Tire Size Suggestions

I'll be putting new tires on the Mach 1 this spring and I'm looking for some advice. I prefer the stock old school look so I'm running 15"x 8" Magnum 500"s and BFG Radial TA's. I'm debating between 255x60, 275x60 or 295x50. I'd love to see some pictures of any of these 3 sizes on an 8" wide rim if you have it. I know that a 295 on an 8" rim is pushing it but BFG states 8"-10.5" rim width for that tire.

Here is mine when I had BFC Comps. 245 on front and 295 on rear on stock wheels. The 295s will look bulgy in stock wheels but they work. The 295s fit with no issues.

Thanks for the great pictures, beautiful car! Was stock size magnum 500's not 14"x7"?

Randyi00 said:

Thanks for the great pictures, beautiful car! Was stock size magnum 500's not 14"x7"?

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Stock 15" 500s. I don't know if they were original but the Marti indicated it came with Magnums.

Randyi00 said:

Thanks for the great pictures, beautiful car! Was stock size magnum 500's not 14"x7"?

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Factory 71-72 Magnums were 15X7

I'm running 255/60 in the front and 275/60 in the rear on 15X8 wheels.

I run 245-60×15 front & 275-60x15 rear
American Racing Aluminum version of Magnum 500's

Well, I'm stuck in the 14" wheel size group. I have 235-60-14 on Magnum 7" front and 245-60-14 on 8" rear and that's plenty of tire for spirited cornering.

I know tony's got you covered on what you asked for, but you could always get a set of 15x10 Magnums for those 295s.

I went with Cragar S/Ss 15x8 fronts, and 15x10 rears (with 5.25" backspacing). The front Cooper Cobras are 245/60R15s and the rears 295/50R15s. (for some reason, the letters on the fronts try to 'brown-out' after time, and I wound up having to sand them with some 400-grit to make 'em white again - can't wait to burn off the rears so I can get some proper BFGs on it). Yes, those are the old school Lakewoods I found when I first got the car - 'blasted and repainted, then threw them back on)








There are a few guys with the 15x10 Magnums floating around - it's a really cool look!

Good luck!

Hemikiller said:

Factory 71-72 Magnums were 15X7

I'm running 255/60 in the front and 275/60 in the rear on 15X8 wheels.

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Those wheels and hub caps look very cool. I like them.

Mister 4x4 said:

I know tony's got you covered on what you asked for, but you could always get a set of 15x10 Magnums for those 295s.

I went with Cragar S/Ss 15x8 fronts, and 15x10 rears (with 5.25" backspacing). The front Cooper Cobras are 245/60R15s and the rears 295/50R15s. (for some reason, the letters on the fronts try to 'brown-out' after time, and I wound up having to sand them with some 400-grit to make 'em white again - can't wait to burn off the rears so I can get some proper BFGs on it). Yes, those are the old school Lakewoods I found when I first got the car - 'blasted and repainted, then threw them back on)

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There are a few guys with the 15x10 Magnums floating around - it's a really cool look!

Good luck!

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I really like the look of the 295's on a 10" Magnum 500 but they are near impossible to find in Canada and ordering from the US would end up costing me about $600 per wheel.

Cleveland Crush said:

I run 245-60×15 front & 275-60x15 rear
American Racing Aluminum version of Magnum 500's

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That's a beautiful car and I really like the look of the 275's on the rear. Thanks for the pictures.

Hi Randy,

My 2 cent's worth. Ok, you dig the old school 15 inch look thing. (all due respect to the 14 inch rim guys) All good. If your chasing the Magnum 500 rims with the white lettering muscle car tires scene, then sorry, the bad news is living in Canada or Australia, or anywhere else in the World other than America, is going to rip your pockets off, money cost wise, as current inflation/ import/ shipping/ taxes/ dollar exchange rates have gone crazy. Doesn't matter what size rims or tires you're chasing. Sorry, but if you can't pay, you can't play. That said, i went for the killer combo. Handling, performance, and knockout looks.

The happy medium with minimum issues with the '71 to '73 guys is 8x15 rims all 'round with 245x 60 tires up front and your choice of 245x60/255x60/ 275x60 tires out back. The interesting thing is those last three tires mentioned, have a different rolling radius due to the different overall diameter of each tire (the 275x60 tires having the biggest overall diameter with a larger height sidewall).

