Mikelly Posted September 27, 2000 Share Posted September 27, 2000 ...Question, did you have to use shorter springs and mount your coil over perch higher than the tire to get the clearance to allow for wider wheel/ tire combos??? I'm thinking of purchasing the Ford Mustang Cobra R wheels, which are 17X9.5 with a 5.9 back spacing and I'm wondering how to mount my coilovers.... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Danno74Z Posted September 27, 2000 Share Posted September 27, 2000 Mike, I also am struggling with the same questions. I have the complete rear-end out of the car and took a couple of measurements this morning. I placed a straight edge on the wheel mounting flange and then measured across to the existing lower spring perch. This dimension is 5.125". I also measured the diameter of a 14" rim with a 195 tire on it and go 24.5". I ran out of time, but if my memory is correct the existing tire and rim places the tire (the bulge) centerline next to the existing lower perch. Tonight, I will mount my tire back on get an exact measurement of the distance between the spring and tire but I think its about ½ " or less. At work I took a peek at two cars in the parking lot and got a mix bag on spring locations. One Eagle Talon had the springs above the tires and an Accura were below the top of the rims. Both vehicles appeared to have plenty of room to upsize rims and/or tires. If I follow the directions from GC and place the lower spring perch where they suggest - 5.5" up from the base of the strut tube (rear). This should place the spring below the rim of the wheel and tire. All this needs to be verified. Danno74Z Quote Link to comment Share on other sites More sharing options...
Mikelly Posted September 27, 2000 Author Share Posted September 27, 2000 ZDr. of Roanoke advised that I mount the perch above the rim/ tire combo and to use a 7 inch spring so I could get the type of tire clearance a 17X9 inch wheel will need. Thats why I asked for opinions form those who have odne it, because what you found is exactly what I found... I'll have to get the parts in hand and go from there maybe... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 27, 2000 Share Posted September 27, 2000 Mike, I have Jim Biondo's old wheels, (WRD 3 piece): 17x9 on the rear and 17x8.5 up front. I also have the Arizona Z brakes on the car. The Wilwood hat used for the rear is 1/2" thick at the mounting flange, so take that into account for the backspacing numbers I'm giving next. Rear backspacing: 149 mm (5.87") Front backspacing (w/ 1/8" spacer): 142mm (5.59") I've sectioned 1.5" from the strut tubes, and used 240Z front cartridges in the rear, and Rabbit cartridges in the front. To get these wheels to (just barely!) fit I had to use a 8" spring so that the spring perch on the Carerra coilover was not touching the rim lip. Any lower (longer spring) and the spring would interfere with the tire and rim, any higher (shorter spring) and the rate goes through the roof, to keep from stacking the coils on bumps. As it was, I wouldn't try much less than a 260-275 lb/in spring, as any lower rate springs would probably coil stack on bumps. Please note that this was using the stock upper strut isolator and stock upper spring perch with muffler tubing welded to the center to center the spring. If you go to camber plates, things change. 7" springs? What rate were they talking about? I'd think that for the weight of the Z (600-ish pounds in the rear on each tire), you'd need a very stiff spring at 7" to keep from coil stacking. One thing you could do is use a longer spring and use camber plates, as this usually (depending on the camber plate and spring perch designs) lowers the car. There for, you could use the longer springs to raise it up, over the 8" springs and stock isolator/perch setup I used. I'm thinking about cutting down the stock isolator by 1/2" and using 9" springs. I haven't found a rate I like in the few 9" 2.5" springs I've found. ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@home.com">pparaska@home.com - Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 27, 2000 Share Posted September 27, 2000 I'm running 17x8, 15P offset. The fronts have narrower springs (ex-Honda), and I think a higher spring base (they're adjustable, for ride height). The rear is dead standard 260Z (280Z to you) struts. The only rubbing is on the rear, between the outer edge of the tyre and the inner guard. Let me know if you want more detail and I'll take whatever measurements you need. There's a coupla pics on my web page, if that helps. Quote Link to comment Share on other sites More sharing options...
