hey Manny,

You called me a sage, hehe. At least one person here knows the definition of a rishi. Didn't hit me until last nite. I was like, "Oh ****, he took the time to look it up." That's sweet.

I'm thinking about changing my name to SageFC now. What do you think? hehe.

Thanks man,

Rishie

 

Rishie...

nah I just got lucky that sage and "rishie" were similar

 

well, I gave in and will be withdrawing some money from the "rebuild/turbo fund" so rishie can order them for me...so in a week or so these will replaced my stock wheels, whcih are for sale btw

 

Suuuhhhweeeeet!!!

 

i'll be doing the same..........

 

ttb came in and dropped the funds. He'll be a happy man when I get back from SEMA. congrats tinou.

Rishie

 

i'd be happier if you suddenly gave me a buy 3 wheels get one free offer

 

Yeah, wouldn't we all.

 

I'd be happy with a set of four with the 5th wheel for half-price

 

What are the benifits of using wider tires vs larger diameter tires. Will wider tires make my 7 slower? Is it a good idea to use larger tires for the rear wheels?

 

According to Fred Puhn in his book "How To Make Your Car Handle" He says "For best handling use a rim width at least as wide as the tire tread."

This means for a 205mm tire he recommends a minimum of 8" rim!

Futhermore he states, "You benifit from a rim up to several inches wider than the tread." "Usually the wider the better on rims, and you can use a rim up to 2" wider than the tread on most racing tires."

So he seems to recommend 8" rim for 155mm tires (at least on 1970s race tires."

I think w/ +42 you might have to stick to 205 (as you suspected) if you don't want to run spacers. 225/50 16 on my +30 8" rims is VERY close to hitting the spring perch (like normal tire deflection hitting it close...) Those are actually my rears, my fronts are only 7.5" +30.

I think the extra rim width even while sticking to 205mm wide tires will be noticeable. Does 8" +42 fit w/ 205mm tires? I don't even know...

 

KS...what wheels are you getting? If you have a +42, you'll rub your front fenders. You will not need spacers. The rears should look very good.

For an 8" rim, I would suggest a 225/50, 235/50, or 245/45 in the rear. 215/50 will stretch and would probably do really well in the front. You will need to roll the fenders a bit. You sould run +32 in the front.

 

More contact patch, better handling. But, more weight, slower acceleration.

What model FC do you have?

 

Just a general tip: the sidewall height is a major factor in tire & rim width matching. You can run 275s on a 7" rim if the sidewall is huge, for instance, but that won't work (or at least won't be recommended) with short sidewalls.

This information is all publicly available on the spec sheets that TireRack.com has on their web sites for all the tires they carry.

-Max

 

I agree with this but what you're recommending is not entirely true. For instance, a 245/45-16 Hoosier R3S03 tire bead-to-bead measurement is ~9.25 inches. Thus Fred recommends at least a 9-inch rim to work well with this tire. Hoosier R3S03s are race tires, and have very wide bead-to-bead measurements. Actually a 9.5-inch width would be better. The wider rim allows the tire to expand to its intended shape. The narrower rim width tends to compress the tire too much and decrease the tire's effective rubber-to-road contact patch.

You'll need to measure the bead-to-bead distance on a 205-mm road tire for you to follow Fred's advice properly. Because the aspect ratio for a road-going 205-mm width tire will be much taller than a 45-series Hoosier, I suspect the bead-to-bead distance will be LESS than 8 inches (the 205-mm section width). IOW, the tire's bead-to-bead distance will NOT be the same width as the tire's section width--the fattest portion of an unmounted tire.

Fred's advice wouldn't be very practical for road-going wheels/tires, as there won't be much tire sidewall to protect wheel rims from curb rash, but handling feel and ultimate contact patch is maximum using Fred's suggestion.

Because of the road/track compromise, the general rule of the thumb for rim width/tire width matching is to choose a rim width that's at least 90% of the tire's section width (instead of the bead width), or a tire width that's 110% of the wheel rim width.

Thus a 205-mm section tire should be mounted using a 7.3-inch rim width, because a 7.3-inch wide rim/ 8.1-inch tire width * 100 ~= 90%

Of course there are no 7.3-inch rim widths available unless you go custom, so you'll need to choose either a 7-inch or 7.5-inch rim width. For racing purposes, 7.5-inch wide is better. For road use, the 7-inch wide rim would allow more tire sidewall to protect rim lips from curb rash damage.

Going the other way. If you have a 7-inch wide rim, you'll want to match a tire width that's no more than 110% of the rim width. Your tire width will be 7.7 inches which calculates to a 195-mm width tire.

 

Do you need a rim wider than the section width or wider than the tread width? Or is it just bead to bead, which most tire companies don't list in the specs.

Here is the spec sheet for S-03's in the two sizes that would keep the diameter of the tire the same as stock.



So would the best handling rim for the 205/55R16 be 8.4" or 7.6"? Is staying within the tire company's approved rim widths important?

 

I just acquired an 88 RX7 (FC)
which has 185/70R 14 87S tires on it. What are my size options for replacement tires? (I'm looking for economical, long-wearing, good ride in 98% dry conditions.) I'm afraid I don't know anything about tires. Can someone spec out what the different numbers mean, and the ramifications of changing them? Thanks for teaching me auto-kindergarten. BTW, what does FC mean on my model type?

 

I think Fred Puhn was referring to the wheel width being at least as wide as the tread width. You're right that few tire makers list the tread width. If you can measure tire bead distances, finding the wheel width that's at least as wide as the bead width should work well in matchin the right the tire width.

To answer your question, I'd stay in the upper range of the approved rim widths, ie 7.5-inch wide rim for a 205-mm tire width.

The 8.4-inch section width, and 7.6-inch tread width is the measurement taken from the 205-mm tire mounted on the spec rim, which is 6.5-inches wide.

Generally you can expect a 0.2-inch increase in tire section width for every 0.5-inch increase in rim width. Thus the 205-mm tire mounted on the spec 6.5-inch wide rim would increase to 8.6-inches wide when mounted on a 7-inch-wide rim, and then to 8.8-inches wide when mounted on a 7.5-inch wide rim. The tread width will increase by the same 0.2-inch increment with each 0.5-inch increase in rim width.

The best handling will come from the widest tire width you can have given the widest rim you can mount on the tire!

 

Any recommendations for the rear wheel and tire size on a 1993 RX-7 if it used only for drag racing?