jb78L-82

I would have preferred 45's all around but with 3.70 gears with the 4 speed I did not want to numerical increase the rear gear ratio with a shorter tire like the 45's in the rear's (255/50/17's have the same 27 inch diameter as the 255/60/15's)...that was the primary reason. 45's would have given me less tread squirm all around but no go with the 3.70's. I also preferred the staggered look which most modern sports cars have in their stance. I had no rubbing with the 255/60/15's and no rubbing with the 255/45/17's as well. My 10C6Z06 as well as my 12 Lexus IS350 F Sport have staggered tires as well...Most Porsches do and many other cars today.

SHIFT A

I understand that completely; I did 255/50r17 rear (27 inch tall, closest to stock) and 245/50r16 front (25.6 inch tall). I lowered the car to close in on the awkward looking fender gaps, and that made the car look better, but now unproportional gaps at the front and rear sides of each fender show. Plus the lowering took up ground clearance and I often scrap on steep drives and speed bumps, like those rediculous ricers. When I went to 295/45r18 rear (28.25 inch tall), and put the rear in the front 255/50r17 (27 in tall), I ran into those rubbing and performance issues that I mentioned earlier.

Some other combos in plus sizes that I’ve considered (wheel/tire combos get heavier and more expensive as you make your way down the list);

*255/50r17 rear (27.0 in tall), 235/55r16 front (26.1 in). This would be my best choice of plus size if I didn’t have so much HP; but stock to mild (up to about 300 whp) small blocks should do perfectly fine with this rear tire.

255/50r17 rear (27.0 in), 255/50r16 front (26.1 in) may require front fender trimming for older C3s.

255/50r17 rear (27.0 in), 245/50r17 front (26.6 in) may require front fender trimming for older C3s.

255/50r17 (27.0 in) all around. Will require front fender trimming for older C3s.

*295/40r18 rear (27.25 in), 255/45r17 front (26.1 in). May have clearance issues to deal with front and rear. Probably best affordable set-up to handle higher HP and hard cornering that will fit in-between non-flared fenders.

305/40r18 rear (27.7 in) big $, 255/45r17 front (26.1 in). May have clearance issues front and rear.

The only reason I would go with 18s instead of 17s is to get the wider (more needed traction for my set up-400whp) tires that 17s don’t offer.

js1977

Sorry I missed this.

I'm running Kumho Ecsta ASX tires with 255/45/18 in the rear and 235/50/17s in the front.

PainfullySlow

Thank the heavens! Someone who finally understands! I have done extensive MOI studies myself...

Krystal

This is the size I'm using........it's a 255/50/17.......the picture of the 15s are the 255/60/15s so many people still run today..........but I really can't given the limitations and desire to get more from the extensive suspension changes I've made to the car. The contact patch is similar but it really is pretty incredible how much better and faster the newer design tires react and work vs what they replace. As for ride the difference between the two, concerning a stiff ride.....it isn't noticeable.......one rides no better or worse than the other and the fact that the car rides softer, while handling the many imperfections in road surface considerably better that it did before is ALL in the suspension system.

BLUE1972

Just for fun ... I can't resist... .. not getting into it..

The calculation's are neat, but you must consider the location of the mass of the mounting flange and cross section of the flange between the beads for the tire, On a larger diameter rim the mass is moved outward ... never mind.

The early corvettes had F70 tires which were 26.4" to 26.7 (depending on manufacturer) diameter and 27" diameter for winter snow tires. Actual measurements.

The extra clearance in the wheel wells was to allow debris to pass through the wheel well without damaging the car at speed. (?).

For fun measure from the pivot point of the lower A arm to the center of the tire and multiply by the difference in weight (old vs new) and that is the inch/lbs change in force the suspension sees.

Again this is for fun...... I learned a lot when I was working on the run flat tires in the early to mid 70's.

BLUE1972

pictures of spare from 1971, measures 26.35 diameter.

lionelhutz

It's hard to describe. With the better tires, the tire and suspension reaction to a bump is quick and short. Everything is well controlled. With the low performance tires it's drawn out more and the bump can even feels bigger than it really is.

You don't need to have a fully upgraded suspension. I noticed the improvement with cheapish gas shocks and upgraded swaybars as the only real changes from stock.

