Rear tire up-sizing

[ctrlraven]

What other sizes will fit on the back without having a SCT tuner to correct the speedo?

[GA-Marauder]

TAF and a few others went with the BFG T/A KDW2s size 255/55VR18 for the rear, and stock for the front. Try a search for KDW2 and see if anything shows up.

[LVMarauder]

I run 255/55 18 KDW2's great tire. I think the stock rim can go up to 265 but thats barely in contact, tell me if im wrong. But width doesnt effect speedo readings so which are we talking about?

[Bobby Clobber]

Hold on, are these the ones showing on the T/R site for $123 ea as compared to the "backordered not available till 04/22 " o/e tire listed at $134 ea?

From what i've read they are a better tire and certainly wear better/longer.

[SergntMac]

F.Y.I...Generally speaking, it's not a good thing to mix and match tire tread patterns and compound. Adhesion to the pavement in hard braking and cornering, as well as hydroplaning through standing water can become a serious handfull when one end of the car gets good sticky, and the other end doesn't.

[ctrlraven]

Thanks for the input guys, big time help!

[magindat]

Originally Posted by ctrlraven

What other sizes will fit on the back without having a SCT tuner to correct the speedo?

Use this tire size calc for comparison:

http://www.miata.net/garage/tirecalc.html

Keep the overal diameter and revs per mile the same or very close and you'll be fine with the speedo. I will usually allow for no more than 1/2" overall height (diameter) difference since that only represents the diff between a brand new and severly worn tire, therefore not an appreciable margin.

Good Luck!

[ctrlraven]

Originally Posted by magindat

Use this tire size calc for comparison:

http://www.miata.net/garage/tirecalc.html

Keep the overal diameter and revs per mile the same or very close and you'll be fine with the speedo. I will usually allow for no more than 1/2" overall height (diameter) difference since that only represents the diff between a brand new and severly worn tire, therefore not an appreciable margin.

Good Luck!

thanks, that linke helped explain things. so if i went with the 255/55 kdw2s its dia says 29.0"/revs 694.0 and the oem tire is 28.6"/revs 705.0 so my speedo should only be off by 1 or 2 mph by what the that tire size calc says?

[magindat]

Originally Posted by ctrlraven

thanks, that linke helped explain things. so if i went with the 255/55 kdw2s its dia says 29.0"/revs 694.0 and the oem tire is 28.6"/revs 705.0 so my speedo should only be off by 1 or 2 mph by what the that tire size calc says?

A speedo is never off by a fixed MPH. It's of like .2 MPH per 10, (1.6@80) or something like that. Figure it that way. Further, such small differences are the same as would be reflected by tire wear. the calc gives you how far off at 60, as I remember. Just divide by 6 to get amount per 10. The spread will be wider at 80 than 60.

[Dragcity]

Use a percentage for proper application at various speeds. If the tires are say 8.6 % smaller, then the speedo shows you are going 8.6 % faster than you really are. (and you actually travel 8.6% less than your Odo shows.)

My winter tires are 7.5% larger than OEM. Therefore, I move 7.5% faster than my speedo shows, and cover 7.5% more distance than my odo shows.

I set up some formulas in an Excel sheet to assist in finding the proper difference in F/R sizes. Just applied the OEM % change to a given diameter tire and let the calculation tell me what other size I needed to find.

I can re-construct the sheet if you need it....

Have fun, you'll learn lots about tire sizes and availability...

[SideshowBob]

Originally Posted by SergntMac

F.Y.I...Generally speaking, it's not a good thing to mix and match tire tread patterns and compound. Adhesion to the pavement in hard braking and cornering, as well as hydroplaning through standing water can become a serious handfull when one end of the car gets good sticky, and the other end doesn't.

OK, so you just replace the fronts with the same brand and model tire as the rears. Now, assuming you're going with 255/55-18's in the rear and stock size in front, what brand do ya'll recommend?

[ckadiddle]

The KDW2s are good for dry and wet conditions, but you gotta remember they are NOT for snow. Another tip: on some tire sites the KDW2 tire is called KDW NT (for New Tread) instead of KDW2. I did a lot of research on the web for tires of the OEM size and the 255/55 18 size. There are other options besides BFG KDW tires, but frankly the other brands that would be same as OEM sizes were even more expensive than BFG.

[GA-Marauder]

Originally Posted by SergntMac

F.Y.I...Generally speaking, it's not a good thing to mix and match tire tread patterns and compound. Adhesion to the pavement in hard braking and cornering, as well as hydroplaning through standing water can become a serious handfull when one end of the car gets good sticky, and the other end doesn't.

If this was in regard to my post, by stock on the front I was just referring to the size.

[Cobra25]

Originally Posted by LVMarauder

I run 255/55 18 KDW2's great tire. I think the stock rim can go up to 265 but thats barely in contact, tell me if im wrong. But width doesnt effect speedo readings so which are we talking about?

Can the 265, or 275 KDW2's fit on the stock rear rim correctly?