February 24, 2017 at 5:18 pm #20357
I am looking for tires to fit on OEM 17″ rims of my 987 (205/55 6.5×17 fronts and 235/50 8×17 rears). I am finding staggered sets in the recommended OEM sizes extremely hard to find.
However by my reckoning 225/50 17s will fit on the 6.5 rims and on the car with 0 clearance problems and there are lots of staggered sets using that as the front. Using https://www.wheel-size.com/calc/?wheel1=205-55-17X6.5ET55&wheel2=225-50-17X6.5ET55 as a reckoning tool.
Anybody else face this problem — is my thinking reasonable? Any issues I should consider?February 27, 2017 at 9:16 am #20359Wayne SpiegelbergParticipant
Hi Brian, it appears you haven`t had much response so here is my 2cents.
I would not mount a 225 on a 6.5″ rim as it would stress the bead in spirited driving.
The width is fine with a lower profile of 50 for your car but a wider rim would be recommended.
Regards WayneFebruary 27, 2017 at 9:43 am #20360
The rims I have so I don’t want to change. Is there some other tire size that would work with these rims that would provide a wider range of staggered options?
Maybe a different tire for front and back?February 28, 2017 at 12:41 am #20361andy wrightParticipant
I would definitely not recommend having different tire brands/types front & rear. The different characteristics of the tires will make the car less predictable and less balanced during at the limit driving.
To avoid any drastic change in overall diameter (which will make your speedometer inaccurate) why not try the following:
Front 215/50/17 Dia. 25.5″ (OEM 25.9″) OK on a 6.5 rim width.
Rear 255/45/17 Dia. 26.1″ (OEM 26.6″) OK for an 8″ rim width.
Above based on BF Goodrich G-FORCE SPORT COMP-2
Diameters will change slightly depending on manufacturer and tire type, but should be close.February 28, 2017 at 9:36 am #20362
So you are suggesting changing both back and front sizes? What about 215/50 front and the OEM 235/50 back? Any reason for not choosing that combination?
The speedo is rear wheel based I assume?February 28, 2017 at 11:07 am #20365andy wrightParticipant
I am pretty sure the Speedo sensor is on the gearbox, so yes the rear tire size will influence the readout.
I guess it depends what you are trying to achieve with the tire size change. Obviously a wider front tire should provide more grip and less understeer (if this is in fact an issue), but as Wayne pointed out if you get too wide on the OEM rim (6.5″) then the tire tread does not sit flat on the road and you lose some of the advantage. If you stay with the stock rear tire size, you are changing the relative grip levels front/rear, which may not be an issue, but will change the balance of the car. Maintaining the same tire width differential of 30mm (205 vs. 235) should maintain the same balance which would suggest that 215 front and 245 rear is the ideal combination for a next size up tire change. The sidewall ratio will affect both the ride and the tire footprint. Generally a higher numerical sidewall ratio gives a better ride while a lower number puts more tread on the road.February 28, 2017 at 11:41 am #20366
My main goal was finding more options (and if truth be known cheaper options) for the 17″ wheels. No other real goal. I was finding very few OEM size options and those that I did find were more expensive than tires for 19″ wheels (that I bought recently and plan to use anyway). There are lots of options for OEM size tires for 19″ OEM wheels in a wide range of prices and capabilities (but not 17″ ones — which seems strange as I am thinking there are lots of those wheels out there).
I was planning on leaving the 17s in the garage as backup so I might just pass on new tires — the ones mounted are useable (but getting a little old).
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