So, I'm looking at some Michelin PSS 305/30/19's with a diameter of 26.3 and a 235/40/19 with a 26.4 diameter. This is on tire rack. Is a 40 up front to tall for my lowered with PSS 10's? Sorry if my questions are lame but I need to figure this out.

 

jim, yes
go with 305 30 19 and 245 35 19 or 235 35 19.

 

well jim.. you're in the right place to think out loud! lol good luck.. 19's huh?
no problem

 

In reading more I see that it is the Rev's per mile that are important.

 

for the viscous coupler of the front diff, yes. running 19's is a choice that can be made without adverse consequences provided the tires sizes are within , and no more than 3% difference, front to rear.

theres no less than 100's of threads on this also as i'm sure you've found.

 

You need to ignore those diameters since they're meaningless and focus on the rotational diameters. The 40 is too tall for the front as well.

I would stay away from the 245. I've tried them and they were fine with regular up/down travel, but had significant rubbing issues when turning. It wasn't just at lock but started well before lock. Stick with the 235/35-19 and 305/30-19. Those sizes should fit just fine without any issues even with your car being lowered.

 

Scott, Thanks for the head's up. I read another post with this set up. I've been checking the rev's and I have choices. So the 235/305 is a good way to go.

 

You're welcome Jim. What I had gone to before switching to track tires for the street in the summers was running a 235/35-19 & 305/30-19 combo and I had no PSM issues, rubbing, or anything else. The one other thing to pay attention to is how worn the fronts are when replacing the rears with the normal cycle of replacing the fronts every other time you replace the rears. Their rotational diameter can differ significantly at that point depending on wear level.

 

Scott so even if the PSS Michelin's are 817 and 792 rev's per mile I'm still okay? I'm not good with math guys so give me a brake!

 

You're at 3.059976% difference in rolling diameter so you're right at the limit, but should be ok. Like I mentioned earlier in the thread though, some people (a small number I believe, not a highly prevalent problem) have problems if they go over even 2%, never mind 3%. Other guys have run slightly over 3% and never had any issues.

Based on the number of people running that combo on this forum without any problems, I think you'll be just fine with only a very small chance of any PSM issues. FWIW, my experience is the problems only come up when doing things like going through a long sweeper at speeds of 40+ where all four wheels need to adjust to the wheels rotating at different speeds for several seconds or more (lightly pressing the brakes in sweepers has always made it worse for me versus being on the power or coasting) . In a straight line or when turning for a short duration they don't seem to cause issues.

 

Not sure where this mythical 3% comes from. I've never seen it published anywhere, in any literature, kind of an urban myth. However, 3% larger rear is not the same as 3% larger front. What is known is the fact that both the front and rear final ratios are 3.44. If you understand how the AWD system works, it will logically tell you that in order for the rear to transfer any torque to the front, the rear wheels must rotate slightly faster than the fronts. If the fronts rotate faster, they are actually providing driveline drag. The viscous coupler is primitive and relies only on the difference of input / output speeds.

 

So maybe I should start another post and if I don't get any answers here I can do that. I looked on tire rack for installers in my area and I saw places like Big Brand Tire in Ventura where I live. Can I trust these guys to do it right and not mess up my wheels? I can ship the tires anywhere in the L.A. Ventura area so anyone have favorite installers they could recommend.
Thanks.

 

tire man 3 locations in camarillo/calabasas and t-oaks is ok. they will match any internet price too so no need to limit yourself to tire rack unless you want to, though the guy damon @ t-rack is very helpful, all major tire places will match the internet now i have found. they have no choice.

they key to all this once you've decided, is the alignment. mounting them is no big deal. i begin with the x73/gt2 alignment, and tweak from there. i can't speak to 19's lol. but that oughta give ya some more reading/studying for in here GL with em.

 

Well, I've decided to stay with 18's for the time being. My fronts have a lot left to give so I'm just going to replace the rears for now. So mounting and balance is no big deal. Every time we change tires we need to realign? That was another question I forgot to ask, thanks. I've been to Tire Man in the past. I can stop by and talk to them first. Alignment? More to learn.... cool!

 

18's good for you
yes, mount/balance are a daily thing thay any place can do. ordinarily it wouldn't be necessary to re-align, BUT since i assume you don't know when it was last done? i would do it. again, if your car is lowered? begin or simply go with x73/gt2 specs. they're in all alignment computers. if stock height? go with stock numbers to start.

tire man is adequate to the task, unless you're going with corner balancing etc etc. not needed at this stage imo. but maybe later if you get "serious" lol