I was doing a little SWAG on the Sprint-T and tires and I came up against another problem. I can only hook up so much HP no matter how big I get the tires, because of weight. Traction is a function of weight and tires, and there is a hard limit to traction with a car as light as the Sprint-T trying to use UTQG 200 treadwear tires. I can get a little more power to the ground with sticky race rubber, but depending on the weight of the car I’m looking at 300 to 500 HP without boiling the tread off the tire before getting the pedal to the metal. More than that and I’m never getting my foot to the floor.
What I’m looking at is with the Subie engine and the T5 transmission I can stop cranking up the boost around 300 WHP, with the Pentastar V6 and the 8 speed transmission I can stop trying for more than 375-400 WHP because that transmission just weighs that much, the LS3 and the 4l70 I can pretty much leave in stock tune, and the LS7 I will need to put a block of wood under the gas pedal to keep rear tires on the car unless I’m running the softer compound of the race slicks I have available. Street tires will require really feathering the gas to maintain traction with just the stock 505 HP tune.
Now these are just what they used to call “back of the envelope” calculations but they are the best I can do with the data I can get, and the low precision of the data. Seriously I’m looking at ±0.1 G precision on a 0.8G predicted grip for the 200 wear tires, or 0.7 to 0.9G and a huge difference in performance between those numbers, so lets say we are talking about the LS7/3 we are looking at maybe 400-430 WHP on the low end, just shy of 500 at the high end. And as far off as I was on the unsprung weight at the front end I’m not putting much faith on these numbers either. But if the data is correct and I used to correct formulas, If I’m running an LS7 then I don’t need to use the dyno for anything more than fine tuning for gas mileage and verifying the stock tune is working correctly. Pretty much the same for the LS3 except I have more room on the other side of the equation, I could get away with maybe the 480 HP tune, but not the 525 HP tune.
And I didn’t get much sleep last night, and I’m starting to get a headache, so bedtime.
Seriously, I put a lot of miles in this week for as old and decrepit as I have become. I know 59 isn’t old in an absolute sense, I mean there are turtles older than that, but as much abuse as I have put my body through it certainly feels old. And it isn’t the bottoms of my feet that are bothering me, it’s across the top of the arch. I think maybe I’m overdue for a foot massage and that’s why that part of my feet hurt.
On other things I just saw where a pedestrian bridge in FL collapsed during construction, and the thing that bothers me the most about it is I can’t see any rebar sticking out of the broken concrete where the bridge collapsed. It might just be the fact the reproduction of the video via Twitter is just not high enough resolution to see the rebar, but there are a lot of little pieces of concrete that should have some kind of reinforcement keeping the pieces together so they break in larger pieces. And I just got back (21:24) from watching YouTube video of the disaster, and even at full-screen I can’t see any rebar sticking out of broken concrete, leading me to believe there wasn’t any or if there was it was too small and not enough of it.
I wish I had something to report about the Sprint-T, but except for brief flashes of inspiration the only thing that will provide progress in this build will be $$ in large quantities. I did a quick check of weight and if I build the frame from aluminum except for the roll bar, we are looking at a weight of 37 pounds for the frame compared to 70 or so for the kit frame that flexes like wet noodles and has no rollover protection. So with a little here and a little there we are looking at a sub-1400 pound car that has 305 HP on regular gas and gets 20 MPG without even trying, while embarrassing Corvettes and Vipers at stoplights. Heck, if I can make it hook up it would embarrass Hellcats and Demons at stoplights. But the kind of tires I would need to use to do that don’t wear well, like less than 100 UTQG wear rating. In comparison Goodguys requires 200 wear rating or higher to compete and most consumer tires are higher than 350 and go as high as 500. Of the tires I have been looking at most of the 245/40-15 are 200-300 wear rated, and the 255/60-15 are 400-500. So wear ratings of zero might have good traction for a few miles, but then you have cords showing through the tread.
I have to go do email and other mundane things now, so this is all for this post.
Watching the Canadian GP on the idiot box while waiting to walk down to the phone store and pay the bill. Aside from Hamilton running away and hiding from the rest of the field it is a good race to watch with lots of close racing all up and down the order. And in a few minutes the Cup race from Pocono starts.
You have heard the saying about a picture being worth a thousand words, and my usual post is about half that. So instead of talking about the difference in the driving position I marked the body with the rear of the conventional driving position to go with the previously marked far forward driving position.
The forward mark is the same one I used before, same piece of tape even. The rear mark is what I get by putting my feet behind the original firewall. That tiny piece of tape was the inside edge of my butt marker from when this body was going to be a front engine bucket with two seats. Yes, my butt is that narrow, the outside edge is the edge of the floor where the body turns up. And moving my butt that far forward only changed the weight bias from 63% rear to 60% rear without the 0.25″ floor pan under said butt.
