What benefits do larger diameter wheels have? I know you can fit larger brakes behind them, and for this post I'm not considering "looks" a benefit. Also, I read that wheels of larger diameter theoretically yield a higher top speed. Is this true? If so how? Also that larger wheels are harder to get going and have greater braking distances. Is there any formula of how many mphs of top speed is gained per in. of wheel?Same question for loss of acceleration and increased braking differences?

*This is all going off the wheels being of equal weight. Just different diameters.

 

When you upgrade to larger diameter wheels you need to keep the rolling radius the same as stock otherwise it will throw your speedo out.
This is achieved by using a larger wheel and a lower profile tire.The smaller tire wall is stiffer and improves cornering ability slightly.
Most people change wheels just for the looks,but weight reduction is also a factor.

 

I know what your saying, but let me change it up. Lets say you switched from a 16x8 to a 17x8. Instead of running a 245/45/17, you ran a 245/50/17. That would add up to be an one inch increase in over-all tire diameter. How would that affect the things I mentioned in my first post?

 

It would hinder acceleration and your speedo would read slower than you were actually going.(I think).You can have it reprogrammed by using one of those hypertech programmers,to allow for fluctuation of diameters.
Check the sticky at the top of the page about the frequently asked questions("general topics),it will be a lot more informative than me.LOL.

 

Larger Wheel Diameter (= larger INNER diameter, no effect on tire diameter)
1) larger brakes fit.
example:
16" 4th gen wheels will fit 11" rotors (LS1-style)... no more.
17" 4th gen wheels will fit 12" rotors (C5/C6 style)... no more.
18" vette rims will fit both the 12.5"rotors (C5/C6 style), as well as the 13" Z06 Monster brakes
19" vette rims will fit pretty much any brake you wanta stuff in there 9I believfe 14.5" rotors are possible)

how much brake you need depends on how often you brake hard in series (repeated stops). Racing... biggest, coolest braking you can afford is ideal. For daily driving, I find it unlikely anything more than LS1 brakes are nessesary (though I have a C6 upgrade myself cause I tend to overdo stuff like that; its a weakness ).

2) increased wheel weight, though somewhat offset by tire sidewall decrease... though usually guys go to WIDER wheels/tires as well... and that adds alot more weight.
example:
245/60zr16 on stock T/A rims (16"x8") = 45#
275/40zr17 on actual ZR1 rims (17"x9.5") = 50#
315/35zr17 on actual ZR1 rims (17"x11") = 52#

All 3 outer tire diameters are all the same, yet the WIDER rims obviously add more weight. you'll note however that the 17x9.5 rims are 1.5" wider than the 16x8" rims and weight 5 pounds more, while the 17x11 rims are 1.5" wider than the matching front wheels and only weighs 2# more. If you found a comparable 245 tire on 17x8" rims (like a mustang for example) you'd probably find they weigh about 48# (not 45# like our 245/16's).
Obviously weights will all vary a few pounds based on material, forging/casting patern, etc.., but the ones above are all GM-cast aluminum wheels (chromed), with new tires (tires range +/- a pound depending on mold). Worn out tires will usually be 1# or more lighter than a new tire.

TIRE OUTER DIAMETER
1) Top tire speed is determined by the tire construction itself... not the rim. Most Z-rated tires have datasheets that show the top speed possible on the tire and you'll see that top speed increases with the tire inflation pressure, and decreases with higher tire loads (how heavy the vehicle is). In top-speed runs (i.e. Bonneville Salt Flats) you tend to select tires that have 1) thread BLOCKS instead of STRIPS in the grip... more thread gaps = better cooling of the tread, and 2) narrow enough tires that still have the weight ratings to get the job done... wider (stock size) tires are nessesary for open road racing (160mph with CORNERS... ). In either sport I've heard that given the choice between two tire diameters (say a 25.5" tire and a 28" tire) the larger tire would be favored due to increased cooling even though it would add rotating weight. Not everyone agree's with these guidelines of course, but talking to open road racers in the area this are defintely factors those guys toss around when shopping for rubber.

2) top speed at the drag strip is different matter entirely, as are the tires used. Obviously you don't have miles and miles of road course or salt flats to get up to speed or plan on sustaining speeds near 200mph. The ability to dissipate heat in the LONG run (say 45 minutes+) is less of an issue.

In drag racing the outer tire diameter (at rest or after "ballooning" at the top end) will be choosen to complement the gearing of the car. If you have a car that is slightly "overgeared" you can drop it down somewhat by going to a larger tire diameter (on the drive tires... adjusting the "skinnies" diameter is unnessesary), this will be determined usually by shift points in the run, but can also be affected by the launch. Again, there are different ideas out there... some like smaller stock-like tires with 4.10's, while others will prefer a steeper gear like a 4.3 (arguably weaker than 4.10's) and larger rear tire ("potentially" more contact patch, and defintely more sidewall to wrinkle/load).


So yes... larger rims can fit larger brakes (allowing for better REPEATED stops), but they will weigh more causing more initial to overcom for braking/turing/acceleration. Larger tires will also weigh more, but they will cool better in top speed runs and give you more sidewall for better launches (and possibily a smoother ride, though the increased sidewall is offset by increased unsprung tire weight).

 

Larger diameter wheels, with shorter sidewall dimensions generally increase handling capabilites. But with the 4th Gen's live rear axle, the gains are limited. While a fully independant rear suspension may allow a 19" or 20" wheel/tire combo to handle increased cornering loads and improve the dynamics in transitions, the live rear axle can not provide the variable geometry required to compensate for the lack of flexibility in the shorter sidewall.