TIRE TRACTION ??

Bruce, the only time "skinny" tires pay off is when you're trying to dig through mud or slushy snow in a  4WD.

On asphalt (and concrete), the more rubber-the better. Think about drag racers, road racers and auto-crossers, the best tires for those "disciplines" are usually extremely wide slicks (no tread) because the more rubber-the better.

On street tires, you need a compromise however because you're inevitably going to encounter water. Everything changes when water is on the road. More rubber still gives more traction but only if you have sufficient avenues for water to escape from between the tire and road-surface, that's why tire manufacturers put grooves and siping to evacuate water from beneath their tires. We call it: tread or tread-pattern but in essence it's simply fancy grooves to get rid of water.

I would think you would have to have the wheels cut and re-shaped to put as much tire behind the hub as possible for some reason I can't remember what that is called

negative offset

ALL the true performance cars now are ALL Wheel Drive (AWD).   Check out the Carrera 4S which was introduced in 2005. Or the new Acura NSX (with electric motors to boot).  An AWD 550 would be outstanding!

Thanks Will I just could not think of it lol 

On the street (within reason), the more tread you can run the better, as the flotation issues that exist in the sand and dirt aren't nearly as critical on pavement. In our cars (Speedsters or Spyders) we're limited by what we can get under and inside the bodywork. 185's or 195's (on  5- 6" wheels) are generally enough for the front, as that end of the car is pretty light (especially on a Speedster) and the VW beam and suspension/steering parts weren't engineered for too much tire and wheel. With that much horsepower, the back needs all the tire you can fit- 205's, 215's or (preferrably) 225's on custom 7 or 8" wheels. It would be great to go wider, but without flaring the car wickedly, I don't know. The center mounting flange of the back wheels would be spaced to use as much of the space to the springplates as possible. To be honest, with anything over 200 or so horsepower in such a light car (Speedster or Spyder), I don't think you're going to find a rear tire to truly hold it down and keep it under control. You'll be able to spin the rear tires at will. 

Just before Christmas I had the rear pair of 15x6" Fuchs widened 1" to the inside for my Speedster. They now resemble 911R 7's (made to get more rear tire under the straight sides of the early 911's) and with irs and type 1 drums it looks like 205's (maybe even 215's?) will just fit (on the right side- haven't tried it on the left yet). I will have to narrow the trailing arms to fit the wider type 3 drums, but 1 step at a time....Al

Al I forgot what car you have but if you have front discs you could do discs in the back as well.  I have fuchs, 7 inch 16's in the rear and 6s in the front ... 

FYI running 195/55-16 front 205/55-16 rear ... now I know with the disk brakes that is all the tire I could fit. 

I have an older Intermeccanica, Ray; 1 of the first 600something built when they were located in the LA area. I got a good deal on the rear type 3 stuff ($160? at a local swap meet year before last with new shoes, wheel cylinders and I think drums), and have used them on a Cal Look and baja bug before so on the car they will eventually go. I have Ghia discs on the front and will probably run 185/60-15's on the front and 205 or 215/60-15's on the back.

IIrc yours is an Intermeccanica as well? Irs with type 1 or Porsche trailing arms?

Having built several 300+hp Subaru powered Spyder's with 2.5L STi engines I can share some real world experience.  First off, you are extremely limited in the space you have to fit a tire without adding flares to the body.  IF you keep the rear somewhere around -0.5 to -1.0 camber, you can fit a 205 rear tire.  Anything larger will hit both the inner edge of the spring plate (or 4 link bars with DeDion or coil suspension) and will rub the inside of the outer fender lip as well.  For this spec of build we've run BFG Radial TAs on the street and Hoosier Speedsters on the track.  We'll reference the Hoosiers since they are the stickiest possible at an 050 tread wear.  Off they line they stick fairly well as long as you modulate the throttle...  where they get really hairy is when you come up on boost... once you come up on full boost, there isn't a 205 tire that will hold.  Nothing like running 80MPH in 3rd, shifting into 4th and standing on the throttle while the rear tires just blow off at 100MPH.  :-)

Now, we also did an "R" body kit that was wind tunnel tested specifically for the track.  This KILLS the look of the Spyder and makes it look much more like a GP/LeMans Prototype style of car.  What it does benefit is that you can run 225 (or possibly slightly wider) rear tires.  On the last one we built we ran 8s and 9s with 225s.  I can say there was little to no negative side effect in cornering.  Hard acceleration had slightly improved traction but overall the feel/story was the same.  When the car came up on full boost it just roasted the rear tires, regardless of gear or speed.  

