*IS* wider better? Tire width vs. vehicle size/weight

Because I need to buy new wheels, my first reaction was to "go big or go home". However, I stumbled across a comment in a wheel review the other day that caused me to question my original choice.

The vehicle in question is a 1990 Dodge Daytona. It's primarily a street car with intended autocross and occasional road course duties in mind. It weighs less than 3000# wet. The combination that was on it was: 16x7 +30mm with 225/50/16 tires. My "go big or go home" plan was 18x10 +15mm w/15mm spacer-adapters and 285/30/18 tires. Yes, this will require body modifications to "fit". I don't care about that.

The comment that made me question this is that, is this car actually too light to make good use of that size tire for my intended purposes? Would it be able to get the tires up to an acceptable operating temperature, or should I actually look at something more like a 265 tire so that more load is put into the tread, thus more heat?

There's a significant difference in cost (to me anyway) between these options, so I want to make sure I spend my money wisely on the new setup.

Thanks to all for the insight.

Do you have the power for the 285s? I am all about light weight wheels and unsprung weight. I run lots of 9lb volk te run with super sticky 205 rubber on my cars that are 1600-2450lbs.  Then I have cars with 305 and 285 sticky rubber as well, but those cars have massive power and weigh 2900-3500 lb 

What is your purpose for the car? Drag race? Corner carver? Looks?

For me lots of people spend money on tires and cheap out on heavy low quality wheels.  Looking at the bigger picture first and working from that, I think works out best IMHO

In reply to Reaper1 :

Too wide just adds drag both frictional drag from the rubber squirming and aerodynamic drag from pushing extra air around.  
 

It's not just the tire though. Heck Can Am cars weighed less than 2000 pounds, had 450+ cu in big block Fuel injected Chevy's making 1000 horsepower back in the late 1960's. The drive tires were as much as 24 inches wide.  But very soft rubber!!  I digress

cars of your era have lousy suspension geometry.  Maybe fine for the narrow tires ( 6 inches of tread  was considered wide)  and typical drum brakes of the period.   However  modern tires can easily exceed 10 inches of  tread. With wildly different profiles.  

Tradeoffs like "too wide" depend heavily on the course and how much time you spend cornering vs how much time at high speeds (such that the aero drag from the tires is an issue).  It also depends on how much of the tire is exposed to the air stream vs hidden inside fenders.

I suspect that for autox wider is always going to be better, and for road courses you're going to have to test and compare to know for sure.

Miata autocrossers are starting to use 15x12 wheels with 295/35/15 Hoosiers. I heard a rumour that 315/30/15s may become available. This for a car that weighs 2300# or less.

I'm very curious why youd want to go with an 18" dia.  That sounds like a bad idea.  If it were me I'd stick in the 15-16" range.  And then figure out the widest I could go.

In reply to codrus :

Wider is not always better even in autocross where aero doesn't have the impact.

Wider means you have to drive further than a narrow car.  Even if it's only a foot a corner, add up all the corners and those feet is what you've got to overcome just to break even. 

A few things come to mind about this car, how much power is the engine making, coil-over or stock suspension, and do you have a LSD?

As for tires/wheels size on a G body I would not go over 17" diameter wheel I found fitment issues with out cutting the car. As for width I would hold up at 245 mm, reason being the K-frame will start breaking away from the body. I have heard someone pulled the K frame bolt boss of an Daytona.

My last G body ran 245/40/15 on 10 inch wheels, worked well.

Paul

Terry Fair has found in his race and test cars that wider is always better.  In his 2011 Mustang he found that without exception, every time he increased tire width his lap times dropped.  He finally wound up with a 335F 345R setup and broke all kinds of lap records.  Granted, that's road racing in a heavy car with a lot of power, but even on his BRZ he's running I think 305s on all corners.  The big downside is cost.  265s would definitely be cheaper and for the average user sufficiently fun.  Since you said it's primarily a street car with some autocross use, I would take that into consideration.