In my case, i went for the killer combo and got 15inch Magnums. That is 8X15 rims up front and 10x15 rims on the rear. Tires wise, it had to be 245x60 up front and 295x50 out the back. So what do i get with this package? I get fantastic handling and performance. I get decent plug and play for the fit up with not too many bad mod issues. I get very close to the exact same rolling radius for front and back wheels, and lastly, i get the killer look.

As Tony mentioned above, you can get away with putting 295x50 tires outback on stock rims (8x15 rims i assume), but it is not recommended. I have not experimented myself, but running 255x60 tires up front (a wider tire) means you loose some handling performance. Correct me if i'm wrong here guys.
Eric and i have talked about rear wheel rim offset issues in the past. That's important if you end up running 10x15 rims with the 295x50 tire combo. My 10x15 rear Magnums have a 5 inch back space. This enables you to fit the wheels up with minimum to no wheel arch rubbing issues. The negative trade off is you have to install heavy duty rear springs to lift the car up a little at the rear for clearance, but get a killer look with a slightly jacked up arse end and a fairly lowered front. A great stance in my opinion. I was running 15x8 Magnums up front with 245x60 Mastercraft tires. Then,15x10 Magnums at the rear with 295x50Mastercraft tires. I was getting the odd rare, rear wheel arch lip rubbing issue with that setup, but recently have switched to Vitour Galaxy tires (same sizes as the Mastercrafts), which have a more rounded shoulder to them. This has completely eliminated any rear wheel rub issues i had before. I am very happy with them as such all 'round. They are much cheaper to buy than the other popular brands like Mastercraft /Cooper Cobra/ BF Goodrich etc.

See my pic below with the previous Mastercraft setup. Hope that all helps,

Greg.

What a nice set of many different wheel and tire configurations in this thread. I know the OP asked for thoughts beginning at 245 wide tires. I am fine with that, and although I fall into a lesser range numerically, I think visually I strike a balance that takes into consideration the positive impact of less unsprung weight on both handling and acceleration. On both our 1969 Shelby GT500 and our 1973 Mach 1, we are using Magnum 500 15 x 7" wheels (I believe original on only the Shelby, added later with the Mach 1 which were originally E70 x 14 bias ply tires). They are now running with 235R60 x 15 tires radial tires on the Mach 1, and old school reproduction Goodyear Polyglass GT F60 x 15 bias ply tires on the Shelby.

Now, at this point I will be the first to say the Shelby handled far better with radial tires on it. I intentionally found a set of reproduction Polyglass GT bias ply tires because that is how the car initially came when new, and I wanted to stick with a high degree of conformity to the original vehicle - just because. That said, when the day comes the Shelby needs new tires I will select a nice set of radial tires for it in P235R15. I have heard that there is one reproduction tire now offered in a radial version of the Polyglass GT. If so, that is how I will go. If not I will look for the best radial tire suited for the Shelby.

Anyway, I found long ago that as nice as wider tires are for traction, especially with TractionLok/PosiTraction, it is possible to over-do a good thing. The larger tires, and wheels, bring to the table higher weight. Weight in the wheels and tires wreak havoc on overcoming inertia when beginning to spin the powertrain up in motion. And, when it comes to handling, less unsprung weight is always better than more unsprung weight. I, admittedly anecdotally, feel anything larger than G60 x 15 (or radial equivalent P235R60 x 15) is beginning to push into the area of more unsprung weight than I wanted to have to deal with. That said, the F60 x 15 tire on the Shelby is akin to a P225x60, a little smaller than the P235R60 tires on the Mach 1 that originally came with 14" wheels. Long ago I ran with a set of a friend's G60 x 15 wheels and tires on my 1969 Mach 1, and the inner fender & quarter metal rubbed/cut into the outer parts of the rear tires. I have not had any issues with the F60 x 15 tires on the Shelby. It is possible G60 x 15s would be fine on the Shelby, but I opted to err on the side of caution. They still look plenty meaty and do good job keeping me planted on the pavement. I will more research on fitment before replacing the tires on the Shelby, and if I can get away with P235R60s that is what I will get.

So, finally, we got to the end of this post. If nothing else, the tires and wheels on out 69 Shelby and 73 Mach 1 look great, and handle well. Although I do not track these vehicles, nor pretend to track them on public roadways, I can tell what works well both aesthetically and with real world performance. I qm a happy camper.

