Hello guys. Tire Rack website shows 8.5 inches tread width for the Bridgestone Potenza RE71RS and I see that you have 9.8 inches tread width here. What's going on?
Photography Credit: David S. Wallens
What happens when you own a tire company and want some appropriate rubber for your own sports cars? You get it done.
Since 1982, X Comp and its associated brands have been successfully building a variety of tires for a wide range of markets: tractor-trailers and golf carts, ATVs and off-road trucks. In 2016, the company entered the off-road motorsports arena with a number of sponsored drivers, generating extensive exposure.
But company owner Jeff Kreitzman is also a car enthusiast and wanted his own brand represented on his sidewalls. So the company jumped into that market with the X Comp H/P, a high-performance, road-legal 200tw tire for street, track and drift use.
An attribute of this tire: value pricing. In the 315/30R19 size, for example, the X Comp undercuts the Falken Azenis RT660 by some $40 per tire–so in round numbers, about 10%.
Since it was initially only available in large rim diameters from 19 to 21 inches, however, it wasn’t compliant for many events that use SCCA national rules. In November of last year, though, that all changed as a pair of 18-inch sizes were added to the roster.
Without sufficient time to evaluate the suitability of the tire before the January 1 eligibility cutoff for the 2024 race season, the SCCA Solo Events Board placed the tire on its exclusion list. Once more performance data becomes available, it will reconsider.
Testing the X Comp presented a small logistical challenge for us, as it doesn’t come in the 15- and 17-inch sizes that we usually test. But an 18-inch size would fit our Golf GTI project car, so we made plans to test this one at the Florida International Rally & Motorsport Park.
With so little information out there on the X Comp, we had no idea where it would land on the performance scale. Was it really too fast to be legal?
So we called in a trusted benchmark, the Bridgestone Potenza RE-71RS. We ran this tire to a podium finish at last year’s Tire Rack One Lap of America presented by Grassroots Motorsports–it’s both fast and civil–so we ordered up a fresh set. Like the X Comp, both tires were sized 245/40R18.
From left to right: Bridgestone Potenza RE-71RS, X Comp H/P
We didn’t have two sets of identical wheels, though, so we did what many FWD competitors do: ran our wider Titan 7 wheels up front. This wheel-width stagger is not uncommon and can better match the higher nose weight with a more supportive wheel-and-tire combo. In this case it looks a little odd, but getting good comparable data is all we really care about.
[Track tires for a daily driver: Bigger isn’t always better?]
After breaking in both sets of tires and with a limited test window, we watched the weather forecast. Sure enough, as we approached the track on test day, we were met with a light drizzle.
But this is Florida: Don’t like the weather? Wait an hour or two. Which we did, and it cleared. Yay.
We mounted up the Bridgestones first and went out to recon the track for residual moisture. After about 15 minutes spent dialing in our shift-ing and braking points, we pitted and let the car cool down during the lunch break. Then we could test.
Fastest Lap: 1:20.4
On the Road: Very progressive steering response that’s strong on center. The stiff carcass transmits bumps, although the softer compound damps the finer impacts. Some drone, but for the performance, a minor concession.
On the Track: First lap out, we hit some traffic, but the second lap delivered a flyer that’s very indicative of the tire’s full potential. In fact, that lap was the fastest that car has ever lapped the FIRM. The Bridgestone delivered excellent grip, especially at off-corner power-up, a key ingredient for our 300-horsepower hot hatch.
Given those two hard push laps, the RE-71RS began to heat soak and lost some grip on subsequent circuits. Unlike our usual test mules, the GTI really punishes its front tires with big asks of cornering, braking and acceleration. It’s a heavy car with small wheel wells, meaning a bit too small of a footprint. With lap times now consistently upward of a full second slower, it was time to pit.
Fastest Lap: 1:23.5
On the Road: Similar to other Super 200s: Biased toward some hum with the occasional rock fling but the tradeoff is good steering feel that’s solid on center. When presented with a lot of road crown, a bit of pull.
