"TRUE" 35 inch tire ?

wild1joker

Well-Known Member
Joined
Mar 22, 2008
Location
fayetteville,nc
I'm looking at a new set of tires . My 315/75/16's are only 33 1/2 inches tall. because I have a 3 speed auto and 4.56 gears - I'm running 3000 rpm's at 65 mph. So I am looking for a tire that is actually 35 inches tall. Do I have to go to a 36 to get a 35 ? what tires are close to the advertised height ?
 
Buy Q78s
 
Most of the interco tires are actually larger than their quoted size. For instance the Q78 mentioned above is 35.5" actual inches
 
This is my daily driver. Any suggestions on a radial tire that is still good off road ? Q78 is Bias. A 36 Irok radial is over 36 inch? Which 37's
are the lightest ?
 
Look at a 37x12.50x16 truxxus Mt. Off the top of my head, I think they're under 70# which is less than most radial 35s and the highway ride is great.
 
How are you measuring that a 35 inch tire is 33.5 inches diameter? Please tell me you're not holding a tape measure next to the tire while it's mounted and holding up the weight of the vehicle?
 
I checked both mounted and dismounted .with the tire mounted on the vehicle - it measures 33.5 inches.... I took out the brand new spare tire and measured it = 34 and 1/8 inch. ( that is the dismounted size)
 
wild1joker said:
I checked both mounted and dismounted .with the tire mounted on the vehicle - it measures 33.5 inches.... I took out the brand new spare tire and measured it = 34 and 1/8 inch. ( that is the dismounted size)
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Saying that a 35 inch tire is 33.5 because you're measuring the loaded radius with the vehicle on the ground is meaningless. Yes, a tire is not the nominal diameter anymore when you inflate it to some pressure, and mount it at some camber, and put a heavy vehicle on top of it. It's like saying you bought a 15 inch coil spring, and then you installed it on the car and now it's not 15 inches anymore... o_O

Wrap a tape measure around the tire (not across the tire) and do the math to get diameter from circumference; that's what your tire diameter actually is. You'll be closer to your rough 34.125 measurement, which is still not 35 inches but at least it's not a meaningless loaded radius measurement.

If you're setting your gearing based on nominal tire class sizes (35 inch, etc.), you're going to be disappointed when things don't match up the way you want. That's just being realistic..

You can usually find specs on whatever tire you want, so you can find the actual diameter if you're going to try and adjust your engine RPM just from changing models of tire... It sounds like you need different gearing though, not different tires. A different 35 inch tire isn't going to change RPM that much, and you still won't know what the loaded radius will be until you buy them, inflate them, and load them up.

In other words, if you're trying to change highway RPM, you can't just put "35" into a gearing calculator and expect accuracy. ;)
 
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Nitto or toyo run very close to stated size. Bfgs in a 37 run very close to a true 35 and as said earlier most intercos run true to size if not slightly larger.
 
Fabrik8 said:
How are you measuring that a 35 inch tire is 33.5 inches diameter? Please tell me you're not holding a tape measure next to the tire while it's mounted and holding up the weight of the vehicle?
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Question relating to inertia: As the vehicle speed increases, how much would the od of a tire increase in relation to speed? I know with dynabeads/airsoft, speeds of 20+mph cause them to settle, so that tells me that the rubber carcass would also be pushed outwards from the wheel. I know it would be dependent on compound and construction.
What say ye, technical genious?
 
XJsavage said:
Question relating to inertia: As the vehicle speed increases, how much would the od of a tire increase in relation to speed? I know with dynabeads/airsoft, speeds of 20+mph cause them to settle, so that tells me that the rubber carcass would also be pushed outwards from the wheel. I know it would be dependent on compound and construction.
What say ye, technical genious?
Click to expand...

There's a lot of variables in there, so it's not an easy thing to nail down. The carcass weight and stiffness, where that weight actually is on the carcass, rotational speed obviously, vehicle weight versus lift/downforce versus force from inertia, etc. (summation of forces on the Z axis in SAE coords), some other things all have an effect. Pressure has a effect too because at higher pressures you're already taking some of the compliance out of the carcass (roughly equivalent to spring preload).
It's definitely something that is important to characterize in race tires to keep chassis height where you want it, and on circle track cars to make stagger work for your advantage. ;) That's a very different range of rotational velocity though.

You can see that OD change with your naked eye on a rail dragster, that's the best example I can think of.
 
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Ahhh... :rolleyes:
Just a random thought and an open airway to ask for answers.
 
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