Tire width increase vs lap times: General opinions?
11-09-2011, 04:53 PM
#1
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Tire width increase vs lap times: General opinions?
Just looking for general opinions from the experiences here. What laptime improvements have you seen when increasing the tire widths on your car? Assuming a same/reasonably similar compound, if possible, to reduce the variables for this discussion. Assuming a width increase of 10 percent (or whatever percent you changed), what was the (percentage) laptime reduction? I understand there are variables such as how much of the track is corners versus straight, or if your tire width increase was also contributing to the overall suspension width (outside sidewall to outside sidwall, so to speak), etc, etc.
I'm just trying to get a better handle on the "ROI" when I get some new tires over the winter.
Thanks for any constructive information.
I'm just trying to get a better handle on the "ROI" when I get some new tires over the winter.
Thanks for any constructive information.
11-09-2011, 05:07 PM
#3
Tech Contributor
Hi Mike,
As you know, it is generally agreed that wider is better. We would even go so far as to assert that, with the torque and weight of a Corvette, it would be difficult to fit tires that are "too wide".
That said, the biggest gains in lap time will be achieved by refining BALANCE of the racer, and some of this refinement might be found in fitting wider tires at one end, or the other, or BOTH ends. (The rear might benefit from the additional power-on traction, while the front may gain something from the wider track to which you allude.)
Of course, the tricky part is that the converse is also true: One can screw up the fine balance of a car that uses 9½" wheels on all four corners by changing to 11" wheels in the rear. The result will be HIGHER lap times.
Our tire testing typically involves trying different compounds of tires, against different suspension settings, and has never included back-to-back comparison of solely tire widths. So this is only an educated guess:
IF the camber and toe settings "like" the wider tire, and IF the F-to-R balance of the car is already very good, then an additional 1" in tread on each corner could be good for 1 to 2 seconds on most tracks. Of course, like everything else, the driver would need to fully utilize that additional grip.
(I probably should have simply agreed with Jason, because he is so right!)
Ed LoPresti
As you know, it is generally agreed that wider is better. We would even go so far as to assert that, with the torque and weight of a Corvette, it would be difficult to fit tires that are "too wide".
That said, the biggest gains in lap time will be achieved by refining BALANCE of the racer, and some of this refinement might be found in fitting wider tires at one end, or the other, or BOTH ends. (The rear might benefit from the additional power-on traction, while the front may gain something from the wider track to which you allude.)
Of course, the tricky part is that the converse is also true: One can screw up the fine balance of a car that uses 9½" wheels on all four corners by changing to 11" wheels in the rear. The result will be HIGHER lap times.
Our tire testing typically involves trying different compounds of tires, against different suspension settings, and has never included back-to-back comparison of solely tire widths. So this is only an educated guess:
IF the camber and toe settings "like" the wider tire, and IF the F-to-R balance of the car is already very good, then an additional 1" in tread on each corner could be good for 1 to 2 seconds on most tracks. Of course, like everything else, the driver would need to fully utilize that additional grip.
(I probably should have simply agreed with Jason, because he is so right!)
Ed LoPresti
Last edited by RacePro Engineering; 11-09-2011 at 05:53 PM. Reason: Additional
11-09-2011, 05:16 PM
#4
Burning Brakes
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Look for an article in Grassroots Motorsports, a few months back. They did this tire test, which they do every year. To get the straight dope on the newest tires.
One of the questions they tested was, are wider tires automactically faster due to increased grip? yes, to a certain point. and then times fell off, if you get crazy wide.
Very good article
One of the questions they tested was, are wider tires automactically faster due to increased grip? yes, to a certain point. and then times fell off, if you get crazy wide.
Very good article
11-09-2011, 05:20 PM
#5
Burning Brakes
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Ed LoPresti, do you guys make parts for high performance/racing aircraft? I'm a new pilot, and I have seen that name for high performance aircraft parts.
