Andretti Posted March 16, 2018 Report Share Posted March 16, 2018 So I bought the Alcoa's a number of years ago and have been running them on my 2006 Mustang GT. At this point, I am needing to replace the tires as they are now exceeding 10+ years since manufacture. The problem is that I'd like to see if I have any option for running wider tires, but its been long enough since I purchased them from shelby that I no longer know what the offset of the rims are. I have phoned shelby directly and they seem to have no idea what the offsets were even available during the time frame I purchased them (approx 2008-09), so they suggested calling Alcoa directly, but I can't even get them to answer the phone to even ask. I also still have the bill of sale, and it is not listed on it. So my question would be is there any way to determine the offset by the inside stamping of the rims? Below is exactly what is either stamped into the wheel or etched (as noted) on the outer lip of the wheel. Here is what is listed inside each set of rims: For the 20X9's: Stamped: Alcoa Forged Made in the USA AF1247 20X9J T-DOT MACHINE DIE# GAO23621M 100209 On the rim edge is etched: B6HG87 #29 M-4 I currently have 255/35/r20 Hankook Ventus V12 evo's on these. For the 20X10's: Stamped: Alcoa Forded Made in the USA AF1246 20X10J T-DOT MACHINE DIE# GAO23619M 092309 On the rim edge is etched: G6HG98 #12 3M I currently have 275/35/r20 Hankook Ventus V12 evo's on these and am wondering if or how much wider I might be able to go. Any help would be appreciated. Andretti Quote Link to comment Share on other sites More sharing options...
William Rodgers Posted March 16, 2018 Report Share Posted March 16, 2018 I do not recall the offsets, someone will chime in to help. If you’ve been using them you already know they work, I’m not sure how offsets are going to help you, are they close to rubbing now? As far as wider tires do you have a Supercharger? If not it’s a waste of money IMO. I even have a Supercharger and I stuck with 275 back/255 front like you currently have. What type of driving do you do? Good luck!!! Quote Link to comment Share on other sites More sharing options...
Andretti Posted March 17, 2018 Author Report Share Posted March 17, 2018 3 hours ago, carnut12 said: I do not recall the offsets, someone will chime in to help. If you’ve been using them you already know they work, I’m not sure how offsets are going to help you, are they close to rubbing now? As far as wider tires do you have a Supercharger? If not it’s a waste of money IMO. I even have a Supercharger and I stuck with 275 back/255 front like you currently have. What type of driving do you do? Good luck!!! I was curious about the offsets because I'd really like to possibly go to 285/35 rears, but I assumed I'd need to know the offset of the wheels to help determine if they'd rub or not prior to installation (and thus too late). I have done a ton of mods on the car, but I haven't concentrated much a ton on engine performance. Upgrades thus far engine wise consist of a cold air intake, a set of 1-3/4 kook headers and the 3"X2-1/2" kook x pipe installed, and I had a performance tune made for it when I had it dyno'd last week after the header install. The headers and X pipe are the first stage for prepping for a 2.9 Whipple supercharger in the not too distant future. As far as driving goes, the car is just one I drive when I feel like it or when its nice out. I don't race it or anything like that and I only drive it in spring/summer/fall when the weather is nice. That being said, I dont 'need' a supercharger, but I've always wanted to get one for it, so that is the plan I'm sticking with. Quote Link to comment Share on other sites More sharing options...
Shelbygolfpro Posted March 17, 2018 Report Share Posted March 17, 2018 Can’t go wrong adding some forced induction! I’m running 2.3 whipple with around 550hp and it’s such a blast. Unfortunately, I can’t help you with the Alcoa offset, but if you are adding some blower power I definitely recommend at the minimum 285 in the rear even if you don’t get spirited very often. Good luck! Quote Link to comment Share on other sites More sharing options...
89Saleen215 Posted March 19, 2018 Report Share Posted March 19, 2018 The offsets are: 24mm (5.96" backspace) for the 20x9 and 36.7mm (6.97" backspace) for the 20x10. If you don't want to change the computer for the speedo then you should be able to run 295/30's with no rub. I did this for my first couple set's, but I didn't like the sidewall height. So I then ran a 295/35 and my latest is the max: 305/35's, but I have a tuner to fix the computer for the speedo. I have 275/35's on the front. HTH Quote Link to comment Share on other sites More sharing options...
08 ORANGE SS-725HP Posted March 21, 2018 Report Share Posted March 21, 2018 On 3/19/2018 at 2:53 AM, 89Saleen215 said: The offsets are: 24mm (5.96" backspace) for the 20x9 and 36.7mm (6.97" backspace) for the 20x10. If you don't want to change the computer for the speedo then you should be able to run 295/30's with no rub. I did this for my first couple set's, but I didn't like the sidewall height. So I then ran a 295/35 and my latest is the max: 305/35's, but I have a tuner to fix the computer for the speedo. I have 275/35's on the front. HTH How do the 305/35's fit in the back on the 10" rims? Do they stick out beyond the fender at the top and what clearance is there on the inside? If you have any pics, please post. Thanks Quote Link to comment Share on other sites More sharing options...
