430 Those with 19/20" wheel combos... what tires for no errors?

225/35/19 and 285/30/20 would be my pick. Why change everything up if you don’t have to?

 

I think this is a very good topic, thanks for starting it kenneyd!

I have been working independently trying to figure out what combinations work best from reading forum posts here and in other places. The Excel sheet I have attached is a pure work in progress and I am uploading it in hope that it can help someone on their journey and that it can be fed back here and we can grow this database.

From what I have gathered:

- The year of the F430 and various ECU versions may alter the behaviour of the electronics when they react (or not) to tire size changes. Therefore it is really important to state the year of the F430 with a working combo.

- 19 inch wheels at the front seem to be the general consensus to best ride quality, the rear is not affected as much when going up in wheel size.

- Staggered combos, i.e. 19 inch Front / 20 inch Rear combos seem to work fine.

- Some tire combinations will affect ABS and others not

- The E-Diff needs to be monitored as it is not always noticeable if it is being affected (Scuding electronics should help here). The E-Diff can also be disabled with the Scuding electronics, although I don't think that is necessary if the tire sizing is correct; I personally like having it on.

- Some problems with electronics only manifest at higher speeds so it is hard to tell from "normal" driving.

- There must be some sort of tolerance built in to compensate for tire wear as it changes the circumference of the tire..

- There are some great combos possible in theory in a spreadsheet, but I couldn't find in real life the tires in those sizes from brands I wanted to use.

 

Such values are purely theoretical. The tire pressure is also decisive for the rolling circumference. How should one take this into account when the same pressure in tires of different dimensions causes a different rolling circumference?

 

I’m running 19/20 setup with Michelin cup 2’s sized in 235/35/19 & 325/25/20 for my 2006 F430 F1, no errors or issues.
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From what i understand the dia wont change with pressure.

The ediff is calibrated for those exact rim and tire sizes from factory. Will changing tires and rims within closely matched size be an issue day to day? Probably not. Would i recommend it? Probably not.

The problems will manifest itself at higher speeds or over time.

 

(Long winded response, sorry! I had to explain it to myself "out loud" to see if my logic made sense, and so that others can pick holes in it so we end up with something better)

The tolerance/wiggle room of the system is what Kenneyd and others (including me) have been trying to ascertain. There are plenty of F430s with aftermarket wheels, surely if all had issues it there would be more about this on the forums?

Tire diameter definitely changes and it's easy enough to see visually on deflated tires unless they are runflats. Tire diameter also changes with wear from driving. The question is what is the tolerance of the system for these factors, as this tolerance will help us determine the "wiggle room" for different tire sizes that we can use. Rim sizes don't matter if overall tire diameters are identical. And tire diameters only matter because of the circumference as I assume the car systems measure rotations of tires in order to make decisions (more on my assumptions below). The tire diameter also changes with braking, acceleration, cornering etc.

Some calculations:

Front 225/35 R19 has a 640mm diameter and a 2011mm circumference
Rear 285/35 R19 has a 682mm diameter and a 2143mm circumference

Rear tire has a 6.6% bigger circumference.

Very basic research data says that, tires have an average of 8mm of tread and the minimum legal tread depth is 1.6mm (UK).

Let's just assume you lose 2mm of tread on a now semi-used tire. That is 4mm off the diameter (2mm on the top and 2mm off the bottom).
> The front tires would now have a 1998mm circumference.
> The rear tires would now have a 2130mm circumference

The rear tires will still have a 6.6% bigger circumference. I heard a story once about an F430's e-diff acting strangely with very worn tires. This could have been due to the smaller diameter of the now worn tires, but could also have been due to tires having so little traction that they spun more easily (more on how I think the system works below). However as the same 6.6% difference exists, this means that the system should not see a difference and therefore worn tires (other than grip) should not be such an issue.. in theory.

But, in the real world, perfectly uniform tire wear rarely happens so perfectly, especially on a higher powered RWD car.

If you had brand new tires, but you did a massive burnout, and now the front tires are still essentially brand new and the rears have lost 2mm of tread, the rear tire will drop to having a 5.9% bigger circumference compared to the front tires. A 4mm tread size reduction in the rear tires (fronts still new) would take it to 5.3% etc. Now factor in tire pressures, road temperatures and cornering all squishing the tire in certain circumstances and this means there must be a tolerance of some sort built in to the system otherwise it would constantly be getting upset at any form of driving.

The difference between 6.6% and 5.3% is just 1.3%. But to comparing 6.6% to 5.3% there is around a 20% difference! That's a pretty big difference. So the assumption here is that a 1% change should cause no issues (hopefully)!

> Brand New Rear 285/35 R19 has a 682mm diameter and a 2143mm circumference, with 4mm tread missing it has a 2118mm circumference.

So, assumption should be that a replacement tire setup of around 2118 - 2143mm should almost certainly be suitable. In theory a little more than 2143mm should also work too (think real life scenario of new rear tires ratio to semi-worn front tires).

For rears, these all are well within a 1% range if the front tires are kept at the same size
285/30 R20: 2133mm (-0.5% from factory size)
295/30 R20: 2152mm (+0.4% from factory size)
345/25 R20: 2138mm (-0.2% from factory size)

If you mess with both front and rears, then it gets more complex - that's what my spreadsheet might be able to help with and also why I created it.

