Selecting the correct tire size for Plus size wheels
The first thing to understand when considering tire sizes is that the "Series" as in 60 Series, 50 Series, etc. is not a measurement of the sidewall height in the same way that the width measurement is the size of the tread width. The "Series" measurement is a ratio of the sidewall height in relation to the tread width. So a 195/60 14 does not have the same sidewall height as a 205/60 14 because the width is not the same, therefore, the sidewall which is in direct relation to the tread width measurement. This "Series" ratio is one of the most confusing things about tires, don't ask why they made their measurements this way, they would have been best off with a direct sidewall measurement, but that's not what they did.
When selecting a tire size for either a wider tire on your OEM wheels or for a larger wheel size, it is important to maintain as close to the OEM tire diameter as possible if you have any intention of keeping your speedometer accurate. Two percent is generally considered within reasonable variation, but the lower the variation the better. It is best to use one of the many wheel and tire calculators on the internet. Changes in wheel widths will account for some minor variations, but the following are general guidelines based on the several wheel calculators:
Kip Anderson has stated that 225 width tires will not fit on the back of the Impulse JI without a shallower wheel offset and fender flares.
The bolt pattern of Isuzu car and Storm wheels is the same whether you are dealing with a FWD, AWD, or RWD model.
4 x 100 mm is the bolt pattern. Lug bolts are 12 mm x 1.5 thread pitch.
The hubcentric ring in the center of the lug bolts of the 1985-89 I-Mark and Geo Spectrum, 1990-93 Impulse, Stylus, Geo Storm, and Asuna Sunfire is 56.5 mm which is somewhat uncommon. This becomes a problem in finding wheels for these cars. Aftermarket wheels are typically made with large hubcentric ring size of something like 74 mm and then use ring inserts made of plastic or aluminum to adapt the same wheel to numerous hubcentric ring sizes. Unfortunately, 56.5 mm adaptor rings are totally unavailable from any source. Wheels can be ordered by specification with a 56 mm ring (relatively common) insert and the center bore of the insert can be enlarged using a sanding drum on a drill to ever so slightly enlarge the 56 mm center bore to 56.5 mm to fit the hubs of these cars.
The hubcentric ring in the center of the lug bolts on the 1983-89 Impulse JR is 57.1 mm in diameter. This size is relatively uncommon and this can be a serious problem if you are trying to fit a wheel intended for another model vehicle onto an Impulse JR. The only other wheel sharing the 4 x 100 mm bolt pattern with the 57.1 mm hubcentric ring is Audi. Wheels intended for a smaller hubcentric ring than 57.1 mm can be bored out and made to fit the Impulse JR. Wheels intended for a larger hubcentric ring can be adapted with a donut like ring insert available from many aftermarket wheel companies. Most aftermarket wheels have very large center bores and are meant to be used with these hubcentric rings so that they can be adapted to a wide variety of applications.
This can become a very difficult issue when trying to find hub adaptors so that you can use the deeper FWD offset wheels (35-48 mm) in place of the shallower offset wheels of the Impulse JR (24 mm).
The stock offset for the JR is 24 mm with the stock 14x6 alloy wheel and 195/60-14 or 205/60-14 tire.
The JR has plenty of space in the wheel well and there is a bit more flexibility with this one than most, though it is almost impossible to find any variety of wheels with an offset in the area of 24 mm. This offset is common only to the 1980's BMW 3 Series, Opel Kadette, Opel GT, Opel Manta, and the 1980-84 Isuzu I-Mark. Wheel adaptors (hub adaptors) and spacers can be used to adapt the vehicle to use FWD offset wheels and this will allow for a much wider selection of wheel styles.
Using wheels up to 7 1/2 inches in width with the same 24 mm OEM offset will work quite well.
Most of the English Piazza owners are going to a 20 mm offset to space the wheel slightly closer to the fender line for a beefier appearance, and they have noted no clearance problems even while lowering the car as much as 2 inches.
