FFR Tire Calculator: Click here

This is topic FFR FAQ HELP! Wheels and tires in forum Roadster Grandstand at FFCobra Discussion Forums. To visit this topic, use this URL: http://www.FFCobra.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=002815  Posted by oldguy668 (Member # 86) on May 17, 2002, 06:49 AM:   Positively, absolutely, without a doubt, the most important contribution anyone can make on this topic is factual data. Please don't post replies like "I got a real good deal on some XYZ wheels at Joe's Roadster Parts". Post facts; Axle type (width between mounting faces), wheel diameter and backspace, tire brand and size (important because not all 274/40's are the same), interference problems, model year of spindles, ride height. Data, data, data. When that's all accounted for, then you can tell us what a real good deal you got. Happy motoring   Posted by Wade Chamberlain (Member # 220) on May 17, 2002, 07:01 AM:   Ok, here's my setup along with it's "issues".... REAR 15x10 PS Engineering wheels from FFR BFG Radial T/A 295/50R15 Stock width '88 4-lug drum brake rear Can't beat the look, but it will rub the body on a hard dip. You'll have to run the ride height about as high as you can go, or fabricate some bump stops. Quads will fit (BARELY) if reversed. Gabriels have the most clearance I've found. FRONT 15x7 PS Engineering wheels from FFR BFG Radial T/A 235/60R15 Stock '88 spindles Stock lower A-arms No issues here except the wheels WILL rub the A-arms (worst noise I've ever heard) at full lock unless some judicious grinding is done at the lower A-arm lip. An alternative would be to use stops in the rack to limit it's travel.   Posted by ToddButtrick (Member # 115) on May 17, 2002, 08:20 AM:   I'm running a solid axle 5 lug SN95 disc rear that has been narrowed 2.5" per side. Horizontal quads need to be relocated inboard at axle end and the bottom vertical shock mount needs to be relocated about 2" inboard on the FFR supplied lower CA bracket. New axles from Moser. I'm running stock 88 donor stuff in front and converted to 5 lug. REAR: 15x9.5 PS Engineering GT-40s direct from PS Eng. 4.25" Backspace 275/50R15 BFGs FRONT: 15x7.5 PS Engineering GT-40 direct from PS Eng. 4.38" Backspace 235/60R15 BFGs ISSUES: The front calipers rubbed the inside face of the wheel when I first installed. They had to be shipped back to PS and have more material taken of the inside of the web to clear the calipers. - Click to enlarge -   Posted by FFR2372 (Member # 32) on May 17, 2002, 10:10 AM:   Todd, That thing is beautiful! Nice job. I'm running 2000 FMS Roadster "R" wheels, 18X9.5 with 5.87 backspace, stock stuff. FRONT 18x9.5 with 265/35ZR18 Comp T/A's. I have SN95 spindles, model year 1995, and in this configuration I have the FFR tube LCA's and the stock old style FFR UCA's. This setup puts the edge of the tire right at the lip of the fenderflare. Judicious measuring reveals that if I went with the pin drive FFR lowers, the stock IFS bracket and the Pole Position adjustable uppers I could move the edge of the tire inboard about 1/2", at a cost of about 1K. Screw it, I'll drive it like this  REAR 18X9.5 with 295/35ZR18's. I am running the FFR IRS package in the rear, the only deviation from stock is my giant 13" rotors and Wilwood brakes. I have approx. 1/2" clearance between the tire and the 2X3 crossmember, I will do a sawzall cut on the crossmember shortly. There is approx. 1" or more clearance between the tire and the outer fender lip. I may install a 1/2" spacer and race style wheel studs to move the tire out, mostly to center it in the wheel well.    Posted by oldguy668 (Member # 86) on May 17, 2002, 12:16 PM:   Question for FFR2372: Do you know the spacing across the rear from one mounting face to the other? We know that Fox solid axles are about 59 3/4" and the SN95 is about 61 1/4". If we knew the similar dimension on your IRS setup, those of us who wanted to use 18 x 9 1/2's could do a "feasibility study" with a calculator. Thanks for great info. Todd: Nice car..nice wheels.   Posted by FFR2372 (Member # 32) on May 17, 2002, 12:59 PM:   Olddude, Luckily enuff, I've got my car torn down again, so when I get home today I'll go and measure it.    