Danno74Z Posted September 27, 2000 Share Posted September 27, 2000 Mark, A quick question on your rims. How much room do you have left (in the rear) between your tires and springs, and if you wanted, could you have fitted a 9" x 17" inch rim in the back using the 15P offset. Thanks - How about those Australian Swimmers! Kick some butt. Danno74Z [This message has been edited by Danno74Z (edited September 27, 2000).] [This message has been edited by Danno74Z (edited September 27, 2000).] Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted September 27, 2000 Share Posted September 27, 2000 quote: Originally posted by Mikelly: ...Question, did you have to use shorter springs and mount your coil over perch higher than the tire to get the clearance to allow for wider wheel/ tire combos??? I'm thinking of purchasing the Ford Mustang Cobra R wheels, which are 17X9.5 with a 5.9 back spacing and I'm wondering how to mount my coilovers.... Well not running 17's but principles are still the same. As pete says check out your geometry, I'd try to fit an 8" spring in their if you can but if not 7" is OK. Your choice, where do you want you wheel? flush with outer lip or tight to strut or possibly both just trying to fit it period with that size. My 280ZX will be different from yours but Pete makes some great points in that going to a custom top perch (if your strut tube top is same as mine I have a sperical bearing PN) will increase upper 'room' to fit a longer spring. With OE upper perch I needed to go to 7" springs to keep the lower perch above my tire. The bottom of my threaded tube is dead centre with my tread so I flush ground that washer that supports the threaded tube as flush as I could with plane of tire etc and got 1/8" or so clearance their with 245's on my 16x8's (custom spacers etc).[threaded tube is ~1/8" thick max and sits v. tight to tube so only decreases potential rim clearance by that 1/8, washer was 3/8's or so but no point leaving the xtra on! in a small spot I needed clearance anyhow] Tire won't flex up top so that's lots of clearance for me their. If you can fit 8" springs now then go ahead and set it up as such. Your adjustment won't be above the strut base so not as many q's as I think some create. I see it more as a spring length choice and not so much as where to put the 4" tube as their isn't that much variance in that choice. Not sure why you're so concerened about bottoming out a 7" or for that matter an 8" spring Pete? You'd need some additional 1500 lb load on that ONE corner with a 7"/300lb/in.(assume 2" static compression, shock takes some) spring which I see as v. extreme for a non-rally car. I haven't come close to bottoming mine out yet, will have to check rear rate, front's are 350. Shorter springs do have a more limited choice of rates in the more affordable springs. 8" seems to have all the choices one could need. Once I put in my upper plates I could likely go back to 8" springs but no real reason since 7's are working. I will order 8's though if I get a 'soft' set for winter driving. .02c CD clear as mud? Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted September 28, 2000 Share Posted September 28, 2000 Okay guys - I'm real confused now. Rear of my car is bone stock righ tnow. I intend to goto coil-overs from MikeFoto and these will likely be 8inch springs as I understand it. I'm going to be going to 5lugs and most likely 17inch wheels. Width I hadn't intended to go past 8inches becasue I didn't think a 9 would fit without flares. I'm looking at TSW wheels - the Trophy and a couple of others. I've not a clue as to how to modify the rear struts - I'd like to not section them. I understand that the coil-over sleeve slides over the tube and has a bottom bead welded to keep it from sliding all the way down. From the JTR book I understand that there are some spring clearance issues. What I'm not clear on is how to support the top of the spring and what measurements I need to take to keep the lower perch (?) from rubbing anywhere. Can someone who's got something liek this setup snap a pic? The JTR book has a decent one and they even highlighted it by putting some white carboard behind the assembly but I'm not sure how what we're discussing here differs from that. Can someone snap a pic of the upper perch too? Mike, I'm not sure exactly when my 5lug conversion and wheel swap will be done. However, if you're willing to assist me with it I can probably get my hands on an R wheel pretty easily. I can buy the coil-overs from Mike or GC whenever - I've nto already done it because I've got other fish to fry but I can move this up the list if I've got assitance avbailable. My original intent was to use my wheels on the Mustang as an interim test solution. These are 17X7 5lugs from a 94-95 GT. If you want a guinea pig to learn with and measure just let me know - I'm pretty confused right now and a bit intimidated by the whole thought of tearing my entire rear suspension out for a rebuildupgrade... Psst - we can make a tech article out of it too. Hope to have the hood in the paint shop Friday so I can work on that as well... