I have recently installed 15x7 wheels with 45 mm offset for the track. The wheels are made by Team Dynamics in England and distributed in US by TeamdynamicsUSA. They weigh 13.2 lbs (I checked them).
For tires, I use 225/50/15 Michelin Pilot Sport Cup R compound front and rear. I removed the plastic trim in the rear fender and the fender liner in the front fender. I rolled up the fender lips using a baseball bat. My car is lowered 1.75" front and back using threaded body coil-overs. I took it to the track for the first time with these tires and I had no rubbing in the back, but when braking and cornering simultaneously, I had rubbing in the front, which I resolved almost completely with a little extra fender rolling. There was no rubbing when cornering without braking or when braking in a straight line. The tires do not rub on the inner suspension parts with 45 mm offset. It might be possible to use 50 mm offset wheels, but I am not absolutely certain. (50 mm offset moves the tires closer to the middle of the car than 45 mm offset wheels). I do have some rubbing of the front tire when braking very hard from 4th gear down to a second gear corner where the entry to the corner is steeply uphill (Mont Tremblant's Namerow corner). This did not occur at Watkins Glen. The rubbing is due to the joint between the fender and the monocoque above the tire. I will need to grind this down about 1/2" where it is rubbing. It should be less of a problem as I move to stiffer front springs. When running in the rain on the stock RE-010’s, I did not have the rubbing on the inner fender joint. The stock RE-010 195/55/15’s have an unloaded measured diameter of 23 1/2”, while the Sport Cup 225/50/15’s have an unloaded measured diameter of 24 1/8”. Thus the Sport cups are 5/16” closer to the fender joint.

I chose 225 width section tires because that is what Realtime Racing has used on their cars since 1997. They have used 225/50/15, 225/50/16 and now use the mandated size of 225/45/17 in Toyo T1-S. They have used NSX 16x7” rims (and calipers) with 55 mm offset and 0.25” spacers with 225/50/16 Goodyear GS-CS race tires with 3-4 degrees negative camber on the front, Volk TE-37 15x7” with B.F. Goodrich 225/50/15 RA-1’s, and the SSR Competition 17x7.5” or 17x8” wheel in the last few years with the Toyo street tires. I have looked at their cars and the tires certainly fill the wheel wells. How they avoid rub I am not sure (no liners or plastic lips certainly). I do know that this year they are running 900 lb front springs and that last year they won the championship with 800 lb front springs, so I would imagine the car is not exactly dropping down too much at the front under braking. (They were running 800f/1200r before and now 900f/1400r when I spoke to them at Mosport.) I also checked 2 ITR's in a local race series and they were both using 225/50/15 Toyo RA-1's (the series tire). I had 450 lb front springs and some rubbing. The front camber was at -2.3 degrees for these tires. I wanted to make the 225's work since others have done it. The tires weigh 20.4 lbs each, making each wheel and tire combo weigh a total of 33.6 lbs, whereas the stock ITR wheel with an RE-010 195/55/15 weighs 35.0 lbs. So my set-up is wider and lighter.

I have taken a few pictures showing the clearance between the stock brake calliper and stock ITR wheel, as well as for the wheel and tire to upright clearance. I also have some pictures of the Team Dynamics Prorace 1 wheel in 15x7 with 45 mm offset, on which are mounted Michelin Sport Cup 225/50/15 R compound tires. The brake calliper clearance is much larger than with the stock ITR wheels. Plus there is even room for more negative offset. The camber was set at -1.5 degrees for the pictures, and the car was lowered 1.75 inches. Camber was later set to -2.3 deg.

A few pictures to show clearances:

