TTAC Commentator Heath writes:
A couple of months ago I got the SVT suspension for my Focus. Not want to blow the budget any more I left the 205/50/16s that the Focus came with and there is a unhealthy amount of sidewall flex with the 50 (Pirelli P6). The SVT had 215/45/17.
My question is when its time for new tires, should I go for 40 or the 45. I’d like to stay on the 16″ rims as don’t really want to get new 17″ rims as well.
Sajeev responds:
If you stay with 16″ rims and go for a lower profile tire, the change in circumference messes up the speedometer, gearing (lower profile means more gear and less economy) and increases the unsightly gap between the tire and the body. We did this for TTAC’s entry for the 24hours of LeMons, and the gearing advantage was totally worth it. On a street car? I doubt it.
If you compensate by fitting a wider tire (225/45/16, for example) on a stock wheel, the tire’s outer tread blocks will not meet the road, and it’ll look like the back end of a steroid-injected baseball player. Which is phat. Except when its not.
So I don’t recommend this. I’ve never seen anyone recommend it. Here’s my question back to you: don’t you want a more responsive tire with more grip? One of my cars still has 60-series tires, and its quite good. I run the stickiest summer tires and their level of precision is even more appealing than keeping my cosmetic tire-to-wheel-to-body ratio in check.
Kevin writes:
Sajeev, I need some more speed in my Astra XE 5MT. It’s new to the US I know but lots of them sold in EU, Brazil and elsewhere since it was introduced in 2005. Isn’t there a 1.6 L turbo version in some markets? Or could I get some GTC parts somehow?
Sajeev responds:
From what I’ve read, you can swap an Ecotec 2.0T or its successor (in Europe), the 1.6T. I would join the appropriate forums to learn the differences between the 2.0 T in the Cobalt SS and the Astra. If the 1.6L is better, find a parts supplier in Europe and ship it here. I’m hoping the 2.0T from the Cobalt works because it’s a well-known package for stateside tuners and finding parts will be a breeze.
Either way, slap the turbo motor in, get a higher flow exhaust, custom tune on a chassis dyno and you should be good to go. Also check the differences between the turbo clutch and yours. And getting a limited slip differential will certainly help the massive torque steer you’ll encounter.
I applaud your creativity, but take it from the guy with a one off, 6-speed, Mercury Cougar: you’d better love that car. Nobody in their right mind will pay anywhere near your final tab for this tweaked Saturn. Not to mention that you (and me) can probably buy a far superior performance car for the same price and much less effort.
Kevin, regardless of GM’s position in the next few years, we know what’s happening to Saturn. They are on the chopping block, and as such there is no way I’d throw thousands of dollars at one of their cars. In a few years that Saturn’s gonna be worthless. Trade it now on a Cobalt SS and get the power you want in a brand that’s more likely to be around for a while longer. Well, we hope so, anyway.
Heath,
What do you mean an “unhealthy amount of sidewall flex?” Are you autocrossing the car? If so, a second set of steel wheels with Kumhos are the ticket.
On a street car, however, the stock sidewalls, believe it or not, are the hot setup. Better ride quality, less proclivity for bending a rim in your nearest pothole, in addition to what Sajeev said.
A compromise would be to increase your tire pressure slightly. Can make a HUGE difference!
In addition, people don’t usually realize that a short stiff sidewall may give you quicker steering response, but a taller sidewall generally allows the contact patch to stay in better contact with the pavement in corners, where the shorter sidewall tire would be pulling tread OFF the pavement!
The CPU measures road speed against engine revs. If there is too much of a discrepancy, the check engine light will come on. Over and over again.
I’ll second the motion to keep the normal tire height the same – the degradation in ride quality will not be worth any handling improvement on the road. The type of tire and the correct inflation pressure will make a greater difference than 1cm less sidewall.
doctorv8 : In addition, people don’t usually realize that a short stiff sidewall may give you quicker steering response, but a taller sidewall generally allows the contact patch to stay in better contact with the pavement in corners, where the shorter sidewall tire would be pulling tread OFF the pavement!
There’s a reason why F1 cars have tall sidewalls…and there it is.