11-09-2011, 05:30 PM
#6
Racer
Jason's right...what's end goal? time attack, couple of suicide laps and then in? average speed over a 15 lap sprint race? average speed over a 2 hr enduro?
In my personal testing there is no real outright speed difference between a 10.3" tread tire, 10.8", and a 11.4" (A6 275-295-315). You can even throw the really wide 255 A6 in there for at least some tracks in terms of equal speed. Lots of variables though (proper wheel width, style of track, track surface, etc).
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
In my personal testing there is no real outright speed difference between a 10.3" tread tire, 10.8", and a 11.4" (A6 275-295-315). You can even throw the really wide 255 A6 in there for at least some tracks in terms of equal speed. Lots of variables though (proper wheel width, style of track, track surface, etc).
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
11-09-2011, 05:50 PM
#7
Tech Contributor
Although I am certain we have common connections back to "the old country", the only similarity between the aircraft LoPrestis and us is our common interest in aerodynamics. (Get this - they run their wings UP-SIDE-DOWN!)
Actually, I wish we were in that industry -- we might be MAKING money . . . . .
Ed
11-09-2011, 08:43 PM
#8
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Hi Mike,
As you know, it is generally agreed that wider is better. We would even go so far as to assert that, with the torque and weight of a Corvette, it would be difficult to fit tires that are "too wide".
That said, the biggest gains in lap time will be achieved by refining BALANCE of the racer, and some of this refinement might be found in fitting wider tires at one end, or the other, or BOTH ends. (The rear might benefit from the additional power-on traction, while the front may gain something from the wider track to which you allude.)
Of course, the tricky part is that the converse is also true: One can screw up the fine balance of a car that uses 9½" wheels on all four corners by changing to 11" wheels in the rear. The result will be HIGHER lap times.
Our tire testing typically involves trying different compounds of tires, against different suspension settings, and has never included back-to-back comparison of solely tire widths. So this is only an educated guess:
IF the camber and toe settings "like" the wider tire, and IF the F-to-R balance of the car is already very good, then an additional 1" in tread on each corner could be good for 1 to 2 seconds on most tracks. Of course, like everything else, the driver would need to fully utilize that additional grip.
(I probably should have simply agreed with Jason, because he is so right!)
Ed LoPresti
As you know, it is generally agreed that wider is better. We would even go so far as to assert that, with the torque and weight of a Corvette, it would be difficult to fit tires that are "too wide".
That said, the biggest gains in lap time will be achieved by refining BALANCE of the racer, and some of this refinement might be found in fitting wider tires at one end, or the other, or BOTH ends. (The rear might benefit from the additional power-on traction, while the front may gain something from the wider track to which you allude.)
Of course, the tricky part is that the converse is also true: One can screw up the fine balance of a car that uses 9½" wheels on all four corners by changing to 11" wheels in the rear. The result will be HIGHER lap times.
Our tire testing typically involves trying different compounds of tires, against different suspension settings, and has never included back-to-back comparison of solely tire widths. So this is only an educated guess:
IF the camber and toe settings "like" the wider tire, and IF the F-to-R balance of the car is already very good, then an additional 1" in tread on each corner could be good for 1 to 2 seconds on most tracks. Of course, like everything else, the driver would need to fully utilize that additional grip.
(I probably should have simply agreed with Jason, because he is so right!)
Ed LoPresti
I appreciate your intelligent and mature response (
), versus the smartass post before yours. I'm a design engineer (a couple decades at one of the big 3) and I enjoy discussing the technical details of the parts I use. As a general rule we all try to run some decent tires (width and compound), but what's the general/average curve of width vs grip? For example, I think we all agree that the C6 Z06 is a great car (and it has a lot of tire). How much of the car's cornering performance is the tire versus the other items (weight, ride height, etc) that the base C6 and Z51 models don't have? Or, take this same Z06 and put similar brand/compound tires on it, but with 10% less tread width (20-30 mm skinnier), what happens to the skidpad results? In a perfect world the answer would be simple (ie: 10% slower around the pad), but what's the actual number? Is it 8%, or 12%, or ???. I know there's no definitive all-encompassing answer, but I'm fine with educated guestimates with reasons to support that answer.
