How will you go faster?

[Stan Weiss]

Stan,

Can you implement a gear change compensation for each size tire? The performance difference would increase even more with the smaller tires.

Mike,
I am not sure what you asking. Do you mean the shift RPM? What I used was a file I had done for someone using their dyno data and then a guess to extend (from 5300 to 6000) it to where they were shifting and it modeled well against their time slip.

Stan

[rfoll]

"U guy have got that 60 ft to ET change relationship inverted back ward.
If you chop x off your ET. it typically also chops Y off the 60 ft.
But if you just cut the 60 ft by x amount its worth X amount at the stripe." I disagree, my quickest et is always a result of a better 60', and always a multiple of the 60' difference. I also have stacks of time slips to show this. We are talking about acceleration measurement, not leaving 5 minutes early for an appointment. For the record the exact quote from the book is "Normally a variation in the 60-foot time creates two to three times as much difference in the overall ET." I had been observing this for years and was pleasantly surprised to see it in writing. Unfortunately he doesn't go on to explain. Inquiring minds want to know.

[1980RS]

This is interesting with the shorter tire having a better 60ft. time. If that's the case why did my 60ft's get better with a taller tire?.
Always ran a Biased 28X9" tire, switched to a 30X9" radial slick and the 60ft. times dropped. Tested this several times and the results were the same.
Best 60ft time with my 28X9's was in the 1.55 range
Best 60ft time with my 30X9's was 1.48

Is the radial that much better?

[Stan Weiss]

My simulation was done with only a change in tire size.

In other words there is / was no changes made for any difference the tire size might have for traction.

Stan

[289nate]

According to info in a book "How to hook and launch", a tenth at the 60' translates to nearly 3 tenths at the stripe.

To test the concept, I compared the same car but with different diameter rear tires.
The torque curve and gears were the same.

Tire size.........24".........25".........26"
Time 60ft.......3.501.......3.955......4.587s
Speed 60ft......40.66......39.10......37.27mph
G force 60ft....1.173.......1.125......1.080g
Time 1/4........9.013.......8.321......9.080s

The smallest tire (like a shorter gear) increased the G force, increased mph, with best 60 ft time.
But it did not produce the best quarter ET.

The largest tire (like a taller gear) reduced the G force, reduced mph, with worst 60 ft time.
It also did not produce the best quarter ET.

It becomes apparent that simple observations produce inaccurate results and that the
whole problem is more complicated than what meets the distant eye.

Are those 60 ft times in seconds??? I am assuming this is a computer simulation.

Edit: somehow I didn’t get all the new posts before my reply. Lol

[6.50camaro]

This is interesting with the shorter tire having a better 60ft. time. If that's the case why did my 60ft's get better with a taller tire?.
Always ran a Biased 28X9" tire, switched to a 30X9" radial slick and the 60ft. times dropped. Tested this several times and the results were the same.
Best 60ft time with my 28X9's was in the 1.55 range
Best 60ft time with my 30X9's was 1.48

Is the radial that much better?

The best I can say is your engine torque, the converter flash and gearing worked with the 30" tire. This allowed you to take advantage of the 6.25" greater roll out of the 30" tire. for every tire revolution you went 6.25" farther. Break that down more in 60' the 30" tire made 7.47 revolutions and the 28" tire made 8.18 revolutions. If your engine torque, converter flash and gearing allowed you to maintain the same tire rpm thru the 60'. The 8.18 revolution of the 28" tire you would go 64.75' in1.55 seconds with the 30" tire. So you hit 60' sooner. All the math aside your combination is better suited for the 30" tire. Dan

[rebelrouser]

"U guy have got that 60 ft to ET change relationship inverted back ward.
If you chop x off your ET. it typically also chops Y off the 60 ft.
But if you just cut the 60 ft by x amount its worth X amount at the stripe." I disagree, my quickest et is always a result of a better 60', and always a multiple of the 60' difference. I also have stacks of time slips to show this. We are talking about acceleration measurement, not leaving 5 minutes early for an appointment. For the record the exact quote from the book is "Normally a variation in the 60-foot time creates two to three times as much difference in the overall ET." I had been observing this for years and was pleasantly surprised to see it in writing. Unfortunately he doesn't go on to explain. Inquiring minds want to know.

