would different tire widths perform worst or better?

Fox89GT · 01-03-2001, 06:05 PM

Say I run 225/50 in front and 245/50 in the rear. Would my handling suffer in this combination vs. having all the same size tires all around? Also, what is everyones opinion on the optimal tire size for an '89 fox body. Going bigger is not nessasary better. My guess is 245/45/16.

autoX · 01-03-2001, 11:05 PM

Tires really are kind of a science. I will try to give you as many answers to your questions as I can... First of all, you need to know that better or worse handling all depends on contact patch. That is the amount of rubber that you have on the road. Obviously the more rubber you can put on the road (the bigger the contact patch), the better your car will handle. As for bigger contact patch in the rear - well, Mustangs have an inherent problem called understeer. Understeer is basically when your front tires lose adhesion to the road before the rear tires do and you get a car that pushes through the corners. By running a smaller tire in front than the rear, you are only going to make this problem worse. Also, a 225-50 up front and a 245-50 out back means that your car would sit higher in the rear than in the front. That in itself would probably not be optimal for handling. YOu would have to run a 225-55 up front and a 245-50 in the rear for the tires to be the similar circumferences. I would have to advise to run 4 tires the same size if you want a better handling car... I run 245-50-16s on a 16x8 inch ROH rims and have no problems (well very minor problems) with rubbing on very tight corners (those rims have a perfect backspacing for that size of tire. The tires really fill the fenderwells nicely). I love that tire/wheel combo on my car and it handles great.

------------------
Red '90 GT - My Daily Driver w/ Kenny Brown braces & Springs, 6 KYBs, Caster/Camber Plates, Factory Five Control arms, Poly Bushings, 3.55 gears, Hurst shifter, Dynomax cat-back, Cervini 2 1/2 cowl, & Polished ROH ZR6 wheels... Griggs torque-arm and panhard bar waiting for installation!

Fox89GT · 01-04-2001, 04:21 PM

Gee, your car looks similar to mine. I also like the ROH wheels. I think they are similar to the SS Impalas, also. They do look good on the Fox bodies, though. Can I ask how much you paid for them? I've heard that you can mail order from the directly. Will have to check that out.

What part of you fender well does the tires touch? I think from '90 and up the fender wells are bigger. I might have a harder time with rubbing since mine is an '89 and I lowerd it about 1.25". I think I might go with your combination. Looks way cool...

Opps...caliper should be 73mm, gotta fix that.

------------------
FMS wires, tune up kit, strut tower brace, KB subframes, Steeda G-brace, C/C plates, rear sway bar and sport springs, B&M shifter, flex fan, 3.55 gears, 63mm calipers, SVO Master Cylinder and SS braided lines.

[This message has been edited by Fox89GT (edited 01-04-2001).]

[This message has been edited by Fox89GT (edited 01-04-2001).]

drudis · 01-04-2001, 10:48 PM

I would recommend same size tires. Why...
The Mustang understeers (plows) to begin with. Smaller tires, overpowered by bigger rear tires, only makes this situation worse.

As for wheels, the ROH 16x8 wheels were my first set. I ran 245-50's and then 245-45's on all four. The 45's were a soft compound and fit better (lower profile) in the 9:00-o-clock position of the driver's wheelwell on a 1989 fender.

My current combo is 275-40 R1's on 17x9-1/2" wheels on all four corners. Yeah, this took some work, but the results are well worth it!

------------------
Darius Rudis
Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-)
My Mustang Page

autoX · 01-05-2001, 12:10 AM

NO I don't mind you asking - but my answer won't help you much. I actually picked them up used (found them in the local paper) for $500. The guy before me had them polished I guess you have to special order them polished and they guy who bought them new didn't know that. When he got them and the face was unpolished (they only plish the lip), he paid an extra $85 per wheel to get the entire wheel polished! It seems like I have seen those wheels in the Mustang mags for like $165 ea, but I don't know that ROH is still making that wheel. I never see it advertised anymore. I even checked their website a few months back and they didn't even show it there... Oh, and yes, they are almost exactly like the Impala SS wheels. I love them because they are dished out and have some depth to them...
The part of the fender that rubs - on a tight corner the tire rubs on the front of my fenderwell where the ground-effect wraps into the fenderwell. I also rub on the back of the fenderwell from the inside edge of the tire. I also noticed a little bit of shiny metal (i.e. rubbing) right at the top of the fenderwell where the fender rolls under. Boy, when I describe it like that it makes it sound like they rub everywhere! It really isn't bad. As for the fenderwells, I was thinking that the '91-up Pony cars had the bigger fenderwells, because that is when they went to the 16 inch pony rims... I could be wrong, however...

moosejaw · 01-05-2001, 02:34 AM

Thanks for the info, even if it wasn't my post!

