Dragmeisters Andrew, Calvin & Patrick...'splain tire choices, please.

I got my autocross tires out of the discard pile at a local road racing track. While they were used Hoosier SM7 road racing tires they did grip pretty well, and they were free.  I drag raced on two Michelin snow tires that were included in the purchase price of the car and a pair of Mickey Thompson ET Drag tires that I got off Craigslist for $50. They were 10 years old but would launch better than the Hoosiers. All told , I only spent $50 , plus mounting cost for 6 tires to go to the Challenge.

For anyone in SE Michigan there are currently a dozen Hoosier SM7 tires for sale on Craigslist at $35 each. They would be fine for any small car to autocross on.

To Andrew, Et al:

Your advice, comments, posts are  always welcomed.  You just don't suffer fools gladly.

I guess one of the biggest challenges I find in the used tire department for both autocross and drags is tire size. 22" tall tires and 26+ tall tires aren't too hard to find, but 23-24" tall tires wide enough to prevent wheel spin don't seem to be very common. I need to step down to 15" wheels but other than 205 wide Miata tires I don't see many options. I guess I need to spend time hanging out with the import tuner crowd.

Robbie said:

Ovid_and_Flem said:

In reply to wheels777 :

Thx, Andrew.  So for a 2400 lb rwd challenge car with an honest 300 hp what would you pick?

What tire height (gearing) might be the more important question, or at least something that needs to be considered.

This was what hurt tetanus the Miata truck. It went from spinning into third last year to being unable to spin but accelerating slower *everywhere* else.

What changed? The sticky tyres were taller impacting effective gear ratio and very predictably reducing acceleration everywhere.

Zero doubt that the first foot was faster with slicks, but the spin actually enabled the engine to make more power and deliver some fraction of that to the track, more than the zero-slip lower RPM could.

Reality is that the engine is under powered for the resulting ratio and the best fix, as always, is boost. But do pay attention to the effective ratio, the miata truck would have beaten last year's time with say a 5:1 diff in it, and all else equal.

What changed? The sticky tyres were taller impacting effective gear ratio and very predictably reducing acceleration everywhere.

I talked to Steve about this beforehand and offered both 20 and 23" diameter slicks. The 20" slicks are discontinued and hard to find!  Already mounted on 10lb wheels courtesy of my 2001 Honda Insight Hybrid. LOL

In reply to Patrick :what sort of penalty would a lack of drag slicks impose on the higher horsepower lower weight cars?  

I'm trying to do a budget vs equipment spread sheet to determine where to spend my money and I have no experience with drag racing.  Nor do I have any idea of what still useable slicks should cost.  

Further if I'm using radial tires in the front would bias ply drag slicks not be  acceptable?  

How old can a set of slicks be before they no longer offer a benefit?  

In reply to frenchyd :

Well, I can tell you that autox tires are hardly better (if not worse) than street tires for drag racing. And that is on my relatively low HP  high weight cars. Slicks seem to be able to make almost a 1 second difference in the 60' time, and that translates to a lot in the 1/4.

I don't think there are any rules against radial front and bias ply rears. As to performance I have no idea.

OK...let me throw another question in.  What tire presume are you running on different tires?  Differences between bias slicks, drag radials, Street radials? In 2016 we dropped pressure on ax tires down to 22 psi with some minor performance gains in 60 foot times.

But still sucked.

I don't have much to contribute, I'm reading along and soaking up the good information here.  Also, what does "IC" reference?

Indy-Cougar-Guy said:

I don't have much to contribute, I'm reading along and soaking up the good information here.  Also, what does "IC" reference?

IC= Instant Center,  I think.  But way above my pay grade.

Deals with anti squat, weight transfer, good launches, suspension set up.

Robbie said:

In reply to frenchyd :

Well, I can tell you that autox tires are hardly better (if not worse) than street tires for drag racing. And that is on my relatively low HP  high weight cars. Slicks seem to be able to make almost a 1 second difference in the 60' time, and that translates to a lot in the 1/4.

I don't think there are any rules against radial front and bias ply rears. As to performance I have no idea.

A second difference is only if you do a2b testing and all you did was bolt them on. I can test and get radials right down to slick times, but the key word here is testing.

Just the little bit of guessing at the track lowered my first Miata time from 17.2 to 16.9. I know I could have easily gone even faster with another pass or three but I was happy to still have a running and driving car. All I did was lower the tire psi to 27 from 45 in the nt01’s, increase launch rpm from 3500 to 5500, and stayed shifting at 6500. 7000 rpm shifts would have been better, but I was already smelling lots of clutch after two back to back passes with no lift shifts.....

