Previous Thread
Next Thread
Print Thread
Tire Diameter Selection #2611075
01/23/19 03:08 PM
01/23/19 03:08 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
73 Cuda, 340, 727TF, with 3.55 gears. Is there an optimum rear tire diameter for this gear? Obviously diameter affects motor rpm at highway cruise but there is also an effect on how the car accelerates out of the hole and off a corner. I'm trying to plan for new wheels and tires and tire size will determine what wheel and offset I get. I want to go with 18" wheels because the selection of performance tires is better than 15 or 17. Got a B-body rear for it and will install with the offset spring shackles. Want as much width as I can safely get (285 min) but there are options for height from 25"-29". How have you compromised? Seems that 25-26" is the sweet spot?

Re: Tire Diameter Selection [Re: gzig5] #2611318
01/23/19 11:36 PM
01/23/19 11:36 PM
Joined: Nov 2004
Posts: 25,050
Texas
GoodysGotaCuda Offline
5.7L Hemi, 6spd
GoodysGotaCuda  Offline
5.7L Hemi, 6spd

Joined: Nov 2004
Posts: 25,050
Texas
I suppose you should consider which factors are most important for you and the intended use.

Autocross, road course and street driving have different requirements, then throw aesthetics into the mix, if that is much of a concern. Since you probably have tires now, I would run a few courses and see where you think the car needs the rpms to go, are you lugging the engine often? or are you taching it out often but there isn't quite enough time to upshift before the next turn? Adjusting tire height can help tune to the application.

A taller tire will tend to hold straightline traction better due to being able to absorb more torque within the sidewall. On the other side, it will generate a higher slip angle during cornering. As with most things, it's all somewhat of a compromise on what your car needs the grip the most.

Aesthetically, I run 27" tall front tires and 28.5" rear tires with 17" and 18" wheels on my e-body. I like having tall tires and am not the biggest fan of rubber band tire looks. However, they are quite a bit heavier than their shorter friends. A 26.2" 295-series tire is 30lbs and a 28.5" 295-series tire is 33.5lbs, 7lbs heavier per axle in rotating weight...which is far worse than static weight. For my intended use [spirited street], that doesn't matter much. In the same breath I also run a close ratio 6-speed, it's hard to not have the right gear for the situation with that many to choose from.


1972 Barracuda - 5.7L Hemi, T56 Magnum 6spd - https://www.facebook.com/GoodysGotaHemi
2020 RAM 1500
[img]https://i.imgur.com/v9yezP9.jpg[/img]
Re: Tire Diameter Selection [Re: gzig5] #2611453
01/24/19 08:37 AM
01/24/19 08:37 AM
Joined: Dec 2003
Posts: 22,695
Bitopia
J
jcc Offline
If you can't dazzle em with diamonds..
jcc  Offline
If you can't dazzle em with diamonds..
J

Joined: Dec 2003
Posts: 22,695
Bitopia
I would pick the best tire for the car, and say if a 295/35/18 fits, I'd change the rear end ratio to fine tune, rather then the other way around, having a spare ratio rear end is nice. Since this is the "handling section", and you run a TF, I'd lean towards a 2.94, being 3.23 is not enough change for the effort, and 3.08 is very rare. Also Pick your tire on future likely availability if this a driver, which seems always risky nowadays. I had to wait nearly a year to get my replacement 295's, although the supply seems to have improved in the last year or so. Tires are the most important handling decision one makes, and wider is always better. biggrin

On my DD,

Summit:
Bridgestone Potenza RE760 Sport Tires 102349
Bridgestone 102349 - Bridgestone Potenza RE760 Sport Tire


https://static.summitracing.com/global/images/prod/large/bdg-078345.jpg?rep=True
Not Available


Tire, Potenza RE760 Sport, 295/35-18 Radial, 99 Load Range, W Speed Rated, Blackwall, Each


Bridgestone Potenza RE760 Sport Tire

Brand:Bridgestone
Manufacturer's Part Number:102349
Part Type:Tires
Product Line:Bridgestone Potenza RE760 Sport Tires
Summit Racing Part Number:BDG-102349