Posted by DragonSnake (Member # 76) on May 17, 2002, 02:07 PM:   EDIT: I fixed the offset calculation per oldguy's suggestion. I created a wheel backspacing/offset calculator to help me find wheels that will work on the FFR. The tables below show the results of the calculator for various wheel widths. IMPORTANT NOTE: In my calculation of offset, I add 1 inch to the wheel width to make up for the fact that wheel manufacturers measure their widths from the inside of the mounting lip, but their backspacing from the outside of the lip. I am assuming each lip is .5" wide. THIS MAY BE DIFFERENT FOR DIFFERENT MANUFACTURERS. Wheels shown in RED are Roadster R reference sizes that are known to work on FFR's Fox Body Front and Rear Width Backspacing Offset 8 4.95 11 8.5 5.45 18 9 5.95 24 9.5 6.45 30 10 6.95 37 10.5 7.45 43 11 7.95 50 11.5 8.45 56 12 8.95 62 SN95 Rear Width Backspacing Offset 8 5.42 23 8.5 5.92 30 9 6.42 36 9.5 6.92 42 10 7.42 49 10.5 7.92 55 11 8.42 61 11.5 8.92 68 12 9.42 74 My initial assumption is that the Ford Roadster R wheels (17 x 9) are the appropriate size. The calculator uses a reference wheel (Roadster R by default) and gives you the offset and backspacing of any sized wheel so that the relationship of the wheel to the fender lip remains constant. This means that as you choose wider or narrower wheels, the extra width will be added or removed from the inboard side of the wheel, thus leaving the curbside appearance the same. This is strictly theoretical, but I think it makes a good place to start when looking for "non-standard" wheels for your FFR. It would be nice to get a table made-up for pin-drives and IRS. Does anyone have reference wheels for a standard pin-drive and IRS wheel? Any feedback? -Joe Posted by Russ 3048 (Member # 51) on May 17, 2002, 02:27 PM:   I am using the donor's stock Turbines. Stock suspension and donor brakes. What is the largest tire combination that I can use? What about if I want the same size on all 4 tires? Russ 3048   Posted by oldguy668 (Member # 86) on May 17, 2002, 04:51 PM:   Dragonsnake: You're on the right track, but you've neglected to recognize that the backspace and offset are calculated from two different dimensions. The offset is based upon the spacing from mounting face to centerline, and the backspace is based on the space from mounting face to the edge of the rim. So, most wheels will have a backspace that is about .5" greater than the value that would be calculated from the offset. The SN95 9" wheel, therefore, has a backspace of 6.42", but an offset of 36mm. The offset and backspace calcs will jive if you imagine a 9" wheel as being 10" wide, at its outermost point. Happy motoring   Posted by GregR (Member # 213) on May 17, 2002, 05:57 PM:   Bullitt Wheels Here's what I did to use the '01 Mustang GT "Bullitt" wheels: I used the '86-'97 Aerostar passenger side axles and drums to convert the rear to 5-lug. Used Lincoln Mark VII rotors to convert the front to 5-lug. Nothing has to be done to the rear axle to use the Bullitt wheels in back. The front rotors do need some minor machining for the wheels to fit. The outer edge of the front hub needs to be machined at a 45 degree angle, like this: The biggest problem to overcome is the fact the Bullitt center caps won't fit in front because the dust caps stick out too far. I solved this by machining some out of aluminum on a lathe. They only need to be about 1/2" tall. Sorry I don't have a better picture but here's what they look like on the car. - click to enlarge - Greg   Posted by oldguy668 (Member # 86) on May 18, 2002, 07:06 AM:   FFR2372: I've seen some 18 x 9.5's with backspaces of 6.06 and 6.46. If you feel that your 5.87 BS wheels are projecting out 1/2" too far, do you think one of the other available backspacings would have worked better for you?   Posted by FFR2372 (Member # 32) on May 18, 2002, 11:41 AM:   Oldguy, Maybe, but I wanted to use the Ford Roadster "R" wheels. My wheels are brand new take-offs from a 2000 "R". Now that I ponder the situation, if I had a 6.46 BS, the tires would definately hit the inner fender aluminium. I wanted bolt on simplicity, I should have used the 17X9 "R"s from the '95's. I'll get you that flange to flange measurement today.   Posted by oldguy668 (Member # 86) on May 18, 2002, 05:19 PM:   FFR2372: Would the 6.46 BS wheels have created a problem for you in front or back. If it's in back, I'll wager you have a standard Fox rear end width...about 59-59.25 from axle flange to axle flange.

