How much do bias-ply slicks expand?

GrandSportC3 · Post by **GrandSportC3** » Fri Feb 01, 2008 7:39 am

Right now, I'm running 29.5 inch tall radial slicks (not Drag Radials) and they do not expand more than 1/4 inch max...
Now, I've read (but can't find the article anymore) that bias-ply tires expand a lot more than that.. However, I don't know how to figure out the exact amount that they expand.
The reason that I need to know is because I'm thinking in switching to a 29.6 inch tall bias ply tire (ET Drag 29.5 x 10.5W - 15)
and I don't know if it will clear. Right now, I have just over 1/2 inch clearance with the 29.5 inch tall Radial slick and I wonder if 1/2 inch clearance is enough? Does anyone know?

MileHighMan · Post by **MileHighMan** » Fri Feb 01, 2008 10:46 am

Grandsport. I run that tire on my Camaro and only have about 1/2in clearance from the front of the tire to fender. 13psi, 140mph high gear burnout, nothings touching. Good Luck. Dan.

GrandSportC3 · Post by **GrandSportC3** » Fri Feb 01, 2008 10:56 am

MileHighMan wrote:Grandsport. I run that tire on my Camaro and only have about 1/2in clearance from the front of the tire to fender. 13psi, 140mph high gear burnout, nothings touching. Good Luck. Dan.

Thanks!! Then it should work for me!!

David Redszus · Post by **David Redszus** » Fri Feb 01, 2008 4:37 pm

The issue of tire growth has been debated by chassis engineers for years.

While there is a case to be made that the rotation of a tire produces centrifugal forces that make a tire grow, there is a counter argument that considers the compression of the tire due to increased loading resulting from weight transfer.

Then the tire engineers kick in with the idea of longitudinal tire distortion which might reduce the rolling radius. The the aerodynamics guys want you to consider the aero dynamic downforce effects on tire loading.

Then there are the tire designers who insist that carcass design, air pressure and tire carcass temperature must be considered as well.

Current practice is to use an ultrasonic height sensor at the axle to measure rolling radius all the way down the track.

Post by **Baprace** » Sat Feb 02, 2008 1:54 am

this may not even apply today, but 30 years ago, my Firstone drag slicks sized 14w x 32 x 15 with 5 lbs of air on 14 inch wide rims would grow approximently 2 1/2 + inches on radius at 145 mph. If three fingers (great measurement huh?

) didn't clear the vertical body panels the tires would always rub.

hsutton · Post by **hsutton** » Wed Feb 13, 2008 2:15 am

A local here has a 28" M/T 10.5S on his Mustang with about 1/2"- 3/4" at both ends of his wheelwell. The left (driver side) didn't have trouble and may have had a little more clearance but the passenger side got into the front of the wheelwell and completely chewed the tire up about a half inch from the outer edge. Made a pretty big mess out of the front of the fenderwell too. After some additional trimming to make sure the close areas had sufficient clearance he's had no more trouble. According to a friend with a data logger his 10.5W x 28" E.T. Drags grow to about 28.62" at 156mph. The static rollout of these tires is 88". That would mean they are 28.01" to start with. I'd guess they might be growing about 1/2" at 145 mph. The 29.5" tires have much taller sidewalls so they would probably grow a little more too. P.S..... Why not just go to the 28" x 10.5W tires as they bite great on wide wheels (10"- 12").