Looks vs. Performance ...... What do you think?
09-14-2005, 02:05 PM
#76
Nordschleife Master
Originally Posted by M758
I said both tire were 225/50's one on 16" wheels the other on 15". Both were the same tire type too Kumho Victoracers. Both I assume ran at the same pressure as there would be no reason to change this. They were run with in an hour and 1/2 of each other on the same day with no change in track conditions. The driver was still learning the track, but the second session was on the 16" where he should have been faster, but was not. 15x7 Phone dials and 16x7 Cup 1's were tires used on 2450 lbs 924S. Now for those not familar with Vicotoracers the are as fast right new as in the first 5-6 heat cycles so tire grip was not an issue. Feedback from the driver was that tires stuck really good, but the car seemed slow. This was due to taller gearing mostly. The two second change was noted by comparing hot lap times from the first session on 15's to the second on 16's. In general there was a 2 second change between the laps of the tow sessions. As a control I also was on track in those two seesions my lap times were consistant between the those two seesions so this confrims no large change in track conditions.
That enough data for you?
That enough data for you?
09-14-2005, 02:19 PM
#77
Race Director
Originally Posted by Fishey
Sure but given that the 15" have a smaller circ and lowers the gearing that can be a big benifit in a race in a parkinglot. However this does not mean the car handled any better then it did on 16" rims. It could easily be the gearing diffrence that is effecting the times of the car.
I never said the difference was not related to tire diameter. In fact I feel smaller tire diamete is major reason to stick with 15" wheels.
Really it not important which one handles better. What was proven clearly to me is that a car with a 225/50 tire with 15" wheels is FASTER than on 225/50 and 16" wheels. This applies to a low hp 944 or 924S.
When it comes to performance what I look for is overall lap times. Grip is part of that as well as gearing influences. Sure a 944 with 335/35 18's may stick like you would not believe, but dragging that tire around is probably not worth the extra grip. In the case of the 225/50 15" or 16" the grip levels are probably very close, but the biggest gain from the 15" is lower mass and smaller diameter.
That has been my point all along. I don't seem to understand why you can't believe that.
09-14-2005, 02:24 PM
#78
Just a car guy
Rennlist Member
Rennlist Member
Join Date: Jan 2002
Location: South Lyon, Michigan, Ewe Ess Eh
Posts: 9,927
Received 835 Likes
on
524 Posts
Originally Posted by Fishey
Sure but given that the 15" have a smaller circ and lowers the gearing that can be a big benifit in a race in a parkinglot. However this does not mean the car handled any better then it did on 16" rims. It could easily be the gearing diffrence that is effecting the times of the car.
There are several factors involved here and think most have been covered. Let's summarize to keep it simple.
1) overall tire diameter. This is detemined by tire width, aspect ratio and rim diameter (the same numbers on the sidewall of every tire). It is possible to go in either direction from what was initially installed on the vehicle by messing with the tire size and hence overall tire diameter.
2) Unsprung weight. Smaller wheels and tires tend to be lighter than larger wheels and tires. Large differences in unsprung weight can be detected in ride comfort, acceleration times and lap times.
3) Rotational mass (inertia) of the wheel/ tire assembly. This has the most effect on braking and acceleration. Higher mass outward from the center of the wheel is worse than low mass or mass concentrated near the center of the wheel.
4) Trade offs. That's what this topic is all about. Are you willing to give up some performance for larger, heavier wheels and tires? What about tread (section) width? How wide can you go? How wide should you go?
5) Appearance. It's all subjective. Personally, I will accept a less attractive wheel that is light rather than a heavy and more 'attractive' wheel.
6) Rules. Quite often those pesky rules get in the way and limit your options.
One thing I'd like to see disappear from this discussion of saying the wheel changes gearing. See above - it is the tire size that does that.
Carry on....
Last edited by Scott at Team Harco; 09-14-2005 at 02:43 PM. Reason: This thread is worthless without pictures
09-14-2005, 02:32 PM
#79
Rennlist Member
Originally Posted by Geo
I've only attended on PCA CR and that was at Parade last year. Virtually all of the 944/924S cars had 15" wheels.
Also, as Joe pointed out, 16x7 wheels have been legal for these cars in SCCA ITS for a while now.
Also, as Joe pointed out, 16x7 wheels have been legal for these cars in SCCA ITS for a while now.
I was not at that event, but Ive attended about 20 other PCA Races, watching and participating.
Edit: (my error on quoting myself) on the 16" wheels: how long have the 16 been legal? I am referring to about 4-5 years ago. Also when comparing a 225/50 on a 15" to a 225/50 on a 16" rim, of course go with the 15". But the initial discussion was regarding wider and heavier versus narrower and lighter, not comparing the same width wheels and tires, with different heights.
09-14-2005, 02:44 PM
#80
Race Director
Originally Posted by Scott at Team Harco
One thing I'd like to see disappear from this discussion of saying the wheel changes gearing. See above - it is the tire size that does that.
Carry on....
However using 15" wheel means you can run a 225/50 15 tire. This tire has smaller overall diameter with the same side wall as does a 225/50 16 tire.