Will that tire fit? Check out the FFCobra Online FFR Tire Calculator: Click here.

PS Engineering: http://www.Roadster427sc.com/index_Roadster.htm

Team III: http://www.team3wheels.com/

Trigo: http://www.trigowheels.com/

What does 245/45-17 mean anyway?

Tire diameter can be computed as follows:
(Sidewall Height + Sidewall Height) / 25.4 mm/inch + Rim Size, or
(110.25 mm + 110.25mm) / 25.4 mm/inch + 17 inch= 25.68 inch.

Or just use the FFCobra Tire Calculator.

[M3] "And the split combos are often 245/45/17 front and 275/40/17 rear.
So (245*2*0.45)/25.4 + 17 = 25.7"
and (275*2*0.40)/25.4 + 17 = 25.7"
or even (315*2*0.35)/25.4 + 17 = 25.7" for a wider rear.

You can get the same wheel height for different tire widths by choosing the proper aspect ratio. Just be sure the width of tire you choose will fit the 9" width of your Roadster R rim. The 315s need a 10" rim. The 275s are marginal according to some manufacturers."

[FFRM] Standard Mustang Donor wheel/tire configuration:  15x7" wheels, 4-lug, 235/60-15 and 255/60-15 tires.

[BP] The popular 15" wheel combo is to run 8" fronts with 235/60-15 tires. And 9-10" rears with 275/50-15 or even 295/50-15. You might have problems with 295's, so check for clearance before operating.  Remember that with the high sidewalls and Mustang stock rear end, the rear can flex side-to-side so that the tires could rub.

[BP] Most popular 17" wheels/tire combination: 17x8" front, or 17x9" with FFR lower control arms.  Some 8" fronts might rub, check before operating. For the front, use 245/45-17 or 275/40-17 for racing applications.  For the rear, use 17x9" or 17x9.5". Some guys have used 10" wheels, but you might have some clearance problems. Most guys run 275/40-17, but I run 285/40-17 with rubbing.

Tire Pressure :[GL] "If you are using 17's with 245/45's and 275/40's- Front 23psi rear 27psi. If you are using 15" with T/A's 25psi front 30psi rears. When I get the coupe figured out with 275/40's in the front and 335/35's in the rear I will let you know. Use the same tire pressures all the time. On a race track you may need to very the pressures a couple of pounds depending how the car feels."

[JM] " Front @ 28psi 235x60x15 Compt TA's, Track 32 psi. Rear @ 22-24psi 275x50x15 BFG DR's, Track 15-16psi"

[WD] "Front 24psi, rear 28psi. Sumitomo HRZ 225/50x16 front and 255/50x16 rear.  Use for both street, track and auto-x. Some auto-x will use 1 to 2lb change depending."

Question: [BB] "I have converted FFR# 2383 from 4-bolt to 5-bolt wheels using the following:

1.front are 1984 Lincoln continental rotors
2. rears are the five bolt conversion from Ford Motor sports via Summit.

Question: can I run 5-bolt Roadster R's 17 x 9
all around with a 5x4.5 bolt pattern and a 5.95 inch offset. Any help would be appreciated, as some wheel suppliers do not know."

Comments:

[D55] "Almost no supplier can help you, but if you knew the manufacture of the Roadster wheel you could get the help needed. I had to send wheels back to Summit and got my help from the manufacture, of the wheel I finally went with."

[RO] "If you have the standard mustang rear width and the mustang spindles the Roadster Rs fit just fine. See pics on the site below. I assume you got the 5 lug drum conversion from Motorsport. Ranger axles and drums is what you got and it will be fine been done lots of times here."

Question: [JC] "I noticed the FFR manual recommends 235/60-15 on front (which is fine since everyone makes them) and 255/60-15 tires for the back. Problem is nobody makes a tire that size. At least not anymore. I check the big three first (BFG, Mich, Goodyear) and then checked all of Tirerack with no luck.
Is there anyone out there who is running these on back?"