The stock offset for the JT is 49 mm with the stock 13x4.5 steel and 155/80-13 or 13x5 alloy wheel and 175/70-13 tire, or 46 mm with the stock 14x5 alloy wheel and 185/60-14 tire.
The JT is typical of the FWD cars and is pretty tight for space in the front wheel wells. Clearance is tight on both the inward side at the frame on turning as well as with the strut body and on the outward side between the tire and the fender lip. Excessive lowering becomes a real problem with wider wheels and tires on these models, though there should be little problem with the correct offset and up to 1 3/4 to 2 inches of lowering.
Momo/Konig recomends a 35-38 mm offset for all wheel sizes. Note that this may be an error in their database.
The stock offset for the 90-93 models varies based on model and trim level from 40 mm with the stock 14x5 steel or alloy wheel and a 185/60-14 tire to 40 mm with the stock 15x6 alloy wheel and a 205/50-15 tire.
The 90-93 models are typical of the FWD cars and is pretty tight for space in the front wheel wells. Clearance is tight on both the inward side at the frame on turning as well as with the strut body and on the outward side between the tire and the fender lip. Excessive lowering becomes a real problem with wider wheels and tires on these models, though there should be little problem with the correct offset and up to 1 3/4 to 2 inches of lowering.
Momo/Konig recomends a 35-38 mm offset for 14x7 to 16x7 wheels. They recomend a 35-42 mm offset for 16x7.5 to 17x7.5 wheels.
Mike Robinson has noted that he has some rubbing problems with his 35 mm offset on 15x6.5 wheels on his Stylus which is lowered about three inches. He has had rubbing on the inward side at the frame on the front when cornering and on the outward side on the rear, and commented that he has solved most of the problem by rolling the rear fender lip for more clearance on the outward side.
"I have a set of the Euro T/As and I definately do NOT recommend them. The sidewall is way too mushy to be driving on, and the grip is so-so at best." Jason Silverberg
"I've got BFG Comp TAs (205/50-15s) on my Impulse RS. Treadware has been great, performance, wet and dry, as good as the dealer said -- which is to say a notch lower than a super-sticky, short-life, full-performance tire. Got mine mounted, installed, balanced, etc. for about 0." Zeke Ulrey
"I have BF Goodrich touring HR4 on my Stylus and like them too. They have a stiff sidewall and you feel every bump, and corner well. They are not worth much when the road is wet however." Michael
"I have BF Goodrich Comp T/A ZR's on my sunfire, and damn do i love them, rides a bit rough but the handling benefits are totally worth the extra cost." "I would highly reccomend the BF Goodrich Comp T/A ZRs, I have a set on my car and wow do they stick, tread wear is reasonable for such a tire and they are excellent in the wet. however once conditions get any worse than rain, my car stays in the garage. BFG also has a Comp T/A HR4 that might be a bit better than the ZRs in the snow. My car came with the Comp T/As but i don't believe they're too insanely expensive, but performance has its price." Dave Grant
"I like the BF Goodrich TA radials (205-50-15) They are cheap ( per) and seem to handle well. Plus they are a good 1/2" wider than any other 205-50-15 I've seen." Michael Kuriger
"I have a set of Bridgestone Protenza RE900s and I love them! I'm getting ready to get another set, these are a little wore. They are pretty sticky, but don't seem to wear out too fast under normal driving. I have tried everything on these tires and they have never squealed in a turn. I was coming home from work one day and took my favorite turn (around 80 degrees or so) at 65 mph, the car floated a little before it grabbed, bottomed out my Intrax springs, but the tires only hummed a little and I think that was them rubbing the wheel well. So I would definitely suggest these tires to anyone. They aren't priced to bad either, around 90US bucks." Brad Blickenstaff
"I just bought the Bridgestone RE910s, and they are a world of difference!! First, they have a very good looking sidewall with a rim guard and a modern tread design. That's on first impression. Once on the car though, it gets better. They are smooth, quiet, have low impact harshness, and great turn in. We've had a mix of snow and rain in Toronto, and I've been impressed, It's only been a couple of days, but with a treadware rating of 400, hopefully this impression lasts a while!"