OK F1 race just ended and Hamilton finished like 20 seconds ahead. Except for the usual first lap/early race carnage most of the attrition was brake failure except for one engine vibration retirement to keep from scattering the engine on the track. So now I switched to the Cup race at Pocono which is still in Stage 1 and drivers are already complaining about brakes going away, which partly shows why I want to make sure I can get enough tire to make good use of the big brakes on the TGS2. I know with the rear weight bias the front brakes won’t get as much use as they would with the front engine, and the rear brakes will see much higher temperatures than with the front engine.
And Junior just missed a shift and damaged the engine. And now it has been a few laps and Jimmy Johnson and Jamie McMurray both just had brake failure in the same turn, same lap to crash within feet of each other with McMurray catching fire from the impact damage. Jimmy absolutely nailed the wall, almost knocking it down. He got out under his own power but had to catch his breath a bit before taking the mandatory ambulance ride, while McMurray was in such a hurry to get out of his burning car he didn’t disconnect the AC hose and was walking around after the wreck with part of it hanging off the back of his helmet. Race has been red flagged because of the mess in turn 1, when Jimmy hit a lot of parts and pieces fell off the car and fluids ran on the track.
And Ryan Blaney just beat Kevin Harvick to the checkered flag. Sorry I got hung up with watching the race and forgot to report on it, but if you were interested in the race you would watch it I guess. And to add fuel to the Ford v Chevy wars, Harvick did the 3-2 instead of 3-4 shift and his Ford was fine but the Chevys all blew up in the same situation. And a Ford won.
I just saw an interesting use for coal, a carved anthracite trophy at Pocono. I don’t know if the eagle is made from coal but what is under it is.
And it’s time for me to walk to the phone store and pay the bill.
This has been A Week. Excuse me this has been A Week. I spent all day Monday on DART or DCTA buses or trains to do that echocardiogram thing. But I did see an interesting car.
I got to watch my heart beating again while they did the echo, which was cool.
Tuesday was go to the lab rat and get the 24 hour BP monitor and the jug to collect my urine for the next 24 hours, and also I got hit by a huge blast of grass pollen, so bad that when my allergy pill took effect I fell out of my chair trying to do a post which I discarded because it made even less sense than that post I did while dehydrated and tipsy. And how can I tell you how much fun it is to tote a jug of your own urine around? Next paragraph. Anyway I didn’t hit anything valuable or breakable on the way down out of the chair, so I counted my lucky stars and decided to sleep it off in bed for the next 2 hours, which didn’t prevent me from falling asleep early that night
Wednesday was get rid of the half-full gallon jug of urine, and the damnable blood pressure monitor that was squeezing my arm to death. The jug got a lot of stares on the bus with the biohazard sticker and the “Danger Acid” sticker. Then it took 2 tries to draw blood. I think the needle went through the vein because no blood would come out with the needle in and when they took the needle out it wouldn’t stop bleeding. Then I got stabbed in the other arm. After lunch I went to a place that does a 45 minute leg and foot massage with a 15 minute back massage for $30. I felt much better after that than I usually do after the full hour on a full body massage. Then I was going to get a haircut, but there was a wreck on the Tollway that made a normal 20 minute bus ride almost twice as long, which made me miss my connecting bus which got me to the stylist after my stylist already left for home. So my head is still shaggy. “How shaggy?” you ask. Well my back hairs go all the way up my neck and the only way to tell head and back hair apart is the back hair is going white already, and slightly more wavy than my head hair. And my character in Shadowrun just integrates the back hair into his regular hair style, flattop all the way back and down like a horse’s mane.
And during down time I did some more research and changed the race tires again, for a set of Formula Atlantic tires. Good grip for a car about the same size and weight as the Mid-Bucket and I can find wheels that fit the tires and the bolt circle of my car. Amazingly it is way easier to find 15 X 14 wheels with a 5 X 4.5 bolt circle than 16 X 12 wheels. So the front wheels will be 15 X 10, the rears 15 X 14 and I may be able to get the car balanced without adding an antiroll bar.
And it is almost dinner time and I need to get cleaned up.
At least until it rains, then all bets are off.
The tires (by Hankook) are not that bad in the wet, but put them on a 1600 pound car with brakes that can stop a much heavier car even without power assist and then add water in typical TX thunderstorm amounts and with a car that is naturally tail-happy… Wet weather driving will be done quite cautiously.
The main problem I’m having now is getting the right size wheels for the tires I chose, especially the front ones. You wouldn’t think 15 X 6 wheels would be so hard to find at a reasonable price, but they are. The rear wheels are comparatively easy, but where it really gets hard is getting both wheels in the same style and in compatible offset. In fact I’m having so much trouble finding the compatible offset I’m strongly considering using wheel spacers up front to make the mounted offset compatible.
That’s just for the street, for racing I don’t give a flying fig if the fronts match the rears as long as the widths and offsets are right and the wheels are light enough. And it is looking like the race slick wheels are not going to match styles at all, the front tires are 22/6.0-15S while the rears are 23.5/10-15S in a softer, more grippy compound. I’m definitely swapping at least the rear springs and shocks when I race SCCA so that I get a better balanced car. That and I’ll need to lower the car anyway as the race slicks are about an inch taller than the street tires which would totally screw up the undercar aerodynamics unless I dropped the rear back down to match the front. And since I’m swapping one set of shocks and springs anyway it won’t take but a few minutes longer to swap both sets. The time consuming part would get done beforehand as I adjust the ride height and set the damping on the shocks before labeling which corner they go on and putting them in some kind of carrying case.
