08 ISF Wheels.
Is there any reason not to run taller sidewalls on the ISF. The car won't be lowered.

Front: 255/45/19 (7.3% increase in circumference)
Rear: 275/40/19 (6.5% increase in circumference)

I'm trying to get a bit smoother ride. I've considered 18" wheels, but again, if there's no reason this won't work then I'll probably try it.

Trying to search this on the web really helped me learn about my monster truck, but not this.

 

I’ll sum up how this entire thread will go to save you some time.

You will be encouraged to buy 18s and run taller sidewalls. 265/40/18 square is a popular option, and about the tallest side wall you can have.

Some will say that’s not enough, you need coilovers. We will then mostly all disagree on what coilovers are best, and it will turn into a friendly debate on function.

Unfortunately, ride harshness is subjective, so we can’t give you definitive help. In general, taller sidewalls only help if the tires themselves ride better. Some do, some dont. The same issue exists with coilovers.

Eventually, someone will say the ISF is a sports car and will never ride smooth. At least someone else will agree lol.

AMHIK.

 

Generally speaking, you don't want to put the speedometer and odometer out by that much, 3% maximum (+ or -) is generally considered the sensible limit.

There is also a lot to be said for the brand of tire and it's age (if not new).
Also a possibility the tires and/or suspension are stiff from sitting. When I got my F last year, it was crazy harsh, after 2-3 weeks of regular use, it smoothed out substantially, although it still rides like a 4-door sports car.

Also...
**Fixed.

 

Appreciate it:
* If both the front and the back are changed out out to the same circumference/height, I don't see how a significant change in circumference would change/hurt the mechanical/electrical systems of the car (The speedo will read low. What else?). i.e. my GX with AWD has significantly larger tires than stock: No problems.

* Driving dynamics are for sure impacted by tires. I do plan to track at some point, but if that becomes a thing for me then I'll want different tires and probably track specific wheel/tires.

* I agree it will never ride smooth. I'm talking smoother than it is now.

I knew this wouldn't be appreciated by the majority of the forum, so I guess I was trolling a bit. On the other hand I'm trying to test my idea against the collective knowledge of the hive mind.

I've been reading a lot of threads for that past few days trying to get more of a feel of what's been done in the past. Signal to noise ratio is pretty bad, but it seems like many people have had success with 245/40/19F and 275/35/19R. Both of these are about 3% larger and I feel like a reasonable compromise between what I proposed above and the default answer of 245/35/19F and 275/30/19R.

Convince me :P

 

I keep hearing this 3% rule being tossed around but it makes no sense. Why 3% and why not 2% or 1%? Who decided that 3.1% was too much? My personal experience and opinion, I put on whatever tires I want as long as they fit. Go tell the jeep guys they can't put a bigger tire on than stock. I mean really, if the tire doesn't rub, and you know how much the speedo is out, who cares? Is there also a rule saying you can't have an exhaust 3% louder than stock, or modify your car to have 3% more hp?

 

I agree with you. I have changed tire sizes on numerous vehicles with no Ill effect. I’m curious where this opinion came from.

 

^^^^The electronics, axle ratio, stagger, and load rating all care. Just because some folks with all terrain vehicles and some guys with trucks put on gigonda wheels and tires doesn't make it right for a pleasure vehicle or a hi-po car. I also have a truck and when I increased the wheel size from 17" to 18" I was careful to keep the wheel/tire combo the same OD. My nephew has a small Toyota pickup with wheels and tires that are too big for the vehicle (he likes the look). The thing has no pickup (pun intended) and drives like crap IMHO.

Lou

 

What specifically about the electronics, axle ratio, stagger, and load rating cares?

The increased tire diameter will effect acceleration on paper, but it will be negligible. Very few are running OEM diameter it seems.

My is350 came with oem 225/45/17 on front and I ran 255/35/19 square with zero adverse effects. That’s almost a 4.2% increase in height. That kept the OEM ratio in the rear, but added over an inch to the front. No issue with the loss of stagger or electronics. I have had the same diameter on there for over 4 years now.

Maybe I don’t follow what you mean by load rating? If you mean the load on the hubs, it’ll be fine. I added plenty of weight to the front of the is350 with those 19s. No notable effects other than increased road feedback and reduced sidewall height. If you mean the load rating of the tires, I’m not sure how that adversely effects anything since you can choose your tires load rating when you pick your tires.

I have had sports cars where I added an inch plus of tire height. There are some members running 275/35/19 in the rear with no reported adverse effects. One even ran it in the front with no problems other than extreme rubbing, so he downsized.

Going bigger will generally reduce torque and increase weight, lowering performance. But the car will be fine.

 

^^^^Of course I disagree with everything you have said, but this is America and you certainly have a right to be heard. I'm only responding to your post to answer a couple of questions.

I don't believe that to be true.

Load rating is the Max Load Capacity stated in lbs. of the tire and differs by size. It is important. IMHO, to stay at or above that rating when replacing with a different size. I have attached the specs for the 255/35/19 (standard for the rear of an ISF).






Lou

 

I’ll happily rub dirt on my face and post a picture in this thread if anybody can show definitive proof, beyond speculation, that changing from the oem tire size is somehow harmful to a car, with the exception of massive tires that won’t fit on the oem body without catastrophic rubbing.

I’d wager that people who say that running different tire sizes causes problems, have never actually done it and had problems on a sports car. This is barring someone throwing 40s on a car and blowing a diff, which is an obvious no no. We’re talking about adding or subtracting an inch here at most.

I have zero problems with being wrong, I’m human and we all take turns being wrong all the time. Anyone is welcome to prove I’m wrong, that’s why we are discussing it. I’m genuinely curious.

Until then, Both of my cars running non OEM tire sizes without any problems can serve as the definitive proof on the debate. I’ve simply proved it’s not true. So has the dozens of members running aftermarket wheel and tire diameters (albeit most of them are slightly smaller than Oem). So has everybody into DONKS, and most everybody with bigger off-road tires on 4x4s, with some exceptions of people just going overboard.

Zero debate that the proper minimum load rating for a tire should be chosen. But there are many options in tires to overcome that. You just shouldn’t go to low in load rating.

OP, your only worry is not rubbing. Feel free to throw bigger tires on your car, and pm me if you have questions.

Please don’t take this as argumentative. I’ve added the mud in the face part simply for fun, and I will honor it.

 

^^^^OK - I never said anything about different tire sizes, I am specifically talking about changes to the OD! When I had my ISF, I ran 255/35/19 in front and 295/30/19 in back on modified RCF wheels. Those sizes are significantly wider than stock with the same OD as stock. IMHO the ISF in stock form is under-wheeld and under-tired. Nuff said on this topic

Lou

 

2IS guy here. I installed taller tires on my car, I went from 225/35/19 to 225/40/19 and 255/30/19 to 255/35/19 and have ZERO problems because of it. Actually now my speedometer shows exact speed, verified with my friend's new Audi S5 and my GPS. Love more comfortable and very enjoyable ride on my Pirelli Cinturato P7.
Cheers.

 

Was mistaken about the "3% rule":

If the OD of the front and rear have 3%(+) differential, it can cause ABS malfunction light. (even for 2WD)

 

Any evidence beyond postulation?

 

^^^^Boy, you are not going to let this go JWarr00 should not have been "mistaken" on the 3% rule. As far as ABS malfunction, I have no idea, but probably not the case.

Lou