Challenge Drag Tire Decisions

Somebody help me before I make a bad decision on drag tires for my Challenge car.

I'm bringing the 2016 Challenge Opel GT back this year and want to actually get the power to the ground this time.  These smallish cars are kind of fun (not) to find cheap take off tires that actually fit.  The way I understand it actual drag tires would greatly improve my ET since it will spin in 1st and 2nd on street tires.  I've found a pair of Hoosier Quick Time 245/60-15 DOT drag tires second hand, but supposedly new for $150 for both, but at 26.2" tall and 11" wide I'm pretty sure they're going to end up rubbing on the wheel arches with even the slightest body movement.  Although they sound too tall they are actually the shortest ones I have come across without paying retail for new.  It seems the 27 and 28" tall slicks are a lot more common.  Then there's the matter of ideal gearing and how much will to tall a tire negate the benefits of running a drag tire in the fist place.

Using an online calculator with a final drive of 4.88 (1.308 3rd gear x 3.73 diff) and the 7300 rpm rev limiter as the target rpm, The ideal tire size is just over 23" dia. (a tad larger than my autocross tires)

If I drop the target rpm below the rev limiter to say 7100 rpms, the calculator gives me 24"dia as ideal.  In order to get to where the 26.2" Hoosier comes in line with the gear ration I have to drop the target rpm all the way down to 6500 rpms.

I really don't want to pass up a good deal on real drag tires, but if they won't really provide a significant benefit there's no sense in wasting budget funds.

Any words of wisdom?

Front wheel drive drag tires are much better sizes for you. 20x8 or 22x8 I think are common.

Check out Honda forums? Cl scored me a pair of 22x8x15s last fall.

what does the powerband of your Opel look like?  6500 vs 7100 may not be a large deficit

Weight is a big factor too, as well as gearing. 

Weight is 2290 with driver and the power curve should look something like this Stock SR20det dyno example

Rear end is 3.73 and gears are as follows: 

1st- 3.321
2nd- 1.902
3rd- 1.308
4th- 1.000

I'm expecting to be at the top of 3rd at the end of the 1/4 

No, I meant weight of the tires.

26.2x11 is a LOT more tire with the weight a LOT further from center of rotation than say a 22x8. It will take quite a bit more to accelerate just the tire itself.

No matter what you do I'm excited to see this beastie again.

Ahhh, yes.  The effect of the larger moment of inertia on the angular acceleration will gobble up some of the power that is supposed to be pushing the car forward. Good point.

Big slicks are dream/part killers for small cars. It will do as much harm as good in the end. PROPERLY sized slicks will be a game changer. Just buy 23" slicks! 

Okay. You have all helped convince me. I'll keep looking for small diameter slicks.

If anyone is looking for 26's here's the link for the ones I found. They actually come with wheels also. Hoosier Quick Time 245/60-15

That's not a bad deal on either. See if you can fix an import tuner in town. Thanks might have a lead on the smaller fwd drag tires as pointed out above. 

i dunno

i ran some calcs on http://glennmessersmith.com/shiftpt.html#data using the power curve you provided and gear ratios (no vehicle weight) and it looks like on a 23" tire, you're hitting 97mph at the top of 3rd (6900rpm), and 6600rpm in 4th is 121mph.  

based on https://robrobinette.com/et.htm, your car with 220whp and 2290lbs should pull a 1.73 60' time and boogie down at 12.45 @107.2mph, so you'd be in 4th it sounds like based on the calc results above.

on a 26"tire, 6900 in 3rd is 109mph.  one less shift saves ~.3-.5sec depending on how hard you slam them.  but, the rpm drop from 1st @ 7000 to 2nd  is 3000 or so, which is pretty steep on such a tall tire.  i think i'd plan to shift to 4th on the short tires and let the effective gearing help you accelerate

In reply to stylngle2003 :

Thanks for posting those links. The shift point calculator is especially helpful. I was going to attempt those calculations by hand at some point and you just saved me the trouble.