1. My ITR with Team Dynamics Prorace 1 wheels 15x7 45mm offset


2. Team Dynamics Prorace 1 wheel with Michelin Pilot Sport Cup 225/50/15


3. Gauging Stock ITR caliper to stock ITR wheel clearance


4. Measuring Stock ITR caliper to stock ITR wheel clearance at 0.185"


5. Gauging Stock ITR front wheel to stock ITR upright clearance


6. Measuring Stock ITR front wheel to stock ITR upright clearance at 0.740"


7. Team Dynamics increased wheel to caliper clearance


8. Gauging Stock ITR calliper to Team Dynamics wheel clearance


9. Measuring Stock ITR calliper to Team Dynamics wheel clearance at 0.498"


10. Gauging 225/50/15 tire to upright clearance on Team Dynamics wheel with 45mm offset


11. Measuring 225/50/15 tire to upright clearance on Team Dynamics wheel 45mm offset at 0.710" (more room here!)


12. Gauging Team Dynamics front wheel to stock ITR upright clearance


13. Measuring Team Dynamics front wheel to stock ITR upright clearance at 0.557" (more room here too!)


In the end I should have ordered 48 or 50 mm offset wheels, as there seems to be lots of clearance. Even at 50 mm offset, which is 5 mm (0.2 in.) closer to the upright than what I am using at 45 mm offset, there would still be .36" clearance between wheel to upright, and 0.51" clearance between my 225/50/15 Sport Cups. The extra offset would have helped in reducing fender to tire clearance problems. While I am certain the fender liner would still have to be partially removed, the fenders might not need quite as much rolling. You can see evidence on the second picture of the rolling by the red paint from the baseball bat I used on the top of the tire. Only trial and error will tell for sure.

I hope you find these pictures and measurements useful, as I sure could have used them before I took the jump and bought all my stuff. All I could seem to get from the forums was a ton of inconsistent and mostly incorrect information from a lot of people who obviously didn't know what they were talking about, since people made assertions without ever installing the wheels or measuring clearances, let alone drive on a track with the set-up. I wanted to fit 225 wide tires on my 1.75" lowered ITR, and I did and they fit, with a little massaging. They should fit yours too if you really want maximum grip for corner carving. The car feels fabulous on the track with its “big” rubber. I measured 1.310 g’s of lateral acceleration peak at Watkins Glen a few weeks ago with this setup, in one corner, the “ankle”, and I was regularly over 1.2 g’s. The corners are a little banked at Watkins Glen, in the range of 6 degrees on some corners I have heard. At Mont-Tremblant, I got over 1.15 g's. Hope this helps and good luck with your setups!

May the lateral force be with you!

 

Thanks for taking the time to do all the measuring and picture taking

I've been wondering the same things and you've helped alot.

From the second pic, though, it doesn't appear that you'd have too much problem with rubbing on the outside. You said you would've rather had +50 offset, but why wouldn't you want to take advantage of the wider track of the lower offset? If it's the diving issue upon braking, just get stiffer springs. Maybe I missed something. Anyway, great post.

 

thanks for taking the time to post this.

here are my photos when they were up at Mosport a couple years back.



just to confirm the 225/45/17 R shaved Toyo T1S on the SSR 17 in. Competitions using a shorter 4.785 final drive with them though.

It does look as though they lowered it more than the 1.75 in.



My understanding is that the fenders were rolled.

My friend Duane Wickham of RTR and the late Jerome Zimmerman (RIP) talking shop.

 

The tire that RTR is currently using is the only size that they are allowed to use. With very few exceptions in World Challenge Touring Car, all cars must use the 225/45/17 tire in the T1-S model. The Toyo site lists the diameter of this tire as 25.1". The stock ITR tire, the RE-010 has a listed size of 23.5" on the Bridgestone site (which is exactly what I measured), and therefore there is a significant difference in diameter between stock and the series tire. A 1.6 " difference in diameter is very significant. Bridgestone also lists the weight of the 195/55/15 as 20 lbs, making the stock wheel weigh 15 lbs since I measured the total at 35 lbs. vs. 20.9 lbs for the T1-S tire and the SSR Type C 17x7.5 wheel weighs 12.7 lbs for a total of 33.6 lbs, which is exactly what my Michelin Sport Cup 225/50/15 with 15x7 wheels weigh. However my wheels are very much cheaper than the SSR wheels, and probably much more solid. Peter Cunningham said that the SSR wheels had the unfortunate habit of turning into the shape of stop signs when they get bumped too hard. My wheels list for $125, while Tirerack is selling the SSR 17x8's for $379 each. Makes for an expensive stop sign, but if you are forced to use a 17" tire, then this is the type of money you have to pay to get a combined weight which is the same as my option.

I would also think that the rotational moment of inertia for the 17" wheel and tire is much higher than for a 15" wheel and tire, since the weight of the rim is further out, and the moment of inertia goes up as r^2. My guess is the teams would not use 17" wheels if they were free to choose for this reason, except for the fact that you can use bigger brakes. Also of note is that ABS is now banned, but when Mike Galati ran his own team with his ITR and beat Realtime and won the championship, he was running ABS and thus the stock brakes with just Hawk blue pads, while Realtime was running big Brembo brakes. When I spoke to him at Mosport, he told me that not having had ABS the year before had cost him many points whenever it rained. I just drove for 2 days in the rain at Mont Tremblant and I was able to reel in a ton of non ABS Porsches at the end of the straight with my ABS. I would not want to take it off.