In reply to 79rex :

Wide 15" tires are generally 22.5" tall.  For cars that want a wide 25" tall tire, there aren't many choices outside of 18".  The short tires lower the 2nd gear max speed for autocross and can require regearing the diff.  Sometimes there are ground clearance issues too.

It's been posted, and bears repeating, that wheel and tire weight should be considered. 

Sure, big budget racers may find lower lab times with bigger tires and wheels, but they can also afford the super lightweight forged wheels, and throw them away if they get damaged.

mr2s2000elise said:

Do you have the power for the 285s? I am all about light weight wheels and unsprung weight. I run lots of 9lb volk te run with super sticky 205 rubber on my cars that are 1600-2450lbs.  Then I have cars with 305 and 285 sticky rubber as well, but those cars have massive power and weigh 2900-3500 lb 

 

What is your purpose for the car? Drag race? Corner carver? Looks?

The plan for power is to make 300+whp. It's a V6, so torque is not an issue. I totally understand about unsprung weight. I was running RPF1's, and am looking at going back with them or Cosmis wheels. Mainly the car will be street and autocross. Occasional track day. Looks are secondary to function to me.

79rex said:

I'm very curious why youd want to go with an 18" dia.  That sounds like a bad idea.  If it were me I'd stick in the 15-16" range.  And then figure out the widest I could go.

Really it had to do with tire choice availability and clearing larger brakes in the future.

frenchyd said:

In reply to codrus :

Wider is not always better even in autocross where aero doesn't have the impact.

Wider means you have to drive further than a narrow car.  Even if it's only a foot a corner, add up all the corners and those feet is what you've got to overcome just to break even. 

So, 2 things. Reality is that this is a 30 year old car built on a nearly 40 year old FWD platform. It will NEVER be competitive against today's cars. Also, I simply am not that good of a driver. I do it for fun. I have no grandious dreams of taking home any FTD awards or being some sort of "champion" except in my own mind! ;)

Donebrokeit said:

A few things come to mind about this car, how much power is the engine making, coil-over or stock suspension, and do you have a LSD?

As for tires/wheels size on a G body I would not go over 17" diameter wheel I found fitment issues with out cutting the car. As for width I would hold up at 245 mm, reason being the K-frame will start breaking away from the body. I have heard someone pulled the K frame bolt boss of an Daytona.

 

My last G body ran 245/40/15 on 10 inch wheels, worked well.

 

Paul

Paul, I intend for the car to be making 300+whp. It has lowered stock suspension (with a LOT of upgraded parts, so not really "stock"), and yes it has a LSD.

I don't care about having to modify the body to make wide stuff fit. I always kinda wanted it to look like an old IMSA car, anyway, so...

As for someone pulling a K-frame boss off...all I can say is if that happens, either there already was a problem (rust, missing weld, etc.) or they REALLY hit something VERY hard!

I sincereley appreciate the relaying of the personal experience with the chassis.

79rex said:

I'm very curious why youd want to go with an 18" dia.  That sounds like a bad idea.  If it were me I'd stick in the 15-16" range.  And then figure out the widest I could go.

As Ojannen said, it had to do with tire size choices that are available. I want to stick with ~25" tall tire, but as wide as needed. I also intend to upgrade the brakes and need larger than 16" wheels to make that happen.

My personal preference is go as wide as a stock fender will allow with minor modifications (ex. rolled lips, turnbuckles to push fender out) and with that largest size spend the money and get the best competition based tire you can afford on a decent rim.

Tires are were all your other work meets the pavement, I've seen the biggest gains on changing tires.

My current setup is on a 85 fox mustang, 2900lb car with a full tank of full and 395rwhp. and Im running BFG comp-2, 275/40R17.... Now this tire I wouldnt recommend it was due to being cheap and having a deal. They are quite hard and need to be heated up a fair amount, and once there it tyically doesnt take much more heat to make them greasy.

The girlfriends car is a 74 Astre, 2400lb with a full tank and makes 280rwhp. We decided on her to go with Toyo Proxie RTR, 235/40R15. and despite the size difference I can almost bet that the better rubber on a smaller tire will out perform. We havent had a chance to test it yet