XR4Ti Archived Tech Articles
Post Date: Thu, 21 Oct 1999 Subject: 225/50 15 Front tires on an XR? List: IMON List Members, I dug in the archives. Really! I am positive that I can fit the 225/50 15's to the rear of my XR. Been done. However, the only mention in the archives I can find of 225 width front tires is with 16" wheels only. Boooo. I'd like to run the 225/50's on my DSP autocrosser, but am concerned with the clearance issue on the strut tube and the spring seat on the strut (as opposed to concerns about rubbing the fender, which is legal to be trimmed, reshaped as needed in my class). I have looked over Tim Brewster's 17" wheel pictures on my Picture Pages, and it does appear as though my major concern is with clearance to the spring seat as I go wider. Some data: 195/60 15 height - 24.21 inches 225/50 15 height - 23.86 inches With this math, it would seem I would have more room under the spring perch for clearance (vertically), but since I am going with a wider wheel (probably 15x7 Wolfrace) and tire, then I am going to be closer (horizontally). I just looked at my beater XR with 195/60 14's (height of 23.21 inches) and it looked as though it had less than an inch of vertical clearance (only need 1/2 over the stock 15 setup). Main problem, no race tire that I know of comes in a 215 width in 15 inch size. So I either chance it with the 225 (the rock) or go easy with the 205 (the hard place). Any opinions on what I have stated? Any experiences? I guess it's time to get on the phone with Bill Cobb. --------------- Post Date: Sun, 24 Oct 1999 Subject: Re: 225/50 15 Front tires on an XR? List: IMON List Members, I received quite a great response to my request for information on the 225/50 15 tires (front specifically). Most information was sent directly to me, so I'm sending a summary post and then I'll follow up with my recent developments and decisions. A list member who shall remain unidentified due to the nature of his statement suggested: > ... I haven't looked at it closely > but... why couldn't you grind off > the spring perch just enough to > clear the wheel/tire? I find this rather interesting. I just looked over some new Boge struts I have in the garage for a better idea of the situation. The spring seats toward the center of the spring perch on the strut. The end of the spring coil also fits closest to the point where I'd be grinding the perch for clearance. After the coil is in place, it looks as though there is at least 3/8ths of an inch of perch before the edge. Structural issues aside, this makes grinding the perch for clearance very possible. I don't think I would do this without reinforcing the area around the removed metal, however. Also I have to take the rules into consideration, and since it is being driven to events, I'll have to switch to race tires at the track, meaning, I'll be exposed for a brief period. Terry wrote: > If you don't care about the fender clearance, > you can move the wheel outboard by picking > a different offset, or with a spacer. Either way, > you will move the center of the tire contact > patch outboard. ... I'd say go for the 225's if > you can and offset the wheels. In the Street Prepared class of SOLO II, you are allowed to modify and or flare the fender (and bumper) for tire clearance. This means if I do rub the spring perch, I can put a small spacer between the wheel and hub to gain more clearance. Then if need be, I can trim, flare, or hammer the fender out of the way as needed. Sounds like I'd have to kiss my plastic wheel arches bye-bye. Fritz wrote: > Im running 225 50 15s front and rear on > my XR using a Saab 9000 wheel. Rears > are no trouble and fronts will rub as > suspension goes to full bump. The > rubbing is at the peak of the fender lip. Most people who replied about rubbing (with the 225/50's) stated that it was at the peak of the fender lip. I quoted Fritz because of the increased interest level of his post with the info about his SAAB 9000 wheels. The point of rubbing also brings up some interest because of a post a list member made. I think it was Jason Smith who said that the later model (87.5, I think he quoted) XR has fender lips that are somewhat flared vs. the earlier "slab-sided" models. I've got a cladding-less 85 XR in front of the house now and can confirm that the early cars had no flared lip (insert Elvis joke here), but the later cars that we own have their plastic flares on, so no confirmation. ---added text--- Update: Thurs, 30 Nov, 2000. A direct comparison between an 85 XR with no plastic arches and an 87 XR with no plastic arches indicates that the fender lips are flared identically. ---end added text--- I believe where it rubs is a function of offset. Davis wrote: > Did you dig into the Merkur Encyclopedia? > http://www.merkurgarage.com/encyclopedia/tirenwheelsizing.html I dug. Don't know if the URL is still the same now that Allan has switched to a frames format, but I was able to find the info easily without cut-n-pasting the URL Davis sent. I'd recommend visiting the Encyclopedia. You'll learn a bunch about a bunch. (Encyclopedia now hosted at http://www.company23.com/aslocum) David Brumbeloe also posted a bunch of good info right to the list that I won't repeat here. As with all things, some of the info is debateable as he states that 225/50 15's won't go up front (without flares). Some have done it, but the range of variables is pretty wide here for debate without a lot of complexity. Either way, David seems to have done a lot of testing (wonder how much I could get done if