Would a 9.5 front/back with 275/40/18 work?

GewoW · 03-09-2010, 03:56 AM

I'm not to crazy on tire sizes. I know OE are 18 with 265/40/18. I heard 285 would work, but am looking for the best option here.

Also, can anyone suggest good summer tires that don't break the bank. I heard of the Vredestein US but they don't make proper 18'' sizes. What about 275/35/18? Vred makes those... 4 PS2s at 275 run about 1650 US shipped to Canada from TireRack.

Would I need spacers on the front? Will anything stick out?

Any opinions on tire setup/tire types is welcome. The car would see light track duty.

Best
G

Paddy · 03-10-2010, 12:30 AM

Quote:

Originally Posted by GewoW

I'm not to crazy on tire sizes. I know OE are 18 with 265/40/18. I heard 285 would work, but am looking for the best option here.

Also, can anyone suggest good summer tires that don't break the bank. I heard of the Vredestein US but they don't make proper 18'' sizes. What about 275/35/18? Vred makes those... 4 PS2s at 275 run about 1650 US shipped to Canada from TireRack.

Would I need spacers on the front? Will anything stick out?

Any opinions on tire setup/tire types is welcome. The car would see light track duty.

Best
G

275/35/18 works all around for me on 10" rims, I Paid USD$750 for a set of Vreds for that setup just a few weeks ago.

Search for my post Apex Arc-8 18x10 Vredestein .... in this forum for pics.

P/S I'm very happy with the Vreds.

Also (assuming you have track set and DD set): with 9.5 all around as a track set, you can bring your 2 DD rears to the track as spares.

GewoW · 03-10-2010, 06:21 AM

Thanks a lot for that man. Lemme ask you though - since I'm new to tracking, if I decide to go 10'' all around - given your experience with the increased oversteer, is it that big a deal compared to staggered?

G

Paddy · 03-10-2010, 11:10 AM

Ideally, the more rubber on the road the better. On track I think the key to speed is smoothness and if you learn to be smooth the chances of the back end coming out will be greatly reduced. Some folk like drifters like major oversteer because they want to slide around corners.
In my experience, when the back end comes out it is very predictable and very easy to correct (except for the few occasions I spin out at autox).

I 'd recommend DSC on for your track days which should keep you from spinning. For autox I always run DSC off and have a ton of fun steering with the throttle (not necessarily the fastest way round the track but sooo much fun). Our autox track at Qualcomm stadium has no obstacles (except cones) so it's pretty safe to spin out, plus we rarely get much above 60mph on a technical track.

GewoW · 03-11-2010, 03:31 AM

Tanks again for a very informative post. Let me just ask you one thing though- is your car lowered? I'm sort of wondering what 35 size sidewalk would look like with an 18" wheel - would it fill the arches enough or just look out of place?

Paddy · 03-11-2010, 11:16 AM

Quote:

Originally Posted by GewoW

Tanks again for a very informative post. Let me just ask you one thing though- is your car lowered? I'm sort of wondering what 35 size sidewalk would look like with an 18" wheel - would it fill the arches enough or just look out of place?

Nope not lowered, the photos I posted in the Apex Arc-8 thread show back/front 35 wheels compared to stock 40's.

The sidewall height of wider 275 but lower profile 35 is almost the same as 265/40 (few millis less actually)

275*.35=96mm

265*.40=106mm

so 10mm diff between 275 and oem 265s

on front it's even better

254*.40=98mm (so fronts would be almost identical)

Paddy · 03-11-2010, 11:32 AM

P.S one thing I found out during my research before upgrading wheels, that you might be interested in.

The area that a tire contacts with the ground is called the "contact patch".
This area is constant for a given vehicle weight and tire PSI and is approx equal to the weight/psi.

The shape of the patch is important, a narrower but longer patch gives better longitudinal traction (useful when accelerating).
A shorter but wider patch gives better lateral grip, useful in cornering.

When you change your 245 front for a 275 you don't actually get any more rubber contacting the road, what happens is that the contact patch shortens and widens (resulting in the same area). So a wider tire helps with cornering but not necessarily with straight line traction.

Kev · 03-11-2010, 11:46 AM

The speedometer is already under-reading with stock tires by about 3-5% in the first 100mph. If you switch to a shorter tire, it'll only exacerbate the problem. Your car will log slightly more miles because your odometer calculates the mileage based on revolutions per mile using stock dimensions.

GewoW · 03-11-2010, 01:28 PM

Thanks again Paddy!

That was my next question - the spedometer issue. Can't you re-calibrate this? Would BMW do this for you (or who would)?

kloh · 03-21-2010, 12:18 PM

Anyone have a formula to determine how much higher or lower your speedometer would read with different size wheels/tires?

Dartanium · 03-21-2010, 01:53 PM

Quote:

Originally Posted by kloh

Anyone have a formula to determine how much higher or lower your speedometer would read with different size wheels/tires?

http://www.miata.net/garage/tirecalc.html

input OEM data, then your new tire size data and compare, usually within 5% so not much to worry about it

kloh · 03-21-2010, 01:58 PM

awesome, thanks!

