Are 17" + wheels that important for good handling???

[Sammy B]

First post...be easy.

I'm in the process of re-doing the entire suspension on my '67 Lemans. My goal with the suspension is to get the car to handle as close as possible to a modern vehicle.

So far, I've installed new springs all around, replaced all the front suspension parts (center link, tie rods, ball joints, idler arm, etc), Lee's power steering box, fat front and rear sway bars, poly-graphite all around, Bilsteins in the front and probably Koni's in the rear. I also have SC&C Stage 1+ UCAs and tall ball joints in the mail.

With all the stuff that I've done so far, how much difference will running a 17" wheel make? I currently have the original 14" Rally IIs with BFG Radial T/A's.

[Z06killinSBF]

They have less side wall flex resulting in more precise steering/handling.

Although the AC Cobras had 15's.

[vintageracer]

The AC Cobra illustrates the point of how less sidewall flex can make a huge difference in handling and why modern cars and particularly modern tires make such a huge difference. The tire sidewall flex on Cobras in the 1960's was HUGE!

AC Cobras were very poor handling cars. To drive one fast you had to use the huge horsepower and dirt track the car through the turns. Crummy bias ply Goodyears and and that heavy engine made the AC Cobra a handfull to drive. AC's were fast and had a lot of power but actually drove poorly. It took a GREAT driver like Dave McDonald or Ken Miles to drive one fast!

Today in vintage racing the Cobras are much faster than in the 60's mainly due to tire technology. You still do a lot of dirt track driving, just not as much.

Do not believe me. Go rent actual movies of real races from 1963-1966 when Cobra's were in their heyday. You WILL see what I mean and how poorly AC Cobra really did handle in the corners. But that horsepower really made up the difference!

[Apogee]

A 17" wheel allows you to fit decent sized modern brakes to finish off the handling package you've got already. You stick with 14" wheels and you're more or less stuck with brake technology from the 60's. You also have a ton of performance tire options in the 17"+ range...I can't think of much of anything for 14 inchers, but I honestly haven't looked either. Brakes and performance rubber are probably two of the biggest bang for the buck modifications you can make to your car if you push it to the limits.

[Sammy B]

Thanks for the replies.

The last owner of the car had already installed a front disk brake conversion. Nothing fancy, just standard 11" drilled/slotted rotors. I may eventually upgrade to disks in the rear and bigger rotors and calipers in the front, but for now the brakes are staying.

After looking around a bit, I really don't care for the way the 17s look on an A body, which is why I'm torn between going with the better handling of a 17" or the more factory look of a 15" or 16" American Racing style rim. If the handling benefits of a 17" rim are negligable compared to a 15" or 16" rim, I'll probably just go smaller.

[MrQuick]

really? I kinda like the 15" look too but just look at these!

[parsonsj]

It's a compromise. You want the best brakes you can get (bigger wheels) but the smallest moment of inertia possible (smaller wheels). For most street cars in the 3000-3500 lb range, that means a 17" wheel is probably optimal. There seems to be a lot more tire choices these days in 18" wheels, so many of us end up there.

jp

[Sammy B]

Great looking Chevys, however I really like the classic 'muscle car' look. Personally, when I look at a classic with anything over 16" rims, all I see are the wheels. I may end up going with a set of 17" grey C-5s from Coys. The grey seems to be a little more subtle than a polished or chrome rim.

Bottom line is, I hate to spend all this money on an updated suspension and not reach the cars full potential by using a sub-standard wheel/tire combo. As a reformed off-roader, I definately agree that the tires are the most important component in maintaining traction.

[cluxford]

I'm caught to between old school cool and the true PT experience.

As such I have decided 13" C5 Vette front and rear brakes
17" Budnik rims
and 325 x 45 x 17 M&H Tyres (rear obviously) up front will be 235 x 40 x 17

This will give me a nice sidewall "prostreet" style look but stoppers big enough to rein in the 800+ Hp of the 632 CI Merlin III big block I am putting in it......