I am in a similar situation about to purchase tires and was going to get the same size all the way around, but for a different reason. Now I have a better reason.

I purchased the Cobra R rims (9.5 width) and transfered my old tires to them. In the shop we have a BF Goodrich poster of the 95 Cobra R (same rims) and the tire size on them is 255/45/17. I figured I would just use this size from now on. It should be easier to get, easier to lookup (just reference the 95 Cobra R) and be a good match for my braking setup.

Darius your car is great. I have viewed your Michigan Speedway videos many times. What a blast that must be (Michigan). We seem to share opinions on a lot of mechanical things. Anything done on a car should be done so it makes sense and doesn't break.

Once again thanks for the tire comments. Do either of you use a tire pressure monitoring system for the street? I was considering it for the new tires. Any comment?

Mike

drudis · 01-05-2001, 09:31 PM

Quote:

Originally posted by moosejaw:
Darius your car is great. I have viewed your Michigan Speedway videos many times. What a blast that must be (Michigan). We seem to share opinions on a lot of mechanical things. Anything done on a car should be done so it makes sense and doesn't break.

Once again thanks for the tire comments. Do either of you use a tire pressure monitoring system for the street? I was considering it for the new tires. Any comment?

Mike

When I found otu they were having SAAC24 there, I said I'am going. My wife asked "how much" and I said "I dont care!!!"

It was a blast. You can see in that ONE lap I nearly _lapped_ the field. These guys had their Boss429's... and would ROAR up to 110mph, then the 4.56 gears ran out. I raced past a 427Cobra at 135mph. When we pitted, I thought he was gonna yet at me for tailgating. He came over and said "you passed me like you put your blinker on... while I was white-knuckling it..."

As for the tire pressure monitoring, IMOHO not worth it. Oh, I do take tire temps and pressures during one session of roadcourse racing. But for the street, I just set it and forget it for weeks. Occasionally I do check on it.

------------------
Darius Rudis
Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-)
My Mustang Page

01-03-2001, 06:05 PM	#1
Fox89GT Registered Member Join Date: Sep 2000 Location: Bay Area, CA Posts: 55	would different tire widths perform worst or better? Say I run 225/50 in front and 245/50 in the rear. Would my handling suffer in this combination vs. having all the same size tires all around? Also, what is everyones opinion on the optimal tire size for an '89 fox body. Going bigger is not nessasary better. My guess is 245/45/16.

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01-03-2001, 11:05 PM	#2
autoX Registered Member Join Date: Nov 1998 Location: Portland, OR Posts: 113	Tires really are kind of a science. I will try to give you as many answers to your questions as I can... First of all, you need to know that better or worse handling all depends on contact patch. That is the amount of rubber that you have on the road. Obviously the more rubber you can put on the road (the bigger the contact patch), the better your car will handle. As for bigger contact patch in the rear - well, Mustangs have an inherent problem called understeer. Understeer is basically when your front tires lose adhesion to the road before the rear tires do and you get a car that pushes through the corners. By running a smaller tire in front than the rear, you are only going to make this problem worse. Also, a 225-50 up front and a 245-50 out back means that your car would sit higher in the rear than in the front. That in itself would probably not be optimal for handling. YOu would have to run a 225-55 up front and a 245-50 in the rear for the tires to be the similar circumferences. I would have to advise to run 4 tires the same size if you want a better handling car... I run 245-50-16s on a 16x8 inch ROH rims and have no problems (well very minor problems) with rubbing on very tight corners (those rims have a perfect backspacing for that size of tire. The tires really fill the fenderwells nicely). I love that tire/wheel combo on my car and it handles great. ------------------ Red '90 GT - My Daily Driver w/ Kenny Brown braces & Springs, 6 KYBs, Caster/Camber Plates, Factory Five Control arms, Poly Bushings, 3.55 gears, Hurst shifter, Dynomax cat-back, Cervini 2 1/2 cowl, & Polished ROH ZR6 wheels... Griggs torque-arm and panhard bar waiting for installation!

