Question about tires

[curbie]

Ok...as everyone probably already knows by now, b/c I've announced it 20,000 times...I have a '00 Tib. Stock tires and rims. I went to Tire Discounters and asked about the low profile tires. They told me that I can't go any size smaller of a tire/rim on my Tib b/c they're small enough and if I went any smaller...it would be pretty much very bad for my driving. Now then....what the guy at Tire Discounters did suggest...was that I could go sizes larger.... which I gave him a look like ---> and thought WTF are you talking about? Ok...if I want low profile tires...why on God's good earth would I want larger size tires/rims? Can someone please tell me?

I want to get low profile tires with new rims, so if anyone has any advice on what size tires I could get for my Tib without having any problems with the handling or the size of tires effecting the car, please tell me! I'm completely in the dark here and don't know if the guy is full of poop or what. Thanks!

[nisco]

wait... did you think low pro tires meant smaller rims?.. i had trouble following that rant.....

largest i believe you can go without shaving and trimming the fenders is 17in.... whats stock on an 00... 15s?


ok i jus finished reading you post over again.... and why would you want to go smaller?
unless you plan to go all out drag racing you wouldnt need anything smaller...
you go bigger to look better.. more rotational mass..

[curbie]

Originally Posted by nisco

wait... did you think low pro tires meant smaller rims?.. i had trouble following that rant.....

largest i believe you can go without shaving and trimming the fenders is 17in.... whats stock on an 00... 15s?


ok i jus finished reading you post over again.... and why would you want to go smaller?
unless you plan to go all out drag racing you wouldnt need anything smaller...
you go bigger to look better.. more rotational mass..

nisco> Ok...so what you're saying is that I should go with at least a 17in ...and then I can also get that in low profile tire size...right? I wanna get some rims to go w/ them tires. they offer a bunch of things free like caliper painting and more! lifetime warranty, plus balancing is free, bla bla bla...

[scottsee]

it effects the geomitry of the wheels. which effects the wheel speed sensors. you can go to as large or small of rims as you like, as long as you dont change the circomfrance of the tire. matter a fact the smaller your rim size is the softer of ride you will incounter. you'll be riding on a larger volume of air.

[curbie]

Originally Posted by scottsee

it effects the geomitry of the wheels. which effects the wheel speed sensors. you can go to as large or small of rims as you like, as long as you dont change the circomfrance of the tire. matter a fact the smaller your rim size is the softer of ride you will incounter. you'll be riding on a larger volume of air.

I may be reading your post wrong scottsee, but the way it sounds...I dont want mud tires. I want the low profile tires with new rims. So I'm wondering what size would be best...nisco says i could prolly go 17's w/o shaving the rims...but i guess 16's would be aight..just to make sure nothing is shaving or scratching.

[BigTDawg]

Originally Posted by curbie

I may be reading your post wrong scottsee, but the way it sounds...I dont want mud tires. I want the low profile tires with new rims. So I'm wondering what size would be best...nisco says i could prolly go 17's w/o shaving the rims...but i guess 16's would be aight..just to make sure nothing is shaving or scratching.

he said nothing about mud tires what he said was you can get any size rim and tire and have no problems as long as the diameter of the tire is the same for example bigger rim lower profile tire smaller rim larger profile tire

[nisco]

the larger size rims you get, the less tire youll have (if you stay in the same circumfrence as stock)

like measure from 1 point on the edge of teh tire.. to the other point directly across...

[scottsee]

when you change circumference you alter everything. you can go any size rim you want as long as the circumference of the tire dosn't change.

when you change the circumference you change the rotation durration, meaning your wheel speed sensors wont accuratly display your speed. going down in overall size will make you display a slower MPH then you are actually going, lager sizes will do the oppisit.

you also run into performance problems when you alter the size of tires on a stock transmission. your gear ratios are specificly set up for your stock tire size. i'll post up more information w/ equations to explain myself when i get home.


effective ratio = (old tire diameter / new tire diameter) * gear ratio

example. the 04 tib v6 has a final drice ratio of 4.428 and a tire size of 215/45R17's making the over all diameter 22.6181. lets say you wanted to replace them with 235/30R17's. the overall diameter of that tire is 20.5511. with the equation above you would have a new gear ratio of 4.8733.

why do we care? well the tibs max tq peak is around 181ft-lb @ 4000rpm. so if were planning on downshifting from 5-4 on the freeway to get max responce at passing you need to know this shit.

example:
Gear ratio = (rpm x tire diameter) / (mph x 336)

so at 4000rpm x stock 22.6181 diameter wheels divided by 65mph x 336. You'll want to have a 4.142 final drive ratio to reach 4000rpm at 65 downshifting to forth gear. sence stock final drice ratio is 4.428, RPM will hit at 3719.52. close enough. so you can see why changing the size of your tires effects the overall performance of your car. small tires raise the final ratio and larger one lower it. the last thing you'll want is a 4.8733 ratio, you'll loose performance. i wont bore you anymore with math. its time to drink beer and bbq. Memorial day weekend baby.