But, you do have a number of decent upgrades and would find better performance tires complement your suspension very well.

ignatz

Appreciate your reading last morning's efforts. I had a job where masses and inertias mattered. I was mostly curious about how much power was really needed to spin up a wheel. When you see race cars lose a tire the momentum they carry at those speeds is pretty awesome. But ... I am not a suspension expert and sometimes get schooled by others on this forum with a lot more actual experience.

With your 18's and larger sidewalls you also lowered your overall gear ratio and that would affect acceleration.

That is another thread, not this one. In exploring the topic I once found a far more knowledgeable presentation with equations and dimensions using our cars as an example with all the numbers plugged in. It was a two part slide show exploring longitudinal and lateral acceleration. And I posted on part 1 and got some good discussion. I went to look for it the other day and saw that the slides had been taken down. Couldn't find it with the 'wayback' machine either, but I did find the individual slides somehow so I'll see what I can do. Contacting the author would be preferable, it really was some good stuff.

ignatz

OK, now you're moving into the realm of calculus, integrating the mass across the entire wheel's radius. I just made two assumptions about where most of the weight was. I think I will leave it at that.

BTW: I have that spare downstairs somewhere, I think I will see what it weighs.

SHIFT A

You are 100% correct, and we should all know how gearing effects acceleration.

I didn't want the thin rubber band look I see with most 18 inch combos, but I wanted the added performance tire options that are available in 18 inch sizes, which is why I chose the taller 295/45r18 tire (28.25 inch tall). With my 17 inch (255/50r17 UHP) combo, I always have to hold back on the throttle too much (I don't like that feeling) so that I don't spin in place off the line, or fly off the side of the road on the curves; I've done some unintentional drifting which is not very fun.

I just cant make up my mind to sacrifice my preference of classic looks, a bit more ride comfort, ground clearance, and acceleration performance (as long as the hold grip) that the 15 inch wheel/tire combos offer, for greater handling performance going with bigger wheels/tires.

I am talking to more people about how the 15 inch drag radials handle the curves, and am hoping these will suit me better based on my needs/wants. I know I cant have both performance aspects to the max, and there will be some trading off.

jb78L-82

I know nothing about drag radials other than they must have very soft rubber for maximum straight line traction and very soft sidewalls to aid in the traction department(ever see drag radials sidewalls flexing?) I highly doubt that a drag radial would even offer comparable side wall grip to a BFG TA street radial in terms of cornering, handling and steering response. Logic tells me that a straightline drag radial is probably going down the wrong road for a superior handling 15 inch street tire. You really need to look at road racing 15 inch tires, at the very least.

SHIFT A

Street drag radials like the Micky Thompson ET Street S/S are constructed the same as a regular street tire with steel belts, etc. The exception is that they have larger contact patch with a much stickier compound. The flexing drag tires you are referring too are the bias ply drag tires made just for the strip.

BLUE1972

Yes Calculus and force dynamics.. I was an R&D engineer back in the day. Would have loved the new computers back then.

A slide rule was a PIA. Thank goodness for my HP calculator.

I now wonder how we did all the calculations when designing the run flats back in the 70's.

I agree it's deep ... and I'm not taking my slide ruler out ... .

ignatz

I go further back to the mid 60's. My bosses could destroy me with back of the envelope calculations if I solely relied on computers. I fear it's not that way anymore.

______________

Oh yeah, 51.5 #'s but I forgot to look at the tire size. Smaller to reduce weight and now I've left the spare off all together.

AirBusPilot

275/40x17F 285/40x17R

IMO, perfect wheel gap.

Torqued Off

This car has to have been lowered.....do you have rubbing problems anywhere on the car?

jb78L-82

From the best 255/60/15 tire thread currently on the forum first page:

https://www.corvetteforum.com/forums...-vs-price.html

https://www.performanceplustire.com/...60-15:ty:Tire/

This might be Nirvana for you 15 inch tires fans.........

V RATED !!!!!!!!!!!!!!

https://www.performanceplustire.com/...60-15:ty:Tire/

AirBusPilot

None.

jb78L-82

My car with the 255/45/17's in front has zero rubbing as well, on a lowered front end with 1/2 coil cut