And I have good company in having issues with controlling which way the car is going. Even the best hike the inside front wheel .
And on that note I close this post and bid you farewell.
I couldn’t do it. There was no way to get the oversteer out of the Mid-Bucket without going to bigs and not-so-bigs. The extreme rear weight bias just was too much for all my tricks and tweaks. I can’t fight physics and no matter what I did I still ended up with oversteer at the limit. Sometimes it was only hang the tail out and go slow oversteer, but most of the time it was understeer up to a point, balanced and then snapping loose and driving backwards off the road.
Now running racing slicks is no problem, bigs and littles is a common setup for mid-engine race cars. Lots of choices that would be balanced at the limit. Just-driving-around tires I also have solved as this is a common setup for hot rods. No, where this is a problem is street tire autocrossing, the thing I’m building this car for. Naturally.
If I stay with 15″ rims I’m pretty much boned as the 245/40 size is pretty much the widest tire I can get in ≥200 UTQG wear rating. I can use that in the rear and run a 195/50 front and get balance but not ultimate grip. My competition will be running 335 wide in the front, and even wider in the back. Granted I’m driving <1600 pounds and they're almost twice that, but still I'm going to be down on grip overall compared to the competition.
The next size up in rims with performance tires is 17", which gives me a whole lot more choice in sizes. The downside is I lose the automatic lowering for racing because the 17" rim increases the diameter of the tire by 2", it's just physics. For the same width and profile the 17" rim is always going to be 2" taller than a 15" rim. I'm still going to be a tiny bit shorter than my street tires on 15" rims, but not by much. And the thought comes to mind that if I'm going to have to use tall tires to race on why do I need to get just driving around tires? I'm not going to be driving a traditional Bucket so why run traditional street wheel and tire sizes? The treadwear requirements for the street tire autocross make the tires usable for daily driving, so why not drive them on the street?
And I'm starting to repeat myself while I type (I deleted 2 whole paragraphs) so this is a good time to quit.
Billed @€0.02, Opus the Unkillable
I was out of the house almost 7 hours today. I had a 20 minute procedure done in Lewisville and spent just over 6.5 hours getting to and from it. And I had to skip lunch because I was constantly running around to catch a bus or train with never enough time to stop to buy food. So, I had a lot of time to sit and think about things, and when I wasn’t thinking about things I was thinking about my second-favorite subject, the Mid-Bucket.
The big thing weighing on my mind about the bucket is getting rid of its inherent oversteer. There’s just way too much weight on the rear axle for 4 equal-size tires, and not enough tire selection in 15″ rims any more to be able to correct it with bigs and littles without giving up a ton of front grip. While I realize that excessive front grip is the problem, my philosophy is don’t give away what you have too much of in relation, get more of what you don’t have enough of. So, while I’m willing to find larger rear tires to get more rear grip, I’m completely unwilling to get smaller front tires to get less front grip. This is a race car, you always, always, ALWAYS want more, especially more grip. It may be a race car that I’m going to drive to the race and (hopefully) drive home, but it’s still intended to race and win.
Before I get back to the bigs and littles there are ways to keep the tire size “square” (same on all 4 corners) and reduce oversteer without completely killing the front grip. That can be done with restricting wheel travel on the front while getting absurd amounts of travel on rebound on the rear with long travel shocks and bump stops that only allow the same amount of compression as the front suspension, so that as the car rolls over on the outer tires the inside rear tire is still carrying a lot of weight because it still hasn’t extended the spring fully.
Another way is aero loading the rear more. That one is a little more tricky as rear grip will vary as the square of speed, so the car will still be loose at low speeds but potentially plowing tight as the car goes faster. This is not the way to go. Obviously I’m going to go for as much downforce as I can get, but balanced, and after I get the mechanical grip balanced, not before and definitely not “instead of”.
And I keep falling asleep on the keyboard so Nighty-Night…
Well I had two pumps, one that failed somewhere in the piston and the other one that had a rotting hose from the pump to the chuck. I only have to send one back, so I put all the bad parts in the return box and assembled all the good parts into a working pump. I then used that pump to get my tires back up to the minimum 70 pounds per square inch to prevent pinch flats on potholes.
And after I did that I felt like Superman™ so I tried to mount the tires to the wheels I had just mocked up that afternoon. It was a struggle, but as you can see:
I got the front edge even with the bead on the tire, but I need to pump the tire so the back side matches the front.
It’s hard to see from that angle, so this is easier.
So what I do now is talk to my diabetic friends about getting some used needles and syringes to pump up the tires to meet the beads of the rim.
And there’s something good coming on Science Channel, so I have created enough with the words and pictures, Opus the Unkillable