Yep I got a stack of time slips that show the same thing. On the same day with same conditions and same MPH If the 60 foots pick up a little the ET picks up as well. MPH is an indicator of horsepower. I have to run a 10.5 tire and have a big engine 540CID so starting line on a hot day is not always as consistent as I would like.

[rebelrouser]

My simulation was done with only a change in tire size.

In other words there is / was no changes made for any difference the tire size might have for traction.

Stan

It is not only traction, gear ratio multiplies torque, tire diameter affects the amount of torque being applied at the rear tires.

[289nate]

Most of the class racers seem to focus almost entirely on the 60 foot and 1/8 mile times. This is how they can get a surprisingly good ET for the mph. Even with a manual transmission.

I have had a slow 60 ft time run a good mph. But I’ve never had a bad 60 turn into a good ET. Started with 2.1’ish 60 ft times back in the day. Got down to 1.5’s. It was never a 1:1 ratio between 60 ft and ET. More like 1.5-2. Never saw close to 3. New combo should have potential for 1.3xx. But it’ll take some work on my part running a manual.

[Mike Laws]

Stan,

Can you implement a gear change compensation for each size tire? The performance difference would increase even more with the smaller tires.

Mike,
I am not sure what you asking. Do you mean the shift RPM? What I used was a file I had done for someone using their dyno data and then a guess to extend (from 5300 to 6000) it to where they were shifting and it modeled well against their time slip.

Stan

Stan,
As tire diameter is reduced, the effective gear ratio (ring & pinion) provides for a higher engine RPM.
In your example: If the gear ratio with the 30" tire was optimal for engine RPM, the engine will be beyond it's best performance RPM with the shorter tires. I would expect even better performance by using a lower (numerically) ring & pinion in order to maintain the best engine RPM.
I thought there might be a formula for ring & pinion change that relates to tire diameter.
Make better sense?

[n2omike]

Always ran a Biased 28X9" tire, switched to a 30X9" radial slick and the 60ft. times dropped. Tested this several times and the results were the same.
Best 60ft time with my 28X9's was in the 1.55 range
Best 60ft time with my 30X9's was 1.48
Is the radial that much better?

Yes. On a well prepped surface, the radials ARE that much better.

[Stan Weiss]

Stan,

Can you implement a gear change compensation for each size tire? The performance difference would increase even more with the smaller tires.

Mike,
I am not sure what you asking. Do you mean the shift RPM? What I used was a file I had done for someone using their dyno data and then a guess to extend (from 5300 to 6000) it to where they were shifting and it modeled well against their time slip.

Stan

Stan,
As tire diameter is reduced, the effective gear ratio (ring & pinion) provides for a higher engine RPM.
In your example: If the gear ratio with the 30" tire was optimal for engine RPM, the engine will be beyond it's best performance RPM with the shorter tires. I would expect even better performance by using a lower (numerically) ring & pinion in order to maintain the best engine RPM.
I thought there might be a formula for ring & pinion change that relates to tire diameter.
Make better sense?

Mike,
The example I used was not a optimized setup. This is a street / strip car that has 3.55:1 rear gears with the 30" tires. While it was shifted @ 6000 RPM it crossed the 1/4 finish line @ about 4765.

Stan

PS - tire size and gear to match 30" with 3.55
28" - 3.313
26" - 3.077
24" - 2.84

[David Redszus]

How can a car with a 60 foot above 3.5 seconds be in the 9.s?
Erland.

Erland
We have to consider the effects of all gears used.

The posted results were determined using a specific vehicle torque curve, gear sets,
rear end ratio, weight, air density, aero and rolling resistance.

It did not include the effects of a torque converter. The results are for relative comparison and
not expected to be completely accurate.

A tire size is a gear, and a smaller tire is a shorter gear. But too short is not helpful. Neither is a gear
that is too tall.

[David Redszus]

Yes. On a well prepped surface, the radials ARE that much better.

Tire performance is another bag of worms.
A tire is a gear, an air spring that changes with pressure, and comes with various compounds that change with temperature.

A lot of time and money has been spent testing tires. And the job is far from finished.

[hoffman900]

Yes. On a well prepped surface, the radials ARE that much better.

Tire performance is another bag of worms.
A tire is a gear, an air spring that changes with pressure, and comes with various compounds that change with temperature.

A lot of time and money has been spent testing tires. And the job is far from finished.

We know from road racing that radial slicks are worth a few mph in trap speeds over bias ply slicks.