wait Besides, there not even finished yet Link to comment Share on other sites More sharing options...
Kev 16v Posted February 23, 2012 Report Share Posted February 23, 2012 Now now boys, calm down. Good things come to those who wait Besides, they're not even finished yet Link to comment Share on other sites More sharing options...
GTsillycar Posted February 23, 2012 Report Share Posted February 23, 2012 Link to comment Share on other sites More sharing options...
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