Comments:

[SF] "I believe the manual recommends 275/50-15 for the rear. The 60 series are to tall."

[WC] "Tirerack has 7 or 8 different tires in 255/60R15. You sure you had the right size typed in???? Here's the link.
http://www.tirerack.com/tires/Sear chTiresBySize.jsp?startIndex=0&width=255%2F&ratio=60&diameter=15&pagelen=20&pagenum=1&pagemark=1&do=Search

I don't think the 255/60's are too tall, but the 275/60's are. The 275/50R15's work well, and a few of us are running 295/50R15's too."

[RS] "I'm running 235/50-15 on the front and 295/50-15 on the rear. The rear tires stick out a little bit past the sides but work well. They aren't correct by some purists and maybe they're right, but they work for me."

[Co] "I`m going on 235/60 R15Z front and 255/60R15Z on the back, all BFG Comp T/A R1, DOT legal but very low profile! The 235/60 R15V are available from Pirelli P600 and for the back go on 275/55 R15V or Z Pirelli F7, in former times used by De Tomaso Pantera."

[1775] "I have 235x50x15 front..275x50x15 rear"

[Rs] "actually have coil over Carrera shocks and have no problem with clearances."

[Jw] "If I had it to do over again I WOULD NOT GET 15in wheels. I have IRS w/MKVIII brakes. The clearance is so close I have to be real careful about where they put the wheel-weights. The disks like to peel them off."

[JC] "Thanks for all the info guys. I got some 235/60s and 255/60s from BFG today. I have been told the difference in diameter size from factory tire is small for the speedo difference."

What wheel size should I use for the track?

[MC] "I built my car with the 15" Team III wheels, 'cause they look somewhat original.
(Enzo @ Finish Line $1340.00) At first I thought the Roadster R's looked funny but now I like the look almost as much. It's about a toss-up. The 15" Team III's are more expensive but the tires are cheaper (275/50-15 & 235/60-15) and less of them to choose from. There's a ton of choices in 17" tires for the Roadster R's! (I think if you do the math on the silver Roadster R's and tires there's about 3 hundred difference.)

I plan on driving my car daily and thought the 15" tires should ride better. (My Bimmer has 17" and I know the difference in ride.)

Take a look at "chabels" blue FFR with the 15" Team III's for a good example."

[M3] "The 17's don't give you more choices of "racing" tires, they give you more choices in performance tires. My car will be used primarily for daily commutes as well, and I chose 17's because even a daily driver ought to corner halfway decently. I've had BMWs with 15 inch tires and 17 inch tires and in my mind the difference is night and day with not much ride comfort given up for the extra handling benefits."

[RA] "I spent all last doing the tire wheel thing.  I can get 4lug Roadster r.. in silver 17x9 for 599..... 275/40/17 rears and 255/40/17 fronts for about 470... so you are looking at about 1100 bucks.... mind you the tires are the least expensive I have found...."

[BR] "The only problem with the Roadster R's is that I'm running drum brakes in the back and they don't hide it like some of the other rims."

[My427] "I like the way the 15" wheels look because the tires have more sidewall showing than with the lower profile 17" wheels."

[t50] "Ride quality on the street is more a result of spring rates and shock settings than tire/Rim size. I had 18 inch Rims/tires on a Mustang, It rode like a Cadillac. The first comment made about the rims was how harsh it must ride, but it wasn't true. The cornering was much better with the bigger rims. The Roadster looks more original with the 15 inch rims. Your pick whatever you like better."

[1630] "for a street car, I would definitely go with 15" wheels because they look more period.

I have pics on my site of my car with both a 17 and 15 wheels- and I think the $100 15"ers look better than the 400+ 17"ers.

poor street tire selection in 15". the car will handle perfectly well with a 15" wheel."

[sm] "I don't plan on racing my car either and plan to go with the 15 inch wheels for the more period look. I plan on running 295-50 in the rear and 245-60s in the front and can get a Goodrich or Goodyear performance tire that should meet my needs. I don't think you will have to worry about 15 inch performance tires disappearing - there are MANY classic cars that will require these sizes for a long time. I thought about 16 inch wheels as a 'happy medium' but found that there is less of a selection these wheels."