Again, I appreciate your sincere reply.
11-09-2011, 09:17 PM
#9
Le Mans Master
In my personal testing there is no real outright speed difference between a 10.3" tread tire, 10.8", and a 11.4" (A6 275-295-315). You can even throw the really wide 255 A6 in there for at least some tracks in terms of equal speed. Lots of variables though (proper wheel width, style of track, track surface, etc).
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
11-09-2011, 09:33 PM
#10
Safety Car
How is it a smartass post? He's right... most of us in TTA have been getting faster and faster going down in tire size. Less rotational weight, lower overall diameter creating a better effective gear ratio, less friction drag/rolling resistance etc.
11-09-2011, 09:42 PM
#11
Melting Slicks
Jason's right...what's end goal? time attack, couple of suicide laps and then in? average speed over a 15 lap sprint race? average speed over a 2 hr enduro?
In my personal testing there is no real outright speed difference between a 10.3" tread tire, 10.8", and a 11.4" (A6 275-295-315). You can even throw the really wide 255 A6 in there for at least some tracks in terms of equal speed. Lots of variables though (proper wheel width, style of track, track surface, etc).
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
In my personal testing there is no real outright speed difference between a 10.3" tread tire, 10.8", and a 11.4" (A6 275-295-315). You can even throw the really wide 255 A6 in there for at least some tracks in terms of equal speed. Lots of variables though (proper wheel width, style of track, track surface, etc).
My opinion is that you get to a point based on your car's weight/wheel width/power, where you have "enough tire". Anything beyond that is just dragging around extra weight.
I can tell you this, how the tire fits on the rim, how the sidewall works, tire height, sidewall height, etc. may be MORE important than just measuring the tread width.
While a wider tire might not give a faster best lap time, sometimes some additional width helps the tire run cooler and overheat less. This can be a double edge sword, sometimes better after 20 minutes of track time, but in an autocross the wider tire won't warm up as fast and is harder to get hot, so sometimes you are throwing away more than just the first run because you aren't getting the tires up to temp.
11-09-2011, 09:58 PM
#12
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Another thing to consider is that a wider tire does not inherently give you a larger contact patch. (Sometimes quite the opposite)
Usually a taller tire will give you a larger contact patch which will improve lateral grip and therefore increase cornering speeds. It can also help exit speeds/out of corner grip. This assumes proper gearing ratios for the tire height.
Depending on the track this may make a larger difference in lap times.
As stated by others, generally a wider tire will help manage heat so if you are only doing autocross, TT or Time Attack then a just wide enough (narrow) tire will be the faster setup.
Usually a taller tire will give you a larger contact patch which will improve lateral grip and therefore increase cornering speeds. It can also help exit speeds/out of corner grip. This assumes proper gearing ratios for the tire height.
Depending on the track this may make a larger difference in lap times.
As stated by others, generally a wider tire will help manage heat so if you are only doing autocross, TT or Time Attack then a just wide enough (narrow) tire will be the faster setup.
11-09-2011, 10:06 PM
#15
Safety Car
Keep in mind that in a competition class (TTA in this case) there is also a penalty for a wider tire. So yes, you're getting faster with the 255 width, because that allows you to do other things to the car which help more than the narrow tire hurts.
As with anything, there is no easy curve that shows tire vs lap time. Sooo much depends on set-up to go with the tire, and so much depends on whether you are using the tire. I tend to have similar lap times when I run 275 sq versus 315 square. Does that mean there is no difference? Of course not. It could be that I'm not taking advantage of the wider tire as a driver, it could mean that my 315's were older than the 275's, it could simply mean that the track and temperature were faster one day over the next.
My best guess, however, is that while the car probably had more "ultimate grip" in steady state, the increased lag in steering and overall lower response of the car in transition may have hurt as much as ultimate grip was helped.
