Page updated on 12-14-2017

upgrade tires from 15's to 17's


Fredddeeyy
08-29-2013, 08:02 PM
Hey guys. I really need help with this one. I have a '91 caprice with 15x225x70 profile tires. The tires are Firestone Firehawks Daytona 500's. Stock were 215 profiles. I get the "rubber band effect" when I jerk the wheel real hard, where the sidewall flexes and makes the car "snap" from side to side. This almost got me killed on the tri state once when some idiot tried to occupy the same spot I was in, at the same time! I had to swerve doing seventy per and almost lost control because of this sidewall flex.
I believe that if I go with 17 inch rims, and put 50 series profile tires on, then this sidewall flex will be greatly lessened. I would also like to go with higher speed rated tires in the 215 width size for fuel milage. I know my choice of tire width is strange, but this is my long term project car and the mods I am making are centered around handling and economy improvements, with a power increase being only a happy side benifit.
Anyway, my questions are: can I get 17 in. rims that simply use a center hubcap (cheap) or do I have to go with the fancy mag wheel types? Would the hubcap rims give me such a gas milage penalty because of extry weight that I might be better off going with the fancy mag type wheels? Also, a few people have told me that I would sacrifice some of the handling and traction if I went with 17 inchers, even if the overall width was the same as the 15's with the 70 profile tires. Comments?
Last, what specs should I be aware of when looking for the rims?
I know you have talked about the "rubber band effect" before, but I simply cannot find it! I am greatful for all help offered. Thanks!

j cAT
08-30-2013, 11:26 AM
not too sure on finding a steel rim to handle a 255 50 R17 tire.

my 1996 impala now has the KUMHO ASX tires all season . bf goodrich no longer carries this OEM size.

the tires that I have are not good for winter driving. I do not recommend using these for winter use unless you live in a warm winter climate. so you would need to have 2 sets of tires. the 215 75 R15 I believe is the OEM standard size. This is the spare tire size that came with my vehicle . and over the many years GM used this size on this type vehicle/platform .

on your handling issues . I would replace the front sway bar bushings all. I would also install a rear stabilizer bar. the shocks should be replaced with the sport Bilstien shocks. the front springs may need be replaced if original I would guess they are weak.

with the 255 50 r17 tires the vehicle will be lower to the ground. this will help with dry pavement handling provided your other suspension is in good shape.

my 1996 gets 25 MPG on the hywy @70 MPH. these tires have low rolling resistance.

aftermarket wheels are mostly cheap chinese crap metal. be careful on your selection .

Fredddeeyy
08-30-2013, 10:46 PM
Thanks for the reply, cat. I tried the bilstien shock lowed spring thing already, and it really did not work for me. I live around country roads in portage, Indiana, and on the bumbs the rear end would fishtail,, and the car was so low there was always the danger of hitting the concreat barriers in parking lots, etc. And I don't think it actually helped with the handling. l went back to the heavy duty monroesand longer cop car springs and I am now much happier. I also put Hotchkiss stahblelizer bars on and energy suspension bushings in. Since this car is a daily driver and may see towing duty next year, I would say this is all I should do to it.
I should also mention that when I first got the car I was getting 22 mpg around town, and over thirty on hundred mile trips. I got the egr replaced,I think it was stuck closed, and the mpg sank to just over 14 around town, 22 :-) longer trips. What's that about?!?
Anyway, I want to go to 17 inch rims and 50 profile tires to eliminate the rubber band effect. I will also be switching from the 225's which are now on it back to the original 215's for the gas milage improvement. I want to keep the speedo as spot on as possible and keep its present ride heigth. Do you know if they have ever made 17 inch rims that simply use a hubcap? Also, would going to a higher speed rated tire have a noticeable effect on sidewall flex (the rubber band effect)?
Again, thank you for the response. Fred

