Tire experts. Lowering sidewall. Any setbacks?
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,066
Likes: 0
From: Crofton MD
Tire experts. Lowering sidewall. Any setbacks?
I am replacing my runflats with BFG KDW-2's most likely.
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
Le Mans Master
Joined: Oct 2005
Posts: 8,641
Likes: 1
From: Location : Location :
Originally Posted by Hammie
I am replacing my runflats with BFG KDW-2's most likely.
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
Going to a 275/40 up front would be a nice choice up front instead of 255/ 40 and would give you the same side wall . 295/35 out back is close to the same size in side wall so I dont think you will fell much differance. The site that I like to use to look at tire sizes is this one check it out
http://www.miata.net/garage/tirecalc.html
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,066
Likes: 0
From: Crofton MD
Very good info. I appreciate your help. I don't want to go to a 275 up front because that'll be pretty expensive compared to what I'm doing now. I'm only on thinspokes, too, not Z06's. Will the 255/40 be okay matched with the 295/35 in the rear?
Burning Brakes
Joined: Feb 2001
Posts: 936
Likes: 0
From: Reston VA
A couple of things to consider:
If you are going to use the stock rims, the KDW2 for the front fall at the edge of the limitations for the 8.5” rim (8.5 “– 10”) and are designed for a 9” rim. This means that while the tire would fit, it will not fully expand to it’s normal width. The rear however, will not meet the tire’s design criteria of 10”-11.5”/ designed for 10.5”, so I wouldn't do that if I were you. Generally speaking, because of their smaller diameter, lower profile tires on stock wheels will lower the care slightly (depending on the tire), make the ride a bit harder and require more RPM’s to go the same speed as stock sizes. Alignment might come into play as well. Now I’m not saying you shouldn’t do it. Just offering some food for thought. Do your homework and you’ll be OK. Good luck. – C.
If you are going to use the stock rims, the KDW2 for the front fall at the edge of the limitations for the 8.5” rim (8.5 “– 10”) and are designed for a 9” rim. This means that while the tire would fit, it will not fully expand to it’s normal width. The rear however, will not meet the tire’s design criteria of 10”-11.5”/ designed for 10.5”, so I wouldn't do that if I were you. Generally speaking, because of their smaller diameter, lower profile tires on stock wheels will lower the care slightly (depending on the tire), make the ride a bit harder and require more RPM’s to go the same speed as stock sizes. Alignment might come into play as well. Now I’m not saying you shouldn’t do it. Just offering some food for thought. Do your homework and you’ll be OK. Good luck. – C.
Tech Contributor
Joined: Oct 1999
Posts: 41,062
Likes: 9,825
From: Charlotte, NC (formerly Endicott, NY)
You want to stay within reason on the front to back diameter relationship. The original sizes show 25.7 and 26.7 in diameters respectively. The front tires are 96.2% of the rears. I have run 25.3 diameter front and rear (100%) and haven't had any issues with ABS, TC or AH which use relative wheelspeeds as part of their activation algorithm. I know if the rear tire has a smaller diameter than the front (> 100%) the TC will activate the rear brakes. The sizes you are thinking about are 25 and 26.1 in diameter and look like they pretty closely hold to the stock relationship (95.7% for the new combo). I am not sure how much smaller the front tire can be in relationship to the rear before there would be problems from going to small. But, I do have to believe as long as you do not go below 93% the systems will still work as they should.
Bill
Bill
Pro
Joined: Dec 2003
Posts: 502
Likes: 1
From: Fountain hills AZ
Originally Posted by Hammie
I am replacing my runflats with BFG KDW-2's most likely.
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
Race Director
Joined: Jan 2002
Posts: 19,557
Likes: 1,470
From: I love you & miss you Linda
2017 C7 of the Year Finalist
St. Jude Contributor
Originally Posted by Mr. C's 5
A couple of things to consider:
If you are going to use the stock rims, the KDW2 for the front fall at the edge of the limitations for the 8.5” rim (8.5 “– 10”) and are designed for a 9” rim. This means that while the tire would fit, it will not fully expand to it’s normal width. The rear however, will not meet the tire’s design criteria of 10”-11.5”/ designed for 10.5”, so I wouldn't do that if I were you. Generally speaking, because of their smaller diameter, lower profile tires on stock wheels will lower the care slightly (depending on the tire), make the ride a bit harder and require more RPM’s to go the same speed as stock sizes. Alignment might come into play as well. Now I’m not saying you shouldn’t do it. Just offering some food for thought. Do your homework and you’ll be OK. Good luck. – C.
