Category Archives: Radical

Radical vs Stohr Differences

So a lot of folks have been asking me my impressions driving the Stohr versus the Radical,
which I drove for the past four seasons. I was surprised how similar they really felt. I’ll try to see if I can enumerate the differences I felt, and will post it here…


  • Trail Braking – Aside from the increased high-speed grip, this is what I noticed
    most about the Stohr. The Radical did not like to be trailbraked. I suspect
    a lot of that was due to the excessive rear bias I could never work out of the car, due to the large rear calipers. The Stohr trailbrakes beautifully, perhaps also due in part
    to the 11″ longer wheelbase. T2 at Pueblo, I could turn in as I brushed the brakes, and the car would seemingly pivot around its nose. Speed there was awesome
  • Front Grip – Folks say that the Stohr tends to understeer with the tunnels
  • and the “standard” front, but I felt like the front was a bit more grippy than the Radical was. If so, I’m really looking forward to having the WF-1 style front-end some day – at higher speeds like T5 T6, it was always the front that washed out, not the rear.
  • Overall/High Speed Grip – There’s only one fast complex at Pueblo, Turns 5/6,
    and there the Stohr was way quicker. Almost flat every lap, versus hefty lifts in the Radical unless everything was *perfect*
  • Straightaways – The Radical always felt like it hit a wall at higher speeds. The
    Stohr definitely doesn’t as badly. Highest speed the Radical reported last time out was 132, and the Stohr showed 137 at least once – I haven’t downloaded the data to see the peak speed. That’s with the GSX-R versus the Radical’s busa.
  • Bumps – the Radical is MILES better at soaking up bumps than the Stohr. Some of that
    is four years worth of tinkering with the Radical’s springs and shocks, whereas the Stohr runs double the springrates, and I haven’t the foggiest where the shocks were set. I found bumps in T1 I didn’t even know existed!
  • Convenience – the larger cockpit of the Radical makes it much easier to buckle
    yourself in, and also, getting the rear deck off is an easy one-man job. Not so for the Stohr on either count.


  • Turn-In maybe it’s just foggy memory, but I don’t feel like one car was way
    more pointy than the other. That surprised me given the difference in springrates, but perhaps the Radical’s anti-roll bars are at work here.
  • Ease of Maintenance – I reserve the right to change my opinion, but the Stohr doesn’t seem any more difficult to live with than the Radical, once the bodywork is off. Nothing seems confusing or terribly hard to get to, although I’m not looking forward to ever doing anything with the fuel cell. The parts generally seem to be much higher quality, although I’m sure that will be reflected in their expense when I have to replace them. But, the convenience of pulling the body off, and sitting on my favorite bucket to service the car remains, which I enjoy.


Moving On

As with the Corvette, and the Eclipse before it, I’m moving on to a different race car. This time, it’s to a 2002 Stohr DSR out of Atlanta.

It’s been almost exactly four years with the Radical, and a great four years it’s been! Running solo, a season of the SCCA’s first time trials, a track record at Hastings, the Rookie of the Year club Racing award, and so on. It will be hard for the Stohr to see me through so many milestones, but I bet it sure will be fun!

I may still be updating here from time to time, as the Radical is staying local, so we’ll see how the old girl does.

As for the Stohr, I shall continue my development log just as I have before…


all_packed_up title2

Gas, Oil

VIDEO: Race 2 Beginning – Behind Pat

With a nice solid month to prepare for Pueblo after the La Junta race, I loaded up the ol’ orange car and headed down to Pueblo for our July double regional.

I headed out on Friday to do a bit of testing. I wanted to do some A->B->A tests with my dual
element wing. Plus, not having been to Pueblo since October of last year, I wanted to make sure there were no horrible imbalances or other oddities I had created with my various updates to the car.


I headed out first session with a set of Hoosiers from La Junta’s test day, figuring they would still have some reasonable life for basic shakedown testing. No such luck! The rears had gone off to greener pastures, so the car had heee-yuge oversteer everywhere on track. I was spending so much time keeping the back-end behind me, the best I could muster was a 1:36 lap. With respect to Dorsey Schroeder, this was “slow loose”!

So, I came in and put in one of my sets of Goodyears from John Berget, which were my tires from La Junta as well. Testing from La Junta had shown that the 160 Goodyears were clearly quicker than the R35 Hoosiers (perhaps not a fair comparison…), and that the 20×8 Goodyear front fits the Radical better than does the 20×7.5 Hoosier.

