should I slap 245/45/17 toyo R1Rs on mai C-Street car?

[7thgear]

Due to a long-standing and healthy sponsor relationship with Toyo, the Canadian autocross scene will continue to allow the R1R for use in the street tire category (all other rules are copies from SCCA).


this year I won two (2)! tire contingency awards by being scoring highest on pax overall in our Regional Series and highest pax overall in the Canadian Autoslalom Championship while driving on Toyo R1Rs


while I could get the largest size possible and try to pawn them to some Porsche owners, this seems like too much work from my perspective...


so I figure I'd rather buy a 2nd set of wheels and maybe experiment next season (which wont start until May-ish)


this year I completed 15 events on 235/40/17 on the OEM rim, with my mod being the stranno bar. Overall I was happy this year.


a friend of mine, who also went to the Canadian Nationals in his BRZ, was also gunning for the Toyo contingency but was running on a loaned set of 225/45/17 R1Rs... and while day 2 didn't go that good for him, day 1 he was 0.06x seconds faster than me... made me wonder if that extra 10mm was worth it.



on the other side of the hill, i can get a 245/45/17, whole 1" (overall) larger in diameter over OEM. If my calculations are correct, would give me an extra 6ish km in 1st ger and 7ish in 2nd.

SO 2nd gear would redline around 103-105.


This is entirely course specific.. and for the tracks that we run here in Ontario, i believe a taller gear would help me at 4 of the 8 that we run, and pose a slight inconvenience at the other 4.. so i don't fucking know.



so there's my dilemma... i get 2 free sets of tires and I'm killing myself figuring out what to do


the other alternative is just to get more of the same in the interest of consistency


or do what @SeanRTR and stagger front/back 225/245 and see whats up.

[wparsons]

245/40/17 is exactly the same OD as 215/45/17 in most tires, so no extra speed. There's a 0.2" difference on the R1R's, while ZII's and RS3's are identical OD in both sizes.

http://www.tirerack.com/tires/tires....omCompare1=yes

I definitely wouldn't go 225/245 staggered, you'll be way too pushy like that. Mine with 225 square and stock sways has too much understeer with the current alignment (-2* all around) and springs (Swift Sport, FRS rates, which are slightly less oversteer biased than stock rates).

Are the R1R's stiff enough to run a 245 on a 7" wheel, or are you looking at jumping out of CS for the 245's?

[7thgear]

sorry!


I meant /45 not /40


I actually wouldn't want to mount a 245/40.. that I wouldn't feel safe about.


the /45 is advertised as having a gentler wheel width allowance than even the 235/40 (7.5-9.0 vs 8.0 -9.5)




and no, I don't want to jump out of CS just yet.

[7thgear]

also the reason why stagger might work is because of geometry


even with a front bar, the front end rolls.


and with limited camber, the roll would force the tire to tilt. When I flipped my tires the inside edge was brand spanking new (you saw it in person), that means that part of the tire is barely working under braking.


technically speaking a narrower tire with a more flexible sidewall will hug the road better


but, on the other hand, we've seen how going bigger in autocross just seems to work better... something I could never explain.

[Thorpedo]

IMO:

Don't stagger, don't go taller than 245/40 (due to squirm). I ran a 245/40 on a 7.5 and it was too wobbly for me to keep track of. I can't imagine a 245/45 on a 7". Yes the taller tire will accept a more narrow rim, but I can't see anything positive coming from that in an autocross environment. The extra kph are negligible for time. You will lose some time due to decreased acceleration (which effects last for the entire time you are accelerating) whereas the extra kph only benefit you at the very end of the section while you are on the limiter.

Edit: Also keep in mind that the rotating mass of the tire will be further out on a taller tire decreasing acceleration even more.

[SeanRTR]

I ran the staggered setup, and it was fine. All the BS about the car being too pushy is just that....BS. More rear tire pressure made the car nice and loose, just like before. I ran slighly more rear rebound with the staggered setup, that's about it. Was it faster? Inconclusive, but this setup was pretty successful on most courses and surfaces.