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 28, 2000 Share Posted September 28, 2000 Danno, I'll check how the spring-side clearance is in the next coupla days and let you know. Remind me someone: is Positive offset towards the outside or inside of the car??? I can never remember this stuff. And yeah summer's getting close. Altho we had a killer snow season (didn't get there dammit), you can still ski ok now.... Ohhhh swimmers! Sorry just saw your edit.... Well yeah must admit it's got a slight national hysteria happening. But, you guys on the other side of the pond there would have to be pretty happy too.... Just hope Marion Jones did the cooking in that household Mark. [This message has been edited by zedskid (edited September 27, 2000).] Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 28, 2000 Share Posted September 28, 2000 Ross, I'll have to investigate the rear rate a bit more. Alot of this was from listening to Jim Biondo and Les who used to be at Carrera Shocks. They both felt that going to less that 275 on an 8" spring was asking for trouble on the rear of a Z. I just occurred to me that I need to find out what the wheel rate to spring rate is for the car, then I can make some calculations as to what would be a minimum rate and stroke for a n 8 inch spring. Time to pull the Puhn, and Carroll Smith books out... But eyeballing it, it looks like the wheel rate would be about 8 or 9/10 of the spring rate. I'll measure it. (lift the wheel with a jack a certain amount at the center of the tread, and measure the movement in the spring). BTW, what is a good multiplier to use for a road race car and a road car, as far as the static weight at the corner, and what the max load would be if you hit a dip, etc? Quote Link to comment Share on other sites More sharing options...
Guest scca Posted September 28, 2000 Share Posted September 28, 2000 i dont know where to begin. coilover rates are taken into account by the length. a hypercoil 300lb spring is 300lb whether 7,8-10 or XX inch. each length spring is made with a different wire dia and coil space. so a 8" 300 lb if that worked ok you would just order a 7" 300lb. (assuming they make that length) i dont think you would want to shorten struts with 17" wheels- said this before though... I believe that 8" rims can go beside a coilover spring NOT a stock spring. (i'm ONLY talking about UNFLARED cars so if you have flares none of this counts!) for 8.5" and wider you need to put the coilover above the tire for more clearance. i have seen 17x9" wheels on a unflared car with coilovers above the tire clearance was 1/4" to strut tube it has the outlaw brakes and all on it and no spacers- custom made rims.havent seen a pic of petes car but i wonder if shortening the fronts to rabbit inserts is a necessity or not? IMO i would rather have the longer tube with more insert and longer spring and camber plates . with a 300 lb spring i'd be suprised if you could get the suspension to move >3" on a big bump. - i'm using 200lb and its stiff for a street car IMO. ------------------ Mike http://www.fonebooth.com raceparts and brakeupgrades Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 28, 2000 Share Posted September 28, 2000 Mike, I understand that an XX rate spring is just as stiff in an 7" free length as it is in an 8", or another free length spring, but the issue I was getting at was that if the car weighs 600 lb per corner, and you use up some of the spring's stroke with holding up the weight of the car at stand still, you only have the remaining stroke of the spring left to absorb bumps or take weight transfer onto before you get to no stroke left and coil bind. That's why I was told that for an 8" (2.5" ID) spring in the rear, less than about 275 lb/in would not be stiff enough, and you'd end up coil binding on large dips, etc. I hope that's wrong. I have 300 lb/in in the rear and I'd bet it will be too stiff to my liking. I'll do your coilover test when it gets on the road and see if I can go a good bit lower on the rate. As for why you don't think a car with 17" wheels needs shortened struts, I don't understand. I thought this was the preferred method of lowering the car, as lowering springs take away bump travel. I want to keep the stock 240Z isolators, so that takes that method of lowering the car away for my purposes. I guess I don't understand what wheel diameter has to do with whether you would want to section the struts or not. My car is unflared, with 17x9s (149mm backspacing, 1/2" thick Wilwood rortor hats) and 245/45-17 Michelin Pilots. I have the coilover tube situated so that it's at the top of the 1.5" shortened 240Z rear strut, placing the very bottom of the tube next to the rim lip. There's only 1/8" of clearance between them. Jim Biondo had this exact setup on his unflared car and he said the wheel never touched the tube. The wheels are very stiff. The tire clearance to the spring perch is about 3/16". Close, but it won't touch either according to Jim. I guess I need to take some pics of this. I tried before but had a hard time getting anything decent. I'll give it another shot. I hope you are right about the 300 lb/in springs not being able to give even 3" of bump. Because they compress about 2" with the weight of the car, I'd guess, and that would only leave 2.75" left for bump travel. The 300 lb/in 8" free length springs I have only have a 4.75" stroke. Quote Link to comment Share on other sites More sharing options...
