Autocross - choice of wider wheels or lighter wheels (same size tire) any difference

[toycar]

Moving from Street to STH. Been using light 16x7 (14 pound ish), but I do have a set of 16x7.5 (17.5 pound ish). Sticking with 215/45 RT660 for now.
I'm thinking this is a "six of one / half a dozen or another" choice - but thought maybe someone has some insight on which might shave a 0.05 second or so.

 

[Cdnmr2v6]

I don't have the rules in front of me, but I would always try to run the biggest tire possible on the lightest wheel I could afford. It depends on how competitive you want to be, but I would stay with the lighter wheels if given that choice.

 

[M-Sport fan]

I don't have the rules in front of me, but I would always try to run the biggest tire possible on the lightest wheel I could afford. It depends on how competitive you want to be, but I would stay with the lighter wheels if given that choice.

AGREED! Especially since you will get only a 'spitting hairs' improvement on turn-in response from only a half inch wider wheel, given that the 660s have a fairly stiff side wall to begin with.

 

[toycar]

Thanks to both M-Sport fan and Cdnmr2v6;
I'll stick with my 16x7 with 215/45/16 for now. The only upsize from there I've heard is 225/50/15 on a 15x8 wheel - I'll keep my eye out for a set of those on the classifieds. Another benefit is my lighter 16x7 don't need hubcentric rings while my 16x7.5 do - I always find them a bit of a pain.

 

[slyez]

Personally I would go wider if I needed to choose lighter vs wider. The car is super camber challenged, and high center of gravity. You need the support in the tire to not have it roll over too far or you will be running super high pressures to keep the contact patch in the right place. We have tested this. going from 7" wheel to 8" wheel is a big difference in time on a road coarse. Both with 225 tires. Went from 16x7 rpf1 to 15x8 TD race 1.2 and the 15x8 was substantially faster. This was A052 on 16x7 the R888R on 15x8. You can take from this what you want them being different tires, but the a052 is supposedly as fast or faster than the R888R, but we were over a second faster best lap on the 15x8 R888R combo on a roughly 2 minute track. RPF1 combo was roughly 4lb lighter per corner also.

 

[slyez]

btw, when we take 100lb out of the car, everything else being the same, it was not worth as much, a few tenths. Track conditions changed, but looked like .3s on a 1:10 lap time track. I dont think (and our tests support) weight is worth as much as better use/more tire.

 

[Cdnmr2v6]

Yes, I would always try and go for a wider tire, but that wasn't the original question. Back in the day people with ITR's would put 245+ on the OE 6.5" wheels.

 

[slyez]

nope, I didnt say wider tire, wider wheel. Our testing was with wider tire than OP by a little, but wheel width was independent of tire width. I say go for a wider wheel per tire width. 215 falken 660 would be better on 8" wheel than 7", is what I am trying to say. That 1" in wheel width would trump a few lb of wheel weight any time. That is my answer to the original question again.

 

[M-Sport fan]

Personally I would go wider if I needed to choose lighter vs wider. The car is super camber challenged, and high center of gravity. You need the support in the tire to not have it roll over too far or you will be running super high pressures to keep the contact patch in the right place. We have tested this. going from 7" wheel to 8" wheel is a big difference in time on a road coarse. Both with 225 tires. Went from 16x7 rpf1 to 15x8 TD race 1.2 and the 15x8 was substantially faster. This was A052 on 16x7 the R888R on 15x8. You can take from this what you want them being different tires, but the a052 is supposedly as fast or faster than the R888R, but we were over a second faster best lap on the 15x8 R888R combo on a roughly 2 minute track. RPF1 combo was roughly 4lb lighter per corner also.

A little but;

IF this above scenario was on a FiST; did the 225/45-16 A052 rub at all, and if so where?
Factory suspension, or lowered on coil overs/something else?

 

[slyez]

They did rub slightly on aftermarket coilovers. The inside of the tire rubbed the spring perch when the max camber was used on the spindle. with 43 offset RPF1. I think there was slight rub also when bumps were hit mid turn, on track. Not exactly sure where that was coming from, probably fender liners? The rim/tire combo did not rub when the car was in HS trim. At least not that I recall.

 

[bhmax]

I don’t have experience running the same tire on different width wheels, but I’ve bought a car where the previous owner put tires on that were much too wide for the wheels. Ruined the front end grip in corners due to not having enough support. I’ve always looked at the quoted tread width on Tire Rack and try to keep the wheel width that wide or wider.

