Tim Comeau Posted July 8, 2010 Share Posted July 8, 2010 People were asking so I just weighed them again. No lead weights No valve stems Just the wheels. 7 x 15 23.3 (early) offset Phone dials 17 lbs 7 x 15 23.3 (early offset Cookie cutter. 15 lbs 7 x 15 52.3 (late/ABS) 0ffset Phone dials 17 lbs I was getting a few ounces of variation ( .2) among multiple times on the digital scale so the data is accurate, but maybe not perfect. Quote Link to comment Share on other sites More sharing options...
Tim Comeau Posted July 8, 2010 Author Share Posted July 8, 2010 Couple other wheel details. If you have a front wheel bearing cap come loose, the phonies will trap it. Cookies won't. Cookies are easier to get the steel lug nuts on because the phonies have more recessed holes. Quote Link to comment Share on other sites More sharing options...
cbuzz Posted July 8, 2010 Share Posted July 8, 2010 The weight of wheels play no significant role in our cars. If we were all F1 caliber drivers and able to turn laps within .1-.2 seconds then it may make a difference. The best way to go fast is practice laps with tire temps and in car lap times. Make the car reasonably good and try to minimize driver mistakes. There is no better money spent than improving the driver. The loose nut between the steering wheel and gas pedal is always the biggest problem. Have fun guys. Quote Link to comment Share on other sites More sharing options...
Tim Comeau Posted July 9, 2010 Author Share Posted July 9, 2010 That was my point when asked at Buttonwillow. Foxx and Milledge thought it was insignificant that I could concentrate over 100 lbs of ballast on the passenger floor, but that the spinning mass of the different wheels was significant. Quote Link to comment Share on other sites More sharing options...
Big Dog Posted July 9, 2010 Share Posted July 9, 2010 It is significant. Quote Link to comment Share on other sites More sharing options...
DavidH Posted July 9, 2010 Share Posted July 9, 2010 My money is on the great driver in the crappy car. Not the crappy driver in a great car. That is why we have spec racing...It reduces the impact of one of the variables. Quote Link to comment Share on other sites More sharing options...
Sterling Doc Posted July 9, 2010 Share Posted July 9, 2010 It is significant. Really? Show me the difference between these two acceleration curves below (TM data). There is more than a two lb. difference, and a slight gearing advantage. Below is a repost of my data comparing 205 RA-1's to 225 R-888's last year. ----------------------------------- 944 Spec directors are looking at our options for tires in the next year. The unloved R-888's are out. RA-1's are back. Before this news broke, the 944 Spec directors started considering the Spec Miata sized RA-1's as an option, as those were known to be available in 2010, and likely beyond. This size is also shared by the Spec E-30 class, as well. To look into the feasibility of this, the 2 fastest Midwest 944 Spec drivers swapped a fresh set of 225/50/15 R-888's and 205 RA-1's. Both sets were fresh and shaved to 3/32nd's to give each their best shot. Results were remarkably consistant. Best laps were within 1/10th for one driver 3/10's for the other, all essentially at lap record pace (fastest lap was .006 off of the 1:24.4 LR!). One surprise is that we expected the shorter effective gearing, and lighter weight of the RA-1 to improve acceleration. You can see on the graphs below that that there was no discernible difference in acceleration. Acceleration, and speed at the end of the straight was a wash. Grip was also very similar. Ride height was lower the RA-1's (lost a few fins of the oil pan ) and the smaller tire looked a bit puny. There is some interest in going to the 205 RA-1's anyway, for cost savings, and commonality with the other Spec classes. Weigh in over at 944 Spec.org if you have an opinion on this. I do, but will not disclose it yet. Data and a few pics below. RA-1 data is in blue, R-888 in black. These are the best laps on the two tires, with 1/10th second. You can see where I hit the rev limiter with the shorter tires in turn 3. R-888's on the left 205 RA-1's on the right Car on 205 RA-1's Quote Link to comment Share on other sites More sharing options...
Big Dog Posted July 9, 2010 Share Posted July 9, 2010 I certainly agree, with the 2009 National Champion, that the driver makes a big difference. However, the issue is two equal drivers, not one great driver and one crappy driver. Sterling Doc, I guess I don't understand the point of a comparison between two different tires as being relevant to the issue of a difference in wheel weight. Joe P. (our resident engineer) calculated a reasonable weight penalty for a lightened flywheel (rotating mass) and came up with 40 pounds to offset the advantage and that weight difference is much less than the wheels. I believe that he (or someone) looked at this issue in the past. Having more unsprung weight multiplies the weight issue dramatically, from what I understand. I will admit that I am not an engineer and have NO personal knowledge of such things. If there is an engineer in the house that can shed some light on the interesting debate, please weigh in. In any event, this is just an interesing side conversation because the rules are the rules, at this point, and late offset cars have no option on wheels. Big Dog Quote Link to comment Share on other sites More sharing options...
drivinhardz06 Posted July 9, 2010 Share Posted July 9, 2010 Joe P. (our resident engineer) calculated a reasonable weight penalty for a lightened flywheel (rotating mass) and came up with 40 pounds to offset the advantage and that weight difference is much less than the wheels. And the wheels (even without tires) have a larger dia. Where the mass is can be more important than the mass itself (moment of inertia). And like you say, there's the unsprung weight issue as well. Want to change the real world shock valving on a spec shock? reduce the mass it has to contend with. heck if I was a 944 guy in a spec series and I had a choice of 'em, I'd run the lighter ones. a lot of folks laugh at stuff like that, but IMHO there is no single magic bullet, it's the cumulative effect of doing 10 or 20 detail oriented things like that. Quote Link to comment Share on other sites More sharing options...