In short, we have not found a combination that will hold 300hp in the 1400-1500 lbs of a Spyder, but it is still a TON of fun, albeit a bit scary...

As for too much tire, yes it is possible, but I believe these figures will be at the extremes and maximum performance levels.  My experience here comes from us running the classic 24hr at Daytona last year. We ran Goodyear Eagle slicks and Avon slicks. We brought a good friend of my father and Chuck's with us, Rick.  Rick is a NASCAR engine builder and former NASCAR tire tech.  He ran temps and other info on our 904GTS tires at the track.  A quick back story, Randy Beck's 904GTS was flared 2" so that he could ditch the factory 10" wide rears and run 12"s.  We stretched a 13" slick on the 3 piece 12" rims.  What we found was that  the wider tires were cooling off too quickly and never getting to optimal temps like the 10" slicks did.  Lap times were similar, and the car stuck the corners a tiny bit better in the tighter sections, but slipped a bit more after a longer straight...  Doing tire temps when pitting showed a tire that was too cool compared to a comparable 10" slick.  Again, this is info from a track that allowed us speeds near 190MPH and driving conditions that aren't easily replicated (and not possible to replicate in a Spyder) but it does demonstrate that "too much" tire is possible under certain conditions. (both brands of tire had similar results)

All that said, you can still have a LOT of fun in a 300hp Spyder, but it is extreme overkill.  If you'd like I can put you in touch with a few clients who have this combination.  One runs several tracks in CO and has some good insight on having 300hp in a Spyder...

Al ... yes I have an IM with Irs type I back end (as you know early 944 is the same stuff. ). & 911 front end and sway bars front and rear.

Vented disks front & solids rear

It stops well with this setup

Ray

further I should say that I felt my original IM was too light in front so I got IM on my new one to have a new gas tank made which is positioned front and low to put more weight on the front axles   15 US gallons I think it helps a bit 

I am running 265 hp in my 2012 tube frame Intermeccanica.  Summer Vredestein's 195/60 front on 6 inch rims and 205/60 on 7.5 rims on rear.  I don't track and I only drive spirited and I have yet to let my rear tires loose or even spin them.  I don't don't drop the clutch from a start and only need to push the tach to 4K and I'm already ahead of the pack.  I guess if I pushed it harder it would let go.   Mind you, my car is a fatty at close to 2500 pounds but it is rock solid and planted.  

Carey, 300 hp and 1500lbs=scary:-)

With my IM6, at approximately 290-300 hp, I have 205/55x16 front on 6" wheels, and 225/50x16 on 8" wheels rear.

I can easily get 'slippage' on acceleration, but overall, it's a very manageable drive.  Of course, it weighs more than a Spyder, but it's still not all that heavy.  And Henry does widen the rear fenders for a little more space back there. 

FWIW, I am running Yokohama Advan Neova R tires.

Bob, those are great tires.

The extra 15+% weight over the rear wheels in the rear engine configuration also helps with traction (in a straight line).  Move that weight forward for a neutral balance and it's a different game...

The 904GTS, also 993 3.6L powered, is 50/50 balanced like a Spyder but comes in at 1820lbs with a full cage, 1700lbs on the street car.  :-)

That makes sense Carey, most of our roads are straight. 

I know my car should feel rear end heavy, but I've never experienced the slightest issue when cornering.   The car is just so solid and planted (as Marty says above).

What I really miss in my car is twelve months of driving...

I calculated a 180hp spyder and it has the same Power to weight as an R8 .... the center weight surely is a difference.  Thanks for sharing that info Carey.

I second that vote Bob.  I can't wait for Global Warming GW to be real enough that I can drive my car for 12 months a year as well.  I guess for now I'll have to settle for 6 months driving while I wait for GW. 