[Magntik]

I'm not as well versed as some of the other guys, but I'll throw in my 2 cents.
I just went from a 15" wheel and 60 series rubber to 18" and 40 series rubber, and my '67 Firebird drives like a totally drifferent car!!!!

The steering "feels" more responsive, it feels like less body roll and like I am actually driving through the corners.

This is my first experience with wheels larger than 15", and it is worht it.

I understand what you are saying about "seeing all wheel" b/c after I ordered my wheels, man did I second guess it. I kept worrying that it would look like a "donk" or whatever you want to call them.

But the driving experience has all but made me forget about all that.
Now I wish I would have upgraded sooner.

I think it's easy for the guys that have been running larger wheels forever to say its a good idea, but take it from someone that just did it, it really is everything the others guys have said.

[69TAPoser]

This is an interesting question. I have some friends that are trying to talk me out of 18" wheels for my project saying it will have an ADVERSE effect on ride (which I understand is different than handling). It is pobably important to think about both ride and handling. It would be interesting to hear from people that have gone fron 15" to 17"-18" and how this effected both the ride and handling.

Magntik-

Do you have any side pics of you Bird with the 18s? Sounds like you don't regret going with 18s? You like the look of the 18s on the Bird? What tire widths are you running?

Phil

[Sammy B]

Thanks Magntik, that's exactly what I was looking to hear. Unfortunately, since I'm doing all my suspension work at the same time, I really won't know how much of a difference just the wheels will make. With such a heavy car, I wouldn't think that a taller rim will make the ride too harsh, but who knows... This will be may daily driver when finished, so I don't want to shake my teeth loose.

Anyone else want to share their experience with going from a 14" or 15" to a 17" rim? Love to hear it.

[Jim Nilsen]

The larger the diameter of the wheel ,the smoother the ride. It's the law of physics that makes it that way. It is all based on deflection at the wheel and not the tire. A 32'' tire on a 15'' wheel will ride soft when the tires are soft but when you hit a bump it will depress the tire and then deflect off of the wheel. The time it takes to transfer all of that motion will jerk the passengers and vehicle at the point of finally getting the rim over it. this is not smoother,it is however softer sounding because of the large sidewall.

If you still don't understand deflection just take a hard tire dolly and some other thing with bigger wheel and hit the same size bump and just feel what is smoother.

I know that when you get to 30 series tires and high impact bumps that it feels like you are riding on the rims because there is no deflection but it is still smoother for the suspension movement.

Tires are not meant to be suspension other than off-road.

Getting the right profile tire is what it is all about when it comes to the handling and ride you want and there is a level of compromise to it. Ever wonder why some cars have all of the lowering parts installed and are at the same distance from the ground and the wheels are tucked up inside. They gained handling and have a car that is at a livable ride height. Many get into trouble that get the wheels before the suspension and vice versa.

[Magntik]

Magntik-

Do you have any side pics of you Bird with the 18s? Sounds like you don't regret going with 18s? You like the look of the 18s on the Bird? What tire widths are you running?

Phil[/quote]

I posted in a different thread, not to good at the picture thing.

I was worrying at first, no regrets.
Love the looks, love it more after I install the 3" DSE drop leafs I just bought!

The fronts are 18 x8 245/40/18
The rears are 18 x 10 275/40/18 Thinking 285/40/18 would have been a better choice.

[Magntik]

I haven't done anything major.
Sub-frame connectors, Hotchkis 2" drop springs/ Eldelbrock Shocks up front, with rubber bushings every where that I replace about 5 yearsw ago. Just got DSE leafs for the rear.

Thanks Magntik, that's exactly what I was looking to hear. Unfortunately, since I'm doing all my suspension work at the same time, I really won't know how much of a difference just the wheels will make. With such a heavy car, I wouldn't think that a taller rim will make the ride too harsh, but who knows... This will be may daily driver when finished, so I don't want to shake my teeth loose.

Anyone else want to share their experience with going from a 14" or 15" to a 17" rim? Love to hear it.