Sterling Doc Posted July 9, 2010 Share Posted July 9, 2010 My point is that a more than 2 pound change in weight made no measurable difference in acceleration. And weight in the tire has even more inertia than weight in the rim. Is there a difference? Sure. Is it big enough to measure, even with sensitive equipment? No. Keep in mind, the later cars have better suspension geometry d/t their 30mm longer a-arms - causes less camber loss with suspension compression. That difference is also real, but tiny in practice. If we try and equalize every non-measurable difference, the rules would become untenable. In the end the slightly greater weight of the the late offset wheels is nicely offset by the better suspension geometry. There is no allowance for late cars to run early wheels, so no one can have it both ways. It balances out, and simple is better. If the 2 lbs per corner means a lot to you, backdate your car to early offset - it's legal. I would not expect to go faster, though. The flywheel spins much faster than the wheels in most gears, magnifying it's impact. The weight penalty rule there is purposely relatively severe to discourage it's use, even in the short term, and to make no doubt that there will be NO performance advantage in any situation by using it. BTW - I have a late-offset car (drove an early offset last year) Quote Link to comment Share on other sites More sharing options...
schwank Posted July 11, 2010 Share Posted July 11, 2010 Why backdate suspension components? Just put the cookies on the late cars and go! No clearance issues and we have several local guys that do just that. Quote Link to comment Share on other sites More sharing options...
Sterling Doc Posted July 11, 2010 Share Posted July 11, 2010 The extra 30mm of track width is not legal in 944 Spec rules. It would give late offset cars the better geometry, extra track width, and the lighter wheels. This would tip the balance toward the later cars. It would also add the hassle of selling late wheels and having to buy early offset. Quote Link to comment Share on other sites More sharing options...
philstireservice Posted July 11, 2010 Share Posted July 11, 2010 This is a very interesting thread. A bit of info from Enkei, 1 lb of wheel weight removed is like taking 20lbs out of the car. Also a narrower track will help the car turn in quicker. Rotating mass is incredibly important, but as has been said here, it takes more than just one item to affect change. I am 100% in agreement that the absolute best money spent is on seat time and the driver skill improvement. With more skill comes more ability to take advantage of the performance mods that may improve lap times, etc. Quote Link to comment Share on other sites More sharing options...
schwank Posted July 11, 2010 Share Posted July 11, 2010 The extra 30mm of track width is not legal in 944 Spec rules. It would give late offset cars the better geometry, extra track width, and the lighter wheels. This would tip the balance toward the later cars. It would also add the hassle of selling late wheels and having to buy early offset. D'oh, I did not know that. A set of cookies is no more than a spare set of phonies so the cost argument seems void here. Especially when it seems you can backdate the whole suspension at a much higher cost, it comes down to the argument that the track width is equal to 8lbs of unsprung weight. The numbers I have always heard are ~10lbs cabin weight for each lb of unsprung weight removed. So between 80lbs and 160lbs effective delta for the wheels? That is certainly a significant difference! I am not experienced enough to compare that to the benefit of a slightly wider track width though. Just my .02... I run Cup anyway but follow here for the random tech discussions. And I'll be running a mix of cookies and phonies on my late car this year so this is relevant to my interests Quote Link to comment Share on other sites More sharing options...
Sterling Doc Posted July 11, 2010 Share Posted July 11, 2010 Cookies look better than phonies When I did have an early offset car, I did prefer running the cookies for looks & performance. In the end, with all the offsetting factors, it's just not enough difference (if any) to micromanage the rules over. Interestingly, I did a rough check on camber change through the range of front suspension travel with a bubble gauge and some tape a while back. I'll have to dig out the number later, but I was surprised how well my late offset car did, as most McPherson strut cars really suffer when lowered. Would be interesting to run the same test numbers on an early offset car. I'd be willing to bet more camber loss with the early offset, but how much? Quote Link to comment Share on other sites More sharing options...
944-Spec#94 Posted July 12, 2010 Share Posted July 12, 2010 Look, Most early offset cars run cookies. All late offset cars (including the 924S) run phone dials. Interstingly the 924S should be pretty poor on paper. Narrow track, heavy wheel, sort arm suspension. Yet charlie has been winning with it. Bottom line is this. All of these factors together in practice make performance difference that is less than the lap to lap variation of each driver and less than difference between drivers. If you really want to change things around you can. Just go and to the legal update/back dating to get there. Heck you can even turn a 924S chassis into an 944 chassis. Front is just bolt ons, but rear requires the stock 944 rear flares. More work, but legal if you do it. Quote Link to comment Share on other sites More sharing options...
cbuzz Posted July 16, 2010 Share Posted July 16, 2010 It may not look good on paper but it is on rails mid corner. If we could clone my car we would all drop a couple of seconds per lap. I am anxious to see how it does at Miller. How many days left? Quote Link to comment Share on other sites More sharing options...
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