Wheel Diameter: 18 in.
Tire Size: 295/35-18
Sidewall Style: Blackwall
Tire Construction: Radial
Tire Diameter: 26.10 in.
Section Width: 11.85 in.
Minimum Recommended Wheel Width: 10.00 in.
Maximum Recommended Wheel Width: 12.00 in.
Directional: No
Speed Rating: W
Load Index: 99
Asymmetrical Tread Pattern: Yes
UTQG Tread Wear Rating: 340
Traction Rating: A
Tread Depth: 10/32 in.
DOT-Approved: Yes
Run-Flat Technology: No
Tube Required: No
Max Load Single (lbs): 1,709
Quantity: Sold individually.

Bridgestone Potenza RE 760 Sport tires let you drive in any car, on any road, with maximum driving pleasure. The moment you shift gears and turn the wheel, the RE 760 Sport tires go into action, giving you quick response and precision control. The RE 760 Sport tires feature inside offset twin ribs, a semi-slick shoulder design, a 3D center block, and wide straight grooves, so you'll appreciate their ability to hug, hold, turn, and stop on any road condition--wet or dry. You'll be comfortable and secure riding on Bridgestone tires.


Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
Re: Tire Diameter Selection [Re: jcc] #2611509
01/24/19 12:26 PM
01/24/19 12:26 PM
Joined: Jan 2003
Posts: 5,385
Pikes Peak Country
T
TC@HP2 Offline
master
TC@HP2  Offline
master
T

Joined: Jan 2003
Posts: 5,385
Pikes Peak Country
Originally Posted By jcc
Also Pick your tire on future likely availability if this a driver, which seems always risky nowadays. I had to wait nearly a year to get my replacement 295's, although the supply seems to have improved in the last year or so. Tires are the most important handling decision one makes, and wider is always better.


Anymore, tire sizes are changing so rapidly that the above bolded can be pretty relevant to continued availability. If you can find a size that was available OEM on a vehicle, or better yet, several vehicles, the odds of it being around longer are much improved over an oddball size, perfect fit, but diminishing availability tire.

Re: Tire Diameter Selection [Re: gzig5] #2611692
01/24/19 05:37 PM
01/24/19 05:37 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
I'm probably overthinking this but it's freaking cold out and the car is in offsite storage so I can't pop out to the garage to ponder my questions.

Goody,
I've always appreciated the stance on your setup and I'd run that for a daily but I bet there are better handling combos out there. Maybe that is the solution, an extra setup for the weekend fun?

The wheels/tires on it now are a hodge-podge of crap I put on to replace the 20yr old stuff it came with so it would be safe to go on the highway as cheaply as possible. I wouldn't think of doing an event with 255/70-15 Coopers on the back. They are 29" tall but they look pretty cool. I've got an A833 OD manual trans that will go in at some point down the road and help with highway rpm, but right now there are other priorities. Car has a ways to go

IMG_1669.jpg
Last edited by gzig5; 01/24/19 05:38 PM.
Re: Tire Diameter Selection [Re: gzig5] #2611822
01/24/19 10:15 PM
01/24/19 10:15 PM
Joined: Nov 2004
Posts: 25,050
Texas
GoodysGotaCuda Offline
5.7L Hemi, 6spd
GoodysGotaCuda  Offline
5.7L Hemi, 6spd

Joined: Nov 2004
Posts: 25,050
Texas
Originally Posted By gzig5
I'm probably overthinking this but it's freaking cold out and the car is in offsite storage so I can't pop out to the garage to ponder my questions.

Goody,
I've always appreciated the stance on your setup and I'd run that for a daily but I bet there are better handling combos out there. Maybe that is the solution, an extra setup for the weekend fun?