j cAT
08-31-2013, 02:28 PM
Thanks for the reply, cat. I tried the bilstien shock lowed spring thing already, and it really did not work for me. I live around country roads in portage, Indiana, and on the bumbs the rear end would fishtail,, and the car was so low there was always the danger of hitting the concreat barriers in parking lots, etc. And I don't think it actually helped with the handling. l went back to the heavy duty monroesand longer cop car springs and I am now much happier. I also put Hotchkiss stahblelizer bars on and energy suspension bushings in. Since this car is a daily driver and may see towing duty next year, I would say this is all I should do to it.
I should also mention that when I first got the car I was getting 22 mpg around town, and over thirty on hundred mile trips. I got the egr replaced,I think it was stuck closed, and the mpg sank to just over 14 around town, 22 :-) longer trips. What's that about?!?
Anyway, I want to go to 17 inch rims and 50 profile tires to eliminate the rubber band effect. I will also be switching from the 225's which are now on it back to the original 215's for the gas milage improvement. I want to keep the speedo as spot on as possible and keep its present ride heigth. Do you know if they have ever made 17 inch rims that simply use a hubcap? Also, would going to a higher speed rated tire have a noticeable effect on sidewall flex (the rubber band effect)?
Again, thank you for the response. Fred

with the tire selection you pick a size [use tire rack] that has the same RPM / mile. the tires that I have should be the same rpm/ mile compared to the 215/75/r15.

the EGR valve may not be opening properly. if an aftermarket EGR it could be calibrated wrong. as these age they open too much causing a lower MPG.

don't know much about steel rims with the 50 profile tires. I would think it is possible. your vehicle does not require Z rated tires so you have many options.

the lowering springs of the Hotchkiss product line have many many remove them. they are of low quality. what we do is cut down the cop car springs with a cut off wheel to lower the vehicle about 1.5 inches. this makes the springs stiffer.

the rear sway maybe do to the vehicle not being level. also the rear bar works good. I actually took off my rear bar to repair rusted hardware / mounting of this bar . as the cleaning process was going on and hardware selection I drove the vehicle with the rear bar removed and at hywy speed the vehicle did move more when changing lanes.

what happens is the cop springs raise the vehicle too much.

now on my 96 I measure the vehicle height at the wheel well. mid point of the tire position from the bottom of the fender opening thru the tire mid point to the ground.

on my vehicle this is 27.25 inches on the four points . the vehicle is level and is at the correct height. if its within 1/4 inch that is ok. I suspect that the right front will be lower because of more work and load.

Fredddeeyy
09-01-2013, 10:58 PM
You raise an interesting point about car height. I simply never considered the fact that the cop car springs would make the car sway in hard turns. Thing is, I did have the care lowed a great deal with the bilstien shock and springs, and it really did not seem to help handling any. to my perception when I put the cop car springs and heavy duty monroes back on, the handling seemed the same to me, even with the car being raised a few inches above the stock heght. Keep in mind when I first got the car, the springs were completly shot, so I don't believe the car is actually that much higher then stock.
I should also mention that in a year or two, I will be retired and living out of a travel trailer, which I may pull with the Caprice after a few comp cam upgrades, including the tri power cam, head, lightweight valve gear, and performance headers. I should have this done this year and will post a report on this site as to what the results are. Anyway, I think I am really better off with the car being a bit higher for the time being.
What really seemed to make a significant difference (improvement) in its handling were the equelizers and the cop springs. Even with the raised height. Also,the car was in its lowered state during that incident on the expressway, I know the front end was tight, so I am confident the handling problems are directly related to the tires sidewall flex.
Again, thank you for your kind responses, friend. If I can find the type of 17 inch rims that I am looking for, with the hub cap, I will let you know who sells them. I will also let you know if upgrading to 17 inch from 15 actually helps the problem. Take care!