The reason this is important is that with a stock size of 215/60 on 15" wheels. most 944 NA's don't get more performance from that tire size. Few performance tires are made in that size plus there is all that sidewall to deal with. So most folks think of a "plus one". In fact the 944 Turbo did this to improve cornering. They install a 225/50 on 16" wheels. Now the nice thing about this tire size compared to a 215/60 R15 is it HAS close to the same overall diameter as stock. So it looks better is good for the street as it maintains the factory final drive ratio.
Now this has falsly given the impression that 16" or larger tire are the "way to go for performance". Well there is another approach that works quite well for track cars, but is not ideal for street cars. That is the 225/50 R15 tire size using that orginal stock wheel. This tire size offers the same section width and aspect ratio as the "plus one" tire/wheel combo, but is potential lighter (assuming same tire and dependant on wheels) and offers effectivly a lower final drive ratio.
So if you have 215/60 on stock 15x7 wheels you have two performance upgrades. 1) is 16" or 17" wheels and appropriate tire sizes. the other 2) is using the same wheels and putting a smaller diameter tire on them.
Personally I think the 225/50 or even 225/45 (yes these are out there) on 15" wheels is tough combo beat on a 944 NA or 924S. Once you get to the higher powered 944S2 or turbo you can probably stand the bigger tire and wheel combo .
The other advantage with the 225.50 R15 tire is 1/2" lower CG...
09-14-2005, 02:50 PM
#81
Race Director
Originally Posted by Oddjob
The Club Race at Texas Motorspeedway in July 2004? From the results, there were only three I class cars there, a 924S and two 944s.
I was not at that event, but Ive attended about 20 other PCA Races, watching and participating.
I was not at that event, but Ive attended about 20 other PCA Races, watching and participating.
There was an I-stock 924S that ran 16" wheels not long ago. However that car was sold and turned into a 944-spec car. Infact that WAS the car I mentioned that did the 15" vs 16" wheel test.
09-14-2005, 02:53 PM
#82
Nordschleife Master
Scott, My response was to the rims sizes 225/50/15 and 225/50/16 the overall combo of the wheel/tire is about 1" smaller circ then the 16" Wheel/Tire combo. Sorry for the confusion.
09-14-2005, 02:58 PM
#83
Just a car guy
Rennlist Member
Rennlist Member
Join Date: Jan 2002
Location: South Lyon, Michigan, Ewe Ess Eh
Posts: 9,927
Received 835 Likes
on
524 Posts
Originally Posted by M758
Technically you are 100% correct,
However using 15" wheel means you can run a 225/50 15 tire. This tire has smaller overall diameter with the same side wall as does a 225/50 16 tire.
The reason this is important is that with a stock size of 215/60 on 15" wheels. most 944 NA's don't get more performance from that tire size. Few performance tires are made in that size plus there is all that sidewall to deal with. So most folks think of a "plus one". In fact the 944 Turbo did this to improve cornering. They install a 225/50 on 16" wheels. Now the nice thing about this tire size compared to a 215/60 R15 is it HAS close to the same overall diameter as stock. So it looks better is good for the street as it maintains the factory final drive ratio.
Now this has falsly given the impression that 16" or larger tire are the "way to go for performance". Well there is another approach that works quite well for track cars, but is not ideal for street cars. That is the 225/50 R15 tire size using that orginal stock wheel. This tire size offers the same section width and aspect ratio as the "plus one" tire/wheel combo, but is potential lighter (assuming same tire and dependant on wheels) and offers effectivly a lower final drive ratio.
So if you have 215/60 on stock 15x7 wheels you have two performance upgrades. 1) is 16" or 17" wheels and appropriate tire sizes. the other 2) is using the same wheels and putting a smaller diameter tire on them.
Personally I think the 225/50 or even 225/45 (yes these are out there) on 15" wheels is tough combo beat on a 944 NA or 924S. Once you get to the higher powered 944S2 or turbo you can probably stand the bigger tire and wheel combo .
The other advantage with the 225.50 R15 tire is 1/2" lower CG...
However using 15" wheel means you can run a 225/50 15 tire. This tire has smaller overall diameter with the same side wall as does a 225/50 16 tire.
The reason this is important is that with a stock size of 215/60 on 15" wheels. most 944 NA's don't get more performance from that tire size. Few performance tires are made in that size plus there is all that sidewall to deal with. So most folks think of a "plus one". In fact the 944 Turbo did this to improve cornering. They install a 225/50 on 16" wheels. Now the nice thing about this tire size compared to a 215/60 R15 is it HAS close to the same overall diameter as stock. So it looks better is good for the street as it maintains the factory final drive ratio.
Now this has falsly given the impression that 16" or larger tire are the "way to go for performance". Well there is another approach that works quite well for track cars, but is not ideal for street cars. That is the 225/50 R15 tire size using that orginal stock wheel. This tire size offers the same section width and aspect ratio as the "plus one" tire/wheel combo, but is potential lighter (assuming same tire and dependant on wheels) and offers effectivly a lower final drive ratio.