Heath,
Congrats on the SVT suspension – it will make a huge difference to your Focus. If you can’t afford the jump to new 17″ rims and tires, stick with your stock size and go for some sticky high performance rubber. The Kumho Ecsta SPT or Fuzion ZRi in 205/50/16 are about $80 each at Tirerack if you can get away with summer tires all year round and combined with slightly higher tire pressures will be a great match to your new suspension.
Another great investment would be a track lapping day with good instructors who can help you determine the correct tire pressures (use the sidewall chalk trick) and show you how to get the most out of what your car can do. I did this and it was a tremendous and humbling learning experience and a ton of fun!
Sajeev Mehta: There’s a reason why F1 cars have tall sidewalls…and there it is.
I wish Mazda would have gotten the memo.. instead, they put 19″ wheels with rubber band tires on the RX-8 R3 and 17″ wheels with teensy 205/40-17 tires on my Miata. *sigh*. This will be the first car of my life where I will be downsizing the wheels, two sizes down.
thanks for suggestions, Sanjeev & co. I thought there would be issues with dropping the tire profile. needed some confirmation. so either 17″s or summer 16″s
well what happens is at higher speeds or uneven roads (or both) there will be a sequence of lateral movement from side to side at the back.
The best way to fix that in my opinion would be for the Interstate people to properly seal instead of some dude flinging a tarry stoney mess around with a shovel, off the back of a truck
regards
Another note on the SVT package: Good move not upgrading the wheels, my friend and his wife both own SVT Foc… Foci?… and the Focus wheelbearing does not like the 17 inch wheel… you’d be replacing bearings after 30K miles or so. The last time I talked to him about it, neither Ford of the aftermarkets had redesigned the bearing to handle the larger wheels. I have a set of Goodyear ReponseEdge Eagles on my Impala SS, so far I’m impressed with those over the softer tires that were on the car when I purchased it.
Sajeev, I need some more speed in my Astra XE 5MT. It’s new to the US I know but lots of them sold in EU, Brazil and elsewhere since it was introduced in 2005. Isn’t there a 1.6 L turbo version in some markets? Or could I get some GTC parts somehow?
Sell your car. Buy a faster car. Cobalt SS / MazdaSpeed 3 / GTI / Si, etc.
If you decide to change tire sizes, here is a handy calculator to help minimize speedometer error.
http://www.miata.net/garage/tirecalc.html
It’s a shame about the Miata’s 17s… but that said, it rides much better on them than many other modern (cough heavier cough) cars with the same fitment.
Revs versus measured road speed won’t change with smaller tires. The same number of revs will always equal the same number of tire revolutions in the same gear, no matter what wheels you have on. The ECU doesn’t have a fifth wheel sticking out the floor pan measuring road speed. Whatever it measures at the final drive speed sensor (or ABS sensor) is what it sees. The only issue is odometer error… which is relatively minor going from 205-45 to 205-50
205/50R16s… I felt the same way about them when I upsized from 205/45R16s (stock fitment on my car is 195/50R16s). You’re getting a 3-4% speedometer error going down from 50 to 45, and the ride suffers a whole lot, but you gain sharper turn-in.
Aside from the turn-in, nothing much else is different. In fact… I pumped up my tires to about 35 psi and performance is more than acceptable… I still want a set of 45s for track, but I’m not going to be downsizing on my street rims anymore.
225/45R16s match 205/50R16s exactly, but they’re way too wide for stock rims, which will actually make your sidewall flex problem worse. Instead, I’d go for an extreme performance summer tire with a good, stiff, sidewall, like the AD08 in the same 205/50 size and leave it at that.
Heath,
Rim width and offset makes a difference here. Increase the rim width to minimize sidewall flex.
Rims should never have less than ~80% of tire width. A 205 tire is just over 8 inches wide. Thus for best handling the rim should be about 6.5 inches. Rims are measured at the inside edge, as the tie see it. And yes, tires are metric and wheels are inch.
The widest rim that a 205 tire should see is about 7.5 inches. Wider than that and the sidewalls will be bent outwards in the wrong direction and the tread will not lay flat on the ground.
If the wheels are offset too much towards the outside of the car, positive offset, it will look neat but wear out the wheel bearings. That’s what happens with the SVT wheels. Diameter is not the issue, offset is.
As others have mentioned, tire presure can make a large difference. But don’t exceed the max tire presures on the sidewall.
Bob
I worked my way through college selling tires and wheels. Once, a customer came in with a Miata he planned to autocross.
