Sticky #8: Size options when upgrading tires and/or wheels

ttam23, I have Michelin Pilot Sport, 235/40 ZR 17 and 335/35 ZR 17 on a narrow body Pantera with a low stance. No rubbing issues except the rear part of the front inner fender when steering wheel is turned max. Fender lips are rolled, I don't know if the tires would rub if fender lips weren't rolled

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Looks nice. I like the set up.

I always find the side view of these cars interesting.

The clearance under the front radiator support always looks huge in the pictures.

On my car if I make a fist, if I hold it vertically, it will not clear. I have to turn it horizontally to clear.

Maybe I should check the size of my hands? Big Grin
TTAM, its not just the OD of the tire but also the section & tread width that needs checking. About 9.5" wide tread widths can be accommodated under stock front fenders. But to do this along with removing the spring spacers AND pulling the wheels back for additional caster (always a good thing on high speed cars), there probably will be light contact in a variety of areas. First will be the wheel arches- the fender lips MUST be rolled under. Next is when turning left or right at full-lock, the edge of the tread may contact the left cowl drainpipe; make it oval with a big hammer in the required area. The tread may also touch the inner fender panel behind the brake hose bracket; again, a shallow pounded- recess will be needed. On the right side, the wiper shield may contact the tread in turns; remove and reshape; one vendor has reworked shields in which the peak has been cut away and a flat area substituted, to ease this mod. Finally, with slightly lowered cars, there may be contact at the extreme lower edges of the inner front fender near the radiator support bracket.

Not all these areas in all narrow-body Panteras will normally be needed, but they might- be ready. Our '72 L had all the above in contact. As a last mod, check very carefully the clearances between the flexible brake hoses and front tread edges; on some lowered, caster-increased Panteras, the right flex hose gets uncomfortably close or touches. Wearing through the rubber line could really spoil your day! And if you've replaced the stock lines with stainless steel, the tough ss line jacket will shave expensive rubber off the inner edge of the tire.

Running a max-width front tire as above frees up options for a larger width REAR tire along with decent handling. Running less than 9.5"-width fronts AND 335-width rears will INCREASE understeer that probably cannot be otherwise adjusted out with different swaybars or coil-over shocks. Or, you can go slow and handling issues will not show up. In back, selecting a 26-1/2"-26-3/4" OD tire will allow the stock speedo and odometer to work accurately.

Lots of things to consider when you attempt to improve on what Dallara gave us in 1970.
quote:
Originally posted by George P:
The front wheel well openings were rolled by the factory on the Pantera L, but not the earlier Panteras.



Mine are not rolled. It is #4460. 9/72 build date. '73L model.



I have the 15" Campis 8/10 on the car with P7 225-50-15 in front and 285-55-15 on the backs.

Talk about maxing out the wheel width on a tire? Yikes.

I do like in particular that tire on the fronts because with removing the spring spacer that tire lowers the front of the car noticeably without the car looking slammed.

The nose is down there with the go carts, so I don't think it is unfair or derogatory to call it an Italian go cart at all?

It's about 41 inches to the roof with the spring spacers out of there.

I am going to change out the rear tires though to the MT LT 26 x 12R15 tires.

I think they are a better fit cosmetically to the rear and aren't as stressed out on the 10 inch rim as the P7 is.

I can't immagine that P7 on an 11" rim. Not arguing that the manufacturer isn't saying that it's ok or not.

I just know on the 10" rim vs. 285 relationship looks very precarious.


I also had bad experiences with BFG on maxing out the tire to the maximum recommended wheel width.

I had two tires split the treads and throw pieces of them off down to the belts on the carcass.

BFG refused to warranty them saying that it was a mis-application by me because it was not the RIM DESIGN WIDTH. Their chart clearly showed it was the maximum recommended width but they said that voided the warranty since it was more than the DESIGN width.



I can testify that maximing out the tire like that virtually eliminates any flex in the tire wall of the P7 which kind on makes me wonder why even bother with a radial back there at all. The fitment negates the value of the radial all together?

To me that is much more of what you would do on a race car rather than a street car, meaning there is NO play in the tire in the rear as a result...like a bias racing tire would be.


Voiding the warranty on a tire is a joke anyway. When it comes down to it you are buying a new tire because the warranty was based upon list price and a pro-rated number on it. No one pays list price on tires.
I have read this post multiple times and every time I get dizzy! I use to work with dimensions and rattling off reams of figures was the norm, but nothing as boggling as this.

I think I have begun to grasp the concept of wheel offsets, tire widths and possibility of scrubbing, but I just wanted to verify the few basics, please correct me if I am wrong

To me, offset is the value of a wheel I am interested in and to determine it, I can easily measure wheel width and backspace.
offset = backspace - wheel width/2.