Nobody ever talks about unsprung weight - you make a good point. However, the few pounds in difference per wheel are more than offset by the extra traction provided by larger contact patches of superior tires (radials vs. bias, as you mentioned), which (in my opinion) equates to negligible effects to be noticed by the average driver.

I admit that I have no basis of comparison, considering my Mach 1 was a rusted mess when I got it (not running or driveable in the least). I have no appetite for going back to the 195/70R14 'pizza cutters' that came with the car, other than for a photo-op. All things considered, mine handles VERY nicely... especially with all of the traction additives I've gone with: sub-frame connectors, bigger front sway bar, rear sway bar, heavy-duty springs, KYBs, wider tires, and even the old-school Lakewood traction bars.

Now, if you really want to talk about the effects of unsprung weight, I would share my experiences with my Jeep. Switching from 31x11.50 mud tires on 15x8 steel rims (steel belted radials weighing-in at roughly 65 lbs per wheel) compared to the 33x15.50 TSX Super Swampers (8-ply steel belted bias tires weighing-in at almost 130 lbs per wheel... 76 per tire, 48 per rim) had huge impacts. Off road traction was phenomenal, however braking and acceleration suffered greatly. I've further muddied the waters by upgrading to 35x12.50s Super Swamper Radials on 15x10 aluminum rims (weight savings of roughly 20 lbs per corner over the 33" TSXs), which should increase on-road traction (more siping on the tread lugs, and being radials should have an impact) along with less unsprung weight. I'm also upgrading to power brakes (rather than 'just' mechanical disc/drums). Even though I know how the Jeep drove before all of the things I'm doing to it now, it's going to be a whole different experience, since I've also swapped the I-6 & 4-sp for a V8 & automatic as well. Much like with my Mach 1, my Jeep's going to be like a whole new car when I finally do get it back on the road. (sorry for going so far off topic)

Unsprung weight is important but as @Mister 4x4 mentions, the delta weight is relatively small. Unsprung weight has to be looked at as percentage of sprung weight. So, let's assume the sprung weight including axle, leaf springs, brakes, wheels and tires is about 350 lbs. I could be short or long. The weight of our cars in the rear is about 1,800lbs - that's mine with driver. That gives a ratio of 19.4%. If say, you have bigger tires and so bigger wheels (assuming they are all steel), maybe you are adding an additional 30 lbs (way too much). Going to our sprung vs unsprung ratio that will bring us to 21.1%. I am making a lot of assumptions in this calculation but the point is that unless you add a significant amount of wheel/tire weight the difference will be too small too notice. Just going to alloy wheels and disc brakes reduces unpsrung weight significantly.
The ratio at the front will be more critical since the unsprung weight is significantly less than the rear, but the tire size at the front is a lot smaller.

PS: I am just reading a book by Fred Puhn that discusses all this stuff.

Wider tires do not always mean better traction. There's a certain amount of downforce on each tire; with wider tires, the force per square inch becomes smaller, and thus traction may be reduced, particularly in cases of hydroplaning. What's really important is the tire compound and its friction coefficient with the ground.

Some interesting points to this blog. Which brings me to something I've thought of for many years now. Back when "Mags" were first conceived, they were, in fact, made of magnesium, stronger than the steel wheels they replaced, while offering less unsprung weight. I"m sure there is also an aspect of brake cooling to a spoked design. As the custom wheel craze progressed, the wheels were less expensive to produce, when aluminum was used, and it continues to be so today. Yet, some custom aluminum wheels are actually heavier than the factory wheels they replace. And so it is, that many wheel combinations used today reflect more of the owner's taste in looks, than a pragmatic performance choice

I'm went with 245/60/15 on7s up front and 255/60/15 on 8s out back. I did the 7s and the 8s for the staggered look. Sidewall bulge is a pet peeve of mine. 245/60s on 7s and 255/60s on 8s look about right. The 275/60s just have way to much bulge in my opinion. I feel the 255s put a flatter foot print down do to the sidewall and tread being more square.

Cleveland Crush said:

I run 245-60×15 front & 275-60x15 rear
American Racing Aluminum version of Magnum 500's

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I’m sold on that look too, your car’s stance is exactly what I’m going for. I just went to DT and ordered the same BFG setup. I’m running all 4 @ 15x7’s with 245/60/15 up front and 275/60/15 in the rear. Thanks for the pictures.

Your wheel and tire combo looks great! Your paint is pretty spectacular also, did you lay it out yourself?