SteveW Posted November 4, 2011 Share Posted November 4, 2011 From doing some research I have found that the OE Rays wheel size is : Front - 18 x 8.0" - ET30 Rear - 18 x 8.5" - ET33 I've been thinking about getting some 19's that fill the arches better and don't sit inboard of the body but want to preserve the virtual wheel centre on the front due to the virtual kingpin axis set up of the suspension. So I want to move the front wheels out 20mm but keep the centre of the wheel in its current position give or take a mm or two to maintain the virtual kingpin through the wheel centre. Therefore, in theory, if I maintained the same wheel width and went to an ET10 wheel this would move the wheel out by the 20mm needed. However, this would then move the wheel centre 20mm outboard of the virtual kingpin, likely to lead to dodgy handling. So to maintain the wheel centre position I'd need to add 40mm to the inboard edge or as close as you can get. In wheel sizes the front wheel would need to increase to a 9.5" wheel. The changed offset of ET10 moves the wheel outboard by 20mm and the wheel centre. By then adding 38.1mm (1.5") to the inboard edge moves the wheel centre back inboard by 19.05mm. This would then result in the virtual kingpin being maintained, more or less. However whether a 19 x 9.5 would fit on the front without rubbing I don't know, I would have to do some measurements. There is also an additional issue potentially. The wheel studs are only a certain length and by changing the offset I'm not sure if you would need longer wheel studs putting in your hubs - proper ball ache! The bolt hole recesses may be more recessed on the bigger offset wheels allowing the OE studs to fit. If OE studs don't fit then the same can be achieved by running an ET30 wheel with a 20mm hub-centric spacer and a 9.5" wide wheel. On the rear I think the normal spacer width is 25mm...so in this case an ET8 wheel would be needed to move the wheel out by 25mm. This isn't as big an issue on the back because you don't have a virtual kingpin axis to worry about so the wheel centre can be outboard. The only problem is the track width front and back is different, whether you would notice though I doubt. The ET8 wheel has moved the wheel edge out by 25mm you can simply increase the width by 25mm on the inboard edge to maintain a similar set up. Again an ET33 wheel could be used with a 25mm spacer to avoid the potential issue with stud length. Again I'm not sure if this would come into it because the bolt holes could well be machined deeper so the OE studs fit. Other options , provided there was clearance on the inboard edge, again I would need to measure, would be ET8 and 10 inch wide or 10.5 inch wide ET 33 with a 25mm spacer. So In summary Front A 9.5 inch wide wheel at ET10 would move the front wheel out by 20mm and maintain the virtual kingpin in the right position relative to the wheel OR a 9.5inch ET30 wheel wheel with a 20mm spacer. Rear Not quite as important so an ET8 wheel could be used with a 9.5" wheel to maintain a similar set up. Hope this all makes sense and if anyone disagrees or I've counted wrong I'm more than happy to take a kicking and change it lol. Quote Link to comment Share on other sites More sharing options...
BulletMagnet Posted November 4, 2011 Share Posted November 4, 2011 Kingpin? Quote Link to comment Share on other sites More sharing options...
Ian Posted November 4, 2011 Share Posted November 4, 2011 IMO you would get some rubbage especially as your lowered. Some people on here gett rubbing on ET12 wheels. The perfect offset for the Z is 15/18, that gives a flush look without causing rubbing issues. How much are you lowered by & what size tyres are you planning to run? I used to run a 19x9.5 (245/35) & 19 x 10.5 (275/35) Both ET22 with no rubbing and lowered quite a bit Once I changed the rears to a 285/35 though, it used to rub a lot Quote Link to comment Share on other sites More sharing options...
seamybaby Posted November 4, 2011 Share Posted November 4, 2011 I running 19x10s all round with at et20 offset......and its lowered 30mm.... 255/35/19 fronts and 275/35/19 rears no rubbing issues... Quote Link to comment Share on other sites More sharing options...
Ruddles Posted November 4, 2011 Share Posted November 4, 2011 Running (245/35)19x9.5/(275/35)19x10.5 et12, lowered 25mm. Arches rolled....flush! Quote Link to comment Share on other sites More sharing options...
SteveW Posted November 4, 2011 Author Share Posted November 4, 2011 Kingpin? The kingpin axis is basically the point which the wheel pivots around when steering. There are other things to consider, like inclination, offset and angle. Ideally you want the kingpin axis through the centre of the wheel (thus a offset of 0) or you can get odd handling. However to get the kingpin 0 offset you need a virtual kingpin axis. This is the point of the joint that lives just above the tyre on the front suspension. It enables the car to have a virtual kingpin axis thus the tyre pivots arounds its centre resulting in no scrub and the best 'feel'. Most new cars try and have a virtual kingpin axis and offset of 0, its a fairly recent development in production cars as in the past a 5 link set up was needed which I beleive Audi had a first bash at in the 80's. Quote Link to comment Share on other sites More sharing options...
ATTAK Z Posted November 4, 2011 Share Posted November 4, 2011 I found this interesting http://www.super7thheaven.co.uk/Glossary Quote Link to comment Share on other sites More sharing options...