If you are going to use the stock rims, the KDW2 for the front fall at the edge of the limitations for the 8.5” rim (8.5 “– 10”) and are designed for a 9” rim. This means that while the tire would fit, it will not fully expand to it’s normal width. The rear however, will not meet the tire’s design criteria of 10”-11.5”/ designed for 10.5”, so I wouldn't do that if I were you. Generally speaking, because of their smaller diameter, lower profile tires on stock wheels will lower the care slightly (depending on the tire), make the ride a bit harder and require more RPM’s to go the same speed as stock sizes. Alignment might come into play as well. Now I’m not saying you shouldn’t do it. Just offering some food for thought. Do your homework and you’ll be OK. Good luck. – C.
ESPECIALLY with the 295/35 on a 9.5" rim 
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Michael S. Palmer
Pro
Joined: Dec 2003
Posts: 502
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From: Fountain hills AZ
Originally Posted by Hammie
I am replacing my runflats with BFG KDW-2's most likely.
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
I want to go from the stock
245/45/17 and 275/40/18
to
255/40/17 and 295/35/18
I wanted to go wider just so I won't slide out anymore, but my MAIN concern is ride quality. I like a nice ride, which I'm sure will be better after the runflats anyhow. Will these drops in sidewall make much of a difference? I understand the drop won't be TOO much, since I went a bit wider, but what do you all think?
Melting Slicks
Joined: Sep 2005
Posts: 2,625
Likes: 1
From: Rhode Island
Originally Posted by Hammie
Very good info. I appreciate your help. I don't want to go to a 275 up front because that'll be pretty expensive compared to what I'm doing now. I'm only on thinspokes, too, not Z06's. Will the 255/40 be okay matched with the 295/35 in the rear?
Race Director
Joined: Aug 2003
Posts: 16,270
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From: "It's 106 miles to Chicago, we've got a full tank of gas, half a pack of cigarettes, it's dark, and
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-‘18-'19
NCM Sinkhole Donor
I'm running a 275-35x18 on a 9" rim in front and a 305-30x19 on a 10" rim in back. Overall height of the respective tires are as follows:
OEM Height Revs/Mile@45mph
F)245-45x17 25.7 809
R)275-40x18 26.6 783
New
F)275-35x18 25.6 814
R)305-30x19 26.25 788
Source:
http://www.michelinman.com/assets/pd...otsportps2.pdf
As you can see - I haven't dramatically changed the overall height of the tire/wheel combo - I've dramatically changed the appearance of the car by filling the wheel wells and increased the footprint, all without changing the stagger (the relationship of the sizes front to rear) or number over revolutions per wheel, which should keep the speedo pretty much as is.
Even though I've gone to a much lower profile (aspet ratio) tire - the ride quality doesn't seem to have been degraded. The car still rides very good, even with Bilstein Sport shocks, lowering and Hotchkis sways. I went with the Michelin PS2 - and so far I'm very happy with that choice.
The BFG KDW is what I had previously and I liked them a lot, great ride, quiet and pretty sticky.
OEM Height Revs/Mile@45mph
F)245-45x17 25.7 809
R)275-40x18 26.6 783
New
F)275-35x18 25.6 814
R)305-30x19 26.25 788
Source:
http://www.michelinman.com/assets/pd...otsportps2.pdf
As you can see - I haven't dramatically changed the overall height of the tire/wheel combo - I've dramatically changed the appearance of the car by filling the wheel wells and increased the footprint, all without changing the stagger (the relationship of the sizes front to rear) or number over revolutions per wheel, which should keep the speedo pretty much as is.
Even though I've gone to a much lower profile (aspet ratio) tire - the ride quality doesn't seem to have been degraded. The car still rides very good, even with Bilstein Sport shocks, lowering and Hotchkis sways. I went with the Michelin PS2 - and so far I'm very happy with that choice.
The BFG KDW is what I had previously and I liked them a lot, great ride, quiet and pretty sticky.
Last edited by blacksedan87; Feb 13, 2006 at 02:01 PM.