And yes, jason is a smartass (and occasionally even funny), but the man speaks the truth. It depends.
As with anything, there is no easy curve that shows tire vs lap time. Sooo much depends on set-up to go with the tire, and so much depends on whether you are using the tire. I tend to have similar lap times when I run 275 sq versus 315 square. Does that mean there is no difference? Of course not. It could be that I'm not taking advantage of the wider tire as a driver, it could mean that my 315's were older than the 275's, it could simply mean that the track and temperature were faster one day over the next.
My best guess, however, is that while the car probably had more "ultimate grip" in steady state, the increased lag in steering and overall lower response of the car in transition may have hurt as much as ultimate grip was helped.
And yes, jason is a smartass (and occasionally even funny), but the man speaks the truth. It depends.
11-09-2011, 10:07 PM
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11-09-2011, 10:11 PM
#17
Safety Car
Assuming the same overall diameter, contact patch is a function of air pressure and tire width has no effect. A wider tire has the same contact patch in square inches, but the CP itself is wider (and of course therefore thinner along the longitudinal axis), and thus more effective in lateral loading, aka "grip".
11-09-2011, 10:17 PM
#18
Racer
I tend to have similar lap times when I run 275 sq versus 315 square. Does that mean there is no difference? Of course not. My best guess, however, is that while the car probably had more "ultimate grip" in steady state, the increased lag in steering and overall lower response of the car in transition may have hurt as much as ultimate grip was helped.
Autocross (or even a tight road course) is a totally different animal.
Jason's answer was probably the most accurate, he just didn't elaborate.
11-09-2011, 10:29 PM
#19
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Keep in mind that in a competition class (TTA in this case) there is also a penalty for a wider tire. So yes, you're getting faster with the 255 width, because that allows you to do other things to the car which help more than the narrow tire hurts. I'm inferring from this that someone in the sanctioning organization has come up with a "formula" equating tire width changes to weight/hp/aero/etc changes in order to level out the competition or laptimes. I posed a question similar to that (tire width changes versus weight changes) a few months ago, but didn't get much feedback on that topic. My original question was an attempt to find out what sort of "formula" or rule of thumb fellow drivers use to get an idea of what cornering/laptime change is commonly seen with increases or decreases in tire width.
As with anything, there is no easy curve that shows tire vs lap time. Sooo much depens on set-up to go with the tire, and so much depends on whether you are using the tire. I tend to have similar lap times when I run 275 sq versus 315 square. Does that mean there is no difference? Of course not. It could be that I'm not taking advantage of the wider tire as a driver, it could mean that my 315's were older than the 275's, it could simply mean that the track and temperature were faster one day over the next.
My best guess, however, is that while the car probably had more "ultimate grip" in steady state, but the increased lag in steering and overall lower response of the car in transition may have hurt as much as ultimate grip was helped.
And yes, jason is a smartass (and occasionally even funny), but the man speaks the truth. It depends.
As with anything, there is no easy curve that shows tire vs lap time. Sooo much depens on set-up to go with the tire, and so much depends on whether you are using the tire. I tend to have similar lap times when I run 275 sq versus 315 square. Does that mean there is no difference? Of course not. It could be that I'm not taking advantage of the wider tire as a driver, it could mean that my 315's were older than the 275's, it could simply mean that the track and temperature were faster one day over the next.
My best guess, however, is that while the car probably had more "ultimate grip" in steady state, but the increased lag in steering and overall lower response of the car in transition may have hurt as much as ultimate grip was helped.
And yes, jason is a smartass (and occasionally even funny), but the man speaks the truth. It depends.
11-09-2011, 10:46 PM
#20
Racer
They try but a big problem is you can't just go by what's on the sidewall. All "275" tires are not the same width, and they vary in actual size wildly. On a 10.5" rim, a Hoosiers 255 is slight wider than their 275. Their 295 should be 20mm wider but it's only about 8-10mm wider, etc