the Tire Rack let me have the run of their facility for a weekend). Well, here is what I'll very likely be doing. I'll be running 15x7 Wolfrace Thrust wheels with 225/50 15 BFG R1's (not sure if they are Comp T/A or g-Force T/A yet) all the way around. The Thrusts have a 38 mm offset meaning a bit more perch clearance. I guess this is just a wait-and-see thing now. Many thanks to all who replied on and off-list whether I recognized you or not. Your input and time is much appreciated and when I start dominating DSP in my region, it'll all be because of you! ---------- Post Date: Thu, 31 Aug 2000 Subject: Re: tire sizes List: email@example.com Hello all, I'll be working on a write up soon for my XR4Ti Tech and Content Page on fitting 225/50 15's to an XR, front and rear, so I'll try my hand at this question. > I was wondering if anyone can let me know > if 215/50 15 will work on all 4 corners of the > XR4Ti. As the information Godfrey shared with us, originally posted by Neil Swanson, states, it's more an issue of tire offset than of width (ride height too). A bad combination of offset and tire size will lead to rub. First, you aren't going to be able to fit 215's on stock wheels (okay, so maybe you can, but I wouldn't try it). So you are probably running an aftermarket wheel. If the offset is in the 35mm-37mm range, you'll probably be just fine with 215/50's. Clearance on the spring perch isn't an issue (and the distance between the tire and the perch is a constant at all times, barring factors like tire compliance and out of round). With good offset (35-37mm or so), you'll not run into the spring perch at all. The issue will be with the front portion of the wheel opening. Just to catch you up, my springs are BAT's 40 mm lowering springs (about as low as Rapido's springs) and I am running Powerflex polyurethane bushings everywhere. My 225/50 15's are BFG Comp T/A R1's (autocross tires). The only time I rub is under heavy bump/cornering loads with the tire turned to about 1/4 to 1/2 turn. This rubbing as been permanently remedied by mild reshaping of the fender with my hands and a mallet. Also, this is with the plastic arch removed. It's been reshaped enough, and the lip has been rolled up so the arch doesn't just screw on any more. I'll work that out soon enough. The 215/50 is 10mm more narrow (about 4/10ths of an inch) in section width (the widest part of the tire) and it's 4/10ths of an inch smaller in overall diameter (view manufacturers specs for actual OD and section width). This means you be that much farther away from the fender lip. A horribly rough estimation puts the edge of your tire (215/50), closest to the lip, about 14mm farther away from the lip than mine (225/50). I think 215/50's will bolt right on with a wheel of good offset. I don't think there will be an issue at all in the rear tires. I got a tiny rub (the kind that I have since termed "a polishing") on the left side rear under hard right corners. I also get a polishing from the back edge of the tire under full lock on the right side front tire. ---------- Post Date: Wed Nov 29, 2000 Subject: XR4Ti - 225/50 15 tires List: firstname.lastname@example.org and email@example.com Hello all, I ran 225/50 15 BFG Comp T/A R1's on all corners of my XR this autocross season. I've been planning on posting the information on how I got these tires to fit on the car. Well, I started the write up for my "XR4Ti Racing Preparation" web page. It got good enough that I decided to copy the information into an email to this list. After all, it will be a little while before the Street Prepared page is complete, so I figured I'd pass on this information as soon as possible. Here is the info: ---------- I am currently running 15x7 Wolfrace Thrust wheels with 35mm offset. This is the correct setup for this wheel width. No wheel contact issues anywhere. One of the main points of concern with aftermarket wheels on the XR is contact between the wheel weights (typically the stick-on type) and the tie rod. You don't want to lose a weight. I've had no such issues with the Thrusts. The wheels were provided by Bill Cobb of Racing Wheel Services. For my first full season in autocross I chose to run 225/50 15 BFG Comp T/A R1's on all four corners. I got an incredible deal on the tires. I'll very likely run Kumho V700's next. It's my understanding that they have a grippier compound and wear longer as well. Most people don't try to fit 225's up front. As the front end of the XR seems to be the traction limited end (at least in autocross), I wanted to keep even tire sizes on all four corners. Fitting the 225's up front wasn't a straight bolt-up arrangement, even with the proper wheels. The outer corner of the tire, where the tread meets the sidewall, makes contact with the inside of the fender lip at about 10 o'clock on the driver's side and at about 2 o'clock on the passenger side. This is really only a problem under heavy cornering loads. For easy driving, contact shouldn't be an issue, but that's not what we are talking about. I rolled the fender lip upward at the point of contact and I haven't had trouble since. Note that I also haven't reinstalled the front plastic fender arches. It will take some mild rework to do so, as the point where the tire contacts is near a screw hole used to mount the plastic arch. After bending the fender in, the screw hole no longer lines up. Someone running 225/50 15 street tires stated that he essentially glued the arch back on to the car. While this works, I'm sure there is a better solution. Note: I mentioned that the glued arches are with street tires. It is possible that a 225/50 street tire will require more work to the body of the car to get rub-free fitment, simply because they are more flexible than the race tires I had. Also, when the tire is at full lock to the right, the trailing edge of the passenger side tire rubs the inside of the wheel well just enough to rub through the plastic fender liner and buff the paint off the metal underneath. A hammer and ten seconds could cure this problem with ease. Some light blows will move the metal away enough to prevent any clearance issues. Fitment of the 225/50 15's to the rear is far more straight forward than the fronts. With the wheels I used, the installation was a direct bolt-on with one very minor hitch. When turning the car hard right, the inner sidewall of the driver's side tire would contact the fender liner and the frame rail slightly. This was the only audible tire-to-body contact I heard at any time. This contact may be specific to my chassis, but not necessarily yours. The contact was right at the seam between the frame rail for the rear bumper impact absorber mount and the unibody. Once again, a hammer and ten seconds cured this problem. No rubbing since, and the shell wasn't bent enough to even be noticed. ---------- Post Date: Wed Nov 29, 2000 Subject: Re: XR4Ti - 225/50 15 tires List: firstname.lastname@example.org Hello all, Brad wrote: > Since I'll have AVO's out front (providing more inboard clearance), I > suspect I should be able to go with 38mm offset wheels (16 x 7) and avoid > any potential fender lip rubbing with 225/45 x 16's. Don't count on it. With my setup, when the steering wheel is at full right lock, the trailing edge of the passenger side tire buffs the paint off the metal (frame). A rub mark is visible if you yank that wheel. Moving the tire inboard may avoid the fender contact, but will make contact with the shell worse. This sounds like the inverse of the analogy, 'robbing Peter to pay Paul'. Now you are paying Peter while robbing Paul. Okay, that was bad. > However, you've created some concern for me on going with that offset for > the rears on two points: > 1) Potential contact with frame rail (as you have mentioned) Note that our cars may be different enough at the crucial contact point in the rear that there may not be a big issue. The problem area on my car was the joint between the unibody "frame rail" and the portion of the frame that the rear bumper impact absorber is mounted in. There is a weld in the area, and the differences in shells may be significant enough to change things. After all, it did rub only on the left side. Who knows if the right side is the same, but it has more clearance due to luck-of-the-draw construction (or if it's related to the fuel filler neck). > 2) Potential contact with either/both twin Borla tailpipes I would consider this concern serious. I suspect that you will indeed run into clearance issues between the tires and both tailpipes. I'll be putting snows on my wife's 88 with Borla duals. If I remember I'll test fit a racing wheel on both sides to see if the issue is a concern. My racer has no exhaust on it, other than the Sacramento Mustang 3" mandrel bent downpipe. I'd be willing to bet that a full length 3" exhaust exiting in stock location would have contact issues. plan on side exit when I do put it on. > (even though I'm running without liners) FWIW, liner/no liner is inconsequential. They probably stick out less than 3/16 of an inch at the crucial point. I did indeed rub through the liner and buffed the paint off the metal. > The second point concerns me more, since closeness, not just contact, > with the tire is an issue with a hot exhaust pipe. I doubt there would be any serious concerns about tire delamination from excessive exposure to heat. The exhaust pipe is probably a maximum of 200° to 250° F at any given time. With a reasonably small gap of 1/4 of an inch, along with the consideration of a cooling airflow through that gap when the exhaust is the hottest (while moving), not to mention the fact that the tire is rotating (so you have a lot of area to heat and it's going through heating and cooling cycles from the rotation), I don't think heat is a concern. I think there would have to be direct contact, while the tire was stationary for there to be a real problem. Rubbing while the tire was turning wouldn't do too much more damage than if the rubbing was happening with something cool. Just my opinion. > I suppose spacers could be a possible solution, but 3/16" would be the max > I'd go since we're dealing with hub-centric wheels. If you go with a larger spacer, they make spacers with hubcenters machined in, so a larger spacer is possible. Remember most cars out there have hubcentric wheels too. Also, I forgot to inlcude my suspension mods. My car is pretty darn low. I'm running BAT's 40mm lowering springs. BAT considers those race only, but I have more rear ride height with these than with Rapido's lowering springs. So street use is fine, if you avoid things like speedbumps. The car is low enough that I usually have to jam my shoulder under the car and lift it slightly to get a jack (standard medium-duty Craftsman) under the frame. I also have the entire assortment of Powerflex polyurethane suspension bushings. If the car were as low, without bushing flex control, tires may contact the body more frequently when the suspension moves around.Back to the Tech Articles main page
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