The wheels bolt to the lug stud flanges and this width should be the starting point for any wheel evaluations. From online sources, I found the front track given as 57” with the OEM 7” Campy’s and their 0.25” offset. From this I gather the front flange to flange width would be 57.5”. Is this correct thinking?
Track = 57.5” - 2 X offset

Using the track and the tire sectional width, I can figure a tire outside width. For the OEM with 185s, that would be 64.3”.
Outside = Track + sectional/25.4

If correct in my thinking, I can use the flange width and the offset of the desired wheel to figure the new track. For example, in George’s post with the wheel table, he stated the 8” clone Campy’s had an offset of 0.86”, thus given a new track of 55.8”. With a 245 tire, one can expect rubs. This combo would have a width of 65.4” (or have the tire about 0.6” farther out than OEM combo). Going with the 9” clone and its 1” offset, the outside width would reduce to 65.1” and be OK.

My comparison of using the OEM 8” with their 0.75 offset reduces the track to 56” and with the OEM 225 tires had the outside width of only 64.9”.

So it appears to me that an outside tire width of less than 65.4” is the limit. I am still dreaming I’ll use the OEM wheels, but this implies that the BFGoodrich TA 215/60r15 93S for 7” I was considering might scrub with its outside width of 65.5”

(oh, I did make an excel sheet to do the crunching)

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You're close!

The problem with your calculation is, wheel width is defined as "the measurement from the inside of the outer tire bead lip to the inside of the inner bead lip. Your calculation would be "off" by 1/2". I'm sure what you meant by "wheel width" was the total distance across the wheel (outside edge to outside edge) but that requires someone to interpret what you meant by wheel width. The problem I have with the diagram above is, wheel width and rim width are interchangeable terms. You're always better off measuring wheels the way wheel manufacturers do.

Offset = (backspace minus 1/2") minus half of the wheel width, converted to millimeters. As an example, an OEM 15" x 8" campy has 5-1/4" backspacing. To convert the backspacing to offset, the equation is: (5-1/4" - 1/2") - 4" x 25.4 = 19mm (actually it's 19.05mm but offset is always rounded to the nearest mm).

The single most mis-understood aspect of wheel measurements (and there are many) is how to adjust your measurements for a tire bead lip that's less than 1/2" thick. For the purposes of calculating backspacing, you always assume your tire bead lip is 1/2" thick, even if it's not. That's the industry standard. As an example, If HRE made an 8" wheel for the front of a Pantera and used OEM backspacing specs (5-1/4" BS), the backspacing would actually measure 5" if you measured it with a tape measure, because HRE's "lips" are only 1/4" thick. The invoice would say 5-1/4" BS / 19mm offset however.

You can see where problems arise. If the person who purchased those HRE wheels didn't know about the 1/2" rule, he might tell his friend "my wheels are 8" wide on the front and I just measured the backspacing for you". "It's 5", so you should order the same because they're perfect"!
The Tech Service Bulletin 9 that describes the factory/dealer method for 'rolling' front fender lips for more tire clearance, is dated Nov 2, 1973. So I wouldn't expect earlier unmolested Panteras to have factory-rolled fender lips. It's quite easy to do; I've seen it done in a parking lot using a ball bat with no wheel removal. Took about a minute each fender, with no paint cracking.
quote:


Originally posted by JFB #05177:

... I have read this post multiple times and every time I get dizzy! I use to work with dimensions and rattling off reams of figures was the norm, but nothing as boggling as this ...



Joe

I don't want your mind to be boggled.

There's a formula I use, when determining how far a tire's outer sidewall extends outwardly from the hub's wheel mounting surface:

(tire cross-section ÷ 2) - off-set (negative offsets are added)

The front tire's sidewall is flush with the fender's edge at approximately 126.5mm

The rear tire's sidewall is flush with the fender's edge at 150.5mm
Just to confuse the wheel and tire issue even more; sometimes Pantera owners have tire rubbing problems and it has nothing to do with wheel offset and tire size/manufacturer at all. It's caused by simply having aftermarket shock absorbers. The Pantera's suspension travel is limited by the shock absorber. The OEM shock absorbers have less travel than most aftermarket shock absorbers, even though the overall length is about the same. If you only have rubbing when the suspension compresses and you have aftermarket shocks, it can usually be eliminated by installing an additional bump rubber in the shock absorbers.

I have 18"x12.5" rear wheels with 335/30-18 tires and height adjustable Koni gas shocks (from Pantera East) on my stock bodied Pantera. Initially I had a rubbing problem with the inside of the tire rubbing against the upper frame section. After installing an extra bump rubber, I have ZERO rubbing and the rear suspension feels no different than it did before.

Credit for this tip goes to Dennis Quella.
Thanks Lui, Panterror, & JTPantera. That was exactly what I was looking for.

I received a Christmas card from Pantera Performance in Castle Rock, Colorado a couple years ago with a Pantera running some really big shoes. I don't remember how big the wheels and tires were but I remember thinking that the cars midsection (cockpit area)looked like it sat really high. It had a pretty large front air damn which was low to the ground but being either a GTS or narrow body there were no ground effects in the cockpit area to make it appear lower.

