I will have to replace the tires since the stock 275/60/17 are quite over.

I was thinking about to put a set of 22" rims and tires on my 1997 SST like I saw on a Dakota around here: very cool! (someone will yell at me for that.. but I like those rims)

Is there any problem on running 22" tires?

the size should be 265/35/22, obviously i won't go offroad!

can 22" tires help to lower the gas consumption? here gas is amost twice than US!
I assume the overall diameter is increased than stock 17" tires but I haven't done the math yet.

thanks

 

i did the math! i get -2.3%!!! that's no good!


tire circumference




current: 2393.26 mm
new: 2338.29 mm


real speed at 112 Km/h: 109 Km/h

-2.3%

 

math? oh man... that looks hard to do

 

weight is more of a factor than circumfrence. circumfrence only changes the speedo.. i would imagine a 22 inch rim would weigh more than a 17, but the difference in weight of rubber might make up for it. get a scale and weigh the two. that would tell you if you are going to get better gas mileage. my guess is it's going to be such a small difference you're not going to notice a change. probably a difference of a mile or two out of a whole tank.

 

i found a website, only italian sorry but comprehensible, which calculates the differences between tires: very cool!

http://lnx.deeptuning.it/pneum.php


you just enter the tire sizes before and after and you get the difference, in metric of course.

i got 5 kilometer less for 100 km. it's 5%

thanks anyway!

 

Well, I'm running the now out-dated factory 20"s on mine, the tires are 275/60s, which is equilvalent to a diameter of 33"s. I don't have a lift on my truck, and I just barely have enough clearance in the front for them... In fact, when I turn all the way, the tires rub the inner fender slightly, I'm going to mod that with some fiberglass before long, but for now, it's no big deal... Anyway, as long as you don't go over 33"s in total diameter, you should be OK... Or get a lift or take out the inner fender (get ready for a messier engine though). I had to calculate the differnce in the tire size too... Just remember that the first number, 275, is the tread width, and the 2nd is the percentage of the first... So a 275/60 is 275mm wide and 165mm tall. So, to figure your total diameter, just add 165mm, 17", and another 165mm (remember, a tire is round, there are two treads that need to be counted for a diameter measurement...)... Since you have the same size tire as me, but on a smaller rim, I can tell you right now that you 17"s are 30" in diameter with tires... So figure everything from there...

I had 16"s on mine first, then 17"s, now 20"s... Weight is a factor, yes, but more importantly, gearing is a factor... It takes a lot more torque to start a 20" or 22" than a 17" or 16". I have the 3.55:1 rear and an automatic behind a 5.2L... With the 20"s, in city driving sucks.. I lost about 1.5 mpg in city... of couse, if you don't mind taking longer to accelerate, you won't have this problem.. Now, once you've got them spinning, they go alot faster... Bigger wheels are going to hesitate, then take off... So overall, your 0-60 should be about the same, but you'll notice when the truck starts to move as the engine enters it's torque curve and everything starts spinning.. If you have taller gears, you won't have this problem.. The flipside is the increased enconomy on the highway... The 20"s are a 12.5% increase over my original tire size, so mathematically, I should be making 112.5% of 18mpg (that's a little over 20mpg) On long trips where I can jsut set the cruise and fly, I tend to get about that, sometimes 21 or 22, depending on weight, road conditions, wind, weather, and the number of stops I have to make... The main thing though is the loss of in-city economy... I plan on changing my gearing later on when I restore the truck, maybe a 3.96:1 or even a 4.10:1, but I don't know about that yet... Like I said, they hesitate, then they go fast... Just be ready to give it a little more juice off the line if you want to keep you acceleration the same...

Racing with the 20"s compared to the 17"s cost me a half of a second actually... (17.0 secs with the 17"s, and 17.5 seconds with the 20"s in the quarter) Most of this in the first 60 feet... My speed at the end of track was actually about 10mph faster with the 20"s though, but the hesitation got me as far as racing goes... anyway, it illustrates my earlier point...

 

I forgot to mention that my engine has about 300,000 miles on it too, so I'm sure that a newer engine would produce better economy stats... I love my 318, it's a great engine, but I know it's no "spring chicken," as my father would say... it doesn't smoke, burn oil, leak, ping, knock, or anything yet, in fact, it's still the orignal tranny behind the thing... although, after the racing, that's about to have to be restored... stalling-up an automatic is a good way to ruin all those clutch packs... hehe... it's fun though...

 

well, your reply is very interesting!

what do you think replacing stock 275/60/17 with 265/70/17?

the math says


current circ.: 2393.26 mm
new circ.: 2522.07 mm


real speed at 112 Km/h: 118 Km/h

increase: 5.38%


since the tread is decreased of 10 mm and the % of is is increased by 10 I expect the tire weight is wuite the same


that's only a temporary solution since i don't have 2 grands for a complete set of 22" with tires and the stock tires need replacement soon!

could I have the same problems? eat more gas in city driving?

thanks

 

with that little of any increase, i doubt you will notice much difference, if any at all... but, it really is a hassel to have to figure out your whole speedo... like mine... jeez... i have a '97, so they make no general-use programer... i have to either take it to the dealership, where they charge a minimum of $75 for any change, or spend $400 for a custom programmer, which wouldn't be bad, except that I can only use it on this truck... right now i just ahve everything memorized... 62.5mph on the speedo is 70... 58 is 65... so on... yeah... it's crazy... all my friends say "this truck seems like it's going faster than that" when they look at the speedo... i just laugh at it now...

oh, and, oddly enough, the weight of the 20"s i have is not much more than that of the 17"s... however, the 20"s are aluminum, and the 17"s are steel... big difference there...

 

well, i don't care too much of real speed, i could read it in my GPS receiver...

haha it only sucks with speed radars!

my 17" are aluminum (97 SST) so, with an increase of 5.38% i think i should save gas (just a little) on long runs.

if i got it well, on short runs itÃ*s harder to start because of the increased ratio.. so i could eat more gas on city driving because of repeatedly stops and stats, right?

thanks