On the Track: The X Comp delivered some fairly consistent laps, although heat built up throughout the exercise slowed our pace. The tire was simply not in the same ballpark as the Bridgestone, however, easily 3 seconds a lap slower.
Data analysis showed similar braking distances between the two tires, but apex speed was much lower with the X Comp. More importantly, the Bridgestone could simply accelerate better off each corner–essentially, the RE-71RS allowed each straight to start sooner and at a higher speed. Now multiply that by each turn.
Fastest Lap: 1:20.6
To verify that neither the driver nor track surface had changed significantly over the course of the day, we returned to the track on the RE-71RS to bracket our efforts. Off and on throughout the session, we encountered some traffic, but we used those laps as mini-cooldowns that allowed for more full-pace laps in between. The times shown are the clean laps, two of which are very close to our earlier best. Satisfied with the veracity of our data, we packed up.
The X Comp isn’t a Super 200. It’s not going to win at Solo Nats. Based on pace, it’s clearly much more of an endurance-focused tire–still, even in that category, it ranks near the bottom.
It is, however, a value-priced option for those seeking the larger sizes common on modern performance cars. Need to put sporty, value-priced tires on a later Mustang, Cayman or Camaro? This could be your bogey.
Hello guys. Tire Rack website shows 8.5 inches tread width for the Bridgestone Potenza RE71RS and I see that you have 9.8 inches tread width here. What's going on?
Yep, 9.8 is Section Width for each tire, not tread width. Good eye!
Missed that in the proofing process. That chart was created after the story left my hands and the mistake wasn't caught on review.
Sigh...
I like these tires, but m y Golf-R understeers bad. Despite the -3.5° camber and 38 PSi hot (these values are from the front tires) it understeers bad. The RE71RS over heat quickly, and the "V" markers on the front tires are trespassed. I got the thickest anti-roll bars front and rear, they are 25.6mm in the rear and up front too.
What can I do ?
Gerhard
In reply to GAM :
I haven't owned a FWD in 20 years now, so this may not work the way I think it should, but try disconnecting your rear sway bar. My Miata would not turn in to save its life, due to really limited camber. Popped the rear end links off the sway bar, and that helped turn in quite a bit.
In reply to GAM :
I would have left the rear bar bigger than the front. Have you tried messing with your toe settings?
Fcyaa said:Hello guys. Tire Rack website shows 8.5 inches tread width for the Bridgestone Potenza RE71RS and I see that you have 9.8 inches tread width here. What's going on?
Yes, thanks for catching that. I've adjusted the chart in the story.
In reply to GAM :
Understeers bad could also be overdriving a corner; does the car swap ends quickly, or does it only plow all the time?
Also, more rear stiffness (generally) will let the back end come around easier. The faster you go the more the car turns from responsive to squirrelly as you up rear stiffness, though.
Let's talk about rear stiffness and FWD for a moment.
It doesn't work the same as on the typical well-balanced (50/50) RWD platform like a Miata or BMW. In those cases, altering relative roll stiffness front-to-rear will affect the car through out the entire cornering phase -- entry, mid, and exit. It does this by altering how much weight is transferred at each end.
With the typical nose-heavy FWD car, it's pretty easy to transfer *all* of the weight at the rear of the car in a corner. That's what causes the rear to top-out the suspension and come off the ground. Once you have enough rear roll stiffness for this to happen, either through anti-roll bar or springs, you cannot further alter the balance of the car. You *can* alter when this happens in a turn, however. Stiffen the rear enough and it begins rotation super-early in the corner, understeers in the middle and then allows for earlier throttle application on exit to balance the tendency for oversteer.
This is commonly called setting the car up just this side of "killing you on entry" so you can get early drive off the corner. Go too far, however, and you're that "tank slapper guy". We've all seen that guy.
Hmmm,..I sense a tech story here....
Andy Hollis said:Hmmm,..I sense a tech story here....
In reply to Andy Hollis :
Great stuff, what I've experienced in my Mini, though if you drive in the rain with the car set up to "kill you on entry" it just might.
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