Running Square - wheels and tires

[2001ultima]

Are there any opinions on running a set of the same size wheels and tires front and rear to obtain optimum handling? Say we modified the front to fit a 305 or 315 tire and then run that same size in the rear.

Or would you still prefer to have the larger 335 in the rear?

Opinions would be appreciated.
.

[ROWDYRENAULT]

First of all buy a gym membership because you,re going to need it. If you think the steering is difficult now try some 315s in the front. Then you better do some exercises to shorten your legs plus find flat light projectors both in an attempt to accommodate the greater diameter , the current 245s touch both the front and rear of my cars front wheel wells now. Then you will need to flare the fenders at least 3 inches and change the entire fender line to fit the greater width which will look "not so good" . You better include traction control because the last thing these monsters need is less traction from a smaller tire in the rear. Plus you can plan on going slower in a straight lint because of the substancail front drag increase caused by the butt ugly flares and the front of the car will need ride higher or those front flares will need to go from butt ugly to a member of the coyote family to accommodate the much taller tire. Outside of all that, as the kids in California say "no problem" sorry for the sarcastic remaks but 12 hours on a plane get my anti social tendieces in rare form. Lee

[2001ultima]

Lee, Good to hear you opinion. Thanks. Jim

[RAT GTR]

Well Lee, what if you just ran 245's on all four corners. That way you wouldn't need to modify the front wheel wells?

[ROWDYRENAULT]

O.K. Bob, tell you what, when you run the Silver State this Fall, why don't you try that out and get back to me on it. What was it last time 203 or 207 MPH through the speed traps? I bet those 245s will work real good. you'll only need to figure out how to get the rev limit to 9 or 10,000 RPM to get over 200mph again. love and kisses , Lee

[vinnie01]

Nathan width wouldnt alter gearing but it would reduce mechanical drag

[UltimaCH]

I guess Lee was just joking...

[ROWDYRENAULT]

O.K. guys I was wrong, a 345/30/18 is 25.9 inches tall and a 245/35/18 is 24.8 inches tall. This equates to a 5% difference in rolling radius which very crudely means you would need 5% more RPM to run the same speed or approximately 7560 in Bobs car to retain a 203 or 207 top end I forget which. Actually it would be higher due to slippage ect ect but life is short.
This is by far the least significant reason that this is a very bad idea. Look, I enjoy reading about ideas that guys come up with that have a potential for improving the car. The rear wing that could change attack angle discussed a while back was interesting. The discussions about different gearboxs that might work are interesting, some of the mods done to aero features of the car, anything the guys from the race team add and with rare exception anything Steve D posts I am going to read and agree with. Lots of owners with lots of both problems and solutions get me to read this blog almost every day. But sometimes the idea is just not in the realm of reality and this is one of them. All I am trying to point out is that the far reaching effects that this radical change in tire size would make makes me believe that the author had not really thought about it in any detail at all. NO OFFENSE MEANT just stating a opinion. the next post he makes I will read and consider with interest and a open mind. Lee

[srreck]

245 rears for the Ultima are like bicycle tires.........Please no.

[RAT GTR]

Oh, come on Lee -- I think the thing to do is put 245's on all around, then add air shocks, and go to East LA and see what competition we have driving up and down Whittier Blvd!

[andygtt]

You would ruin the handling on a Ultima IMO if you did reduce the rear tyres that much as the geometry is designed for this width... so to make it work you will prob need changes to wishbone, pickups, offsets etc etc.

However saying that you would have traction issues going down isn't right, I run 265's on my Noble without traction issues, and I have 700bhp and can use it all in 2nd and if the tyres are really warm 1st... plus you have more tyre choices.
Of cause doesn't look as cool as running 335's

[2001ultima]

All good perspectives, thanks. The start of the thread was a proposal to run 305s or 315s front and rear, size width limited by the front space limitation. Some Ultima owners have fitted 295s. Some have fitted 19 inch as well. My idea was for a track setup to better balance the car. The car is light and I have ~450 HP and am looking for the best track setup. I was hoping someone may have had tried this track setup.

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Yes, I would agree for a top speed run, a narrow front tires with lots of air pressure and the tallest rear tires would be best and for a 700+ HP Ultima than the widest rear tire would be best.

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I track my car and am planning a new set of wheels so I thought I would see what people thought. It doesn't seem like anyone has run a setup like this. I am definitely going to increase the front size to 295s minimum. Maybe 295s front and 335s rear are better then 305/315s front and back. Or maybe there is no noticeable difference. I'll keep you posted.

[F.C.]

2001ultima said:

All good perspectives, thanks. The start of the thread was a proposal to run 305s or 315s front and rear, size width limited by the front space limitation. Some Ultima owners have fitted 295s. Some have fitted 19 inch as well. My idea was for a track setup to better balance the car. The car is light and I have ~450 HP and am looking for the best track setup. I was hoping someone may have had tried this track setup.

---

Yes, I would agree for a top speed run, a narrow front tires with lots of air pressure and the tallest rear tires would be best and for a 700+ HP Ultima than the widest rear tire would be best.

---

I track my car and am planning a new set of wheels so I thought I would see what people thought. It doesn't seem like anyone has run a setup like this. I am definitely going to increase the front size to 295s minimum. Maybe 295s front and 335s rear are better then 305/315s front and back. Or maybe there is no noticeable difference. I'll keep you posted.

Be careful as the aspect ratios don't go hand in hand for tire width for instance you could go wider and find you have less contact patch than the you had in the first place with the same A/R. there can be differences across brands as well!
Its worth looking this up and taking some time with.

[macgtech]

Wider tyres tend to not cope with higher levels of camber as much as narrower tyres.

Tyre width ratios F:R should generally be in proportion to the static weight distribution.

Also bear in mind wider tyres = wider wheels = more unsprung weight and rotating mass.