@Bob: IM S6 @Marty Grzynkowicz  Not trying to take anything away from the handling of the Speedster, and I am sure Henry has improved the handling over the original car (and most replicas) also, but talking about performance at the "edge".  Also not sure if Henry has ever "performance tested" his newer IM6 package either, but the best lateral acceleration #s I've seen from a Speedster rep was around 0.77g.  That car had a custom chassis, custom IRS rear, engine pushed forward slightly, 205 stickies, etc...   

For comparison; our Spyder pulled 0.94g on Michelins (Motor Trend tested) and the GTS pulled 1.14g on Pilot Sports (Dream Car Garage tested).  Chuck tested the Spyder to slightly over 1g on slicks, but I don't have the exact numbers...  

Carey, IM's have the engine and tranny moved forward a few inches so those numbers might be close to what is possibly going on with IM's but I am only speculating.  But then it took a Corvette years to get to 0.8 if I am not mistaken. 

In any case it's the shape were in love with not the track performance for most of us ... you know there is getting to be a lot of white haired guys behind the wheel   

Carey:  I would never try to compare a Speedster with a Spyder in terms of what you detail above.    A well sorted Spyder should better a well sorted Speedster when you get to the 'edge', as  you say.  Those figures are impressive, to be sure.

 They are two different animals completely, meant for different ways of having fun. 

  I couldn't agree more, although the latest iteration of Speedsters from several manufacturers push the envelope towards performance more than ever...

Your right Carey, the dream of more power is always there till the guy loses it on the wet and rolls it as was the unfortunate story of one list member with 350hp in a speedster.  The front end is pretty light to go much faster than 100mph in these cars and not get take off, of course that is if you want to live to tell the story. 

Key phrase here: "it is extreme overkill."

The whole concept of a 300-hp Spyder reminds me of a mechanical engineering project class I profiled in college. The professor would change the project each year, set a goal and let the students go at it in teams. The one I watched: create a device that will carry a payload through an infinite medium of styrofoam packing peanuts. More points for speed, more points for payload weight. GO!

My buddy came in second, using a cordless drill motor and conventional auger design. The winner used ultralight rubberband propulsion. 

My favorite entry? The Tim "The Toolman" Taylor, MOAR POWAR design that involved thresher tines, a chainsaw engine, and dry ice to cool it. The thing really didn't work, and the professor eventually decided it would be too dangerous to unleash it inside the giant tube of packing material he was using as the test bed. Something about the very real danger of a fire, releasing clouds of "deadly bromine gas."

That entry was, to me, the epitome of Americanness. It was over-powered by design, and the designers wedded themselves, with a veritable death grip, to that unsuitable engine. It was way too complex, with more complex sub-sytems bolted on (a 500-to-1 brass gearbox, onboard oxygen, the afore-mentioned dry-ice cooling, etc.) to correct for that elemental error in the design. 

This is the real-world meaning of "extreme overkill." Proceed with discretion.

350hp in a Speedster? It was before my time. Anybody know any details?  I'm guessing turbocharged type 1? pics?

                     THESE THINGS YODA MUST KNOW!!!

I had a 120 hp aircooled spyder and a 165 hp watercooled spyder.  On a road course both would drive circles around my current 145 hp IM.  They are lighter and the handling is not comparable.  I've had my IM sideways at pretty low speed but NEVER had either of my spyders sideways even on challenging road courses.  With the spyder if the tail goes out a little around corners you counter steer and give it a bit more throttle and real in the tail.  Easy Peasy.  Man I need another spyder.  I would say that at speeds approaching 100 mph the front end of both my spyders started feeling very light...scary.  I can easily drive at 100 mph in my IM...solid as a rock.

Carey - wish Chris and I had been there at the Rolex 24 last year.  We would have been thrilled to Spot for the 904.  At that speed, I assume you guys were running in the GT class - same class we spotted for with TRG.  We spotted for Wolf Henzler in 2012 when he made up 45 seconds in the last 70 minutes to place second behind Andy Lally - one hell of an ending!

