Drag Tire & Wheel Setup: FWD Edition

A few weeks back, we had the very informative thread about tires and tire setup for drag racing. I'm now hoping to head out in the next few days and pick up some decent deals on tires I've found- but have a few different options that I need to figure out and could use some help with.

Basically- how is it best to setup a moderately-powerful turbocharged FWD car on the drag strip (the Rampage pretty certainly won't be putting down the power of, say, the ScAries but should hopefully be more powerful than stock)? With a RWD, it's generally 'as much rubber as possible' on the rear, and skinny tires up front- but obviously that doesn't work on a FWD and even simply reversing it doesn't quite work either (because you need to be able to turn getting on and off the strip...).

Does it still make good sense to run really narrow wheels & tires on the back of a FWD car?

Is it better to have taller or shorter tires on the front of a turbocharged automatic FWD? Do I still want as high of a diameter tire as can fit properly under the car as you would with a RWD?

Related somewhat- suspension setup. I've read that the rear should be set to be as stiff as possible, something fairly easy with the air shocks in the back of the Rampage- is this correct?

Thanks!

You never want as tall a tire as will fit, you need to use your tire diameter as a means to help achieve the desired final drive ratio.  Taller tires will slow you off the line because you’re effectively gearing numerically lower.  I think you’re going to want to look for a 22x8 (m&h racemaster may be the only company making them) sport compact slick for your rampage, and while I have never tried it I have seen plenty of fwd drag cars with rear skinnies.  Another option would be a shorter drag radial.

I will keep my eyes open for shorter drag tires, i’m generally looking every couple weeks anyway.  

I want to know as well. One thing I have learned for heavily modified FWD cars is that the transmissions can become weakpoints, and drag launches are especially hard on them. Smaller diameter tires REDUCE the torque load on the transmission while taller tires INCREASE the torque load. So big tires can break transmissions.

p.s. let me know what deals you have found, I may be interested in similar stuff for the saab truck.

One trick I have seen that seems really cool is to mostly negate the need for an LSD up front by putting an air shock on ONE back wheel. If one front wheel spins, either pump up the rear across from it to add diagonal weight, or air down the rear on the same side to remove diagonal weight from the other side. Since you can only change diagonal balance and not front/rear or side to side with ride height, it doesn't matter whether you are adding air or letting air out.

not much to offer, but am interested in hearing what the hive has to offer

https://www.youtube.com/watch?time_continue=37&v=v4XXZLPhCTE

Robbie said:

I want to know as well. One thing I have learned for heavily modified FWD cars is that the transmissions can become weakpoints, and drag launches are especially hard on them. Smaller diameter tires REDUCE the torque load on the transmission while taller tires INCREASE the torque load. So big tires can break transmissions.

p.s. let me know what deals you have found, I may be interested in similar stuff for the saab truck.

One trick I have seen that seems really cool is to mostly negate the need for an LSD up front by putting an air shock on ONE back wheel. If one front wheel spins, either pump up the rear across from it to add diagonal weight, or air down the rear on the same side to remove diagonal weight from the other side. Since you can only change diagonal balance and not front/rear or side to side with ride height, it doesn't matter whether you are adding air or letting air out.

The 3-speed auto used on Turbo-Dodges is based on the 727 Torqueflite and is pretty stout in stock form, more stout with some help with a MVB, better cooling/more fluid and a limited slip/welded diff.

You can also shim the front sway bar as an ersatz weight jack.  In combination with rear air shocks to assist with movement (not weight transfer, that happens regardless of what you do), you could pull some decent 60-foot times with some practice.

In reply to Robbie :

I've heard several times, at least in regards to the Rampage/other TD's, that for the drags if you're running slicks that limited slip or a spool (which is what I've been considering) generally isn't necessary.

Right now, the most appealing options are either a 20x8x14 slick (https://cincinnati.craigslist.org/pts/d/14-inch-racing-slicks-on/6334645265.html) or a 28x9x14 slick (https://chillicothe.craigslist.org/wto/d/t-racing-slicks/6377742055.html). Honestly I'm a bit worried whether the 28's will fit, but I think I could make it work. These are the most appealing options because I have a set of 14" wheels that came with the car- I may have to track down a pair of 15" wheels though since there appear to be more options for the 15's.

Pretty certainly going to be picking these up for the rear to go on the two space-saver wheels I picked up a few weeks ago: https://dayton.craigslist.org/wto/d/hoosier-drag-fronts/6385348186.html

the 28s will be HUGE and HEAVY. I'd probably stay away from those. I'm scanning my CL like a hawk for 22x8x15 drag slicks or something close as 15 inch saab wheels are common and cheap. Let me know if you guys see anything please.

Adding slicks for FWD launches is the best way to find your next weakest link.  More related to autox than drag but similar issues.  I replace stock axles frequently after breaking as they are far easier and cheaper to deal with than hurting the trans.

+ many on the shortest and wides tire you can run pending gear ratio considerations.

In reply to Patrick :

Thanks!

Looking at the options, it looks like if I keep the 14's the only options in new tires I can find are 26" diameter tires. If I drop down to 13" or up to 15" diameter wheels (13's can be had pretty cheaply, 15's are a bit more but not unreasonable- and if I'm not using the 14's I'd likely be selling them for recoup). 14" just appears to be an unpopular wheel diameter for drag racing...

84FSP said:

+ many on the shortest and wides tire you can run pending gear ratio considerations.

If I can find a better deal on 14" A/X tires than the WIIIIDE 13" wheels/tires I picked up from Stampie, it would be interesting to use those wheels (they are pretty darn wide...) with drag tires..