03-09-2010, 03:56 AM	#1
GewoW #thatsanicemovebro 202 Rep 3,920 Posts Drives: E92 M3 LSB/Black 6MT Join Date: Mar 2007 Location: Montreal, Canada iTrader: (4) Garage List 2011 BMW M3 [9.34]	Would a 9.5 front/back with 275/40/18 work? I'm not to crazy on tire sizes. I know OE are 18 with 265/40/18. I heard 285 would work, but am looking for the best option here. Also, can anyone suggest good summer tires that don't break the bank. I heard of the Vredestein US but they don't make proper 18'' sizes. What about 275/35/18? Vred makes those... 4 PS2s at 275 run about 1650 US shipped to Canada from TireRack. Would I need spacers on the front? Will anything stick out? Any opinions on tire setup/tire types is welcome. The car would see light track duty. Best G Last edited by GewoW; 03-09-2010 at 04:08 AM..
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03-10-2010, 06:21 AM	#3
GewoW #thatsanicemovebro 202 Rep 3,920 Posts Drives: E92 M3 LSB/Black 6MT Join Date: Mar 2007 Location: Montreal, Canada iTrader: (4) Garage List 2011 BMW M3 [9.34]	Thanks a lot for that man. Lemme ask you though - since I'm new to tracking, if I decide to go 10'' all around - given your experience with the increased oversteer, is it that big a deal compared to staggered? G
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03-10-2010, 11:10 AM	#4
Paddy Captain 74 Rep 664 Posts Drives: 18' M2, AW Join Date: Nov 2005 Location: San Diego iTrader: (1)	Ideally, the more rubber on the road the better. On track I think the key to speed is smoothness and if you learn to be smooth the chances of the back end coming out will be greatly reduced. Some folk like drifters like major oversteer because they want to slide around corners. In my experience, when the back end comes out it is very predictable and very easy to correct (except for the few occasions I spin out at autox). I 'd recommend DSC on for your track days which should keep you from spinning. For autox I always run DSC off and have a ton of fun steering with the throttle (not necessarily the fastest way round the track but sooo much fun). Our autox track at Qualcomm stadium has no obstacles (except cones) so it's pretty safe to spin out, plus we rarely get much above 60mph on a technical track. __________________
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03-11-2010, 03:31 AM	#5
GewoW #thatsanicemovebro 202 Rep 3,920 Posts Drives: E92 M3 LSB/Black 6MT Join Date: Mar 2007 Location: Montreal, Canada iTrader: (4) Garage List 2011 BMW M3 [9.34]	Tanks again for a very informative post. Let me just ask you one thing though- is your car lowered? I'm sort of wondering what 35 size sidewalk would look like with an 18" wheel - would it fill the arches enough or just look out of place?
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03-11-2010, 11:32 AM	#7
Paddy Captain 74 Rep 664 Posts Drives: 18' M2, AW Join Date: Nov 2005 Location: San Diego iTrader: (1)	P.S one thing I found out during my research before upgrading wheels, that you might be interested in. The area that a tire contacts with the ground is called the "contact patch". This area is constant for a given vehicle weight and tire PSI and is approx equal to the weight/psi. The shape of the patch is important, a narrower but longer patch gives better longitudinal traction (useful when accelerating). A shorter but wider patch gives better lateral grip, useful in cornering. When you change your 245 front for a 275 you don't actually get any more rubber contacting the road, what happens is that the contact patch shortens and widens (resulting in the same area). So a wider tire helps with cornering but not necessarily with straight line traction. __________________
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03-11-2010, 11:46 AM	#8
Kev Critical Care Anesthesiologist 481 Rep 8,828 Posts Drives: SMB F83 Join Date: Aug 2006 Location: Seattle, WA iTrader: (24) Garage List 2009 Porsche 911 Ca ... [9.50]	The speedometer is already under-reading with stock tires by about 3-5% in the first 100mph. If you switch to a shorter tire, it'll only exacerbate the problem. Your car will log slightly more miles because your odometer calculates the mileage based on revolutions per mile using stock dimensions. __________________ kev { divinum est sedate dolorem } "your friendly neighborhood critical care anesthesiologist"
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03-11-2010, 01:28 PM	#9
GewoW #thatsanicemovebro 202 Rep 3,920 Posts Drives: E92 M3 LSB/Black 6MT Join Date: Mar 2007 Location: Montreal, Canada iTrader: (4) Garage List 2011 BMW M3 [9.34]	Thanks again Paddy! That was my next question - the spedometer issue. Can't you re-calibrate this? Would BMW do this for you (or who would)?
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03-21-2010, 12:18 PM	#10
kloh Lieutenant 48 Rep 420 Posts Drives: 2009 E92 M3 Join Date: Mar 2009 Location: Southern California iTrader: (0) Garage List 2009 E92 M3 [0.00]	Anyone have a formula to determine how much higher or lower your speedometer would read with different size wheels/tires? __________________ ED Vehicle: 2009 E92 M3 6MT \| Space Gray, Fox Red Ext, Carbon Leather \| Mod Progress: Flickr Photos ED Tour: Aug 3 - Aug 10 2009. (Trip Blog \| Route map). ED Progress: Delivery Aug 4th; Drop off at Frankfurt Aug 10th; Redelivery Oct 9th.
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03-21-2010, 01:58 PM	#12
kloh Lieutenant 48 Rep 420 Posts Drives: 2009 E92 M3 Join Date: Mar 2009 Location: Southern California iTrader: (0) Garage List 2009 E92 M3 [0.00]	awesome, thanks! __________________ ED Vehicle: 2009 E92 M3 6MT \| Space Gray, Fox Red Ext, Carbon Leather \| Mod Progress: Flickr Photos ED Tour: Aug 3 - Aug 10 2009. (Trip Blog \| Route map). ED Progress: Delivery Aug 4th; Drop off at Frankfurt Aug 10th; Redelivery Oct 9th.
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