red88jeep
09-04-2014, 12:17 AM
Hi. I have a 91 caprice wagon standard model. It is a bit heavier than the sedan and has a 2 in wider rear axle from the factory. I found that out when I tried to add a rear sway bar. It did not fit. The 255 55r 17 were the tires fitted to the ss caprices from factory. I found some alloy wheels with the zero off set to match the SS wheels. They fit fine. They lower the car about a half inch. Stock suspension with rear auto ride air shocks. It helped the handling but hurt fuel economy a bit. If you are having squirming around problems, you need to go through the steering and suspension with a fine tooth comb and check for worn or bent components and get real picky on both front and rear alignment. Something is out of whack. The car will always be a bit sloppy compared to today's new cars, but should track straight and corner reasonably we'll with out drama. Just do not expect sports car handling. More a well sorted half ton 2 wheel drive pickup. You can go a +2 size to an 18 inch wheel with the appropriate tire size too. 18s are more plentiful and more affordable. The market kinda bypassed the 17's. Ron, white 91 caprice wagon 5.0 wheezer v8.

red88jeep
09-04-2014, 12:35 AM
Also be sure to check the rag joint in the steering column and all the bushings in the center link above the rear axle that connects to the differential. It controls the side to side motion of the rear axle. Also check to make sure your pitman arm and idler arm are perfectly parallel in the straight ahead position. Also. The rear end stepping sideways a bit on bumps is a standard feature on solid rear axle suspension cars. That's one reason why performance cars mostly use independent rear suspensions. It eliminates the bump transfer to the opposite side. Ron

red88jeep
09-05-2014, 06:33 AM
Just a thought, but a biggie for tire response is air pressure. You mentioned you had the low profile tires on when you got the sidewall flex. Low profile performance tires often need to run higher than factory standard pressures to extract the performance from them. The tire store will have a chart for different pressures depending on application. I start with the standard pressure settings on the door and adjust accordingly. It's quite amazing What a few pounds can produce. If you bump up to 5 lbs over stock, you will sharpen response at the expense of ride. If you drop a few lbs the ride will be smoother but more sloppy in cornering. Go to far either way and you can get into over inflation or under inflation with adverse wear and handling. The spec chart on my tires have a different inflation recommendation vs the factory spec on the door. Fooling around with tire pressures is easy and cheap. All you need is a tire gage and air pump. There are a number of places on the web that give recommendations on what to do to get optimum performance out of your tires. Remember, max tire pressure is on the sidewall of the tire for cold inflation. Your car is heavy. 215 tires are probably a bit over worked on the cornering department. I believe most we're sold with 225 or 235 rubber. Fuel economy on a 225 vs a 215 will probably be more affected by construction and tread and rubber compounds. A sticky performance tire will use more gas than a slippery economy or touring tire.

Blue Bowtie
09-06-2014, 10:01 AM
A sticky performance tire will use more gas than a slippery economy or touring tire.

While your advice regarding tire pressures is correct, I'm not sure that a blanket statement about rubber compounds and mileage are universal. I recently installed a set of Nitto NT555s on my '94 SS. Compared to the hard-as-rock BFGs that came off the car, these stick like gum rubber (even in water) but I have noticed no loss of fuel mileage. I run them at 44 PSIG, just like the numerous previous sets of BFGs.

j cAT
09-06-2014, 01:24 PM
While your advice regarding tire pressures is correct, I'm not sure that a blanket statement about rubber compounds and mileage are universal. I recently installed a set of Nitto NT555s on my '94 SS. Compared to the hard-as-rock BFGs that came off the car, these stick like gum rubber (even in water) but I have noticed no loss of fuel mileage. I run them at 44 PSIG, just like the numerous previous sets of BFGs.

the BFG stock tires never lasted long for me 30K miles and worn from side to side all 4 tires even. IMO these were soft rubber tires that did poorly in rain. what I found since these BFG'S are no longer available is the KUMBO ASX tires are good in the rain and much better handling. so far wear is NIL..I run them at 38psi front and 30 psi rear. this keeps the tread flat to the pavement good even wear..

Add your comment to this topic!