[curbie]

Originally Posted by scottsee

when you change circumference you alter everything. you can go any size rim you want as long as the circumference of the tire dosn't change.

when you change the circumference you change the rotation durration, meaning your wheel speed sensors wont accuratly display your speed. going down in overall size will make you display a slower MPH then you are actually going, lager sizes will do the oppisit.

you also run into performance problems when you alter the size of tires on a stock transmission. your gear ratios are specificly set up for your stock tire size. i'll post up more information w/ equations to explain myself when i get home.


effective ratio = (old tire diameter / new tire diameter) * gear ratio

example. the 04 tib v6 has a final drice ratio of 4.428 and a tire size of 215/45R17's making the over all diameter 22.6181. lets say you wanted to replace them with 235/30R17's. the overall diameter of that tire is 20.5511. with the equation above you would have a new gear ratio of 4.8733.

why do we care? well the tibs max tq peak is around 181ft-lb @ 4000rpm. so if were planning on downshifting from 5-4 on the freeway to get max responce at passing you need to know this shit.

example:
Gear ratio = (rpm x tire diameter) / (mph x 336)

so at 4000rpm x stock 22.6181 diameter wheels divided by 65mph x 336. You'll want to have a 4.142 final drive ratio to reach 4000rpm at 65 downshifting to forth gear. sence stock final drice ratio is 4.428, RPM will hit at 3719.52. close enough. so you can see why changing the size of your tires effects the overall performance of your car. small tires raise the final ratio and larger one lower it. the last thing you'll want is a 4.8733 ratio, you'll loose performance. i wont bore you anymore with math. its time to drink beer and bbq. Memorial day weekend baby.

All I have to say is....d@mn... sure has been one hell of a lesson for me! Thanks for the very helpful info! I guess my next question would be...how do I find out what my specs are? I'm assuming they're in my drivers manual for my tib? (It's a 2000) Unless you already know the specs...could you tell me if buying lower profile tires would be worth it, or should i just keep the same tire size and get new tires all together? I at least need new tires, i just thought that i could get lower profile tires b/c i've liked the way they look on other cars.

[scottsee]

agian. you can do anything you want as long as you dont change the circumfrance. when you go to lower aspect ratio rim/tires you increase handeling, but loose ride quality. with larger aspect ratios you get better ride quality, but loose cornering abiliy. choose a setup that is up to you, if you want awsome ride quality, just change your rims, if you want better handeling with sacrificed ride quality move up a larger rim and smaller aspect ratio.

[tibby01]

maybe he meant width when he was speaking of size. a wider tire will give you better traction and handling. the profile of the tire refers to the width of the sidewall, i.e. the height of the tire.

on the stock rims, i would go one tire WIDTH up to 205/55/15. you have a much larger selection of tires with that size, and wont have any rubbing issues.

[curbie]

Ok...so I reserected this thread, b/c I sent tiby01 a PM and haven't heard from him. He posted a while ago some pix of his new tires he recently had put on. I was wondering what size those tires/rims were. I mean, he has the exact same tib as mine, so I wondered what size those were so I could go get some tires/rims of the same size. *Note* I don't intend to get the exact duplicate...just the same size!

so...could tiby01 or someone else please tell me!?

[tibby01]

if i were you, go with a 16x7 inch rim with a 42mm offset.

tire size 215/45/16

you're speedemeter will BARELY be affected...prob. not even noticeable.

i went with 205/45/16, but only because i will be lowered, and didnt want any possibility of rubbing. also because my wheels are only a 40mm offset. i probably could have gone with a 225/45/16, but wanted to make sure.

[curbie]

Originally Posted by tibby01

if i were you, go with a 16x7 inch rim with a 42mm offset.

tire size 215/45/16

you're speedemeter will BARELY be affected...prob. not even noticeable.

i went with 205/45/16, but only because i will be lowered, and didnt want any possibility of rubbing. also because my wheels are only a 40mm offset. i probably could have gone with a 225/45/16, but wanted to make sure.

Tiby01> and so the tire size and rim size you gave me are for low pro. tires? I'd like to get low pro. tires. My ride isn't lowered. Actually, I think it sits pretty low enough! Thanks again!

[tibby01]

low profile tires are just tires with a shorter, stiffer sidewall. there is no set line on low profile vs non low profile tires, or atleast i dont think there is.