You going back this year?   Or are you all broke from running last year!?  

 @Gordon Nichols

We ran in the "classic" which isn't as intense as the Rolex 24, but was a BLAST nonetheless.  And YES it put a hurting on the 'ole checkbook...  We do plan to go back in November and run it again.  

They put us in Group F which was a hodgepodge of unlimited/unrestricted HSR approved cars that did not fit into classes A-E or were never eligible to run Daytona previously.

Whew !....See.....This is what I was referring to on another topic ! Ask a question and the answer may be like trying to get a drink out of a fire hydrant !  Thanks for the info !

Based on your responses, maybe i should tone it down on the HP ? Why ? Because it looks like it's pretty tough to get that kind of HP on the ground without spending a lot of bucks for something rarely used (based on the type of driving I do). Additionally, the 100 mph threshold scare factor means something to me with all my grey hair and supposedly gained wisdom. However, there's a little of that kid part is still in me ! This would not be a factory order. It would be a "home build" for the most part.

Carey....How much HP would you suggest ? I would like to use a Subaru. Would 220 to 250 HP be a better choice ? I'm sure you have a list of other parameters I should look at as well

Also. I was thinking about the ratio of tire footprint area to pounds per sq inch on that area to rubber durometer softness/stickiness.  Are there any charts or formulas that relate to this ?        Bruce

The cost of running in the Rolex 24:

A friend of ours ran the Rolex in 2009 but contracted with TRG to provide all of the support - car prep, 2 weeks of practice, the week of the race, car transport to/from, defined spare parts (usually 3 of everything off of a list) and on and on.  

I seem to remember the bill for that support for the month of January was around $185,000.   And that was for a gentleman racer who DNF'd.  

BUT!  The experienced gained........Priceless!   He's been back (in the Continental series) ever since.  

Just for us as spotters, the event passes were over $300 each with $100 of that a pass to stand up on the grandstand roof!   Daytona is NOT a cheap date.......

Bruce:   A couple of things to consider;

First is whether the 200-250 hp is normally aspirated (NA) or turbo'd (T).  Non-turbo power (torque) comes on more-or-less as a constant build then flattens out.  Turbo'd power starts lower than NA (usually because the engine develops less power without the turbo boost) then quickly builds as the boost comes on and keeps on building til the wastegate pops and holds you there.  While T power is more accelerating in a straight line, it can become a real chore to tame that power in the twisties, especially with a car as light as a Spyder.  For winding roads I would prefer the more "refined" torque of a NA car.  

Secondly, I personally would not run that much power in a swing-axle car, especially with the quick power transitions from turbo boost.  Get on it a little in a corner and it tracks near the limit of adhesion.  Flex your right big toe and it looses adhesion and leads with the rear bumper.....almost instantly.  Not a pretty sight.  

Within the limits defined by Carey, I would run as much rear tire as possible.  I had 225's on 7" wide rims on the rear of my Speedster and never got them to break loose on a track (to be honest, I ran out of balls before the tires ever ran out of grip).  I don't know if they would fit, but I would find a way, with 205's on the front.

my dos centavos.

Gordon Nichols posted:

The cost of running in the Rolex 24:

A friend of ours ran the Rolex in 2009 but contracted with TRG to provide all of the support - car prep, 2 weeks of practice, the week of the race, car transport to/from, defined spare parts (usually 3 of everything off of a list) and on and on.  

I seem to remember the bill for that support for the month of January was around $185,000.   And that was for a gentleman racer who DNF'd.  

BUT!  The experienced gained........Priceless!   He's been back (in the Continental series) ever since.  

Just for us as spotters, the event passes were over $300 each with $100 of that a pass to stand up on the grandstand roof!   Daytona is NOT a cheap date.......

How much would it cost to run or attend a Seiko 24, if there was one? It would have to be less, as I can buy one of those watches for about $100.00.

Jah... Jah  "pro racing" a little on the high-side...$ wise 

 ReV

@aircooled  Personally I think our stock EJ25 is more than enough power for most.  It is a dyno proven 175hp and it is in bone stock OEM Subaru form, stock ECU, easy to maintain, easy to service, straight forward.  That said, I can see the car with an extra 50hp  (maybe even a touch more) from a NA mill so the power was linear.  It would be much easier to control than a turbo car, and much easier to build/maintain.  

