Author Topic: Tire Size (Read 7839 times)

RUTurbo · « **on:** March 03, 2009, 09:47:29 PM »

Hey all, Spring is on its way and I could really use some new tires for my SSR Type C's, question is to anyone using a wider size tyre than 245 on their 18x8's?? If so have their been any issues regarding fitment / tire wear?? Was hoping someone has already taken one for the team and tried this since I'd really like to run some 275's this summer.

MGar · « **Reply #1 on:** March 04, 2009, 02:12:10 AM »

You can't run a 275 on an 18x8. It's neither safe, nor effective (with at least standard tires, Hoosiers are a different story). The tires will pooch out, and you'll end up with the same size contact patch, and more rotating mass.
If you want to run a 275, you can get an 18x9 rim. OZ makes a rim that is on closeout, 18x9, that fits all the way around. You can run 275/35/18 all the way around without rubbing. I'm doing just this, 275/35/18 Dunlop Direzza Z1 Star Spec.

I believe you can get away with 255 on the stock rim, but none wider. What type of tire are you currently running? Changing the type, from say a UHP All season to a Extreme Traction category tire like the RE-01R, RE-11R, Z1 SS, BFG GS-D3, etc will produce a noticeable increase in lateral grip.

RUTurbo · « **Reply #2 on:** March 04, 2009, 07:17:15 PM »

Thanks for the info, right now I have a set of Dunlop Direzza Sport Z1's on my wheels, going to keep the same tires just wanted to see if I could go a wee bit wider. I dont like the Ultraleggra's so I'll probably stick with 245's. Though I think some special order OZ Alleggerita HLT's are in my future.

MGar · « **Reply #3 on:** March 04, 2009, 11:32:05 PM »

I'm not a fan of the look either, but you can't argue with the price/performance.

Howster · « **Reply #4 on:** April 22, 2009, 02:44:57 PM »

I too have the SSR Type C RS wheels, but with the Vredestein Sessanta tires from Europe. Beautiful tires. However I am wanting to also go a tad wider, but with the same manufacturer. They offer a 255/40/18 and wondered if anyone has gone that route on any tire. They are so inexpensive for such a great performer and wonder why more folks aren't giving them a shot. Big in Europe and used on everything from Bimmers to Porsche to Lambo to Ferrari. Plus they are just too sexy to look at. If anyone is interested I can send photos with them on my SSR's, but I am not familiar with uploading images to this site. I can however attach to an email. Just drop me a line.

Wondering how off the speedo would be with this size as well. I know there are some techies out there who might have an answer. I know it wont be much, but just doing the research. I have used the conversion formula to get the differences in width and height, but that doesn't tell me how much the speedo will be off. Thanks for any assistance.

Cheers,

howster

Sky 5 · « **Reply #5 on:** April 22, 2009, 04:19:58 PM »

Quote from: Howster on April 22, 2009, 02:44:57 PM

I too have the SSR Type C RS wheels, but with the Vredestein Sessanta tires from Europe. Beautiful tires. However I am wanting to also go a tad wider, but with the same manufacturer. They offer a 255/40/18 and wondered if anyone has gone that route on any tire.

I saw these tires last weekend and they look great. Very unusual tread design for those who want something new and different. Howster, the tire size calculator I use showed the speedo to be only off by 1.4mph (reads a wee bit high). Also, it recommends a minimum rim width of 8 1/2".

Critterman · « **Reply #6 on:** April 22, 2009, 07:26:47 PM »

I just bought 255x45x18's on 8.5 rims. They are off .6 mph

Howster · « **Reply #7 on:** April 23, 2009, 02:23:55 AM »

I will verify the need for an 8.5" rim for the 255 series tire. If that is the case I won't worry about it, but was told I could get away with it on my SSR 8" wheels. Thanks for the assist.

Howster

Critterman · « **Reply #8 on:** April 23, 2009, 08:22:30 AM »

I wanted to go with 265x40, but they said I needed a 9" rim for those and they wouldn't mount them. Didn't feel like trying to find someplace that would mount 265's on 8.5 rims, so I went with the widest I could.

LatinVenom · « **Reply #9 on:** April 23, 2009, 01:36:34 PM »

I was told the 255x45xR18 are fine on our 8" rims. This was way back on the BB by the original tire vendor the BB had then.

Sky 5 · « **Reply #10 on:** April 23, 2009, 04:00:37 PM »

Quote from: LatinVenom on April 23, 2009, 01:36:34 PM

I was told the 255x45xR18 are fine on our 8" rims.

Looks like 255/45 will fit on the 8" rim,
but the 255/40 will need at least another half inch because of the lower profile.

Critterman · « **Reply #11 on:** April 23, 2009, 08:15:01 PM »

the 255 x 45 is .6 mph off.

rhit_rs · « **Reply #12 on:** May 05, 2009, 07:15:35 PM »

Quote from: Critterman on April 23, 2009, 08:15:01 PM

the 255 x 45 is .6 mph off.

Are you quoting this at a specific speed?

Changing tire size changes the ratio between transmission output shaft speed and vehicle speed. Therefore, at higher vehicle speeds, the speedometer will have a larger error. To correctly calculate the actual vehicle speed based on the reading on the speedometer after you have changed tires size, you need to multiply by the ratio of the tire diameters. For example:

If your stock tires (245/45/18) were the Goodyear RS-A's, they were 26.6" tall (per tirerack.com). If you switch so say a BFG KDW2 in 255/45/18, which is 27" tall (per tirerack.com) the equation would be as follows:

Actual speed = (New tire diameter/Old tire diameter)*Speedometer reading

In this example, actual speed when the odometer is reading 60mph would be:

(27/26.6)*60 = 60.9 mph

If you're only going 30, the actual speed would be 30.45mph.