Beau Posted November 4, 2011 Share Posted November 4, 2011 Im running 9.5 all round with an offset of +15, with 265 front and 285 rear. No Problem! Quote Link to comment Share on other sites More sharing options...
SteveW Posted November 5, 2011 Author Share Posted November 5, 2011 Thanks for the replies folks, I'm only lowered 15 and 17mm on Tein a tech so scrubbing hopefully won't be a worry. Interesting you had some scrubbing issues with less offset than I calculated would be ok. But then again I was basing that on narrow tyres, I.e 225 and 245 I was thinking of running 265/275 on the back and 245/255 on the front. I hadn't really given profiles much thought at this stage as was trying to work out which offsets were needed. Thanks Quote Link to comment Share on other sites More sharing options...
docwra Posted November 5, 2011 Share Posted November 5, 2011 Umm, spacers dont affect steering and offsets dont affect handling. Where have you got this from, Ive not heard it anywhere else, including racecar setups ....... If you really want to get down to the technicalities Id be looking at rollcentres and akkerman angle before whatever you are talking about (Im struggling to see any logic behind what you are saying actually) Im running effective 10J ET -42 on the front of my car and IMO it handles better than it did as standard. The steering arms, suspension struts, brakes and everything else is in the same place as if I was running 7J ET50. If you are claiming that the relative weight on each side of the mounting face makes some kind of difference, I can tell you it doesnt. If the car was that sensitive you would feel something shift when you put the brakes on, no? The fact that you seem to think you need longer wheel studs for wider wheels isnt helping TBH. Quote Link to comment Share on other sites More sharing options...
Ian Posted November 5, 2011 Share Posted November 5, 2011 IMO your over thinking this. What wheels are you thinking of? As all this research into king pins could all be ruined by you putting on a heavy ass set of wheel Quote Link to comment Share on other sites More sharing options...
SteveW Posted November 6, 2011 Author Share Posted November 6, 2011 Umm, spacers dont affect steering and offsets dont affect handling. Where have you got this from, Ive not heard it anywhere else, including racecar setups ....... If you really want to get down to the technicalities Id be looking at rollcentres and akkerman angle before whatever you are talking about (Im struggling to see any logic behind what you are saying actually) Im running effective 10J ET -42 on the front of my car and IMO it handles better than it did as standard. The steering arms, suspension struts, brakes and everything else is in the same place as if I was running 7J ET50. If you are claiming that the relative weight on each side of the mounting face makes some kind of difference, I can tell you it doesnt. If the car was that sensitive you would feel something shift when you put the brakes on, no? The fact that you seem to think you need longer wheel studs for wider wheels isnt helping TBH. Thanks but unfortunately the akermann angle on the zed isn't adjustable and running an incorrect offset or a set of spacers does affect the handling. By moving the wheels further outboard of the kingpin axis you introduce tyre scrub on both sides of the car because when you steer the wheel is no longer pivoting about its true centre. Additionally it can affect grip under braking as well as the self centreing characteristics. Taken from a website discussing vehicle handling-"The Kingpin Angle, along with the Castor, dictates the self-centring action of the steering and the affect the steering will have under braking. Fitting larger wheels can alter the Scrub Radius if the correct offset is not chosen which in turn can affect the handling." when I designed the 5 link suspension system on our Formula Student car at uni a few years back this was one of the key design criteria, to ensure the was 0 scrub radius and the kingpin axis was directly through the wheel centre to generate the best handling characteristics. Hi Ian, I probably am over thinking things, I am renowned for this amongst my mates lol. I've not decided on any particular wheels yet was just doing some out load thinking. Cheers Steve Quote Link to comment Share on other sites More sharing options...
docwra Posted November 6, 2011 Share Posted November 6, 2011 Fair play man, Im no engineering student Surely though, by the same logic if you are making you tyres wider you are increasing the tyre scrub over whats optimum? Any negative effect is countered by more grip anyway? EDIT: Aaaah, Ive got it, what you are saying is that the positions of the edges of the tyre relative to the mounting face of the wheel should stay the same as OE, got it. Wider wheels arent a problem as long as the extra weight/tyre is in the right place. I actually found when I ran my Zed with the standard wheels on the front with 20mm spacers the car was less surefooted, weirdly Ive not had the problem with my current wheels spaced 25mm, this might be why. Interestingly Ive not had the same issue on 200SX's or Skylines with spaced/different width front wheels though. Quote Link to comment Share on other sites More sharing options...
Neilp Posted November 6, 2011 Share Posted November 6, 2011 are you planning on racing this car? Quote Link to comment Share on other sites More sharing options...
SteveW Posted November 6, 2011 Author Share Posted November 6, 2011 Neil do you mind if I answer that with a Fair point......point taken Quote Link to comment Share on other sites More sharing options...
Neilp Posted November 6, 2011 Share Posted November 6, 2011 Neil do you mind if I answer that with a Fair point......point taken Quote Link to comment Share on other sites More sharing options...
SteveW Posted November 7, 2011 Author Share Posted November 7, 2011 Quote Link to comment Share on other sites More sharing options...
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