New tires, now problems?
Thread Starter
Pro
Joined: Apr 2007
Posts: 635
Likes: 0
From: Mc Farland Wisconsin
New tires, now problems?
Hey guys, i bought some new tires and had them mounted today. car is a 2000 m6 coupe, had 335/30 r18 on the rear and i bought 315/30 r18 to replace, the tires were alot cheaper for being a little bit smaller. The fronts are 285/40r17 if that matters. I left the shop and now i get a traction control message on the DIC with even a little bit of spin which was normal but it stayed on longer than normal. About a 1/2 mile down the road is a large hill, and it curves around and while going up that hte traction control message went on and stayed on all the way up and down the hill until the next curve, total time about 1/4 mile, and it cut me down to about 20 mph. Is this just a coincidence and there is a different issue, or does it have something to do with my new tires?
Thanks in advance!
Thanks in advance!
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Rule 1 when altering tire sizes...Always keep the rear tires taller than the fronts.
You picked a very short rear tire, and have a rather tall front tire. Bad combination.
Traction Control works by monitoring the front and rear wheel speeds. When it detects the rears turning faster than the fronts, TC engages and cuts power. Tire diameter obviously affects that wheel speed "logic" as the hub sensors report.
Your two options at this point are to:
Size your tires so that the rears are taller than the fronts, or...
Turn off Traction Control after you start the car.
You picked a very short rear tire, and have a rather tall front tire. Bad combination.
Traction Control works by monitoring the front and rear wheel speeds. When it detects the rears turning faster than the fronts, TC engages and cuts power. Tire diameter obviously affects that wheel speed "logic" as the hub sensors report.
Your two options at this point are to:
Size your tires so that the rears are taller than the fronts, or...
Turn off Traction Control after you start the car.
Thread Starter
Pro
Joined: Apr 2007
Posts: 635
Likes: 0
From: Mc Farland Wisconsin
But they are smaller width wise...I just went out and measured and sure as $hit, the rears are shorter than the fronts...I just looked for tires and it also seems that finding a smaller tire for my front is fairly impossible, as I beleive i would need something in the range of a 275/35 r17. Soooo, does anybody want to buy some very good shape 285/40 17? 
Pro
Joined: Oct 2006
Posts: 588
Likes: 1
From: Santa Ynez Ca.
Does anyone know how much taller the rear must be to avoid the DIC message. I'm getting ready to mount 275/35/18's on the front and 305/30/19's on the rear. The diameter of the fronts is 25.6 and the rear is 26.2 for a difference of only .6" larger in the rear. Is this enough to avoid having a problem? Thanks for any advice.
Melting Slicks
Joined: Oct 2007
Posts: 2,383
Likes: 13
From: Kinston North Carolina
Consusis is 1/2 inch from what I've read here. It probably varies car to car, that's just my opinion. (not worth much
) I ran a set for about a week, 1/4 inch taller in the rear, no codes. YMMV
) I ran a set for about a week, 1/4 inch taller in the rear, no codes. YMMV
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Le Mans Master
Joined: May 2005
Posts: 6,366
Likes: 249
From: Fort Lauderdale, Florida
You should be able to find a 275/40 for the front though it might not be short enough. You should run a 35 series tire in the rear. 1/2" difference is enough front to rear diameters.
Pro
Joined: Oct 2006
Posts: 588
Likes: 1
From: Santa Ynez Ca.
According to the tire calculator I get .6" difference running a 275/35/18 front and a 305/35/19 rear. If .6" is enough difference I'd like to stay with the 35 series in the front to keep the visual sidewall measurement as close as possible. I think they look better that way.
Thanks for your comments.
Thanks for your comments.
Team Owner
Joined: Mar 1999
Posts: 28,753
Likes: 9
From: San Jose/Bear Valley CA
CA Events Coordinator
Rule of thumb used to be one inch from front to rear. We have found out over the years some cars can run the same size front and rear and not have a problem while others go crazy. 
Too bad you had to find this out after you purchased new tires.
Too bad you had to find this out after you purchased new tires.
Tech Contributor
Joined: Jan 2007
Posts: 19,398
Likes: 1,139
From: Dyer, IN
Rule 1 when altering tire sizes...Always keep the rear tires taller than the fronts.
You picked a very short rear tire, and have a rather tall front tire. Bad combination.
Traction Control works by monitoring the front and rear wheel speeds. When it detects the rears turning faster than the fronts, TC engages and cuts power. Tire diameter obviously affects that wheel speed "logic" as the hub sensors report.
Your two options at this point are to:
Size your tires so that the rears are taller than the fronts, or...
Turn off Traction Control after you start the car.
You picked a very short rear tire, and have a rather tall front tire. Bad combination.
Traction Control works by monitoring the front and rear wheel speeds. When it detects the rears turning faster than the fronts, TC engages and cuts power. Tire diameter obviously affects that wheel speed "logic" as the hub sensors report.
Your two options at this point are to:
Size your tires so that the rears are taller than the fronts, or...
Turn off Traction Control after you start the car.
Instructor
Joined: Aug 2009
Posts: 182
Likes: 1
From: Burlington Ontario
285/40R17 OD26.0
315/30R18 OD25.4
335/30R18 OD25.9
Thats totally off. Your rear tire needs to be around 26.8 - 27.0
You should have had an issue with the 335s as well. On the 18 inch wheels you need to up the profile by 1 size. From a 30 to a 35
Rod
DreamTire
315/30R18 OD25.4
335/30R18 OD25.9
Thats totally off. Your rear tire needs to be around 26.8 - 27.0
You should have had an issue with the 335s as well. On the 18 inch wheels you need to up the profile by 1 size. From a 30 to a 35
Rod
DreamTire
Race Director
Joined: Oct 2002
Posts: 16,477
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Hmmmm.....not soo sure this logic applies here. I must know a dozen guys(including myself) running stock size up front (245/45/17) and 315/30/18 drag radials. By your suggestion, this should cause a significant problem, because there is even more of a disparity in the height(aspect ratio) between front and rear. In all cases, no problems, including myself.
Aspect ratio is the sidewall dimension expressed as a percentage of the tire's width.
40% 0f 285 is a greater value that 45% of 245 is.
In this example, his 285/40s are about 3/8" taller than your front tires.
On paper, the 245/45/17 and 315/30/18 combo should also cause occasional false TC engagement...but if you find it's working for you, then consider yourself lucky. (Oh wait, seems you already do
)
Tech Contributor
Joined: Jan 2007
Posts: 19,398
Likes: 1,139
From: Dyer, IN
You do realize the 245/45/17 is a shorter tire than the 285/40/17 the OP is running on the front?
Aspect ratio is the sidewall dimension expressed as a percentage of the tire's width.
40% 0f 285 is a greater value that 45% of 245 is.
In this example, his 285/40s are about 3/8" taller than your front tires.
On paper, the 245/45/17 and 315/30/18 combo should also cause occasional false TC engagement...but if you find it's working for you, then consider yourself lucky. (Oh wait, seems you already do )
Aspect ratio is the sidewall dimension expressed as a percentage of the tire's width.
40% 0f 285 is a greater value that 45% of 245 is.
In this example, his 285/40s are about 3/8" taller than your front tires.
On paper, the 245/45/17 and 315/30/18 combo should also cause occasional false TC engagement...but if you find it's working for you, then consider yourself lucky. (Oh wait, seems you already do
)
Team Owner
Joined: Mar 1999
Posts: 28,753
Likes: 9
From: San Jose/Bear Valley CA
CA Events Coordinator
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
The other thing to consider is how many folks running drag radials actually leave TC on all the time. That's all it takes for this to become a non-issue.