I was concerned that 18" front wheels and 19" rear wheels may give you that same high cockpit look. However, from the pictures posted I don't see that with the 18's and 19's. Thanks for posting.

I will see if I can find that Christmas card (I probably tossed it) so I can post it.

Devin
The front & rear wheel arches & chassis of each Pantera model are designed for tires of specific diameters.

In this picture 6018 had 18" front tires (245/35ZR18) 20" rear tires (325/25ZR20). It has an Amerisport front spoiler. The lower rear control arms are level with the road, notice how well the rear tires are centered in the rear wheel arches with the control arms set that way. The front end has been lowered until the chassis is level. Since the difference in tire diameter front to rear is 1.65" (less than 2") the front tires are not centered in the front wheel arches, the tops of the wheel arches overlap the tops of the front tires. But I don't think anyone would accuse 6018 of looking too high, which is why I'm replying to your post.

If the back tires had been a little larger in diameter, closer to 27" OD, they would have filled the rear wheel arches even better than the 325's did, the rear of the car would have been higher, to level the chassis would have required raising the front of the car. That would have centered the front tires in the front wheel arches better. And the diameter of both sets of tires, front & rear, would have filled the wheel arches relatively evenly. After that, you have to consider wheel off-sets, not only for suspension geometry & rubbing concerns, but for cosmetic concerns too. You want both sets of tires to be inset from the edge of the fenders about the same. Otherwise it looks wrong. Looking at the side view of 6018, the front tires are inset more than the rear tires.

Regarding wide bodies, the ideal cosmetic "stance" of Group 4 replicas are similar to narrow body Panteras. BUT ... GT5 & GT5-S Panteras need front & rear tires which are closer to 24" diameter front & 24.5" diameter rear, because that's how the wheel arches were designed. But its not possible to find modern tires in such small diameter. So with the GT5 & 5-S don't lock yourself into the frame of mind looking for the widest tires, balance that with tire diameter. You're gonna want front tires in the 24.5" to 25" diameter range, and rear tires that are 1/2" larger in diameter than the fronts.

-G

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George,

Thanks for the picture and the great wealth of information. I agree that your car doesn't appear to sit too high. Those 20's in the rear really do fit the rear wheel well arch nicely. I never would have noticed the slight off center of the front wheels without you pointing them out.

I have searched high and low for the Christmas card that had the Pantera on it that appeared to be sitting too high, but I have not had any luck.

Thanks again for all the advice and information. It is much appreciated.

Devin
Call me old fashioned but I think the designer got it right with the wheel size relative to the body proportions. It's too bad that 15 inch tires are very limited but to my eye, much bigger wheels make the cars look a bit cartoonish. Having said that, these things are individual choices which I respect.
quote:
Originally posted by Robbie:
Call me old fashioned but I think the designer got it right with the wheel size relative to the body proportions. It's too bad that 15 inch tires are very limited but to my eye, much bigger wheels make the cars look a bit cartoonish. Having said that, these things are individual choices which I respect.


I agree. It's like me with purple hair, piercings and tatoos. It just doesn't make any sense at all?
quote:
Originally posted by Garvino: Panterror, What width of wheels and tire sizes are you running on your GTS?
Thanks. Devin


Polished Kinesis K29s, 19”x 13” (6.5" backspacing) rear and 18” x 9.5” (5" backspacing) front.
Michelin Pilot Sport, 345/30/ZR19 Rear and 265/35/ZR18 front.

Best,
K
The last couple of weeks I have been checking the availability of various tire sizes for Panteras since I am looking to replace my wheels and tires.

I have looked at 17", staggered 17" & 18", 18", and staggered 18" & 19".

I have tried to compare all the various size combinations to this threads recommended tire diameter due to wheel arch and diameter size difference from front to back.

Interestingly, the tire combination with the biggest tire selection (based on my research on Tirerack and OnlineTire) is the following:

225/40/18 front
285/35/19 rear

The 225mm tire is 8.86 inches wide and 25.09 inches tall. The 285mm tire is 11.22 inches wide and 26.85 inches tall. These fall pretty close to the recommended specs on this thread:

Front tire diameter: 23.9" to 25.0"
Rear tire diameter: 25.9" to 27.0"
Recommended greater rear tire diameter size difference: 1.7" to 2.3"

I currently am running 17"s with a 9.25" front width and 12.4" rear width. I really like the wider widths but was very impressed with the amount of different tire brands availability in the above sizes.

Just thought I would share my findings so far.

Devin
David,

I did notice that also. I just just was shocked by the enormous amount of brands/models available for the 225mm/285mm combo versus the 245mm/325mm combo.

I definitely like the 245mm/325mm combo better due to tire width, etc. They also fall within the recommended specs for appropriate sizing. However, after my current difficulty with my specific 17" tires being unattainable, my practical self says go with something that has a huge availability now so that in the future you don't have problems.

But then again who said owning a Pantera was ever practical? Thanks again - I appreciate all you help.

Devin

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