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Discussion in 'Model S: Driving Dynamics' started by dna4life, Jul 14, 2012.
Would staggered wheels work on on my Model S, being that it is rear wheel drive?
If they fit without rubbing, I don't see why not. Most likely the suspension will be dialed in for understeer, so that might make the understeer stronger.
What do you want to stagger? Are you thinking wider rear wheels?
I floored the performance S today (admittedly with 5 people in it) and couldn't get the rear wheels to break away and didn't detect any traction control interference. Has anyone else had a different experience?
I would think that the traction control is always involved when flooring it at a low speed. Wouldn't you always just ruin your tires otherwise?
It might be had to notice the interference due to the way the software handles it.
I've been told that without the traction control, the car will absolutely light up the tires.
By this do you mean shred them (spinning in place) or something else?
Spin the wheels, make lots of smoke.
Staggering the wheels makes sense in a car with a weight bias to one end. IMHO, it makes no sense in a 50% weight distribution car.
There's a reason they won't let you turn off the traction control during the test drives .
I had no passengers and could feel the traction control kicking in whenever I romped on it at low speeds. That being said, Model S's traction control responds WAY faster than the Roadster's. When the Roadster slips the computer takes what seems like forever to recover. Model S it was fractions of a second. Very well done.
Wouldn't that depend on the torque characteristics of the power plant? I mean, and I'm treading on thin ice here, if the car has an issue with traction at launch, wider tires (regardless of weight distribution) would reduce some of the slippage, no?
There is more to a car than straight line acceleration on dry pavement (the quest of faster in this area is just plain dumb, IMHO). There is vehicle controllability during an emergency maneuver, stopping power, wet handling ability, etc. all of which staggered tires will hurt rather than help (Yes, VSC will disguise this to a certain extent but VSC can't overcome the laws of physics).
Everyone is bringing up good points about wheel/tire sizing and its practical useage. However, I plan to run a staggered setup on the Model S for looks. This is going to be a commuter car for me on my very short commute. I love the look of staggered wheels with aggressive offsets and sizing. I don't plan to go too crazy since wider wheels have a big impact on efficiency and it will kill my range.
I plan to get the 19" wheels from Tesla and will be going to the aftermarket for a nice light set of 20x9 wheels to fill up those massive arches on the Model S.
Why 20" wheels:
Better tire selection and better wheel selection
Why 9" wide wheels:
Because I can
Why change what Tesla did from the factory:
Because it will look better to me
For those that are interested here are the specs for the stock wheel options for the Model S. I got these from Ted M (one of the Tesla employees/engineers) at that DC drive event:
The Model S lug pattern is 5x120 with a 40mm offset.
The standard wheels are 8x19" and the 21" silver and Performance carbon grey wheels are 8.5x21".
Edit: Use the BMW 5 series if you are looking for a vehicle that runs 5x120 bolt pattern. Be prepared to pay a premium for wheels since Bimmers always come with the "luxury tax" added on to wheels designed for them.
Thinking along the same lines. Bavarian Auto is famous in the BMW world and are just 10 miles from my house. They are a Beyren wheels dealer and I am liking the 20" Multi spoke.
BMW Parts and BMW Accessories | Bavarian Autosport
BMW Wheels by Beyern - Multi Spoke Design - BMW 7 Series Wheels, BMW 6 Series Wheels, BMW 5 Series and BMW 3 Series Wheels - BMW Custom Aftermarket Wheels from Beyern Wheels
I know there are tire threads ad nauseum in this forum, but most of them deal with snow and or pothole concerns. Can you explain to me how a wider rear tire (in a staggered configuration) would compromise emergency maneuvering, stopping power, wet handling et al? I just have a different understanding, but I realize that I am not well-versed in tire physics, and in the above mentioned threads, you have demonstrated a great deal of knowledge on the subject. I appreciate anything you can share.
Not answering for Jerry but in my experience road racing, autocrossing, etc. wheel sizing is less important than tire sizing (assuming that you don't go completely rediculous with wheel size). You can match the effective contact patch on all four corners by balancing the size of the tires fitted to the rim. For instance running a 10 inch wide wheel in the rear and a 9 inch in the front can be somewhat negated by using a 245 section rear and a 245 section front. In this example you would have a "lively" rear end that will rotate on demand under lift throttle conditions or power over conditions (applying copious amounts of throttle). On the flip side you could run a 265 section rear and 235 front and you would get understeer.
