Tested: Can sticky tires make your straight-line speeds slower?

[Editor's Note: This article appeared in the December 2013 issue. Some information may be different today.]

Story by J.G. Pasterjak • Photography as Credited

Friction is what makes tires fun. The more they generate and the more grip they have, the more smiles they put on our fa…

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By going to a wider tire, you increase the footprint and the frontal area, both increasing drag .

There is a ton of anecdotal data about this out there if you look at drag racing. Drag slicks are well known to 'eat mph' and if you know your race weight and before and after trap speeds it's pretty easy to ballpark some power consumption numbers. Now in that case a lot of it comes down to sidewall deflection and the very stick compound is probably in 2nd. In street tire terms I think the mpg loss is MOSTLY attributable to aero impacts from the front tires with actual rolling resistance being secondary. 

Another stark way to find the losses from tire 'upgrades' is to see the kind of range that EVs lose when you put 'autox tires' on them. It's considerable..

Wider tires can cost you top speed due to increased drag and turbulence, but a lot depends on the individual car.  Miatae (in stock form anyway) have almost no front bumper or fender coverage of the tires, they just hang out in the wind.  Other cars are better considered in this regard and probably pay less of a penalty at high speeds.

My s2000 with 255 Bridgestone re71r tires and an aggressive autocross alignment loses about 3-4 mpg on the highway compared to normal tires and a modest alignment. The effect is real.

It also doesn't appear you weighed the tires to see what effect that would have.  Heavier tires take more energy to spin up to speed (remember, all cars have 5 flywheels:  one on the engine and one on each corner)

It seems a better test would have been to stay as close as possible to the same tire size and weight and only adjust the compound.  Introducing two extra variables isn't very scientific.

I never noticed the mpg loss on my integra, it seems to get a solid 25-27 mixed mpg with autocrosses and occasional commuting, but I am wondering, how much of an affect if any do sticky tires affect dyno tuning on a roller? 

Would have been nice with some correlation to the logs from the track, to see if it's a measurable difference on the straights 

Vigo said:

There is a ton of anecdotal data about this out there if you look at drag racing. Drag slicks are well known to 'eat mph' and if you know your race weight and before and after trap speeds it's pretty easy to ballpark some power consumption numbers. Now in that case a lot of it comes down to sidewall deflection and the very stick compound is probably in 2nd. In street tire terms I think the mpg loss is MOSTLY attributable to aero impacts from the front tires with actual rolling resistance being secondary. 

It's a rule of thumb that going from a limited slip diff to a spool will make a car run about a tenth slower.  This kind of boggles my mind because tires are always running under a slip percentage when under load, so you'd think that any minor circumferential differences would get lost in that, but enough people have noted the effect that it is hard to ignore.

It would be an interesting data point if you could take a narrow tire and a wide tire of the same make and model, to isolate exactly what the difference in fuel mileage was due to frontal area.  Just run the car in a straight line  on a long highway to eliminate cornering effects.

I used to run a very stock race class on tracks with long straights and while the competition always squeezed on every bit of rubber width they legally could, I felt that wider tires might impair top speed more than they would result in saved cornering times and could actually reduce lap times. 

It's a rule of thumb that going from a limited slip diff to a spool will make a car run about a tenth slower. 

So why would I run a spool, then?  Just a matter of strength?

BA5 said:

It's a rule of thumb that going from a limited slip diff to a spool will make a car run about a tenth slower. 

So why would I run a spool, then?  Just a matter of strength?

Strength, cost, and lack of wearable parts (in the diff, as wear would increase on many other parts, most notably tires). Also in some forms of motorsport the fully-locked axle is preferable to allowing any kind of differential action even ignoring the strength and wear issues - drifting, drag racing and dedicated offroad 4x4s for example.

In reply to Pete. (l33t FS) :

Do LSDs handle drag racing demands better than other rear ends?

So my idea to pencil out this weekend is a tire inflation system tied to brake and throttle input. Air down into the braking zone air up as you accelerate out. I'd of course include an adjustable delay. May get the best of both worlds tall skinny tires on straights and a short fat patch for corners. Further refinements could be on the fly adjustability front to back. 

I enjoy seeing these old threads/links to articles I helped on pop up. I could have made life easier for JG without going thru all the math, but breaking it down hopefully helped someone else come to some useful conclusions...

GameboyRMH said:

BA5 said:

It's a rule of thumb that going from a limited slip diff to a spool will make a car run about a tenth slower. 

So why would I run a spool, then?  Just a matter of strength?

Strength, cost, and lack of wearable parts (in the diff, as wear would increase on many other parts, most notably tires). Also in some forms of motorsport the fully-locked axle is preferable to allowing any kind of differential action even ignoring the strength and wear issues - drifting, drag racing and dedicated offroad 4x4s for example.

Drag racers have noted that a limited slip is slightly quicker over a quarter mile.  I do not know if anyone has analyzed whether this loss happens only at the top end or at the launch, and if someone has then I would be interested in the data.

The main issue with them is strength, and I have not seen any limited slips for common rearends that allow axles larger than 31 spline.  If you have 35 or 40 spline axles, you need a spool, since that is basically your only option.

Spools are also generally one HECK of a lot lighter, which is important for, say, circle track racing, where acceleration and deceleration inside a certain window is more critical.

Two things to add:

In my SSC Miata the car was faster on 185s vs 195s but after about 2-3 laps the narrow tires would start to overheat.

When I raced 125cc GP bikes you did things like running the smallest tire possible as well as really small chains (something like 410).