At 80, the error is larger with the actual speed being 81.2mph.

I don't mean to nitpick, but the error is a percentage of speed (in this example 1.5%), not a constant number.

Josh

Critterman · « **Reply #13 on:** May 06, 2009, 11:02:01 AM »

True and you are correct.

I do know that on my way to work there is one of those radar speed signs, you know the ones that tell you your speed. With my old tires, speed dead on 60 it would flash 62. With my new tires dead on 60, sign flashes 62. My GPS on the other hand used to say 62.1 at 60 and now says 62.4 at 60, so nothing makes sense and they are close enough that you shouldn't get a ticket.

Sky 5 · « **Reply #14 on:** May 06, 2009, 05:32:48 PM »

Quote from: Critterman on May 06, 2009, 11:02:01 AM

With my new tires dead on 60, sign flashes 62.

Does this mean that the odometer will also rack up mileage faster than it should?

Chemist · « **Reply #15 on:** May 06, 2009, 06:01:44 PM »

OK, because I often talk/type without doing the calculations first, here goes:

If the speedometer reads lower than actual speed, it must be recording less than actual distance, right?

Sky 5 · « **Reply #16 on:** May 06, 2009, 07:01:39 PM »

Quote from: Chemist on May 06, 2009, 06:01:44 PM

If the speedometer reads lower than actual speed, it must be recording less than actual distance, right?

That's the tricky part. Speed may be registering differently due to tire/wheel size.
But, a mile is still 5,280 feet... no matter how many revolutions it takes the tires to get there?

KWhale · « **Reply #17 on:** May 06, 2009, 07:03:53 PM »

Quote from: Chemist on May 06, 2009, 06:01:44 PM

OK, because I often talk/type without doing the calculations first, here goes:

If the speedometer reads lower than actual speed, it must be recording less than actual distance, right?

That's correct Chemist. The odometer thinks you are only traveling 58 miles in 1 hour (as displayed on the speedo), when you are actually traveling 60 mph as an example. If your difference is say 1.5% under speed (and that is a constant amount for any speed you are traveling by the way), then the odometer would record 1.5% less miles than actual. The opposite is obviously true if you are reading a higher speed on the speedo than you are actually traveling at.

Healix · « **Reply #18 on:** May 07, 2009, 12:52:36 AM »

Quote from: RUTurbo on March 03, 2009, 09:47:29 PM

Hey all, Spring is on its way and I could really use some new tires for my SSR Type C's, question is to anyone using a wider size tyre than 245 on their 18x8's?? If so have their been any issues regarding fitment / tire wear?? Was hoping someone has already taken one for the team and tried this since I'd really like to run some 275's this summer.

I guess I am the one who took one for the team. I have 275/40's on the rear, and on OEM chrome. It is not as bad as everyone seems to think. Since mine is still a N/A 2.4L, I drive it primarily as a cruiser, so fats in the back look nice, but not performance minded. More for style than performance. Hard exits feel a bit soft in the rear, but the tires fit better than one might think. No hassles at all from Discount tire. If you are looking to drive it hard, don't do this. But 275/40 fits, and that's on an 8in wheel (I know, I know, highly unrecommended, and I agree, but did it anyway), and with a 9in wheel width, I believe you will fit fine, assuming your offset is standard.

lil goat · « **Reply #19 on:** May 07, 2009, 07:30:54 AM »

I have heard that our stock wheels are 8.5" but can't verify it, the SSR's are 8" I have gone to the extreme of having a local SSR dealer call SSR and request they make them in a 9". I was told they were a special run for Tire Rack and they would have to have another run done. A minimum run is 40 sets, so that would be 80 pairs of back wheels if you wanted staggered like I do.

DeepBlueGXP · « **Reply #20 on:** May 07, 2009, 10:09:40 AM »

Quote from: Healix on May 07, 2009, 12:52:36 AM

I guess I am the one who took one for the team. I have 275/40's on the rear, and on OEM chrome. It is not as bad as everyone seems to think. Since mine is still a N/A 2.4L, I drive it primarily as a cruiser, so fats in the back look nice, but not performance minded. More for style than performance. Hard exits feel a bit soft in the rear, but the tires fit better than one might think. No hassles at all from Discount tire. If you are looking to drive it hard, don't do this. But 275/40 fits, and that's on an 8in wheel (I know, I know, highly unrecommended, and I agree, but did it anyway), and with a 9in wheel width, I believe you will fit fine, assuming your offset is standard.

I'd like to see pics of those

Critterman · « **Reply #21 on:** May 07, 2009, 10:13:32 AM »

Stock wheels are 8", widest recommended tire is the 245, with an 8.5 rim you can go to a 255, with a 9" rim 275.

lil goat · « **Reply #22 on:** May 07, 2009, 10:46:36 AM »

I know lots of people who have put 255's on the stock rims, not that it is recommended but they will go on, I know the spec is 8" I thought I read somewhere it was actually almost 8.5 but just under so they call them 8"

Imaj · « **Reply #23 on:** May 07, 2009, 12:23:02 PM »

Well, could someone measure a rim to tell of it's real size? Wouldn't that tell us the true numbers?

Sky 5 · « **Reply #24 on:** May 07, 2009, 04:41:34 PM »

Every bit of literature written about the Kappas specify 18" X 8" factory wheels.
The 255/45 tires will fit fine on them; but 255/40 or 255/35 ... no dice!

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Author Topic: Tire Size (Read 7839 times)

lil goat

lil goat