One BIG consideration with a turbo build is efficient cooling of the charged air, which is another complete topic itself...  We have done it, and done it well, but it isn't an easy task and requires a LOT of moving parts.  You can pretty much forget air to air and have to go water to air for the intercooler, which also means a 2nd radiator just for intercooler air, and a pump, and a way to monitor it... etc, etc...

Other things to consider, yes... good brakes are very important (we require it on crazy builds like this), a quality built transaxle that will hold the power (also a requirement for aforementioned builds), gearing to maximize the drivability within the aerodynamic capabilities of the car, best tires you can get, to name a few.  If it is going to be tracked at all then you also have to consider other safety items (fire suppression, corner worked switches, cage, etc), but from the sounds of it you are planning a street car?

@Gordon Nichols  We were certainly the Beverly Hillbillies of the 24hr.  Our tow rigs were 2500HD pickups with 30' trailers, not semis with stackers.  My support crew consisted of shop guys, my dad, Chuck, Randy, Rick,  and anyone else who could be paid in beer.  We rented an AirB&B, and while it WAS a penthouse overlooking Daytona Beach, it was cheaper than a motel and we crammed as many in there as we could.  The overflow stayed in Chuck's brother's RV at the track...   We carried our own 55gal drums of 110, a few sets of slicks, and a handful of spares.  Absolutely nothing like the "real" racers that surrounded us. All that and it STILL made me cringe when I tallied everything up... not to mention the $50K melted down 3.8L RSR engine... UGH.

Yeah, Carey.......    But you all had the time of your lives, didn't yah?

And where else can a spectator attend an event of this stature and get a garage/pit pass to let you wander right up to the cars and drivers before the race and BS with the mechanics?

First year we spotted (2009), we froze our butts off on the grandstand roof at 2-6am, but our car won the GT class.  Next time we spotted, Mrs. Buckler, TRG owner's wife, gave us these spiffy Arctic Parkas as a thanks for helping make the 2009 win.  That next year, TRG #67 came in second.  We got to keep the Parkas.

BobG:

You can run in the Seiko 24, but the watch you would win looks like this:

My VW transaxle codes list has several codes for a transaxle with Limited Slip Differential (LSD).  How rare are they?  Sounds like "AR" code KG 3.87 LSD one would be the hot ticket without rebuild work. Assume the Type 1303 is foreign model.

AL        1500           4.375         T181 Thing LSD

AP        1600           3.875         T181 Thing LSD

AQ       1600           4.125          LSD from 1971-1972

AR        1600           3.875          KG with LSD from 1971

AU        1600           3.875          Type 1303 with LSD from 1973

Apparently, these are all US codes which can have an LSD too:

AX
AY
AV
AW
CY
PE

What the difference on the T3 trans (other than wider rear brake drums)?

DB        1500/1600          4.125          Type III SA to 1968 with LSD

DD        1500/1600         4.125       Type III IRS from 1969 with LSD

Looks like near all the Semi-Autos had LSD, can that be moved to a 4 speed?

    BC           4.375            1300           Semi-Auto
     BC           4.125            1600           Semi-Auto
     BF           4.125            1600           Semi-Auto
     BH           4.125            1300           K-G Semi-Auto
     BK           4.375            1300           Semi-Auto

Carey....I hadn't even thought about the inter-cooler required for a turbo. Air to air is nice but not very efficient. Heck... in other applications air is used for an insulator. I can readily see why your using liquid. Turbos are "peaky" and it's hard to tell when they're going to come on. I guess a NA version is the goal at this point and yes, I'm not going to be on a track with curves.  What is the highest HP Subaru engine available ? I have in mind to use a VW IRS trans with the usual Rancho strengthening components incl. a LSD.  Jeeze....Here we go  !!!!.......Bruce

For that amount of power (250-300+ hp) I would be looking at a HD Quaif differential instead of an LSD "Super-Diff", and with that the $$$ goes way up.