Unsprung weight vs tire availability

So, a bit of a thought exercise. I was planning upgrades for the mr2 and was trying to pick the best tire size to upgrade to. Most sw20 people seem to be swapping to 17 in wheels for the performance tire choices, but most budget options are heavy. I was thinking wide 15 in or 16 in (15x7, 15x8), to save on unsprung weight ad rotational issues with a manual steering rack, but I will have limited tire choices. Also, high quality wheels are cheaper in these sizes.

So GRM, do I save weight or go with wide tire availability? The car is mostly a canyon carver and I have stock wheels for autox.

My recommendation is 16x7 Enkei RPF1s from Tire Rack and your favorite 225/45-16s (Toyo R1R would be my choice). That should offer light weight, more or less replicate the stock tire diameter, and would even keep it STS legal should you want to run in that class.

I have an SW20 myself (with a manual rack, even) and have pondered this question often.

Do the rpf1's come in a staggered rear size (16x8) or would I need to stagger tire size?

I'm not sure what other sizes the Enkeis come in, sorry.

It's only my opinion, but I prefer the way my MR2 drives on a square tire setup, so that's what I researched.

In reply to Will:

No problem man, I appreciate the info. I think I will be keeping it staggered. Centerline has some interesting 15 in forged options if you are looking. I was just looking at their wheels last night and saw some as light as 13 lbs.

Tirerack has Kosei K1-TS 15 x 7 at $134 ea and they weigh in at 11.4 lbs are hard to beat.

alstevens wrote: Tirerack has Kosei K1-TS 15 x 7 at $134 ea and they weigh in at 11.4 lbs are hard to beat.

Got a direct link? Tire Rack's site is telling me they don't have that wheel for the SW20.

Light weight is pretty useless if you saddle yourself with crap tire availability. I typically try to start at the tires and work my way back to the wheels, iteratively narrowing my choices down until I'm satisfied with both.

What range of tire outer diameter and width do you want for the front? What range of tire outer diameter and width do you want for the rear? Is there a max and/or min total tire stagger you'll accept on both width and diameter of the tires? Do you want to run the same wheels on all four corners, or are you willing to stagger.the width and/or diameter of the wheels as well?

Driven5 wrote: Light weight with crap tire availability is useless. I typically try to start at the tires and work my way back to the wheels, for the most part.

This. Find the best tire for what you're going to do and work backwards.

You can get Slipstreams for your wheels and the good thing is that the ST Autocross crowds keep the tire manufacturers making 195 and 225 15" tires. I have been looking into that too but instead decided to sell it soon.

Will wrote: My recommendation is 16x7 Enkei RPF1s from Tire Rack and your favorite 225/45-16s (Toyo R1R would be my choice). That should offer light weight, more or less replicate the stock tire diameter, and would even keep it STS legal should you want to run in that class.

7" wide wheels are way too narrow for 225/45s. I'd recommend a minimal of a 8.5" wide wheel for 225/45s.

Just get some 205 on 7.5s.

don't know the particulars of the tire(s) you're considering … but the rule of thumb is the width of the tread (tire specs) should equal the width of the rim ….

that is the ROT for street tires … for something like Hoosier A6's …no problem

I've seen 285's stuffed on to 6 1/2" rims … on a national winning DS car

The only reason to do that (super wide tire on narrow wheel) is class regulations. Squared shoulders is the best compromise between grip and response. I think GRM did a test a while back on the same thing... big fat tire shoved onto a 7.5" (I think 245 width or 255) didn't get much better in time vs a square-shoulder setup (225s I think) but the quality of response on the 225s was much better.

Driven5 wrote: Light weight is pretty useless if you saddle yourself with crap tire availability. I typically try to start at the tires and work my way back to the wheels, iteratively narrowing my choices down until I'm satisfied with both. What range of tire outer diameter and width do you want for the front? What range of tire outer diameter and width do you want for the rear? Is there a max and/or min total tire stagger you'll accept on both width and diameter of the tires? Do you want to run the same wheels on all four corners, or are you willing to stagger.the width and/or diameter of the wheels as well?

This is actually how I came up with the wheel/tire sizes others are recommending against. I looked for top-tier performance tires available in something close to the stock diameter--as short as the SW20's gearing is, I don't want to make it shorter. 225/45-16 is a good match.

What to put them on? Wheel availability for the SW20 isn't what it is for a Miata. It's difficult to find a remotely lightweight wheel wider than 7" until you go up to 17" diameter--which, to me, is just way too big.

I decided I'd rather have wheels that are too narrow rather than tires that are too short. If others disagree, that's fine, but I didn't pick the wheel/tire sizes without reason.

Will the SW20 fit 225/50-16? That probably has the best high performance tire availability of any 16 inch size, but might be a little on the tall side. It won't save quite as much weight, since it's about the same OD as a 225/45-17. Sound like it might improve gwaring a little though. Then maybe mix it with a nice light 195/55-15 or 205/50-15 setup on the front. That would probably provide the best long term availability in staggered high performance tires without going to 17's...But I have no idea what range of tire sizes can reasonably be fit to one of these, or how they might end up looking.

Hint: When looking for staggered tires on tirerack, search out the sizes separately and not just with their staggered size search. That search only looks shows results where they also share the same speed rating, whinch isn't a concern if you never plan to exceed the max speed that even the lower rated tire (typically the smaller one) is good to. Thus it may leave out some perfectly viable options.

jsquared wrote: The only reason to do that (super wide tire on narrow wheel) is class regulations. Squared shoulders is the best compromise between grip and response. I think GRM did a test a while back on the same thing... big fat tire shoved onto a 7.5" (I think 245 width or 255) didn't get much better in time vs a square-shoulder setup (225s I think) but the quality of response on the 225s was much better.

my point was that street tires don't seem to like being squeezed … whereas Hoosiers don't mind

as I mentioned … tread width = to rim width is usually the best

You want to go with wide tire availability so you have more options for your next set of tires. On Tire rack, 205/50/15 are practically an autocross only tire size. Tire Rack and other wheel vendors will have lightweight 16" and 17" wheels.

Tire Rack offers 16x7.5s wheels for the car and recommends 205/45R16s for that size wheel for that car. Maybe not the most common size, but the Hankook Ventus R-S3 (Version 2), Toyo Proxes R1R, and Bridgestone Potenza RE-11 are all available in that size.

I've been running 225/50R16s on my E36 (that was a stock size), and I wouldn't recommend that size. Just too much sidewall. My latest set of that size is Kumho V710s on 16x9.5s.

Driven5 wrote: Light weight is pretty useless if you saddle yourself with crap tire availability. I typically try to start at the tires and work my way back to the wheels, iteratively narrowing my choices down until I'm satisfied with

+1 for this.

I can tell you about 15x7s, selection isn't super wide but it is pretty good, you can get all the EPS tires for those and all different kinds of slicks. In this size you can run 195/50/15 with a nice little stretch to stiffen the sidewall, 205/50/15 with a bit of a squeeze if you can live with the excess sidewall height, or 225/50/15 with a major squeeze...not much gain for that size on this rim, but it'll work in a pinch.

15x8 has a narrower selection but it's all EPS and slicks. 225s can fit with a very slight squeeze, 205s can fit with a bit of a stretch and 195s can still fit without a crazy amount of stretch.

15x9 is a size that frankly only makes sense for a dedicated track car. 225s will be a significant stretch fit.