The wheels/tires on it now are a hodge-podge of crap I put on to replace the 20yr old stuff it came with so it would be safe to go on the highway as cheaply as possible. I wouldn't think of doing an event with 255/70-15 Coopers on the back. They are 29" tall but they look pretty cool. I've got an A833 OD manual trans that will go in at some point down the road and help with highway rpm, but right now there are other priorities. Car has a ways to go



I still don't understand what the end goal is here. What type of "event"?
How low of a treadwear can you live with? Compound has an enormous impact on handling, much more so than a specific size.
What else has been done to the car?



1972 Barracuda - 5.7L Hemi, T56 Magnum 6spd - https://www.facebook.com/GoodysGotaHemi
2020 RAM 1500
[img]https://i.imgur.com/v9yezP9.jpg[/img]
Re: Tire Diameter Selection [Re: gzig5] #2612013
01/25/19 12:53 PM
01/25/19 12:53 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
Events would consist of a few auto-x events and as many track days I can fit in at Road America, Autobahn, and wherever else I can get to. Car is in no way ready currently. I bought it in non-running shape in April and had to put it up in November. Made progress but still a ways to go. So goal is get it as capable on the track as I can and still be able to drive it several times a week. I'm not afraid to run a track oriented tire on the street. Original question was prompted by boredom and how drag racers will change/optimize their gear based on the tire they are running. I was going the other way, tire size based on gear. Probably a moot point for road course and will be more influenced by what performance tires are available in certain sizes.

Re: Tire Diameter Selection [Re: gzig5] #2612166
01/25/19 06:05 PM
01/25/19 06:05 PM
Joined: Jan 2010
Posts: 1,440
NW Chicago suburban area
Mopar Mitch Offline
pro stock
Mopar Mitch  Offline
pro stock

Joined: Jan 2010
Posts: 1,440
NW Chicago suburban area
gzig -- As for events, and that I see you live just north of Milwaukee, consider the Milwaukee region SCCA and the WAI pylon racing groups... they hold most of their events at the Brewer's Stadium during the Spring-Summer-Fall.

For track days, consider looking at the events hosted by www.mcscc.org (midwestern council of sports car clubs)... most events held at Blackhawk Farms, also one at Milwaukee mile, and one at Road america, and sometimes one at the Joliet Autobahn. HPDE typically morning, then HSAX afternoon. As I'm an active member of the MCSCC (President of the www.NSSCC.org ), we are also looking at hosting "Street Car Battles" which will combine timed HPDE with HSAX... details in the works for season 2019.

Good luck with getting the car running and setup... I suggest that you have two-sets of rims.tires... regular cruising (could easily be taller 15" tires, such as 245-60/255/60/275/60 - 15s along with a set of low-profile 17 or 18" tires, at least 275-40-17 f/r on the perfect-fit Year One 17x9 rims f/r with some 200 TW tires... or jump to 18x9 or 10 and run 275-35-18 f/r tires of 200 TW.. many more tire choice within 18" diameters.... seek 200 TW for best compromise of street/hwy/track.

IF you'd choose 16" rims, then at least 16x8 rims with an easy 255-50-16 size.. from BFG Comp series (I run these for HPDE/HSAX track events... TW ~340?... yes there are better softer tires, but they're not bad... and I already have the 16x8 rims... vintage mini-lites, as well as 15x8 same rims with BFG T/A 255-60, 275-60 tires for "cruising").

Regardless, be willing to flush your fender lips as needed and stiffen your suspension... get some bigger torsion bars (at least 1.12 dia), and stiffer leafs... and I recommend double adjustable shocks (QA1 or Viking etc)... and of course bigger sway bars f/r... and then a better driver's seat with a harness.

And the list goes on-and-on-and.

I hope to meet you someday at a local event... Plan to come to Blackhawk Farms the wknd of July 5-6-7 as I'll be co-Chairman of that race wknd for MCSCC NSSCC. I crave for Mopars to join the fun!

Last edited by Mopar Mitch; 01/25/19 06:08 PM.

