vettes garage

Hi,
I'm new to this forum in my country i dont think ill find an answer for this��.
I bought 305/35/20 mt for the rears and after i get them on the car felt unstable after that i talked to my buddy from the us and he says with that tire i should fill 22 psi and that what i have done
The problem is that it makes the tpms messege "tire pressure too low"
I tried to change that with my autel ms908
And the lowest psi i can adjust the sensors is 25 psi

What do you think is the correct tire pressur for street?

Thank you and sorry for my english.

robert miller

With you running that low of pressure you will wear out the tires super fast. That tire has a softer side wall is the place that you are getting the feel you are talking about.

That feel is coming from the road that is unlevel and having dips and waves in it. You will have to life with it are chg out the rear tires.

But you need to put as much air in it to get the sensors to go off for you. Robert

vettes garage

Ok,thank you.
Some of the forum memebers must know how much psi i need to fill for sporty street use

robert miller

This tire being a 20 inch rim & also being a DR tire. I cant tell you on that to much to factor into your question. Like your RWHP & RWTQ but with that said since your settings goes off at 25 psi start at that point and work it from that. I know even as a DR but in a 20 inch tire the side wall is not going to work much like you want it to do in getting you more hook up in it...

I even went in my z51 car from a 20 inch to a 19 inch rim to get a better rear tire on it. I went with a R888 305 30 19 on the rear. At full aired up with my tires no crazy stuff on the street even at 140 plus mph.

Elite275

What type of pressure are you running in those on the street and track?

Higgs Boson

I'd be at least 30 psi for street use. You don't want to make any turns with 20-25 psi.

Air them down for the track to 20. 30 for the street. A DR is nothing like an 888 though.

robert miller

Seen even 18 psi in mine on the track. But was running a 15 inch rim with a M&H DR in a c5 auto car still was DOT.

Now if the OP wants to talk about the car going from side to side in the rear on the street it was really bad if you got over 90 mph on any type of bad road on the street.

vettes garage

thank you for all,
The car have procharge and methanol,
Running about 700rwhp.
unfortunately i think the problem is the wheel height, its taller about 4cm.
now i fill it with 30 psi
And the tpms is fine but i get messege says "service rear axle" "stabilitrak"
And abs,esp,brake indicators are on too.
When i plugged autel maxisys all faults says "electronic brake control modul invalid data"
And "rear drive clutch configuration not programmed" .
anybody know what is the problem?
it will be disapointing if that size cant be fitted on c7.

Higgs Boson

try updating the tire revs/mile in the tune. what you are getting is not related to tire pressure. it sounds more like a traction control system issue.

vettes garage

With stock tires the car drives perfectly

Higgs Boson

which is why i said to adjust the revs/mile in the tune with non-stock diameter tires so the TC system doesn't see it as a problem.

305/35/20 are 28.4 inch tires, very tall.....

710 rev/mile vs the stock tires at 754 rev/mile, that's 44 more revolutions per mile which is a pretty good amount....they are 1.4 inches taller than stock.

do you have a lot of HP? why do you need such a tall tire? if you are under maybe 650 rwhp they will probably do more to slow you down....

Elite275

Do you update this every time you swap out tires if there is a difference in diameter or only if exceeds a certain threshold?

Higgs Boson

I am weird so I always update it but there is a small range where it isn't necessary...stay around 27" tall and you are good to go.... down to 26.5 I would update it or the computer might think it is wheelspin and over 27.3-27.5 I would update it or the computer will get confused like the OP's.

Personally, I would not go over 27" tall tire, especially if you have lowered the car at all as it could rub on the passenger side fender liner bulge that houses the evap canister (in front of the rear tire).

If you are stock height or raised up then I guess you could be ok, but you would have to shoot me before I ever raised a car, lol.

blue_bomber697

Can this be done easily at a dealer? My new tires will be 27.8" in diameter which sounds like you recommend updating the tune. My tuner however is in another city, is this something thats going to make the computer bring up errors if I don't get it fixed right away?

vettes garage

Ok,
Look up i said the car have 700 whp.
Come on i never heard of someone who raised up his vette and if he is hes got to be retard or something like that.
Someone familiar with this problem?
I will go to the tuner just next week,
I cant do anything at standart shop to solve this?
again my shop have the maxisys but i dont know if it can do something with that.
Dealer isnt an option here ,
the car is import and here imported cars like vettes has got no dealers because the official dealer bring just the camaro and not the vette.

Higgs Boson

still quite the tire height, either way....

I guess english isn't the primary language in your country so I am willing to disregard this post. I hope everything works out for you.

vettes garage

You are right English isn't the primary language here i'm from israel.
But it doesn't mean you need to disrigard my post i understand what you said but you giving me no answer just saying what i said earlier in different words.
I know the tire is taller 1.4 inch its like 4 cm.
Here in israel we have only one gm dealer which called "umi"
They dont import vettes at all that car is personal imported.
The dealer dosent want even look at the car, so im in a pita!!
I'm asking again can my shop do something with autel maxisys to reprogramming the revs/mile?
Thank you very much.

Higgs Boson

I didn't disregard your post, I made a recommendation on how to fix it. I have no idea what Autel Maxisys is or what the capabilities of anyone or any business is in another city much less another country.

If you are looking for a recommendation on how to adjust the calibration then I suggest you look into learning to tune your own car with HPTuners or EFILive or the like. If you don't want to get that extensive then I am sure you can find simpler devices that just recalibrate for gear and tire changes.

My apologies, I thought you were asking why you were experiencing something, I didn't know you wanted a lesson on how to fix it and for me to check Yelp Israel as well for you.

I hope you get it fixed!

vettes garage

Still having problems,
Thats make me crazy .
I guess ill have to buy the hp tuners.
But still i think its shouldnt be that complicated to change tire size.
No one here running 305/35/20 on rears?

blue_bomber697

35 thickness on a 20" tire makes the tire too tall so it's not a common or recommended set-up. 305/35/19 is the proper way to go.