I ran several laps, and came in with a 1:32.5, about a second better than I had ever run before. Now that’s progress!

Interested in testing some aerodynamic effects, I removed the 2-element wing, and installed the Radical factory wing at maximum angle. The net result was a slight 1-2mph gain in straightaway speed, but the reduction in rear grip made it much harder to get around track, so I couldn’t match my 1:32 time.

I reinstalled the 2-element wing, and reduced the flap angle somewhat to get a bit of straight speed back. Happy with the balance, I removed the front dive planes to see what affect they have. Again, their cost was perhaps 1-2 mph of straightaway speed, but the new inability to hold nearly flat through 5-6 complex cost more time than the straight speed was worth. So, I put them back on, and had a nice car for Saturday.


Saturday was a hot day. Really hot. Damn hot. 108* hot.

Practice was largely uneventful, and I ran most of the session just enjoying myself, finding people to pass and play with. In the midst of all this seriousness, we tend to forget to have fun, right?

I threw on my newer set of Goodyears for Qualifying. Boy were they better! I ran a slightly shorter qualifying session to preserve the tires for Sunday, confident that my times would be good enough for pole position. As it turns out, I had a new best of 1:31.50, a solid two second improvement over my previous best. Not quite to the 1:29.xx I had hoped to beat the previous CSR record, but still quick nonetheless.

The only concern was that I started to notice the car stumbling out of 2 and 3, showing low fuel pressure on the dash. Problematic, since the car had 5+ gallons of gas in it during those times. I guess the higher speeds plus the longgggg Radical cell was allowing the pickup to starve, even with the collector in the fuel cell. Crud.

So, this made the race a bit of a problem – was I going to be able to get through without persistent starvation problems costing me the race? Worse, although normally better, they announced races would be 18 laps instead of the normal distance of 14 (?) or so, so now I had extra laps to contend with? Double crud.

So, my strategy was this: I warmed up the car in paddock, then shut it off and filled it absolutely to the top. I drove over to grid, and shut the car off until we were signalled to leave for the pace lap.

I did everything I could to preserve gas where I could. Kept the revs low on the pace lap, high gears etc. Gathered up the field as usual and….they waved off the start! OK, that’s fine, one less lap for me to do under green, right?

Well, not exactly. One of our new PSR drivers had gotten to grid late, and had made his way up through the field on the pace lap (BIG BIG NO NO) to take his grid spot. Seeing this, the start was cancelled. We were all black flagged, and sat for approximately 42 years on grid, in our hot race cars, in the sun, with no umbrella. It was hell.

Finally, after an interminable wait, we restarted, but the race distance had been reset to zero. Oh no! Already being worried about fuel consumption, now I had two fewer laps worth of fuel! Triple Crud!

So finally we got our green flag. I ran the first 3 laps completely flat-out to build up a gap. Joe was in my mirrors briefly but disappeared eventually. Grant was not a factor, and Pat was still breaking in his 2008 ‘busa, and taking it easy. Chris Waterman had a revs problem and was just cruising to get finishes. That left Paul, who quickly disappeared from my mirrors.

I spent the rest of the race short-shifting, around 8K RPM, coasting a bit at the end of straights like they say to do on TV (hah!), and using higher gears when possible. My biggest problem was the unbelivable heat – which I have never had a problem with before. I took the checker, although in my doggedness and heat-addled state, didn’t realize it. It was halfway around the last lap before a corner worker gave me the “chill-the-f-out” sign with his hands that I realized the race must be over.

I came in and got out of the car, feeling more than a bit unsteady. Wow. Not a very eventful race, but a nice flag-to-flag win, alright! Although I’d never seen him in my mirrors, Paul said he could just barely see me the whole race, and I always stayed a turn or so ahead of him. I was running to a 1:35 or so pace, so that was evidently enough.


Sunday was a little bit cooler than Saturday, thankfully. Again, I threw my old set of tires on and played around, since the car felt good, the air was cool, and durnit, I wanted to go play!

Qualifying was also relatively uneventful. I put my “Good” set of tires back on, and turned a few laps, again, coming in once I knew I had a pole time.

By our race, the cool morning had given way to an oppressively hot day. Once again around 105 air temp, and probably at least 140* or so on the tarmac.

The race was a much more ‘normal’ start. Paul started second place next to me. I did my usual slowish run up to the flag, to take advantage of the Hayabusa’s torque. The green flew, and both Paul and I got good starts. However, all was for nought, as Pat came ROCKETING by us by 2/3 down the straight. Holy Cow!!!