Polishing turbine wheels

[JB] "Cleaning up my turbine wheels has been the hardest part of building this whole car. They have some sort of indestructible coating on them that was obviously developed by NASA. After I soaked them in every toxic chemical know to man I ended up sanding it off. Later someone told me you can get it off by blasting them with baking soda. If you do a search on my web site for wheels, you’ll see a lot of four letter words. I'm thinking you’re going to have to get this coating off before you polish them. My advice would be to get someone to do it for you!"

[DH] "To get that factory coating off of the wheel you need the chemical methyline chloride. It is the active ingredient in most paint strippers. However, most strippers do not have a sufficient percentage to touch the coating. You need to find Kleen Strip Aircraft Paint Remover, product number AR-343. That is the only stripper I found that would touch it. Apply it very liberally and wait for the stripper to act on the coating. Do not let the stripper dry out. Plan on about one hour per wheel. Use a tooth brush to agitate the clear coat after it starts to bubble up. Do not get the stuff on your skin unless you are into chemical burns and don't let the EPA see you stripping these wheels in your driveway."

[DW] "Aircraft stripper is the only one I have found that will strip the clear coat - everything else failed miserably. I have done several sets of wheels and it is very effective. Be warned this stuff will kill if you try it indoors or even in the garage with the doors open. When painting it on make sure to wear a respirator or you will get a good dose very quickly - and it is not pleasant."

Halibrand's

Question: [wg] "I have a calendar picture of a 66 427SC and I swear it has a deeper dish GT40 style wheel at the rears and Halibrand S/C type fronts-which is what I want to duplicate. This photo I have has gray centers-to dark to count spokes. If I'm going to drop 1600-2000 for wheels I want to get it right the first time."

Comments:

[SV] "I think if you go with Trigo pin drive wheels, you'll get the original deep dish look."

- Click to enlarge -

[Ad] "How about the "kidney" wheels...they are unique and look very period correct. I would do those wheels if I were doing one today."

Team III wheel: http://www.team3wheels.com/ac/

Halibrand kidney bean: http://www.halibrand.com/

[RL] "IN ANSWER TO YOUR ORIGINAL QUESTION ,SOME ORIGINAL 66 427 RoadsterS DID COME WITH SC WHEELS IN THE FRONT AND GT40 WHEELS IN THE BACK ,THIS WAS DUE TO A SHORTAGE OF THE SC WHEELS AND THEN THE GT40 WHEEL SUPPLY DRIED UP ,THIS IS WHEN THE SUNBURST WHEEL GOT DESIGNED AND WAS USED ON THE LATER CARS ,THIS INFO IS DIRECT FROM THE SAAC REGISTRY"

[Gas] "Goin' to put in my order for them purdy Compomotive HB wheels and I was wondering what size to get that would be a good fit without rubbing and such. I had heard that there is a better selection of tires available in 16" diameter so am probably goin with that. I need a width and offset"

[IL] "don't know about 16" vs. 17" as far as availability, but I have Compomotive HB wheels on my car that fit the IRS great. They are 17"x10" with 6.5" backspace. If you go up to my web site you can see a picture of them. Note that they are pictured on a solid axle but I converted my car to IRS after complication largely because the backspace was to aggressive for the stock solid axle, I had a bad tire rub."

[WP] "If you have the IRS, you can get the pindrive arms front and rear to get the real deep dish wheels. They really look great on the car with the deep dish:"

- Click to enlarge -

- Click to enlarge -

(above) Fully Polished PS Engineering Pin Drive wheels in 17"