clint78z Posted September 28, 2000 Share Posted September 28, 2000 Well being a offraod guy as well I am fairly well aware how spring rate affects handling . I also have 5 position adjustable Rancho 9000 shocks in my stock pathfinder . A big heavy vehicle that has a fairly high Cg, alot lower than most SUV's . I play sports car in it, and practice smooth driving techniques as well . Our streets here a pretty poor with potholes and cracks . I tend to lean towards the softer springs, I am probably going to head towards an Eibach progressive wind . I am still debating wether or not to go with Koni adjustables or a 5 way Tokico's . If anybody has experience with these shocks I would like opinions . Intresting running a stock upper mount, this would probably elimate alot of noise and ride harshness . This might be an option I will look into . Can you do a coilover with progressive spring, I have never seen to many people use this combo. On a 240Z corner weight is about 600lbs that means at rest 200lb/in springs will be compressed 3", so if you have 7" springs that means you have 4" of travel left. That seems like a fair bit, that seems like a big bump to bottom this out . Mabey if you are airborne ?? One other thing to mention even if you have spring travel left, you might bottom out the shock something to check anyway . Want my suspendion to suck brains out in the corners, and not bang my teeth on the rougher roads . Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 28, 2000 Share Posted September 28, 2000 For a Carerra 8" free length 300 lb/in spring the stroke (how much it can be compressed from it's free length state) is 4.75". For a 200 lb/in 7" spring it's going to be only about 4" of stroke, so after using 3" of it to hold up the car, you only have 1" left for bump travel! Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted September 28, 2000 Share Posted September 28, 2000 quote: Originally posted by clint78z: Ross what does the spherical bearing setup look like, does it use any type of rubber mounting to isolate road roise . The raer springs should be stiffer than the fronts right? (edited September 28, 2000).] It's incorporated into my (uninstalled) caster camber plates centrepiece, no rubbers at all, bearing fits the strut 'piston-rod' allowing it to rotate with it's top being fixed to the tower (piston rod passes thru bearing, strut nut bears ontop, like a heim joint centrepiece). Not sure how much road noise coming thru their will be a factor with the spring rates I'm running and those being bantered about:-) Stiff is stiff at this point:-(O) max pucker factor As well you then need a roller bearing (torrington) below or above the spring so it can also rotate freely as strut is turned it way want to stay in it's position........on the bottom is best in case you ever get the spring unloaded it's still resting on this bearing so a lesser shockload is sent to it Forgot to mention one easy way to check out various susp. travels that I did. I made all my 'bumpstops' so they could be pulled down the piston rod (ie. not fixed at the top, fixed by friction but not centre retaining hat), reach b/t your spring coils and pull it down to the bottom of your strut and drive it hard, see how far up your strut it ends up, this will be your max. travel 99% of the time. I shortened the 'stops' that came with my Tokico's as they were some 2"+ in length which I did not want (progressive/taper mind you), cut them in 2/3 or so FWIW. Quote Link to comment Share on other sites More sharing options...