"I recently put a set of RE910's on my '91 RS and I've been more than happy with them. They have excellent wet and dry (and snow!) grip and have a UTQ rating of 400. Not only that, but they offer a rim protector guard, which is unusual in this price range. Overall, I've found them to offer tremendous value." Nader Gorgi
"i'm happy with the 205/50-15 Bridgestone Potenza RE910 on my '91 RS. they're T-rated, 400-tread/A-traction/B-temp. don't go over 32 psi on the rear--i've been running 35F/30R." David Chanin
"previously forced, due to money considerations, to buy Dunlop GT Qualifiers (and hating them!)". Chris Rhoades
"Dunlop SP 8000 are impressive on my dad's supercharged Miata, letting him accelerate quite briskly in rain without spinning." Troy Hockerman
"I purchased a set of Dunlop D60A2 JLBs from Discount Tire Direct last September. They are all season performance tires with a 300+ treadware rating. A helluva lot better than the Good Year GT+4s that I had. A lot cheaper,too! a pop! Got them installed and balanced for another each. They ride extremely well in rain and light snow. I haven't hydroplaned and haI haven't gotten stuck at all last winter. They also seem a bit stiffer than the GY GT+4s." Victor Dumeng
"I just bought the Bridgestones, and they are a world of difference!! First, they have a very good looking sidewall with a rim guard and a modern tread design. That's on first impression. Once on the car though, it gets better. They are smooth, quiet, have low impact harshness, and great turn in. We've had a mix of snow and rain in Toronto, and I've been impressed, It's only been a couple of days, but with a treadware rating of 400, hopefully this impression lasts a while!" Kerry Chin
"I have D60A2 JLB's on my 89 JR and the handling was superb compared to the GT+4's that I had. Handling on snow was improved dramatically! With the GT+4's the car would not stay still on a straight away with snow. I had to drive very slowly to keep from moving the steering wheel so much. With the JLB's, the car barely moved astray and I could dive a bit faster. I highly recommend them , especially with their 350+ treadware!! Oh, and yeah, to get them to squeal, I took a turn at around 45mph where the GT+4's would be squealing at 30mph!! TO think I paid 7 for each GT+4 when I paid for each JLB's!!" Victor Dumeng
"If anyone needs/wants a tire that handles superbly in the rain, look at the Falken Ziex. They have a deep track down the center that's like the Goodyear Aquatread. Never have I felt so secure diving thru a puddle at 60 MPH as I do now. Plus they have a good treadwear rating (400, I think) but don't have that 'Handling By Mattel' feel to them." Chris RhodesFirestone
"I have Firestone Firehawk SVX v-rated 205/50 r15s. They seem better in the rain than my original RE-93s. The RE-93s would tend to "saturate" with water on the roadway and feel real heavy to steer. The SVX's seem great all the time." Vince Vonada
"I have used the Goodyear Eagle ST tires on my 86 Impulse, and found that they wear quickly, grip average on dry surfaces, and are almost totally helpless on a wet surface or snow. In addition, they would not last for more than 20,000 miles. I would not recomend them to anyone." Bill Luton
"...my .02 on Goodyear tires: stay away. I used to work at a Goodyear, and from what I saw working there, they all cup, no matter what. Better much better tires can be had for lots less." Troy Hockerman
"My tire of choice is Lee Turbo Action. Laugh if you must but these tires are tough as nails. (had them bend a few without taking damage.LOL) Handling is moderate but I'm also still running the 185-60-14, they do like rain, no problem with snow or ice (Flagstaff had 2 or 3" of ice that year very hard to walk on if your not use to it) , and they'll do off road quite nice. Phoenix always has the roads torn up plenty of chances to shred tires." T. Y. Bear
"My friend has some Nittos and they're sticky as hell.. Great tires, but wear out quite easily (especially if you do the e-brake and sliding action). They aren't very well though for wet surfaces.quot; John Syko
"I just last week had a set or Toyo FZ4's put on my Asuna and these are the best tires I have had so far. I have tried the Yokohama’s but the tread compound was really soft and the tires only lasted 8 months. The Comp T/A's are good but trust me you will feel every bump in the road. So far the Toyo's have been great V groove so they are great in the wet, but the only bad thing is that due to the tread pattern they pick up a lot of stones. The shop were I had them installed gave me 30 days to see what I think but for the money I will be keeping them." Simon Matthews
"I just replaced a set of Yokohama AVS-Intermediates (15") with Toyo FZ-4's (16") on my '91 Impulse XS and I completely agree. It's not really a fair comparison because the Toyo's are 205-45 VR16 and the Yoki's were a well-worn 205-50 ZR15.