People have done the VW 185’s up front with bias slicks in back for decades....

In reply to Ranger50 :Thank you Robbie that was informative.  

Now do I run a TH 400 with a shift kit or my racing 5 speed?  The 5 speed is  a true race transmission   (dog rings and a quick change gear set with spare alternative gears) with a still usable 7 &1/4 triple disk Tilton clutch and flywheel. 

While the manual gear box would be a lot faster in a race it makes driving it on the street nearly impossible.  Part of the fun would be that V 12 in a little MGTD and there are a lot of venues I can drive it to but darn few where I could race it.  

Mixing tire typed front to rear on a drag car isn't like the old tales about not mixing bias plies and radials on the street.  Generally you're going to have whatever your normal street tire is on the front and your drag tire on back.  Generally skinnier on the front is better(assuming rwd) as wide tires will move you more with less steering input.  My car is way more comfortable on the strip at 122mph on 205 tires on the front than it was on 245 hoosiers at 114mph.  Now the challenge life of the car is done I'm putting on some normal 195-205 narrow tires when it sees dragstrip time.  

I wouldn't try and run a street tire on a 300+hp light car.  That's just me, i've been burning street tires on the dragstrip for years.  My belair is around 3200# with 330hp and a 2.73 gear and it will spin through first gear on a decently prepped strip with 245 wide street radials.  

As far as cheap tires go, keep on craigslist and whatever else you use.  I passed up some free 275/60-15 drag radials a few months ago.  Had too many tires sitting around.   I'm going to keep my eyes open for some 275/40-17 drag radials for next year.  Hopefully i find some cheap ones.  Found a pair of 315/35 hoosier r7 for 200 new with stickers as well as new 22x4x17 goodyear front skinnies for $100 from the same guy.  

In reply to Patrick : I understand what you mean by having too many tires sitting around,  I recently had to pay to get rid of some race tires simply because space was getting too crowded.  

What sort of price is a good deal on used drag tires?  1/2 of new,  1/4 of new,  10% ?

how do I tell if a drag tire is too hard?  Assuming I don't have a durometer with me.  Is it the old stick a fingernail into the tread and the deeper it goes the newer or better the tire is?  Numbers on the sidewall? How old is too old?  

I do the fingernail test.  My previous tires are dated 2009 and they are still sticky.  I try and stay under 6 years but challenge budget dictates take what you can get.  

I can usually find tires for $150 or less per pair if i wait long enough.  Last year's tires were $100, this years were $100 with wheels.  

As long as they're cheap enough, even if the tires are worn, hardened, etc. and nowhere near as good as a new set, they're still likely to be far better on the drag strip than an autocross tire. 

rslifkin said:

As long as they're cheap enough, even if the tires are worn, hardened, etc. and nowhere near as good as a new set, they're still likely to be far better on the drag strip than an autocross tire. 

Pretty sure I did a 1/4 mile burnout on Hoosier A6 tires at the 2015 challenge. 

Good tires are the best performance bang for the buck on a low budget car. 

Drag slicks have the advantage that they are almost always stored out of direct sunlight. Hell, sometimes they're even stored in climate controlled areas! Also, noone buying bargain basement used drag slicks cares about lifespan, which means if it isn't hooking (after usual other tricks like lowering pressure within reason) then just do a longer burnout! Even 'ancient' slicks work FAR better than street tires if you get them hot enough.  In summary, old drag slicks dont suck as bad as old autoX slicks or old street tires. 

Honestly, any car that can spin a tire half or all the way through first gear stands to see huge ET gains from a drag slick. The trick is not running one in a way that costs you as much as it gains you. I.e. too tall or wide, or running at at 12psi when you could have hooked up at 22psi anyway. 

In reply to Vigo :

And even in the autocross world, old slicks can still be better than new not-slicks.  A friend tried it once.  New Z1 star specs vs old, mostly worn A6s and also compared to fresh A6s.  The A6s were much faster.  The old ones were slower than the new ones, but still significantly faster than the Z1SS (they pretty much split the difference IIRC).  

I used road racing Hoosier R7s as autocross tires. Conventional wisdom says you can't get them up to temperature on a short autocross course. We got them hot enough that we twice had let 4 psi out of them, starting from 30 psi cold. 

On the strip I used some 10 year old M/T ET Drag tires. They passed the fingernail test and would launch noticeably better than the Hoosiers in my driveway. I assumed that difference would carry over to a tacky strip, but I didn't test the theory.  

This was with a light car (Miata) and 180ish HP.