Guest needwaymorespeed Posted September 29, 2000 Share Posted September 29, 2000 Originally posted by pparaska:Mike, I understand that an XX rate spring is just as stiff in an 7" free length as it is in an 8", or another free length spring, but the issue I was getting at was that if the car weighs 600 lb per corner, and you use up some of the spring's stroke with holding up the weight of the car at stand still, you only have the remaining stroke of the spring left to absorb bumps or take weight transfer onto before you get to no stroke left and coil bind. That's why I was told that for an 8" (2.5" ID) spring in the rear, less than about 275 lb/in would not be stiff enough, and you'd end up coil binding on large dips, etc. I hope that's wrong. I have 300 lb/in in the rear and I'd bet it will be too stiff to my liking. I'll do your coilover test when it gets on the road and see if I can go a good bit lower on the rate. As for why you don't think a car with 17" wheels needs shortened struts, I don't understand. I thought this was the preferred method of lowering the car, as lowering springs take away bump travel. I want to keep the stock 240Z isolators, so that takes that method of lowering the car away for my purposes. I guess I don't understand what wheel diameter has to do with whether you would want to section the struts or not. I understand wanting to section the struts so that you can keep youre suspension travel but what if you icreased the o.d of the tire diameter to compensate for the lowering of the car- regular z car tire is od of 24.5??? install a tire with od of 25.5 to 26 then you would still have youre clearance right??? I wish there was a way to run the stock isolators and camber plates or run camber plates isolated with rubber!! Dont want to run with out some rubber there the ride is miserable that way!! Curtis Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 29, 2000 Share Posted September 29, 2000 Let me play devils advocate for a moment.. I know the 17" rims look cool as all get out, but are'nt they notoriously harsh riding and super susceptable to road hazard/debre/curbs/speed bumps (just a thought of accidently running over a belted truck tire carcass makes pictures of dollar signs just fly out of my wallet)? And the short sidewall would also appear to be easy to damage a rim hitting a curb or severe bump too quickly? Granted I don't look for stuff to run over, but in Ca. where I live the number of heavy trucks leaves a good deal of debre on the road as they lose tires etc. Ever have to dodge a overstuffed wing chair on a interstate? This statement was just meant to get opinions, and is not in anyway a commentary on whats right or wrong on anyones car (I truly believe there is no such thing as right or wrong when it comes to garage engineering, there are just some things perhaps more successful than others). Lone "Life is a sport, you either play it or watch it!" Quote Link to comment Share on other sites More sharing options...
clint78z Posted September 29, 2000 Share Posted September 29, 2000 Yes you are right pparaska, I forgot to take into account wire size 7" of coil not 7" travel . My bad !! Ross what does the spherical bearing setup look like, does it use any type of rubber mounting to isolate road roise . The raer springs should be stiffer than the fronts right? I wonder how Walker Morgan did his 17X9's he did not mention coilovers to me [This message has been edited by clint78z (edited September 28, 2000).] Quote Link to comment Share on other sites More sharing options...
Mikelly Posted September 29, 2000 Author Share Posted September 29, 2000 Let me clarify why I'm gonna go with 17s... I've been looking into tire selection and in a 15 inch wheel, if you plan to go wider than a 225 inch in any Zrated tire... well goodluck finding a choice... Yokohamo makes a wide selection of 15s in their AVS intermediate, but that is about it. With my car flared, I can stuff way more tire under the back of the car, so I'd like to get a 275 or wider under the rear. 17s are the way I'm going because even 16s are limited. Believe me, I like my wheels, and have no need to follow fads or trends.. however, in searching for slicks (road race), it seems the trend there is to go 17s as well if you want as choice in sizes.. Back int he 90s when I weas really into the track scene 15s were abundant, but not today. I wish that were still the case! So I'm going with 17s and I'd like to go with 17X9 or 17X9.5 and I might go with the Cobra R wheel, and I might get another set of centerlines, not made up my mind yet, although I really like the Centerline AZTEC, maybe in a powder coated color.. leaving the outer rim polished and the spokes white or black... Who knows. If I do that, then I don't have to worry about any of this since Centerline will make any backsopacing I want and in any bolt pattern AND their wheels are 19# in a 17X 9.5 which is nicer on the brakes and acceleration department! Decissions decissions... Keep the comments coming.. very informative thread! Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Mikelly Posted September 29, 2000 Author Share Posted September 29, 2000 BLKMGK, Order your coilovers and lets get this done... I really want to see how it goes. I'd run an 8 inch spring and see what we can get under that puppy! I'm gonna do a little more research, but for spring size availability it seems that 8inch springs give more of an option! Just say when! Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
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