Changing Rear Rim Size on Diablo? Damage To Drive Train???

Not sure about damaging the awd system, but the only reason your speedo would be off is if the tires aren't sized properly. The outside diameter of the tire is what will affect the speedo. If you increase the wheel size, you have to decrease the sidewall on the tire. It's called plus-sizing. Here's a quickie on the subject.. http://www.discountedwheelwarehouse.com/Wheel_Fitment_Guide.cfm

Finding the right size tires in the size you need could be impossible though. In that case you could just get as close as possible and deal with the speedo error (it'll get you out of a speeding ticket.. one time ) or just have the speedo recalibrated.

-R

 

Dave,I havent heard the possible damage to the 4wd system before.I will get the answer to that in the A.M. though.I doubt it,but you never know.

P.S. I asked her,but she didnt know for sure.

 

Dave
They are correct. From what I've been told you can't change wheel or tire size and should replace all tires at the same time. That's right if you get a flat you should change all tires. The reason is that uneven tires or incorrect OA dia puts strain on 4WD system. That also means tire PSI is very important. I'd get a manual pronto!
Best

 

Remember it's the OA dia that matters not the width. (aspect ratio # + wheel dia.)
Best

 

I may be wrong about this ... but I know the Diablo had a viscous coupling differential, not a locked one by any means. This shouldn't cause any problems.

Ooooh ooooh, just thinking though, does the Murci have an Audi parts-bin style AWD system with a 50/50 power split and a locked diff?

Bill in Brooklyn

 

Yes Dave,they are correct,if you didnt resize the tires to the original diameter.As long as you keep the total the same,no problem.I will take some good pics of GOLDEN BOY and post them later.

 

Hey A.J.
Call Clay or Ritchie at Butler tire. They can do the car for you and they have supplemental insurance incase they screw up and damage the car with incorrect sizing. They have been beggin' us to put some of there wheels on our cars on a consignment basis but we cant do it to a new car per Lambo orders. They really worry about that from the factory. I have seen a diff burn up in person on a car and it is not pretty. Guy had 20's all the way around and bad O.D.

Chris

 

COOL.What wheels do they have?

 

Hey Racer,
It is a problem I promise you! You have to be more than exteremly careful. I would recommend consulting with someone completely in the know. Most really high end tire shops have the books and knowledge to get you exacltly the right sizing you need. If you have to replace a viscous coupling it will cost you in excess of 25k. I just don't want for you to go through that. Don't you already have Maya's on your car from when you bought it? Those look pretty nice.
A.J., they did a car for us at the auto show. I don't know if you remember Butler's booth but they had a black on black Murci of mine with two kinds of rims(one make on one side and another make on the other). They have supplemental insurance riders so if they put the incorrect size wheel tire combo on your car and it burns a diff they will pay to have it fixed. If any of you need wheels and tires and are questioning what you should get, call me on my cell at 404-643-6603 and I will put you in touch with the guys that can help.

Chris

 

What are the overall Dia. differences exactly. I believe ANY difference will hurt. What does the manual say? Have you asked a Lambo Tech? I'm just going off what I've heard.

 

Dave,
As far as I know, Napolis is right...ANY difference could cause a problem with the drivetrain.

 

Hey Racer,
YOu cannot use ANY deviation in O.D. It will damage the AWD system I promise you. I have seen it happen first hand on a Murcie and it was not pretty. Keep us posted if you do happen to change the wheels and tires out. I am anxious to see the difference. I have also been told that if you do tires on the car you should consider doing all four, the tolerances are that exact. Good luck with it though, I know others have changed stuff. You know how you should contact, the guy who owns Meridian Auto that does ads in the Du Pont Registry. He has a Murcie and Gallardo that he has modded I believe. He may be a good reference and he posts on this forum.

Chris

 

Look forward too seeing it.

Chris

 

I know nothing about Lamborghinis but I am a long time All Wheel Drive Guru and I will tell you from experience that you must have the correct size tire all the way around, with different size tires on the car mainly front to back 18 front vs 19 rear this will burn all 3 diffs front center and rear. The only way to prevent this is to lock the center. Locking the center will cause the car to corner funny all 4 wheels will turn at the same time and same rate of speed when you turn left the inside tires will want to keep the same speed as the outside tires and you will get a chirp and the car will jerk all the way around the corner at low speeds and you will also get feathered tires. same goes for towing the car, all 4 wheels must be off the ground when transporting and AWD car. not like someone with a Murci is going to get one towed front wheels only.

Nissan makes the best AWD system ever invented, its used on the Skyline. Rear wheel drive only until the rear tires start to slip, within a 1/4 of a revolution of the wheels the 2 fronts are engauged turning the car into All Wheel Drive, which car be turned off with a switch next to the steering wheel to make the car full time rear drive, this rules for drifters.

So you get the power and gas mileage of a rear drive car with on demand All wheel drive. and without the 15% horsepower loss of having full time All wheel drive.

 

I thought that keeping the same front/rear circumference ratio would make everything just fine.
What kind of center differential do you have? Open? Torsen? Elec controlled? If it's open, do whatever pleases you. If it's a Torsen, stick to OEM front/rear ratio (if rear tire circumference is 8% more than stock, then front tires must be 8% larger than stock), if you have anything more sophisticated ... uh, I have no idea!

 

You know what... This I think is why the front diff has a slightly different gear ratio than the rear, to make up for the difference in tire sizes front and rear.

 

They are LSD front and rear.