Could a NASA rule change regarding tires turn an also-ran into a contender? Maybe, we figured, this reorganized structure could benefit our 1991 Toyota MR2 Turbo. Instead of saying we’re looking to exploit a loophole, let’s call it taking advantage of a rule change.
The NASA Time Trial rules look at weight and horsepower before adding in multipliers for other modifications–things like aero, gearbox type and, yes, tires. With fuel, safety gear and driver, our MR2 weighs around 3070 pounds.
Thanks to our suspension and brake modifications, NASA allowed the MR2 to make about 220 horsepower when running cutting-edge 200tw rubber like the Falken Azenis RT660 or Yokohama Advan A052. But according to new rules, we could add 10 horsepower if fitting the Toyo Proxes RR.
[100-treadwear tire test | Nankang Sportnex AR-1 vs. Maxxis Victra RC-1 vs. Toyo Proxes RR]
Thanks to the relatively low power levels of our 30-year-old sports car, that’s a nearly 5% bump in max power when running a theoretically more radical tire.
The temptation was too great to resist, so we set out to do some testing: Falken Azenis RT660 versus Toyo Proxes RR. We’d run the same tire sizes for both offerings–235/40R17 fronts and 255/40R17 rears–on our König Hexaform wheels.
[Project MR2 Turbo: How to Find the Correct Wheel and Tire Combo for an Odd Fitment]
Horsepower vs. Grip
We tested and retested our MR2 in three configurations: on the Toyos at 220 horsepower, on the Falkens at 220 horsepower and, after throwing on another pound of boost, on the Toyos at 230 horsepower.
We’ll cut to the chase: The Falkens produced the best single lap at a lower horsepower figure. However, we’ll temper that by saying we held this test at the Florida International Rally & Motorsport Park, a track that doesn’t allow our MR2 to get past 110 mph or so. On a track with longer straights–say, Road America or Road Atlanta or VIR–that power difference would make a bigger difference on the clock. Keep that in mind while we decipher our laps.
The data trace showed the Falkens (red trace) carrying faster speeds through momentary-load corners, like The FIRM’s high-speed kink.
In The FIRM’s long, sweeping, left-hand Turn 8, the Toyo’s prodigious and stable sustained lateral grip (blue trace) produced a much smoother speed trace. The Falken’s neediness showed up in several tiny speed adjustments as the less precise tire hunted for the edge.
We fully expected the slick, stable Toyos to produce better braking performance, but the Falkens often had an edge here. The Falkens (red trace) were easier to modulate and produced greater stopping forces. The Falkens also delivered easier brake release, with the data frequently showing faster and smoother instances of corner entry.
Both tires were extremely easy to drive on, but the Toyos were slower to react to inputs, which was not just a subjective opinion–the data agreed. The flipside of that: Once the Toyos took a set in a constant-radius corner, that set was highly stable.
Conversely, the Falkens were eager–excited, even–to turn, but they also took some fine-tuning to remain on the edge. Credit the faces of the tires: The Falkens have a tread pattern, while the Toyos are essentially slicks. More tread block deflection means more corrections. Once the Falkens wear, however, expect them to settle down a bit.
When the times came in, we found a 0.25-second lead for the Falkens at 220 horsepower over the Toyos at 230 horsepower. The data showed that the additional horsepower delivered higher speeds at the ends of the straights when–and this is important–exit speeds from the previous corner were equal.
But in so many cases–particularly those short, flick-type corners–the Falken’s superior exit speeds delivered an advantage that couldn’t be overcome by the additional horsepower. The speed difference could be erased in some cases, but on The FIRM’s short straights, it couldn’t be completely negated.
That said, both tires were delightful to drive on. Although the Toyos were a little slower to react to inputs, their overall demeanor was stable and highly predictable. And consistent. Just dead nuts consistent. Every lap, every corner, felt exactly the same, regardless of whether we were on fresh-off-the-trailer cold tires or fully warmed-up hot rubber. The Falkens, on the other hand, definitely had a temperature sweet spot. They wanted to be warmed up but could lose grip if they got too hot.
Photography Credit: Chris Tropea
The real choice here may come down not to pure lap times but to use case. Need to drive on your tires to and from the track? Falkens all day long. Get a good power bump from the rules allowances and plan on running on tracks with epic straights? Maybe a semi-slick like the Toyo is a better choice.
Great article JG! On my TT5 Miata, I couldn't get into the 1:19's at The FIRM until I switched to Goodyear Supercar 3R tires. I was running the Toyo RR up to that point. 205/50-15 square setup. RR's were consistently in the 1:20.5's. The 3R are a little more sensitive to heat than the RR. I've run a couple of 1:19.9s and a 1:19.8, spread between when the tires were brand new to when they had 12 heat cycles. See you out there!
bratte said:I've run a couple of 1:19.9s and a 1:19.8, spread between when the tires were brand new to when they had 12 heat cycles.
That's a really impressive tight spread over that many heat cycles. I'd love to see a chart of those lap times vs ambient temps and speed traces. Like, I'm wondering if some of what should have been tire falloff after 6-7 heat cycles was compensated for by good weather of your skills and fmiliarity with the tires increasing. Of if they just are that consistent.
In reply to JG Pasterjak :
JG,
The fastest time of 1:19.8 was set on the second heat cycle of the tires. The ambient temp was 70 degrees (10/23/21). The 1:19.9s were a couple of months apart. One was on a 75 degree day(12/19/21), at around 7 heat cycles and the other was an 85 degree day (3/18/22)at 12 heat cycles.
The data doesn't really show much difference between steering angle input or max combined G between when the tires were new and the last 1:19. That said, the performance has started to fall off after 12 heat cycles. Pretty consistent performance from a tire that I would consider a bargain priced option in its category.
Brian
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