- Click to enlarge, PS Engineering -

- Click to enlarge, Compomotive

Click to enlarge

Click to enlarge

GT-40 Polished, click to enlarge

Chrome Roadster-R, click to enlarge

Notes on Temperature Averaging

• Averages have more meaning when Camber, Tire Pressure, Stagger, Toe in and basic set up are correct. #1 rule in racing is to have all four wheels pointed straight ahead in order to consistently win races
• You can see slightly higher front averages (5 to 10 degrees or so) due to absorption of heat from the engine and brakes
• Hot inboard edges of rear tires can indicate too much rear tire stagger which can slightly skew temperature averages
• New tires give the best results when taking temperature averages. Maximum heat is generated with all areas on the tire in new condition. More detail will be shown as no edges are ground off or over used. Camber curves are shown with more clarity. A racer should take advantage of their investment in a set of new tires and take special note of these average temperature readings
• If the driver were to slow down so as to not slide the front tires when a car had a tendency to push then the hotter rear average would indicate a push instead of the generally assumed loose condition. Since most drivers drive as hard as they can they usually slide the front tires when the car has a tendency to push causing the front tires to overheat. When this condition is present the driver usually comes in for adjustments during a practice session rather than abusing the tires lap after lap.
• If one end of the car is sliding or spinning extra heat will be generated by that end until the adhesion in those tires is used up. At this point of overheating the tires will probably never have the same grip that they had before they were over used and tire temperatures will drop due to the poor condition of the tires and less friction being produced. Care should be taken to know the driving style of your driver and condition of tires in order for the temperature averages to be a useful tool
• Generally, temperature averages that are more equal LR/RF against RR/LF will show a car that will be better on a long run, however some short track racers may find some extra speed in a short race with 10 or so degrees difference with the LR/RF showing the extra heat. The tires in this situation are actually being overworked a small amount gaining you the extra speed. Sometimes in a short event the tires will put up with the extra abuse resulting in faster lap times in the short distance. In a longer event the car would be fast for a bit but fade the back as the event wore on. The proper amount of differential will be learned from experience
• Excessive difference between Left and Right side temperatures can show a car that will be fast for a short period and then fade as the right side tires get over used due to the left side tires not doing their share of the work
• Excessive Front Averages generally indicate a pushing condition
• Excessive Rear Averages generally indicate a loose condition
• Tire temperatures should be taken as quickly as possible for the best readings and the probe needs to inserted to the same depth each and every time. Reading should be taken as close to the cord as is reasonable
• Used properly, temperature averages can be a fine tuning tool for a car that is already in the ball park and can be an indicator of future performance. Temperature Averaging can show a car that is starting to push or be loose before the driver senses the problem. Many times with new tires the car feels great to the driver because of the extra friction in the new rubber. The new tire can cover up a handling problem where the temperature averages would show the detrimental heat build up at a given end or cross. The closer you get to the optimum set up the more value you will get from the Temperature Averages. Temperature Averages used in conjunction with driver feedback, a good stopwatch, experience and crew chief voodoo is the best crystal ball you can find today

[BM] For future reference, here's the rotor/hub-to-wheel clearance on the various 17x9 wheels I tried:

PSE Halibrand/GT-40: 0.55" (0.5" too short)
Compomotive GT-40: 1.15" (barely clears)
Roadster R: 1.75" on ends/2.0" in middle (plenty)

The front rotors are 13" Roadster R's. The rear wheels/brake setup (12.65" Roadster R rotors/Dynalite calipers) fit fine.

I have empirical data that says the Roadster (PBR) calipers require 0.625" hub to spoke clearance; Roadster R calipers require the same clearance as the Wilwoods (1.1"), and the aftermarket 6-piston Wilwood or Brembo calipers require 1.25" to 1.3".

[Barry Mattingly] "Heads-up on the 4- and 6-piston Wilwood front brake setups if you use PSE wheels - these wheels (regardless of offset) will NOT fit without the use of spacers and longer wheel studs. The problem lies within the depth or clearance between the hub mounting face and the back edge of the wheel spokes.

I have standard offset (for SN95 spindles) 17"x9" GT-40 style PSE wheels. The 4-piston Dynalite calipers need 1/2" or 5/8" spacers; the 6-piston Superlite calipers need 3/4" spacers. I got a set from Gordon Levy. Make sure the studs you buy are only longer by the width of spacer, or the 'shoulder-type' closed end lug nuts used by PSE will not work.

The Compomotive Halibrand style wheels and Ford Roadster-R wheels will clear the Dynalites without spacers, and possibly the Superlites; the Roadster-R's will clear both without spacers.

PSE can machine a slight amount off the back side of the spokes, but not much more than 1/8". Make sure you tell Phil when you order your wheels - you may want to have him allow for less offset to make up for the spacers (to maintain track width and body clearance).

Again FYI - if you plan to race the car, be aware some sanctioning bodies will not allow spacers, unless they are pinned or bolted to the wheel hub or wheel."

Go back to the FFR FAQ