My plan for next year? Having two pairs of rear tires so I can essentially change the gear ratio. Shifting to third gear....that shit doesn't work. The time it takes to shift to third, and come back to second gear, I think is NEVER worth it. Unless you are able to hit 65+ MPH in third gear, and have a good spot to down shift to make it work. I can match RPM's, I can heal-toe, it's not talent related....the shit does not work. This was the largest thing that held me back at nationals, I was all over the rev limiter in second, but just not enough to justify an upshift, and then negotiate a down shift.

For 90% of local events, 235/40/17 is going to be the hot size. However, I think 235/45 is probably the size I'd pick for my 'tall gearing' which would be needed at most national events. 245/45/17 seems too tall....but I like the idea of having an extreme 'tall gear option tire', but for most courses this won't be favorable I feel.

If we're talking about an event like we did in London, ON at Centralia, well that course was so fast (75-80+ MPH), no tire under the sun on an FR-S is going to keep you in second gear anyway, so the short tires would be again be faster, as both will require a shift.

Last year running the staggered setup proved to me that matching the front and rear tire width is not critical, at least if you have adjustable shocks where you can dial in the balance accordingly. I don't think you've gone this route yet, so that may effect your decision.

Next year I'll determine if running a short tire on the front, and a tall tire on the back effects handling by changing the ride height delta front to rear. I may try something extreme for tight local events like a 215/40/17 Rear , and then a 235/45/17 to take with me for national events. If you can adjust to your cars change in handling with the dramatic tire changes, you can tune in the shocks to make the car more driveable 'on the limit' but other than changing tire size, you can't drive or tune around your second gear ratio, as using third gear on a sub 65 MPH course is just not an optoin.

Probably more info above than you needed, but for your events, that I suspect are mostly tight slower stuff, with a few crazy Centrailia events mixed in, I think 235/40/17 is your best all around tire size. It would ONLY be worth it to consider a 235/45/17 or 245/45/17 if you're getting a large amount of courses that having you stuck on the rev limiter for mutliple seconds at a time, that would put you in the 62-63ish MPH zone if you could stay in 2nd. Keep in mind our cars have ZERO power, and every corner exit you'll be giving away time on the taller tires. If you don't frequent the second gear rev limit on your current courses, DO NOT go with taller tires.

[7thgear]

no such thing as too much useful information




thank you for your input everyone!

[renfield90]

The R1R will be 200 UTQG soon. This was announced at the SEB town hall at nats.

There's also a pic from SEMA showing off the R1R as a 200 tire. The display size was a 195/50/15. Cheeky.

[7thgear]

the other thing at the back of my mind is the 225/45/16


this would make for the smallest diameter out of all of them.

the 235 is the largest section width tire I've ever driven on a 2700lb-ish vehicle.

My old Impreza ran on 205s... (RE11) and quite honestly I can't say I feel any sort of improvement from the 235s. Is it all placebo?

The guys that say they keep getting faster with fatter tires.. they add so much doubt to my calculations it's nerve wracking! arggg.

[renfield90]

Originally Posted by SeanRTR

I ran the staggered setup, and it was fine. All the BS about the car being too pushy is just that....BS. More rear tire pressure made the car nice and loose, just like before. I ran slighly more rear rebound with the staggered setup, that's about it. Was it faster? Inconclusive, but this setup was pretty successful on most courses and surfaces.

My plan for next year? Having two pairs of rear tires so I can essentially change the gear ratio. Shifting to third gear....that shit doesn't work. The time it takes to shift to third, and come back to second gear, I think is NEVER worth it. Unless you are able to hit 65+ MPH in third gear, and have a good spot to down shift to make it work. I can match RPM's, I can heal-toe, it's not talent related....the shit does not work. This was the largest thing that held me back at nationals, I was all over the rev limiter in second, but just not enough to justify an upshift, and then negotiate a down shift.