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,066
Likes: 0
From: Crofton MD
So I'm missing something here. I know I need to keep my diameters about the same, and keep the front diameter smaller than the rear. However, I'm getting mixed reviews about my sizes. Some of you seem to say not to do it on my 8.5 and 9.5 sized rims, some seem to say its okay. I don't know which advice to take. The BFG KDW-2's don't seem to come in a better size for my app, unless you guys have a recommendation? I really value your advice if you do have a better size recommendation:
http://www.tirerack.com/tires/Sizes....ce+T%2FA+KDW+2
Thanks everyone.
http://www.tirerack.com/tires/Sizes....ce+T%2FA+KDW+2
Thanks everyone.
Race Director
Joined: Aug 2003
Posts: 16,270
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From: "It's 106 miles to Chicago, we've got a full tank of gas, half a pack of cigarettes, it's dark, and
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-‘18-'19
NCM Sinkhole Donor
Originally Posted by Hammie
So I'm missing something here. I know I need to keep my diameters about the same, and keep the front diameter smaller than the rear. However, I'm getting mixed reviews about my sizes. Some of you seem to say not to do it on my 8.5 and 9.5 sized rims, some seem to say its okay. I don't know which advice to take. The BFG KDW-2's don't seem to come in a better size for my app, unless you guys have a recommendation? I really value your advice if you do have a better size recommendation:
http://www.tirerack.com/tires/Sizes....ce+T%2FA+KDW+2
Thanks everyone.
http://www.tirerack.com/tires/Sizes....ce+T%2FA+KDW+2
Thanks everyone.
http://www.bfgoodrichtires.com/asset...rce_ta_kdw.pdf
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,066
Likes: 0
From: Crofton MD
Originally Posted by blacksedan87
According to the size chart that I posted above - the front should be okay as the minimum recommended size is a 8.5" for a 255. The back shows a minimum of a 10" for a 295. I went with a 305 on a 10" which is slightly small. For a tire that wide, the chart calls for a minimum of a 10.5" in my application. You won't be committing a cardinal sin - it's just not the optimal combination. A 285-35x18 would be a better size and it is available in the tire you've selected ........
http://www.bfgoodrichtires.com/asset...rce_ta_kdw.pdf
http://www.bfgoodrichtires.com/asset...rce_ta_kdw.pdf
Race Director
Joined: Aug 2003
Posts: 16,270
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From: "It's 106 miles to Chicago, we've got a full tank of gas, half a pack of cigarettes, it's dark, and
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-‘18-'19
NCM Sinkhole Donor
Originally Posted by Hammie
Hey there, I dont see 285/35/18. There's 285/40/18, but wouldn't that cause a problem mated up with my 255/40/17?
You're right - I glanced at it and mis-read it. :o I would go with the 295-35x18. That 1/2" in rim width isn't going to be a big issue.
Here's an angle that might show you how mine looks.....
Last edited by blacksedan87; Feb 13, 2006 at 02:42 PM.
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,066
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From: Crofton MD
In order to just save a lot of headache, I may go with the NITTO 555's, since they seem to carry our stock sizes. However, the rear is P275/40 ZR18 103W. Is the P at the beginning anything I need to worry about? Sorry if it's a stupid q but i'm not entirely smart on rubber.
EDIT: Or I can go 255/40/17 and 285/35/18. This looks like it will fit without problems. Again, advice is valued. My car doesnt make much power over stock, just intake and exhaust. Just want something that'll look nice and ride well.
EDIT: Or I can go 255/40/17 and 285/35/18. This looks like it will fit without problems. Again, advice is valued. My car doesnt make much power over stock, just intake and exhaust. Just want something that'll look nice and ride well.
Last edited by Hammie; Feb 13, 2006 at 02:57 PM.
Burning Brakes
Joined: Feb 2001
Posts: 936
Likes: 0
From: Reston VA
Originally Posted by Hammie
Hey there, I dont see 285/35/18. There's 285/40/18, but wouldn't that cause a problem mated up with my 255/40/17?
The 27" diameter and 771 revs per mile is not too far of the EMT's 26.7/781. Might work. - C.
Race Director
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
I would stick with your original planned sizes..the 255/295 combo.
If you're on stock runflats now, you'll find the ride quality will be better after the switch.
If you're on stock runflats now, you'll find the ride quality will be better after the switch.