I am thinking about putting 255 45 R17 tires on the front and 255 50 R17 tires on the rear. I know this will affect the speedometer and trip computer but are there any negatives that I have to be careful about. Do I have to worry about ABS and traction control even if the larger tires are on the rear only?

 

Tony,

I have the 19 inch rims and the stock tire size is 255/35-19 rear and 245/35-19 front. I installed new tires a few months ago and got 285/30-19 rears and 275/30-19 fronts. They fit with no rubbing at all, so you don't have to worry about the width at all. The miata.net tire size calculator shows that your tires would have a radius of 13.5 inches compared to 12.9 on mine. That's 1.2 inches taller overall, but it would put your tire .6 inches closer to the fender. I don't think it would rub, but it might look kinda funny.

 

The simple answer is no....yes you will effect the rolling radius and your speedo will be more in-acurate than it is (maybe you never know it might make it more acurate )

But I am curious why do you want to increase the wall size, I understand doing the width but the 17" wheels look like they are too big as it is?

 

LOL! No responses for two hours, then three within three minutes. I think we were all watching the same football game.

 

I doubt you can even tell the difference in these tires. I wouldn't worry about it. You might find this much difference in tires the same size by different manufacturers.

 

I just want to fill out the rear wheel wells a little. Should do the trick with an extra inch diameter. However, I don't want a harsher ride thus my reluctance to go with a larger rim. If I had a coupe maybe but scuttle shake and no CATS have relegated me to sticking with the 17s.

 

Front and rear rolling tire circumferences must be within a certain percentage or ABS and DSC will be impacted. I can't site the exact threshold, but at some point (and not a whole bunch), if wheel sensors, front to rear, differ by some amount, the CUs will interpret it as wheel slip.

Here is an online tire size calculator that will give you tire circumference delta in % if you're going with staggered sizes. I don't like to exceed 3%-5% myself, but again, I'm unsure of the threshold.

http://www.1010tires.com/TireSizeCalculator.asp

 

Even if you went with larger rims they would not technically 'fill the gap', as the rolling radius changes very little.

Why dont you just lower the XK by an 1", it will not effect your ride.

It is only when you lower more than that things get hard, and it will improve the stance.

I wish I didn't have cats suspension, it is nothing more than a gimmick that does not work very well and costs a fortune to replace the shocks

 

Yes that is the information I was curious about. The difference in the radius and circumference is 3.87% from the front versus rear tires. Is it an acceptable range? I have noticed other MYs using seperate combinations such as the 2001 XKR Silverstone with (Front) 255/35ZR20 and (Rear) 285/30ZR20. However, the difference is only 1%. I don't want to screw up the ABS or DSC.

 

3.87% should be OK. I cannot be quoted here (or if someone wants to blast me), but I believe the threshold is 15%. At least it was on older ABS systems. I've never personally tested anything close to that on a modern Jag to verify the crossover point.

BTW - stick just with Circumference (rolling circumference) and forget radius as you can really "play" with tire sizes and rim sizes (dia and width) yet still maintain a small, reasonable delta % on staggered installations

 

Larger rear tyres are OK but smaller will actuate the traction control as the ABS calculates the rear as spinning faster and attempts to control the 'slip'.

I once had a Silverstone for 'trac' issues on the highway. It turned out someone had rotated the front and rear wheels. The ABS saw the rear wheels turning at a faster rate (smaller tyres) and tried to control the 'fault'.

Slightly slower (larger tyres) does not trigger a response from the controller.

bob gauff

 

Glad this came up. I have the proper 245/45/18 front and 255/45/18 size tires on stock Double Five 8" wide front, 9" rear wheels. My tires are Dunlop Sport 9000 unidirectional front, with a distinct "Curved V" tread pattern; and Continental Conti-Pro Contact rear. (Mis-match curteousy of previous owner, rears are new) The Dunlaps make all kinds of noise and try to "steer" the car with irregularities in the pavement. I don't like it! So I was thinking of putting the 255 Conti's in front and buying matching 265s or 275s rear. The additional benefit from wider tires being having some ballooning to protect the rims from curb rash!

(A) Will 255s fit without rubbing in front?
(B) Will wider tires exaccerbate (worsen) the "tire steering" effect or is that a trait of "V" Tread design?
(C) Will 275s or even 285s fit in the rear?

I was surprized REV SAM you could fit 275s/285s front/rear, that's pretty big. Are your rims wider than mine -- 8 & 9"? Do you get that "tire steering" effect? Could be my toe-in/out is off a bit; haven't checked alignment on car yet. At roughly $200 a piece I want to make a good decision on size. I think the Conti's are a decent tire and I'd like to have a matching set of tires. The Dunlops are just too noisy.

 

The 275s fit in the wheel well with no problem. TECHNICALLY they are slightly too wide for the rims, but they were mounted without any issues and they perform wonderfully (i have the Continental Extreme Contact DWS). They bulge out slightly from the rim, but I like that for the reason you mentioned. You should have no problem moving your rears to the front. You have a taller sidewall with those 18 inch rims, so the sidewall has more room to adjust to the rim width.

 

By the way... you're only putting an extra centimeter in width on the front rim. Half of that is on each side of the rim. That's only five millimeters. You probably won't even notice a difference.

 

So is "Tram-line" the descriptive term used for when the grooves in the road surface grab your tires and they steer in that direction; or as I said earlier "tire-steering"?

Are the aggressively "V-GROOVED" tires more likely to exhibit this trait? I haven't had a modern HP sports/GT car before --- I run good ole BFG T/As 60 series on my classic cars, so I have no experience with modern low profile tires.

 

The only time I had that problem caused by tires was when I had a bias-ply tire on one wheel and a radial on the other. I think it's more likely to be caused by a poor alignment or worn front suspension joints/steering linkages.

 

Pirelli P Zeros are well known for tramlining, alot does have to do with the condition of your roads.

Our roads in the UK are terrible and the only tires I have come across that have been an improvement are the Dunlop Sport Maxx

My XJS will drive quite happily even without me steering but with 255s on the front and 335s on the back you do have to expect it.

The widest I beleive you can get safely on a double 5 is 265, 275 will go on just dont go around corners at 100mph and you will be fine. The widest I would consider on a front is 255, but again this goes back to tramlining and UK roads. If you roads are as smooth as race tracks you will be fine

 

Rev Sam, with your new tires, if you get a chance over the weekend, can you post a couple pics of the profile and from its tread view, I'd like to see the difference in space from fender and outside the lip of the rim. thanks in advance!

 

For what it's worth...

I have a 2001 XKR Silverstone with the 20" rims, 9" wide at front and 10" on the rear and it's got the Pirelli p-zero tires with 255/35 directionals in front and 285/30 on the rear. The tires seem to fill out the wheel wells nicely, but it does have the small black fender strips on the rear...

It does seem to suffer from 'tramlining', but the roads are horrible in Tulsa (Orange Barrel Capital of America) and I also haven't had the car long enough to know if I have suspension issues.

 

Hi from snowy NJ. newbee to forum. Have 255/45/17 all around. They look and perform great on stock '98 XK8 rims. Went oversize because original perrelli's were dry rot when I bought car. Didn't want to spend $1500. Got Kuhmo's for $500. At the time only inexpensive tires that fit. They're wearing like iron, over 55k on them, but little hard riding. Thanks for all the help over the years keeping my baby on the road daily.