Mopar Mitch "Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers! Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!
Re: Tire Diameter Selection [Re: gzig5] #2612180
01/25/19 06:34 PM
01/25/19 06:34 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
Thanks Mitch, Good stuff there. I'm already saving for Viking shocks and big torsion bars. Lots of stuff to do and I may be a little premature in this but it's fun to discuss and gather information. Pretty sure that I'll be on 18" wheels due to the better tire selection and ability to fit big brake rotors. I have a total of $200 in the brand new tires and wheels the car is riding on now but the offset on the rears is not optimal and that tire is right at the fender. They'll get me by as I work on the higher priority items. Like I said, it isn't ready for the track yet, but I have a set of 13.5" rotors and calipers off my E39 M5 that I'm going to see if I can adapt to the stock spindle. If that doesn't work out, I'll do one of the 13" kits that Dr Diff has. Definitely will need more brake capacity than the stock disks. Just ran out of time this fall before I had to take it to storage. Going stir crazy thinking about it and not being able to work on it.

Re: Tire Diameter Selection [Re: gzig5] #2612564
01/26/19 02:17 PM
01/26/19 02:17 PM
Joined: Jan 2003
Posts: 5,385
Pikes Peak Country
T
TC@HP2 Offline
master
TC@HP2  Offline
master
T

Joined: Jan 2003
Posts: 5,385
Pikes Peak Country
Originally Posted By gzig5
Events would consist of a few auto-x events and as many track days I can fit in at Road America, Autobahn, and wherever else I can get to. Car is in no way ready currently. I bought it in non-running shape in April and had to put it up in November. Made progress but still a ways to go. So goal is get it as capable on the track as I can and still be able to drive it several times a week. I'm not afraid to run a track oriented tire on the street. Original question was prompted by boredom and how drag racers will change/optimize their gear based on the tire they are running. I was going the other way, tire size based on gear. Probably a moot point for road course and will be more influenced by what performance tires are available in certain sizes.


RE the bolded; maybe for higher end guys or those with modular/quick change axles who can change gears by two teeth and do it in ten minutes. For the average bracket racer, a gear set with third member is easily $1500 plus plus an hour to change the gears. Compared to a $200 pair of slicks, it much cheaper and easier to swap tires.

SO, your optimal rear tire size is 25=26" tall. You want to put a 275/35R17 under there. This has a broad range of street, UHP, and race tires available in prices from $100-500 each...or copy Rylispro's 315 square set up on his Cuda.

Re: Tire Diameter Selection [Re: TC@HP2] #2612587
01/26/19 02:50 PM
01/26/19 02:50 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
Originally Posted By TC@HP2
or copy Rylispro's 315 square set up on his Cuda.


This isn't out of the question if I can get light wheels with the correct offset that won't break my retirement fund. Might have a work an extra six months before I go just to fund car stuff!

Re: Tire Diameter Selection [Re: gzig5] #2612761
01/26/19 09:02 PM
01/26/19 09:02 PM
Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
goldduster318 Offline
pro stock
goldduster318  Offline
pro stock

Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
Not sure how it would look, but 275-35-18 is a tire size with a huge amount of choices. I have them on my car - I have some more "streetish" Continental ExtremeContact DW tires (IIRC 340 treadwear). There are several amazing tires in 200 treadwear available in that size.

My opinion is also that 18" wheels are the optimum size for a 25-27" tall tire in a handling application.


'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
Re: Tire Diameter Selection [Re: gzig5] #2612782
01/26/19 09:45 PM
01/26/19 09:45 PM
Joined: Jun 2018
Posts: 350
Mequon, WI
G
gzig5 Offline OP
enthusiast
gzig5  Offline OP
enthusiast
G

Joined: Jun 2018
Posts: 350
Mequon, WI
I've got a square setup on my 2000 BMW M5 running 275/35-18 with Pilot Super Sports. Fantastic street tires that do pretty well on the track. I wish I could fit those wheels on the Cuda but the pattern is wrong, but I do know the tire will fit with the right backspace on a stock rear end. I'm hoping to fit a wider tire in the back, as much for look as performance. The BMW is going down the road this spring to make room for the Cuda.







Powered by UBB.threads™ PHP Forum Software 7.7.1