It really depends on your driving style and desires for handling characteristics.
I'll try, you can decide how successful I am.
First a few basics (note all numbers are done for ease of math only):
1. Contact patch area depends on the air pressure and the load, so a 1000 lb. load on a 50 psi tire gives a 20 in[SUP]2[/SUP] contact patch.
2. The width of the tread determines how long the contact patch is. A tire that has a tread 10 inches wide will have a contact patch length of 2 inches.
3. A wide but short contact patch gives a higher g-force than a narrow but long contact patch.
4. A narrow but long contact patch gives more acceleration and braking traction.
5. A narrow but long contact patch will slip sideways less when going over an expansion joint or other road irregularity during a turn.
6. Ideally the road pressure on the contact patch is even throughout the contact patch. This is usually not the case and some tires have a more even contact patch pressure than others.
Tires have what's know as slip-angle. This isn't a very good term because the tires don't actually slip. A tire on ice would slip (sideways) but then the slip-angle would be zero. What the slip-angle is is the difference between a line drawn through centre line of the wheel and a line drawn through the centre line of the tread (in the rolling direction). As the profile gets lower the slip-angle is reduced. If the tires have different slip-angles front to rear then the car will either tend to push the front out (understeer) or push the rear out (oversteer). An extreme example of what happens with different slip-angle tires that many people have experienced--in North America, other places don't allow silly stuff like this--is putting on only two snow tires and the car becomes squirrelly even at low speeds on dry pavement.
If the tires on the rear are wider than the tires on the front but the weight is equal and the pressures are equal, then the rear tires will have a higher g-force than the front tires. The slip-angle will be different too (likely smaller but...) It's often not noticeable until you reach the limits of adhesion of the tires, and if you're not expecting it--and sometimes even if you are--or don't know what happens at the limit of adhesion the car can do some surprisingly nasty stuff. With a car that has an even weight distribution, like the Model S, having the same tires all around produces the same g-force front and rear and the same slip-angle so the behaviour is very predictable at the limits of adhesion. The problem here is that the vehicle behaviour can change suddenly at the limits of the tire's adhesion.
The other problem is that most of the above assumes all things are equal--with real-life-tires all things usually aren't equal or even close to equal. Belt construction, bead area construction, and tread compound are a few of the things that can be different. Even the same size and model of tire made in a different production run can be different if the tire manufacturer has silently improved the tires. (Whether the tire purchaser thinks an improvement has been made is sometimes a matter for debate.)
Now you can have a reasonable amount of confidence by taking your car on a skid pad (best) or race track (can be almost as good) and pushing it (with the staggered tires) to the limits (actually you push it to just beyond the limits) to see what actually happens with the tires you installed (of course, it's also possible to flip the car doing this--unlikely with a Model S but probably not impossible). However, skid pads aren't that easy to find and access is usually limited. Also this kind of testing usually wipes out the set of tires being tested, so purchase a second set.
You can also rely on the electronics (VSC in particular) to get you out of trouble but it's best to have your vehicle set up so that you have a hard time getting into trouble in the first place. Electronics are good but they can't overcome the laws of physics.
As far as wet handling goes, there are two situations that happen: hydroplaning and viscoplaning.
A. Hydroplaning happens when the the wedge of water that builds up in front of the tire reaches the tire pressure. In our example above, when the wedge of water reaches 50 psi, the tires will lift of the pavement. The wider the tires are, the shorter the contact patch, and the lower the tire pressure, the sooner hydroplaning will occur.
B. Viscoplaning occurs when the tires slip on a slippery substance such as oil, leaves, pavement markings, etc. It can occur at any speed. It's most likely to happen during the first rain after a long dry spell as the water causes the oil to float out of the pavement irregularities.
The thing about low profile tires is that they are a wonderful cash-cow for the tire manufacturers. They wear out quicker and cost more than tires with a sensible profile. In most cases they also ride harder and are noisier as well. However, the public has been sold that wide low profile tires are better, give more traction, etc. which are half-truths at best. Low profile tires do provide crisper steering feel (except over that expansion joint where they slip sideways and provide a real nervous nelly moment) and a higher g-force at the expense of just about everything else (again, all thing being equal which they usually aren't).