Regardless, I'm really impressed with the Toyo's. They're quiet, ride well and absolutely fantastic in rain. The Yoki's seemed a little happier near the limits of traction and were crisp and responsive on the ragged edge. The Toyo's get sort of 'greasy' feeling just before they let go. More warning than the Yoki's, but this only seems to really matter on those cloverleaf-off-ramp-skidpad-thingies, anyway. In normal spirited driving, the FZ-4's are really responsive and provide great feedback." William Wilson
"I am currently running FZ4`s (toyo) on my RS. they are my second set and i really like them, for an all season tire they offer very high preformance for the money, Being a AWD i cant see spending more on summer tires, IMHO. Mind you, that is also on stock rims. 112$ CAN each." Fraser Cassells
"I bought a set of Yokohama S306 for my 1989 Impulse Turbo. A couple miles later, I realize that these balloons I am driving on are definitely not performance-oriented. They stick pretty well, but the turn-in feels so soft and mushy." Soren Rounds
"I purchased the S306's against my will, too. My car squeals over the silliest of turns now. They don't feel unsafe, just noisy. And I get looks from people, like I'm some kind of maniac." Vijay Gidad
"I only use Toyo tires, 800 plus for I-Mark, T-1 Proxie for Impulse RS. I could not be happier." "I have Toyo Proxes T1 Plus and find them excellent. I did not want all season tire. Dave Batson" Dave Batson
"I haven't really pushed the T-1's on my car yet, but they've had excellent wear and seem to stick pretty well. No problems in the rain with them either." Mike Robinson
"I have used the Yokahama A 378 tires on my 1986 Impulse, and believe that for this particular vehicle, they are the best touring type tire available. Grip is good on all surfaces, wet, dry, or snow. Wet traction is superior to anything I've seen in any tire available. Wear life is exceptional, lasting 30,000 miles and longer. I also tried these tires on my 1991 Stylus, and found that they are not suited well for the front wheel drive layout. Traction on dry and wet for the drive wheels is not very good. Cornering traction and tread life continue to be high points, but for for starting from a stop, these are not a very good choice for a FWD car." Bill Luton
"I have been abusing Yokohama A509s on my 89 Impulse for a while now. Treadwear is not too good, I am in need of new tires already (about 13,000 miles). They gripped very well wet and dry when new. They still work well on dry pavement even though they are almost bald now. I will probably buy the A509 again when it starts raining here in the fall." Soren Rounds
"My brother and I both have a set of Yokohama A520's which are working quite well." Troy Hockerman
"I'm running Yoko 520s (205/45-16) and I've been 4000 miles on them now. They grip ok, except in the wet when you go into a slide without enough notice. In the dry they are quite grippy though. Problem is, they come with 8mm tread and I'm down to 6mm on the back and 5mm on the front already. That means less than 10,000 miles for a set of tyres." John Appleby
"I splurged for Yoko AVSi Intermediates and absolutely LOVE them. If I could afford it, I would get them again in a heartbeat!" Jason Silverberg