After this followed some of the most fun laps of my short racing career. Based on qualifying times, I was about 5 seconds a lap faster than Pat, a LOT! Pat has years of experience behind him, and knew precisely where I could and could not have a chance at passing him. He was battling a clearly evilly loose race car, sliding all over the place, and absolutely driving his heart out. Absolutely amazing stuff.

Twice I got by him leading into the straight, and he simply drove right back around. Holy cow! Paul said he even got by at one point, and he simply drove by both of us again. Lap after lap we were side-by-side, or nearly coming out of 2, 3, 4, 7, and 8, but always, he would just rocket away as soon as he got on the gas. Once I nearly had him into 9 but had to dodge a bit when he broke earlier than expected.

However, a few laps in – disaster! I was behind Pat trying to decide how to get by him and build a gap over the course of a lap such that he wouldn’t just immediately drive by again on the straight. So, I concluded I’d have to do something in 2, since he gapped me badly down the straight, but was very slow on the corners. He went slightly wide, and I ducked down inside again. However, the car immediately spun. I corrected, but the car lazily kept going around, and I spun off onto the inside between two and three. I saw Rob coming in the
Red PR6 and hit the brakes to avoid rolling into him. I got the car turned around, covered in dust, and got going again just behind Grant.

Now in catch-up mode, I chased Grant down HARD, and passed him a lap or so later. Off in the distance I saw Rob in the PR6, and set about trying to track him down. It actually happened a lot faster than I thought. Rob later said that he backed off, thinking I didn’t have time to catch him, but we were only 8-10 laps into a 18 lap race. I caught Rob into Turn 9, and was able to get away for a couple laps.

Before long, the temperatures started to take their toll however, and the tires disappeared. All of a sudden, I went from 1:33-1:35 laps to holding on for dear life running 1:38’s. I was having to brake and turn in OH so gently to keep the car behind me, oversteering everywhere. Turn 7 was a huge excercise in car control each time out. Turn 6 turned
into a drifting expedition.

With these sort of antics, it wasn’t long before Rob had caught back up, and we spent the rest of the race battling within 5-10 feet of eachother. He was clearly faster. However, I had also spent a number of laps behind Pat, learning where you can and can’t get by at Pueblo, so I knew where I could back off and give myself some time to breathe. Several times he got up next to me in 7, but I always kept the outside line and was able to be inside for Turn 8. About 4 laps from the finish, he had an excellent chance to get me downhill out of 4, but
Joe Weathers, having engine trouble, balked Rob and I was able to squeak by.

Finally, FINALLY, the checkered flew with Rob just inches behind me, and we congratulated eachother as we rolled down the straight.

In the end, it was an entire race of close, clean racing – what a tremendous race!


Again, I got out of the car hot as can be. This time I smelled a bit of fuel, and heard a hissing sound. long story short, a post-race inspection showed that the rear bulkhead had separated from the car, allowing header heat to radiate directly on the fuel cell. Not only did this melt the fuel cell, but that was why I was getting so bloomin’ hot
in the car!

Also, I ended up with a class win. Unbeknownst to me, Pat’s engine had exploded later in the same lap that I spun, and that pass of Rob ended up being for the class win.

As it turns out, it was due to the incredible amount of oil coming out from behind his car – note the pictures of my car. This ended up being educational in regards to airflow over the car, and around the two-element wing I had cobbled up for the car. Cool stuff!

Finally, it would seem that – perhaps obviously – Goodyear R160’s are no good on a 1200# Radical in 100+ degree heat. The fronts were blistered all around the inside edges, and the rears had about 1″ of cord all around the inside. Small wonder the car was as loose as it was. I guess I get to take away a small amount of pride for managing to hold on with such bad tires underneath me. Small victories…

Tire Tidbits

Cleaning off my desk today, and found some notes from a conversation with Richard at Rilltech, in regards to tires. He mentioned:

  • The 20×8 GY is slightly narrower than the 20×7.5 Hoosier (verified on their websites)
  • A good combination can be R35 on the outside tires, and R25 on the inner
  • Depending on your car’s balance, perhaps even R35 on the outside front, and R25 elsewhere

From what I can tell, the approximate order of compound is:

R25 < R160 < R35 < R270

But, who knows?

Another race in the books

My latest race writeup is up and posted from this weekend’s event
at La Junta. Quite an eventful weekend, to be sure!

