Anyone come across any good calculators or way to estimate what tire width you should have based upon how much torque your car is putting to the ground so you don't spend your time just burning your tires forever?


I'd imagine you'd want your torque curve from a dyno or at least reliable software, TC stall speed, TC torque multiplication ratio (whatever that thing is called), rear-end gearing.... Not sure what else...


I just realized that with the torque numbers that all the software is estimating for my top-end build, and my 700r4/4L60e 1st gear, 355 rear end and 235 or 245 (can't remember) width rear tires, I'm not going to be able to remotely take advantage of the torque but I don't really know what width tires I theoretically SHOULD go with to put the power to the ground. (I screwed up and bought wheels and tires before I figured out my whole combo because the car still had the original tires from 1979 on the fronts and they scared the crap out of me and I didn't want to die by having one blowup at speed so I just went to tirerack.com and clicked through the wizard as fast as I could and drove to the TireRack location in NW Indiana and had them install them the next day...)

-I realize that the width of tire that's actually going to fit is going to drive this decision more than anything else, but I'm looking to understand the theory and any "rules of thumb" for torque vs. tire width...


Adam

 

When i first installed my 700R4 in the late 80's I had 355 ci and it ran pretty good with 3500 stall and 4.11 year end manual lockup in 4th gear without any kick down function. I started out with 17X11 rear wheels with 295 width.

Later on the SR 383 got installed and i went up to 315 and then 335. traction was a problem and 700r4 had lost it's appeal and I went to TKO600

Shown on differrent 3000 mile trips because of the front tire size change.

 

Just to complicate matters, tire diameter plays a big role in contact patch area.

 

What?!? How? Please explain.


Adam

 

What year Vette?

What size rims when you were on 335s? Not the 17" x 11", I imagine.


I've got 235R50 18s on it now; 8.5" width rims... SIGH... screwed that purchase up...



You can now buy a 2.84 ratio first gear for 700r4s / 4L60es; they're like $550 plus the labor to have someone else install it, becuase I'd never attempt that myself. -I'm hoping that having a 4L60e and the TCI EZ TCU computer and possibly paddle shifters in my future means that 1st gear doesn't HAVE TO be such a big deal as I have precise control over when it shifts.

Monster wanted $650 EXTRA to put the 2.84 gear in the transmission and I figured there was NO WAY that was worth it to me. I'll have fun burning tires. -I'd rather pay $650 for a traction control computer and drive shaft RPM sensor than pay that for a lower gear in my transmissions...



Adam

 

Drag racers routinely run very low pressure in the rears for more contact. Then centrifugal force would keep the tires round at speed. It's just a matter of pressure in the tire equaling the weight of the car. 30 PSI only has one half the contact area that 15 PSI has. Sidewall rigidity comes into play, but not as much as pressure. Back in the days when I was a stupid kid that did street racing, we would always reduce air pressure before setting up.

 

Adam, a taller tire of the same width will have more rubber on the road because of tires bending. Steel wheel on a steel track is a different story.

8.5 inch wheel can maybe use up to 275 width. You have to go to tire rack and dig into specs and see the recommended wheel width. I have 12 or 13 inch rear wheels and 9 or 10 inch fronts. They used to be 11 and 9 inch.

My vette is a 79.

I had the what is it 3.08 1st gear and 4.11 for nearly 20 years. you get through first gear so fast it is of very little matter. It is second where the motor get the car really moving. The first is to low and second is too high. It was not a well thought out endeviour.

 

There are way too many factors to consider for any recommendation. Like stated already, inflation pressure plays a big roll in the contact area, as well as weight, compound, tread depth, etc.

 

Hit the nail right on the head. When I had my 700r4 I found 1st a complete waste of time. Roll maybe 10 feet before shift to second.

Anyway, I had 295 50 15's at the time, and would leave the stop easy, shift into second easy,....then nail it. When the 406 came onto the cam....the rear of the car would hula hula. My soft shift approach proved to me the shock of the gear change was not the reason I was loosing traction. It was the tires being over powered by the engine.

I went to 295 55 15 MT drag radials, which are a slight bit taller, but the big difference is the R-2 compound. No more hula hula,...and pretty much the same size tire.

 

It is more about the tire compound. A 275/50/15 MT drag radial will hook much better than 295/50/15 BFG tire. Even though the BFG is wider

 

A great, great tip! I just ran across PaulDana's 1979 C3 tire sizing thread and it answered pretty much all my questions around max size and appropriate back spacing.

I can't believe that the tire compound could make up that much difference...

There's no way I'm going with a 15" tire; 18" for me all around.

From what I have gathered so far, for traction you want softer compounds; low rolling resistance tire compounds (for fuel economy) are generally harder so make a decision there.


Changing my wheels and tires is certainly far away right now but my plans would be 18" all the way around with 8.5" width front wheels and 235-255 tire widths with 10" wide wheels on the rear with 4" back spacing and 275 or 285 /40 / 18s with 5" back spacing.

(Or if I get a hell of a deal on some 17" wheels I'd probably go that route but I really like a low profile tire with a stiff sidewall.)


Adam