XR4Ti Archived Tech Articles

    225/50 15 Tire Fitment - An extensive series of posts and write-ups on the installation of 225/50 15 tires to the front and rear of the XR4Ti.

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:         merkurowners@merkurowners.org

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 

> 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 

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:         merkurowners@merkurowners.org and xr4-hardcore@egroups.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:         xr4-hardcore@egroups.com

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.

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Published by Chris Anglin.