Boxter 550- advice?

[prancingdawg]

Tire size for my 99 miata: if I go to a 15" wheel and 225/45 R compounds would that be better than my current setup with the 14"ers? I noticed this weekend that Eric and Michael were runnung 15s.

Can you also explain why, or why not?

Pdawg

[gigi]

What does tire size matter? I'm confused. Isn't bigger, better?

[gigi]

BTW, Pdawg. You misspelled boxster

[prancingdawg]

You're very observant, Geeg. Bought a car yet?

[damnyankee]

Gigi - Does size matter?

[prancingdawg]

Well I for one think size matters...and speed (or slowness, as the case warrants)


We're still talking wheel size, right?

[drum3]

There is always a point where big is too much!!Mind outta the gutter guys !... At some point the weight of your wheel tire combo becomes too much for your horsepower to over come. Finding the perfect balance between traction,gearing and weight is what seperates us also rans from the National contenders(that and ability!)with the 15 they may be able to get taller gearing,a little more traction, but also a little more weight,this would work ok on long flowing courses where you can keep your momentum up, but would hurt on the slower tighter courses where the 14 would have the gearing and weight advantage.I plan on having (when my budget allows) a set of 13's for shorter coursesand 15's for the longer courses.The 15's give better traction(wider tread patch) and allow me to stay in 2nd gear longer,but do hurt the acceleration slightly,with the 13's the car accelerates better I have to change gear much more frequently,(and I suck at changing gears ).So its all a matter of which suits your driving style,car and the courses you most often compete on.

[drum3]

and there is a 14" 225 available,although I dont think it would work well on the stock wheels.

[prancingdawg]

Huh. Well I've been looking at it from the perspective of distance covered. It would seem to me that a 15" wheel given the same power would cover a bit more distance- ie, an extra inch per each revolution- and therefore you could conceivably cross the finish line sooner. Of course if you can keep the unsprung weight down as well.


Any other thoughts on this?

[prancingdawg]

OC, that wooden work if the tire circumferences were more or less the same. SOme 14 and 15 in sizes have identical circumferences!

[MattP]

prancingdawg said:

Huh. Well I've been looking at it from the perspective of distance covered. It would seem to me that a 15" wheel given the same power would cover a bit more distance- ie, an extra inch per each revolution- and therefore you could conceivably cross the finish line sooner. Of course if you can keep the unsprung weight down as well.


Any other thoughts on this?

If the power is the same at the hub, the power will not be the same at the outer edge of different diameter tires. This is for a CSP car, right? Shortest, widest tires and wheels that fit over stock brakes would be my choice.

[drum3]

mattp said:

prancingdawg said:

Huh. Well I've been looking at it from the perspective of distance covered. It would seem to me that a 15" wheel given the same power would cover a bit more distance- ie, an extra inch per each revolution- and therefore you could conceivably cross the finish line sooner. Of course if you can keep the unsprung weight down as well.


Any other thoughts on this?

If the power is the same at the hub, the power will not be the same at the outer edge of different diameter tires. This is for a CSP car, right? Shortest, widest tires and wheels that fit over stock brakes would be my choice.

Shortest widest only work better for certain cars and on certain courses.If you run courses on the shorter tires that continually force you to change to 3rd back to 2nd and so on,you might be better off with a slightly taller tire that lets you stay in 2nd.You lose time everytime you have to shift(regardless of how good you are).On a medium course my neon ran as good with 13s as it did with 15s,but it did better in different sections with each tire.switch to a Divisional type course,long flowing,very few slow sections,the 15s were almost a second faster.On a slow tight course where gearing is important the 13s get almost a second faster than the 15s.As i said it depends on the course,the car,the driving style and if you only have one set of wheels you have to find the happy medium.Last I checked I thought Dawg was in ES.It would be better IMHO to go with the 14's and a 205,theres not enough wheel width to run a 225(although Craig ran them on his Honduh's 6" wides).The 15s would hurt acceleration, but on longer courses would allow you to stay in 2nd much longer but we dont have many courses like that around here.

[prancingdawg]

My calculations show the 15" wheel tire combo that Eric Peterson uses is good for about a half second versus the 14". He was on v710s if i recall. The 225 does fit on the 15" rim, but won't go on the 14". The 14 weighs 21 pounds and is 22.8" diameter, while the 225/50 WR15 is 24 pounds at 23.7" diameter. Doesn't take into consideration the extra weight of the wheels and tires though. Or the weight of the driver etc. Or skill. Just tire size.








I drive in CS, a 99 miata, BTW. Both wheels legal for this car.

[drum3]

For local events I'd run the 14s,If I was doing lots a National stuff I'd try the 15s and shift less.