So if you have 215/60 on stock 15x7 wheels you have two performance upgrades. 1) is 16" or 17" wheels and appropriate tire sizes. the other 2) is using the same wheels and putting a smaller diameter tire on them.
Personally I think the 225/50 or even 225/45 (yes these are out there) on 15" wheels is tough combo beat on a 944 NA or 924S. Once you get to the higher powered 944S2 or turbo you can probably stand the bigger tire and wheel combo .
The other advantage with the 225.50 R15 tire is 1/2" lower CG...
09-14-2005, 03:00 PM
#84
Just a car guy
Rennlist Member
Rennlist Member
Join Date: Jan 2002
Location: South Lyon, Michigan, Ewe Ess Eh
Posts: 9,927
Received 835 Likes
on
524 Posts
Originally Posted by Fishey
Scott, My response was to the rims sizes 225/50/15 and 225/50/16 the overall combo of the wheel/tire is about 1" smaller circ then the 16" Wheel/Tire combo. Sorry for the confusion.
By the way, you need a better avatar. Don't you have a pic of your car that will work?
09-14-2005, 03:04 PM
#85
Site Sponsor
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: Aug 2002
Location: A great big building in the woods, FL.
Posts: 6,527
Likes: 0
Received 4 Likes
on
3 Posts
Originally Posted by Oddjob
Travis,
So you effectively ..... decreased weight (by 12 lbs) and went wider (7” PD – 8” Fuchs)?
So you effectively ..... decreased weight (by 12 lbs) and went wider (7” PD – 8” Fuchs)?
I am not going to get into the details of unsprung weight and where it is most noticed. There is plenty of documentation on it. Just search online or grab a book. Don't take my word for it because obviously I am talking out of my *** on this one.
And... if you cant find 245-50-15 in R compunds then you are not looking hard enough.
Back on topic... I bet the guy who started this thread is stiing there scratching his head. Asking about suspension/wheels in the tech forum is like asking about politics in the off topic forum.
09-14-2005, 03:15 PM
#86
Race Director
Originally Posted by Travis - sflraver
And... if you cant find 245-50-15 in R compunds then you are not looking hard enough
I see hoosier has a 245-50 15. Down side is that it is 24.65" in diameter. That is the same size as 245-45-16 (24.68"). So with shorter side wall 16" tire is probably better in that case.
Dunlop also has a Sport 8000 in that size too.
Tire rack does not carry a 245/45 15 tire This tire is 23.68" diameter and very close to the 225.50 R15 's 23.86" diameter.
09-14-2005, 03:22 PM
#87
Race Director
Originally Posted by Scott at Team Harco
One thing I'd like to see disappear from this discussion of saying the wheel changes gearing. See above - it is the tire size that does that.
09-14-2005, 03:25 PM
#88
Race Director
Originally Posted by Geo
Well, you rally guys are certainly a different sort of bunch. I know my tires don't have gears.
Yeah... remember ice spiked rally tires kind of look like gears.
09-14-2005, 03:29 PM
#89
Just a car guy
Rennlist Member
Rennlist Member
Join Date: Jan 2002
Location: South Lyon, Michigan, Ewe Ess Eh
Posts: 9,927
Received 835 Likes
on
524 Posts
Originally Posted by M758
Yeah... remember ice spiked rally tires kind of look like gears.
OK - I found a picture of what I was talking about. Tires that are geared...
Last edited by Scott at Team Harco; 09-14-2005 at 04:34 PM.
09-14-2005, 05:39 PM
#90
Three Wheelin'
Confused about tire sizes
Please excuse my ignorance, but can someone point me to a thorough explanation of tire sizes?
I want to get turbo twists for my '89 951. Here are two choices currently on ebay:
1) fronts 7" x 17", rears 9" x 17"
w/ MICHELIN PILOT Tires: 235/35 x17" front, 285/40x17 rear.
2) 7.5x17" with 205-50ZR17 front and 9x17" with 255-40ZR17 rear. Off-set is 52mm frt. and 47mm rear
Yes I now know that #2 is overpriced, but what's the difference? Would I be able to see or feel the difference between 7" and 7.5" fronts?
The listings are:
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT
and
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT
I'm not going to race (I don't think), this will be a weekend car.
Also so you guys don't think I'm going to free-load here forever, I just paid for my membership
Kevin
I want to get turbo twists for my '89 951. Here are two choices currently on ebay:
1) fronts 7" x 17", rears 9" x 17"
w/ MICHELIN PILOT Tires: 235/35 x17" front, 285/40x17 rear.
2) 7.5x17" with 205-50ZR17 front and 9x17" with 255-40ZR17 rear. Off-set is 52mm frt. and 47mm rear
Yes I now know that #2 is overpriced, but what's the difference? Would I be able to see or feel the difference between 7" and 7.5" fronts?
The listings are:
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT
and
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT
I'm not going to race (I don't think), this will be a weekend car.
Also so you guys don't think I'm going to free-load here forever, I just paid for my membership
Kevin