14 vs 16 gear ratio effect

16 inch are not any taller, the aspect ratio is smaller. Same overall diamater. They would markedly improve your cars overall manners.

Dave

 

You wouldn't be effected at all. You might be Affected... sorry, mom was an English teacher.

If the wheel and rim choice is done correctly (16/50 series), you get a +2 "effect" and you should maintain something very close to the same diameter (and hence rollout) as the 14/70 series combination. As the rim gets bigger, the sidewall gets smaller - overall tire height stays the same or very close. In which case there is no taller condition to deal with. What you DO GET is a slightly harsher ride but a bit more performance in the form of a shorter/stiffer sidewall... good trade IMHO. You also get the ability to fit larger brakes should you so desire. If the wheel offset is the same - 14 vs. 16 - you will actually increase clearance around objects you may worry about interference on.

Rick

 

A simple sentence to help remember which is which:

"Special Effects Affect the audience."

 

Sorry, here's some relevant content. With different sized wheels, use a tire size calculator to get the same (or very close) overall circumference. Here's an online calculator I like to use:

http://www.miata.net/garage/tirecalc.html

For instance, a 215/55-16 gives exactly the same circumference as the stock 205/70-14.
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and breaks don't make our cars stop! well, unless it "breaks down."
(and I should probably capitalize)


" Originally Posted by ramosel
You wouldn't be effected at all. You might be Affected... sorry, mom was an English teacher."

 

Perhaps a tad off the subject but is there any weight difference with a 14" wheel with the larger tire versus an aftermarket 16" lightweight wheel (say a BBS) and a smaller tire?

 

If that is this case once the rubber hits the road the 14" wheel and tire combo will have more sidewall deflection than the 16" wheel and tire combo, and hence the 14" would have a slightly smaller rolling diameter than the 16".

 

Rollout is Rollout. Deflection just doesn't affect it. We did a lot of testing with a Goodyear rep on our race car when we converted to BIG radials and dropped our ride height. Weighted or unweighted, a tire will have the same rollout. Its an odd twist of logic but it works out that way every time we tested it. Severe under or over pressure are the only things that altered rollout.

Rick

 

What about acceleration and braking? I did a similar change on my old rx7. The overall diameter was unchanged, but due to the extra width, the wheel+tire was heavier in 16" than 14". Hadling did get a little better, but acceleration and braking were much worse with the extra rotating mass. It also looked a lot better. If it wasn't for the improved looks, I would have stayed with the 14".

For 308, I've heard that the aftermarket 16" is much heavier than the factory 14", so expect worse acceleration/braking. But, I do think the aftermarket 308 16" looks great.

 

I ran the original cromodora 14's with 70 series rubber for a while on my 308, then switched to 16s (the superformance.co.uk replica 16s) and didn't notice any deterioration in ride quality (very surprising). Although, I didn't go with 50 series rubber on the 16s...instead, I went with 55 series rubber (205/55/16 front, 225/55/16 rear) Goodyear Eagles. Yes, the gearing is very slightly taller but that's actually pretty welcome as I don't really need to have 4,000rpm to go 75 on the freeway as was the case with the 14s....more like 3,500rpm now, and 1st gear is still plenty low.

The 14s look nice and ride great and are original for the early 308s. The 16s (with good tires) are more sure-footed and ride surprisingly well. The car is really a GT cruiser, not a cafe racer...

 

It is odd but absolutely correct. The logic is easiest when you think about steel belted radial. The steel belt will not change length for anything, so the distance you go with 1 complete revolution is always exactly the same. When weight or pressure change the amount of tread that is contacting the ground changes, but the distance per revolution never changes because the length of the steel belts never change. For me the best way to think about it is bulldozer tracks.

 

Mike,

I understand your logic, specifically, the steel belt is a fixed length that doesn't change, however, I'd have to disagree with the conclusion here. Yes, the length of the belt is fixed, however, it's the effective diameter of the wheel that determines rolling distance (pi X D). If the tire has a lot of sidewall deflection, thereby reducing the running diameter, the rolling distance (circumference) is going to be less. Again, you're right, the steel belt doesn't change length, but the effecitive diameter can change despite that depending on tire pressure, tread wear, etc.

But practically speaking the sidewall deflection on a properly inflated 70 series tire isn't going to make that much difference v. a 50 series tire. Probably negligible would be my guess.

 

Cliff,
As usual, your logic is impeccable. In fact I even was in your camp until 2007. When we went to big radials on the race car and a new data logging package I had to have very VERY accurate rollout figures for the front and rear tires along with front and rear wheel rpm monitors. You're a racer boy - you know why... <wink> I shan't say more. I was concerned that the radials, having even more sidewall deflection, were going to exhibit this reduction even more. Whether bare wheel and tire or fully loaded on the car, my 4 turn rolloouts were the same. I couldn't understand it. I thought I was doing something wrong. Our Goodyear rep laughed and showed me with calculations why what you (and I) thought should happen, just doesn't. What DOES change with deflection is contact patch and thusly - shape. You don't change diameter or circumference, just shape. But, circumference doesn't change - so for you to get from point A back to point A on a tire, you have to go one full revolution and you can't shrink or expand that distance when the rubber meets the road. If you drop the pressure to just inflated (1-2 psi) and then run the pressure up to 60 psi you can make small changes in circumference and rollout. But considering we normally operate from 17-28 psi (cold/hot), even putting heat in the tire doesn't change rollout. Oh, you can change rollout with your right foot given enough horsepower, time and stupidity.

Rick

 

As Rick said, I used the think the same think. The flaw is that as soon as you put any load at all you no longer have a circle and pi x D no longer applies. You need to know the perimeter of the tire and math wise that requires you to do a nasty integration or use a simplifying assumption, which is steel is basically incompressible/expandable so the perimeter is constant regardless of shape. With that assumption you can calculate the perimeter easily as pi x D for the unloaded tire, but you are left with roll-out can’t vary with tire pressure.

 

Ride and traction vs tire pressure and sidewall height is a whole different question and pressure makes a very big difference.

 

Hi Dave,

I have Goodyear Ds-G3s (225/40-18 and 255/35-18) on my 77 and i was surprised at the relatively small increase in harshness over the Michelin "Energy" stock size tire & wheel.

But there was a quantum gain in steering precision and grip. The 18 inch goodyears have about 1% less circumference.

Current high performance tires are the biggest single improvement you can make to the handling of the car.

Shocks, springs and bars will make incremental improvements, significant improvements, but you will trade some ride quality for greater responsiveness. It just depends on how far you go with spring rates, shock settings and bar sizes.

You might consider looking at the Tire Rack's ratings for maximum performance tires. Look for the qualities you think are most important to you and the type of driving you do. This is a great aid in decision making.

hth,
chris
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Hi Rick,

Very interesting - I think I follow the logic and that's an intruiging twist. So, to put it bluntly (maybe this is oversimplification?) the effective diameter doesn't change with load, just the shape of the contact patch? Just for hypothetical debate, suppose the tire pressure was right down - say 2psi - wouldn't the rim of the wheel be riding "closer" to the road surface (greater sidewall deflection) and then wouldn't the effective diameter be less? Taking it to the extreme, a completely flat tire is essentially running on the bead of the wheel rim - the wheel rim is presumably a fixed length - wouldn't that cause a reduction in rollout??

I think my brain may be melting down with these mental gymnastics! In any case, an interesting debate. Incidentally, what kind of race car??

Cheers.