01-04-2001, 04:21 PM	#3
Fox89GT Registered Member Join Date: Sep 2000 Location: Bay Area, CA Posts: 55	Gee, your car looks similar to mine. I also like the ROH wheels. I think they are similar to the SS Impalas, also. They do look good on the Fox bodies, though. Can I ask how much you paid for them? I've heard that you can mail order from the directly. Will have to check that out. What part of you fender well does the tires touch? I think from '90 and up the fender wells are bigger. I might have a harder time with rubbing since mine is an '89 and I lowerd it about 1.25". I think I might go with your combination. Looks way cool... Opps...caliper should be 73mm, gotta fix that. ------------------ FMS wires, tune up kit, strut tower brace, KB subframes, Steeda G-brace, C/C plates, rear sway bar and sport springs, B&M shifter, flex fan, 3.55 gears, 63mm calipers, SVO Master Cylinder and SS braided lines. [This message has been edited by Fox89GT (edited 01-04-2001).] [This message has been edited by Fox89GT (edited 01-04-2001).]

01-04-2001, 10:48 PM	#4
drudis Moderator Join Date: Dec 1999 Location: Livonia, MI, USA Posts: 1,194	I would recommend same size tires. Why... The Mustang understeers (plows) to begin with. Smaller tires, overpowered by bigger rear tires, only makes this situation worse. As for wheels, the ROH 16x8 wheels were my first set. I ran 245-50's and then 245-45's on all four. The 45's were a soft compound and fit better (lower profile) in the 9:00-o-clock position of the driver's wheelwell on a 1989 fender. My current combo is 275-40 R1's on 17x9-1/2" wheels on all four corners. Yeah, this took some work, but the results are well worth it! ------------------ Darius Rudis Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-) My Mustang Page

01-05-2001, 12:10 AM	#5
autoX Registered Member Join Date: Nov 1998 Location: Portland, OR Posts: 113	NO I don't mind you asking - but my answer won't help you much. I actually picked them up used (found them in the local paper) for $500. The guy before me had them polished I guess you have to special order them polished and they guy who bought them new didn't know that. When he got them and the face was unpolished (they only plish the lip), he paid an extra $85 per wheel to get the entire wheel polished! It seems like I have seen those wheels in the Mustang mags for like $165 ea, but I don't know that ROH is still making that wheel. I never see it advertised anymore. I even checked their website a few months back and they didn't even show it there... Oh, and yes, they are almost exactly like the Impala SS wheels. I love them because they are dished out and have some depth to them... The part of the fender that rubs - on a tight corner the tire rubs on the front of my fenderwell where the ground-effect wraps into the fenderwell. I also rub on the back of the fenderwell from the inside edge of the tire. I also noticed a little bit of shiny metal (i.e. rubbing) right at the top of the fenderwell where the fender rolls under. Boy, when I describe it like that it makes it sound like they rub everywhere! It really isn't bad. As for the fenderwells, I was thinking that the '91-up Pony cars had the bigger fenderwells, because that is when they went to the 16 inch pony rims... I could be wrong, however...

01-05-2001, 02:34 AM	#6
moosejaw Registered Member Join Date: Apr 1999 Location: St.Louis,MO Posts: 274	Thanks for the info, even if it wasn't my post! I am in a similar situation about to purchase tires and was going to get the same size all the way around, but for a different reason. Now I have a better reason. I purchased the Cobra R rims (9.5 width) and transfered my old tires to them. In the shop we have a BF Goodrich poster of the 95 Cobra R (same rims) and the tire size on them is 255/45/17. I figured I would just use this size from now on. It should be easier to get, easier to lookup (just reference the 95 Cobra R) and be a good match for my braking setup. Darius your car is great. I have viewed your Michigan Speedway videos many times. What a blast that must be (Michigan). We seem to share opinions on a lot of mechanical things. Anything done on a car should be done so it makes sense and doesn't break. Once again thanks for the tire comments. Do either of you use a tire pressure monitoring system for the street? I was considering it for the new tires. Any comment? Mike