Would be a bit of a waste though given I also picked up a spare set of tires from the Georgia Tech guys (since the wheels/tires originally came from them...)

28’s are huuuuuge.  I have a new set of 28x11x16 here and they’re pretty well only usable for very large wheelwells.  We put that size on the parking lot build firebird last year and they only worked because the body was chopped away.  If you want i have a 22” tire downstairs too and can overlay it on the 28 and text you a picture to show just how massive the 28’s are.

28s don't fit much besides pickups without fenderwell work.  Even stock big tire stuff like C5s don't take 28s easily.  

For diameter, my recommendation is to throw together a spreadsheet that will tell you what your speed is at redline in whatever gear you want to be in at the end of the dragstrip based on different tire diameters.   If you have an ET target, use an online calculator to get an idea what speed you are likely to be going at the end, then add a few MPH to it for a fudge factor. 

If the correct tire size is ridiculously large or small, consider trying to run in a different gear, or accepting that you won't be accelerating at your best in your top gear.

I did some measuring, and unfortunately even the 27" drag fronts I'd hoped to get for the rear are too large. :/ Guess I keep looking...

Ack, im always late to turbo dodge threads. 

Your car is an automatic with a 1:1 3rd gear and 3.02:1 'effective' diff ratio. You probably won't want to spin past ~5500 in 3rd. The shortest drag tire you could reasonably expect to get your hands on are those 20" slicks (they're discontinued. I own a pair).  Even with 20" tire diameter, that gearing and rpm will get you to 108mph, which means you have about 20mph of headroom. That's a euphemistic term for 'not being geared properly for the power you have'.  But, i would still go that way because every taller tire is just going to make your gearing less optimal than that, and 108mph is a good, realistic ceiling for what you could expect to make on that stock motor without doing anything fancy. 

I don't think you should really worry about getting enough traction under the car. Even those 20" slicks will be enough. The autos are super easy to launch and have a tall first gear. The car is light. It won't need a diff, weight jacking, or anything else besides some restraint to get a good 60'. You probably WOULD be able to spin them at some point, but it would only be while 'doing it wrong' i.e. making a useless and dangerous amount of cylinder pressure at 3000rpm that is more likely to break your engine than improve your ET. You can build a simple 2-step boost control system with a 2nd cheap boost controller and an rpm switch. Just set the RPM switch a couple hundred rpm higher than your converter stall rpm and the 1st stage boost controller literally becomes a 'launch adjustment knob'. Floor both pedals and tune it in with the knob. 

You should be able to go 12s with a pretty dang basic setup. 

So, a more general drag tire/wheel question:

With total tire diameter being equal, is it better to have a larger wheel (and shorter sidewall) or a smaller wheel (and taller sidewall)?

Since they don’t make the 20’s anymore that I can tell, the next step up is 22” tires, which come for both 13” wheel and 15” wheels- neither of which I have at the moment. So would it be better to get 13’s or 15’s?

I'd think 13" wheels would be the better choice.

The taller sidewall gives the tire more deflection and theoretical traction.

The smaller wheel moves the moment of inertia closer to the axle so even if the weight is the same, it's easier to spin up to speed.

Yeah, i'd say it depends on the wheel and tire but drag tires are very lightly constructed so since in this case tire is lighter than wheel and more tire sidewall makes the launch more forgiving, i'd say it is better to hit the same diameter with less wheel and more tire. Not that you have options, mind you! If you want a 20" slick it's basically the set you miraculously spotted on craigslist, or give up.  If you want to go up to 22-23" then you will have actual options.

I’m kind of on the fence about picking up the pair of 20s because the seller has been pretty adamant that he’s not budging on price- it doesn’t matter much for Challenge budget since they’d be two of my set of ‘free’ tires (if I used my own wheels), but I also have to somewhat watch actual costs too. 

Ashyukun said:

I’m kind of on the fence about picking up the pair of 20s because the seller has been pretty adamant that he’s not budging on price- it doesn’t matter much for Challenge budget since they’d be two of my set of ‘free’ tires (if I used my own wheels), but I also have to somewhat watch actual costs too. 

That’s a tough balance to work with, i feel you.  That’s why some people show up with stickered $1400 A7’s and some people show up with used road race tires.  I can’t justify that to my personal budget. 

Can you find a drag radial in a 20”ish tall tire?  They’re making some small ones these days.  I’ve started actively looking daily again around here for you.

The problem with drag radials is that a modified turbo dodge 2.5L is going to make ~300-400lb ft of torque so it's sort of like recommending drag radials to a 600hp Honda.  There is really noone in the turbo dodge community that has had good experiences with drag radials. 

I know they make 'drag radials' today that people go 8s in the 1/4 mile on, but sadly i dont think any of those models have sizes that are appropriate for a small fwd. Hopefully things have changed by now and i'm wrong, but in general the TD community has written off drag radials because noone ever comes back with good things to say.

I've gotten the impression that some of the new drag radials out there are pretty much like ET Streets.  A street tire in name only.  Lots of sidewall flex and little tread.  Still, I'd think actual slicks would be cheaper than those tires.

I grabbed a set of 22x8x15 drag slicks a week or two ago for $125. Might've been a little pricey but they are exactly what I want, now I just need to get the two cheapest 15 inch saab wheels I can find!

I ran the Challenge Miata with 22x8x15 Mickey-Thompsons. The autocross tires were 205/50/15 Hoosiers, so they are almost exactly the same width and the Mickeys were an inch shorter. Plenty of room in the wheel wells.