With regards to my choice of offset, I wanted to stay as close as possible to the standard ITR offset which is 50 mm, since this keeps the scrub radius (distance between projected kingpin axis and tire center line at the ground) at the designed value. Moving the tires out with say 38 mm offset wheels means you are working the suspension in a way it was not designed to. A 12 mm change in scrub radius is quite significant. Any time you increase the scrub radius, it makes steering the car more difficult since an increased scrub radius distance means you need more torque on the steering wheel, and it also changes the feedback into the wheel from the tires interacting with the road. I just assumed Honda did their homework when they chose 50 mm offset, and anybody who says different had better get out their suspension analysis program.

The increase in track is really minimal in a percentage terms, since the stock track width is 58.3" with the stock offset. Changing to 38 mm offset on both sides gives you a track width of 24 mm more than stock or about 59.25". The % increase is only 59.25/58.3 or 1.6%. I wanted to be able to lower the car as much as possible while simultaneously using the widest tires possible, since there is much more gain to be made here. Assuming the stock center of gravity height is in the range of 20", lowering the car by 2" gives you a 10% change. Since weight transfer is proportional to both C.G. height and track (inversely), the 10% benefit is much greater than the 1.6% benefit if you had to choose just one. It was my feeling that moving the tires more outward with 38 mm offset wheels would reduce the potential for lowering the car due to rubbing on the fender. I think this is why people use 205 tires with the Kosei 38 mm offset wheels. I also think people are using the 38 mm offset because they don't know any better, Tirerack gives out bad info on the phone (they certainly did to me when they told me I would have rubbing problems on the suspension unless I used 38 mm offset wheels), the Kosei in 45 mm has been very hard to get, and many other wheels are only available in this 38 mm offset. For the reasons listed above, I came to the conclusion that 38 mm offset wheels for an ITR are not the correct choice.

Michael, while in the RTR picture shown above it looks like the car is lowered more than my 1.75", you have to consider that their tire is at least 1" more in diameter than the 225/50/15's shown in my second picture. You would have to overlay the pictures to get a truer sense of the amount of lowering. Looks can be deceiving! I can assure you that the nose of my car is very low with just 1.75" of lowering. It could be lower, but it might be hard to pull out of the fueling station at a track event. I sure seem to buy a lot of fuel and be going nowhere these days.

As regards rubbing, what the second picture does not show is that when you are braking and cornering at the same time, the tire is turned and crossing the line of the fender, which is coming down due to braking. This causes the outside of the tire to rub on the fender's outer edge. If the tire is more inside with a higher offset, then wheel rub is less likely. In the end, unless you can look at someone else "work", this is all an experiment. Now I was just wondering if anyone could make some 245/45/16's on some 16x8's fit in there, since they are smaller in diameter than the 225/45/17 that RTR is using? I could always use a little more grip, but I'm sure it's gonna cost me more.



Modified by descartesfool at 6:29 PM 8/16/2003

 

I must say I'm surprised it's working, but hey, numbers and measurements don't lie I'd always been led to believe that the magic combination for 225 tires is:

38mm offset wheels
5mm rear spacers
Roll the fenders

Is it possible (actually...I think it's bloody likely) that a 225-45-15 Hoosier (which is my choice) is actually wider than a 225-50-15 Michelin?

Excellent post. Stick around.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">The tire that RTR is currently using is the only size that they are allowed to use. With very few exceptions in World Challenge Touring Car, all cars must use the 225/45/17 tire in the T1-S model. The Toyo site lists the diameter of this tire as 25.1". The stock ITR tire, the RE-010 has a listed size of 23.5" on the Bridgestone site (which is exactly what I measured), and therefore there is a significant difference in diameter between stock and the series tire. A 1.6 " difference in diameter is very significant. ...

Peter Cunningham said that the SSR wheels had the unfortunate habit of turning into the shape of stop signs when they get bumped too hard...

I would also think that the rotational moment of inertia for the 17" wheel and tire is much higher than for a 15" wheel and tire, since the weight of the rim is further out, and the moment of inertia goes up as r^2. My guess is the teams would not use 17" wheels if they were free to choose for this reason, except for the fact that you can use bigger brakes.

Michael, while in the RTR picture shown above it looks like the car is lowered more than my 1.75", you have to consider that their tire is at least 1" more in diameter than the 225/50/15's shown in my second picture. You would have to overlay the pictures to get a truer sense of the amount of lowering. Looks can be deceiving! I can assure you that the nose of my car is very low with just 1.75" of lowering. It could be lower, but it might be hard to pull out of the fueling station at a track event. I sure seem to buy a lot of fuel and be going nowhere these days.

