Cascade Crew

izcain · Posted: Wed Oct 11, 2006 10:10 am Post subject: M/T traction

Well I was browsing on TGO and I found where a guy claims he put on 325/50/15 DR M/T on a 15X10 rim with 5.5BS and I was wondering if anyone here has done this and if so did they have to do mods to the fenderwell? I have already done some light mods to fit the 295/65/15 M/T's in there but I would like a tire that is now quite so tall. Also I have been hearing a lot lately about M/T's having trouble hooking at the track after steet driving them cause they are claiming the rubber is getting hard and will not soften up after the heating. Has anyone had this problem?

QwkTrip · Posted: Wed Oct 11, 2006 1:46 pm Post subject:

That would be a very large tire. I suspect he doesn't have enough backspacing and failed to mention how far they stick out from the side of the car and how often the fenders ride on the tread.

If my memory serves me properly, an 18x10 rim with 6.0 inch backspacing will fit the rear wheel well on some cars. I don't remember exactly which tire combo was used. However, looking at the BFG website it seems the proper match is a 285/35-R18 with overall dimensions on a 10 inch rim of,

11.6 width
26.7 height

In comparison the MT website specs out the 325/50-R15 on a 10 inch rim of,

13.0 sidewall width
11.0 tread width
28 height

That's a pretty big difference. But I think you can figure this out pretty easy. Get the specifications on the tires/wheels you have today and measure critical clearances in your wheel well. Make adjustments to your measurements for the new wheel/tire combo and you'll know whether or not they will fit.

For example, I had a '68 El Camino and wanted to stuff the rear wheel well. I measured out the critical dimensions from the wheel hub and figured out I needed a 9-inch wide rim with 5.5-inch backspacing to center the rim in the wheel well. My measurements suggested I could use a 295/60-R16 tire. I measured a bunch more times until I convinced myself to go ahead and order the wheels and tires. Sure enough... fit like a glove with finger width clearance on both sides of tires. It was kind of funny because the tire shop looked at the loose tires and thought I screwed up royal. I claimed they would fit once on the rims and they actually bet me they wouldn't. I won.... barely. Very Happy

QwkTrip · Posted: Wed Oct 11, 2006 2:27 pm Post subject:

I just had another thought. I have 17x9 with 5 inch backspacing and 275/40-R17 drag radials. Those tires sit about as far out towards the outside of the car as I would go. They actually look a little silly because the tires are on the edge of the wheel well and actually look small from the rear view. I wish I had a 5.5 inch backspacing in the rear.

But anyway, if I was trying to put the 325/50-R15 tires on my car then I would hold the outer edge where my current tires sit and try to fit everything to the inside. That means I would choose 10-inch wide rim with 6.5 inch backspacing. The question is... do you have room?

Current tire width = 10.9
New tire width = 13.0

Current hub position from outer edge of tire = [(10.9 - 9.0) / 2] + 4 = 4.95 inch

New backspacing = [(13.0 / 2) - 4.95] + (10.0 / 2) = 6.55 inch

izcain · Posted: Wed Oct 11, 2006 4:07 pm Post subject:

Well my current combo is 15X8's with 4.5 BS and a 295/65/15 M/T ET but someone was telling me that the 275/50/15 M/T Drag racdial was equivalent to a 295/50/15 regular highway tire is this correct?

QwkTrip · Posted: Wed Oct 11, 2006 7:44 pm Post subject:

All the tire dimensions are listed at the manufacturer's website. Just compare the two tires. The tire measurements are shown for a particular rim width. If your rim is different, then the tire measurements will change. A wider rim will increase width and decrease height. A more narrow rim will decrease width and increase height.

http://www.mickeythompsontires.com/strip.php?item=ETStreetRadial

http://www.bfgoodrichtires.com/specs/g-force-t-a-kdw/22.html

izcain · Posted: Wed Oct 11, 2006 8:59 pm Post subject:

Well if im reading this correct the 275 has the same tread width as the 295 only 2 inches smaller in diameter. hmmm..... Thanks for the links!

Nathan J · Posted: Wed Oct 11, 2006 9:27 pm Post subject:

I know a 325 will fit for sure with the right backspace and a little work hehe, did it to a friends camaro, took a 4 pound hammer and a big wooden stick to move the inner fenders in in front and back, took about 3 hours to make it work, to give enough room for tire growth on the top end, it did look badass lol, know that same camaro is a full backhalf car though so.
Nathan

izcain · Posted: Wed Oct 11, 2006 9:42 pm Post subject:

Do you know what rims he had as far as width and BS?

After doing some research I guess you can deduct something like a tenth off your times be removing 10 pounds of rotational mass..... if that is so going from my 295/65/15's to 275/50/15's is going to net me a 18 pound loss alone just in tire roational mass. That should help a lil I would think.

QwkTrip · Posted: Thu Oct 12, 2006 4:12 pm Post subject:

And the beauty of that is you can do it anywhere. Flywheel, driveline, transmission, wheels, ect. It's a 2-for-1 deal. The car loses weight and the rotational mass of the drivetrain becomes less at the same time. Cool

I had a 1/2 mass flywheel on a supercharged '94 Vette. The engine was definitely more willing to rev up under no load than a normal LT-1 (I had a stock '94 convertible for a short while too). Just quicker throttle response in general.