For 90% of local events, 235/40/17 is going to be the hot size. However, I think 235/45 is probably the size I'd pick for my 'tall gearing' which would be needed at most national events. 245/45/17 seems too tall....but I like the idea of having an extreme 'tall gear option tire', but for most courses this won't be favorable I feel.

If we're talking about an event like we did in London, ON at Centralia, well that course was so fast (75-80+ MPH), no tire under the sun on an FR-S is going to keep you in second gear anyway, so the short tires would be again be faster, as both will require a shift.

Last year running the staggered setup proved to me that matching the front and rear tire width is not critical, at least if you have adjustable shocks where you can dial in the balance accordingly. I don't think you've gone this route yet, so that may effect your decision.

Next year I'll determine if running a short tire on the front, and a tall tire on the back effects handling by changing the ride height delta front to rear. I may try something extreme for tight local events like a 215/40/17 Rear , and then a 235/45/17 to take with me for national events. If you can adjust to your cars change in handling with the dramatic tire changes, you can tune in the shocks to make the car more driveable 'on the limit' but other than changing tire size, you can't drive or tune around your second gear ratio, as using third gear on a sub 65 MPH course is just not an optoin.

Probably more info above than you needed, but for your events, that I suspect are mostly tight slower stuff, with a few crazy Centrailia events mixed in, I think 235/40/17 is your best all around tire size. It would ONLY be worth it to consider a 235/45/17 or 245/45/17 if you're getting a large amount of courses that having you stuck on the rev limiter for mutliple seconds at a time, that would put you in the 62-63ish MPH zone if you could stay in 2nd. Keep in mind our cars have ZERO power, and every corner exit you'll be giving away time on the taller tires. If you don't frequent the second gear rev limit on your current courses, DO NOT go with taller tires.

Some interesting ideas here. I'll be very curious to see how these work.

I'm gunning for you next year.

[jdrxb9]

Originally Posted by 7thgear

the other thing at the back of my mind is the 225/45/16


this would make for the smallest diameter out of all of them.

the 235 is the largest section width tire I've ever driven on a 2700lb-ish vehicle.

My old Impreza ran on 205s... (RE11) and quite honestly I can't say I feel any sort of improvement from the 235s. Is it all placebo?

The guys that say they keep getting faster with fatter tires.. they add so much doubt to my calculations it's nerve wracking! arggg.

Anyone gone any further than a thought experiment on the 225/45-16?

Apparently they've been available for a while, but I just noticed Dunlop is offering the ZII Star Spec in this size and its the first 16" I've seen that might be worth testing for CS: vs the 235/40-17 its only 0.2" narrower (by spec), but gives a 2% gearing advantage and lowers the whole car by 1/4"

Yes, you'll run of out 2nd gear sooner (~56.7 vs ~57.8), but if you want to do well on a local/small lot or think you'll be shifting to 3rd anyway... Plus, they are cheap and I have some almost-CS-legal 16" winter alloys I could repurpose for testing...

[tahdizzle]

I'd use the 235/40/17. Thats supposed to be the magic one :P

[7thgear]

Originally Posted by tahdizzle

I'd use the 235/40/17. Thats supposed to be the magic one :P

This past season I did 15 events on the 235/40/17 and received a new set as a contingency


but my other contingency I went ahead and asked for a 225/45/16, which I will experiment with come spring.


As much as I want to switch to Dunlops, for personal development i'll stick with the Toyos so i'll maintain some data consistency.

[jdrxb9]

Originally Posted by tahdizzle

I'd use the 235/40/17. Thats supposed to be the magic one :P

see 7thgear's other thread for his experience running that tire in 'CS': http://www.ft86club.com/forums/showthread.php?t=72991

IMHO with no real 'back-to-back' data, running the 235/40 is 'pushing it' with a ZII and is 'too far' with a R1R

Originally Posted by 7thgear

... I went ahead and asked for a 225/45/16, which I will experiment with come spring.

As much as I want to switch to Dunlops, for personal development i'll stick with the Toyos so i'll maintain some data consistency.

- look forward to your findings!