Car Updates

Lots of updates to report on for the car between this race and last, which I’ll get to as I have time, including:

  • A new front splitter setup
  • new tire sizes & compounds
  • rerouted brake bias cable line
  • new APR Performance rear wing elements

Technical Redux

Thought I would distill some of the measurements/knowledge gained from this weekend of racing, various changes, etc:

Experiment #1: Wooden front splitter

This was a huge success. No loss of straightaway speed relative to the Radical fiberglass splitter. Had several “offs” and it emerged 100% unscathed. I have some slight rubbing on the bottom, but even at 1 7/8″ front ride height (the Goodyears are shorter than the Hoosiers, no wear to speak of. I’m stoked. Length is 24″ from bulkhead to front of the car, with a small angle cut out for tire clearance, width is 60″. Three “jiggle strip” brackets of .090 aluminum to hold the nose down. Weight is about 13# per, and cost including brackets is about $50 apeice. This is good value.

Some details of the construction: I used 5/8″ plywood, and for the shape, traced the profile of the existing Radical splitter. The length from the front of the tub to the end of the splitter is 24″, which I chose because that means I can get 2 splitters per sheet of 4×8 plywood. The splitter is fastened to the bottom of the crushbox with countersunk socket-head bolts, with tinnerman washers (from Aircraft Spruce) to spread the load. The jiggle strips holding the nose down are .090 aluminum, bent in a “Z” with about 3/8″ rise, and 2″ in width. The center one is 10″ long, and the two sides are 5″ long. Two Dzus fasteners hold the corner of the nose in. A can of black spraypaint finished the job.

Experiment #2: Larger front tires

Also a big success, back-to-backing 20x7x13 Hoosier withthe 20×7.5×13 Hoosier. The car was immediately faster, by approx 1.0 sec with the larger front tires. Difference was in corner entry and mid-corner speeds, according to the data, I could really haul ass into the corner, crank it down to the apex, and then go nuts with the throttle on corner exit. Big difference.

Experiment #3: Goodyear vs Hoosier
At least between these sets of tires, the Goodyear R160’s were clearly faster than the R35 Hoosier was. Higher corner speeds everywhere, and they were wearing better for me as well. Tire temps were about ~20-30* warmer with the goodyears, but everything was still cool enough to indicate I might even be able to get away with R25’s, even though it was nearly 90* outside. Further testing to determine, but for now, the GY’s were definitely quicker.

Experiment #4: APR Performance wing elements

A qualified success. Significant additional drag, but significant additional grip. Net laptime gain of approx .5 to .75s on a pretty straight track. I continued to reduce wing angle throughout the weekend, and picked up a few of the lost MPH on the straight. Traces under the suction side of the wing (courtesy of somebody with an oil or water leak ahead of me) show airflow separating on the odd “flat” portion of the APR main element profile, so I may try one of their normal “non-cambered” wings that has a more traditional shape to it, and perhaps that will be more efficient, while still providing the additional grip. Corner speeds were way up from a month ago – 5-6mph in 80-100mph corners. The elements I’m using are their 7.5″ and 5.5″ elements, with a small bracket to mount to the existing Radical uprights.

Misc Other Tidbits

  • I ran the car low on fuel for the first time, and experienced fuel starvation with a significant amount of fuel left in the tank (i.e. at least 2 gallons). This is with a Fuel Safe collector in a ~8 gallon fuel cell. I’ll eventually move to the “fuel pot” method that others have used to correct this, but for now, will just continue running the car tipped up with fuel.
  • Put some hi-temp paint on the rotors. Burned the 800* paint, but not the 1200* paint. Anybody else ever tried this?
  • As mentioned above, I ran the car the last day at 1 7/8″ F, 2.3/8″ rear ride heights, with no ill effects, on 450/650# springs. Was surprised to find this when arriving home, but it worked quite well, so I’m leaving the car where it is for now. Mild rubbing on the bottom of the front ~1″ of the splitter underside, but that’s it.
  • I relocated the brake bias cable with the Tilton 90* fitting, to prevent the cable from binding on the clutch. This IMMEDIATELY improved brake feel, so that had to have been causing problems. I was able to brake later and deeper at IMI, and all weekend at La Junta. Once I had the bias set, the car feels great on the brakes.
  • The Digi-Gear is still unreliable, so I am going to go to absolute basics and power/ground it directly off the battery and see if it will work then.