Back then, the OEM fitment was 185/60R14. He insisted on buying a set of chrome 17″ wheels upon which he fitted slightly taller (in overall diameter) 205/40ZR17’s. I tried to tell him that I doubted his car would handle much better, but there was no changing his mind.
Several months later, when he was in buying tires for his wife’s car, he admitted that I was right.
He didn’t know if it was the higher unsprung weight due to the heavy chrome wheels, the taller gearing which resulted from the greater overall diameter of the new tires, or the greater burden of friction brought on by the sticky Z-rated rubber (believe it or, in extreme cases, such as with very light-weight vehicles, wider, stickier tires can slow cars down through corners as their friction becomes more of a liability than their traction is an asset). Regardless, he said his car “felt” faster through the corners, but the times said the opposite.
A year later he ordered a set of 185/60HR14 Yokohama autocross tires for his OEM wheels.
As a past owner of a svt, not sure I would waste the money either. Spend the coin on buying an svt, and add the super charger kit. BTW, I never had any issues with my focus, and drove it for 65K miles. I think the suspension upgrade is a nice start, but the real SVT offered so much more. the money you spend upgrading yours will probably buy you a clean SVT. I sold mine with 65K, in perfect condition (Sajeev can verify how well I take care of my cars) for 8500. I’m sure you can get a killer deal now. If you do upgrade to 17s the tires make a big difference. The original contis are the best, stick with them.
Re: SVT wheel bearings
I believe this is a “feature” shared with the Contour SVT. Ford originally designed the Contour to have 14″ or 15″ wheels (hence, the speedo is slightly off). The SVT version had 16″. In development, the mules chewed up wheel bearings and Ford ended up using beefed up bearings from the Mondeo. Still, if you do any racing or autocrossing, you’ll put enormous stress on the bearings and wear them out more quickly. Take it from me – I’m on my 2nd set!
There’s a reason why F1 cars have tall sidewalls…and there it is.
Yeah, but it isn’t the reason stated.
F1 suspensions don’t have springs. Instead they allow their carbon fiber control arms to flex. Still, that flex is very limited and also very stiff. Tires are used as the main “spinging” medium in that they allow the car to maintain a consistent attitude front to rear vis-a-vis the track surface and the frontal area to maintain optimum aerodynamic efficiency. The tires also allow the car to slightly “compress”, lowering itself to the road, increasing aero efficiency while still allowing the car to pass ride height minimums when static.
As far as the SVT Focus question, there have been a few misrepresentations.
The wheel bearing failures with the 17″ rims are due to using an incorrect wheel offset and/or using a heavier wheel/tire combo. Early SVTs had the “European” wheel option where the wheels closely resembled the OZ “Superleggera” (Super light) models. The later five spoke SVT wheel was a bit heavier. Whatever bearing failure that occured, it wasn’t due to the increased size of the rim.
The other thing is using the SVT suspension in a regular Focus. The SVT suspension is optimized to run a stiffer sidewall tire. Therefore, to get the most out of the suspension, you need to run a lower profile tire whether that be in a 16″ or 17″ size. The SVT Focus uses a 17″ wheel to maintain the overall standard wheel diameter while running a lower profile tire and to provide clearance for the 300mm front disc brakes.
Frankly, installing the SVT suspension without installing the proper tires is a waste of effort. You would realize a greater gain putting on a lighter wheel/high performance tire combo than you ever would just replacing the suspension.
Another note:
One of the reasons you would want to run a smaller wheel/tire diameter is to provide a de facto lower final drive ratio to provide a bit better acceleration, especially out of a corner. Hence, the way to go on an autocrosser.
While hard to find, a good tire size for a ZX3 Focus with the 16″ rim is a 215/45/16 tire. It gives you a slightly bigger footprint, a slightly stiffer sidewall, while only slightly altering overall wheel diameter.
With he Focus, I would stay with the original tire size unless you buy new wheels, just as Sajeev said.
With the Astra, I also think Sajeev had a good idea with the 2.0L Turbo Ecotec. I am pretty sure it will directly bolt up to your car, but be sure to verify before spending any money.