 

[M-Sport fan]

^^^The problem is that many installers look at those same maximum wheel widths per tire size, and follow them as absolute gospel, refusing to mount a given tire size on even a HALF INCH 'too wide' a wheel.

 

[Dpro]

^^^The problem is that many installers look at those same maximum wheel widths per tire size, and follow them as absolute gospel, refusing to mount a given tire size on even a HALF INCH 'too wide' a wheel.

Ya stupidity prevails in the tire fitment industry. None of those idiots look at actual measured section width. Thank god we have independents around here that use their brains rather than blindly following.

I would say agree taking weight out of the car is not that important . I will say that taking weight off wheels is extremely beneficial for performance. I have experienced that.

 

[PhoenixM3]

Personally I would go wider if I needed to choose lighter vs wider. The car is super camber challenged, and high center of gravity. You need the support in the tire to not have it roll over too far or you will be running super high pressures to keep the contact patch in the right place. We have tested this. going from 7" wheel to 8" wheel is a big difference in time on a road coarse. Both with 225 tires. Went from 16x7 rpf1 to 15x8 TD race 1.2 and the 15x8 was substantially faster. This was A052 on 16x7 the R888R on 15x8. You can take from this what you want them being different tires, but the a052 is supposedly as fast or faster than the R888R, but we were over a second faster best lap on the 15x8 R888R combo on a roughly 2 minute track. RPF1 combo was roughly 4lb lighter per corner also.

Couldn’t tire circumference and it’s affect on gearing have contributed to your results?

 

[slyez]

Could have, but looking at aim data there was no real time lost or gained on the straight sections, so it doesn't appear that the change in diameter affected acceleration much. Surprising to us also. I can share the data logs by pm if you like.

 

[slyez]

I guess that some of it could be explained more by the diameter affecting overall ride height and cg due to the larger diameter, but i assure you the tire on the narrower rim was not using it's tread as effectively whatever the cause. Bottom line is get what you want, we will choose rim width over rim weight.

 

[Dpro]

I guess that some of it could be explained more by the diameter affecting overall ride height and cg sure to the larger diameter, but i assure you the tire on the narrower rim was not using it's tread as effectively whatever the cause. Bottom line is get what you want, we will choose rim width over rim weight.

I think 8’s definitely help our cars. I can attest though having Dekagrams going to Titans and now back to Dekagrams the car drives much better on the Dekagrams which are pretty much 3 lbs lighter per corner. 17x8 Titans 17.4 pounds per wheel 16x8 Dekagrams 16x8 +40 14.6 pounds.

 

[The_Ryan]

Wider wheels 100% help. Me and another FiST were running the same size RT660s, me on a 8" wide Deka's since i just run local groups, and he runs with SCCA and local groups as well, so he only had 7" wide OZ that were a bit lighter than my deka's. He had WAAYY more wear on the shoulders going down to the lettering, and I was beating his time by a good amount despite him for certain being a better driver.

 

[pinchvalve]

Thanks to both M-Sport fan and Cdnmr2v6;
I'll stick with my 16x7 with 215/45/16 for now. The only upsize from there I've heard is 225/50/15 on a 15x8 wheel - I'll keep my eye out for a set of those on the classifieds. Another benefit is my lighter 16x7 don't need hubcentric rings while my 16x7.5 do - I always find them a bit of a pain.

FYI - I used rings to make my other sets of wheel hub-centric and I hated them. They always got stuck when the rotor heated up and were impossible to remove when going back to my street wheels. Then I was talking to a rep from a wheel manufacturer (can't recall which) and he said that the rings are only there to ensure that the wheel is centered when mounted. The FiST has the type of lug nuts that center the wheel for you, so the rings are not needed. The rings hold 0% of the weight of the car, they do nothing once underway. So tossed mine and have been running without for years with no issues at all.

 

[dhminer]

FYI - I used rings to make my other sets of wheel hub-centric and I hated them. They always got stuck when the rotor heated up and were impossible to remove when going back to my street wheels. Then I was talking to a rep from a wheel manufacturer (can't recall which) and he said that the rings are only there to ensure that the wheel is centered when mounted. The FiST has the type of lug nuts that center the wheel for you, so the rings are not needed. The rings hold 0% of the weight of the car, they do nothing once underway. So tossed mine and have been running without for years with no issues at all.

I ran Fifteen52s without rings for a year or so. No problem at all. Switched wheels and now have them, but only because they came with the wheels so I figured why not?