My logic of how the system works (I welcome ideas and corrections etc):

The E-diff should be constantly comparing the wheel speed between the rear left and rear right wheels, and tries to distribute power evenly to both wheels using electronic signals to the pump that drives the diff to achieve this instead of doing so mechanically. The mode you have the car in (sport, race etc) probably changes the sensitivity of the system or the speed with which it reacts. The car also has other sensors such as steering angle and will know when you are cornering and so it can calculate the corner radius of inner wheel vs the outer wheel's corner radius and keep the power evenly distributed compensating for the rear wheels' different speeds, This may be the first case where the tire size is an issue as the computer needs to have some figures programmed in for the circumference of the tire, in order to complete its calculations. Adding a significant spacer on any of the wheels may affect the calculations during cornering too.

Many people believe that the system also tries to compare wheel speeds with the front tires. If that is the case, then this is where the front to rear tire ratio also comes into play - rim sizes are irrelevant though as they do not change the diameter of the turning wheel. If the system is very rigid (and there are indications that it may be) then the front to rear ratio of tire size matters, as does the circumference of the front and rear tires. For example, the car would expect, in a perfect, smooth straight line driving scenario for every rotation of the rear tire and 1.066 rotations of the front tire. Anything deviating too much from that means that something is happening and for example if the rear tire is making 2 rotations and the front 1, then the rear tires are not getting traction and slipping and it may intervene..

I am sure that there are other scenarios, but in my mind the two above are the main ones and the issues that may affect the e-diff may also probably affect the ABS system and braking.

And then of course we may all be doing the usual overthinking that these systems are that intelligent when they may in fact be quite basic. Race versions of the F430 ran mechanical diffs, so clearly they still though the e-diff needed further development..

Of course I welcome any input, corrections etc!

 

That is a good combo, and actually the closest I have seen to the OEM ratio of 6.6%!
(btw I make it out to be 6.8% which is even closer!)

 

What do you all think about:
245/35/19
+2.4% circumference from stock
305/35/19
+1.9% circumference from stock

On Titan7 T-S5
19x8.5 5x108 +25
19x11 5x108 +30

2007 F430

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In general, ABS problems start to occur when the difference from OEM front to rear ratio is somewhere in the 4-5% range up or down. Like any rule of thumb, some excursions from that RoT work fine, and others do not. The sensors do not care about absolute values of tire diameter, just the F-R ratio, since all they can measure is rotation speed.

 

I think I understand you: So it looks like a 0.5% from front to rear; 1.9% and 2.4% change. So, I should be good. Right?

Awesome comment, idk how you know all this! Thanks


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There is a difference in the system throwing an error cel and actually it not. But realise it is designed for the ratio from the factory
The systems and programming are extremely clever, changing it will change how the system reacts, and it wont be in a good way

Similar to tuning a car that has traction and stability control
In stock form the control loop is designed for that power and if you push hard its very safe
Tune your car and its out the window, you can end up in bad situations easily

I personally would not be changing tires and wheels because if you push hard you may end in an unfavorable situation

If you just cruise and get away without a cel then so be it, still not a great idea imho

 

What tire size will you run?


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Answer to my question from Stef. You need to make sure front to rear ratio is in tolerance, along with no more than 3% diameter change. In your case, looks good!! Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login

Actually, there are 2 independent aspects to be considered when changing tire sizes:

1) The E-DIFF has a very narrow toleration which is based on a front to rear ratio between the front wheel diameter and rear wheel diameter. This ratio should be as close as 0.938 (OEM front: 640.10mm / rear 682.1mm).

2) The Bosch ABS/ASR ECU tolerates about 3% wheel diameter difference on each individual wheel. Anything higher will cause the ABS/ASR to intervene faster by braking one or several wheels. The speedometer will also display an incorrect speed and total mileage.

Actually, I would activate the E-DIFF only when the road conditions are bad (wet/ice) and certainly not when driving spirited. The E-DIFF isn't really a safety system, it's just there to interactively lock the rear axle, something you don't want to happen on track or when driving in a spirited way. Although, it can be useful to have limited power being transferred to the rear axle when the road conditions are really bad.

With front tires 245/35/19, for the ABS/ASR you should be fine and in the 3% limit (diameter 640mm->654mm = 2.19% - rev/mile 800.3->783.2 - +2.1km/h @ 100km/h)

With rear tires 305/35/19, for the ABS/ASR you should also be fine and in the 3% limit (diameter 682mm->696mm = 2.05% - rev/mile 751->735.9 - +2km/h @ 100km/h )

For the E-DIFF, your new diameter front/rear ratio will be 654/696=0.9397 which is pretty close to 0.9384. If you only occasionally activate the E-DIFF, you should be perfectly fine.

Just make sure that your much larger tires won't rub against the wheel arch/fender, especially the tire sidewall. 2cm larger is quite a bit and may cause an issue when braking hard in a sharp corner for instance (important weight transfer to one wheel).


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@kenneyd thought I'd check in to see how the new setup is going so far? I'm about to order wheels too (thinking Finspeed) May I ask what offsets you went with, and does it rub at all?