89Saleen215 Posted March 23, 2018 Report Share Posted March 23, 2018 (edited) Sorry if the pic's aren't that good, but here are some. These are BFG G-Force Comp-2 A/S tires that have a 12.3" section width and a 11.4" tread width. More specs can be found on TireRack (BFG G-Force). Edited March 23, 2018 by 89Saleen215 added pic Quote Link to comment Share on other sites More sharing options...
89Saleen215 Posted March 23, 2018 Report Share Posted March 23, 2018 ...and the last one... Quote Link to comment Share on other sites More sharing options...
tomshep Posted March 24, 2018 Report Share Posted March 24, 2018 I would do 275/35 front and 295/35 rear. Tom Quote Link to comment Share on other sites More sharing options...
Andretti Posted March 28, 2018 Author Report Share Posted March 28, 2018 (edited) On 3/19/2018 at 1:53 AM, 89Saleen215 said: The offsets are: 24mm (5.96" backspace) for the 20x9 and 36.7mm (6.97" backspace) for the 20x10. If you don't want to change the computer for the speedo then you should be able to run 295/30's with no rub. I did this for my first couple set's, but I didn't like the sidewall height. So I then ran a 295/35 and my latest is the max: 305/35's, but I have a tuner to fix the computer for the speedo. I have 275/35's on the front. HTH I just saw this, so thank you for the information. I've been looking for this for over a year now literally. I am a bit surprised though....I would have swore there were multiple options for the offset size , as I actually thought my 20X10's were like 43mm to 45mm. Do you know with any certainty if there was only the one size (I mean no offense, I'm extremely appreciative for ANY info at this point, so thank you very much)? I agree, I'd rather not spend the money to deal with the speedometer 'fix', so that might address the tire sizes I was considering. But to be honest, I didn't think I could fit something that big (305's) underneath the fender anyway....my 275's on the 20X10's are pretty close (I even have one rub mark). Thank you for your help! Andretti Edited March 28, 2018 by Andretti Quote Link to comment Share on other sites More sharing options...
Andretti Posted March 28, 2018 Author Report Share Posted March 28, 2018 On 3/23/2018 at 11:56 PM, tomshep said: I would do 275/35 front and 295/35 rear. Tom Would 275/35's fit without rubbing on the front using the 20X9'swith the mentioned offset?? I wasn't sure if he was only referring to the rears or what. I definitely want to go for a wider tire if I can. Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted March 28, 2018 Report Share Posted March 28, 2018 I have 275 on the front with no problem but that is with 20X10 Alcoa's. Not sure what the different offset would do. I don't think it would be a problem. Quote Link to comment Share on other sites More sharing options...
89Saleen215 Posted April 3, 2018 Report Share Posted April 3, 2018 I have 275's on the front using the 20x9's. Quote Link to comment Share on other sites More sharing options...
The Chairman Posted April 4, 2018 Report Share Posted April 4, 2018 Ditto. Have 275/35 on 20x9’s on the front and rear (which are 20x10’s). Can probably go 295’s on the rear with no problem as stock is 285’s on 9.5” rims. Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted April 4, 2018 Report Share Posted April 4, 2018 I have had 20x10 - 275 35 20 on my car since 2012 and I have never had a problem. I just ordered 305 for the rear. I will post the pictures in a couple weeks. Quote Link to comment Share on other sites More sharing options...
Andretti Posted April 4, 2018 Author Report Share Posted April 4, 2018 Thank you all for the replies about what you were able to run using the Alcoa's on your fronts. Hopefully I can use the info to make a more informed decision when I replace the tires shortly. Thanks again. Quote Link to comment Share on other sites More sharing options...
Andretti Posted April 4, 2018 Author Report Share Posted April 4, 2018 1 hour ago, sheppd01 said: I have had 20x10 - 275 35 20 on my car since 2012 and I have never had a problem. I just ordered 305 for the rear. I will post the pictures in a couple weeks. Please do. What brand of tire are you planning on? Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted April 4, 2018 Report Share Posted April 4, 2018 I have 20x10 275 35 20 Michelin SS front and back right now. I am going with firestone Indy 500 this time. It is cheaper than the Michelin SS and I could not find those in the size I needed anyway. Quote Link to comment Share on other sites More sharing options...
Glenn Greenwell Posted April 4, 2018 Report Share Posted April 4, 2018 Running Firestones on my Shelby and really like the ride and handling. GG Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted April 7, 2018 Report Share Posted April 7, 2018 The tires have arrived. I hope to have them on this Tuesday. Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted April 9, 2018 Report Share Posted April 9, 2018 They are on and fit just fine. Quote Link to comment Share on other sites More sharing options...
sheppd01 Posted May 1, 2018 Report Share Posted May 1, 2018 Update. 305/35/20 Firestone Indy 500 tire will rub on a stock height KR but just barely. So they go on the other car. Quote Link to comment Share on other sites More sharing options...
tomshep Posted September 10, 2018 Report Share Posted September 10, 2018 I am running Nitto Invo. SS run large and the 295/35s I used had the death wobble. Search it if you are unfamiliar. Invos run a little small or average. Nice ride, nice price. Tom Quote Link to comment Share on other sites More sharing options...
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