This is why I'm suspicious of R31 struts on 1600's. You can use FWD offset rims (an Adelaide Datsun workshop promotes this combo heavily) but they don't say how this affects the handling when you are making such a big change to the scrub radius. I assume you get toe in under braking and toe out on acceleration.. what are the consequences of this - wear on bushes, very high loads on the steering arms...?
Tom ----- Original Message ----- From: "E Smith" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, February 02, 2003 8:34 PM Subject: RE: Wheels - Chris S > The worst situation occurs when larger diameter wheel is used with increased > backspacing (eg late negative offset strut skyline rims) on early struts. > This changes the effective pivot point of the wheel (where a line through > the strut body intersects the road surface). The pivot point should be in > the centre of the tyre in most early suspension sytems. Later system like > skyline changed the point using offset ball joints). > The offset from the tyre centre line to the interection point is called the > scrub radius. A variety of handling problems (changes to toe in on turns and > straight line stability among them) arise from changes to scrub radius. > > Cheers, > Feral Errol > <http://www.datrats.com.au/> > > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]On Behalf Of Terry Rudd > Sent: Saturday, February 01, 2003 3:05 PM > To: [EMAIL PROTECTED] > Subject: RE: Wheels - Chris S > > > Chris, > > I'm not too sure what you're saying in the first sentence but I'll try to > clarify (or confuse the hell out of everyone) a few things about using big > wheels on a street 1600. The offset has only an indirect relationship as to > the vertical placement of two different width wheels. It's the backspace > that changes the vertical position i.e. where the wheel sits inside the > wheel well. What is unusual in your case is that you are intending to use a > tyre section width which happens to be the same in both cases (and using > Andrew data which I can't fault) the 16" tyre will sit 12mm closer to the > strut (at the top of the tread) than your 13" tyres. The difference in the > offsets is not that relevant other than to determine the different > backspaces. > > Where you may have a problem is in the horizontal plane depending on the > suspension heights (specially in the rear on a 1600), as a 205/60x13 tyre > has a loaded overall diameter of 23.0" and a 205/45x16 has 24.7" - this > means the top of the 16" tyre sits higher inside the wheel well, it will > lengthen the overall gearing significantly and also creates a legality > problem (assuming street use car) which I'll explain (next Para). A stock > L18 would notice the gearing difference, a turbo wouldn't all that much. > > The other small problem with using a 16" wheel on a 1600 is the brakes which > Errol alluded to and this is why the RTA will not pass a wheel/tyre > combination which is more than +15mm over standard (23.2" on a 1600) without > an engineers report which to obtain you would need a serious brake upgrade > and this has nothing to do with power etc, a stock L16 would have the same > requirement. Then there is the max increase for track (+25mm) implications > to consider as well. The RTA (NSW) requirements are here: > http://www.rta.nsw.gov.au/registration/downloads/vsi09.pdf > > > regards > Terry (fitting larger than 15" wheels on a 1600 can be done but it is a real > hassle) > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]On Behalf Of Chris king > Sent: Saturday, 1 February 2003 6:46 PM > To: [EMAIL PROTECTED] > Subject: Re: Wheels - Chris S > > > Andrew, > > Sure the backspacing will change with a change in wheel width but the offset > will not. > > For example i currently have 205's on my 13x6's with a 23mm offset, if i get > 205's on my 16x7's with the same 23mm offset sure the wheel will move closer > to the strut and the guard but the tyre will not move at all ! the wheel > will simply move half and inch inwards and outwards > > so by changing the offset from 23 to 18 i will be just moving the whole > wheel/tyre assembly out 5mm. > > sorry really hard to explain, please shoot me down if im wrong anyone > > Chris King > > ----- Original Message ----- > From: "GREENBURY, Andrew Robert" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Saturday, February 01, 2003 5:49 PM > Subject: Re: Wheels - Chris S > > > > Gday Chris, > > > > What 16*7s are you looking to buy? > > > > Ive been trying to work this sort of stuff recently myself. Because offset > > is from the wheel centreline to the mounting surface, it changes with > > wheel width, so technically you wont just be moving the wheel out by 5mm. > > > > * Your current 13x6s with 23mm offset, have 7in total width=178mm. > > * mounting surface to inside of wheel rim (backspace) = 178/2+23 = 112mm > > * mounting surface to outer rim = 178-112 = 66mm > > > > * The new 16*7s with 18mm offset ahve 8in total width = 203mm > > * mounting surface to inside of wheel rim (backspace) = 203/2+18 = 120mm > > * mounting surface to outer rim = 203-120 = 84mm > > > > ie the outer surface of the new rims will actually be 84-66=18mm closer to > > the guards than your current rims, not just the difference in offsets. If > > you've got >18mm clearance from your current rims to guards (and >8mm to > > your struts etc) then they could fit. But the tyres will require further > > clearance. > > > > This week I tried a 15x6 rim with 6mm offset on my car - this has a > > backspace of 95mm, and mounting surface to outer rim distance of 83mm ie > > pretty much the same as your 16s. Unfortunately, with a 195 50 15 tyre > > they looked like being inline with the guards, so it was questionable > > whether they'd fit at all after the car had been lowered (I should have > > sat on the front to check but I didnt think :( However, I dont > > have rolled guards and 240K struts which stick the wheels out 8mm closer > > to the guards than standard. Same wheel/tyre on the rear had a bit more > > clearance. I ordered some 15x6in with 20mm offset to give an extra 14mm > > clearance to the guards. > > > > Let us know how you get on with the 16s - can you trial fit them to check? > > > > Andrew > > > > > > On Sat, 1 Feb 2003, Chris king wrote: > > > > > My wheels now are 13x6's with 205/60-13. So basically i am not > increasing > > > the tyre width just wheel size and i am moving the wheel out 5mm closer > to > > > the guards. > > > > > > --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