Now I was just wondering if anyone could make some 245/45/16's on some 16x8's fit in there, since they are smaller in diameter than the 225/45/17 that RTR is using? I could always use a little more grip, but I'm sure it's gonna cost me more.

</TD></TR></TABLE>

When I first saw the 17 in. SSR Competitions on the RTR, I surmised that the overall diameter was counterproductive to their gearing and they had to have run a shorter FD...which they confirmed.

I'm only going by appearances and you are absolutely right that looks deceiving and we need an photoshop overlay of the 2 pics scaled to the same size and the axle hub referenced...(any h-t members willing to lend a hand?).

When I talked to Andrew Kantor at Wheel & Tire Zone here in Toronto (Mississauga actually ), he told me that the SSR's are semi-forged...which would explain the stop sign making.

The Bridgestone Pole Position So3, Kumho Victoracers, Hoosier R3S03 , and Toyo T1S come in a 245/45/16...relative weights unknown...don't know if they are in your budget or suitable for your racing demands...compared to your Pilot Sport Cups...kaching kaching...

 

Df,

Don't cut the seam, just pound it over.

Most of us have a hell of a time making our cars work well enough with 23 inch tires. At 25 inches you're hobbling yourself with the necessity to run a higher ride height. Look at how high RTR was running on the 17's. If you can run 25 inch tires at 5-5.5 inches to the rockers and you're not spending alot of time bottomed on the outside front on 8-900 lbs springs then you're not going very fast.

I don't know why you selected Michelins, but I think it could be a toss up between a high car on 225's and a low car on 205's.

Scott, who wonders why you didn't just run the Hoosier 225/45 like everybody else does?

 

Scott,

The sledge hammer is close at hand.

My opinion exactly on the 17" and the RTR cars. They didn't use to run this size and I can only assume that Toyo selected it as the series tire since it is a popular "decorator" size on street cars.

I selected the Michelins based on talking with a lot of Porsche guys. Max grip and max durability. Taking durability out of the equation, Hoosiers at 225/45 (lower, grippier)are my preferred choice. With regards the Michelins, 1.31 peak g's is respectable, and a freind of mine tried them on his M3. He felt they had so much grip that he could hear his chassis twisting in turn 5 at Mosport. At the last Porsche events where I drove my ITR, it was mostly the Michelins or Hossiers on the fastest cars, with a few guys trying out the new Pirelli's. Then again some guys were pretty fast on RA-1's. I just enjoy passing Porsches and BMW's. As for what everybody else does, I didn't know. Thanks for letting me in. I will try the Hoosiers when my Cups wear out. I guess the 45 profile in 225's will drop the spindle by about .45" compared to the 50 profile without using up any suspension travel. Sounds good

 

Df,

By the time you wear out the Michelins, maybe the new Hoosier R3S04 will be out and things will be even better.

I looked over your wheels, and I think I "like" them better than the Kosei as an inexpensive wheel, but the one thing I don't like about them is that, just like the stockers, the spokes protrude out beyond the tire. They'll inevitably get buggered up.

Re the scrub radius thing. We're so much closer to centerpoint steering than a typical strut car that I don't think 10mm off difference in offset is a huge thing. Also, lateral scrub radius in conjunction with caster and kpi doesn't always produce intuitive results with respect to steering induced cross weight change. I haven't thought it out systematically, but some interesting sessions on the scales have produced surprising results that recommend a future study project.

Scott, who understands having fun with the uber-machines...

 

he told me that the SSR's are semi-forged

They are forged while the metal is in a semi-solid state. They are still completely forged, just like any other good JDM wheel (volk, etc).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">
.....I always thought they ran a 17 because it was the best compromise between weight and a soft sidewall. </TD></TR></TABLE>


I wonder how my 15x7.5 +40 cp035's would stack up in a 225.....? My intent is to run some ao32r's... but the ra1's are so tempting! My next BIG tire purchase is still a ways off, so I have time to contemplate... but on the measurements! I have noticed that I have MUCH more caliper clearance with my new wheels, and the small amount of wider track makes the car much more stable (noticably) at high speeds...

The HC guys that I know and talk to about their setups run like 20mm+ with their wider wheel/ tire combo's... their opinion is that WIDER IS BETTER, and I must humbly agree - as they have decades more experience with road racing than I have.....

It would be very interesting to do a double-blind comparison of a few different wheel/ tire combo's and a lateral g sensor on the track to compare lap times and g's.....