[Boesch]

One thing I'm going to throw out there are the sizes that come on new cars. Tires are developed to replace the tires that are on the new OEM cars that everyone drives, that's where the money is at for the tire companies. Most new cars are going to 18" tires, some even larger. (new corvettes run 18/19, new Ford and Chevy trucks with 20") As this trend continues, good performance 17" and smaller tires are going to keep getting harder to find.

That being said, take a look at the ride comfort in new cars and also the handling. Would they be going to the newer larger sizes if it sacrificed ride and performance? Some of todays cars are the best handling available. With all the engineers working on them I'm sure they are examining all the different angles.

...and yes I'm sure someone will mention that a Model T had something like a 22" on it and then they went back down in diameter to get performane. I have a feeling that the 18/19 and suspension on a new C6 will speak for itself on performance and ride comfort.

If you like the look of a 15" on a 60's muscle car, then that is a matter of opinion and no one can argue that. Performance wise though, I think the new car guys are onto something.

[parsonsj]

Would they be going to the newer larger sizes if it sacrificed ride and performance? Some of todays cars are the best handling available. With all the engineers working on them I'm sure they are examining all the different angles.

OEMs make cars that sell at the highest possible profit and lowest possible cost.

You can't argue with physics and moment of inertia. We've had this discussion before ... go have a look. There are several threads on the subject.

Performance-wise, have a look at race cars. Real purpose-built race cars. You won't find such wheels there.

jp

[Boesch]

OEMs make cars that sell at the highest possible profit and lowest possible cost.

You can't argue with physics and moment of inertia. We've had this discussion before ... go have a look. There are several threads on the subject.

Performance-wise, have a look at race cars. Real purpose-built race cars. You won't find such wheels there.

jp

I hear you on the cost part for OEM, but if you look at the price of an 18" wheel/tire compared compared to 17" they most certainly aren't going the cheaper route. 18" wheel = more raw material = more money. 18" tires are more expensive than 17" tires for the most part.

I understand the physics part, that's what my master's degree in Mechanical Engineering degree does. Mass plays a very critical part of the inertia calculations. A lot of today's high tech rims are using low density materials, such as carbon fiber, or using hallow spoke techiniques which allows them to achieve very low mass. The lower moment of inertia is a balancing act between the tire weight and the rim weight. I dont' argue the laws of phyiscs, there are just a lot of variables in the equations.

When you say "purpose driven race cars" which are you referring to? A lot of the American LeMans series are running 18 and 19 inch diameter wheels. The C6R is running 18 inch wheels with 290/33-18 on the front and 310/41-18 on the rear. (courtesy of a Google search) While rotational interia is important, sidewall stiffness and straight line traction are equally, if not more, important for cornering performance.

[parsonsj]

Mass plays a very critical part of the inertia calculations. A lot of today's high tech rims are using low density materials, such as carbon fiber, or using hallow spoke techiniques which allows them to achieve very low mass. The lower moment of inertia is a balancing act between the tire weight and the rim weight. I dont' argue the laws of phyiscs, there are just a lot of variables in the equations.

You've left out the most critical variable: r (radius). MOI varies by r to the 4th power. Mass is important, but nothing is more important than r.

American LeMans series are using OEM platforms, and as such, OEM-sized wheels. Purpose built mean F1, IndyCar, CART, etc. Nobody knows more than the F1 engineering teams about wheel dynamics in a performance application.

I'm not being confrontational; I'm just emphasizing that bigger wheels usually hurt performance, and that nothing here is free.

jp

[Boesch]

You've left out the most critical variable: r (radius). MOI varies by r to the 4th power. Mass is important, but nothing is more important than r.

American LeMans series are using OEM platforms, and as such, OEM-sized wheels. Purpose built mean F1, IndyCar, CART, etc. Nobody knows more than the F1 engineering teams about wheel dynamics in a performance application.

I'm not being confrontational; I'm just emphasizing that bigger wheels usually hurt performance, and that nothing here is free.

jp

Don't forget that F1 also regulates the tire sizes/wheels used by all teams. That's not a design variable for them. A while back that rule was implemented to slow the teams down and generate larger challenges for them.

PS - no confrontation, just discussion. That's what forums are best at!