As for the wheel bearings, if the overall diameter and wheel offset are the same, their will be no additional stress from driving then with the stock wheels. The only issue will be that the tire is part of the suspension. If you have stiffer tires, with smaller sidewalls, any impact from a pothole or curb will result in more energy going into the bearing itself. This leads to more issues than if you have the bigger sidewalls. If roads are smooth where you live, and you can manage to avoid hitting things like curbs, than the 17″s should not give you any problems. My friend had a Focus with full H&R suspension all around, and 17″ wheels that he had on during the summer. He had no problems besides bending one of the wheels when he hit a pot hole. He had this setup for about 40,000 miles. He got rid of the car when he bought an STI.
Changing offset definitely affects wheel bearings. Tire width can affect wheel bearings. Rim diameter itself will not affect wheel bearings.
I wouldn’t decrease the tire diameter; huge wheel-well gaps aren’t pretty. 205/50 has a good sidewall height for an aggressive driver on city streets. What tire pressure are you running? Try 35psi front and 32psi back. I have Michelin Pilot Sport A/S 205/50R17s and they feel great in corners at 35psi, but drop them to 30psi and they become quite flexy.
doctorv8 : In addition, people don’t usually realize that a short stiff sidewall may give you quicker steering response, but a taller sidewall generally allows the contact patch to stay in better contact with the pavement in corners, where the shorter sidewall tire would be pulling tread OFF the pavement!
Sajeev Mehta: There’s a reason why F1 cars have tall sidewalls…and there it is.
I wish Mazda would have gotten the memo.. instead, they put 19″ wheels with rubber band tires on the RX-8 R3 and 17″ wheels with teensy 205/40-17 tires on my Miata. *sigh*. This will be the first car of my life where I will be downsizing the wheels, two sizes down.
It’s all well and good to point out the value of tall sidewalls in F1, it makes you sound all smart and contrarian since the style is bigger wheels, and shorter sidewalls. However I don’t think F1 has much to do with any street car. Just a little reading (http://f1n00b.blogspot.com/2007/07/tires.html) would tell you that the tall sidewalls are a response to the great downforce and the inability of the requisite stiff suspension to deal with the imperfect race track. All of which has little to do with the real world.
Any street car that is not Caparo T1 makes little use of down force compared to an F1 car. As such there is lots of room for suspension to take much of the work on, that the tire does on an F1 car, so there is less need for lots of unsprung rubber with great sidewall height, and in fact there are gains to be had with less of it.
Granted there are various aestehtic, braking, marketing and other reasons engineers choose large rims for modern automobiles, but there is a handling benefit, even though there are reasons not to use a big wheel. I wish there was a great resource online to link to, but I read a great article in Road and Track Q&A section which really got into the meat of why the trend to lower sidewall heights. The real crux of the issue is centred around carcass/contact patch distortion which apparently is the biggest factor at play. Even though most people think the main riason d’etre of the low profile tire is sidewall responsiveness. I won’t go an further because I recognize that is about my limit of understanding of the subject.
Like just about everything that humans naturally try to put into neat little boxes and categroies, tire technology is far more complex than it appears to the average joe casually trying to understand it. The tires that an F1 car runs has nothing to do with anything when talking about a street car.
Nobody’s saying F1 sized tires are right for street cars, just that it proves the point that shorter isn’t always better.
And maybe we should narrow the scope to one street car: extensive testing of the new M3 showed that it was faster around a track with 18″ wheels than 19″. Hence why BMW actually has 18″ wheels as an option on the car.
Heard this from Steve Dinan, FWIW. That guy has resisted putting 20″ wheels in his catalog for a while, only now is he making it happen because everyone wants them.
That said, going to 17″ wheels on Heath’s Focus would be nice, but sidewall flex from his 16s isn’t reason enough to lower the profile of the tires for that particular 16″ wheel.
rpn453: Changing offset definitely affects wheel bearings. Tire width can affect wheel bearings. Rim diameter itself will not affect wheel bearings.
Yes, but as long as overall diameter, offset, and width are the same, wheel bearings will not be an issue unless you hit something if you decide to go to 17″s form 16″s.
You can get some affordable wheels now in 17″ sizes. If you take into account that if you buy a wheel and tire combination, tire rack will mount and balance it for free. If you just buy tires, you will have to pay to have them mounted on your old rims. Also, if you plan on using the car in the winter, you need other tires anyway, and you can have snows mounted to the 16″s, and won’t have to go to a tire shop every fall and spring.