vega Posted April 13, 2011 Share Posted April 13, 2011 First things first for some reason I can't post in the suspension tech area? Its been a while since I have been on here so, not sure what is up. OK, we all know the limited rims and offsets that are available for the s30 chassis. So I have done a bit of research on the topic for a couple months (I also work for bridgestone/firestone so I have experience in this) it turns out that the awd 997 Porsche came factory with wheel adapters on the rear to 1 space them, and 2 for availability. Porsche thus far as been doing this for years, (bolt down to the hub with longer, basically, arp studs for the lug studs) and has had no problem thus far that has been reported aside from misuse which can be said about anything. That being said, from what I have experienced with the Porsche vehicles that I have worked on, they are designed very well, and I would go as far as saying that I actually trust their "engineers". Which as a full time mechanic, generally I am not a friend of automotive engineers... Anyhow I don't see a problem with using wheel adapters that bolt down to the hubs. Now spacers are a no, no. Albeit a wheel adapter CAN be used to space the wheels, which it basically does anyway. Now my question and my point is this. How thick do I want these adapters? I can get longer arp wheel studs so that is not an issue. I want to run 17x8.5 wheels to 17x9. (yes i know fender clearance) I just want the wheels to accommodate larger tires such as say at least a 255 on the rear and 235 or 245 on the front. Any help/info/ideas would be much appreciated in advance. vega- (btw 1978 280z) Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted April 13, 2011 Share Posted April 13, 2011 You choose adapter thickness based on the offset of the wheel you choose. Quote Link to comment Share on other sites More sharing options...
deja Posted April 13, 2011 Share Posted April 13, 2011 Evan Purple240zt is correct. Offet is usually given in mm, just convert it to inches if you need to. http://www.rimsntires.com/specs.jspcan be used to see what thickess you need. Just type in you data with offset and it will tell what the the offset is in inches and what the backspace is. Quote Link to comment Share on other sites More sharing options...
vega Posted April 14, 2011 Author Share Posted April 14, 2011 well say i am using plus 24 offset gt500 rims. Quote Link to comment Share on other sites More sharing options...
Supra510 Posted April 14, 2011 Share Posted April 14, 2011 Figure out the max backspacing using the stock hubs. I'm sure it's on the site somewhere. I have 280zx struts on my 510 and with 18's the backspacing is 4.5 inches. Plug your wheel specs into this http://www.autolounge.net/calculators/tirespacing.html That should tell you the backspacing for your wheels. Use an adapter to make up the difference. I believe adapters run 1 inch and up. I've been using them for years with no issues. Quote Link to comment Share on other sites More sharing options...
vega Posted April 14, 2011 Author Share Posted April 14, 2011 Well the factory z is zero offset and I want to be able to use a 24 without smacking the suspension. Honestly it feels like you guys are being vague, I know your trying to help me, but I just don't get it or something, I feel like there is something I am missing. The suspension and wheel stuff has always got me a bit. Give me sensors, electronics, brakes, engine overhaul, I get it. Suspension (ie camber caster toe and this wheel stuff) has always not quite clicked for me. Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted April 14, 2011 Share Posted April 14, 2011 Honestly it feels like you guys are being vague, I know your trying to help me, but I just don't get it or something, I feel like there is something I am missing. That's because every tire and wheel combination has different clearance requirements. Even the same tire size can vary from manufacturer. And when you talk about those tire widths there is very little clearance left in the wells. You need to pick out the spectific tires and wheels you want and then do some very carefull measurements on your own car with the suspension parts and ride height you run, and consider tire and bushing flex. Tire to body clearance is way too complicated on these old modified cars to just give pat answers. Quote Link to comment Share on other sites More sharing options...
deja Posted April 14, 2011 Share Posted April 14, 2011 Well the factory z is zero offset and I want to be able to use a 24 without smacking the suspension. Honestly it feels like you guys are being vague, I know your trying to help me, but I just don't get it or something, I feel like there is something I am missing. The suspension and wheel stuff has always got me a bit. Give me sensors, electronics, brakes, engine overhaul, I get it. Suspension (ie camber caster toe and this wheel stuff) has always not quite clicked for me. It can be confusing and like others said there is no positive answer. You need to use one of those calculators we mentioned to see if you're in the ball park. From what I see you are not. 24 isn't going to cut it with either rim, too much backspace. Our cars require a max of 4.5" or you're going to hit the suspension. Your 9" rim will have a backspace of 6" and the 8.5" rim will be 5.7". You can add spacers or adapters to get you to 4.5" (1.5 for the 9" and 1.2" for the 8.5"). But then you are pushing the wheel out past 0 off set. Quote Link to comment Share on other sites More sharing options...
Supra510 Posted April 14, 2011 Share Posted April 14, 2011 ^^^^^ Is everything you need to know. Deja mentions pushing the wheel past 0 offset which is true. While it does affect scrub radius, it doesn't affect physically fitting the wheel on the car. As he noted, if you're running a 9 inch wide wheel (which btw is 10 inches wide if you measure edge to edge) with a +24 offset the backspacing is 6 inches. Since there is only 4.5 inches of available backspacing on the car, your wheel will smack the strut. So, you buy the 1.5 inch adapter and it spaces the wheel out away from the strut the appropriate amount. Here's another calculator that's more visual http://www.rimsntires.com/specs.jsp Quote Link to comment Share on other sites More sharing options...
deja Posted April 14, 2011 Share Posted April 14, 2011 I am certainly NOT an mechanical engineer but it seems to me that pushing the wheel too far from 0 offset would put strain on the bearings and axels. Of course I could be totally wrong on that. Then there is that "too much" and I have no idea what that would be. Quote Link to comment Share on other sites More sharing options...
vega Posted April 15, 2011 Author Share Posted April 15, 2011 [quote name=Supra510' t imestamp='1302809366' post='933387] ^^^^^ Is everything you need to know. Deja mentions pushing the wheel past 0 offset which is true. While it does affect scrub radius, it doesn't affect physically fitting the wheel on the car. As he noted, if you're running a 9 inch wide wheel (which btw is 10 inches wide if you measure edge to edge) with a +24 offset the backspacing is 6 inches. Since there is only 4.5 inches of available backspacing on the car, your wheel will smack the strut. So, you buy the 1.5 inch adapter and it spaces the wheel out away from the strut the appropriate amount. Here's another calculator that's more visual http://www.rimsntires.com/specs.jsp 1 what is scrub radius? Thing 2 so all I need is the 1.5 inch adaptor for this to work? (aside from the fact that I will either need to roll fenders or cut- I am still doing body work so I want to do this now to know where I need to do what) Quote Link to comment Share on other sites More sharing options...
clutchdust Posted April 15, 2011 Share Posted April 15, 2011 I am certainly NOT an mechanical engineer but it seems to me that pushing the wheel too far from 0 offset would put strain on the bearings and axels. Of course I could be totally wrong on that. Then there is that "too much" and I have no idea what that would be. To excess, sure. The bearing concern would be if you took away offset by sticking the same width tires farther out on the axle, creating a lever. But my experience with wheel adaptors (which I've been running on my Vette for over 10 years) is that as long as the inside track remains the same relative to OEM, you will have no discernible bearing issues. You will likely want to do this anyway as the point of adaptors is to ensure wider tires/wheels don't contact inner suspension/chassis points. Quote Link to comment Share on other sites More sharing options...
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